Anders Wirsén

Novel pH-sensitive chitosan hydrogels: swelling behavior and states of water

Physically crosslinked chitosan hydrogels were synthesized by grafting D,L-lactic acid (LA) and/or glycolic acid (GA) with different feed ratios. The physical crosslinking was formed due to the hyd ...

Synthesis and characterization of pH‐sensitive hydrogels based on chitosan and D,L‐lactic acid

Novel pH-sensitive physically crosslinked hydrogels were synthesized by grafting D,L-lactic acid (LA) onto the amino groups in chitosan (CS) without a catalyst. The structures of these graft copolymers were analyzed by FTIR and X-ray measurements. Degree of substitution, side-chain length, and yield of copolymers were evaluated from 1H-NMR, salicylaldehyde, and elemental analysis. The crystallinity of chitosan gradually decreased after grafting, since the side chains substitute the NH2 groups of chitosan randomly along the chain and destroy the regularity of packing between chitosan chains. Water uptake of the hydrogels was investigated as a function of side-chain length and degree of substitution. The influence of pH and salt concentration on the swelling behavior of the hydrogels was determined and interpreted.

Structural change and swelling mechanism of pH‐sensitive hydrogels based on chitosan and D,L‐lactic acid

Graft copolymerization of D,L-lactic acid (LA) onto chitosan (CS) was attempted without using a catalyst. pH-sensitive hydrogels were obtained which are based on two different components: a natural polymer and a synthetic polymer. These polyester substituents provide the basis for hydrophobic interactions that contribute to the formation of hydrogels. The swelling mechanisms in enzyme-free simulated gastric fluid (SGF, pH 2.2) or simulated intestinal fluid (SIF, pH 7.4) at 37°C were investigated. Meanwhile, structural changes of the graft copolymers in the different pH buffers were studied by FTIR, and these are discussed together with the swelling mechanisms. The effect of pH on the water uptake of hydrogel was investigated by using McIlvaine buffer with the same ionic strength. The morphological change of hydrogels in different aqueous solutions is investigated by scanning electron microscopy (SEM).

Bioactive heparin surfaces from derivatization of polyacrylamide-grafted LLDPE

Primary amine groups were introduced into polyacrylamide-LLDPE films, using the Hofmann degradation synthesis. The Hofmann degradation was studied at room temperature using sodium hypochlorite and sodium hydroxide at different concentrations. Diazotized heparin was covalently bound to the grafted LLDPE film via the primary amine groups. Surfaces were analysed with ESCA, ATR-IR, chloride titration and Toluidine Blue. Evaluation of the biological activity of the heparinized surfaces was made by measuring the capacity for binding antithrombin (AT) and inhibition of the activated coagulation factor XII (FXIIa). The heparinized surfaces were able to bind up to 3 pmol cm-2 of AT in solution with ionic strengths of I = 0.15 and I = 0.40. No activation of the adsorbed FXII was detected.

The effect of electron beam irradiation on PCL and PDXO-X monitored by luminescence and electron spin resonance measurements

Abstract The effect of electron beam irradiation in air or argon was studied on two hydrolysable aliphatic polyesters, poly(ϵ-caprolactone) (PCL) and chemically cross-linked poly(1,5-dioxepan-2-one) (PDXO-X). A secondary alkylether radical and a tertiary alkyl radical were identified by ESR in PCL and PDXO-X after irradiation in both air and argon. For the samples irradiated in air, peroxy radicals were detected in PCL but not in PDXO-X. For irradiated PCL, the intensities in the luminescence measurements seemed to be dose-dependent. Large amounts of oxidation products were found present in the PDXO-X irradiated in air and the luminescence intensities seemed to be dose-dependent.

Graft polymerisation of acrylamide onto PCL film by electron beam pre-irradiation in air or argon. Morphology in the final grafted state

Poly(epsilon-caprolactone) has been graft polymerised to final graft yields with acrylamide (AAm) as monomer in an aqueous solution by the pre-irradiation method. The synthesis of the samples obtai ...

The grafting of acrylamide onto poly(ε-caprolactone) and poly(1,5-dioxepan-2-one) using electron beam preirradiation. I. Influence of dose and Mohr's salt for the grafting onto poly(ε-caprolactone)

Poly(e-caprolactone) films (TONE® 787) were irradiated by electron beam in air prior to grafting in aqueous solutions of acrylamide. The grafting kinetics and molecular weight of the grafted poly(acrylamide) chains were studied with irradiation doses between 2.5 and 20 Mrad and in the Mohrs salt concentration range of 0.0025-1 wt %. The grafting rate and yield were strongly dependent on the Mohrs salt concentration. By molecular weight analysis of grafted poly(acrylamide) chains, it was shown that the molecular weight is approximately proportional to the mass of the grafted PAAm.

The grafting of acrylamide onto poly(ε‐caprolactone) and poly(1,5‐dioxepan‐2‐one) using electron beam preirradiation. III. The grafting and in vitro degradation of chemically crosslinked poly(1,5‐dioxepan‐2‐one)

Acrylamide was graft polymerized onto the surface of a chemically crosslinked and amorphous biodegradable polyester, poly(1,5-dioxepan-2-one). Electron beam irradiation at a dose of 5 Mrad was used to generate the initiating species in the polyester. The degradation behavior in vitro at pH 7.4 and 37°C in a phosphate buffer solution was studied for untreated, irradiated, and acrylamide-grafted polymer. Differences in weight loss performance were observed between virgin and treated polymers. The acrylamide-grafted poly(1,5-dioxepan-2-one) was totally degraded after 43 weeks as compared to 48 weeks for the irradiated and 55 weeks for the virgin polymer. On the other hand, the treated polymers showed a higher resistance to degradation in terms of weight loss during the intermediate part of the degradation, i.e., between about 5 and 35 weeks. After this period, the irradiated and particularly the acrylamide grafted poly(1,5-dioxepan-2-one) degraded much more rapidly than the virgin polymer.