Poly(2-acrylamido-2-methylpropanesulfonic acid) gel induces articular cartilage regeneration in vivo: Comparisons of the induction ability between single- and double-network gels Munehiro Ogawa, 1,2 Nobuto Kitamura, 1 Takayuki Kurokawa, 3 Kazunobu Arakaki, 1 Yasuhito Tanaka, 2 Jian Ping Gong, 3 Kazunori Yasuda 1 1 Department of Sports Medicine and Joint Surgery, Graduate School of Medicine, Hokkaido University, Sapporo, Japan 2 Department of Orthopaedic Surgery, Nara Medical University, Nara, Japan 3 Laboratory of Soft and Wet Matter, Department of Advanced Transdisciplinary Sciences, Faculty of Advanced Life Science, Hokkaido University, Sapporo, Japan Received 7 July 2011; revised 16 February 2012; accepted 1 March 2012 Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jbm.a.34165 Abstract: The purpose of this study was to determine the in vivo cartilage induction effect of the poly(2-acrylamido-2- methylpropanesulfonic acid) (PAMPS) single-network (SN) gel and poly(N,N 0 -dimethyl acrylamide) (PDMAAm) SN gel in comparison with that of the PAMPS/PDMAAm double-net- work (DN) gel. An osteochondral defect created in rabbit trochlea was treated with PAMPS/PDMAAm DN, PAMPS SN, or PDMAAm SN gel implantation or left untreated. The gel was implanted into the defect so that a 2-mm depth remained. The defects were examined by histologic and im- munohistochemical evaluations, surface assessment using confocal laser scanning microscopy, and real-time polymer- ase chain reaction analysis at 4 weeks. Samples were quan- titatively evaluated with a scoring system reported by Wayne et al. The PAMPS/PDMAAm DN gel-implanted defect was filled with the hyaline-like cartilage tissue. The PAMPS SN gel-implanted defect was filled inhomogenously with hyaline/fibrocartilage tissue. The histology score of the defect treated with PAMPS/PDMAAm DN gel was signifi- cantly higher than those treated with PAMPS and PDMAAm SN gels, and the untreated defect (p ¼ 0.0408, p < 0.0001, and p < 0.0001, respectively) and the scores of the defect treated with PAMPS SN gel were significantly higher than those treated with PDMAAm SN gel and the untreated defect (p ¼ 0.0026 and p ¼ 0.0026, respectively). These results suggested that the PAMPS SN gel has an ability that can induce hyaline cartilage regeneration in vivo, but that the PDMAAm SN gel does not. The current study indicates that the chondrogenic potential of a negatively charged PAMPS gel component plays an important role in the carti- lage regeneration ability of the PAMPS/PDMAAm DN gel in vivo. V C 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 00A:000–000, 2012. Key Words: hyaline cartilage, cartilage repair, double-network hydrogel, polymer, chondrogenic differentiation How to cite this article: Ogawa M, Kitamura N, Kurokawa T, Arakaki K, Tanaka Y, Gong JP, Yasuda K. 2012. Poly(2-acrylamido-2- methylpropanesulfonic acid) gel induces articular cartilage regeneration in vivo: Comparisons of the induction ability between single- and double-network gels. J Biomed Mater Res Part A 2012:00A:000–000. INTRODUCTION Articular cartilage defects are often associated with pain, swelling, and limited mobility followed by degenerative changes and, therefore, are a significant and increasing healthcare concern. In the field of medicine, it has been a common belief that the articular hyaline cartilage tissue cannot spontaneously regenerate in vivo. 1,2 Recently, we have found that hyaline cartilage regeneration can be induced in vivo in vacant spaces within 4 wks when we implant a poly(2-acrylamido-2-methylpropanesulfonic acid)/poly(N,N 0 -dimethyl acrylamide) (PAMPS/PDMAAm) double-network (DN) gel plug at the bottom of a large osteochondral defect created in the rabbit patellofemoral joint so that a 1.5- to 3.5-mm deep vacant space is inten- tionally left in the defect. 3 Concerning the mechanism of cartilage regeneration induced by this DN gel, our in vitro study has found that the DN gel surface can enhance differ- entiation of chondrogenic ATDC5 cells into chondrocytes in in vitro conditions without application of insulin. 3 Our in vivo study has shown that joint immobilization signifi- cantly inhibits the hyaline cartilage regeneration induced by the DN gel implantation and suggested that the mechanical environment is one of the significant factors to induce this phenomenon. 4 However, the mechanism of the in vivo hya- line cartilage regeneration induced by this DN gel has not been fully elucidated. Correspondence to: N. Kitamura; e-mail: nobukita@aol.com Contract grant sponsors: Ministry of Education, Culture, Sports, Science and Technology, Japan; Nakatomi Foundation, Japan V C 2012 WILEY PERIODICALS, INC. 1