In this study different synthetic strategies were developed and applied to introduce solely or in combination heparin/heparansulfate-like functional groups such as N-sulfo, O-sulfo, N-acetyl, and N-carboxymethyl groups into chitosan and cellulose with highest possible regioselectivity and completeness and defined distribution along the polymer chain. Completely substituted 6-amino-6-deoxycellulose and related derivatives were prepared from tosylcellulose (DS 2.02; C6 1.0) by nucleophilic substitution with azido groups only in the 6-position at 50 °C with subsequent reduction to amino groups and completely removing tosyl groups in the 2,3-position. 2,6-Di-O-sulfocellulose was prepared using the reactivity difference between C-2, C-6 and C-3 of cellulose. The reactivity difference between amino groups and hydroxyl groups was used to prepare various N-substituted derivatives. Partially 2,6-di-O-sulfated cellulose was obtained from trimethylsilylcellulose by the insertion of sulfurtrioxide into the Si–O ether linkage. Partially 3-O-sulfocellulose was synthesized by protecting C-2 and C-6 with trifluoroacetyl groups. A copper–chitosan complex was used to synthesize 6-O-sulfochitosan with a DS of 1.0 at C-6 and various partially 6-O-desulfonated products are possible. Using the phthalimido group to increase the solubility of chitosan in DMF, the regioselectivity of 3-O-sulfo groups was improved by regioselective 6-O-desulfonation of nearly complete 3,6-O-disulfochitosan. The platelet adhesion properties of immobilized regioselectively modified water-soluble derivatives on membranes have been tested in vitro. Some regioselectively modified chitosan and cellulose derivatives are potential candidates for the surface coatings of biomaterials if the regioselective reactions are somewhat further optimized.

The biological response of an organism to an implant can be influenced by structuring and/or functionalisation of the implant surface. The goal of our study is to improve the osseointegration of orthopaedic endoprothesis by coating metal substrates with dense or nanoporous titania layers combined with biofunctionalisation of the surface with peptides and proteins.The sol-gel method is used to produce titania coatings on medical relevant substrates such as titanium or titanium alloys. Control of the educt ratios and the processing, like drying the specimens in air (xerogel) or supercritical drying in an autoclave unit (aerogel), results in dense or nanoporous titania films. Pore diameters can be adjusted between 10 and 120 nanometers. A remarkable characteristic of the coatings is the high number of surface hydroxy functionalities even after calcination. These reactive groups give ideal conditions for the biofunctionalisation. The immobilisation of biological active substances is carried out by successive covalent silanisation with an aminosilane using a dicarbonic acid as a spacer molecule, and binding of peptides to the spacers. Biocompatibility and cytotoxicity of the materials were tested with cell culture assays.

In the present paper a new strategy has been studied to introduce solely or in combination N-sulfo, O-sulfo, N-acetyl, and N-carboxymethyl groups into chitosan with highest possible regioselectivity and completeness and defined distribution along the polymer chain. The aim was to generate compounds having lowest toxicity for determining the pharmacological structure–function relationships among different backbone structures and differently arranged functional groups compared to those of heparin and heparan sulfate. The water-soluble starting material, chitosan, with a degree of acetylation (DA) of 0.14 and a molecular weight of 29 kD, allows one to apply most of the known reactions of chitosan as well as some reactions of heparin chemistry successfully and with improved regioselectivity and completeness. On the other hand, a number of these reactions were not successful by application to water-soluble high-molecular-weight chitosan (DA 0.45 and 150 kD). The starting material showed statistical N-acetyl (N-Ac) distribution along the polymer chain according to the rules of Bernoulli, with highest abundance of the GlcNAc–GlcNAc diad along with a lower abundance of triads, tetrads, and pentads. The space between the N-Ac groups was filled up in homogeneous reactions by N-sulfo and/or N-carboxymethyl groups, which also resulted in a Bernoulli statistical distribution. The N-substitution reaction showed highest regioselectivity and completeness with up to three combined different functional groups. The regioselectivity of the 3-O-sulfo groups was improved by regioselective 6-desulfation of nearly completely sulfated 3,6-di-O-sulfochitosan. By means of desulfation reactions, all of the possible intermediate sulfated products are possible. 6-O-Sulfo groups can also be introduced with highest regioselectivity and completeness, and a number of partially 6-desulfated products are possible.

Full Paper: Some regioselective cellulose derivatives were synthesized on the basis of the just started longterm concept by variation of O-SO3, N-SO3, N-Ac, and N-carboxymethyl groups solely or in combination for the development of athrombogenic and antithrombogenic nanocoatings on cellulose membranes. Similar regioselectively arranged functional groups are known partially in type 1 glycosaminoglycane (dermatan sulfate DS, and chondroitin sulfate CS) and all the groups are present in type 2 CAG (heparin HE and heparansulfat HS). The goal of this concept was to use instead of the backbone structure beta 1->4, beta 1 -> 3 (DS, CS) or beta 1 -> 4, alpha 1->4 (HE, HS or regioselective desulfated HE), the beta 1 -> 4 backIhone:structure of cellulose or chitosan, with the same functional groups as in HE. Furthermore different regioselective;sulfated cellulose derivatives, such as cellulose-3-sulfate, cellulose-2,6-disulfate, and cellulose-2,3-sulfates with varied sulfation degrees have been synthesized and Immobilized ionically on cellulose membranes. They were tested concerning their reduction of platelet adhesion from citrated whole blood in a perfusion system as well for AT III affinity. The lowest platelet adhesion and AT III affinity was observed using cellulose-2,3-sulfates and cellulose-3-sulfate derivatives, whereas cellulose-6-O-sulfate derivatives show high AT In affinity and high platelet adhesion. This means that a high 6-O-sulfate content seams to promote anticoagulant properties of the derivatives with high (AT Ill) affinity, whereas low concentrations of 2-O- and 3-O-sulfate groups show the lowest platelet adhesion. The latter seems to be important for developing athrombogenic coatings for biomaterials. The starting material chitosan with molecular weight of 150 KD was used to synthesize additionally some of 2-deoxyaminocellulose derivatives containing N-Ac or N-SO3 or N-CH2-COOH and O-SO3 groups. These derivatives are structurally closer to IIE and I-IS and should enable us to work out the influence of each heparin like functional group in cellulose derivative on the athrombogenic and antithrombogenic properties. We synthesized only some of the latter mentioned derivatives with a distribution of the functional groups according to a Bernoulli statistics. Totally sulfated 2-deoxyaminocellulose-3,6-disulfate derivatives will be regioselectively desulfated by reactions known from heparin chemistry.