Department of Pharmaceutics, National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S. A. S. Nagar,Mohali, Punjab-160 062, India, Institute of Biochemistry, Faculty of Medicine, Polytechnic University, Via Ranieri 67, IT-60100 Ancona, Italy,Green Biotechnology Research Group, The Special Division for Human Life Technology, National Institute of Advanced Industrial Science andTechnology, 1-8-31 Midorigaoka, Ikeda, Osaka-563-8577, Japan, and Department of Medicinal Chemistry & Natural Products,The Hebrew University of Jerusalem, School of Pharmacy-Faculty of Medicine, Jerusalem 91120, IsraelReceived March 2, 2004

Chitosan chemistry and pharmaceutical perspectives.

This review concerns the applications of some polysaccharides in the domain of biomaterials and bioactive polymers. Natural polysaccharides from different sources have been studied for a long time, and their main properties are summarized in this paper; some of their derivatives obtained by chemical modification are also described. The main polysaccharides currently used in the biomedical and pharmaceutical domains are chitin and its derivative chitosan, hyaluronan and alginates. Alginates are well known for their property of forming a physical gel in the presence of divalent counterions (Ca, Ba, Sr) whereas carrageenans form a thermoreversible gel; these seaweed polysaccharides are mainly used to encapsulate different materials (cells, bacteria, fungi). Other promising systems are the electrostatic complexes formed when an anionic polysaccharide is mixed with a cationic polysaccharide (e.g. alginate/chitosan or hyaluronan/chitosan). An important development of the applications of polysaccharides can be predicted for the next few years in relation to their intrinsic properties such as biocompatibility and biodegradability in the human body for some of them; they are also renewable and have interesting physical properties (film-forming, gelling and thickening properties). In addition, they are easily processed in different forms such as beads, films, capsules and fibres. Copyright © 2007 Society of Chemical Industry

Main properties and current applications of some polysaccharides as biomaterials

https://www.tissueeng.net/lab/papers/2006-34.pdf

Micromolding of photocrosslinkable chitosan hydrogel for spheroid microarray and co-cultures

Vascular endothelial cell growth factor (VEGF) has strong stimulating effects on vascularization. Though very potent, VEGF is rapidly degraded due to its short half-life and when administrated by uncontrolled and nonspecific methods; however, its systemic administration in large doses can cause harmful side effects. Controlled release technology would allow delivering desired levels of bioactive VEGF within extended periods and permit examination of the in vivo effects of the compound in a broader way. The objective of this study was to determine the in vitro release behavior of VEGF from calcium alginate microspheres and the potency of this controlled release system in promoting localized neovascularization at the subcutaneous site of the rat model. In vitro release of human VEGF165 (2 and 4 microg/cm3 microsphere) was studied for 3 weeks under static conditions at 25 degrees C, and daily hormone release was measured using a competitive enzyme immunoassay. Following an uncontrolled release within the first 4 days, a quite constant zero-order VEGF release of 50 to 90 and 70 to 120 ng/day was achieved from 2 and 4 microg/cm3 polymer loaded microspheres respectively. In vivo angiogenesis was studied for a period of 8 weeks and evaluated using immunoperoidase staining and histopathological measurements. In vivo studies with rats (n = 24) showed a considerable level of capillary network formation at the epigastric groin fascia of VEGF microsphere-implanted rats starting from the first week. The most extensive neovascularization was observed in the group with 3 week postimplanted 4 microg VEGF containing microspheres; this level of vascularization was quite similar after 8 weeks. While the control group showed no evidence of angiogenesis, the difference in VEGF-induced neovascularization is statistically significant (p < 0.03). Immunostaining of the specimens showed a strong relationship between the release of human VEGF and neovascularization. The controlled VEGF release system described here promotes vigorous angiogenesis and has applicability for tissue engineering and wound healing studies.

Extensive in vivo angiogenesis following controlled release of human vascular endothelial cell growth factor: implications for tissue engineering and wound healing.

An encapsulation device, designed on the basis of the laminar jet break-up technique, is characterized for cell immobilization with different types of alginate. The principle of operation of the completely sterilizable encapsulator, together with techniques for the continuous prodn. of beads from 250 mm to 1 mm in diam., with a size distribution below 5%, at a flow rate of 1-15 mL/min, is described. A modification of the device, to incorporate an electrostatic potential between the alginate droplets and an internal electrode, results in enhanced monodispersity with no adverse effects on cell viability. The max. cell loading capacity of the beads strongly depends on the nozzle diam. as well as the cells used. For the yeast Phaffia rhodozyma, it is possible to generate 700 mm alginate beads with an initial cell concn. of 1 * 108 cells/mL of alginate whereas only 1 * 106 cells/mL could be entrapped within 400 mm beads. The alginate beads have been characterized with respect to mech. resistance and size distribution immediately after prodn. and as a function of storage conditions. The beads remain stable in the presence of acetic acid, hydrochloric acid, water, basic water, and sodium ions. The latter stability applies when the ratio of sodium: calcium ions is less than 1/5. Complexing agents such as sodium citrate result in the rapid solubilization of the beads due to calcium removal. The presence of cells does not affect the mech. resistance of the beads. Finally, the mech. resistance of alginate beads can be doubled by treatment with 5-10 kDa chitosan, resulting in reduced leaching of cells. [on SciFinder (R)]

Characterization of an encapsulation device for the production of monodisperse alginate beads for cell immobilization

Extracellular matrix structures including glycosaminoglycans play a critical role in cell attachment, differentiation, and morphogenesis. We evaluated chitosan ([1-->4] linked 2-amino-2-deoxy-beta-D-glucan) as a biomaterial for hepatocyte attachment because of its structural similarity to glycosaminoglycans. Freshly isolated rat and fetal porcine hepatocytes were seeded on chitosan membranes that had been previously blended with collagen, gelatin, or albumin to improve biocompatibility and surface roughness. The optimal cell density and attachment kinetics were quantified. The metabolic activity was investigated by measuring daily urea and total protein secretion by the cells for 2 weeks. While collagen blended-chitosan membranes provided a good attachment surface for rat hepatocytes, albumin and gelatin blended chitosan membranes were superior for fetal porcine hepatocyte attachment. The optimal attachment was maintained with membranes of medium molecular weight (Mr = 750,000 daltons) chitosan, at 3-4 x 10(4) cells/cm2 after 3 h of incubation. In vitro experiments demonstrated that fetal porcine hepatocytes survived at least 14 days when seeded on the chitosan-albumin matrix, demonstrating that this biomaterial can provide suitable cell attachment scaffolds for creating liver tissue organoids.

Hepatocyte attachment on biodegradable modified chitosan membranes: in vitro evaluation for the development of liver organoids.

Studies on immobilization of urease in gelatin by cross-linking.

Bacillus sphaeticus 2362 spore-toxin complex was encapsulated within aluminum carboxymethylcellulose (CMC) and assayed for larvicidal activity against 2nd and 3rd instars of Culex spp. to determine the release properties of the system. Encapsulation of the bacterium exhibited higher stability toward acidic pH, temperature (50), and UV irradiation (12 W). The stability of spore-toxin viability detected for the encapsulated pathogen was higher than that for the free bacterium, because the procedure prevented the bacterium from being faced directly with microbial degradation, UV and sunlight, temperature, and pH variations. Mortalities in treatments involving incorporation of encapsulated B. sphaeticus 2362 into artificial diet of Culex spp. larvae were observed starting from the 48th h after inoculation. Aluminum sulfate (0.05 M) and 1% sodium CMC concentrations were found to be optimum, because higher gellant and polysaccharide levels caused slower release of the bacterium. Our results suggest that the aluminum CMC-encapsulated form of B. sphaeticus 2362 can be used more efficiently than its free form in the control of mosquito larvae.

Aluminum carboxymethylcellulose encapsulation of Bacillus sphaericus 2362 for control of Culex spp. (Diptera: Culicidae) larvae

Urease immobilization into poly(acrylamide) - gelatin gels

In the present work carboxymethylcellulose (CMC) and CMC-gelatin were used as carrier systems for urease immobilization. Immobilization was based on the formation of insoluble salts of CMC and gelatin with chromium(111) ions. Chromium(111) acetate (CA) and chromium(111) sulfate (CS) were used for this purpose and their effect on urease activity was investigated. The activities of immobilized urease using pure and CMC-gelatin carrier systems were compared. Urease activity was determined by using Berthelot method. Reuse number, pH, enzyme and cross linker concentrations and the incubation period were the factors taken into account in this investigation. Activity of immobilized enzymes were found to be stable for at least 2 months and 16–24 usage. Immobilization percentage obtained under optimum conditions was 40%.

Murat Elçin

Papers

Hepatocyte attachment on biodegradable modified chitosan membranes: in vitro evaluation for the development of liver organoids.

Studies on immobilization of urease in gelatin by cross-linking.

Aluminum carboxymethylcellulose encapsulation of Bacillus sphaericus 2362 for control of Culex spp. (Diptera: Culicidae) larvae

Urease immobilization into poly(acrylamide) - gelatin gels

Immobilization of Urease into Carboxymethylcellulose - Gelatine System