Reconstituted collagen membranes (thickness 20–40 microns), used in periodontal guided tissue regeneration, were prepared by solubilization of bovine serosa and bovine tendon using an alkaline treatment and by solubilization of bovine serosa in acetic acid. Dielectric properties of these materials were determined in the frequency range of 10−5−106 Hz (poling temperature = 313 K, poling time = 3 h, E = 107 V/m), using a General Radio Bridge system (high frequencies) and a discharge current technique (low frequencies). The true pyroelectric coefficient p(T) was determined for these materials by a direct method over an appropriate temperature range. Their magnitude appear to be in the range of 10−4 to 10−5 C/m2 K−1, which is considerably higher than that of the ferroelectric poly(vinylidene fluoride) (PVDF) and its copolymer vinylidene fluoride‐trifluorethylene (VDF‐TrFE).
Recebido em 15/8/01; aceito em 19/2/02 PREPARATION AND CHARACTERIZATION OF COLLAGEN-CHITOSAN BLENDS. Biodegradable polymer blends were obtained using collagen and chitosan. Membranes of collagen and chitosan in different proportions (3:1, 1:1 and 1:3) were prepared by mixing their acetate solutions (pH 3.5) at room temperature. The blends were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier Transform infrared (FTIR) spectroscopy, specific viscosity, water absorption and stress-strain assays. The results showed that chitosan did not interfere in the structural arrangement of the collagen triple helix and the properties of the blends can be controlled by varing the proportion of the collagen and the chitosan.Keywords: blends; collagen; chitosan. INTRODUÇÃOO colágeno é uma proteína fibrosa presente na pele, tendões, ossos, dentes, vasos sangüíneos, intestinos e cartilagens, correspondendo a 30% da proteína total e a 6% em peso do corpo humano.A quitosana é um copolímero constituído de b-(1-4)-2-amino-2-deoxi-D-glicopiranose e b-(1-4)-2-acetamida-2-deoxi-D-glicopiranose, proveniente da reação de desacetilação da quitina, o segundo polissacarídeo mais abundante na natureza.O colágeno e a quitosana têm sido bastante utilizados na medicina, odontologia e farmacologia como biomateriais, pois são polímeros biocompatíveis, atóxicos e biodegradáveis, além de possuírem inú-meras propriedades biológicas [1][2][3][4][5][6] . As blendas poliméricas constituem-se na mistura de pelo menos dois polímeros ou copolímeros sem que haja qualquer reação quími-ca entre eles 7 . O interesse nesta área deve-se às crescentes aplicações práticas destes novos materiais e os principais estudos são voltados para a melhoria de suas propriedades físicas, físico-químicas e de processamento destes materiais, comparadas às propriedades dos polímeros puros 8 . Muitas blendas formadas pela combinação de biopolímeros, têm grande importância na área de biomateriais, sendo que é possível juntar as propriedades individuais de cada material em um só, além da possibilidade de melhorar ou controlar as suas propriedades mecânicas e biológicas através da interação entre as suas estruturas quí-micas diferentes. Recentemente, membranas e hidrogéis provenientes da mistura de colágeno e quitosana foram investigados pelas suas aplicações potenciais no campo dos biomateriais 9,10 . Já foi demostrado que as interações entre o colágeno e a quitosana dependem da organização estrutural do colágeno e da quantidade e distribuição de cargas ao longo das cadeias dos dois polímeros 11 . Estas propriedades estão diretamente relacionadas com o pH do meio, que é uma propriedade de fundamental importância para o estudo da interação entre eles em solução.Este trabalho teve por objetivos obter blendas colágeno-quitosana em diferentes proporções (3:1, 1:1 e 1:3) em pH 3,5, estudar a interação entre estes dois biopolímeros tanto na forma de membranas como em solução e avaliar suas propriedades físico-químicas. PARTE EXPERIMENTAL C...
In this study, we evaluated how different procedures of calcium phosphate synthesis and its incorporation in collagen:chitosan scaffolds could affect their structural and thermal properties, aiming the obtention of homogeneous scaffolds which can act as drug delivery vehicles in bone tissue engineering. Therefore, three different scaffold preparation procedures were developed, changing the order of addition of the components: in CC-CNPM1 and CC-CNPM2, calcium phosphate synthesis was performed in situ in the chitosan gel (1%, w/w) followed by mixture with collagen (1%, w/w), with changes in the reagents used for calcium phosphate formation; in CC-CNPM3 procedure, calcium phosphate was synthesized ex situ and then incorporated into the collagen gel, in which chitosan in powder was mixed. In all procedures, 5% (in dry mass) of ciprofloxacin was incorporated. FTIR analysis confirmed the presence of calcium phosphate in all scaffolds. DSC curves showed that collagen denaturation temperature (Td) increased with calcium incorporation. SEM photomicrographs of scaffolds cross-section revealed porous scaffolds with calcium phosphate grains internally distributed in the polymeric matrix. XRD diffractograms indicated that the calcium phosphates obtained are hydroxyapatite. The pore size distribution was more homogeneous for CC-CNPM3, which also stood out for its smaller porosity and lower absorption in PBS. These results indicate that the in situ or ex situ phosphate incorporation in the scaffolds had a great influence on its structural properties, which also had consequences for ciprofloxacin release. CC-CNPM3 released a smaller amount of antibiotic (30%), but its release profile was better described by all the tested models.
Autologous bone grafts, used mainly in extensive bone loss, are considered the gold standard treatment in regenerative medicine, but still have limitations mainly in relation to the amount of bone available, donor area, morbidity and creation of additional surgical area. This fact encourages tissue engineering in relation to the need to develop new biomaterials, from sources other than the individual himself. Therefore, the present study aimed to investigate the effects of an elastin and collagen matrix on the bone repair process in critical size defects in rat calvaria. The animals (Wistar rats, n = 30) were submitted to a surgical procedure to create the bone defect and were divided into three groups: Control Group (CG, n = 10), defects filled with blood clot; E24/37 Group (E24/37, n = 10), defects filled with bovine elastin matrix hydrolyzed for 24 h at 37 °C and C24/25 Group (C24/25, n = 10), defects filled with porcine collagen matrix hydrolyzed for 24 h at 25 °C. Macroscopic and radiographic analyses demonstrated the absence of inflammatory signs and infection. Microtomographical 2D and 3D images showed centripetal bone growth and restricted margins of the bone defect. Histologically, the images confirmed the pattern of bone deposition at the margins of the remaining bone and without complete closure by bone tissue. In the morphometric analysis, the groups E24/37 and C24/25 (13.68 ± 1.44; 53.20 ± 4.47, respectively) showed statistically significant differences in relation to the CG (5.86 ± 2.87). It was concluded that the matrices used as scaffolds are biocompatible and increase the formation of new bone in a critical size defect, with greater formation in the polymer derived from the intestinal serous layer of porcine origin (C24/25).
Chitosan/carbon nanotubes associations have applications in tissue regeneration. This study reports on the rheological characterization of gels prepared by the mixture of chitosan and single-walled carbon nanotubes (SWCN). Rheological characterization was used to understand the internal structure of gels. Frequency tests of chitosan/SWCN showed that gels have elastic behavior, and an increment in SWCN concentration increases G´ modulus. Gels had an increase in viscosity values of more than 10 times as a function of SWCN concentration. The addition of carbon nanotubes modified the behavior of gels as observed by temperature results. For all gels prepared with SWCN, G´ is higher than G´´ in the temperature range studied. SWCN changes the tridimensional network of chitosan and a new chain arrangement is obtained.
Recebido em 23/8/96; aceito em 21/5/97 COLLAGEN:CALCIUM PHOSPHATE COMPOSITES. PREPARATION AND CHARACTERIZA-TION. Anionic collagen: calcium phosphate composite was obtained by controlled mixing of collagen and calcium phosphate until the consistence of a past. Material was characterized by a Ca/P ratio of 1.55, with a X-ray diffraction pattern similar to that for hydroxyapatite. Differential Scanning Calorimetry showed that the protein is not denatured under the processing conditions. Scanning Electronic Microscopy showed that the mineral phase are regularly covered with collagen fibers, indicating that anionic collagen is efficient in the preparation of stable form of calcium phosphate ceramic paste.Keywords: composite; collagen; calcium phosphate. ARTIGO INTRODUÇÃOA maioria das biocerâmicas atualmente utilizadas serve apenas como suporte ou matriz para crescimento ósseo. Embora efetivo, esse crescimento é um processo muito lento, fazendo-se necessária a busca de materiais que tornem esse processo mais rápido. Os esforços para obtenção de novas biocerâmicas de fosfato de cálcio têm sido direcionados no sentido de melhorar suas propriedades tanto mecânicas como osteoindutoras, o que pode ser conseguido por meio da associação com polímeros sintéticos 1 , biopolímeros 2 , outras cerâmicas 3 e fatores de indução 4 . A grande aceitação das biocerâmicas à base de sais de fosfato de cálcio deve-se, principalmente, ao seu alto grau de biocompatibilidade, que provavelmente está associado à sua similaridade química com os materiais normalmente encontrados no tecido ósseo. Entre as cerâmicas com melhor desempenho estão os biovidros, alumina, β-tricálcio fosfato e hidroxiapatita (HA) 5 . São utilizadas em ortopedia e traumatologia para correções buco-maxilo-faciais, tumores músculo-esqueléticos, traumatismos raquimedulares e coluna cervical e, em odontologia, nos casos de doenças periodontais, implantes dentários, preenchimento de cavidades císticas e aumentos do rebordo ósseo alveolar 6 . Um dos maiores problemas na utilização da hidroxiapatita na forma particulada é sua dispersão para zonas de tecidos moles, causando problemas como a perda de partículas, redução da zona de correção, desconforto para o paciente, podendo até levar a uma nova cirurgia. A utilização de cerâmicas de fosfato de cálcio na forma de pasta é uma boa alternativa para se evitar tais problemas. De modo particular, o que não ocorre com as biocerâmicas ou qualquer outro material rígido, tais implantes podem ajustar-se perfeitamente aos defeitos, sem haver necessidade de moldagem prévia, já que podem ser moldados e endurecidos in situ, assegurando um melhor ajuste aos tecidos circundantes. A combinação de hidroxiapatita com colágeno 7,8 vem sendo sugerida pois o colágeno constitui-se em agente de união biocompatível e reabsorvível, responsável pela prevenção da migração das partículas cerâmicas até a incorporação pelos tecidos, além de ser um bom suporte para crescimento celular.Este trabalho descreve a preparação e a caracterização de um novo tipo de bi...
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