Porous poly(vinyl alcohol)-alginate gel hybrid construct for neocartilage formation using human nasoseptal cells.

BACKGROUND: Limited options exist for the restoration of craniofacial cartilage. Autologous tissue or porous polyethylene is currently used for nasal and auricular reconstruction. Both options are associated with drawbacks, including donor site morbidity and implant extrusion. Poly(vinyl alcohol) (PVA) is a non-degradable flexible biocompatible polymer than can be engineered to mimic the properties of cartilage. The goal of this study was to engineer a biosynthetic hybrid construct using a combination of PVA-alginate hydrogels and human nasal septum chondrocytes. MATERIALS AND METHODS: Chondrocytes isolated from human nasal septum cartilage were expanded and mixed with 2% sodium alginate hydrogel. The chondrocyte-alginate mix was injected into a non-degradable porous PVA hydrogel, creating biosynthetic constructs. A group of these constructs were implanted into the subcutaneous environment of nude mice, while the other group was cultured in a spinner flask bioreactor system for 10 d and then implanted. After 6 wk in vivo, the histologic, biochemical, and biomechanical properties were examined. RESULTS: Histological analysis demonstrated sulfated glycosaminoglycans and deposition of collagen type II in constructs from both groups. Constructs cultured in the bioreactor system prior in vivo implantation demonstrated higher levels of DNA, glycosaminoglycans, and hydroxyproline. An increase of 22% in the compressive strength of the engineered constructs exposed to the bioreactor was also observed. CONCLUSION: A novel porous PVA-alginate gel hybrid was used to successfully engineer human cartilage in vivo. A 10-d period of bioreactor culturing increased levels of DNA, glycosaminoglycans, hydroxyproline, and the compressive modulus of the constructs.

The effect of polyethylene glycol on the stability of pores in polyvinyl alcohol hydrogels during annealing.

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.

Effects of solvent dehydration on creep resistance of poly(vinyl alcohol) hydrogel.

As a synthetic replacement material for osteochondral defect repair, poly(vinyl alcohol) (PVA) hydrogels offer a great potential due to their high water content and strong mechanical integrity. To survive the high stress environment in the joint space, high creep resistance becomes one of the key requirements for hydrogel implants. We hypothesized that reducing the equilibrium water content (EWC) of hydrogels would improve their creep resistance. We investigated the effect of dehydration of PVA theta-gels in various solvent/solution media followed by rehydration in saline solution. Decreasing EWC increased the creep resistance of PVA theta-gels. The most effective medium was isopropyl alcohol for reducing the EWC and increasing the creep resistance of PVA theta-gels.

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/cm, 30 J/cm). 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.

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.

Porous poly(vinyl alcohol)-hydrogel matrix-engineered biosynthetic cartilage.

The objective of this study was to fabricate hydrogel matrix-engineered biosynthetic cartilage using a porous poly(vinyl alcohol) hydrogel (PVA-H) and articular chondrocytes. Chondrocytes were suspended in fibrin gel (FG) or saline carriers and injected into porous PVA-H discs and three-layered constructs (PVA-H between devitalized cartilage). After implantation in nude mice, PVA discs were explanted at 6 weeks and subjected to creep testing for a 20 h period. The three-layered constructs were explanted at 12 weeks and subjected to tensile testing to determine the strength of the interface between the engineered hydrogel and devitalized cartilage. Histological analysis revealed PVA-H porous channels occupied by chondrocytes. Extracellular matrix was identified by Safranin-O and toluidine blue stains. Immunohistochemical analysis revealed a positive stain for COL II and scant staining for COL I. Creep and relaxation response of PVA-FG-chondrocyte constructs was similar to that of native cartilage. The presence of cells and FG significantly enhanced the integration strength of layered constructs (p < 0.05). These results demonstrate that porous PVA-H in combination with FG and chondrocytes provides a favorable microenvironment for tissue engineering of articular cartilage, creating a biosynthetic construct that can adhere to native devitalized articular cartilage utilizing hydrogel matrix-engineered technology.

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.