Eliana A. R. Duek

Síntese, caracterização e degradação " in vitro" do Poli(L-ácido láctico)

The study and application of bioreabsorbable polyesters to repair damaged tissues is a promising research area. Poly(L-lactic acid), PLLA, is the most important bioreabsorbable polyester due to it excellent biocompatibility and bioreabsorption. The aim of this work was to synthesize, characterize and evaluate the in vitro degradation process of PLLA membranes. The polymer was synthesized by ring opening of the cyclic diester of lactic acid, using as catalyst Sn(Oct)2. PLLA presented high values of molar mass (Mw around 105 g/mol) and its chemical structure was confirmed by RMN 1H, 13C and IR. The thermal properties of PLLA were studied by DSC, from which a high cristallinity degree was observed, consistent with the literature. The in vitro degradation of PLLA membranes demonstrated that the crystallinity degree increased with increasing degradation times.

Estudo da interação polímero/cartilagem/osso utilizando poli (ácido lático-co-ácido glicólico) e poli (p-dioxanona) em condilo femural de coelhos

Bioresorbable devices are alternatives for internal fixation. During the treatment, those devices maintain the fixation, degrade gradually and eliminate the need for a remove surgery, decreasing the treatment cost when compared with metallic devices. The aim of this work was to study the interaction polymer/tissue interaction using pins of PLGA and PDS implanted in New Zealand rabbits. The animals were separated in 3 groups which were sacrificed after 3, 6 and 12 weeks after implantation, and the obtained material was submitted to histological analysis. Histological analysis with PLGA implants showed after 3 weeks, the growth of a tissue with mesenchimal characteristics, after 3 weeks, with formation of mature bone aready after 12 weeks. PDS implants after 3 weeks showed a bigger invasion of mesenchimal tissue compared to PLGA and after 12 weeks an advanced degradation occurred, with proliferation of mesenchimal and bone tissue formation. It is concluded that the results are highly positive, with the relevant absence of cells responsible for inflammatory response. Analysis showed that the copolymer PLGA has better ostoinductive properties than PDS, showing biocompatibility acceptable for orthopedics application.

Use of blends of bioabsorbable poly(L-lactic acid)/poly(hydroxybutyrate- co-hydroxyvalerate) as surfaces for Vero cell culture

Vero cells, a cell line established from the kidney of the African green monkey (Cercopithecus aethiops), were cultured in F-10 Ham medium supplemented with 10% fetal calf serum at 37 degrees C on membranes of poly(L-lactic acid) (PLLA), poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) and their blends in different proportions (100/0, 60/40, 50/50, 40/60, and 0/100). The present study evaluated morphology of cells grown on different polymeric substrates after 24 h of culture by scanning electron microscopy. Cell adhesion was also analyzed after 2 h of inoculation. For cell growth evaluation, the cells were maintained in culture for 48, 120, 240, and 360 h. For cytochemical study, the cells were cultured for 120 or 240 h, fixed, processed for histological analysis, and stained with Toluidine blue, pH 4.0, and Xylidine ponceau, pH 2.5. Our results showed that cell adhesion was better when 60/40 and 50/50 blends were used although cells were able to grow and proliferate on all blends tested. When using PLLA/PHBV (50/50) slightly flattened cells were observed on porous and smooth areas. PLLA/PHBV (40/60) blends presented flattened cells on smooth areas. PLLA/PHBV (0/100), which presented no pores, also supported spreading cells interconnected by thin filaments. Histological sections showed that cells grew as a confluent monolayer on different substrates. Cytochemical analysis showed basophilic cells, indicating a large amount of RNA and proteins. Hence, we detected changes in cell morphology induced by alterations in blend proportions. This suggests that the cells changed their differentiation pattern when on various PLLA/PHBV blend surfaces.

Membranas de poli (ácido lático-co-ácido glicólico) como curativos para pele: degradação in vitro e in vivo

Poly (lactide-co-glycolide) is a polymer with bioabsorption and biodegradation properties. The physical and chemical properties of this polymer have been studied in order to modulate its susceptibility to degradation and its interaction with cells and biological fluids, aiming at medical and dental applications. In this work, membranes of poly (lactide-co-glycolide) with and without plasticizer were prepared by solvent evaporation and characterized by in vitro and in vivo experiments. In vitro studies showed that the glass transition temperature decreased due to the addition of plasticizer and, consequently, their flexibility increased. During degradation, crystalline areas and porous appear. In vivo studies showed that the polymer degraded rapidly without causing inflammation and protected areas that were exposed to external agents. Furthermore, membranes improved wound healing time, indicating that they can be potentially used in skin repair.

Development, characterization, and cellular adhesion of poly(L-lactic acid)/poly(caprolactone triol) membranes for potential application in bone tissue regeneration.

Poly(L-lactide)/poly(caprolactone triol) (PLLA/PCL-T) membranes were prepared by solution casting in 100/0, 90/10, and 70/30 (w/w) ratios. The membranes were analyzed by dynamic mechanical analysis, differential scanning calorimetry, and mechanical tests. The thermal analysis showed that the 90/10 and 70/30 preparations were partly miscible systems. The glass transition temperature (Tg ) of PLLA decreases as the PCL-T concentration increases, which implies that PCL-T has a plasticizer function. An in vitro study with osteoblastic cells isolated from the calvariae of rats was performed in all preparations. The results obtained in this study showed that the addition of PCL-T to the PLLA matrix modifies its mechanical, thermal, and biological properties. These blends could be useful for tissue engineering for bone applications.

Degradação Acelerada de Suportes de Poli(ε-Caprolactona) e Poli(D,L-Ácido Láctico-co-Ácido Glicólico) em Meio Alcalino

The in vitro degradation studies of bioresorbable polymers in alkaline medium have been proposed as alternative to the traditional studies in phosphate buffer solution. This work describes the study of the accelerated degradation of the poly(e-caprolactone) (PCL) and poly(D,L-lactic acid lactic-co-glycolic acid) (50/50) (PLGA50), a biodegradable and bioresorbable polymer widely studied for biomedical applications. Samples were prepared with the melt compression method in a cylindrical mold (2 mm diameter), at 160 oC, and submitted to the degradation in solutions of NaOH in pH 12, 13 and 13.7 at 37 oC. The results from the characterization of the mass variation, morphology and thermal properties, using differential scanning calorimetry, showed that the samples of PCL are stable compared to the one of PLGA50. The thermal properties could be extrapolated as a function of time in the physiological pH, 7.4. Once validated, the accelerate study of degradation in alkaline medium proved to be a useful, low cost technique for evaluation of samples with short degradation times.

Characterization of the release profile of doxycycline by PLGA microspheres adjunct to non-surgical periodontal therapy

The aim of this pilot study was to assess the release of locally delivered doxycycline by poly (l-lactide-co-glycolide) (PLGA) microspheres in the periodontal pocket of patients with chronic periodontitis, treated by non-surgical periodontal therapy. Nineteen sites of non-adjacent teeth of four different patients were evaluated. Five milligram of PLGA microspheres loaded with 16 doxycycline hyclate (DOX) was administered per periodontal site. To quantify DOX released into the periodontal pocket, gingival crevicular fluid (GCF) was collected from the sites on days 2, 5, 7, 10, 15, and 20 after DOX application, and high-performance liquid chromatography was performed. Data were statistically assessed by ANOVA/Tukey test. At days 2, 5, and 7, the DOX concentration was stably sustained (23.33 ± 1.38, 23.4 ± 1.82, and 22.75 ± 1.33 μg/mL, respectively), with no significant differences over these assessment times (p > 0.05). At days 10 and 15, a tendency was observed toward a decrease in DOX concentration (21.74 ± 0.91 and 20.53 ± 4.88 μg/mL, respectively), but a significant decrease in GCF drug concentration (19.69 ± 4.70 μg/mL) was observed only on day 20. The DOX delivery system developed demonstrated a successful sustained release after local administration, as an adjunct to non-surgical periodontal therapy.

Blendas de poli (ácido lático-co-ácido glicólico)/ poli (ácido lático): degradação in vitro

Resumo: Placas de copolimero de poli(acido lactico-co-glicolico) tem sido produzidas e usadas como implantes que degradam e sao absorvidos pelo organismo. Implantes que podem ser absorvidos apresentam vantagens em relacao aos implantes metalicos. Nesse trabalho, foram obtidas placas a partir de blendas de poli(acido lactico-co-glicolico)/ poli(acido latico), (PLGA/PLLA) e caracterizadas durante o processo de degradacao in vitro. Verificou-se que as blendas sao imisciveis e a estabilidade termica das mesmas aumenta com a propor- cao de PLLA. O grau de cristalinidade tambem aumenta com a proporcao de PLLA na amostra e com o tempo de degradacao. Alem disso, verificou-se que o PLGA degrada rapidamente e sua presenca e quanti- dade modifica nitidamente a morfologia das blendas. Palavras-chave: Blendas, poli(L-acido latico), poli(L-acido latico-co-acido glicolico), degradacao. Poly (Lactide-co-Glycolide) Acid/Poly (Lactic Acid) Blends: In vitro Degradation Abstract: Plates of the copolymer poly (lactide-co-glycolide) acid have been produced and used as im- plants that degrade and are absorbed by the organism. Implants that can be absorbed are advantageous in comparison with metallic implants. In this work, plates of the blend poly (lactide- co- glycolide) acid/ poly lactic acid (PLGA/ PLLA) were made and characterized during their in vitro degradation process. It was found that blends are immiscible and that their thermal stability increases with the proportion of PLLA in the blend. The crystallinity degree also increases with the proportion of PLLA in the sample and with degradation time. Besides, it was verified that PLGA is degraded quickly and its presence and amount modifies clearly the morphology of the blends.

Bilaminar Device of Poly(Lactic‐co‐Glycolic Acid)/Collagen Cultured With Adipose‐Derived Stem Cells for Dermal Regeneration

Several materials are commercially available as substitutes for skin. However, new strategies are needed to improve the treatment of skin wounds. In this study, we developed and characterized a new device consisting of poly(lactic-co-glycolic acid) (PLGA) and collagen associated with mesenchymal stem cells derived from human adipose tissue. To develop the bilaminar device, we initially obtained a membrane of PLGA by dissolving the copolymer in chloroform and then produced a collagen type I scaffold by freeze-drying. The materials were characterized physically by gel permeation chromatography, scanning electron microscopy, and mass loss. Biological activity was assessed by cell proliferation assay. A preliminary study in vivo was performed with a pig model in which tissue regeneration was assessed macroscopically and histologically, the commercial device Integra being used as a control. The PLGA/collagen bilaminar material was porous, hydrolytically degradable, and compatible with skin growth. The polymer complex allowed cell adhesion and proliferation, making it a potentially useful cell carrier. In addition, the transparency of the material allowed monitoring of the lesion when the dressings were changed. Xenogeneic mesenchymal cells cultured on the device (PLGA/collagen/ASC) showed a reduced granulomatous reaction to bovine collagen, down-regulation of α-SMA, enhancement in the number of neoformed blood vessels, and collagen organization as compared with normal skin; the device was superior to other materials tested (PLGA/collagen and Integra) in its ability to stimulate the formation of new cutaneous tissue.

Haste intramedular polimérica bioreabsorvível (PLLA/PHBV) para uso na recuperação de fraturas ósseas

The growing interest in medicine with the use of bioreabsorbable polymeric materials has been stimulating researchers from orthopedic area to develop more biological solutions, substituting threads, stems and metallic plates for bioreabsorbable polymers in the treatment of fractures. So, we decided to study implants of the PLLA/PHBV blends (two bioreabsorbable polymers) moulded in a mini-injector. Those implants were used for recovery of fractures of rabbit femur and assessed in comparison with the thread of Steinmann (stainless steel, commercially used). After euthanasia with 6, 12 and 24 weeks of implantation of the artifacts, the bones were studied with X ray, histological exam and mechanic test, while the polymeric implants were submitted the scanning electron microscopy (SEM), mechanic test and modular differential scanning calorimetry (MDSC). The X ray showed good calluses bone with the use of the polymer stem as well as with the metallic control. The histological study showed absence of inflammatory reactions or osteolysis. The mechanical test showed bone consolidation in the two groups. In the mechanical test and in the calorimetry studies, the polymeric stem presented signs of progressive degradation within the studied time. With the data obtained, we can state that the implant PLLA/PHBV demonstrated to be as effective in repairing fractures of rabbit femur as the metallic control.