In-situ Preparation And Characterization Of Hydroxyapatite-porous Poly(vinyl Alcohol) Hydrogels For Articular Cartilage Repair

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1 In-situ Preparation And Characterization Of Hydroxyapatite-porous Poly(vinyl Alcohol) Hydrogels For Articular Cartilage Repair Orkun Kaymakci, Hatice Bodugoz-Senturk, Amy Moreira, Orhun K. Muratoglu, PHD. Harris Orthopaedic Laboratory, Massachusetts General Hospital, Boston, MA, USA. Disclosures: O. Kaymakci: None. H. Bodugoz-Senturk: None. A. Moreira: None. O.K. Muratoglu: 1; Zimmer, Biomet, Corin, Iconacy, Renovis, Conformis, Aston Medical, Meril Healthcare, Arthrex, Mako. 2; Biomet, Corin. Introduction: Cartilage repair is an ongoing challenge not only because the poor self-healing ability of cartilage but also the lack of the long term treatment. A candidate material for effective cartilage repair is non-degradable, porous Poly(vinyl alcohol) (PVA) hydrogel, which, when seeded with chondrocytes, allows generation of extra-cellular matrix within the open channel structure. The resulting hybrid material exhibits viscoelastic properties very similar to those of native cartilage (1-2). However, integration of porous PVA to the surrounding subchondral bone is challenging. We proposed to incorporate Hydroxyapatite (HA) in porous PVA to allow fixation to bone. HA is known to promote repair of bony defects (3-4). HA could also improve the mechanical properties of the hydrogel by reinforcing the polymer network (4). The bonding between the hydroxyapatite filler and the polymer network is another important consideration which may affect the mechanical properties and the bioactivity of the cartilage repair material (5). In this study, we investigated in-situ preparation hydroxyapatite-porous PVA material and characterized inorganic material presence and its effect on the polymer network. Methods: In-situ preparation of hydroxyapatite-porous poly(vinyl alcohol) hydrogels: PVA (115,000g/mol, Scientific Polymer Products) and Polyacrylamide(PAAm) (5-6,000,000g/mol, Scientific Polymer Products) were dissolved in deionized water (DI) at 90 C. Alkaline Ca(NO3)2 (Sigma-Aldrich) solution was added into the polymer mixture and stirred for 16h at 90 C. Alkaline diammonium hydrogen phosphate ((NH4)2HPO4) solution was slowly added into the solution. The Ca/P ratio was kept constant at After hydroxyapatite precipitation, a 2:3 mixture of PEG (400g/mol) and PEG(600g/mol) (Acros) was added into the solution and the hydroxyapatite-porous hydrogels were obtained by theta gelation method. One batch was put into DI water directly after gelation (non-annealed). Another batch was dehydrated in PEG400, annealed in air at 80 C for 20 hours and in argon gas at 160 C for 1 hour (annealed). Finally, the gels were hydrated in DI water at 40 C until equilibrium. The equilibrium water content (EWC) and hydroxyapatite content were obtained by a Thermogravimetric Analyzer (TGA)). Tensile properties were determined by pulling dog-bone shaped specimens until failure at a rate of 20mm/min on a tensile tester (Insight, MTS). ATR-FTIR spectra were obtained using FTIR analyzer (Varian 670 IR) at frequency regions of from 400 to 4000 cm-1 using a Germanium crystal. Creep properties were determined by custom build creep analyzers (Cambridge Polymer Group). Gels were loaded at 110N for 90 minutes and relaxed at 11N for 90 minutes in DI water at 40 C. Histological analysis was performed using Hematoxylin and Eosin (H&E) and Alizarin Red stain protocols. Results: FTIR spectra confirmed the formation of hydroxyapatite (Fig 1). The peak at 1030cm-1 was observed only in the spectra of the annealed gel, indicating the presence of phosphate moiety. Staining with H&E and Alizarin Red showed the presence of hydroxyapatite in the interconnecting channels of the annealed porous PVA (Fig 2). HA particles were not present in the nonannealed gels. TGA plots showed that water content of the non-annealed and annealed gels were 82 and 83%, respectively, and the hydroxyapatite content of the annealed gels was 12%. Annealed gels had higher strength and modulus, as expected (6). HA particles could also have reinforced the polymer network, increasing strength and modulus (Table 1). Similarly, annealing and the presence of the HA affected the creep resistance of the hydrogels significantly (Fig 3). Discussion: Hydroxyapatite was in-situ synthesized within the porous PVA gel. We confirmed the presence of HA in the annealed gels by FTIR spectroscopy and histology. HA particles were found inside the interconnected channels of the annealed porous PVA. These particles were not well integrated with the polymer in the non-annealed gels as HA was found diffusing into the rehydration medium. On the other hand, in-situ synthesis of HA and subsequent annealing provided strong bonding of the HA particles to the polymer network which increased the stability of the HA. Significance: In-situ prepared HA-porous PVA gel is a strong candidate as an osteochondral defect repair material. Acknowledgments: References: [1] Bodugoz-Senturk, H et al. Biomaterials, 2008, 29(2): [2] Bichara, D., A et al. Tissue Engineering:Part A, 2011, 17(3-4): [3] Pan, Y., D et al. Journal of Materials Science: Materials in Medicine, 2008, 19(5): [4] Ahn, S et al. 200, Nano Letters 1(3): [5] Fenglan X et al. Journal of Materials Science, 2004, 39(18): [6] Bodugoz- Senturk, H et al. Biomaterials, 2009, 30: Table 1. Tensile Properties

2 Break Stress(MPa) Break Strain(%) Modulus(MPa) non-annealed 0.27 ± ± ± 0.02 annealed 0.34 ± ± ± 0.03

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4 ORS 2014 Annual Meeting Poster No: 1179

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