摘要:

This article reviews the strategies and successes of modifying enzymes by means of biophysicochemical transformations. By judicious choice of methods, it has been possible to modify enzymes through physical interactions, chemical reactions and/or mutagenesis to alter a very wide range of properties ranging from stability and solubility on the one hand to catalytic activity and selectivity on the other.

ISSN:0920-5063    

DOI:10.1163/156856295X00797

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We present a novel method for manufacturing three-dimensional, biodegradable poly(DLlactic-co-glycolic acid) (PLGA) foam scaffolds for use in bone regeneration. The technique involves the formation of a composite material consisting of gelatin microspheres surrounded by a PLGA matrix. The gelatin microspheres are leached out leaving an open-cell foam with a pore size and morphology defined by the gelatin microspheres. The foam porosity can be controlled by altering the volume fraction of gelatin used to make the composite material. PLGA 50 : 50 was used as a model degradable polymer to establish the effect of porosity, pore size, and degradation on foam mechanical properties. The yield strengths and moduli in compression of PLGA 50: 50 foams were found to decrease with increasing porosity according to power law relationships. These mechanical properties were however, largely unaffected by pore size. Foams with yield strengths up to 3.2 MPa were manufactured. From in vitro degradation studies we established that for PLGA 50: 50 foams the mechanical properties declined in parallel with the decrease in molecular weight. Below a weight average molecular weight of 10 000 the foam had very little mechanical strength (0.02 MPa). These results indicate that PLGA 50 : 50 foams are not suitable for replacement of trabecular bone. However, the dependence of mechanical properties on porosity, pore size, and degree of degradation which we have determined will aid us in designing a biodegradable scaffold suitable for bone regeneration.

ISSN:0920-5063    

DOI:10.1163/156856295X00805

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In oral delivery of protein and peptide drugs there is a great need for suitable devices for delivering the therapeutic agent-incorporated microspheres selectively in the intestine. It is essential that the drug-loaded multiple unit carrier system should be protected from the harsh environment of the stomach and deliver the carrier system in the large intestine where drug action or absorption is desired. Gelatin capsules were coated with various concentrations of sodium alginate and cross-linked with appropiate concentrations of calcium chloride and tested in vitro for resistance to gastric and intestinal medium. Gelatin capsules coated with 20% w/v of the polymer which gave the most promising result in vitro were evaluated in human volunteers for their in vivo gastro intestinal tract behaviour. The radiographical studies show that while the uncoated gelatin capsules disintegrated in the stomach within 15 min of ingestion, the alginate coated gelatin capsules remained intact as long as they were retained in the stomach (up to 3 h) and then migrated to the ileocecal region of the intestine and disintegrated.

ISSN:0920-5063    

DOI:10.1163/156856295X00814

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Biomer™ is a poly(ether-urethane-urea) block copolymer widely used as biomedical devices. Extraction process of this polymer has purified its surface of low molecular weight polyurethane chains and Santowhite Powder additive. ESCA and ATR/FTIR have suggested a homogenization of the polymer by enrichment of the first layers with poly(aminomethacrylate) additive after extraction. Therefore, the surface of the extracted Biomer™ exhibits a different wettability and biological response. The treatment causes a significant decrease in fibronectin adsorption and induces a reduction in Staphylococcus aureus adhesion.

ISSN:0920-5063    

DOI:10.1163/156856295X00823

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Hemodialysis membranes made from cellulose (CUPROPHAN, HEMOPHAN) and sulfonated polyethersulfone (SPES) were characterized using the streaming potential technique to determine the zeta potential at their interfaces against well-defined aqueous solutions of varied pH and potassium chloride concentrations. Streaming potential measurements enable distinction between different membrane materials. In addition to parameters of the electrochemical double layer at membrane interfaces, thermodynamic characteristics of adsorption of different solved species were evaluated. For that aim a description of double layer formation as suggested by Börner and Jacobasch (in: Electrokinetic Phenomena, p. 231. Institut für Technologie der Polymere, Dresden (1989)) was applied which is based on the generally accepted model of the electrochemical double layer according to Stern (Z. Elektrochemie 30, 508 (1924)) and Grahame (Chem. Rev. 41, 441 (1947)). The membranes investigated show different surface acidic/basic and polar/nonpolar behavior. Furthermore, alterations of membrane interfaces through adsorption processes of components of biologically relevant solutions were shown to be detectable by streaming potential measurements.

ISSN:0920-5063    

DOI:10.1163/156856295X00832

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The poly(styrene/acrolein) latexes (P(SA)1 and P(SA)2), differing in poly(acrolein) content, were synthesized by the emulsifier-less emulsion-precipitation polymerization of styrene and acrolein. The fraction of poly(acrolein) in the surface layer was 0.35 and 0.50, for the P(SA)1 and P(SA)2 latex, respectively. Latexes were labelled with 2, 4-dinitrophenylhydrazine (DNPH), dansylhdrazine (DAH), and 1-aminopyrene (APY). Surface concentration of labels varied from 4.20 . 10-7mol m-2(for APY label on P(SA)1 latex) to 1.54 . 10-6 mol m-2(for DNPH label on P(SA)2 latex) reflecting the fraction of polyacrolein in the surface layer and bulkiness of the label. The differences between adsorption and covalent immobilization of human serum albumin and gamma globulins onto the P(SA)2 latex and onto its derivatives labelled with the 2,4-dinitrophenyl (DNP), dansyl (DA), and pyrene (PY) groups were small. The observation conforms to the hypothesis that polyacrolein forms domains on the surface of the P(SA) latexes and that after labelling some aldehyde groups are still available for the covalent immobilization of proteins. Labelled and parent latexes were used in the model slide and turbidimetric aggregation tests for the goat anti-HSA. The fluorescent latexes, labelled with APY and DAH, and latexes labelled and with DNPH were found to be suitable for the model tests, similarly as the nonlabelled ones, however, some differences in the sensitivity, depending on the presence and the nature of labels, were noticed. The standard goat anti-HSA serum (Sigma) was detected at maximum dilution equal to 2000 in the slide test, and in the dilution region from 1.8 103to 4.7.106times in the turbidimetric test.

ISSN:0920-5063    

DOI:10.1163/156856295X00841

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor