Tuning the Mechanical Properties of Injectable Physically
Crosslinked Hydrogels
Citation for published version (APA):
Fahimi, Z., Pawar, G. M., Sijbesma, R. P., & Wyss, H. M. (2012). Tuning the Mechanical Properties of Injectable Physically Crosslinked Hydrogels. Poster session presented at Mate Poster Award 2012 : 17th Annual Poster Contest.
Document status and date: Published: 01/01/2012 Document Version:
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Tuning the Mechanical Properties of
Injectable
Physically
Crosslinked
Hydrogels
Introduction
Polymeric hydrogels are widely investigated as synthetic scaffold materials for biomedical applications thanks to their suitable properties such as mechanical behavior similar to those of tissue, biocompatibility and biodegradability, and excellent permeability for oxygen, nutrients and metabolites.
Objective
Covalently cross-linked hydrogels are most frequently investigated, but they have several disadvantages: • Not self healing: Gel breakage is irreversible. • Not injectable: Gels cannot be liquefied as
required for injection.
Need a material that is strong enough to support cells but weak enough to reform during injection.
Here we present a new physically cross-linked material that fulfills these properties. The material is based on a segmented copolymer containing hydrophilic polyethylene glycol (PEG) domains and hydrophobic domains containing bis-urea groups, which lead to physical cross-linking via hydrogen bonding and hydrophobic interactions (fig1).
Results
At low concentrations, the chains form flower-like structures, with only few links between flowers. By increasing concentration, more links between flowers are formed, resulting in a elastic gel of loosely connected flowers. At even higher concentrations, as the overlap concentration(c*) of flowers is
approached, crowding dominates the structure and mechanics of the material (fig2(a)).
From the data in Fig. 2 we can extract the overlap concentration of flowers, which enables us to estimate the approximate number of segments per flower:
Self healing: Because the material is a transient network, after fracture at large strains, it recovers its initial elastic-like properties (fig. 2(a)).
Injectability: By applying a large strain, the material exhibits yielding into a liquid-like state (Fig. 3(a)), but still G’’ is too large for injection. The key factor that ensures injectability is the dramatic shear thinning of the material, shown in Fig. 3(b).
Conclusion:
Mechanical properties of our physically crosslinked hydrogels are readily tunable by concentration and the material has a high potential to be used as a injectable gel. Our hypothesis of the network structure is supported by the rheological data but should be further investigated using other methods such as scattering or direct imaging techniques.
\ department of mechanical engineering
Z. Fahimi, G. M. Pawar, R. Sijbesma, H. M. Wyss
Fig 1. Segmented copolymer with hydrophobic and hydrophilic blocks
Fig 2. (a) Concentration dependence of the storage modulus: 3 distinct regimes are observed. (b) Self healing
𝑐𝑠𝑜𝑓𝑡 𝑃𝐸𝐺 𝑏𝑙𝑜𝑐𝑘∗ = 𝑀 𝑅𝑔 3𝑁𝐴 = 0.1993 𝑚𝑔 𝜇𝑙 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑃𝐸𝐺𝑠 𝑝𝑒𝑟 𝑓𝑙𝑜𝑤𝑒𝑟 = 𝑐𝑠𝑒𝑔𝑚𝑒𝑛𝑡𝑒𝑑 𝑝𝑜𝑙𝑦𝑚𝑒𝑟∗ 23 𝑐𝑠𝑜𝑓𝑡 𝑃𝐸𝐺 𝑏𝑙𝑜𝑐𝑘∗ − 3
Fig 3. (a) Strain sweep of hydrogel (b) Shear thinning at high shear rates
