University of Groningen
Evaluation of nano-antimicrobial coated biomaterials in advanced in vitro co-culture models Ren, Xiaoxiang
DOI:
10.33612/diss.145072016
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date: 2020
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Ren, X. (2020). Evaluation of nano-antimicrobial coated biomaterials in advanced in vitro co-culture models. University of Groningen. https://doi.org/10.33612/diss.145072016
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum.
Summary
135
Biomaterial-associated infections (BAI) are the major cause of implant failure and can develop many years after implantation, which threatens the device functionality and longevity. Therefore, novel antimicrobial biomaterials and coatings to make surfaces less prone to BAI are essential to develop and evaluate in suitable in vitro models.
Chapter 1 reviews the need for co-culture models in the development of novel
antimicrobial biomaterials and coatings, summarizes available co-culture models in 2D and 3D systems, their critical factors and useful outcome parameters in a question and answer style. Tissue cells are always supposed to adhere to and integrate the surface of internal implants in order to protect the implant against infection. As described by Gristina, the fate of internal biomaterial implants in relation with the development of BAI is a “race for the surface” between bacteria and tissue cells. Proper dosing of antimicrobial control-strategies involves finding the balance between bacterial killing and collateral tissue damage, which inevitably arises when antimicrobials are over-dosed. Therefore, traditional mono-culture models tell a small part of the story, evaluating only the performance of a single cell type monolayer or adhering bacteria. Therefore, the aim of this thesis was to develop novel nano-antimicrobial biomaterial coatings and to explore the use of advanced co-culture models for their evaluation.
The soft-tissue seal around dental implants protects the osseo-integrated screw against bacterial challenges constitutes a complicated infection scenario, but there is no adequate in vitro model mimicking the soft-tissue seal around dental implants. In
Chapter 2, we set up a 3D-tissue model of the soft-tissue seal, in order to establish the
roles of oral keratinocytes, gingival fibroblasts and materials surface properties in the protective seal. The challenge of bacterial invasion (streptococci or staphylococci) to the fibroblast layer on the TiO2 surface negatively affected tissue integration of the
surface, demonstrating the protective barrier role of keratinocytes. Importantly, the protection offered by the soft-tissue seal appeared sensitive to surface properties of the implant material. Integration by fibroblasts of a hydrophobic silicone rubber surface was affected more upon bacterial challenges than integration of more hydrophilic
Summary
136
hydroxyapatite or TiO2 surfaces. This differential response to different
surface-chemistries makes the 3D-tissue infection model presented a useful tool in the development of new infection-resistant dental implant materials.
Although the 3D co-culture model was successfully set-up, the materials used to set up the model in Chapter 2 did not have antimicrobial properties. Therefore, a
photothermal, NIR activatable polydopamine coating was developed in Chapter 3 and
evaluated in peri-, post- and 3D-infection models, respectively. Photothermal bacterial killing bears the risk of collateral damage by heat dissipating into tissue surrounding an infection site, thus we addressed the hitherto neglected potential complication of collateral tissue damage by evaluating photothermal, polydopamine-nanoparticle coatings on titanium surfaces in different co-culture models. Contaminating staphylococci on PDA-NP coated titanium surfaces, as can be peri-operatively introduced, reduced surface coverage by fibroblasts and this could be prevented by NIR-irradiation for 5 min or longer prior to allowing fibroblasts to adhere and grow. Negative impacts of early post-operative staphylococcal challenges to an existing fibroblast-layer covering a coated surface were maximally prevented by 3 min NIR-irradiation. Longer irradiation times caused collateral fibroblast damage. Late post-operative staphylococcal challenges to a protective keratinocyte-layer covering a fibroblast-layer, required 10 min NIR-irradiation for adverting a staphylococcal challenge. Summarizing, photothermal treatment of biomaterial-associated-infection requires precise timing of NIR-irradiation to prevent collateral damage to tissue surrounding the infection site.
Photothermal therapy is an effective and long-term method to treat the infection, but the damage to surrounding cells cannot be ignored. To further study a surface favoring tissue integration over bacterial colonization, Chapter 4 was focused on the
development of low levels of Ag nanoparticle loaded or gentamicin loaded nanotubular titanium surface. In mono-cultures, loading of nanotubular surfaces with Ag nanoparticles facilitated bacterial killing but also caused tissue-cell death. Low-level loading with gentamicin provided release rates smaller than of clinically applied
Summary
137
gentamicin-loaded bone cements that killed adhering bacteria while maintaining tissue-cell viability. In bi-cultures, smooth as well as unloaded nanotubular surfaces were unable to kill adhering Staphylococcus aureus and Pseudomonas aeruginosa and could not prevent bacterial killing of gingival fibroblasts and osteosarcoma cells. However, low level gentamicin-loading of nanotubular titanium surfaces effectively eradicated contaminating bacteria in favor of tissue integration. Thus, care must be taken in loading nanotubular titanium surfaces with Ag nanoparticles, while low-level gentamicin-loaded nanotubular titanium surfaces can be used as a local antibiotic delivery system to negate failure of titanium implants due to peri-operatively introduced contaminating bacteria.
In the general discussion of Chapter 5, the advantages and limitations of in vitro
models, photothermal PDA-coated titanium surface, and gentamicin loaded titanium nanotubes are discussed. In vitro co-culture infection models as suggested in this thesis will allow better evaluation of biomaterials and coatings prior to animal experiments and possibly reduce the number of experimental animals. Finally, suggestions for future research are given.
