This paper presents a review of the chemical, physical and morphological characteristics, as well as the existing applications and mechanisms for the production of poly (3-hydroxybutyrate). This biopolymer, which is obtained from renewable sources, degrades when exposed in biologically active environments and is biocompatible, that is, it is not rejected by the human body in health applications. However, in spite of presenting similar properties with some conventional plastics, the PHB exhibits fragile behavior and thermal instability when processed. The literature proposes the use of blends, the development of copolymers or the insertion of additives in an attempt to improve the mechanical and thermal properties of PHB. Key words: Biopolymers; polyhydroxyalkanoates (PHA); Polyhydroxybutyrate (PHB). Universidad EAFIT 269|From Obtaining to Degradation of PHB: Material Properties. Part I De la obtención a la degradación de PHB: Propiedades del material. Parte I ResumenEste artículo presenta una revisión de las características químicas, físicas y morfológicas, así como las aplicaciones y mecanismos existentes para la producción de poli(3-hidroxibutirato). Este biopolímero, que se obtiene a partir de fuentes renovables, se degrada cuando se expone en ambientes biológicamente activos y es biocompatible, es decir, no es rechazado por el cuerpo humano en aplicaciones de salud. Sin embargo, a pesar de presentar propiedades similares con algunos plásticos convencionales, el PHB exhibe comportamiento frágil e inestabilidad térmica cuando se procesa. La literatura propone el uso de mezclas, el desarrollo de copolímeros o la inserción de aditivos en un intento por mejorar las propiedades mecánicas y térmicas del PHB.Palabras clave: Biopolímeros; degradación de PHB; polihidroxialcanoato (PHA); polihidroxibutirato (PHB).

Poly (L-co-D,L lactic acid) (PLDLA) is an important biomaterial because of its biocompatibility properties that promote cellular regeneration and growth. The aim of this study was to evaluate the polymer-tissue interaction of PLDLA implants in the dorsal subcutaneous tissue of male Wistar rats at various intervals (2, 7, 15, 30, 60 and 90 days) after implantation. Physical properties such as the glass transition point (Tg), degradation behavior and other mechanical properties were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), scanning electron microscopy (SEM) and tension tests. Analysis of the degradation of PLDLA membranes in vitro showed that the polymer became crystalline as a function of the degradation time. Mechanical tension tests showed that the polymer behaved like a ductile material: when subjected to constant tension it initially suffered deformation, then elongation and finally ruptured. TGA/MEV provided evidence of PLDLA membrane degradation. For histological analysis, samples from each group were processed in xylol/paraffin, except for the 60 -and 90 -day samples. Each of the latter samples was divided in two: one half was treated with xylol/paraffin and the other with historesin. Light microscopy showed the adhesion of cells to the biomaterial, the formation of a conjunctive capsule around the implant, the presence of epithelioid cells, the formation of foreign body giant cells and angiogenesis. During degradation, the polymer showed a 'lace' -like appearance when processed in xylol/paraffin compared to the formation of "centripetal cracks in the form of glove fingers" when embedded in historesin.

Aiming the development of high-performance biodegradable polymer materials, the properties and the processing behavior of poly(3-hydroxybutyrate), P(3HB), and their blends with poly(ε-caprolactone), PCL, have been investigated. The P(3HB) sample, obtained from sugarcane, had a molecular weight of 3.0 x 10 5 g.mol, a crystallinity degree of 60%, a glass transition temperature (T g ), at -0.8 °C, and a melting temperature at 171 °C. The molecular weight of PCL was 0.8 x 10 5 g.mol -1. Specimens of 70/30 wt. (%) P(3HB)/PCL blends obtained by injection molding showed tensile strength of 21.9 (± 0.4) MPa, modulus of 2.2 (± 0.3) GPa, and a relatively high elongation at break, 87 (± 20)%. DSC analyses of this blend showed two Tg´s, at -10.6 °C for the P(3HB) matrix, and at -62.9 °C for the PCL domains. The significant decrease on the T g of P(3HB) evidences a partial miscibility of PCL in P(3HB). According to the Fox equation, the new T g corresponds to a 92/8 wt. (%) P(3HB)/ PCL composition.

Abstract:The application of polymer-based bioresorbable temporary devices in the medical field grows continuously, and professionals from several areas act to solve problems related to body functions lost due to diseases, accidents or natural wear. Here we study the influence from poly(caprolactonetriol) (PCL-T) on the degeneration process in the copolymer poly(L-co-DL-lactic acid) (PLDLA) membrane, by producing PLDLA/PCL-T blends with 90/10, 70/30 and 50/50 relative concentrations. The data for in vitro degradation showed that PCL-T decreases the rate of PLDLA. This was obtained with the following techniques: Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Gel Permeation Chromatography (GPC) and Scanning Electron Microscopy (SEM). Therefore, it is possible to vary the membrane degradation rate by changing the blend composition, which is a tool to tailor a biomaterial.

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.

In our previous review (Part I -Material Properties), the chemical, physical and morphological properties, applications and mechanisms of obtaining poly (3-hydroxybutyrate) were discussed. PHB is a biologically based polymer that presents itself as an ecological option due to its characteristic degradation before environmental factors and due to the action of microorganisms such as algae, fungi and bacteria. In this second review, aspects related to the types of degradation to which this polymer is subjected and the necessary conditions for its degradation are addressed. Among these mechanisms are thermo-degradation, thermo-mechanical degradation, abiotic degradation, photo degradation and biodegradation. It is understood that the degradation of PHB can be seen as an advantageous feature of this material. This review complements the previous one and uses the same terminology. Universidad EAFIT 207|From Obtaining to Degradation of PHB: A Literature Review. Part II Keywords: Biopolymers; degradation of PHB; poly(hydroxyalkanoate) (PHA); poly(3-hydroxybutyrate) (PHB).De la obtención a la degradación de PHB: Una revisión de la literatura. Parte II ResumenEn nuestra revisión anterior (parte I -propiedades del material), se discutieron las propiedades químicas, físicas y morfológicas, aplicaciones y mecanismos de obtención del poli (3-hidroxibutirato). El PHB es un polí-mero de base biológica que se presenta como una opción ecológica debido a su característica de degradación en la presencia de factores ambientales y debido a la acción de microorganismos como algas, hongos y bacterias. En esta segunda revisión se abordan aspectos relacionados con los tipos de degradación a los que este polímero está sujeto y las condiciones necesarias para su degradación. Entre estos mecanismos están la degradación térmica, la degradación termomecánica, la degradación abiótica, la foto de degradación y la biodegradación. Se percibe que la degradación del PHB puede ser vista como una característica ventajosa de este material. Esta revisión complementa la anterior y utiliza la misma terminología.Palabras clave: Biopolímeros; degradación de PHB; poli(hidroxialcanoato)(PHA); poli(hidroxibutirato)(PHB).

A regeneração nervosa periférica auxilia na regeneração axonal e reorganização das fibras, atuando em lesões resultantes de esmagamento e secção do nervo. Nesse trabalho estudou-se a regeneração do nervo ciático utilizando-se tubos de poli(L-co-D,L-ácido láctico) preparados a partir de membranas obtidas por evaporação de solvente. Os tubos foram implantados no nervo ciático de 20 ratos da linhagem Spreague Dawley, durante 4, 8 e 12 semanas, sendo analisados por Calorimetria diferencial de varredura (DSC), Microscopia eletrônica de varredura (MEV), Cromatografia de permeação a gel (GPC), Análise termogravimétrica (TGA). O nervo regenerado foi avaliado pela técnica de Microscopia de luz (MO). Verificou-se um aumento do diâmetro do nervo em função do processo de degradação do tubo. Análises de DSC e GPC do PLDLA mostraram Tg em 57ºC e massa molar (Mw) de 197 989 gmol-1, respectivamente. Foram observadas nítidas variações nesses valores após 8 semanas de degradação, com Tg em 40ºC e Mw de 170000 g.mol-1. Dados de TGA também indicaram o processo de degradação com Ti em 333 ºC, antes da degradação e 305ºC, após 12 semanas. MEV mostrou formação de poros após 8 semanas de degradação. Esse estudo mostrou que tubos de PLDLA são promissores para a regeneração do nervo ciático.

RESUMO Este trabalho tem como objetivo a preparação de mantas compostas por fibras do polímero biodegradável poli(3-hidroxibutirato) -(PHB) por meio da técnica de eletrofiação. Obtiveram-se mantas sob diferentes condições, variando-se o fluxo, a temperatura da solução, a tensão aplicada e a adição de um agente surfactante. O material obtido foi analisado por microscopia eletrônica de varredura (MEV), calorimetria exploratória diferencial (DSC), termogravimetria (TG), difratometria de raios-X (DRX) e viabilidade celular. A caracterização por MEV mostrou que os melhores resultados, apresentando as fibras com diâmetros constantes de 0,77 µm e sem a formação de grãos, foram atingidos nas seguintes condições: concentração da solução de 10% (m/v) em CF/DMF (9/1), fluxo da solução de 5,8 ml/h, tensão de 17 kV e adição de surfactante (dodecilsulfato de sódio, SDS). Os resultados mostraram que as variações de vazão, tensão e a adição de surfactante não influenciam muito o diâmetro médio das fibras, enquanto o aumento da temperatura diminui este parâmetro. No entanto, a adição de um agente surfactante deixa a manta mais densa e com poros interconectados, além de permitir a proliferação celular, sendo então indicada para produção de mantas para uso como arcabouço.