Lakshmi S. Nair

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.

Curcumin-loaded poly(ε-caprolactone) nanofibres: Diabetic wound dressing with anti-oxidant and anti-inflammatory properties

1 Curcumin is a naturally occurring poly‐phenolic compound with a broad range of favourable biological functions, including anti‐cancer, anti‐oxidant and anti‐inflammatory activities. The low bioavailability and in vivo stability of curcumin require the development of suitable carrier vehicles to deliver the molecule in a sustained manner at therapeutic levels. 2 In the present study, we investigated the feasibility and potential of poly(caprolactone) (PCL) nanofibres as a delivery vehicle for curcumin for wound healing applications. By optimizing the electrospinning parameters, bead‐free curcumin‐loaded PCL nanofibres were developed. 3 The fibres showed sustained release of curcumin for 72 h and could be made to deliver a dose much lower than the reported cytotoxic concentration while remaining bioactive. Human foreskin fibroblast cells (HFF‐1) showed more than 70% viability on curcumin‐loaded nanofibres. 4 The anti‐oxidant activity of curcumin‐loaded nanofibres was demonstrated using an oxygen radical absorbance capacity (ORAC) assay and by the ability of the fibres to maintain the viability of HFF‐1 cells under conditions of oxidative stress. 5 The curcumin‐loaded nanofibres also reduced inflammatory induction, as evidenced by low levels of interleukin‐6 release from mouse monocyte–macrophages seeded onto the fibres following stimulation by Escherichia coli‐derived lipopolysaccharide. 6 The in vivo wound healing capability of the curcumin loaded PCL nanofibres was demonstrated by an increased rate of wound closure in a streptozotocin‐induced diabetic mice model. 7 These results demonstrate that the curcumin‐loaded PCL nanofibre matrix is bioactive and has potential as a wound dressing with anti‐oxidant and anti‐inflammatory properties.

Development of novel tissue engineering scaffolds via electrospinning.

Electrospinning has recently been developed as an efficient technique to develop polymeric nanofibres. Various synthetic and natural biodegradable polymers have been electrospun into fibres with diameters in the nanometre range (< 1 μm). The fibre diameter, structure and physical properties of the nanofibre matrices can be effectively tuned by controlling various parameters that affect the electrospinning process. The dimension and structure of electrospun polymeric nanofibre mats resembles mostly the collagen phase of natural extracellular matrix. This, combined with excellent physical properties such as high surface area, high porosity, interconnective pores of the nanofibre matrices and appropriate mechanical properties, well-controlled degradation rates and biocompatibility of the base polymer, make biodegradable polymeric nanofibre matrices ideal candidates for developing scaffolds for tissue engineering. This article reviews the recent advances in the development of synthetic biodegradable nanofibre-based matrices as scaffolds for tissue engineering.

Induction of angiogenesis in tissue-engineered scaffolds designed for bone repair: A combined gene therapy–cell transplantation approach

One of the fundamental principles underlying tissue engineering approaches is that newly formed tissue must maintain sufficient vascularization to support its growth. Efforts to induce vascular growth into tissue-engineered scaffolds have recently been dedicated to developing novel strategies to deliver specific biological factors that direct the recruitment of endothelial cell (EC) progenitors and their differentiation. The challenge, however, lies in orchestration of the cells, appropriate biological factors, and optimal factor doses. This study reports an approach as a step forward to resolving this dilemma by combining an ex vivo gene transfer strategy and EC transplantation. The utility of this approach was evaluated by using 3D poly(lactide-co-glycolide) (PLAGA) sintered microsphere scaffolds for bone tissue engineering applications. Our goal was achieved by isolation and transfection of adipose-derived stromal cells (ADSCs) with adenovirus encoding the cDNA of VEGF. We demonstrated that the combination of VEGF releasing ADSCs and ECs results in marked vascular growth within PLAGA scaffolds. We thereby delineate the potential of ADSCs to promote vascular growth into biomaterials.

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.

Injectable hydrogels for bone and cartilage repair

Injectable in situ crosslinkable gels are highly desirable clinically as they can be introduced into a body via a minimally invasive manner using endoscopic or percutaneous procedures. Several hydrophilic polymeric systems that respond to stimuli such as light, temperature, pH, ionic concentration as well as those that can undergo chemical reactions to form crosslinked matrices are currently under development. This paper discusses the applications of hydrogels as scaffolds to mimic the native extracellular matrix of bone and cartilage. A comprehensive description of various gelation methods used in hydrogel preparation and their application as injectable cell and protein delivery vehicle for bone and cartilage regeneration is also presented.

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.

Injectable Tissue-Engineered Bone Repair of a Rat Calvarial Defect

Advances in bone repair have focused on the minimally‐invasive delivery of tissue‐engineered bone (TEB). A promising injectable biopolymer of chitosan and inorganic phosphates was seeded with mesenchymal stem cells (MSCs) and a bone growth factor (BMP‐2), and evaluated in a rat calvarial critical size defect (CSD). Green fluorescent protein (GFP)‐labeled MSCs are used to evaluate patterns of cell viability and proliferation.

Fabrication, characterization, and in vitro evaluation of poly(lactic acid glycolic acid)/nano-hydroxyapatite composite microsphere-based scaffolds for bone tissue engineering in rotating bioreactors.

Dynamic flow culture bioreactor systems have been shown to enhance in vitro bone tissue formation by facilitating mass transfer and providing mechanical stimulation. Our laboratory has developed a biodegradable poly (lactic acid glycolic acid) (PLAGA) mixed scaffold consisting of lighter-than-water (LTW) and heavier-than-water (HTW) microspheres as potential matrices for engineering tissue using a high aspect ratio vessel (HARV) rotating bioreactor system. We have demonstrated enhanced osteoblast differentiation and mineralization on PLAGA scaffolds in the HARV rotating bioreactor system when compared with static culture. The objective of the present study is to improve the mechanical properties and bioactivity of polymeric scaffolds by designing LTW polymer/ceramic composite scaffolds suitable for dynamic culture using a HARV bioreactor. We employed a microsphere sintering method to fabricate three-dimensional PLAGA/nano-hydroxyapatite (n-HA) mixed scaffolds composed of LTW and HTW composite microspheres. The mechanical properties, pore size and porosity of the composite scaffolds were controlled by varying parameters, such as sintering temperature, sintering time, and PLAGA/n-HA ratio. The PLAGA/n-HA (4:1) scaffold sintered at 90 degrees C for 3 h demonstrated the highest mechanical properties and an appropriate pore structure for bone tissue engineering applications. Furthermore, evaluation human mesenchymal stem cells (HMSCs) response to PLAGA/n-HA scaffolds was performed. HMSCs on PLAGA/n-HA scaffolds demonstrated enhanced proliferation, differentiation, and mineralization when compared with those on PLAGA scaffolds. Therefore, PLAGA/n-HA mixed scaffolds are promising candidates for HARV bioreactor-based bone tissue engineering applications.

Mechanical properties and osteocompatibility of novel biodegradable alanine based polyphosphazenes: Side group effects

The versatility of polymers for tissue regeneration lies in the feasibility to modulate the physical and biological properties by varying the side groups grafted to the polymers. Biodegradable polyphosphazenes are high-molecular-weight polymers with alternating nitrogen and phosphorus atoms in the backbone. This study is the first of its kind to systematically investigate the effect of side group structure on the compressive strength of novel biodegradable polyphosphazene based polymers as potential materials for tissue regeneration. The alanine polyphosphazene based polymers, poly(bis(ethyl alanato) phosphazene) (PNEA), poly((50% ethyl alanato) (50% methyl phenoxy) phosphazene) (PNEA(50)mPh(50)), poly((50% ethyl alanato) (50% phenyl phenoxy) phosphazene) (PNEA(50)PhPh(50)) were investigated to demonstrate their mechanical properties and osteocompatibility. Results of mechanical testing studies demonstrated that the nature and the ratio of the pendent groups attached to the polymer backbone play a significant role in determining the mechanical properties of the resulting polymer. The compressive strength of PNEA(50)PhPh(50) was significantly higher than poly(lactide-co-glycolide) (85:15 PLAGA) (p<0.05). Additional studies evaluated the cellular response and gene expression of primary rat osteoblast cells on PNEA, PNEA(50)mPh(50) and PNEA(50)PhPh(50) films as candidates for bone tissue engineering applications. Results of the in vitro osteocompatibility evaluation demonstrated that cells adhere, proliferate, and maintain their phenotype when seeded directly on the surface of PNEA, PNEA(50)mPh(50), and PNEA(50)PhPh(50). Moreover, cells on the surface of the polymers expressed type I collagen, alkaline phosphatase, osteocalcin, osteopontin, and bone sialoprotein, which are characteristic genes for osteoblast maturation, differentiation, and mineralization.