RESUMEN
The success of the scaffold-based bone regeneration approach critically depends on the biomaterial's mechanical and biological properties. Cellulose and its derivatives are inherently associated with exceptional strength and biocompatibility due to their ß-glycosidic linkage and extensive hydrogen bonding. This polymer class has a long medical history as a dialysis membrane, wound care system and pharmaceutical excipient. Recently cellulose-based scaffolds have been developed and evaluated for a variety of tissue engineering applications. In general porous polysaccharide scaffolds in spite of many merits lack the necessary mechanical competence needed for load-bearing applications. The present study reports the fabrication and characterization of three-dimensional (3D) porous sintered microsphere scaffolds based on cellulose derivatives using a solvent/non-solvent sintering approach for load-bearing applications. These 3D scaffolds exhibited a compressive modulus and strength in the mid-range of human trabecular bone and underwent degradation resulting in a weight loss of 10-15% after 24 weeks. A typical stress-strain curve for these scaffolds showed an initial elastic region and a less-stiff post-yield region similar to that of native bone. Human osteoblasts cultured on these scaffolds showed progressive growth with time and maintained expression of osteoblast phenotype markers. Further, the elevated expression of alkaline phosphatase and mineralization at early time points as compared to heat-sintered poly(lactic acid-glycolic acid) control scaffolds with identical pore properties affirmed the advantages of polysaccharides and their potential for scaffold-based bone regeneration.
Asunto(s)
Sustitutos de Huesos/síntesis química , Osteoblastos/fisiología , Osteogénesis/fisiología , Polisacáridos/química , Ingeniería de Tejidos/instrumentación , Andamios del Tejido , Células Cultivadas , Fuerza Compresiva , Módulo de Elasticidad , Análisis de Falla de Equipo , Dureza , Humanos , Ensayo de Materiales , Diseño de PrótesisRESUMEN
Tendon tissue engineering with a biomaterial scaffold that mimics the tendon extracellular matrix (ECM) and is biomechanically suitable, and when combined with readily available autologous cells, may provide successful regeneration of defects in tendon. Current repair strategies using suitable autografts and freeze-dried allografts lead to a slow repair process that is sub-optimal and fails to restore function, particularly in difficult clinical situations such as zone II flexor tendon injuries of the hand. We have investigated the effect of GDF-5 on cell proliferation and gene expression by primary rat adipose-derived stem cells (ADSCs) that were cultured on a poly(DL-lactide-co-glycolide) PLAGA fiber scaffold and compared to a PLAGA 2D film scaffold. The electrospun scaffold mimics the collagen fiber bundles present in native tendon tissue, and supports the adhesion and proliferation of multipotent ADSCs. Gene expression of scleraxis, the neotendon marker, was upregulated seven- to eightfold at 1 week with GDF-5 treatment when cultured on a 3D electrospun scaffold, and was significantly higher at 2 weeks compared to 2D films with or without GDF-5 treatment. Expression of the genes that encode the major tendon ECM protein, collagen type I, was increased by fourfold starting at 1 week on treatment with 100 ng mL(-1) GDF-5, and at all time points the expression was significantly higher compared to 2D films irrespective of GDF-5 treatment. Thus stimulation with GDF-5 can modulate primary ADSCs on a PLAGA fiber scaffold to produce a soft, collagenous musculoskeletal tissue that fulfills the need for tendon regeneration.
Asunto(s)
Tejido Adiposo/citología , Factor 5 de Diferenciación de Crecimiento/metabolismo , Regeneración , Células Madre/citología , Tendones/fisiología , Ingeniería de Tejidos/métodos , Animales , Materiales Biocompatibles/química , Fenómenos Biomecánicos , Células Cultivadas , Colágeno/química , Ácido Láctico/química , Masculino , Microscopía Confocal/métodos , Microscopía Electrónica de Rastreo/métodos , Ácido Poliglicólico/química , Copolímero de Ácido Poliláctico-Ácido Poliglicólico , Porosidad , Ratas , Ratas Endogámicas F344 , Tendones/metabolismo , Trasplante HomólogoRESUMEN
Electrospinning has emerged to be a simple, elegant and scalable technique to fabricate polymeric nanofibers. Pure polymers as well as blends and composites of both natural and synthetics have been successfully electrospun into nanofiber matrices. Physiochemical properties of nanofiber matrices can be controlled by manipulating electrospinning parameters to meet the requirements of a specific application. Such efforts include the fabrication of fiber matrices containing nanofibers, microfibers, combination of nano-microfibers and also different fiber orientation/alignments. Polymeric nanofiber matrices have been extensively investigated for diversified uses such as filtration, barrier fabrics, wipes, personal care, biomedical and pharmaceutical applications. Recently electrospun nanofiber matrices have gained a lot of attention, and are being explored as scaffolds in tissue engineering due to their properties that can modulate cellular behavior. Electrospun nanofiber matrices show morphological similarities to the natural extra-cellular matrix (ECM), characterized by ultrafine continuous fibers, high surface-to-volume ratio, high porosity and variable pore-size distribution. Efforts have been made to modify nanofiber surfaces with several bioactive molecules to provide cells with the necessary chemical cues and a more in vivo like environment. The current paper provides an overlook on such efforts in designing nanofiber matrices as scaffolds in the regeneration of various soft tissues including skin, blood vessel, tendon/ligament, cardiac patch, nerve and skeletal muscle.
Asunto(s)
Materiales Biocompatibles/química , Técnicas de Cultivo de Célula/métodos , Tejido Conectivo/anatomía & histología , Tejido Conectivo/fisiología , Electroquímica/métodos , Nanoestructuras/química , Nanoestructuras/ultraestructura , Nanotecnología/métodos , Ingeniería de Tejidos/métodosRESUMEN
Tissue engineering develops organ replacements to overcome the limitations associated with autografts and allografts. The work presented here details the development of biodegradable, porous, three-dimensional polymer-ceramic-sintered microsphere matrices to support bone regeneration. Poly(lactide-co-glycolide)/hydroxyapatite microspheres were formed using solvent evaporation technique. Individual microspheres were placed in a cylindrical mold and sintered at various temperatures. Scaffolds were characterized using scanning electron microscopy, mercury porosimetry, and mechanical testing in compression. After varying the temperature of sintering, a single temperature was selected and the time of sintering was varied. Mechanical testing indicated that as the sintering temperature or time was increased, the elastic modulus, compressive strength, maximum compressive load, and energy at failure significantly increased. Furthermore, increasing the sintering temperature or time resulted in a decreased porosity and the spherical morphology of the microspheres was lost as the microspheres blended together. To more closely mimic the bone marrow cavity observed in native bone tissue, tubular composite-sintered microsphere matrices were formed. These scaffolds demonstrated no statistically significant difference in compressive mechanical properties when compared with cylindrical composite-sintered microsphere matrices of the same dimension. One potential application for these scaffolds is bone regeneration.
Asunto(s)
Sustitutos de Huesos , Animales , Células de la Médula Ósea/citología , Regeneración Ósea , Sustitutos de Huesos/aislamiento & purificación , Adhesión Celular , Proliferación Celular , Células Cultivadas , Fuerza Compresiva , Durapatita/aislamiento & purificación , Calor , Ácido Láctico/aislamiento & purificación , Ensayo de Materiales , Microscopía Electrónica de Rastreo , Microesferas , Ácido Poliglicólico/aislamiento & purificación , Copolímero de Ácido Poliláctico-Ácido Poliglicólico , Polímeros/aislamiento & purificación , Ratas , Células del Estroma/citología , Ingeniería de TejidosRESUMEN
Recently, there has been a great deal of research activity in the development of stimulus-responsive polymeric hydrogels. These hydrogels are responsive to external or internal stimuli and the response can be observed through abrupt changes in the physical nature of the network. This property can be favorable in many drug delivery applications. The external stimuli can be temperature, pH, ionic strength, ultrasonic sound, electric current, etc. A majority of the literature related to the development of stimulus-responsive drug delivery systems deals with temperature-sensitive poly(N-isopropyl acrylamide) (pNIPAAm) and its various derivatives. However, acrylic-based pH-sensitive systems with weakly acidic/basic functional groups have also been widely studied. Quite recently, glucose-sensitive hydrogels that are responsive to glucose concentration have been developed to monitor the release of insulin. The present article provides a brief introduction and recent developments in the area of stimulus-responsive hydrogels, particularly those that respond to temperature and pH, and their applications in drug delivery.
Asunto(s)
Materiales Biocompatibles/química , Sistemas de Liberación de Medicamentos , Hidrogeles/química , Polímeros/química , Resinas Acrílicas/química , Animales , Humanos , Concentración de Iones de Hidrógeno , Poloxámero/química , TemperaturaRESUMEN
Microspheres of chitosan crosslinked with three different crosslinking agents viz, glutaraldehyde, sulphuric acid and heat treatment have been prepared to encapsulate diclofenac sodium (DS). Chitosan microspheres are produced in a w/o emulsion followed by crosslinking in the water phase by one of the crosslinking methods. Encapsulation of DS has been carried out by soaking the already swollen crosslinked microspheres in a saturated solution of DS. Microspheres are further characterized by FTIR, x-RD and SEM. The in-vitro release studies are performed in 7.4 pH buffer solution. Microspheres produced are spherical and have smooth surfaces, with sizes ranging between 40-230 microm, as evidenced by SEM. The crosslinking of chitosan takes place at the free amino group in all the cases, as evidenced by FTIR. This leads to the formation of imine groups or ionic bonds. Polymer crystallinity increases after crosslinking, as determined by x-RD. The method adopted for drug loading into the microspheres is satisfactory, and up to 28-30% w/w loading is observed for the sulphuric acid-crosslinked microspheres, whereas 23-29 and 15-23% of loadings are obtained for the glutaraldehyde (GA)- and heat-crosslinked microspheres, respectively. Among all the systems studied, the 32% GA crosslinked microspheres have shown the sloxvest release i.e. 41% at 420 min, and a fastest release of 81% at 500 min is shown by heat crosslinking for 3 h. Drug release from the matrices deviates slightly from the Fickian process.
Asunto(s)
Quitina/análogos & derivados , Quitina/química , Reactivos de Enlaces Cruzados/farmacología , Diclofenaco/farmacocinética , Composición de Medicamentos/métodos , Quitosano , Reactivos de Enlaces Cruzados/química , Preparaciones de Acción Retardada/farmacocinética , Diclofenaco/administración & dosificación , Cinética , Microesferas , Polímeros/química , Análisis Espectral , Propiedades de SuperficieRESUMEN
This paper reports solubility and partition coefficient data for the structurally similar pesticides, fenvalerate and cypermethrin, measured by UV spectrophotometry in binary mixtures of methanol and water at different temperatures. The solubility of both pesticides is much higher in methanol than in water at all temperatures. Partition coefficients were also measured between water+heptanol immiscible mixtures at 298.15K, and these data show a decrease with increasing composition of methanol in water.