Chitin Scaffolds in Tissue Engineering

Tissue engineering/regeneration is based on the hypothesis that healthy stem/progenitor cells either recruited or delivered to an injured site, can eventually regenerate lost or damaged tissue. Most of the researchers working in tissue engineering and regenerative technology attempt to create tissue replacements by culturing cells onto synthetic porous three-dimensional polymeric scaffolds, which is currently regarded as an ideal approach to enhance functional tissue regeneration by creating and maintaining channels that facilitate progenitor cell migration, proliferation and differentiation. The requirements that must be satisfied by such scaffolds include providing a space with the proper size, shape and porosity for tissue development and permitting cells from the surrounding tissue to migrate into the matrix. Recently, chitin scaffolds have been widely used in tissue engineering due to their non-toxic, biodegradable and biocompatible nature. The advantage of chitin as a tissue engineering biomaterial lies in that it can be easily processed into gel and scaffold forms for a variety of biomedical applications. Moreover, chitin has been shown to enhance some biological activities such as immunological, antibacterial, drug delivery and have been shown to promote better healing at a faster rate and exhibit greater compatibility with humans. This review provides an overview of the current status of tissue engineering/regenerative medicine research using chitin scaffolds for bone, cartilage and wound healing applications. We also outline the key challenges in this field and the most likely directions for future development and we hope that this review will be helpful to the researchers working in the field of tissue engineering and regenerative medicine

ラクトサミノグリカンの合成化学研究 : 未利用二糖資源としてのラクトースの機能化

Oligosaccharide resources can be utilized as fine materials to construct further complicated and biologically important glycoconjugates. In addition to the known oligosacchride resources such as cellobiose, maltooligosacchrides, and N,N'-diacetylchitobiose, lactose which is obtainable from whey in large amount should be also highly functionalized and applied for glycoconjugate synthesis. Since this disaccharide contains a precusor of N-acetyllactosamine structure known as an important unit of complex carbohydrates, chemical conversion of lactose to further functional synthons for oligosacchride synthesis seems to be powerful and versatile strategy for glycosciences. The thesis is composed of six chapters. The first chapter describes general introduction to the significance of molecular recognition in nature based on the interaction of carbohydrates and proteins. In addition, an importance of cluster effects in sugar-protein interaction is described. In order to investigate the significance and mechanism of the cluster effects, we have to prepare some appropriately designed sugar-ligands. For this purpose, use of lactose as a key starting material might facilitate the synthetic procedure of new clustered model-ligands. In order to achieve more effective methodology to design "high density cluster ligands", it might be necessary to synthesize novel type of polymerizable sugar derivatives. Thus, in the second chapter of this thesis, a simple and efficient method for the syntheses of clustering-sugar homopolymers from ω-acryloylamimoalkyl glycosides of N-acetyl-β-D-glucosamine (GlcpNAc) as a simple model of sugar moiety was discussed in order to produce highly clustered glycoprotein models. Apparent association constants of wheat germ agglutinin (WGA) with a variety of clustered glycopolymers were determined and evaluated by measuring the change in fluorescence intensity produced by various concentrations of polymeric ligand. It was suggested that additon of the clustered glycopolymer to WGA induced much greater enhancement of the fluorescence intensity and a significant blue shift of the fluorescence emission maximum of WGA than did addition of the low-density glycopolymer derived from n-pentenyl type.In the third chapter, the syntheses of cluster-type homopolymers from ω-acryloylaminoalkyl glycosides of N-acetyllactosamine [β-D-Galp-(1→4)-β-D-GlcpNAc] derived from lactose were discussed in relation to the easy determination study of sugar-binding specificity of fluorescein isothiocyanated Erythrina Corallodendron lectin (FITC-ECorL). It was clearly demonstrated by using these polymers that fluorometric titration of FITC-ECorL with a variety of LacNAc polymers revealed an importance of the suitable spacing of the inter-sugar residues on the glycoprotein models for the efficient interaction with the binding sites of lectins Since multivalency of glycoprotein-sugar moiety has not been synthesized on the basis of macromolecular models, attention is next directed towards design of triantennary polymeric sugar ligands using acrylamide type aglycon. Thus, in the chapter 4, an efficient synthesis of a new glycoprotein model having clustered triantennary N-acetyllactosamine (LacNAc) using 4-nitro-4- [1-(3hydroxypropyl)]-1,7-heptandiol as a key starting material was examined. Using the Newkome's derivative, several model glycopolymers having different degrees of density of triantennary LacNAc residues were successfully prepared. Finally, in the chapter 5, for the easy and versatile chemical synthesis of oligosaccharide moieties of branching lactosaminoglycan model, new approaches of chemical modification of lactose were described. Use of 1,6-anhydro-β-lactose as a starting material was proved to establish synthetic strategy that permits the syntheses of a series of lactosaminoglycan models, since all hydroxyl groups of 1,6-anhydro-β-lactose can be distinguished by chemical modifications. Concluding remarks will be described in Chapter 6

Synthesis of a tetrasaccharide repeating unit of O-antigenic polysaccharide of Salmonella enteritidis by use of unique and odorless dodecyl thioglycosyl donors

The first total synthesis of a unique tetrasaccharide repeating unit of lipopolysaccharide from Salmonella enteritidis has been accomplished by assembly of dodecyl thioglycosides. The crucial key steps were preparation of a rare branched dideoxy sugar, D-tyvelose (3,6-dideoxy-D-arabino-D-hexose) and sequential regioselective glycosylation at 2,3-positions of a central D-mannose residue 5 with D-tyvelose 6 and D-galactose donors 7

Pre-activation of fully acetylated dodecyl thioglycosides with BSP-Tf2O led to efficient glycosylation at low temperature

Fully acetylated dodecyl thioglycosides found to be used as glycosyl donors by activation with 1.benzenesulfinyl piperidine (BSP) and triflic anhydride (Tf2O) at -78℃, and the glycosyl acceptor was added to the reaction mixture at the same temperature to furnish various disaccharides and Lewis a (Le^a) trisaccharide in good yields

The Mechanical and Biological Properties of Chitosan Scaffolds for Tissue Regeneration Templates Are Significantly Enhanced by Chitosan from Gongronella butleri

Chitosan with a molecular weight (MW) of 104 Da and 13% degree of acetylation (DA) was extracted from the mycelia of the fungus Gongronella butleri USDB 0201 grown in solid substrate fermentation and used to prepare scaffolds by the freeze-drying method. The mechanical and biological properties of the fungal chitosan scaffolds were evaluated and compared with those of scaffolds prepared using chitosans obtained from shrimp and crab shells and squid bone plates (MW 105-106 Da and DA 10-20%). Under scanning electron microscopy, it was observed that all scaffolds had average pore sizes of approximately 60-90 mm in diameter. Elongated pores were observed in shrimp chitosan scaffolds and polygonal pores were found in crab, squid and fungal chitosan scaffolds. The physico-chemical properties of the chitosans had an effect on the formation of pores in the scaffolds, that consequently influenced the mechanical and biological properties of the scaffolds. Fungal chitosan scaffolds showed excellent mechanical, water absorption and lysozyme degradation properties, whereas shrimp chitosan scaffolds (MW 106Da and DA 12%) exhibited the lowest water absorption properties and lysozyme degradation rate. In the evaluation of biocompatibility of chitosan scaffolds, the ability of fibroblast NIH/3T3 cells to attach on all chitosan scaffolds was similar, but the proliferation of cells with polygonal morphology was faster on crab, squid and fungal chitosan scaffolds than on shrimp chitosan scaffolds. Therefore fungal chitosan scaffold, which has excellent mechanical and biological properties, is the most suitable scaffold to use as a template for tissue regeneration

Cyclodextrin-linked alginate beads as supporting materials for Sphingomonas cloacae, a nonylphenol degrading bacteria

Calcium alginate beads covalently linked with α-cyclodextrin (α-CD-alginate beads) were prepared and examined for their ability to serve as a supporting matrix for bacterial degradation of nonylphenol, an endocrine disruptor. Column chromatographic experiment using α-CD-alginate beads with diameter of 657 ± 82 μm and with degree of CD substitution of 0.16 showed a strong affinity for nonylphenol adsorption. Although addition of α-CD (2.7-27 mM) to the culture broth of Sphingomonas cloacae retarded nonylphenol degradation, the immobilized bacteria on the CD-alginate beads were effective for the degradation. Batch degradation tests using the immobilized bacteria on α-CD-alginate-beads showed 46% nonylphenol recovery after 10-day incubation at 25 ± 2℃, and the recovery reached to about 17% when wide and shallow incubation tubes were used to facilitate uptake of the viscous liquid of nonylphenol on the surface of the medium. Scanning electron microscopic photographs revealed that multiplicated bacteria was present both on the surface and inside the beads and the matrix of CD-alginate was stable and suitable during 10-day incubation