Desenvolvimento, caracterização e aplicação de membranas à base de celulose bacteriana e do nanocompósito celulose bacteriana/policaprolactona na ceratoplastia lamelar experimental em coelhos

• Ano de defesa: 2012
• Autor(a) principal: Queiroz, Paulo Victor da Silva
• Orientador(a): Borges, Andrea Pacheco Batista
• Banca de defesa: Benjamin, Laércio dos Anjos , Barud, Hernane da Silva
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Mestrado em Medicina Veterinária
• Departamento: Biotecnologia, diagnóstico e controle de doenças; Epidemiologia e controle de qualidade de prod. de
• País: BR
• Palavras-chave em Português: Úlcera de córnea; Biomaterial; Substituto tecidual
• Palavras-chave em Inglês: Corneal ulcer; Biomaterial; Tissue substitute
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::MEDICINA VETERINARIA::CLINICA E CIRURGIA ANIMAL::CLINICA CIRURGICA ANIMAL
• Link de acesso: http://locus.ufv.br/handle/123456789/5122

Corneal conditions are among the main causes of blindness in both humans and animals. Many surgical techniques are described to recover the cornea s physical structure and refractive state; among them is the use of different types of biomaterials. Due to the cornea s transparency, viscoelasticity and lack of vessels, biomaterials to be applied on them must undergo a careful selection. Bacterial cellulose (BC) and polycaprolactone (PCL) are two well known biomaterials, studied extensively in separate. The purpose of the present study was to produce and characterize membranes made of BC and PCL to be tested as corneal tissue substitutes in rabbit s cornea. Membranes of BC were produced through static culture of the bacteria Gluconacetobacter xylinus. Membranes were then washed, dried and swelled in acetone for 48 hours, followed by immersion in 25ml of 3% PCL solution for 72 hours. Next, membranes of the BC/PCL composite underwent several washes in acetone and were then dried to be characterized by scanning electron microscopy (SEM), X-ray diffraction, thermal and mechanical trials and luminous transmittance. In vivo study was conducted with the BC/PCL composite and with pure BC to evaluate their interactions with corneal tissue. At first, membranes were cut in 8mm diameter to be then applied in corneal tisse. Thirty six female rabbits were separated in three groups of 12 animals each. An ulcer of 5mm in diameter and 0.2mm in depth was created on the right cornea of all rabbits. From the base of the ulcer, the stroma was separated creating an interlamellar pocket, and each group of 12 animals received 8mm diameter BC/PCL composite membrane and the other group received BC membranes on the same size, both adjusted in the pocket. The last group did not receive any membrane, used as the control. Animals were followed for 45 days, where clinical evaluations for signs of pain and inflammation were conducted. Three animals of each group were euthanized on days 3, 7, 21 and 45 after surgery to collect samples for histology (HE and Picrosirius) and SEM. BC/PCL presented 84% of light transmission while pure BC presented 45%. Lower tension resistance and Young s module was observed on the composite compared to pure BC, while the composite presented greater elongation at rupture what demonstrates a greater viscoelasticity of this material. Eyes that received membranes presented moderate inflammation until 30 days after surgery, decreasing progressively until 45 days. Histology revealed the presence of lymphohistiocytic inflammatory infiltrate at 21 and 45 days in implanted groups, at a moderate intensity, as well as giant cells, suggesting chronic inflammatory and foreign body reactions. Fibroplasia was observed around the membranes, a positive sign of biocompatibility. Epithelization was complete only in control group, what shows that membranes surfaces did not allow epithelium growth and maintenance. Picrosirius staining showed a greater proportion of type III collagen at the end of 45 days in both implanted groups, suggesting that the repair process around the membranes was incomplete. SEM showed extracellular matrix and cells adhered to implant surfaces, suggesting integration at 45 days. Both membranes made of BC/PCL composite and BC alone stimulated chronic inflammatory and foreign body reactions and did not allow complete epithelization on their surfaces. Based on these conclusions, we believe that implants made of BC/PCL and BC using the here presented process are not indicated as a substitute for corneal tissue in rabbits.