Thomas Chandy - Academia.edu (original) (raw)

Papers by Thomas Chandy

Proceedings of the 1995 Fourteenth Southern Biomedical Engineering Conference

Chitosan, a natural polysaccharide, having structural characteristics similar to glycosaminoglyca... more Chitosan, a natural polysaccharide, having structural characteristics similar to glycosaminoglycans seems to be non-toxic and bioadsorbable. The chitosan matrix has been extensively investigated in the author's laboratory for a variety of biomedical applications, such as the removal of bilirubin, haemodialysis membranes, for delivery of drugs, charcoal encapsulated chitosan beads (ACCB) for toxin removal, specific immunoadsorbent matrix, chitosan coated hydroxyapatite as orthopaedic and dental dialysis materials etc. Thus, chitosan is a viable material, which can be fabricated into various forms, such as beads, granules tablets, membranes etc, as per requirements. With all these variety of biomedical uses, it appears, chitosan may be a future promise for anchoring the tissue interfaces. This paper highlights the importance of this novel matrix for such biomedical applications

Polysaccharides in Medicinal Applications, 2017

Journal of Surface Science and Technology, 1991

The basic principles involved in understanding the protein-platelet interactions at the interface... more The basic principles involved in understanding the protein-platelet interactions at the interface are discussed. Such concepts which can be utilized in modifying the surface of implants to enhance their blood compatibility along with the role of mediators including various drugs usually consumed by the patients having an artificial prosthesis implanted internally in contact with blood are highlighted.

The adhesion of certain blood cells like red blood cells (RBC), and platelets onto a series of po... more The adhesion of certain blood cells like red blood cells (RBC), and platelets onto a series of polymers with varying wettability was studied in protein-containing (albumin, γ-globulin or fibrinogen) and protein-free mediums. The attachment and stability studies of these cells on, glow discharge treated (GDT) substrates, under various shear rates, to polymethyl methacrylate (PMMA), polyacrylonitrile (PAN) and Chitosan (CM), in presence and absence of serum proteins were also attempted. It appears the adhesion, of these cells is promoted by preadsorption of y-globulin and fibrinogen variably, onto the polymers and the GDT further increases the cell attachment. A significant amount of cell detachment is observed with the bare and the proteinated substrates under various shear conditions. However, the cell detachment did not occur until a critical value of shear stress was exceeded. It is also evident that the GDT immobilized cells are highly stable, when compared with the untreated cas...

Journal of Biomaterials Applications, 1999

Cardiovascular calcification, the formation of calcium phosphate deposits in cardiovascular tissu... more Cardiovascular calcification, the formation of calcium phosphate deposits in cardiovascular tissue, is a common end stage phenomenon affecting a wide variety of bioprosthesis. This study proposes a novel approach of reducing pericardial calcification and thrombosis via coupling polyethylene glycols (PEG) to glutaraldehyde treated bovine pericardium via acetal linkages. The calcification of the PEG modified tissue and the control pericardium (extracted and glutaraldehyde treated) was investigated by in vivo rat subcutaneous implantation models and by in vitro meta stable calcium phosphate solutions. Scanning electron microscopy showed that calcification primarily involved the surface of collagen fibrils and the intrafibrillar spaces. However, the grafting of pericardium with PEG-20,000 had dramatically modified the surface and subsequently inhibited the deposits of calcium. Further, the modified tissue had also reduced the platelet surface attachment. Such a reduced calcification of ...

Clinical Materials, 1994

The principal cause of the clinical failure of bioprosthetic heart valves fabricated from glutara... more The principal cause of the clinical failure of bioprosthetic heart valves fabricated from glutaraldehyde-pretreated bovine pericardial valves is calcification. The present investigation describes the mineralization of glutaraldehyde-treated bovine pericardium (GBP), in an extra-circulatory environment and the possible methods of prevention via metal ions. Calcification was examined on GBP incubated in metastable solutions of calcium phosphate and the role of certain anesthetic drugs, ferric ions and magnesium ions in the media was evaluated. It seems that the addition of ethyl alcohol, pentothal and xylocaine in the calcium phosphate solutions, Fe3+ ions and Mg2+ variably inhibited the GBP calcification. The metals like ions and their combinations also substantially reduced the GBP mineralization. It is assumed that ferric ions may slow down or retard the calcification process by delaying the proper formation of hydroxyapatite while magnesium ions disrupt the growth of these crystals by replacing Ca2+. Hence, it is conceivable that a combination therapy-via local delivery of low levels of ferric ions and magnesium ions-may prevent the GBP-associated calcification. Further, a very low daily intake of alcohol appears to be beneficial to reduce the profile of calcium deposition at tissue inter

Thrombosis Research, 1983

Polymer-Plastics Technology and Engineering, 1987

Abstract Medical devices like catheters, hemodialyzers, oxygenators, heart valves, and blood vess... more Abstract Medical devices like catheters, hemodialyzers, oxygenators, heart valves, and blood vessel prostheses are frequently used in man as a consequence of natural and accidental causes of deterioration of his body. The formation of thrombi on the surfaces of artificial materials occurs upon contact with blood. Progress made over the last 25 years in the area of blood-biomaterial compatibility has been impressive. However, we still do not have a satisfactory thromboresistant material to replace a coronary artery.

Pathophysiology of Haemostasis and Thrombosis, 1987

In a previous study we have shown that vitamin C has some effect on the polymer surface by adsorp... more In a previous study we have shown that vitamin C has some effect on the polymer surface by adsorption to it, which would probably affect the protein adsorption and platelet adhesion. The present work has been extended to demonstrate the influence of vitamin C on the kinetics of protein-polymer interaction, using labeled proteins, in the presence and absence of red blood cells, platelets and white blood cells. It appears that vitamin C causes an increase in albumin surface concentration compared to bare substrate which seems to decrease slightly in the presence of blood cells. On the other hand, the infusion of vitamin C to the fibrinogen blood cells system dramatically inhibits the fibrinogen surface binding. The role of L-ascorbic acid to reduce the protein adsorption in the presence of blood cells is discussed by taking into account (a) the interaction of vitamin C with the polymer surface, (b) the interaction of vitamin C with the proteins and cellular membrane, and (c) the inter...

Journal of Microencapsulation, 1993

A technique is described to encapsulate activated charcoal for haemoperfusion to be used in an ar... more A technique is described to encapsulate activated charcoal for haemoperfusion to be used in an artificial liver support. Activated charcoal was encapsulated within chitosan matrix (ACCB) in different concentrations, and was used as the supports for perfusion of a mixture of solutes, having molecular weight ranges from 60 to 69,000; under a flow rate of 8 ml/min. It seems the ACCB may be a good adsorbent system for the removal of toxic uric acid, creatinine, bilirubin, etc., from solutions; while larger molecules such as albumin are adsorbed less. The encapsulated charcoal did not leach out from the matrix during perfusion, and the system may be useful for detoxification of blood. The haemolytic potential of ACCB has been compatible with polystyrene control tubes. However, further studies are needed to determine their behaviour under clinical conditions.

Journal of Colloid and Interface Science, 1985

Abstract In order to develop artificial materials for prolonged use in the vascular system, the c... more Abstract In order to develop artificial materials for prolonged use in the vascular system, the complicated process of surface-induced thrombosis needs to be better understood. It seems lipids have a profound role toward the thrombosis and hemostasis mechanism, though adequate studies using lipids are not available to demonstrate its part in the thromboembolic phenomena that occur at the blood—foreign material interface. We have studied the interfacial phenomena of three lipids, namely, cholesterol, cephalin, and sphingosine, and their interaction with proteins and vitamin C toward an artificial surface using contact angle and trace labeling methods. Platelet adhesion and plasma recalcification time are also carried out for further understanding of the complex phenomena. The preliminary results suggest that lipids can be adsorbed to the polymer surface and can interact with proteins and platelets at the interface. Furthermore, the behavior of all lipids toward blood—polymer interaction is not similar and may change depending on the nature of lipid, net charge of the lipid—adsorbed surface, and the lipid—protein/lipid—platelet interaction at the interface. Possible interactions of lipid with platelets and proteins are suggested, including the interaction with an artificial surface.

Journal of Colloid and Interface Science, 1983

... We are thankful for the discussions with Miss Asha Latha as well to Miss MK Sheela and Miss G... more ... We are thankful for the discussions with Miss Asha Latha as well to Miss MK Sheela and Miss Geetha Kurien for their technical assistance, We also acknowledge the cooperation received from the Blood Bank group of the Institution. ...

Journal of Biomaterials Applications, 2000

The strength, resorption rates, and biocompatibility of collagenous biomaterials are profoundly i... more The strength, resorption rates, and biocompatibility of collagenous biomaterials are profoundly influenced by the method of cross-linking. The in vitro and in vivo calcification and enzymatic degradation of bovine pericardia (BP) after a series of surface modifications were studied as a function of exposure time. Collagenase degradations of modified BP were monitored by scanning electron microscopy and tensile strength measurements. Bovine pericardium was modified by a combination of different tissue fixatives such as glutaraldehyde (GA), carbodiimide (EDC), diisocyanate (HMDIC), and polyethylene glycol (PEG). GA-PEG-EDC-PEG and GA-PEG-HMDIC-PEG combination treated BP retained maximum stability in collagenase digestion compared to GATBP. In vitro calcification studies and in vivo rat subcutaneous implantations of modified pericardium have shown substantial reduction in the calcification of double cross-linked BP with PEG modification. Further, the biocompatibility aspects of pericardial tissues were established by platelet adhesion and octane contact angle. It seems that cross-links involving amino and carboxyl residues may provide new ways of controlling biodegradation and calcification.

Journal of Applied Polymer Science, 1996

A mild chitosan/calcium alginate microencapsulation process, as applied to encapsulation of biolo... more A mild chitosan/calcium alginate microencapsulation process, as applied to encapsulation of biological macromolecules such as albumin and insulin, was investigated. The microcapsules were derived by adding dropwise a protein-containing sodium alginate mixture into a chitosan-CaC12 system. The beads containing a high concentration of entrapped bovine serum albumin (BSA) as more than 70% of the initial concentration were achieved via varying chitosan coat. It was observed that approximately 70% of the content is being released into Tris-HC1 buffer, pH 7.4 within 24 h and no significant release of BSA was observed during treatment with 0.1M HC1 pH 1.2 for 4 h. But the acid-treated beads had released almost all the entrapped protein into Tris-HC1 pH 7.4 media within 24 h. Instead of BSA, the insulin preload was found to be very low in the chitosan/calcium alginate system; the release characteristics were similar to that of BSA. From scanning electron microscopic studies, it appears that the chitosan modifies the alginate microspheres and subsequently the protein loading. The results indicate the possibility of modifying the formulation in order to obtain the desired controlled release of bioactive peptides (insulin), for a convenient gastrointestinal tract delivery system. 0 1996 John Wiley & Sons, Inc.

Journal of Applied Polymer Science, 1992

Page 1. Prostaglandin El-Immobilized Poly (Vinyl Alcohol) -Blended Chitosan Membranes: Blood Comp... more Page 1. Prostaglandin El-Immobilized Poly (Vinyl Alcohol) -Blended Chitosan Membranes: Blood Compatibility and Permeability Properties THOMAS CHANDY and CHANDRA P. SHARMA* Division of Biosurface Technology ...

Bulletin of Materials Science, 1983

This paper reports our attempts to crosslink low. molecular weight proteins namely trypsin and in... more This paper reports our attempts to crosslink low. molecular weight proteins namely trypsin and insulin using glutaraldehyde on polycarbonate surface and to evaluate how such surfaces may affect the blood compatibility of the polymer, by studying the interfacial energies of the modified polymer surface using advancing contact angle technique. The plasma recalcification time and platelet adhesion studies were also carried out. It has been observed that such low molecular weight proteins retard clotting.

Biomaterials, 1992

Nifedipine was embedded in a chitosan matrix to develop a prolonged-release form. The in vitro re... more Nifedipine was embedded in a chitosan matrix to develop a prolonged-release form. The in vitro release profiles of nifedipine from chitosan beads and microgranules were monitored by UV spectrophotometer. The studies were performed in a rotating shaker (100 rev min-') in 0.1 M HCI buffer (pH 2.0) or 0.1 M phosphate buffer (pH 7.4). Comparison was made between drug-loaded microbeads and microgranules. The amount and percentage of drug release were much higher in HCI than in phosphate buffer, probably due to the salt formation of the matrix (chitosan hydrochloride) at acid pH. The release rate of nifedipine from chitosan matrix was slower for beads than granules. These findings suggest the possibility of modifying the formulations to obtain the desired controlled release of the drug in an oral sustained-delivery system.

Biomaterials, 1997

Aspirin and heparin were embedded in chitosan/polyethylene vinyl acetate co-matrix to develop a p... more Aspirin and heparin were embedded in chitosan/polyethylene vinyl acetate co-matrix to develop a prolonged release form. The in vifro release profiles of these drugs from the co-matrix system were monitored in Tris HCI buffer pH 7.4, using a UV spectrophotometer. The amount of drug release was initially much higher, followed by a constant slow release profile for a prolonged period. The initial burst release was substantially modified with styrenebutadiene coatings. From scanning electron microscopy studies it appears that the drugs diffuse out slowly to the dissolution medium through the micropores of the co-matrix. The released aspirin-heparin from the co-matrix system had shown their antiplatelet and anticoagulant functions. The results propose the possibility of delivering drug combinations, having synergestic effects for therapeutic applications.

Biomaterials, 1991

The hydrolytic and enzymic degradation of poly(t-lactic acid) (PLA) and poly(y-benzyl t-glutamate... more The hydrolytic and enzymic degradation of poly(t-lactic acid) (PLA) and poly(y-benzyl t-glutamate) (PBGA) films, together with a series of surface treatments, were studied, as a function of exposure time. The degradation of these polymers was monitored by weight loss, contact angle, pli changes and tensile strength studies. Glutaraldehyde treatment retained the maximum strength of Pl.A in buffer, followed by carbodiimide, compared with control films. On the other hand, plasma glow reversed the effect. The ability of a-chymotrypsin, carboxypeptidase, ficin, esterase, bromelain and leucine aminopeptidase to modulate the degradation of Pl.A and PBGA was also investigated. Addition of these enzymes to the polymer-buffer system reduced the tensile strength of these polymers variably. Among the six enzymes studied, leucine aminopeptidase showed the highest enzymic effect on the degradation of the glutaraldehyde-treated and bare PLA or bare PBGA films. However, glutaraldehyde-cross-linked Pl.A demonstrated maximum stability in buffers or in all other enzyme systems studied compared with bare PLA. It is conceivable that surface treatments on these polymers might have altered their physical and chemical configuration and the subsequent degradation properties. Surface modifications may provide new ways of controlling the biodegradation of polymers for a variety of biomedical applications.