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Analyzing Network Structures and Performance of Dextran Based Hydrogels Crosslinked with Thiol-Ene Chemistry
Jeong, Jeayoung
Jeong, Jeayoung
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Abstract
Understanding hydrogel network structures and their effects on physical properties and learning how to control them is crucial for effective biomedical applications. This study contrasts the hydrogel network structures and the performances of hydrogels formed by a thiol-ene reaction with those produced by the more widely used Michael addition reaction. Dextran modified with pentenoate groups (PDEX) hydrogels of varying molecular weights were fabricated via photo-initiated thiol-ene reaction and compared to dextran hydrogels crosslinked with divinyl sulfone (DVSDEX) produced through base catalyzed (pH 12) Michael-addition reaction. The initial hypothesis was that thiol-ene hydrogels would exhibit a different network structure, perhaps more uniform structure. The hydrogel network structure was characterized using mechanical tests, solute partitioning, and time-domain NMR (TDNMR), with key synthesis variables including varying polymer molecular weight(150kDa-40kDa), polymer concentration(5%-30%), and crosslinker concentration. Key network parameters, notably crosslink density(px), fiber radius (rf)and mesh size(ξ) were determined from these tests. Results from uniaxial compression showed that PDEX hydrogels had a higher crosslink density at lower polymer concentrations at synthesis compared to DVSDEX, indicating higher reaction efficiency. However, when swollen to equilibrium, no significant differences in properties were observed between the two hydrogel types, indicating that once formed, the gels had the same physical properties. Hydrogel structure was also evaluated by solute size exclusion theory. Partition coefficients (K) for solutes with ovalbumin and vitamin B12 both exhibited showed higher K in PDEX than DVSDEX at varying polymer volume fraction (p2). Experimental K values were to obtain the network fiber radius rf. Size exclusion models fit DVSDEX well over p2 range of 0.04-0.19 with a rf of 1.05nm and 0.99nm, respectively. However, PDEX showed large variation in rf over similar range of p2. These results provided clear evidence that the network structures of the two types of gels were different but did not confirm the hypothesis that PDEX would have a more uniform network. T2 relaxation distributions from TDNMR and rf values were used to determine hydrogel network mesh size. ξ calculated from TDNMR and mechanical characterization for DVSDEX matched well over the range of formulations tested. This important result is evidence that the experimentally simpler TDNMR method yields mesh sizes comparable to the standard method of modulus measurement. Protein encapsulation in hydrogels was analyzed post-synthesis using an aqueous two-phase extraction (ATPE) principles. The results indicated that crosslink density is a crucial factor determining the loading capacity of a hydrogel. For DVSDEX, smaller crosslink density exhibited both higher swelling and partition behavior in an aqueous two-phase system (ATPS), achieving a loading capacity of 23.85. The hypothesis that PDEX hydrogels would follow the ATPE heuristics, similar to DVSDEX hydrogels, was confirmed. Both DVSDEX and PDEX hydrogels exhibited consistent partitioning behavior driven by thermodynamics rather than size exclusion.
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2024-08-31
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University of Kansas
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Jeong_ku_0099M_19690.pdf
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Keywords
biomedical, dextran, drug delivery, hydrogel, pdex, pharmaceutical