| dc.description.abstract | AbstractOsteoarthritis (OA) affects 300 million people worldwide, with roughly 80% of these cases being knee OA. While there are many events that promote OA, injury and maladaptive repair of the meniscal discs is a major factor. Considerable prior research has examined mechanisms behind regenerating avascular meniscal tissue, however, many limitations in both in vivo and in vitro models exist. The literature demonstrates that hyaluronic acid (HA) has viscoelastic properties conducive to tissue regeneration and specifically the rate of stress relaxation creates a regenerative cellular response not yet examined in meniscal cells1. The linear HA polymer has limited mechanical properties; however, functionalization using adaptive chemical moieties to promote crosslinking has been previously used to optimize those properties for tissue engineering applications. Common examples include use as injectables and scaffolds which creates further potential for implementation as extracellular matrix (ECM) mimics for in vitro studies of cell behavior and differentiation. HA functionalized with increasing amounts of pentenoic acid (PHA) provided a thiol-ene “click” chemistry platform to promote chain growth polymerization, and optimize crosslink density to modulate hydrogel network properties, including swelling and compressive properties. Herein, the role of degree of -ene substitution, modulated by the HA monomer to pentenoic acid molar ratio, on crosslink density and resulting network properties was investigated in water, phosphate buffered saline, and human cell complete growth media. Crosslink density was shown modulate the mechanical and physical characteristics of the hydrogels including swelling, compression, viscoelasticity, uniform network formation and degradation. The increased crosslinking led to reduction in swelling, increase in compressive modulus, a shift in the viscoelastic properties and reduction in mesh size and rate of degradation. In PBS and complete growth media with increased ionic strength, osmotic deswelling resulted in reduced swelling and reduced compressive modulus values of the gels. PHA hydrogels showed considerable progress toward the goal of producing a tunable hydrogel that resembles the ECM physically and viscoelastically. The robust production delivered reproducible degree of substitution (DoS) as a function of input ratios. The limitations of the system were apparent as the DoS increased and the possible occurrence of intramolecular thiol-ene reactions were increasing. By performing experiments in ionic solutions to mimic physical conditions it was evident that the ionic contributions from the solutions decreased the range of outputs for the gels due to osmotic deswelling. Even with osmotic deswelling the system is robust and allows for the control of the viscoelastic components of these hydrogels. This control is fundamental for utilization of the PHA system in future stress-relaxation studies. Across all conditions, the viscoelastic properties followed trends shown in native soft tissues including meniscal tissue, which is of interest for future studies. | |
