In vivo approach of calcium deficient hydroxyapatite filler as bone induction factor.

Tissue engineering combine biomaterials, cells and biologically active molecules having as a goal create functional tissues; many of the compositions are blends of a polymeric matrix with ceramic fillers, however, reduction of mechanical resistance can be a drawback on ceramic-polymer systems. In this manuscript, we investigate the potential of calcium-deficient hydroxyapatite (CDHA) whiskers, a needle shape bioceramic, to enhance mechanical and osteoconduction properties on the polymeric matrix. For this purpose, PCL scaffolds incorporating CDHA whiskers were produced by combining solvent casting and particulate leaching techniques to develop a composite scaffold that possess mechanical and biological properties which is useful for bone tissue engineering regeneration. We produced CDHA whiskers using alkaline hydrolysis of α-tricalcium phosphate and characterized by XRD, XRF and SEM. PCL/CDHA scaffolds were fabricated with a final porosity of ~70%, quantified by SEM images. Mechanical properties were evaluated by compression test. As an initial test, PCL/CDHA scaffolds were immersed in simulated body fluid to quantify apatite deposition. In vitro and in vivo studies were performed to assess cytotoxicity and bioactivity. CDHA whiskers exhibited a needle-like morphology and a Ca/P ratio equal to calcium deficient hydroxyapatite. The composite scaffolds contained interconnected pores 177 to 350 µm in size and homogeneous ceramic distribution. The addition of CDHA whiskers influences the mechanical results: higher elastic modulus and compressive strength was observed on PCL/CDHA samples. In vitro results demonstrated biocompatibility on PCL and PCL/CDHA films. In vivo data demonstrated cellular infiltration from the surrounding tissue with new bone formation that suggests bioactive potential of CDHA whiskers. Our goal was to produce a scaffold with a potential induction factor and a favorable morphology, which was proved according to this study's findings.

Porous and dense poly(L-lactic acid) and poly(D,L-lactic acid-co-glycolic acid) scaffolds: in vitro degradation in culture medium and osteoblasts culture.

The use of bioresorbable polymers as a support for culturing cells has received special attention as an alternative for the treatment of lesions and the loss of tissue. The aim of this work was to evaluate the degradation in cell culture medium of dense and porous scaffolds of poly(L-lactic acid) (PLLA) and poly(D,L-lactic acid-co-glycolic acid) (50:50) (PLGA50) prepared by casting. The adhesion and morphology of osteoblast cells on the surface of these polymers was evaluated. Thermal analyses were done by differential scanning calorimetry and thermogravimetric analysis and cell morphology was assessed by scanning electron microscopy. Autocatalysis was observed in PLGA50 samples because of the concentration of acid constituents in this material. Samples of PLLA showed no autocatalysis and hence no changes in their morphology, indicating that this polymer can be used as a structural support. Osteoblasts showed low adhesion to PLLA compared to PLGA50. The cell morphology on the surface of these materials was highly dispersed, which indicated a good interaction of the cells with the polymer substrate.

Synthesis and characterization of poly(L-lactic acid) membranes: studies in vivo and in vitro.

The use of biodegradable polyesters as temporary structural supports in the recuperation of damaged live tissue is a promising area of research. Poly(L-lactic acid) (PLLA) membranes can act as a support for cell fixation and growth or as a barrier against soft tissues invasion in recuperating bone tissues. In this work, five different types of PLLA membranes, which varied in their polymer-solvent ratio and their content of plasticizer were studied. For the study in vivo, 6 mm diameter disks were inserted subcutaneously in the dorsal region of 15 Wistar rats, and the reactions on rats were studied 15 days later. In another series of experiments the samples were immersed in phosphate buffer, pH 7.4 at 37 degrees C, for 30 days. Membranes without plasticizer were morphologically dense and did not allow cell invasion nor tissue adherence, in contrast to membranes with plasticizer. While porosity enhanced cell fixation and growth, it made the membrane more fragile mechanically when compared to membranes without pores.

Devices for use as an artificial articular surface in joint prostheses or in the repair of osteochondral defects.

The covering of ultra high molecular weight polyethylene (UHMWPE) and calcium hydroxyapatite (HA)/tricalcium phosphate (TCP) porous solid substrate with polyHEMA hydrogel has been studied aiming at the development of devices to be used as artificial articular surfaces in joint prosthesis or osteochondral repair grafts. Commercial porous UHMWPE was used. Ceramic porous substrate was prepared by load compaction of an HA and TCP powder mixture obtained by aqueous precipitation technique. Two different compaction loads and grain size distribution was used. Polymer particles were added to the powder mixture in order to increase the substrate porosity after the sintering process. The porous substrate was covered with polyHEMA hydrogel by in situ polymerization. Morphological analysis (SEM) showed that a hydrogel layer formed in the porous solid top surface was fixed to the substrate by mechanical interlocking because the porous surface was filled by the hydrogel. After hydrogel covering, the resultant devices showed a decrease in the compressive elastic modulus that was influenced by the porous substrate material.

Preparation of bioabsorbable nerve guide tubes.

The use of bioabsorbable polymers in applications as temporary structural function, recovering damage in live tissues, is a promising research area. Membranes of poly(lactic acid) (PLA) may act as support to adhesion and cellular invasion or as devices for guided tissue regeneration (GTR). In this study, the same casting technique used to prepare membranes was used to prepare PLA tubes. These tubes can be used for tests in nerve guided regeneration (NGR). To improve flexibility of the device, a bioabsorbable plasticizer was added to the polymer. The initial results showed that the proposed technique allowed the preparation of flexible tubes that can be used for NGR.

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.

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