Alok R. Ray

Bioprintable, cell-laden silk fibroin-gelatin hydrogel supporting multilineage differentiation of stem cells for fabrication of three-dimensional tissue constructs.

Bioprinting has exciting prospects for printing three-dimensional (3-D) tissue constructs by delivering living cells with appropriate matrix materials. However, progress in this field is currently extremely slow due to limited choices of bioink for cell encapsulation and cytocompatible gelation mechanisms. Here we report the development of clinically relevant sized tissue analogs by 3-D bioprinting, delivering human nasal inferior turbinate tissue-derived mesenchymal progenitor cells encapsulated in silk fibroin-gelatin (SF-G) bioink. Gelation in this bioink was induced via in situ cytocompatible gelation mechanisms, namely enzymatic crosslinking by mushroom tyrosinase and physical crosslinking via sonication. Mechanistically, tyrosinases oxidize the accessible tyrosine residues of silk and/or gelatin into reactive o-quinone moieties that can either condense with each other or undergo nonenzymatic reactions with available amines of both silk and gelatin. Sonication alters the hydrophobic interaction and accelerates self-assembly of silk fibroin macromolecules to form β-sheet crystals, which physically crosslink the hydrogel. However, sonication has no effect on the conformation of gelatin. The effect of optimized rheology, secondary conformations of silk-gelatin bioink, temporally controllable gelation strategies and printing parameters were assessed to achieve maximum cell viability and multilineage differentiation of the encapsulated human nasal inferior turbinate tissue-derived mesenchymal progenitor cells. This strategy offers a unique path forward in the direction of direct printing of spatially customized anatomical architecture in a patient-specific manner.

Biomedical Applications of Chitin, Chitosan, and Their Derivatives

3. APPLICATIONS .................................................................................................... 71 3.1. Wound-Healing Accelerators ....................................................................... 71 3.2. Artificial Kidney Membrane ........................................................................ 73 3.3. Drug Delivery Systems ................................................................................ 74 3.4. Absorbable Sutures....................................................................................... 76 3.5. Blood Anticoagulants ................................................................................... 76 3.6. Artificial Skin ............................................................................................... 77 3.7. Antimicrobial Applications .......................................................................... 77 3.8. Miscellaneous Applications.......................................................................... 78

Controlled Delivery of Drugs from Alginate Matrix

Alginate is an unbranched binary copolymer constituted of (1,4) linked α-l-guluronic acid and β-d-mannuronic acid. It is a high-molecular mass polysaccharide extracted from kelp. Edward Stanford di...

Characterization of grafted chitosan films

Abstract Chitosan was prepared from chitin using a deacetylation process. The molecular weight and degree of deacetylation of chitosan were determined by viscosity and infrared spectroscopy respectively. Chitosan films were grafted by 2-hydroxyethylmethacrylate (HEMA) using a 60 Co gamma-irradiation technique. The change in physico-chemical properties of modified films due to graft level of HEMA onto chitosan were estimated. The tensile properties of modified films decreased on increasing graft level. The grafted films showed improved thermal stability.

Development of a New Polypropylene-Based Suture: Plasma Grafting, Surface Treatment, Characterization, and Biocompatibility Studies

Polypropylene sutures (PP) are already used in surgery. Because microbial infection leads to complications, we developed antimicrobial PP suture by plasma-induced graft polymerization of acrylic acid followed by chitosan binding on the remaining carboxyl groups. Mechanical properties and surface morphologies were analyzed on these sutures. Tetracycline hydrochloride (TC) or nanosilver (NS) was then immobilized to PP. The resulting PP sutures evidenced drug release properties and antimicrobial activity in vitro. PP implanted in vivo for 30 days in the muscle of rats showed the absence of adverse effects and a tissue organization. This new polypropylene suture with suitable antimicrobial features appears to be a promising macromolecular material for clinical and cosmetic applications.

Radiation-induced grafting of N,N'-dimethylaminoethylmethacrylate onto chitosan films

Chitosan films were grafted with N,N ′-dimethylaminoethylmethacrylate using the 60Co gamma irradiation method. The effect of solvent composition, monomer concentration, dose rate, and total dose on grafting was studied. The solvent composition has a marked effect on the degree of grafting. Maximum yield was obtained in the water-methanol (1 : 1) system. The percent grafting increased with monomer concentration and was found to be higher at a lower dose rate for a constant total dose of 0.216 Mrad. The tensile strength, crystallinity, and degree of swelling of grafted films decreased on increasing graft level. However, the graft copolymers showed improved thermal stability.

Polyhydroxybutyrate, Its Copolymers and Blends

Abstract Polyhydroxybutyrate (PHB) is an optically active polymer of D(−)3-hydroxybutyric acid. It is a naturally occurring polymer produced by a wide variety of bacteria. It serves as an intracellular storage material for carbon and energy and is accumulated as granules within the cytoplasm [1–4] of the bacteria. The chemical structure of PHB is shown in Fig. 1.

Oriented lamellar silk fibrous scaffolds to drive cartilage matrix orientation: Towards annulus fibrosus tissue engineering

A novel design of silk-based scaffold is developed using a custom-made winding machine, with fiber alignment resembling the anatomical criss-cross lamellar fibrous orientation features of the annulus fibrosus of the intervertebral disc. Crosslinking of silk fibroin fibers with chondroitin sulphate (CS) was introduced to impart superior biological functionality. The scaffolds, with or without CS, instructed alignment of expanded human chondrocytes and of the deposited extracellular matrix while supporting their chondrogenic redifferentiation. The presence of CS crosslinking could not induce statistically significant changes in the measured collagen or glycosaminoglycan content, but resulted in an increased construct stiffness. By offering the combined effect of cell/matrix alignment and chondrogenic support, the silk fibroin scaffolds developed with precise fiber orientation in lamellar form represent a suitable substrate for tissue engineering of the annulus fibrosus part of the intervertebral disc.

The role of 3D structure and protein conformation on the innate and adaptive immune responses to silk-based biomaterials

We have investigated monocyte and T cell responsiveness to silk based biomaterials of different physico-chemical characteristics. Here we report that untransformed CD14+ human monocytes respond to overnight exposure to silk fibroin-based biomaterials in tridimensional form by IL-1β and IL-6, but not IL-10 gene expression and protein production. In contrast, fibroin based materials in bidimensional form are unable to stimulate monocyte responsiveness. The elicitation of these effects critically requires contact between biomaterials and responding cells, is not sustained and becomes undetectable in longer term cultures. We also observed that NF-κβ and p38 MAP kinase play key roles in monocyte activation by silk-based biomaterials. On the other hand, fibroin based materials, irrespective of their physico-chemical characteristics appeared to be unable to induce the activation of peripheral blood T cells from healthy donors, as evaluated by the expression of activation markers and IFN-γ gene.

Enhanced Redifferentiation of Chondrocytes on Microperiodic Silk/ Gelatin Scaffolds: Toward Tailor-Made Tissue Engineering

Direct-write assembly allows rapid fabrication of complex three-dimensional (3D) architectures, such as scaffolds simulating anatomical shapes, avoiding the need for expensive lithographic masks. However, proper selection of polymeric ink composition and tailor-made viscoelastic properties are critically important for smooth deposition of ink and shape retention. Deposition of only silk solution leads to frequent clogging due to shear-induced β-sheet crystallization, whereas optimized viscoelastic property of silk-gelatin blends facilitate the flow of these blends through microcapillary nozzles of varying diameter. This study demonstrates that induction of controlled changes in scaffold surface chemistry, by optimizing silk-gelatin ratio, can govern cell proliferation and maintenance of chondrocyte morphology. Microperiodic silk-gelatin scaffolds can influence postexpansion redifferentiation of goat chondrocytes by enhancing Sox-9 gene expression, aggregation, and driving cartilage matrix production, as evidenced by upregulation of collagen type II and aggrecan expression. The strategy for optimizing redifferentiation of chondrocytes can offer valuable consideration in scaffold-based cartilage repair strategies.