Sangamesh G. Kumbar

Electrospun nanofiber scaffolds: engineering soft tissues

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.

Electrospun poly(lactic acid-co-glycolic acid) scaffolds for skin tissue engineering.

Electrospun fiber matrices composed of scaffolds of varying fiber diameters were investigated for potential application of severe skin loss. Few systematic studies have been performed to examine the effect of varying fiber diameter electrospun fiber matrices for skin regeneration. The present study reports the fabrication of poly[lactic acid-co-glycolic acid] (PLAGA) matrices with fiber diameters of 150-225, 200-300, 250-467, 500-900, 600-1,200, 2,500-3,000 and 3,250-6,000 nm via electrospinning. All fiber matrices found to have a tensile modulus from 39.23+/-8.15 to 79.21+/-13.71 MPa which falls in the range for normal human skin. Further, the porous fiber matrices have porosity between 38 to 60% and average pore diameters between 10 to 14 microm. We evaluated the efficacy of these biodegradable fiber matrices as skin substitutes by seeding them with human skin fibroblasts (hSF). Human skin fibroblasts acquired a well spread morphology and showed significant progressive growth on fiber matrices in the 350-1,100 nm diameter range. Collagen type III gene expression was significantly up-regulated in hSF seeded on matrices with fiber diameters in the range of 350-1,100 nm. Based on the need, the proposed fiber skin substitutes can be successfully fabricated and optimized for skin fibroblast attachment and growth.

Stimulus-Responsive “Smart” Hydrogels as Novel Drug Delivery Systems

ABSTRACT 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. *CEPS Communications #4.

Crosslinked chitosan microspheres for encapsulation of diclofenac sodium: effect of crosslinking agent.

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 #181;m, 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 slowest 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.

Hydrogels as controlled release devices in agriculture

Recently, there has been a great deal of research activity in the development of hydrogels as controlled release devices. The present review provides a brief introduction to various methods of synthesis, properties, types of hydrogels, and cross-linking agents which have been used for the preparation of hydrogels exhibiting suitable properties for agricultural applications.

Polyphosphazene/Nano-Hydroxyapatite Composite Microsphere Scaffolds for Bone Tissue Engineering

The nontoxic, neutral degradation products of amino acid ester polyphosphazenes make them ideal candidates for in vivo orthopedic applications. The quest for new osteocompatible materials for load bearing tissue engineering applications has led us to investigate mechanically competent amino acid ester substituted polyphosphazenes. In this study, we have synthesized three biodegradable polyphosphazenes substituted with side groups, namely, leucine, valine, and phenylalanine ethyl esters. Of these polymers, the phenylalanine ethyl ester substituted polyphosphazene showed the highest glass transition temperature (41.6 degrees C) and, hence, was chosen as a candidate material for forming composite microspheres with 100 nm sized hydroxyapatite (nHAp). The fabricated composite microspheres were sintered into a three-dimensional (3-D) porous scaffold by adopting a dynamic solvent sintering approach. The composite microsphere scaffolds showed compressive moduli of 46-81 MPa with mean pore diameters in the range of 86-145 microm. The 3-D polyphosphazene-nHAp composite microsphere scaffolds showed good osteoblast cell adhesion, proliferation, and alkaline phosphatase expression and are potential suitors for bone tissue engineering applications.

Tendon tissue engineering: adipose-derived stem cell and GDF-5 mediated regeneration using electrospun matrix systems.

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.

Biologically active chitosan systems for tissue engineering and regenerative medicine.

Biodegradable polymeric scaffolds are widely used as a temporary extracellular matrix in tissue engineering and regenerative medicine. By physical adsorption of biomolecules on scaffold surface, physical entrapment of biomolecules in polymer microspheres or hydrogels, and chemical immobilization of oligopeptides or proteins on biomaterials, biologically active biomaterials and scaffolds can be derived. These bioactive systems show great potential in tissue engineering in rendering bioactivity and/or specificity to scaffolds. This review highlights some of the biologically active chitosan systems for tissue engineering application and the associated strategies to develop such bioactive chitosan systems.

Polyphosphazene polymers for tissue engineering: an analysis of material synthesis, characterization and applications

Tissue engineering often utilizes biodegradable polymers in the form of porous scaffolds for regenerating de novo tissues. There is an ever-increasing need for biodegradable polymers as temporary substrates for facilitating tissue regeneration. Compared to the widely used polyesters, polyorthoesters, poly(α-amino acids), and poly(anhydrides), biodegradable polyphosphazenes form a unique class of polymers that has vast potential for tissue engineering applications. Polyphosphazenes are linear high molecular weight polymers with an inorganic backbone consisting of alternating phosphorous and nitrogen atoms with two organic side groups attached to each phosphorous atom. The synthetic flexibility of polyphosphazenes has enabled the development of a wide range of polymers with a variety of physical, chemical and biological properties. These biodegradable polyphosphazenes undergo hydrolytic degradation yielding non-toxic and neutral pH degradation products due to the buffering capacity of phosphates and ammonia that are produced simultaneously during polyphosphazene degradation. This review focuses on synthesis of biodegradable polyphosphazenes, their degradation characteristics, biocompatibility, and their applications as tissue regeneration and controlled delivery matrices with a particular emphasis on systems based on polyphosphazenes alone, polyphosphazene blends and polyphosphazene composites.

Recent Patents on Electrospun Biomedical Nanostructures: An Overview

Nanostructures in the form of tubes, wires, crystals, rods, spheres, and fibers have been fabricated and assembled into various macrostructures for a variety of high technology applications. Nanofeatures impart several amazing properties to these macrostructures including high surface area, surface functionality, and superior mechanical, optical, electrical, and magnetic properties over the parent bulk material. Polymeric nanofibers in the form of nonwoven cloth, membrane, braids and tubes are extensively used for daily needs, and in addition used as filters, protective clothing, and for a variety of industrial and biomedical applications. Electrospinning or electrostatic spinning has emerged as a very popular technique to fabricate polymeric nanofiber matrices. More than 100 different polymers of natural, synthetic origin, their blends and composites have been electrospun into different three dimensional (3-D) macrostructures. Electrospinning provides opportunities to manipulate and control surface area, fiber diameter, porosity and pore size of nanofiber matrices. These nanofiber matrices closely mimic the structure of extracellular matrix (ECM) and influence cellular activities both in vitro and in vivo. Nanofiber macrostructures have been used as a vehicle to deliver therapeutic agents, as scaffolds for engineering various tissues and also serve as an integrated part of biomedical implants. Present review will cover some of the recent important patents that use electrospun nanofiber matrices for various biomedical applications.