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At least 379 records · Page 21Linked to original sources

PubMed1981

Aliphatic polyesters II. The degradation of poly (DL-lactide), poly (epsilon-caprolactone), and their copolymers in vivo.

The mechanisms of biodegradation of poly (DL-lactide), poly (epsilon-caprolactone), and copolymers of epsilon-caprolactone with DL-dilactide, delta-valerolactone, and DL-epsilon-decalactone in rabbit were shown to be qualitatively similar. However, the rate of the first stage of the degradation process, non-enzymatic random hydrolytic chain scission, varied by an order of magnitude and was dependent on morphological as well as chemical effects. Weight loss was generally not observed until the molecular weight had decreased to 15,000 or less. Poly (DL-lactide) differed from the other polyesters studied, the rate of chain scission increasing after the commencement of weight loss. The rate of weight loss was greater and the period prior to weight loss was shorter when the comonomer content of copolymers of epsilon-caprolactone was sufficient to reduce the melting point of epsilon-caproate sequences to body temperature.

Animals↗

PubMed1986

Tissue reaction to polypropylene and polyester in obese patients.

Local tissue reaction was examined after subcutaneous implantation for 8 wk of small pieces of Marlex (polypropylene) and Dacron (polyester) in 11 extremely obese patients. Dacron gave a stronger chronic inflammatory reaction in 7 out of 11 patients, and a stronger foreign body giant cell reaction in all of them: Marlex is therefore perhaps more suitable than Dacron as a reinforcement band in gastric surgery for obesity. At reoperations due to complications after gastric banding the tissue reaction in the omentum which covered the band, was examined in 9 patients. No major difference in tissue reaction in the omentum compared to that in subcutaneous fat was found. None of the reoperations was caused by too strong a tissue reaction to the reinforcement band i.e. Marlex in 8 patients and Gore-tex (Teflon) in one patient.

Biocompatible Materials↗

PubMed1989

Cellular reactions to polyester arterial prostheses impregnated with cross-linked albumin: in vivo studies in mice.

This study was designed to assess the possible immunological responses in mice against polyester prostheses coated with albumin and previously stabilized either with cross-linked glutaraldehyde (GA), at different concentrations, or with carbodiimide (CDI). Prosthetic discs were first implanted in the peritoneal cavities of mice, and T cells and T cell subsets (helper, suppressor, la-bearing T lymphocytes) were then quantified before implantation and at 1, 2, 3 and 4 weeks post-implantation. The percentages of T cells, subsets, and the helper/suppressor cell ratio, as well as the percentage of T cells with la receptors, were similar to the control in all experimental groups. No significant difference and no correlation were observed between the groups wherever tested. Virgin and albumin-coated grafts did not induce any quantitative changes in T cell subpopulations in mice.

Albumins↗

PubMed1989

Experimental evaluation of a gelatin-coated polyester graft used as an arterial substitute.

Protein coating and endothelial cell preseeding have been proposed and studied as improvements to arterial prostheses. In this paper, an impervious polyester vascular graft which had been coated with cross-linked gelatin was compared to a porous one over a period of up to 8 months in dogs. This evaluation involved in vivo methods using radio tracers to study patency and thrombogenicity and in vitro controls of the healing processes. The main advantages offered by coated grafts over uncoated include the absence of preclotting and better biointegration.

Animals↗

PubMed1991

Partially biodegradable polyacrylic-polyester composites for internal bone fracture fixation.

New partially resorbable composite formulations based on components used in surgery were synthesized in rod form (length 15-20 mm, diameter 4 mm). The biostable components were poly(methyl methacrylate) in hydrophobic implants and poly(2-hydroxy ethyl methacrylate) in hydrophilic ones. The biodegradable components were commercially available suture yarn made from poly (alpha-hydroxy esters): polyglycolide, a polyester derived from glycolic acid; and a copolyester of glycolic and lactic acids, polyglactin 910. Biodegradation in phosphate-buffered solution at pH 7.0 and 37 +/- 0.5 degrees C was analysed gravimetrically. There was no measurable loss of mass after treatment for 20-25 d. Composite microstructure was examined by phase-contrast, cross-polarized light microscopy.

Biocompatible Materials↗

PubMed1992

Polyester film strips coated with photographic gelatin containing immobilized glucose oxidase hardened by chromium(III) sulphate.

Glucose oxidase was immobilized into photographic gelatin hardened by chromium(III) sulphate. The enzyme-gelatin mixture was coated on polyester film strips which allowed easy and simple handling during assays. The effect of gelatin and cross-linker concentrations on water content and enzymatic activity was studied. The effect of pH during immobilization and that of incubation temperature on maximum activity were examined. Enzyme leakage tests were carried out during reuse number studies. Consecutive use of strips followed by washing and resting between uses were found to affect the reuse number. A maximum immobilization of 68% was reached under optimal conditions. Mechanical stability and leakage were found to be functions of gelatin and cross-linker concentrations. Photographic gelatin was found to have many capabilities with extraordinary characteristics as a carrier on immobilization.

Biocompatible Materials↗

PubMed1993

Numerical and functional modifications in platelets induced by polyester coated by a hydrophilic polymer.

We evaluated the alterations in number, functionality and release reaction of the platelets contained in plasma, filtered through a polyester filter and coated with a hydrophilic polymer. The alterations in number were examined by counting before and after filtration. The morphological modifications were studied by determining the mean platelet volume. The functional alterations were analysed by a platelet aggregation test, induced by ADP and collagen. The presence of products from the release reaction in filtered plasma was studied using radioimmunoassays of beta-thromboglobulin, platelet factor 4 and thromboxane B2. The results obtained showed that the filtration of plasma through the material did not determine a significant platelet adhesion, did not alter the volume or the functionality of the platelets and induced no release reaction.

Biocompatible Materials↗

PubMed1996

An albumin-coated polyester arterial graft: in vivo assessment of biocompatibility and healing characteristics.

The albumin-coated vascular graft (ACG) and its uncoated polyester substrate, the Vascular II (V-II), were evaluated in terms of biocompatibility and biofunctionality using two in vivo animal studies. Biocompatibility and immunoreactivity were assessed by implanting intraperitoneally in the rat small segments of the ACG and the V-II graft and harvesting them with their surrounding tissue 3d, 1, 2 and 4 weeks later. Cytofluorometric determination of total T cells (CD3), the ratio of CD4/CD8 subsets and the percentage of IL-2 receptor-positive T cells in the peripheral blood has revealed that no significant difference in any of the T cell populations was found between the ACG and the V-II graft. The cellular reactivity of the ACG in terms of acid phosphatase activity at the implant side was significantly greater at 3 d but not at longer periods. Biofunctionality was evaluated by implanting both grafts as a thoracoabdominal vascular bypass in dogs for 11 different periods ranging from 4 h to 6 months. The rate of albumin resorption was such that traces were still present at 1 month, but no longer observable at 2 months. Tissue incorporation into the graft wall was earlier for the V-II (2 weeks) than for the ACG (4 weeks), which showed complete encapsulation, tissue incorporation and endothelialization after 2 months in vivo. Only small differences were observed between both grafts in terms of platelet and fibrin uptake on the luminal surface. The prostacyclin/thromboxane A2 ratio increased to a level higher that 1.0 aorta within 1 month for the V-II and 4 months for the ACG. In conclusion, the Bard ACG has demonstrated excellent biocompatibility in terms of blood T cell behaviour and acid phosphatase activity at the implant site. Finally, its healing response is equivalent to that of the uncoated Dacron prosthesis once the albumin coating has been resorbed.

Acid Phosphatase↗

PubMed1990

Use of polymyxin-coated polyester cloth in the enzyme immunoassay of Salmonella lipopolysaccharide antigens.

Polyester cloth coated with polymyxin B was used to capture Salmonella typhimurium lipopolysaccharide antigens which were then quantitatively or qualitatively assayed using a specific antibody-peroxidase conjugate. This simple, rapid method can be used to assay a large number of samples by employing a large sheet of the polymyxin-coated cloth onto which multiple samples can be blotted. The method is reproducible and economical, since polymyxin B is relatively inexpensive, stable and available in pure form.

Adsorption↗

PubMed1994

Development of the Apex polyester fibre cruciate ligament implant.

This paper describes the work done in developing the Apex polyester fibre cruciate ligament implant. A series of animal experiments showed that the material was the basis for good collagenous tissue ingrowth at the calcaneal tendon and within the knee joint. The rate of increase of strength of ingrowth at the calcaneal tendon was investigated. The slow maturation led to the development of a stainless steel screw and grommet anchorage system, which was also tested in vitro. A long-term animal study of the clinical implant and anchor system showed the implant fibres spaced apart by prolific ingrowth, while no implant particles were found, and there was no evidence of synovitis. The tissue reactions in human use have been found to be the same as in the animals, while ultrastructural study of retrieved specimens has given evidence of long-term collagen maturation.

Animals↗

PubMedDate not supplied

Geometrically structured implants for cranial reconstruction made of biodegradable polyesters and calcium phosphate/calcium carbonate.

The aim of this study was the development of a processing pathway for manufacturing of biodegradable skull implants with individual geometry. The implants on the basis of polylactide and calcium phosphate/calcium carbonate were prepared by a combination of hot pressing and gas foaming. On the inside, the implant consists of a macroporous and faster degradable material (poly(D,L-lactide)+CaCO3) to allow the ingrowth of bone cells. The pore size is in the range of 200-400 microm. On the outside, the implant consists of a compact and slower biodegradable material (poly(L-lactide) and calcium phosphate) to ensure mechanical stability and protection. To overcome problems like inflammatory reactions caused by acidic degradation products of polylactide, the polyester was combined with basic filling materials (calcium salts). The filler neutralises the lactic acid produced during polymer degradation and increases the bioactivity of the material. The stabilised pH was demonstrated by long-term in vitro pH studies. Over a time period of 250 d in demineralised water, the pH was in the physiological range. The in vitro biocompatibility was shown by cell cultures with human osteoblasts. A good proliferation of the cells was observed over the whole test period of 4 weeks.

Absorbable Implants↗

PubMed2005

Surface modification of biodegradable polyesters with fatty acid conjugates for improved drug targeting.

We describe a general method for incorporating target ligands into the surface of biocompatible polyester poly(lactic-co-glycolic acid) (PLGA) 50/50 materials using fatty acids. Avidin-fatty acid conjugates were prepared and efficiently incorporated into PLGA. Avidin was chosen as an adaptor protein to facilitate the attachment of a variety of biotinylated ligands. We show that fatty acid preferentially associates with the hydrophobic PLGA matrix, rather than the external aqueous environment, facilitating a prolonged presentation of avidin over several weeks. We successfully applied this approach in both microspheres encapsulating a model protein, bovine serum albumin, and PLGA scaffolds fabricated by a salt-leaching method. Because of its ease, generality and flexibility, this strategy promises widespread utility in modifying the surface of PLGA-based materials for applications in drug delivery and tissue engineering.

Absorbable Implants↗

PubMed2005

Growth of embryonic renal parenchyme at the interphase of a polyester artificial interstitium.

The construction of an artificial kidney module by tissue engineering or the application of cell-based therapies for the treatment of renal failure requires exact information regarding the cellbiological mechanisms of parenchyme development in combination with different kinds of biomaterials. To learn more about these processes tissue cultures are frequently used experimental tools. However, apart from experiments with early kidney anlagen there is a lack of suitable in-vitro models regarding the generation and long-term maintenance of renal tubules. In the present paper we like to demonstrate an advanced culture technique, which allows to generate tubular elements derived from renal stem cells. For the growth of tubules it is essential to fine-tune the interface between the embryonic tissue and the dead fluid space within a perfusion culture container by offering a polyester artificial interstitium. Culture was performed in IMDM supplemented with hormones and growth factors but using serum-free conditions over 14 days. Formation of tissue was then analysed by immunohistochemistry and two-dimensional (2D) electrophoresis. Culture in pure IMDM leads to a complete loss of tissue formation. In contrast, application of aldosterone (A) induces the development of numerous polarised tubules. Surprisingly, addition of epidermal growth factor (EGF), a cocktail of insulin, transferrin and selenium (ITS), retinoic acid (RA), cholecalciferol (VitD3) or bovine pituitary extract (BPT) does not further improve development of tubules, but leads to intensive cell clustering and a decrease of tubule formation. 2D Western blots of developing tissue probed with soybean agglutinin (SBA) reveal a unique pattern of newly detected proteins. It is found that growth factors do not support but abolish protein spots upregulated by aldosterone. It remains to be investigated, which cellbiological effect stimulates the embryonic cells to develop tubules in competition to cell clusters at the interphase of an artificial interstitium.

Aldosterone↗

PubMed2006

Branched polyesters based on poly[vinyl-3-(dialkylamino)alkylcarbamate-co-vinyl acetate-co-vinyl alcohol]-graft-poly(d,l-lactide-co-glycolide): effects of polymer structure on cytotoxicity.

Branched polyesters of the general structure poly[vinyl-3-(dialkylamino)alkylcarbamate-co-vinyl acetate-co-vinyl alcohol]-graft-poly(d,l-lactide-co-glycolide) have shown potential for nano- and micro-scale drug delivery systems. For further optimization of this polymer class their cytotoxicity needs to be characterized establishing structure-toxicity relationships. Effects of type and degree of amine substitution as well as molecular weight on cytotoxicity were evaluated in L929 mouse fibroblasts using a MTT assay whereas interactions with cell membranes were quantified by LDH release and caspase (3/7)-activation. Finally, direct cell-polymer contact assays were conducted. Ungrafted amine-modified polymer backbone yielded IC(50) values in the range of 0.05-10mg/ml. Generally higher toxicities were observed with an increasing degree of amine substitution. Amine substituents could be ranked as diethylaminopropylamine (DEAPA)<diethylaminoethylamine (DEAEA)<dimethylaminopropylamine (DMAPA) but the degree of amine substitution was more dominant than the type of amine function. Membrane interactions seem to cause necrotic cell reactions in a dose-dependent manner for highly charged amine-poly(vinyl alcohol) (PVA) backbones. To attenuate cytotoxic effects DEAPA-PVA backbones were grafted with biodegradable PLGA side chains at molecular ratios of 1:10 and 1:20. Cytotoxicity of extracts of these polymers was significantly lower compared to ungrafted polymers possibly caused by shielding of polycationic backbone with hydrophobic PLGA side chains. P(33)-20, a polymer containing a sufficiently high degree of amine substitution could serve as a lead candidate for further investigations. In conclusion, structure-toxicity relationships could be established and shielding the polycationic backbone using PLGA side chains seems to be a promising strategy meriting further investigations.

Animals↗

PubMed2004

Molar mass distribution of a commercial aliphatic hyperbranched polyester based on 2,2-bis(methylol)propionic acid.

The determination of absolute molar mass averages (MMA) and molar mass distribution (MMD) of the fourth generation hyperbranched polyester Boltorn H40 (Perstorp Specialty Chemicals AB), synthesized from 2,2-bis(methylol)propionic acid (bis-MPA) as the AB2 monomer and ethoxylated pentaerythritol as the B4 core molecule was studied in dependence on the type of solvent, preparation procedure and solution concentration. Due to a large number of polar hydroxyl groups, ester, and also some residual carboxyl groups, a very stable H-bond network is formed at room temperature, that can-not be completely disrupted by dissolving the sample in solvents such as tetrahydrofuran (THF), N,N-dimethylacetamide (DMAc), a mixture of THF and methanol (9:1, v/v), and a solution of 0.7% LiBr in DMAc. The H-bonds between the polar groups break down completely and the dissolution of Boltorn H40 on the molecular level is achieved only when the sample is thermally pretreated at a minimum 140 C for at least 20 min prior to dissolution in solvents THF/methanol or LiBr/DMAc. Thus, determined MMA and molar mass distribution (MMD) of Boltorn H40 are independent on the kind of the solvent and solution concentration.

Acetamides↗

PubMed2006

A new and effective tension-band braided polyester suture technique for transverse patellar fracture fixation.

OBJECTIVES: Concerning the tension-band principle of internal fixation, this study aims to establish whether any difference in interfragmentary gap exists after bone-reducing forceps are released, when a recommended suture-knot technique and a new technique are tested in vitro on a purpose built machine that features a model of a transverse fracture of the patella. In addition, a standard tension-band wiring technique has also been tested as one form of control. BACKGROUND: Satisfactory compression at a fracture site reduces the risk of failure of fixation, loss of reduction (interfragmentary gap >2mm) and subsequent risks of malunion, delayed union, and ultimately non-union from excessive movement. Stainless-steel wire can provide a stable rigid construct but is associated with complications. Tension-band fixation employing a braided polyester non-absorbable suture provides a less rigid construct. However, satisfactory clinical results and fewer complications are reported. The method by which a suture is tied has an effect on initial compression provided the fracture is reduced. However, it also has an effect on the degree of fracture gap once it is subject to biomechanical distraction. METHODS: By measuring the output of a strain gauge Wheatstone bridge of a purpose built rig that had been calibrated against fracture gap and compression force, the various tension-band fixation techniques as discussed above were evaluated. RESULTS: The tension-band suture technique examined in this work (the modified Wagoner's Hitch) has been evaluated. It has quantitatively shown less fracture gap than other recognised tension-band suture and wire techniques. The results exhibit statistical significance (p<0.001). CONCLUSIONS: This evaluation study has produced quantitative and comparable data of fracture gap as observed with the model of a transverse patella fracture, for both new and established surgical techniques. The contribution this study has made to the knowledge of the subject is that a testing device similar to the one in this study may be useful in the future for conducting preliminary studies of new or established tension-band techniques. The proposed tension-band suture method tested in this dissertation provided statistically significant quantitative data, which may after further work, support its use as an alternative method in the clinical setting.

Bone Wires↗

PubMed2004

Synthesis and surface properties of aqueous dispersions of poly(ester-imide) prepared from anhydride terminated polyester prepolymer and diisocyanate.

Aqueous dispersions of poly(ester-imide)s [P(E-I)s] have been prepared by dispersing the P(E-I)s in water without any external solubilizing agents. P(E-I)s were prepared from anhydride-terminated polyester prepolymer and diisocyanate. The -COOH groups in the polymer were then neutralized using triethylamine and the P(E-I)s were subsequently dispersed in water. The influence of the degree of ionization of polymers on the particle size and viscosity of the dispersion has been studied. The dispersions were crosslinked using polyaziridine. The crosslinked dispersion cast films were characterized for dynamic mechanical properties. As the ionic content increased the particle size decreased and the viscosity increased. When the amount of crosslinker added was varied, for a fixed percentage of ionization, the glass transition temperature Tg shifted to higher values. Critical surface tension (CST) measurements indicated reorganization of hydrophobic groups on the surface after crosslinking.

Cyanates↗

PubMed2006

Thrombogenicity and related biological properties of heparin bonded collagen coated polyester and human umbilical vein prosthetic vascular grafts.

BACKGROUND: Multiple factors contribute to the process of prosthetic graft failure. Some of them are specifically related to the biological behavior of the used materials. To pursue the ideal substitute for the autologous vein graft, many materials have been taken into consideration. Of these, polyester (Dacron) and human umbilical vein (HUV, Dardik) bypass grafts have gained much attention in vascular surgical practice over the years. This study compares the results of both in vivo and in vitro investigations on graft thrombogenicity and neo-intimal formation in collagen-coated heparin bonded Dacron and in HUV bypass grafts. It is an adjunct to our clinical comparison of graft materials in infrainguinal arterial reconstruction. METHODS: In 12 adult Beagle dogs, a patch was sewn onto the abdominal aorta (Dacron, n = 6; HUV, n = 6). At defined interval times, thrombocyte aggregation was measured with nuclear imaging of 99mTechnetium labeled platelets. Post-mortem histological analysis of the interface between the native vessel wall and the patch was performed in all animals. RESULTS: At 4 h (2.67, SD = 0.77) and after 2 weeks (2.21, SD = 0.28) after implantation, significantly higher thrombogenicity was measured in the HUV grafts compared to Dacron grafts (1.98, SD = 0.10 and 1.98, SD = 0.11, P = 0.02 and 0.025, respectively). At 4 weeks, no significant difference could be found (HUV, 2.26; SD = 0.29; Dacron, 2.11; SD = 0.16; P = 0.23). Measurement of 'neo-intimal' thickness after explantation of the patch at 28 days after the initial procedure showed a significant difference: in HUV grafts the mean thickness of the inner lining was 0.76 mm (SD = 0.50), compared to 0.16 mm (SD = 0.10) in the Dacron grafts (P = 0.013). CONCLUSION: HUV grafts showed a higher thrombogenicity at 4 h and 2 weeks after insertion of the graft compared to Dacron grafts. At 4 weeks this difference is not present. After 28 days the inner ('neo-intimal') lining is significantly more pronounced in HUV grafts than in Dacron grafts.

Animals↗