Milind Gandhi

Regeneration of Bombyx mori silk by electrospinning—part 1: processing parameters and geometric properties

We studied the effect of electrospinning parameters on the morphology and fiber diameter of regenerated silk from Bombyx mori. Effects of electric field and tip-to-collection plate distances of various silk concentrations in formic acid on fiber uniformity, morphology and diameter were measured. Statistical analysis showed that the silk concentration was the most important parameter in producing uniform cylindrical fibers less than 100 nm in diameter.

Characterization of cell viability during bioprinting processes

Bioprinting is an emerging technology in the field of tissue engineering and regenerative medicine. The process consists of simultaneous deposition of cells, biomaterial and/or growth factors under pressure through a micro-scale nozzle. Cell viability can be controlled by varying the parameters like pressure and nozzle diameter. The process itself can be a very useful tool for evaluating an in vitro cell injury model. It is essential to understand the cell responses to process-induced mechanical disturbances because they alter cell morphology and function. We carried out analysis and quantification of the degree of cell injury induced by bioprinting process. A parametric study with different process parameters was conducted to analyze and quantify cell injury as well as to optimize the parameters for printing viable cells. A phenomenological model was developed correlating the percentage of live, apoptotic and necrotic cells to the process parameters. This study incorporates an analytical formulation to predict the cell viability through the system as a function of the maximum shear stress in the system. The study shows that dispensing pressure has a more significant effect on cell viability than the nozzle diameter. The percentage of live cells is reduced significantly (by 38.75%) when constructs are printed at 40 psi compared to those printed at 5 psi.

Mechanistic Examination of Protein Release from Polymer Nanofibers

Therapeutic proteins have emerged as a significant class of pharmaceutical agents over the past several decades. The potency, rapid elimination, and systemic side effects have prompted the need of spatiotemporally controlled release for proteins maybe more than any other active therapeutic molecules. This work examines the release of two model protein compounds, bovine serum albumin (BSA) and an anti-integrin antibody (AI), from electrospun polycaprolactone (PCL) nanofiber mats. The anti-integrin antibody was chosen as a model of antibody therapy; in particular, anti-integrin antibodies are a promising class of therapeutic molecules for cancer and angiogenic diseases. The release kinetics were studied experimentally and interpreted in the framework of a recently published theory of desorption-limited drug release from nondegrading--or very slowly degrading--fibers. The results are consistent with a protein release mechanism dominated by desorption from the polymer surface, while the polycaprolactone nanofibers are not degrading at an appreciable rate.

Initial evaluation of vascular ingrowth into superporous hydrogels

There is a need for new materials and architectures for tissue engineering and regenerative medicine. Based upon our recent results developing novel scaffold architecture, we hypothesized that this new architecture would foster vascularization, a particular need for tissue engineering. We report on the potential of superporous hydrogel (SPH) scaffolds for in vivo cellular infiltration and vascularization. Poly(ethylene glycol) diacrylate (PEGDA) SPH scaffolds were implanted in the dorsum of severe combined immunodeficient (SCID) mice and harvested after 4 weeks of in vivo implantation. The SPHs were visibly red and vascularized, as apparent when compared to the non‐porous hydrogel controls, which were macroscopically avascular. Host cell infiltration was observed throughout the SPHs. Blood cells and vascular structures, confirmed through staining for CD34 and smooth muscle α‐actin, were observed throughout the scaffolds. This novel soft material may be utilized for cell transplantation, tissue engineering and in combination with cell therapies. The neovasularization and limited fibrotic response suggest that the architecture may be conducive to cell survival and rapid vessel development. Copyright

Solid Freeform Fabrication of Polycaprolactone∕Hydroxyapatite Tissue Scaffolds

Bone tissue engineering is an emerging field providing viable substitutes for bone regeneration. Freeform fabrication provides an effective process tool to manufacture scaffolds with complex shapes and designed properties. We developed a novel precision extruding deposition (PED) technique to fabricate composite polycaprolactone/hydroxyapatite (PCL/HA) scaffolds. 25% concentration by weight of HA was used to reinforce 3D scaffolds. Two groups of scaffolds having 60% and 70% porosities and with pore sizes of 450 μm and 750 μm respectively, were evaluated for their morphology and compressive properties using scanning electron microscopy and the mechanical testing. In vitro cell-scaffold interaction study was carried out using primary fetal bovine osteoblasts. The cell proliferation and differentiation were evaluated by Alamar Blue assay and alkaline phosphatase activity. Our results suggested that compressive modulus of PCL/HA scaffold was 84 MPa for 60% porous scaffolds and was 76 MPa for 70% porous scaffolds. The osteoblasts were able to migrate and proliferate for the cultured time over the scaffolds. Our study demonstrated the viability of the PED process to fabricate PCL scaffolds having necessary mechanical property, structural integrity, controlled pore size, and pore interconnectivity desired for bone tissue engineering.

Producing nanofiber structures by electrospinning for tissue engineering

Publisher Summary Biocompatible and biodegradable polymeric biomaterials are used to develop biological matrices or scaffolds not only for tissue engineering but also for various biomedical applications, including wound dressings, membrane filters, and drug delivery. These materials include synthetic polymers and natural biopolymers. The natural materials are of considerable interest due to their structural properties and superior biocompatibility. Electrospinning is a unique method capable of producing nanoscale fibers. The simplicity of the electrospinning process to generate nanofibers makes it an ideal process for scaffold fabrication. In the electrospinning process, an electric field is generated between an oppositely charged polymer fluid and a collection screen, the electrode. Tissue Engineering is the application of principles and methods of engineering, and the life sciences toward the fundamental understanding of structure/function relationships in normal and pathological mammalian tissues, and the development of biological substitutes to restore and maintain or improve functions. Nanoscale fibrous materials are the ideal candidates for tissue engineering scaffolds because of their high surface area to volume ratio, greater porosity, and pore-size distribution.

Plasma Surface Modification of Three Dimensional Poly (ε-Caprolactone) Scaffolds for Tissue Engineering Application

In the present study, the effect of oxygen-based plasma treatment on the three dimensional poly (e-caprolactone) (PCL) was analyzed in terms of surface wettability, surface energy, and surface biocompatibility. The surface treatment was carried out for 1, 3, and 5-min durations on three dimensional PCL scaffolds at atmospheric pressure using a radio frequency (RF) plasma treatment system. The solid surface energies of the modified and unmodified PCL scaffolds were calculated by using the Owens-Wendt’s method. To examine the effect of oxygen plasma treatment on cell-scaffold interaction, mouse osteoblast cell line (7F2) was used. Oxygen plasma treatment contributed in decreasing the hydrophobicity of PCL for the 1-min treatment. A change in the surface energy from 39.98 mN/m for untreated to 52.54 mN/m for 1-min treated was observed by the increment in the polar component of surface energy. However, with the extended treatment times (3-min, and 5-min), the hydrophilicity, and the surface energy remained unaffected. The highest mouse osteoblast cells proliferation rate was observed for the 1-min treated sample.