Biomechanical and histological evaluation of hydrogel implants in articular cartilage

We evaluated the mechanical behavior of the repaired surfaces of defective articular cartilage in the intercondylar region of the rat femur after a hydrogel graft implant. The results were compared to those for the adjacent normal articular cartilage and for control surfaces where the defects remained empty. Hydrogel synthesized by blending poly(2-hydroxyethyl methacrylate) and poly(methyl methacrylate-co-acrylic acid) was implanted in male Wistar rats. The animals were divided into five groups with postoperative follow-up periods of 3, 5, 8, 12 and 16 weeks. Indentation tests were performed on the neoformed surfaces in the knee joint (with or without a hydrogel implant) and on adjacent articular cartilage in order to assess the mechanical properties of the newly formed surface. Kruskal-Wallis analysis indicated that the mechanical behavior of the neoformed surfaces was significantly different from that of normal cartilage. Histological analysis of the repaired defects showed that the hydrogel implant filled the defect with no signs of inflammation as it was well anchored to the surrounding tissues, resulting in a newly formed articular surface. In the case of empty control defects, osseous tissue grew inside the defects and fibrous tissue formed on the articular surface of the defects. The repaired surface of the hydrogel implant was more compliant than normal articular cartilage throughout the 16 weeks following the operation, whereas the fibrous tissue that formed postoperatively over the empty defect was stiffer than normal articular cartilage after 5 weeks. This stiffness started to decrease 16 weeks after the operation, probably due to tissue degeneration. Thus, from the biomechanical and histological point of view, the hydrogel implant improved the articular surface repair.

Hidrogel sintético capaz de mimetizar o comportamento mecano-elétrico da cartilagem articular / Synthetic hydrogel capable of mimetism the machanoelectrical behavioral of articular cartilage

A cartilagem articular quando submetida a ação de força compressiva apresenta uma transdução mecano-elétrica. Acredita-se que os potenciais elétricos resultantes desse fenômeno de transdução influenciem a atividade biosintética dos condrócitos. Visando a obtenção de biomaterial que mimetize tal comportamento, para que possa ser utilizado no reparo de pequenos defeitos da cartilagem articular, foi sintetizado e caracterizado um hidrogel polimérico constituído por uma blenda sIPN de poli(Hema), usando poli(MMA-co-AA) como carga. O hidrogel obtido apresentou capacidade de absorção de água superior a 30 por cento e densidade de carga fixa de 0.1 meq/g. Em presença de solução de NaCl, o hidrogel apresentou o fenômeno de transdução elétrica, respondendo com potenciais de até 10mV quando submetido a cargas inferiores a 10 Kg.

Abstract - Articular cartilage under a compressive force shows a mechano electrical transduction. The electrical potentials rnay influence the biosynthetic activity of chondrocytes. Aiming the obtention of a biomaterial able to mimic this behaviour to be used in repair of articular cartilage defects a hydrogel constituted by a blend of poly(hydroxi ethyl methacrylate) with a copolymer of methyl methacrylate and acrylic acid as a filler was synthesised and characterised. The hydrogel obtained showed an equilibriurn water content upper than 30%, a fixed charge density of 0.1 meq/g and showed a mechano electrical transduction with potentials frorn O to l O m V for loads from O to 1 O Kg