Estudo inicial da degradação "in vitro" de poli (L-co-DL ácido lático) sintetizado em laboratório

Abstract

RESUMOO copolímero poli (L-co-DL ácido lático), PLDLA, tem se destacado no campo das próteses temporárias, porque o seu tempo de degradação é bastante compatível com aquele requerido no caso de fraturas ósseas. Neste trabalho, estudou-se a degradação "in vitro" de dispositivos processados na forma de placas do copolímero PLDLA sintetizado em laboratório. As placas do PLDLA foram imersas numa solução tampão fosfato (pH = 7,4) em um banho termostatizado a 37 o C ± 1 o C, durante especificados períodos (0, 2, 4, 8, 16, e 30 semanas), e avaliadas pelas seguintes técnicas: cromatografia de permeação em gel (GPC), calorimetria diferencial de varredura (DSC), microscopia eletrônica de varredura (MEV) e ensaios de flexão por três pontos. Foi observado, através do estudo "in vitro", que o processo de degradação afeta a massa molecular desde a segunda semana de estudo. As análises das curvas de DSC demonstram que o material, inicialmente amorfo, apresenta vestígios de cristalinidade durante o processo de degradação, enquanto que as análises de TGA demonstram que a estabilidade térmica do copolímero só é afetada após 16 semanas de estudo. A análise por meio de MEV mostrou que o dispositivo passa de denso para poroso após 18 semanas de estudo "in vitro". O ensaio de resistência à flexão mostrou que o copolímero consegue reter mais de 80 % de sua resistência após período de 4 meses de imersão, um resultado bastante compatível com aquele requerido para consolidação óssea. Palavras-chaves: Síntese, PLDLA, degradação in vitro. In vitro initial study degradation of poly (L-co-DL lactide acid) synthesized in laboratory ABSTRACTThe poly (L-co-DL lactic acid) copolymer, PLDLA, has achieved outstanding position in the temporary prostheses because its degradation life is up to goog extent compatible with the requirement for the bone fracture repair. In vitro degradation of the in-Lab synthesized PLDLA was studied. The PLDLA plates were immersed in a phosphate buffer solution with pH = 7,4 at 37 o C +-1 o C provided by a thermostat controlled bath for specified test times (2, 4, 8, 16 and 30 weeks) and evaluated by using the following techniques: gel permeation chromatography (GPC), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and three point flexural strength test. From in vitro test, it was found that change in the PLDLA molecular weight due to its degradation is already noticeable since the second test-week. The initially amorphous PLDLA presented traces of cristalline signs according to DSC curves, while the thermal stability of the copolymer is affected only after 16 test-weeks as shown by TGA results. The change of PLDLA pieces from dense to porous took 18 in-vitro test-weeks as revealed by SEM. After four test months, PLDLA was capable of retaining more than 80% of its original three-point flexural strengh, which is up to good extent compatible with the requirements for bone consolidation.

Preparation and characterization of paclitaxel-loaded PLDLA microspheres

“…This property is important because it directly influences the degradation rate of the polymer. Depending on the application it is desirable that polymeric devices should have a low degree of crystallinity in order to facilitate degradation and hasten removal of the remaining fragments of material from the site of implantation, particularly since the accumulation of crystalline polymeric fragments may produce inflammatory reactions 13,14 . The results described here indicate that PLDLA is a suitable material for drug encapsulation and delivery.…”

“…The two main factors that influence drug release from polymeric microspheres are the degradation of the polymer matrix and diffusion, both of which are influenced by the polymer morphology [16][17][18] . The poly (L, co-D,L-lactic acid) (PLDLA, Mw = 70.000 g/mol -1 ), in the 70:30 rate used in this study is an amorphous and bioresorbable material, has a structure that combines the best characteristics of poly (L-lactic acid) and poly (D-lactic acid), i.e., the mechanical properties of the first and the shorter degradation time of the second; these properties have made PLDLA a compound of great relevance in the controlled release of drugs 13,14 . Poly (hydroxy acid) degradation in vitro is generally considered to be heterogeneous and is more rapid in the center than at the surface when the devices are in contact with an aqueous medium.…”

“…This self-catalyzing behavior is common during the degradation of aliphatic polyesters. However, the process depends on the chemical structure and configuration of the polymeric chains, as well as the morphology of the device involved 13,14 . The paclitaxel-loaded PLDLA microspheres used here were obtained from poly (L, co-D,L-lactic acid), the degradation of which involves the hydrolysis of ester bonds.…”

“…In addition, PLDLA microspheres are degraded into non-toxic products in the human body. These characteristics make PLDLA an ideal new drug delivery carrier system 14 . The use of polymeric microspheres for drug encapsulation provides an alternative for drug delivery that helps to maintain the physical and chemical properties of the drug without changing its chemical structure.…”

Estudo inicial da degradação "in vivo" de poli(L-co-D,L ácido lático), sintetizado em laboratório, aplicado como prótese tibial em coelhos

“…Neste trabalho foi estudada a resposta in vivo destes pinos, sendo válido ressaltar que o estudo in vitro, deste mesmo material, já foi realizado num trabalho recentemente publicado [7]. A degradação de polímeros in vivo difere da degradação in vitro, principalmente porque in vivo o implante está submetido aos esforços mecânicos.…”