The work was submitted to the
Saxion University of Applied Science
Intelligent Textile Wound Dressing
Concept development and realization of the overall system of an
intel-ligent textile wound dressing for the light therapy of chronic wounds
Presented as: Master Thesis
by: Pauline Cordes
Matr.-No. 456390
1
stexaminer: Dr. rer. nat. Jan-Carlos Kuhlmann
2
ndexaminer: Dr. ir. Henk Gooijer
Supervisor: Akram Idrissi, M.Sc., Institut für Textiltechnik of
the RWTH Aachen University
2019
Master Thesis
Concept development and realization of
the overall system of an intelligent textile
wound dressing for the light therapy of
chronic wounds
Abstract
The number of people suffering from chronic wounds is developing into a serious medical problem causing high burden on patients, healthcare system and the so-ciety as a whole. Patients suffering from the diseases are severely impaired in their quality of life and the treatment measures create high costs to the healthcare sys-tem and society. To overcome this problem, the development of new therapy meth-ods is necessary.
A prototype of an intelligent textile wound dressing system with integrated LEDs is being developed in order to accelerate the healing process of chronic wounds. Es-tablished joining techniques are selected, which connect the multilayer structure of the wound dressing and multiple material compositions are tested to enable suffi-cient mechanical, thermal and optical properties of the overall system.
Based on the VDI 2221 guideline, two experiments are carried out. First the me-chanical properties of the joints are examined, in terms of drapability. The wound dressing contains two connections, a temporary one and a long-term connection. Sewing, adhesive bonding and hook and loop fasteners are applied and tested as connection methods. A further experiment examines the influence of the material composition on the mechanical, thermal and optical properties of the overall sys-tem.
None of the tested material compositions as well as joints fulfil the mechanical properties of conventional wound dressings. The most sufficient drape of the joint is enabled by a continuous sewn zigzag stitch combined with a hook and loop fas-tening in the edges of the layers. Based on optical tests, the light distribution and transmittance of the overall system could be measured and evaluated. Both the distribution and transmittance proved insufficient. The thermal tests showed a crit-ical heat development of the wound dressing after a short period of use. Weak points of thermal and optical measuring methods are identified and suggestions for improvements are worked out.
Key word: Low-level light therapy, intelligent wound dressing, chronic wounds,
Zusammenfassung
Die Zahl der Menschen, die an chronischen Wunden leiden, entwickelt sich zu ei-nem ernsthaften medizinischen Problem, das die Patienten, das Gesundheitssys-tem und die Gesellschaft stark belastet. Patienten, die an den Krankheiten leiden, sind in ihrer Lebensqualität stark beeinträchtigt, und die Behandlungsmaßnahmen verursachen hohe Kosten für das Gesundheitssystem und die Gesellschaft. Um dieses Problem zu überwinden, ist die Entwicklung neuer Therapiemethoden not-wendig.
Zur Beschleunigung des Heilungsprozesses chronischer Wunden wird ein Proto-typ eines intelligenten textilen Wundverbandsystems mit integrierten LEDs entwi-ckelt. Es werden etablierte Verbindungstechniken ausgewählt, die die mehrlagige Struktur der Wundauflage verbinden und ausreichende mechanische, thermische und optische Eigenschaften des Gesamtsystems ermöglichen.
In Anlehnung an die VDI 2221 Richtlinie werden zwei Experimente durchgeführt. Zunächst werden die mechanischen Eigenschaften der Verbindungen hinsichtlich der Drapierbarkeit untersucht. Der Wundverband ist in zwei Verbindungen unter-teilt, eine temporäre und eine langfristige Verbindung. Als Verbindungsmethoden werden Nähen, Kleben und Klettverschlüsse eingesetzt. Das zweite Experiment untersucht den Einfluss der Materialzusammensetzung auf die mechanischen, thermischen und optischen Eigenschaften des Gesamtsystems.
Keine der Materialzusammensetzungen sowie der Verbindungen erfüllen die me-chanischen Eigenschaften herkömmlicher Wundauflagen. Die beste Drapierbar-keit wird durch einen durchgehenden genähten Zickzackstich in Kombination mit einem Klettverschluss an den Ecken der Schichten ermöglicht. Anhand der Licht-versuche konnte die Lichtverteilung und -transmission des Gesamtsystems ge-messen und ausgewertet werden. Sowohl die Verteilung als auch Transmission erwies sich als unzureichend. Die thermischen Untersuchungen, zeigten eine kri-tische Wärmeentwicklung der Wundauflage nach kurzer Nutzungsdauer Die Schwachstellen der thermischen und optischen Messmethoden wurden erkannt und Verbesserungsvorschläge ausgearbeitet.
Schlagwörter: Low-level Lichttherapie, intelligente Wundauflage, chronische
Table of Contents
1 Introduction ... 1
1.1 Problem analysis ... 1
1.1.1 Company description ... 1
1.1.2 Reason for research ... 1
1.1.3 Field of research ... 2
1.2 List of demands ... 3
1.3 Goal, objectives and research questions ... 5
1.3.1 Goal ... 5
1.3.2 Objectives ... 5
1.3.3 Research questions ... 5
2 State of the Art ... 7
2.1 Medical background ... 7
2.1.1 Wound dressings ... 8
2.1.2 Intelligent wound dressings ... 9
2.2 Textile joining technologies ... 13
2.2.1 Adhesive bonding... 14
2.2.2 Sewing ... 16
2.2.3 Welded seams ... 19
2.2.4 Hook and loop fastener ... 20
3 Methodology ... 21
3.1 Concept development ... 21
3.1.1 Product specifications ... 25
3.1.2 Product breakdown structure ... 29
3.1.3 Morphological case ... 31
3.1.4 Factorial experiments ... 32
4 Materials ... 35
4.1 Creation of the functional layer ... 35
4.1.1 LEDs as light source ... 35
4.1.2 Arrangement of the LED sequins ... 35
4.1.3 Attachment of LED sequins ... 36
4.1.4 Embroidery of the conducting paths ... 37
4.1.5 Inspection of the functionality ... 38
4.2 Diffusion layer ... 39
4.3 Separating layer ... 42
4.4 Development of the connecting joints ... 43
5 Testing methods ... 47
5.2 Elongation of the joints ... 49
5.3 Maximum tensile force of the joints ... 51
5.4 Weight and thickness ... 52
5.5 Light distribution and transmittance ... 53
5.6 Heat development ... 54
6 Results ... 56
6.1 Mechanical properties of the wound dressing at the joint ... 56
6.1.1 Bending stiffness ... 57
6.1.2 Seam strength ... 58
6.1.3 Elongation of the joints ... 59
6.2 Properties of the overall system ... 62
6.2.1 Weight and Thickness ... 63
6.2.2 Heat development ... 64
6.2.3 Light distribution and transmittance ... 67
7 Discussion ... 71 7.1 Joining technologies ... 71 7.2 Overall system ... 74 8 Conclusions ... 78 9 Recommendations ... 79 10 Research reflection ... 80 11 Bibliography ... 81
List of Figures
Figure 1.1. Top view: drawing of the intelligent textile wound dressing including electronical system and wound dressing; Front view:
wound dressing structure at the schematic cross-section A ... 3
Figure 2.1. Grading scale for chronic wounds of increasing severity ... 7
Figure 2.2. Wet wound dressings. ... 9
Figure 2.3. Effect of low-level light therapy by LEDs on wound size with no light, red and blue light ... 11
Figure 2.4. Negative pressure therapy on wound. ... 12
Figure 2.5. Methods of combining textiles. ... 13
Figure 2.6. Construction of an adhesive. ... 14
Figure 2.7. Relation between surface energy and wetting. ... 16
Figure 2.8. Principles of stitching: intralooping, interloping and interlacing. 17 Figure 2.9. Seam types with laying of the fabrics and location of sewing needle stitches. ... 18
Figure 2.10.Hot air wedge welding equipment. ... 20
Figure 2.11.Hook and loop fastener: left mushroom shaped pins and loops, right hooks and loops. ... 20
Figure 3.1. Procedure for the development according to VDI guideline 2221 ... 21
Figure 3.2. Methodological structure of the research ... 22
Figure 3.3. Product breakdown structure ... 30
Figure 3.4. Chosen components of functional layer: a) knitted jersey as fabric, b) LEDs as light source, c) conductive yarn for conducting path, d) flexible conductive silver ink and e) electric wire ferrules for electrical connection to wound dressing ... 32
Figure 3.5. Connection geometry: a) continuous and b) selective ... 33
Figure 4.1. Arrangement of the LED sequins on functional layer as a matrix with dimensions in mm ... 36
Figure 4.2. Upper and lower side of the LED matrix ... 37
Figure 4.3. Inspection of the LEDs ... 38
Figure 4.4. Final design of the functional layer: left) top of the functional layer with resistors connected in series with the LEDs; right) conducting paths connected parallel on the bottom of the functional layer . 39 Figure 4.5. Reflection, absorption and transmission of light ... 39
Figure 4.6. Diffusion layer 1: a) perspective of the spacer fabric; b) front view; c) bottom view and d) top view ... 41
Figure 4.7. Diffusion layer 2: a) perspective of the spacer fabric; b) front view; c) bottom view and d) top view ... 42
Figure 4.8. Conventional wound dressings used as separating layers: a) and c) show the “UrgoSorb Silver” wound dressing SL1 as perspective and image the front; b) and d) show the “UrgoCell Start” wound
dressing SL2 as perspective and image the front ... 43
Figure 4.9. Cross section of the overall system with superimposed seams at Connection 1 and Connection 2 ... 44
Figure 4.10. Connection 1 glued: a) and c) selectively glued and b) and d) continuously ... 44
Figure 4.11. Connection 1 sewn: zigzag stitch a) selective bottom, b) selective top, c) continuous bottom and d) continuous top" ... 45
Figure 4.12. Connection 2: selective hook and loop tape a) diffusion layer and b) separating layer; continuous tape c) diffusion layer and d) separating layer ... 46
Figure 5.1. Test setup of the cantilever test ... 48
Figure 5.2. Materials testing machine Zwick ZmartPro ... 49
Figure 5.3. Force-elongation graph ... 50
Figure 5.4. Zwick material testing machine ... 51
Figure 5.5. Left: Mettler AE 240 scale; Right: FRANK thickness gauge ... 52
Figure 5.6. Test setup of the circuit ... 53
Figure 5.7. Test setup of the thermal experiments ... 54
Figure 6.1. Bending stiffness of single layers and connection for the overall system – Cantilever Tests ... 57
Figure 6.2. Seam strength of specimens for Connection 1 ... 59
Figure 6.3. Stress-strain behaviour of the individual layers and the connections... 60
Figure 6.4. Yield point determination of the separation layers ... 60
Figure 6.5. Young´s modulus of the individual layers and the connections. 61 Figure 6.6. Thickness of the material compositions ... 63
Figure 6.7. Weight of the material compositions... 64
Figure 6.8. Heat development of the functional layer and the material compositions ... 65
Figure 6.9. Thermographic image of the functional layer after 30 min ... 65
Figure 6.10. The material compositions after 30 minutes of lighting ... 66
Figure 6.11. Images of the material compositions with each LED lit with a power of 0,288 W ... 67
Figure 6.12. Brightness of the material compositions as average grey level 68 Figure 6.13. Light distribution of the material compositions ... 69
List of Tables
Table 3.1 Pairwise Comparison to Determine the Weighting Factors ... 25 Table 3.2 Product Specification of the Overall Intelligent Wound Dressing
System ... 28 Table 3.3 Morphological Case ... 31 Table 3.4 Factorial Experiment on Different Material Compositions ... 33 Table 3.5 Factorial Experiment on the Mechanical Properties of the Joints ... 34 Table 6.1 Sample Identifier of the Connection Solutions ... 56 Table 6.2 Sample Identifier and Material Compositions of the Overall
Systems ... 62 Table 7.1 Determination of the Weighting Factors for the Joints Criteria .. 71 Table 7.2 Joining Technology Final Ranking ... 73 Table 7.3 Pairwise Comparison for the Weighting of the Material
Compositions ... 75 Table 7.4 Final Ranking of the Material Compositions ... 76
Abbreviations and formulas
°C Degree Celsius
% Percent
A Area of the specimen B Bending stiffness
CCT Correlated colour temperature CRI Colour rendering index DL Diffusion layer
E Young´s modulus
F1 Linear weight force
FL Functional layer
G Gas
gn Gravitational acceleration
i Variables of the 256 grey levels
ITA Institut für Textiltechnik of RWTH Aachen University
L Liquid
l Length of the test specimen LED Light-emitting diode
LLLT Low-level laser therapy
lü Overhang length of the test specimen
M Grammage
! Mass of test specimen
NASA National Aeronautics and Space Administration
ni Number of pixels
NO Nitric oxide
PA Polyamide
PVAL Polyvinyl alcohol
ri Sum of ratings of each criterion
RWTH Rheinisch-Westfälische Technische Hochschule
SL Separating layer
wi Weighting factor of each criterion
xi Grey level
"̅ Average grey level of the image
$%& Surface tension of the viscos adhesive
$'% Interfacial tension between textile and viscos adhesive
$() Surface tension of the textile
*+, Strain at the yield point - Wetting angle
. Standard deviation
1
Introduction
The following work deals with the development of an intelligent textile wound dressing for the light treatment of chronic wounds, with a focus on the choice of materials and joining techniques of the dressing layers.At the beginning of the chapter, the necessity of the work is described, based on a following literature search. At the end of the chapter, the objectives of this work and the questions to be answered are mentioned.
1.1 Problem analysis
1.1.1 Company description
The Institut für Textiltechnik of RWTH Aachen University (ITA), Aachen is associated with the department of Textile Engineering and belongs to the faculty of Mechanical En-gineering of the Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen. The institute comprises around 100 researchers working in the field of materials, production processes and products for technical applications of textile structures. The ITA GmbH is a partner for industries in the field of research and development, which concentrates on the areas (technical) textiles, chemical fibre, textile machinery, fibre composites, bio-hy-brid & medical textiles. The medical textile department works on four group of subject: medical fibre manufacturing, medical implant systems, bio fabrication and medical smart textiles. The ITA is located in the RWTH Campus Melaten in Aachen.
1.1.2 Reason for research
In recent years, the number of people suffering from chronic wounds has risen sharply. The bacterially infected wounds, which take more than eight weeks to heal, are often underestimated in their burden on the individual, the healthcare system and the society as a whole. Patients suffering from the diseases are severely impaired in their quality of life, and the treatment measures create high costs to the healthcare system and society. In Germany, 5-8 billion euros are annually spent on the treatment of chronic wounds (Klein, et al., 2013). Longer life expectancy suggests that the number of patients suffering of chronic wounds will continue to increase.
Innovative and modern concepts for care, as well as efficient forms of therapy control and support for the home care situations are needed. In terms of efficient forms of ther-apy control previous research showed that low-level light has been documented as a promising alternative to enhance wound healing. Especially the treatment with blue light can improve the perfusion of chronic wounds and has an anti-inflammatory effect which
would accelerate the healing of the diseases (Frangež, Nizič-Kos, & Ban Frangez, 2018; Adamskaya, et al., 2011; Minatel, Frade, Franca, & Enwemeka, 2009).
Therefore, the integration of low-level light into wound dressings could be an alternative method of treatment for patients with chronic wounds. The intelligent dressing, which enables the illumination of chronic wounds, would be more effective in healing the wounds and reducing pain for the patients. Accelerated healing would reduce the amount of dressing changes, the length of hospital stays for patients and would require fewer interactions with physicians. This in turn would save costs for the healthcare system and society. Furthermore, the risk of infections for patients would be decreased and a faster return to a tolerable level of pain would be made possible, allowing patients activity. The collaborativeproject MEDILIGHT, co-funded by the European Union's Horizon 2020 research and innovation program, is already developing a wound dressing for light stim-ulation and wound healing surveillance. However, this dressing is not very flexible and the fixation of the dressing to more complex body areas is difficult. Therefore, this re-search is based on the development of a more flexible, intelligent wound dressing that allows the treatment of wounds at all types of body regions (MEDILIGHT, 2015).
1.1.3 Field of research
The medical textile department of the ITA is addressing this problem and applies re-search on a product for the treatment of chronic wounds. In a cooperation with other companies, the ITA works on a development of an intelligent, flexible, close-to-body wound dressing system that combines diagnostic and adaptive therapy, called LED-SensTex. Here, the healing process of the wound is to be measured by an integrated sensor technology, which can measure the nitric oxide (NO) level. Based on this, an individually appropriate low-level light therapy can be selected, which illuminates the chronic wounds and accelerates their healing process. The lighting is realized via light-emitting diodes (LEDs) integrated in the wound dressing.
The basic structure of the wound dressing for the low-level light therapy takes place in layers, as shown in Figure 1.1. The basis is provided by the functional layer followed by the diffusion and then by the separating layer which faces the wound. The LEDs and the NO sensors are attached to the functional layer, through which the diagnostic and adap-tive therapy can be controlled. The distribution of the light takes place through the middle layer, the diffusion layer, which enables an evenly irradiation of the wound. The separat-ing layer has direct contact with the wound and serves to absorb wound liquids and blood.
In order to meet the hygiene requirements and to improve the sustainability of the wound dressing, the system will consist of two parts. The separating layer is a disposable article that should be able to decoupled from the rest of the system. The second part of the wound dressing with functional and diffusion layer should be suitable for repeated use.
In this research, suitable materials for diffusion and separating layer as well as joining technologies for the required connections of the individual layers are investigated. The implementation of a first prototype of the overall wound dressing system with integrated LEDs that can irradiate chronic wounds and adapt to any body geometry, is the focus of this work. The integration of NO sensors is not considered during the prototype develop-ment. Furthermore, the electronic system, consisting of controller, data transmission and power supply of wound dressing is only marginally discussed.
1.2 List of demands
The end product should be an attachable textile wound dressing that evenly irradiates chronic wounds and ensures a moist environment. In addition, the wound dressing can adapt to complex body regions without increased pressure onto the wounds. The overall system gets applied to the wounds during dressing changes for approximately 30 minutes, up to two hours. The prototype consists of three main components: func-tional, diffusion and separating layer. They make up the overall system.
Functional layer Diffusion layer Separating layer LEDs
Fixation Conducting path Fabric Sequin Contacting Section A - A Wound dressing Electronical system Interconnectors TOP VIEW 5 cm A A
Figure 1.1. Top view: drawing of the intelligent textile wound dressing in-cluding electronical system and wound dressing; Front view: wound dressing structure at the schematic cross-section A
Functional layer
• The functional layer should hold the LED sequins.
• The LEDs shall be arranged in a matrix and connected to conductive paths.
• Conductive path shall connect the electronics LED sequins with the interconnectors. • The functional layer shall adapt uniformly to the complex body parts.
Diffusion layer
• The diffusion layer shall generate a good light distribution and transmittance. • The diffusion layer shall absorb pressure caused by the LEDs.
• The diffusion layer shall adapt uniformly to complex body parts.
• The diffusion layer shall enable the heat, generated by the LEDs, to leak and ensure good heat transmittance.
Separating layer
• The separating layer shall adapt uniformly to different body parts. • The fabric shall absorb wound fluids and blood.
• The separating layer shall have a moisture management that benefits the healing process of chronic wounds.
• The fabric shall be antimicrobial to decrease bacterial growth.
• The separating layer shall generate a good light distribution and transmittance.
Overall system
• The system shall not irritate the skin and adapt uniformly to complex body parts with-out wrinkles.
• The integration of LEDs in the wound dressing shall not increase the pressure be-tween wound dressing and wound.
• The connection between functional and diffusion layer shall withstand repeated use. Whereas the connection between diffusion and separating layer shall enable single use of separating layers.
• The system shall be easy to attach to the body to perform a low-level light therapy treatment lasting approximately 30 minutes up to two hours during dressing changes.
1.3 Goal, objectives and research questions
In this chapter the goal, objectives and research questions of the work are documented.
1.3.1 Goal
In this research, the aim is to develop a prototype of an intelligent textile wound dressing system with integrated LEDs for chronic wounds by selecting established joining tech-niques that tightly connect the functional and diffusion layer for repeated use and allow the removal of the separating layer after single use and obtaining similar mechanical properties as conventional wound dressings and good thermal and optical properties.
1.3.2 Objectives
This chapter describes the measurable objectives in order to reach the goal.
• To find suitable joining techniques which allow the wound dressing to be adapted to complex body regions without creating wrinkles and pressure points.
• To select joining techniques that realize a strong bond between the functional and diffusion layer for repeated use and allows separation of the separating layer from the diffusion layer after single use.
• To select suitable layers for the wound dressing system, which ensure a homo-geneous and sufficient irradiation intensity on the chronic wound.
• To ensure that the heat generated by the LEDs does not create a temperature environment unsuitable for chronic wounds.
1.3.3 Research questions
In this paragraph the main and sub-questions are documented, which will help accom-plish the stated goal and objectives.
Main research question
How to develop and join the layers of a textile wound dressing with integrated LEDs intended for use on chronic wounds under meeting the mechanical, thermal and optical requirements for the overall system?
Sub-questions
• What are the mechanical properties (thickness, weight, drape and elongation) of conventional hydro active wound dressings?
• Which joining technology is most suitable to reach the mechanical properties, required by a conventional hydro active wound dressing?
• Which joining technologies allow a strong connection of the functional and diffu-sion layer and a detachable connection between diffudiffu-sion and separating layer for single use of the separation layer?
• Does the light distribution and transmittance of the overall system allow a
homo-geneous and sufficient irradiation of the chronic wound?
• Which composition of diffusion and separating layer is most suitable to prevent the heat generated by the LEDs from increasing the ambient temperature of chronic wounds?
2
State of the Art
2.1 Medical background
A wound is caused intentionally, accidentally or as part of the process of a disease by a physical trauma. An open wound is defined as break, torn or cut in the epidermal tissue. A closed wound is caused by a contusion. The disruption of a wound can be deeper and can reach down to sub-epidermal tissues including dermis, fascia and muscle (Ather & Harding, 2009). Wounds can be classified into acute and chronic wound, based on the amount time necessary for the healing process. Most wounds heal within three weeks and are therefore called acute wounds. Their healing process is defined in four stages: hemostasis, inflammation, proliferation and maturation (Tyeba, Kumar, Kumara, & Vivek , 2018). Chronic wounds are these that take more than eight weeks to heal and do not heal as per these defined stages. Their healing process is secondary, meaning that there is a tissue defect and the wound is bacterially infected. Diseases such as venous or decubitus ulcers, diabetic foot syndrome and ischemic wounds belong in the category of chronic wounds. Figure 2.1shows a grading scale of chronic wounds where the specifi-cation of grades 1 to 4 is based on the depth of wound and the tissue structures that are affected. Grade 1 Grade 2 Grade 3 Grade 4 Epidermis Dermis Subcutaneous tissue Muscle Bone
Figure 2.1. Grading scale for chronic wounds of increasing severity. Re-printed from “Decubitus Ulcers: Pathophysiology and Primary Prevention,” by J. Anders et al., 2010, Deutsches Ärztebaltt, 107(21), p.373
Grade 1 shows erythema and indurations on the upper skin layer, whereas for chronic wound in grade 2, the cells of the basal layer of the epidermis die and become detached. The death of other cells beyond the basement membrane takes place in deeper layers (grade 3) and can even lead to bones and muscles, grade 4 (Anders, et al., 2010). The number of patients suffering from these diseases increases due to a growing and aging population. According to a study by the EU project MEDILIGHT (2015), more than 40 million patients are affected by chronic wounds in one year. Especially elderly and disabled people suffer from these diseases. The high number causes costs of € 40 billion for the healthcare system and critical problems in clinical practice (Amez-Droz, 2018). Patients who have chronic wounds suffer from slow healing, improper healing treatment and a massive loss of quality of life. (Skorkowska-Telichowska, Czemplik, Kulma, & Szopa, 2013; PRO Care, 2012). For a complication free healing, chronic wounds depend on wound dressings, bandages and antiseptic measures (Skorkowska-Telichowska, Czemplik, Kulma, & Szopa, 2013; Moosmann, 2015).
2.1.1 Wound dressings
The use of textiles in medicine covers a long tradition, especially bandages and wound dressings have prevailed in the years, due to good quality approaches such as biocom-patibility, flexibility and strength. Furthermore, good availability, low price and re-usability are factors for the utilization of the textiles. The modern wound dressing facilitates the wound healing and its functions can be divided into three categories: protective, physical and pharmacological. The protective function protects the skin and keeps external influ-ences outside. At the same time the wound dressing shields the environment from con-tamination of wound secretion and germs. The moisture balance of a wound can be regulated by the physical functions of a wound dressing, by absorption. A pharmacolog-ical function is possible since the wound dressing is in direct contact with the wound and the metabolic system of the skin, therefore it can act as drug carrier (Wollina, Heide, Müller-Litz, Obenauf, & Ash, 2003; Gupta, 2010).
Wound dressings can be passive, active or interactive. A passive dressing obtains only a protective function and covers the wound, whereas active and interactive dressings have an additional physical function that is able to modify the wound environment. Inter-active wound dressings include hydrocolloids, hydrogel, alginates and foams (Ather & Harding, 2009). Furthermore, wound dressings are distinguished between dry and wet dressings. Historically, dry wound dressings were considered as best for healing of wounds. The wounds were covered by woven cotton gauze or nonwoven blends of rayon and other fibres that absorbed exudates (Gupta, 2010; Dill-Müller & Tilgen, 2005). The application of dry dressings is used today especially for the first aid and for primary heal-ing wounds, which are closed by a seam. In mid-1970 research showed a faster healheal-ing of renewed skin without eschar takes place in wet environments. Therefore, today
secondary wounds and in particular chronic wounds are treated with wet dressings that create a moist environment, shown in Figure 2.2 (Bruggisser, Potzmann, & Dudler, 2009).
2.1.2 Intelligent wound dressings
The strained situation in hospitals due to an increasing number of patients with chronic wounds leads to a socio-economic burden on the modern society. As a result, the need for treatments of complex wounds outside hospitals is increasing. New insights into wound healing and the pressure from the health care system have led to new and smarter wound treatments that reduce the burden on the health system and relieve
pa-tients' pain. Two principles of treatments are being investigated. On the one hand the
reduction of infections through pre-measures and early detection and on the other hand the reduction of the total healing time of chronic wounds and the duration of patients in hospitals(Gupta, 2010; Kassal, et al., 2017). Another reason for the increased number of smart wound treatments is the technological development of functional textiles with excellent properties, which are applied for wound healing and prevention (Wollina, Heide, Müller-Litz, Obenauf, & Ash, 2003; Herrmann, Supriyanto, Kumar Jagana, & Manikandan, 2018).
Figure 2.2. Wet wound dressings. Reprinted from Paul Hart-mann AG website, by Paul HartHart-mann AG, (2019), Retrieved from http://hartmann.info/de-de/produkte/wundmanagment/hy-droaktive-wundauflagen Copyright 2019 by Paul Hartmann AG.
2.1.2.1 Reduction of healing time
One measure to reduce the healing time of chronic wounds is light therapy. Light therapy is a therapeutic methodology used for centuries for the treatment of various health con-ditions. The positive effect of sunlight has been exploited and used in ancient Egypt, India and China. Due to the rediscovery of Danish physician and scientist Ryberg Finsen in 1903 light therapy can be realized with the use of artificial irradiation sources. Since 1960, low-level laser therapy (LLLT) has been performed with the efficacy of red light for wound healing. Today also the non-thermal light therapy with LEDs is applied to thou-sands of people for various medical conditions (Barolet, 2008). LEDs produce narrow spectrum light that is produced by converting current into incoherent light. Compared to lasers the semiconductor delivers less power, therefore the risk to damage the skin as well as an accidental eye damage is smaller. Especially in dermatology light therapy is a common used method for the removal of tattoos, port-wine stain, hemangiomas, acne scars and wrinkles (Hellwig, Petzoldt, König, & Raulin, 1998).
The LED therapy was initially developed by National Aeronautics and Space Administra-tion (NASA) which discovered accelerated growth in plants under irradiaAdministra-tion with a spe-cific wavelength. Similar to plants that convert sunlight into plant tissue, LEDs are able to “trigger natural intracellular photo-biomechanical reactions” (Barolet, 2008, p.228). As in vivo studies with rats have shown, blue light improves tissue perfusion by releasing nitric oxide (NO) from nitrosyl complexes of haemoglobin, thus improving blood flow. Since NO is a molecule that is responsible for the dilation of blood vessels, the transport of oxygen and nutrients is increased and at the same time metabolic waste products are removed more easily (Adamskaya, et al., 2011; Osipov, et al., 2007).The longer the wavelength of an LED the deeper the penetration into the skin. Blue light obtains a wave-length of 400-470 nm and penetrates into the Epidermis, the top layer of the skin. The wavelength of red light is longer (630-700 nm) and enables a penetration of 1–6 mm into the Dermis (Barolet, 2008). Besides wavelength the total energy density, time intervals of the irradiation and duration of treatment are important for the optimal therapy (Frangež, Nizič-Kos, & Ban Frangez, 2018).
Research has shown that the irradiation of wounds with blue light has also a positive influence on the healing process of chronic wounds. The blue light has an antimicrobial and anti-inflammatory effect in the beginning of healing processes. It further doesn’t dam-age the tissues like dangerous UV-light. Moreover, such therapy prevents premature closure of the epidermis at the wound surface and provides the cell division inhibitory effect. Additionally, the production of the skin cell keratinocytes is activated which strops the proliferation and fastens the healing process, as shown in Figure 2.3 (Adamskaya, et al., 2011). According to Wheland et al. (2004) light therapy increases the cell grow by 150–200 % over untreated controls. Steinkopf Caetano, Frade, Minatel, Santana and Enwemeka (2009) indicate in their study that the time interval of light treatments of ulcers should be limited to two or three times per week at most. An increased interval could
progressively stimulate collagen synthesis, without allowing an interval at which newly synthesized collagen can mature.
Studies are carried out to develop an intelligent wound dressing with integrated LEDs that generate blue light and accelerate the healing process (Amez-Droz, 2018; Adamskaya, et al., 2011). The enhanced healing process of chronic wounds through light therapy would save time and resources for both patient and health care facilities. Furthermore, it wound decrease the risk of infections for patients, the amount of dressing changes and enable a quick return to a pain level for patients that allow activity (Wheland, et al., 2004).
Blue light therapy finds further application in healthcare. The Royal Philips Electronics N.V., Amsterdam has developed a product called Bluetouch that treats back pain by illuminating the back with blue LED light and stimulating the body’s own process. Similar to the light treatment of chronic wounds, the blue light increases the NO content in the body which improves the blood circulation and provides muscles with oxygen and nutri-ents. This causes a relaxation of the muscles and a pain relief (Koninklijke Philips N.V., 2013). Another product from the company, BlueControl, is also an irradiation instrument but it is used for the treatment of individual psoriasis with blue light instead of UV radia-tion. Negative pressure therapy (vacuum-assisted wound closure) creates a negative
pressure on the chronic wounds by covering the wound with a wound dressing and an
No Light Red Blue
Baseline Day 3
post OP post OPDay 7
W ou nd a re a [% b ase lin e] 0 25 50 75 100
Figure 2.3. Effect of low-level light therapy by LEDs on wound size with no light, red and blue light. Reprinted from “Light therapy by blue LED improves wound healing in an excision model in rats,” by N. Adamskaya et al., 2011, Injury, 42, p.918.
airtight film connected to a vacuum pump, Figure 2.4. The negative pressure creates a moist environment, increases blood flow, reduces wound edema, and removes exu-dates, which accelerates the healing time of chronic wounds. Furthermore, the treatment supports the formation of granulation tissue which causes a reduction in size of the
wound and increases the rate in wound healing (Arvesen, Bak Nielsen, & Fogh, 2017).
Especially the duration of patients in hospital can be decreased since the treatment can be applied at a patient’s home. An effective result appears in postsurgical wounds. (Powers, Higham, Broussard, & Phillips, 2016).
2.1.2.2 Intelligent pre-treatment
The reduction of infections through preceding measures and early detection helps to reduce the number of patients suffering from chronical wounds. An example of a pre-treatment method that is able to detect infections in an early stage is a smart bandage. Such bandages are able to determine and communicate the wound status with integrated physical or chemical sensors or indicators. The pH value of the wound fluid is an indicator of the wound status, since it has an effect on the wound healing. The determination of the pH of the wound fluid has been done with different electronic methods. Examples are the potentiometric sensing with screen-printed electrodes and monitoring the pH-de-pendent oxidation current of uric acid during a voltammetric examination. Additional to the pH value also other physiological indicators are claimed to quantitatively report the wound status such as temperature, moisture, partial pressure of oxygen and bacterial
load. With the bandage that is able to determine the wound status the number of wound
dressing changes is reduced, the stress and pain patients suffer is minimized and
pre-measures can be taken to stop the enlargement of chronic wounds (Pal, et al., 2018;
Kassal, et al., 2017). Bone Muscle Subcutaneous Tissue Negative pressure source and col-lection canister Occlusive dressing
Figure 2.4. Negative pressure therapy on wound. Reprinted from “Wound healing and treating wounds: Chronic wound care and management,” by J.G. Powers, C. Higham, K. Broussard and T.J. Phillips, 2016, Journal of the Amer-ican Academy of Dermatology, 74, p. 613.
2.2 Textile joining technologies
The development of intelligent wound dressings, especially textile-based dressing re-quires the joining of different materials to build overall systems. In the following chapter different joining technologies are presented, that allow the joining of multiple textile lay-ers. The joining of textiles goes further back in time than fibre-based textiles exist. Re-search has shown, that humans used bone and ivory needles 30.000 years ago to join animal skin together (Jones & Stylios, 2013). Today, the joining of textile materials, gar-ments and other finished products can be implemented by numerous joining methods. Broadly the processes are divided into mechanical fastening and bonding. Whereas, bonding can be further classified into adhesive bonding, solvent bonding and thermal bonding. Figure 2.5 shows an overview of joining methods. Thermal and solvent bonds can be seen as a subgroup of adhesive bonding. In both cases material closure occurs since the substrate itself acts as adhesive once it is liquefied (Petrie, 2013). The principle of mechanical fastening can be divided into form closure and traction (Gries & Klopp, 2007). The decision which method is suitable for the connection of two or more textiles depends on several factors. In particular, the required strength, durability, comfort in wear, available equipment and costs are factors that need to be considered. An analyse of requirements helps to figure out which potential method should be applied (Hayes & McLoughlin, 2013). In this chapter, the focus will be on adhesive bonding and the me-chanical fastening method, stitching. Both methods are conceded as connection method for the prototype development of this research.
Figure 2.5. Methods of combining textiles. Adapted from “Adhesive bonding of textiles: principles, types of adhesive and methods of use,” by E.M. Petrie, Woodhead Publishing Limited, 2013, p. 232.
Joining of textile materials Mechanical - Perforation - Entanglement - Stitching - Stapling - Press fasteners - Embroidery - Pressure embossing Thermal - Radiant heat - Through-air - Ultrasonic - Dielectric - Flame - Extrusion - Calendering - Hot wedge - Laser Solvent - Solvent cementing Adhesive - Solvent - Waterborne - Hot melt - Powder - Reactive liquids
2.2.1 Adhesive bonding
The bonding of two or more textiles with adhesive is a commonly applied methodology and one of the oldest technique in design and manufacturing of textile-based products. In contrast to solvent and thermal bonding, the joint of two or more substrates is realised without melting or dissolving of the textiles. An adhesive bond consists of at least three components: the two textile layers and the adhesive. The area where the textile and adhesive mix is called boundary layer. It is decisive for the bonding, as shown in Figure 2.6. The adhesive is a substance that is able to hold at least two fabrics together. The substance consists of a base resinous material with pigments, stabilizers, fillers, plasti-cizers and other additives. The function of the adhesives is to create molecular interac-tions between the substrate and the adhesive is called adhesion (Petrie, 2013; Gries & Klopp, 2007).
Adhesion is applied for temporary and permanent bonding of textiles. Permanent adhe-sion is expected to last the life of the final product. Therefore, the adhesive is required to retain similar strength as the textile and it is rated in terms on their holding power or shear strength divided by the overlapped area. Adhesives for permanent boning are made of thermosets polymeric resin or thermoplastic resin with high heat and moisture resistance to withstand the whole lifetime. Temporary adhesives obtain lower strength and performance properties than permanent adhesives. Indicative for these adhesive is their peel strength or resistance to edge separation divided by the bond width. Generally, these adhesives should hold fabrics firmly together (Petrie, 2013). The adhesive strength
Textile 1 Boundary layer 1 Adhesive layer Boundary layer 2
Textile 2
Figure 2.6. Construction of an adhesive. Adapted from “Füge- und Oberflächentechnologien für Texti-lien,“ by T. Gries and K. Klopp, Springer-Verlag, p.70.
is influenced not only by the adhesive itself, but by other factors such as joint design, substrate, rate of loading, operating procedures (time course of hardening or pot life) and environmental conditions (temperature or humidity). Influencing parameters of the sub-strates are its cleanliness, structure and surface (Gries & Klopp, 2007).
The structure and surface of the applied substrates has an influence on the adhesive strength of the bonding. Depending on the requirements of use and the fabrication pro-cess, the surface structure of textile fabrics can differ. Knitted fabrics obtain more elastic properties than woven or non-woven fabrics. They are able to stretch up to 500 % of their original length. These properties need to be considered when choosing bonding sys-tems. At the same time knitted fabrics obtain a topography that positively influences the mechanical adhesion. Thought the lightness of knitted fabrics increases the migration of low molecular adhesives through the fabric. Woven fabrics obtain denser structures than knitted ones. The adhesive quality can vary between the weaving structures. Satin weave has single floating fibres on the surface of the fabric which can be easily removed and therefore lead to decreased strength of the joint. Nonwoven fabrics are suitable for adhesive bonding. It has to be considered that the specific function of nonwoven fabrics such as stretch, absorbency and softness can be destroyed by the joint (Stammen & Dilger, 2013).
In addition to the structure of the fabrics, the surface has effects on the adhesive quality. Furthermore, the fibre properties and geometrics factors such as yarn diameter, twist and fibre compactness show an influence on the adhesive bonding. A high surface en-ergy of a fabric improves the wetting, spreading and wicking of adhesives and cause an effective adhesive bonding. The Young equation describes the relation between wetting and the surface energy of a textile.
$'& = $'%+ $%&cos (-) ( 1) with
$() Surface tension of the textile
$%& Surface tension of the viscos adhesive
$'% Interfacial tension between textile and viscos adhesive S Solid
- Wetting angle L Liquid
The smaller the wetting angle -, the higher the surface tension and wetting, Figure 2.7. To increase the surface tension of a fabric, finishing treatments such as bleaching, dye-ing and finishdye-ing with optical bleach or softener can be applied (Stammen & Dilger, 2013).
2.2.2 Sewing
Sewing is a common method of joining textiles by attaching fabric layers with needle and threads forming stitches and seams. Both parameters are related to each other, since stitches are necessary to hold a seam. When sewing two or multiple textiles together the stitch and seam have to be suitable for the purpose they are intended as they affect the quality of the end use application in terms of strength, durability, elasticity, appearance and security (Colovic, 2015).
2.2.2.1 Stitches
According to International Organization for Standardization (1991b) a stitch is resulted by one or more strands or loops of threads that can be divided into six classes based on three principles, intralooping, interloping and interlacing, shown in Figure 2.8.
• Class 100: Chain stitches • Class 200: Hand stitches • Class 300: Lockstitches
• Class 400: Multi-thread chain stitches • Class 500: Over-edge chain stitches • Class 600: Over-seam chain stitches
Textile Adhesive Atmosphere $() $'% $%&
-Figure 2.7. Relation between surface energy and wetting. Adapted from “Füge- und Oberflächentechnologien für Textilien,“ by T. Gries and K. Klopp, Springer-Verlag, p.70.
Intralooping describes “the passing of a loop of thread through another loop of the same thread supply” (McLoughlin & Mitchell, 2014, p.380). Chain stitches (Class 100) are an example of intralooping, due to their easy removal they are often applied for temporary applications. Further application can also be basting, tacking, bottom sewing and label setting. In contrast to intralooping, interloping passes a loop of a thread through a loop of anther thread, instead of his own threads. Also, for interlacing two threads are neces-sary, whereas at interlacing the thread is passed around or over another thread instead of through. Interlacing is most commonly referred to lock stitches (Class 300) that obtain good strength. At the same time the stitch can extend up to 30 % and gives the final application comfort and stretch. Furthermore, the stitch class is applied for fabrics where the appearance of the stitch has to be the same on each sides (Colovic, 2015; McLoughlin & Mitchell, 2014).
The multi-thread chain stitch (Class 400) is a combination of a chain and a lock stitch, where a loop of threads is passing through the fabrics and secured with loops of another group by interlacing and interloping. The stitching type that is also often called double-licked stitches applies for seaming operations of all kind of garments. Due to the lower static thread tension and interloped threads the stitch type is good for applications where strength and recovery properties are required. Further the lower static thread tension and the interloped threads decrease the development of puckers. The Class 401, or the two-thread chain stitch is used for seams that require elasticity as the chain stitch elon-gates when extended. Therefore, the stitching type is applied for setting sleeves and attaching elastic materials (Colovic, 2015; McLoughlin & Mitchell, 2014). Over-edge chain stitches (Class 500) are formed with at least one of the sewing threads that passes around the fabric edge. Many variations exist where up to four threads can be used to neaten the cut edge of fabric plies (Hayes & McLoughlin, 2013). The general character-istic of cover-seam chain stitches (Class 600) is that they are formed with three groups of threads, where two of the groups cover the surfaces of the fabrics. The number of threads and interconnection makes this stitch very strong, but elastic at the same time.
Figure 2.8. Principles of stitching: intralooping, interloping and inter-lacing. Reprinted from “Garment Manufacturing Technology,” by R. Nayak and R. Padhye, (2015), Woodhead Publishing Series in Tex-tiles, p.248.
Therefore, common applications of the stitch type are knitted garments, especially un-dergarments, athletic shirts and infant wear (Colovic, 2015).
A stitch can further be described by its size and consistency. The stitch size can be determined by the length, the width between the outermost lines of the stitch and the depth between the upper and lower part of the joint. The consistency describes the uni-formity of the stitch. According to Colovic (2015) light and medium weight fabrics obtain stitch length of about 2,5 mm, medium to heavy fabrics use 3 mm and heavy and thick fabrics should use a stitch length between 3,5 and 4 mm.
2.2.2.2 Seams
A seam consists of a row of stitches that joins two or more textiles together (Colovic, 2015). Different seam types are categorised into specific groups. The most common and most used seams are shown in Figure 2.9
Superimposed seams are two or more fabrics laid upon each other in the same orienta-tion and stitched together near to the edges. The seam can be produced with one or more stitches next to another by lockstitch, chain, over-edge or safety stitches (Colovic, 2015; International Organization for Standadization, 1991a). The seam type is easy to produce and a basic method to connect layers of fabric. The disadvantage of the seam is that the strength of the seam depends on the strength of the sewing thread and is therefore limited. Applications under high load are hence not suitable (McLoughlin & Mitchell, 2014).
Class 1: Superimposed seams Class 2: Double lapped seams
Class 3: Bound seams Class 4: Flat seams
Figure 2.9. Seam types with laying of the fabrics and location of sewing needle stitches. Adapted from “Sewing machines - Seam types - Classification and terminology”, by International Organization for Standardization, 1991a, [ISO 4916], p. 9, 14, 25, 33.
A very strong seam is the double lapped seam which is used in the area of apparel, outerwear and high-performance products. This seam is formed by lapping two plies of fabric and requires that the layers of fabric be lapped and seamed with one or more rows of stitches. A neat seam on the face of a fabric is manufactured with a bound seam, where a binding stripe is folded over the edge of one or more plies of fabric. It is used for decorative purposes and edge refinement and finds use in the manufacture of suitcases, tents necklines and short sleeves on t-shirts. For a flat seam, at least two plies of fabric are needed to sew the abutted edges of fabrics on the same level together by stitching across the edges of plies that are joined. Thereby, a minimum of two rows of stitching are introduced simultaneously. The seam group is often used to reduce bulk around the join, for example for underwear, pyjamas, men´s sports shirts and work clothes (Hayes & McLoughlin, 2013; Colovic, 2015).
2.2.3 Welded seams
The selection of seams and stitches for the connection of a product has a great influence on the quality of the product. If used improperly, the seam can also damage the product. The use of stitched seams for non-porous materials, such as waterproofed, fire or chem-ical resistant materials, causes a perforation that will reduces the performance of the garment. Welded seams prove to be an option to avoid these problems. Welded seams can be manufactured with thermoplastic materials. A temperature increase of the sub-strate causes the melting of the tissue at a certain temperature, whereby the interface of the two layers merge with each other. An applied pressure causes the material flow of one fabric into the other and by cooling a weld is produced. The method achieves ad-vantageous properties in terms of flexibility and conformity of clothing, weight, water re-sistance and strength of the seam. This process can be realised by different welding techniques: hot air, hot wedge, dielectric welding and ultrasonic welding (Colovic, 2015). Heated compressed air is directed at the joining area at hot air welding. A roller applies pressure right behind the hot air to bend the material and cool it. Different profiles of the roller can dedicate the weld impression. The seams produced by hot wedge are melted together by electrically heated jaws which are pressed on the welding area and cause a material flow, Figure 2.10. Different jaws are defining the profile of the weld impression. The third technique applies molecular vibration of a dielectric medium to join to fabrics together. The molecular vibration is caused by an electromagnetic generator placed next to the fabric. The vibration causes friction between the molecules whereby the fabric interface starts melting. Another method is to produce welded seams in ultrasonic weld-ing, where the fabrics are held together under pressure and mechanical ultrasonic vibra-tions are used to soften or melt the thermoplastic material. The needed frequency is 20-40 kHz. The mechanical energy of the ultrasonic vibration causes intermolecular and surface friction which is converted into thermal energy (Jones & Stylios, 2013; Gries & Klopp, 2007).
2.2.4 Hook and loop fastener
The connection method is based on a natural phenomenon, which is newly applied by two technologies. One technology consists of hooks and piles that interlock with each other, the other has mushroom-shaped pins instead of hooks, Figure 2.11. Although hook and loop fasteners produce temporary bonds, they provide high peel resistance, adhesive strength, and good longitudinal shear strength. The advantage of the technique is a rapid connection and release of two textiles is made possible and the ability to apply them on a variety of substrates by sewing, gluing, welding and ironing. A disadvantage of hook and loop fasteners is the interlocking with other unwanted materials, the reduc-tion of the bond after repeated use and difficulties in recycling (Gries & Klopp, 2007).
Welded fabrics
Rollers moving fabric and applying
Hot air directed into nip between fabrics Arm moves wedge
into position
Figure 2.10. Hot air wedge welding equipment. Adapted from “The use of heat sealing, hot air and hot wedge to join textile materials,” by I. Jones, 2013, Woodhead Publishing Limited, p.364.
Figure 2.11. Hook and loop fastener: left mushroom shaped pins and loops, right hooks and loops. Adapted from “Füge- und Oberflächentechnologien für Texti-lien“, by T. Gries, K. Klopp, 2007, Springer-Verlag Berlin Heidelberg, p.118.
3
Methodology
3.1 Concept development
The research is carried out in order to develop a first prototype of an intelligent wound dressing that is able to illuminate chronic wounds and accelerate their healing process. In general, both quantitative and qualitative research methods are used. Qualitative re-search is conducted in the form of literature rere-search and quantitative rere-search is done by testing potential prototypes. With the obtained data, a final prototype can be provided that fits best the requirements for an intelligent textile wound dressing.
1 Clarify and define the task
2 Determine functions and their structures
3 Search for solution principles and their combinations 4
Divide into realizable modules
5
Develop layout of key modules
6 Complete overall layout
7 Prepare production and operat-ing instructions Task Specifications Function structures Principal solutions Module structures Preliminary layout Definitive layouts Product documents Further realisation Fu lfi l a nd a da pt re qu ire m en t Ite ra te to w ar ds a nd b ac kw ar ds b etw ee n pr ev io us a nd fo llo w in g sta ge s
Figure 3.1. Procedure for the development according to VDI guideline 2221. Adapted from “Systematic approach to the development and design of tech-nical systems and products,” by Verein Deutscher Ingenieure (VDI 2221), 1993, p.9.
The general developing approach follows the guideline VDI 2221, Figure 3.1 (Verein Deutscher Ingenieure, 1993). It is a methodology for the general, industry-independent development of technical systems and products. In total five phases are carried out that build on each other, Figure 3.2.
The phases are subdivided into several work stages which all lead to an individual result. The stages can be carried out completely, only partially or repeatedly (iteratively). The procedure of each phase is explained in detail below.
Problem identification
The research problem is formulated and presented. The need for the development of an intelligent textile wound dressing for the treatment of chronic wounds is described, as well as its influence to society. The field of research is defined and a list of demands for the overall system as well as the single layers is documented.
A literature research is conducted to gather basic information, as well as to recognize and close information gaps on chronic wounds, wound dressings and current research topics. Moreover, literature research is carried out on possible joining technologies for the connection of the multiple layers of the wound dressing system. Keywords as chronic wounds, smart textiles, wound dressings, joining technologies and methods are used to search in different databases (e.g. ScienceDirect and SpringerLink).
Problem identification • Research problem • List of demands • Literature research • Product specification Research concept • Product breakdown structure • Morphologi-cal case Design and development • Factorial experiments • Prototype production • Testing Evaluation • Pairwise comparison • Weighting factors Elaboration • Product documenta-tion • Final proto-type fabrica-tion
Phase 1 Phase 2 Phase 3 Phase 4 Phase 5
The inclusion criteria that were used to make a choice about the usefulness of the doc-ument were:
• Published by a scientific source (peer-reviewed, journal) • Non-scientific literature
• Book publications • Previous reports
Articles not written in English or German, as well as articles not available in full text were excluded.
In addition, external requirements from previous researches are reviewed and completed by further requirements, thus the outcome of the working stage is the formulation of the product specification. They must be considered in the following steps of the research and kept up-to-date after each phase, as new knowledge is acquired during the devel-opment process that may affect the specifications previously provided. The final product specification for an intelligent wound dressing is presented in Chapter 3.1.1.
Research concept
Based on the knowledge previously gathered, the functional requirements of the wound dressing are defined. The main function of illuminating chronic wounds with LED light is divided into sub-functions. Additional secondary and elemental functions are identified to form structures that serve as the basis for the concept development. From this, a product breakdown structure is set up, which illustrates the derivation of the main func-tion in elementary funcfunc-tions of the wound dressing. The product breakdown structure can be found in Chapter 3.1.2.
From the functional structure, one can derive the search for individual solutions. For this purpose, a morphological case is created, which contributes to the development and illustration of basic solution approaches, Chapter 3.1.3.
There is a distinction between prototypes for investigating the mechanical properties of the wound dressing and prototypes for the optical and thermal investigation. Conse-quently, two principal solutions are selected for further research. The solutions for the prototypes that were developed to test the mechanical properties of the wound dressing focus on the connection of the layers. The material composition is the same in all solu-tions, while different joining methods are used for connecting the layers. Solutions cho-sen for determining the optical and thermal properties differ in their material composition.
Design and development
In the third phase, two factorial experiments are planned for the investigation of the chanical, thermal and optical properties. The experiment for the determination of the me-chanical properties of the joints can be divided into Connection 1 between functional and diffusion layer and Connection 2 between diffusion and separating layer. Each of the
connections is divided into two additional factors, connection method and geometry. The experiment covers all possible combinations of these connections across all factors, so that the impact of each factor on the mechanical properties can be investigated. The experiment on the overall system is also subdivided into two factors. Here, different ma-terial choices for the diffusion and separating layer are investigated.
After setting up the experiments, the production of the prototypes starts so that quantita-tive tests can be performed to determine if the prototypes meet the adaptation, lighting and thermal requirements of the textile wounds dressing. In Chapter 4 the construction of the prototypes is described in detail. A list of the testing methods can be found in Chapter 5.
Evaluation
The obtained data about the light intensity, thermal properties and the mechanical adapt-ability of the prototypes are interpreted and compared in this phase. After the evaluation, a statement about the overall system of a textile wound dressing can be made and the most suitable material composition can be named as final outcome of the research. The weightings of the results for the determination of the mechanical properties of the joints are acquired by a direct ranking, in which the ranking of the individual criterion is divided by the sum of the rankings. Due to the multitude of criteria that result from the investigation of the mechanical, thermal and optical properties of the material composi-tions, the weighting factors are determined by a pairwise comparison. Each criterion listed in Table 3.1 is compared with each other, in order to determined which criterion is more or equally important to the other. Following ratings are applied:
• 2 = Criterion (horizontal) is more important than criterion (vertical) • 0 = Criterion (horizontal) is less important than criterion (vertical) • 1 = Criterion (horizontal) is equally important than criterion (vertical)
The weightings are calculated by dividing the sum of rating in each horizontal line by the total sum of ratings:
78 = 98
∑;8<=98 ( 2)
with
78 Weighting factor of each criterion 98 Sum of ratings of each criterion
Table 3.1
Pairwise Comparison to Determine the Weighting Factors With Compared Cr ite rio n 1 Cr ite rio n 2 Cr ite rio n 3 Cr ite rio n 4 Cr ite rio n 5 Su m ri We ig h tin g s wi Criterion 1 0 2 2 1 5 25 % Criterion 2 2 0 0 2 4 20 % Criterion 3 0 2 2 2 6 30 % Criterion 4 0 2 0 2 4 20 % Criterion 5 1 0 0 0 1 5 % Total 20 100 % Elaboration
The result of the last phase is the construction of the final prototype that shows the first overall system of an intelligent textile close-to-body wound dressing with integrated LEDs for the use on chronic wounds. Additionally, a product documentation is generated that covers the clear description of the materials applied for the prototypes, the technologies used to build the prototypes and the testing methods carried out.
3.1.1 Product specifications
The intelligent wound dressing system in this research consists of two fundamental com-ponents. One is the electronic system which contains LEDs, conducting paths, intercon-nectors, controllers, power supply and actuators. The other is the wound dressing which is further divided into layers. A detailed product specification with the requirements and requests for the individual components is shown in Table 3.2. The parameters and crite-ria of the product specification were collected based on Chapter 1.2 and from specifica-tions created in previous work, this research builds on (Sukukumar, 2018; Sundarasivam & Omrani, 2018).
The integration of LEDs into a wound dressing should not interfere with the functions of a conventional hydro-active wound dressing for chronic wounds. For this reason, the requirements on draping properties, absorption capacity, moisture management and compatibility are equivalent to conventional wound dressings. The wound dressing “Ur-goSorb Silver” from Urgo GmbH, Sulzbach is used as benchmark for conventional hydro
active wound dressings. In terms of draping properties, the intelligent wound dressing should not interfere with the patient’s movement, develop wrinkles as well as cause no interface pressure. Therefore, the stiffness in bending and the Young´s modulus at the joints of the intelligent wound dressing should match the benchmark, 17,55 mN*cm² and 5,5 kPa. With the additional electronic components and the multi-layered nature of the intelligent wound dressing, it is impossible to maintain the weight of conventional wound dressings. Nevertheless, comfort should stay guaranteed and pressure points pre-vented. Minzuno and Takahash (2017) showed in their research that pressures above 32 mmHg lead to occlusion of the capillary vessels, resulting in ischemic injury. To avoid an interface pressure between the wound dressing and the patients skin the grammage of the wound dressing should not exceed 434,89 kg/m2. According to physicians involved
in the LEDSensTex project, the thickness of the wound dressing should be no more than 1 cm and optimally less than 0,5 cm, to ensure a comfortable fixation and application of the intelligent wound dressing.
The electronic components and the multi-layered construction of the wound dressing shall not affect the absorption capacity and moisture management of conventional wound dressings. The dressing should keep the wound moist and not too wet or too dry, creating an environment with 85 % water content and inherent permeability (Gupta, 2010). Ac-cording to the standard DIN EN ISO 13732-1, first-degree burns may already occur when the skin comes in contact with hot plastics at 48 °C for only 10 minutes and at 43 °C after 8 hours (International Organizastion for Standartization, 2008). In order to avoid tissue changes and burns, the irradiation of wounds should not cause the ambient temperature of the chronic wound to rise above 42 °C after 30 minutes to 2 hours.
In order to enable low-level light therapy with LEDs at 470 nm (blue light) or 630 nm (red light) in chronic wounds, a light intensity in the range of 40-100 mW/cm2 must be
achieved (Adamskaya, et al., 2011; Barolet, 2008; Minatel, Frade, Franca, & Enwemeka, 2009). At the same time, a homogeneous distribution of the light is necessary to achieve a uniform healing process of the wound. For a homogenous light distribution, a deviation of light intensity of 5 % is tolerated.
Due to the fact that the intelligent wound dressing is a medical product, the hygiene requirements are very high. To avoid the high regulation for such a product the separa-tion layer must be a disposable product which can be detached substituted after each use. The connection between the functional and diffusion layer should be durable and allow a repeated use of the system. In terms of sustainability, the combination of diffusion and functional layer should be reusable 50 times, in accordance with the minimum num-ber of washing cycles for textiles required by EN 3758:2012. Therefore, the joints should withstand 50 applications of the system and should be able to be sterilise or washed. A detailed list of the product specifications for the individual functional, diffusion and sepa-rating layer can be found in the Fehler! Verweisquelle konnte nicht gefunden
