Abstract
Biological hydrogels have been increasingly sought after as wound dressings or scaffolds for regenerative medicine, owing to their inherent biofunctionality in biological environments. Especially in moist wound healing, the ideal material should absorb large amounts of wound exudate while remaining mechanically competent in situ. Despite their large hydration, however, current biological hydrogels still leave much to be desired in terms of mechanical properties in physiological conditions. To address this challenge, a multi-scale approach is presented for the synthetic design of cyto-compatible collagen hydrogels with tunable mechanical properties (from the nano- up to the macro-scale), uniquely high swelling ratios and retained (more than 70%) triple helical features. Type I collagen was covalently functionalized with three different monomers, i.e. 4-vinylbenzyl chloride, glycidyl methacrylate and methacrylic anhydride, respectively. Backbone rigidity, hydrogen-bonding capability and degree of functionalization (F: 16 ± 12–91 ± 7 mol%) of introduced moieties governed the structure–property relationships in resulting collagen networks, so that the swelling ratio (SR: 707 ± 51–1996 ± 182 wt%), bulk compressive modulus (Ec: 30 ± 7–168 ± 40 kPa) and atomic force microscopy elastic modulus (EAFM: 16 ± 2–387 ± 66 kPa) were readily adjusted. Because of their remarkably high swelling and mechanical properties, these tunable collagen hydrogels may be further exploited for the design of advanced dressings for chronic wound care.
Highlights
Hydrogels are three-dimensional networks based on hydrophilic homo-polymers, co-polymers or macromers, which are cross-linked to form insoluble polymer matrices [1,2]
Sample nomenclature is as follows: functionalized collagen precursors are identified as ‘CRT-XXYY’, where ‘CRT’ indicates type I collagen isolated in-house from rat tails; ‘XX’ identifies the monomer reacted with CRT; ‘YY’ describes the monomer/lysine molar ratio used in the functionalization reaction
This observation may suggest that the additional functionalization of collagen with bulky 4-vinylbenzyl chloride (4VBC) aromatic moieties is likely to result in a detectable reduction of collagen triple helices, due to the inability of 4VBC moieties to mediate hydrogen bonds [57]
Summary
Hydrogels are three-dimensional networks based on hydrophilic homo-polymers, co-polymers or macromers, which are cross-linked to form insoluble polymer matrices [1,2]. Following the large amount of water absorbed by the dry polymer network in physiological aqueous conditions, the resulting gels are typically soft and compliant This behaviour results from the thermodynamic compatibility of the dry polymer with water, the presence of junction knots, as well as the low glass transition temperature (Tg) of the polymer network in hydrated conditions. In view of these features, the potential application of hydrogels in healthcare was first realized in the early 1960s, with the development of poly(2-hydroxyethyl methacrylate) gels as a contact lens material [3]. The design of multi-functional hydrogels based on naturally occurring biomacromolecules has received a great deal of
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