Abstract
Heparin and four-armed, end-functionalized polyethylene glycol (starPEG) were recently combined in sets of covalently linked biohybrid hydrogel networks capable of directing various therapeutically relevant cell types. To extend the variability and applicability of this novel biomaterials platform, the influence of size and molar ratio of the two building blocks on the hydrogel properties was investigated in the present study. Heparin and starPEG were converted in various molar ratios and in different molecular weights to tune swelling, stiffness and pore size of the obtained polymer networks. Hydrogels with a range of elastic moduli could be generated by controlling either the crosslinking density or the chain length of the starPEG, whereas altering the molecular mass of heparin did not significantly affect hydrogel strength. The concentration of heparin in the swollen gels was found to be nearly invariant at varying crosslinking degrees for any given set of building blocks but adjustable by the size of the building blocks. Since heparin is the base for all biofunctionalization schemes of the gels these findings lay the ground for an even more versatile customization of this powerful new class of biomaterials.
Highlights
Hydrogels have been successfully used in biomedical fields due to their high water content, their advantageous mechanical properties and the weak non-specific interactions with molecular and cellular components of the biofluids [1,2,3,4,5,6,7,8,9]
Since we found that the swelling of the hydrogels depends on the crosslinking degree and the molecular mass of the building blocks, we determined how this change in swelling affected the final composition of the phosphate buffered saline (PBS) swollen hydrogels within the entire range of crosslinking degrees
Tissue engineering strategies require biomaterials with bioactivity and mechanical properties both being variable and independently adjustable over a wide range. To address this aim the network design of a recently developed modular starPEG heparin hydrogel system was extended by varying size and ratio of the two building blocks
Summary
Hydrogels have been successfully used in biomedical fields due to their high water content, their advantageous mechanical properties and the weak non-specific interactions with molecular and cellular components of the biofluids [1,2,3,4,5,6,7,8,9]. The most recent and exciting applications of hydrogels are cell-based therapeutics [10,11,12] and soft tissue engineering [13,14,15,16]. In various approaches it was shown that materials mimicking key parameters of the extracellular matrix (ECM) may directly affect cell growth and differentiation [20,21,22,23]. For hydrogels intended to trigger cellular fate decisions, critical design parameters include both biochemical properties and physical properties [18,19,24,25,26,27,28]. The elastic shear modulus of the fully swollen materials should be tunable in the range of 0.1 to 10 kPa to adjust the elasticity of soft tissues [26]. The hydrogel network should offer the possibility to incorporate appropriate bioactive moieties (e.g., cell binding domains, morphogens)
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