Hydroxytritylcarboxamidomethyl polyethyleneglycol resin, High Load

Poly(vinyl alcohol) (PVA) hydrogels are candidate biomaterials for cartilage resurfacing or interpositional arthroplasty devices requiring high-creep resistance and high water content to maintain lubricity. Annealing of PVA improves creep resistance but also reduces the water content. We hypothesized that maintaining poly(ethylene glycol) (PEG) within PVA during annealing would prevent the collapse of the pores and thus would result in high equilibrium water content (EWC). Our hypothesis tested positive. The PVA hydrogels containing PEG maintained their opacity through annealing and exhibited large pores under confocal imaging while hydrogels not containing PEG turned translucent and no pores were visible after annealing. The EWC of gels annealed with PEG (83 +/- 1.0%) was higher than that of the gels processed without PEG (55 +/- 4.8). The crystallinity of the former was 8.0 +/- 1.7% and the latter was 27.5 +/- 8.7%. The hydrogels processed in the presence of PEG exhibited a significantly higher total creep strain (69 +/- 3.4%) when compared to the PEG-free hydrogels (17 +/- 3.7) under an initial contact stress of 0.45 MPa. EWC appeared to be strongly related to the creep resistance of annealed PVA theta-gels.

PVA hydrogels have desirable characteristics for use as soft tissue substitutes. However, PVA hydrogels are not high strength enough to withstand the demanding in load-bearing environment of human. In this paper, a high strength and low friction PVA-HA/PAA composite hydrogel is obtained by freezing-thawing and annealing method. The microstructure, thermal stability, mechanical and biotribological properties of the hydrogel are studied. Annealing PVA-HA/PAA composite hydrogel has porous structure, interaction occurred between PVA, HA and PAA. HA particles are distributed in PVA matrix and played a role of diffuse strengthening and toughening. Annealing improves the crystallinity and crosslinking of the hydrogel, annealing PVA-HA/PAA composite hydrogel has good thermal stability, strength and mechanical properties. The tensile strength of annealing PVA-HA/PAA composite hydrogel can be up to 3.71 MPa. Annealing PVA-HA/PAA composite hydrogel has favorable lubricating properties, and the friction coefficient is very low.

Poly(vinyl alcohol) (PVA) has been advanced as a biomaterial for the fabrication of medical devices to be used as synthetic articular cartilage because of its viscoelastic nature, high water content, and biocompatibility. Key material requirements for such devices are high creep resistance to prevent mechanical instability in the joint and high water content to maintain a lubricious surface to minimize wear and damage of the cartilage counterface during articulation. The creep resistance of PVA hydrogels can be increased by high temperature annealing; however this process also collapses the pores, reducing the water content and consequently reducing the lubricity of the hydrogel surface [Bodugoz-Senturk H, Choi J, Oral E, Kung JH, Macias CE, Braithwaite G, et al. The effect of polyethylene glycol on the stability of pores in polyvinyl alcohol hydrogels during annealing. Biomaterials 2008;29(2):141-9.]. We hypothesized that polymerizing acrylamide (AAm) in the pores of the PVA hydrogel would minimize the loss of lubricity during annealing by preventing the collapse of the pores and loss of water content. Increasing AAm content increased porosity and equilibrium water content and decreased the coefficient of friction, tear strength, crystallinity, and creep resistance in annealed PVA hydrogels.