ISSN:0920-5063    

DOI:10.1163/156856298X00604

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A new synthetic approach has been applied to obtain novel di-, tetra-, and (multi)-peptide containing polymer conjugates in quantitative yields with a high degree of conjugation. Bis-(N-hydroxysuccinimidyl) esters of PEG (Mw= 200, 600, 1400, 2000, and 3400) were synthesized and studied in a condensation reaction with synthetic peptides: glycine-glycine-tyrosine-arginine (GGYR), a model peptide, and glycine-arginine-glycine-aspartic acid-tyrosine (GRGDY), a sequence known to promote cell adhesion and aggregation. Tetra-substituted derivatives of PEG-based conjugates were synthesized by coupling L-aspartic acid and L-aspartyl-L-phenylalanine through a condensation procedure in organic media. Poly(acrylic acid) and co-polymers (Mw= 2000 and 5000) were studied as a model of multifunctional linear polymers in the reaction with L-tryptophan and GGYR. Alternative polymer-(multi)-peptide conjugates were successfully synthesized using Starburst® dendrimer PAMAM (G = 3), 'short' and 'long'-chain PEG-based active esters and GRGDY. The structure of the intermediate precursors and peptide-conjugates was confirmed by spectral (UV-Vis, FTIR,1H-NMR) and chromatographic (RP-HPLC and SEC) methods. By varying the properties of the interconnecting polymer - such as hydrophobicity, molecular weight, and functionality - a set of polymer-GRGDY conjugates was synthesized.

ISSN:0920-5063    

DOI:10.1163/156856298X00613

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

To investigate the effects of culture conditions on the maintenance of metabolic functions of cultured hepatocytes, long-term hepatocyte culture lasting 20 days was performed under two different culture conditions, i.e. stationary cultures utilizing porous polymer (polyvinyl formal (PVF) resin) as a substratum and conventional monolayer dish cultures without PVF. Metabolic activities specific to hepatocytes were evaluated in terms of ammonia metabolism, urea synthesis, and albumin secretion. Concerning ammonia metabolic and urea synthetic activities, no significant differences in maintenance of these activities were found between the two culture conditions, and these activities rapidly decreased with the elapse of the culture period, especially during the early stage of the experiments. However, after day 10, these activities in the stationary cultures were maintained at a slightly more favorable level than in the monolayer cultures. On the other hand, compared with ammonia metabolism and urea synthesis, stable and well-maintained albumin secretion of hepatocytes (60% of the activity in day 1) was exhibited in the stationary culture experiments, despite that this particular activity under the monolayer culture condition gradually reduced to a very low level (5.7% of that on day 1) at the end of the culture. From the morphological observations, hepatocytes immobilized in the PVF resin revealed individual spherical shapes without forming multicellular aggregation, and it was suggested that this characteristic structure contributed to good albumin secretion of hepatocytes. In conclusion, the advantages of the hepatocyte culture technique utilizing PVF resin over the conventional dish culture in maintaining some representative metabolic function specific to hepatocytes were clarified.

ISSN:0920-5063    

DOI:10.1163/156856298X00622

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Poly(vinyl alcohol) (PVA) foams were used as scaffolds in hollow fiber membrane-based cell encapsulation devices. The surrounding permselective membrane serves as an immunoisolation barrier while allowing metabolites and other small molecules to be freely transported. The internal matrix defines the microenvironment for the encapsulated cells. PC 12 cell-containing devices represent one possible strategy for safe transplantation of dopamine-secreting cells for the treatment of dopamine-deficient diseases such as Parkinson's disease. PC12 cells - a dopamine-secreting cell line - were encapsulated with PVA foam as a matrix material in the lumen of these hollow fibers. In this work, we demonstrate the presence of the PVA matrix increased the catecholamine secretion efficiency of the cells as compared to devices containing a chitosan matrix. Devices were implanted in vivo into rodent striatum and device output of catecholamines was measured preimplant and post-explant. Evoked stores of dopamine remained constant (preimplant vs explant) for devices encapsulated with the foam matrix and increased with devices encapsulated with chitosan matrix. Cell proliferation within devices was inhibited in the presence of the foam matrix. Cell viability and distribution was significantly improved with the inclusion of the foam matrix in both in vitro and in vivo studies. In comparison to chitosan - a typical matrix material for PC12 cells - addition of a foam-type matrix altered the encapsulated cell microenvironment and resulted in more efficient secretion of catecholamines and improved distribution within the device resulting in smaller necrotic regions and a lower rate of cell proliferation.

ISSN:0920-5063    

DOI:10.1163/156856298X00631

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

By means of a cell culture method, the attachment and growth of mouse L929 fibroblast cells were studied on matrices of the (-SDS)- and (+SDS)-keratins, which were extracted from wool in the absence and presence of sodium dodecyl sulfate, respectively. The (+SDS)-keratin showed some toxic effect on the cell growth, but upon washing with a pH 7/phosphate buffer, the protein behaved similarly to a substratum of the (-SDS)-keratin. The comparative culture assay on the keratins, collagen (type I), and glass revealed that the keratins were more adhesive to the cells and more supportive for cell proliferation than the collagen and glass. The results were explained by an enhanced initial adsorption of mediator proteins from fetal bovine serum onto the keratin substrata.

ISSN:0920-5063    

DOI:10.1163/156856298X00640

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Degradable polyurethane elastomers were synthesized using a diester chain extender. The chain extender was synthesized by a diesterification reaction between L-phenylalanine and 1,4-cyclohexane dimethanol to yield a diester, diamine. Soft segment chemistry (polycaprolactone diol, PCL and polyethylene oxide, PEO) and molecular weight were varied and the impact on polyurethane physicochemical and degradation characteristics was evaluated. It was found that the PEO containing polyurethanes absorbed large amounts of water while the PCL containing ones did not, indicating a large difference in bulk hydrophilicity. The rate of water vapor permeance (WVP) through the polyurethane films generally followed the water absorption trends. However, soft segment crystallinity, noted by DSC, for the PCL containing polyurethanes served to reduce WVP values with increasing PCL molecular weight. Polyurethane surface characterization was carried out by water contact angles and XPS. The PEO containing polyurethanes exhibited low contact angles in comparison with the PCL ones. In addition, angle-resolved XPS demonstrated soft segment surface enrichment in all cases typical for phase segregated materials. Significant variation in the physicochemical properties of the experimental polyurethanes was observed indicating potential use in a variety of biomaterials applications. An in vitro degradation study was carried out by incubating the polymers in 0.1 M TBS at 37°C, pH 8.0 for up to 56 days. Degradation was followed by measuring mass loss, change in molecular weight by GPC and surface alteration by scanning electron microscopy. The polyurethane containing PEO was found to exhibit substantial mass and molecular weight loss over 56 days resulting in a porous material of little strength. In contrast, the PCL containing polyurethane displayed modest mass and molecular weight loss after 56 days. This polyurethane retained its strength and displayed little surface alteration after 56 days in buffer. It was hypothesized that differences in polyurethane hydrophilicity as well as initial molecular weight may have been responsible for the dramatic difference in degradation rate observed here.

ISSN:0920-5063    

DOI:10.1163/156856298X00659

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We have begun studies of a novel type of biomaterial derived from a recently-discovered class of ionic self-complementary oligopeptides. These short peptides (typically 8, 16, 24, or 32 amino acid residues with internally-repeating sequences) self-assemble in aqueous salt solution into three-dimensional matrices capable of favorable interactions with cells, and offer promise for useful bioengineering design based on rational changes in sequence. In this paper we present preliminary results on mechanical properties, combining experimental and theoretical approaches, of one particular example of these peptide materials, EFK8. The static elastic modulus was measured using an apparatus designed to allow sample fabrication and mechanical testing in the same system with the sample in aqueous solution. The material microstructure was examined by SEM and the measurements interpreted with the aid of a model for cellular solids. Values for the elastic modulus increased from 1.59 ± 0.06 to 14.7 ± 1.0 kPa for peptide concentrations increasing from 2.7 to 10 mg ml-1. SEM photographs showed the microstructure to consist of a relatively homogeneous lattice with fiber thickness of 10 - 30 nm independent of peptide concentration, but with fiber density increasing with peptide concentration. This behavior is consistent with scaling predictions from the cellular solids model and yields an estimate for the individual fiber elastic modulus in the range of 1-20 MPa. We therefore have provided some initial physical principles for guiding improvement of the mechanical properties of these new materials.

ISSN:0920-5063    

DOI:10.1163/156856298X00668

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor