Hatice Bodugoz-Senturk

Poly(vinyl alcohol)–acrylamide hydrogels as load-bearing cartilage substitute

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.

Quantifying the lubricity of mechanically tough polyvinyl alcohol hydrogels for cartilage repair

Polyvinyl alcohol hydrogels are biocompatible and can be used as synthetic articular cartilage. Their mechanical characteristics can be tailored by various techniques such as annealing or blending with other hydrophilic polymers. In this study, we quantified the coefficient of friction of various candidate polyvinyl alcohol hydrogels against cobalt–chrome alloy or swine cartilage using a new rheometer-based method. We investigated the coefficient of friction of polyvinyl alcohol–only hydrogels and blends with polyethylene glycol, polyacrylic acid, and polyacrylamide against swine cartilage and polished cobalt–chrome surfaces. The addition of the functional groups to polyvinyl alcohol, such as acrylamide (semi-interpenetrating network) and acrylic acid (blend), significantly reduced the coefficient of friction. The coefficient of friction of the polyvinyl alcohol–only hydrogel was measured as 0.4 ± 0.03 against cobalt–chrome alloy, and 0.09 ± 0.004 against cartilage, while those measurements for the polyvinyl alcohol–polyacrylic acid blends and polyvinyl alcohol–polyacrylamide semi-interpenetrating network were 0.07 ± 0.01 and 0.1 ± 0.003 against cobalt–chrome alloy, and 0.03 ± 0.001 and 0.02 ± 0.001 against cartilage, respectively. There was no significant or minimal difference in the coefficient of friction between samples from different regions of the knee, or animals, or when the cartilage samples were frozen for 1 day or 2 days before testing. However, changing lubricant from deionized water to ionic media, for example, saline or simulated body fluid, increased the coefficient of friction significantly.

An intraluminal stent facilitates light-activated vascular anastomosis.

BACKGROUND Photochemical tissue bonding (PTB) is a sutureless, light-activated technique that produces a watertight, microvascular repair with minimal inflammation compared to standard microsurgery. However, it is practically limited by the need for a clinically viable luminal support system. The aim of this study was to evaluate a hollow biocompatible stent to provide adequate luminal support to facilitate vascular anastomosis using the PTB technique. METHODS Forty rats underwent unilateral femoral artery transection. Five rats were used to optimize the stent delivery method, and the remaining 35 rats were randomized into three groups: (1) standard suture repair with 10-0 nylon microsuture (SR), (2) standard suture repair over the stent (SR + S), or (3) PTB repair over stent (PTB + S). For the PTB group, a 2-mm overlapping cuff was painted with 0.1% (wt/vol) Rose Bengal then illuminated for 30 seconds on each side (532 nm, 0.5 W/cm2, 30 J/cm2). Anastomotic leak and vessel patency (immediate, 1 hour, and 1 week postoperatively) were assessed. RESULTS Vessels in all three groups were patent immediately and at 1 hour postoperatively. After 1 week, all animals displayed patency in the SR group, while only 5 of 14 and 2 of 8 surviving animals had patent vessels in the PTB + S and SR + S groups, respectively. CONCLUSIONS This study demonstrated successful use of an intraluminal stent for acute microvascular anastomosis using the PTB technique. However, the longer-term presence of the stent at the anastomotic site led to thrombosis in multiple cases. A rapidly dissolvable stent should facilitate a light-activated microvascular anastomosis with excellent long-term patency.

Abstract P6: A Photochemical Tissue Bonding Approach for Sutureless Microvascular Anastamosis in an Arterial Graft Model

PurPose: Microvascular repair with suture remains the gold standard, but can lead to inflammation and thrombosis, especially in small peripheral vessels. Use of clips, couplers, and rings can assist with technical difficulties but do not minimize risk of thrombosis or endothelial damage. Photochemical tissue bonding (PTB) is a technique that covalently links protein to create an immediate watertight bond, and has been employed by our group for wound closure in several tissues including cornea, skin, tendon, and peripheral nerve. We hypothesize that use of PTB in conjunction with a biocompatible intraluminal stent would result in a watertight seal with minimal endothelial inflammation.