SEARCH · PubMed Health

Results for “Polyesters”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,657 records · Page 92Linked to original sources

PubMed1999

Prospective evaluation of the giant prosthetic reinforcement of the visceral sac for recurrent and complex bilateral inguinal hernias.

BACKGROUND: Recurrent and complex bilateral inguinal hernias are associated with a high recurrence rate. This study evaluates prospectively the efficacy and safety of giant prosthetic reinforcement of the visceral sac (GPRVS) in a group of patients at high risk for recurrence. METHODS: Sixty-four patients with 124 inguinal hernias (60 bilateral and 4 unilateral) underwent repair using a large polyester mesh based on Stoppa's preperitoneal technique. Mean age was 61 years (63 men and 1 woman), and 69% had one or more comorbid medical conditions. RESULTS: Factors predicating a high risk for recurrence included large hernia size (> or =5 cm; 31%, 20 of 64), failure of one or more previous repairs (39%, 25 of 64), and chronic obstructive pulmonary disease (28%, 18 of 64). Mean operative time was 115 minutes (range 45 to 235). Mean length of stay was 3+/-3 days. There were 2 major and 15 minor complications, no mesh infections, and no death. Follow-up was obtained in 95% (61 of 64). After a mean follow-up of 24 months, the recurrence rate was 1% (1 of 124) per inguinal hernia repaired or 2% (1 of 64) per patient. CONCLUSION: GPRVS is a safe and effective addition to the surgeon's armamentarium to treat selected patients with recurrent or complex bilateral inguinal hernias.

Comorbidity↗

PubMed2000

Passive epicardial containment prevents ventricular remodeling in heart failure.

BACKGROUND: We examined the effects of passive containment of the cardiac ventricles with a surgically placed epicardial prosthetic wrap on indexes of left ventricular (LV) remodeling in dogs with heart failure. METHODS: Heart failure (LV ejection fraction 30% to 40%) was produced in 12 dogs by intracoronary microembolization. Six dogs underwent mid-sternotomy and pericardiotomy with placement of a preformed-knitted polyester device (Acorn Cardiac Support Device [CSD], Acorn Cardiovascular, Inc, St. Paul, MN) snugly around the ventricles and anchored to the atrioventricular groove. Six dogs did not undergo surgery and served as controls. Dogs were followed for 3 months prior to sacrifice. RESULTS: In controls, LV end-diastolic volume increased after 3 months (67 +/- 12 versus 83 +/- 8 ml; p = 0.04), while in CSD-treated dogs, it decreased (68 +/- 10 versus 61 +/- 10 ml; p = 0.002). CSD-containment of LV size was associated with increased LV systolic fractional area of shortening, while in controls, fractional area of shortening decreased. CSD-treated dogs also showed amelioration of myocyte hypertrophy and attenuation of interstitial fibrosis compared to controls. CONCLUSIONS: In dogs with heart failure, passive epicardial containment of the ventricles with the Acorn CSD ameliorates LV remodeling and improves LV systolic function.

Animals↗

PubMed1979

Evaluation of a new cardiotomy blood filter.

A new cardiotomy blood filter with a polycarbonate body, a polyester prefilter, and a nylon screen with 20 mu pores was compared with four other commercially available filters. The Optigard filter was found to function as a "surface filter," which effectively removes blood particles larger than its nominal pore size.

Cardiopulmonary Bypass↗

PubMed1999

Iodine-impregnated drapes enable recording of precordial electrocardiogram.

Although we believed that the use of a polyester film drape for primary elective open sternum with delayed sternal closure made it impossible to record precordial electrocardiograms on the drape, we confirmed that it is possible to record electrocardiograms on an iodine-impregnated drape due to the iodine anion electrical conductibility.

Electric Conductivity↗

PubMed2002

Modeling the dynamic composition of engineered cartilage.

Mathematical models to describe extracellular matrix (ECM) deposition and scaffold degradation in cell-polymer constructs for the design of engineered cartilage were developed and validated. The ECM deposition model characterized a product-inhibition mechanism in the concentration of cartilage molecules, collagen and glycosaminoglycans (GAG). The scaffold degradation model used first-order kinetics to describe hydrolysis (not limited by diffusion) of biodegradable polyesters, polyglycolic acid and polylactic acid. Each model was fit to published accumulation and degradation data. As experimental validation, cell-polymer constructs (n=24) and unseeded scaffolds (n=24) were cultured in vitro. Biochemical assays for ECM content and measurements of scaffold mass were performed at 1, 2, 4, 6, 8, or 10 weeks (n=8 per time point). The models demonstrated a strong fit with published data and experimental results (R(2)=0.75 to 0.99) and predicted the temporal total construct mass with reasonable accuracy (30% RMS error). This approach can elucidate mechanisms governing accumulation/degradation and may be coupled with structure-function relationships to describe time-dependent changes in construct elastic properties.

Animals↗

PubMed2001

Macro-porosity is necessary for the reduction of neointimal and medial thickening by external stenting of porcine saphenous vein bypass grafts.

BACKGROUND: placing external non-restrictive macro-porous stents around porcine vein grafts prevents neointima formation and medial thickening in both the short and long term. Whether the porosity of the stent material influences this effect, however, has not been determined. Therefore, the effect on neointimal and medial thickening of external macro-porous (polyester) and micro-porous (polytetrafluorethylene) stents of equal diameter were compared. The effect on expression of platelet-derived growth factor (PDGF), a potent mediator of vascular smooth muscle cell migration and proliferation and its receptors was also investigated. METHODS AND RESULTS: saphenous vein-carotid artery interposition grafting was performed in Landrace pigs with external placement of 8 mm diameter macro- and micro-porous stents contralaterally. One month after surgery, graft wall dimensions, PDGF and PDGF receptor expression and cell proliferation using proliferating cell nuclear antigen (PCNA) were measured on histological sections. Macro-porous stents significantly reduced neointimal and medial thickening compared with micro-porous stents (0.1+/-0.02 vs. 0.25+/-0.03 mm, P<0.002, and 0.10+/-0.02 vs. 0.17+/-0.02 mm, P<0.014, respectively). Macro-porous stents significantly reduced the percentage of cells expressing PDGF and PCNA, compared with micro-porous stents (36+/-9 vs. 80+/-7, P < 0.002, and 11+/-3 vs. 21+/-2, P < 0.02, respectively). The percentage of cells expressing PDGF receptors was similar with both the stent types. Adventitial microvessel formation occurred across macro-porous stents but was markedly suppressed by micro-porous stents. CONCLUSIONS: porosity is crucial to the efficacy of external stents in reducing neointima formation in porcine vein grafts. Decreases in PDGF expression and cell proliferation accompany the reduction in neointima formation. In addition, macro-porous stents allow adventitial microvessels to connect with the vasculature outside the stent, thereby potentially improving oxygenation. Although external stenting is highly effective in reducing neointima formation after vein grafting, the properties of the stent material necessary for this effect have not been defined. This study establishes that macro-porosity is one essential feature required to reduce PDGF expression cell proliferation and neointima formation.

Animals↗

PubMed1983

Reduction of neonatal heat loss by an insulated head cover.

When exposed to a cool environment, the newborn infant responds by nonshivering thermogenesis. The increased heat production is at the expense of body fuel and energy stores. A significant quantity of heat is lost from the head because of its large surface area and the high metabolic activity of the neonatal brain. The purpose of this study was to determine whether dry cranial heat loss could be significantly reduced by covering the head with highly insulated material, and to determine whether plastic lined hats decreased evaporative heat loss. A total of 46 fullterm and premature infants were studied. Hats insulated with material made of olefin and polyester reduced cranial dry heat loss by 73% and 63%. Plastic lined hats reduced evaporative heat loss by 68%. The insulated and lined hats proved to be a simple and safe method of effectively reducing dry and evaporative heat loss.

Alkenes↗

PubMed1991

Afferent nipple valve malfunction caused by anchoring collar: an unexpected late complication of the Kock continent ileal reservoir.

In the construction of a Kock continent ileal reservoir for urinary diversion, significantly high rates of late postoperative complications regarding nipple valves, the efferent limb in particular, have been reported. There are only a few reports on afferent nipple valve malfunction. A total of 42 patients who underwent a Kock pouch operation and were observed for more than 12 months (mean 38 months) was evaluated in terms of afferent nipple valve malfunction. Late afferent nipple valve complications were observed in 10 of the 42 patients (24%). These complications included erosion of the polyester fiber fabric used as a collar (5 patients), stenosis of the afferent limb (2) and obstruction of the afferent nipple by a mucous plug or fungus ball (3). The latter 2 complications were due to mechanical or dynamic obstruction of urine flow caused by a nonabsorbable collar. None of the 10 patients had problems with efferent nipple valve function. Our results suggest that the peristaltic direction of the intestine and the use of nonabsorbable material as a collar are primarily responsible for the late afferent nipple valve complications. Further modifications are needed to produce a stable nipple valve. Otherwise, simpler and more reliable alternative techniques of antireflux anastomosis should be considered.

Adult↗

PubMed2001

Polymers and surfactants on the basis of renewable resources.

A new strategy for the preparation of different polymers and special surfactants was developed. First, unsaturated fatty acid methyl esters obtained from plant oils were converted to terminally unsaturated esters and alpha-olefins by metathesis with ethylene using heterogeneous rhenium or homogeneous ruthenium catalysts. These esters were directly copolymerized with ethylene by an insertion-type palladium-catalyzed polymerization to functionalized polyolefins. Polyesters were synthesized by metathetical dimerization of omega-unsaturated esters and subsequent polycondensation of the produced internally unsaturated dicarboxylic esters or by acidic transesterification with petrochemical diols and additional acyclic diene metathesis polymerization. Omega-epoxy fatty acid methyl esters, achieved by a new method of chemo-enzymatic epoxidation, were converted into polyethers with comb-structure catalyzed by aluminoxanes on the one hand and into sugar surfactants by nucleophilic ring-opening with amino carbohydrates on the other hand.

Carbohydrate Metabolism↗

PubMed1997

Biodegradation of sucrose poly fatty acid esters in soils.

Sucrose polyesters (SPEs) were applied to soil at rates equivalent to 1062 to 1293 kg per hectare and incubated over periods of 100 to 403 days at 20 +/- 2 degrees C in darkness and at a soil moisture of 40% of the maximum water holding capacity. All applied forms of SPEs were aerobically biodegraded to some degree in both American and German soil. However, the mineralization rates varied considerably and were dependent on both SPE and soil type. For example, sucrose octaoleate underwent slow and limited mineralization in the German soils Speyer and Borstel as well as in the American soil Madera, reaching only 6.9-18.4% mineralisation after over 400 days incubation. The same material in the American soils Hollande, Thermal and Uvalde as well as in the German soil Speicherkoog, reached 35-52% after the same incubation period. Of the SPEs most realistic for use in food products, the more liquid (i.e. with the least saturated fatty acids) underwent the most rapid and extensive mineralization. However, the mineralization rates for these materials were distinctly lower than the corresponding ones for sucrose octaoleate. In all cases the extent of mineralization of the SPEs in soil was significantly lower than that of a control fat (synthetic triglyceride mixture HB307), which typically underwent over 50% mineralization in 60 days.

Bacteria, Aerobic↗

PubMed1992

Biosynthesis of poly(3-hydroxyalkanoate) from amino acids.

It was found that an optically active copolyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), denoted as P(3HB-co-3HV), is synthesized by Alcaligenes eutrophus H16 from several amino acids under various fermentation conditions. The optimum condition for the biosynthesis from one amino acid, threonine, was investigated and its biosynthetic pathway was discussed on the basis of the relation between the fermentation condition and the co-monomer composition of the produced polyesters.

Alcaligenes↗

PubMedDate not supplied

Lamellar thickening and cocrystallization of poly(hydroxyalkanoate)s on annealing.

Lamellar thickening behavior of microbial polyesters, poly(3-hydroxybutyrate) [P(3HB)], poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] annealed at various temperatures was investigated to make sure of the occurrence of cocrystallization of both components. All the copolymers showed steep increases in melting points accompanied by partial melting as the annealing temperature increased up to just below the melting points. In contrast, long periods of P(3HB-co-7mol% 3HV) increased to twice, similar to those of P(3HB), with increasing annealing temperature up to just below the melting point, while long periods of P(3HB-co-7mol% 4HB) and P(3HB-co-92mol% 3HV) only increased up to one and a half times. Lattice indices of unit cell of the former crystal were increased slightly, while those of the latter crystal remained unchanged. These results imply that the P(3HB) crystal can occlude the 3HV component to some extent, but hardly includes the 4HB component, and P(3HV) crystal also excludes the 3HB component.

Calorimetry, Differential Scanning↗

PubMedDate not supplied

Synthetic poly(beta-hydroxyalkanoates) with carboxylic acid or primary amine pendent groups and their complexes.

Degradable polyelectrolyte complexes were made by mixing a degradable carboxyl-bearing polyacid, namely poly(beta-malic acid), with a degradable primary amine group-bearing polybase, namely poly(amino serinate), derived from serine. Both oppositely charged polyelectrolytes are functional polymers which belong to the family of poly(beta-hydroxy acid)-type aliphatic polyesters. Poly(amino serinate) polymers were synthesized by a new route starting from the N-carbobenzoxy derivative (N-Z) of DL- or L-serine. These derivatives were allowed to react with mesyl chloride to yield in one step corresponding N-protected derivatives of poly(N-Z-amino serinate) with molar masses in the 20000-40000 range after fractionation. Progressive deprotection of pendent primary amino groups was carried out using a HBr/acetic acid mixture and led to PAS with up to 95% deprotected amine repeat units for less than 15% decrease of the initial molar mass, as shown by N-reprotection with Z groups. Poly(beta-malic acid) and poly(amino serinate) were complexed by mixing aqueous solutions of the two polyelectrolytes: 1-1 neutral precipitates were formed regardless of the respective compositions, provided the molecular weights of both components were high enough. When allowed to age in aqueous media, the solid complexes went rapidly back into solution because of the hydrolytic degradation of at least one of the components. Whether the degradation of one component is affected by that of the other is still unknown.

Amines↗

PubMed2000

Bioabsorbable fixation in orthopaedic surgery and traumatology.

Bioabsorbable internal fixation devices were introduced clinically in the treatment of fractures and osteotomies of the extremities at the Department of Orthopaedics and Traumatology, Helsinki University, in 1984. Since November 5, 1984, a total of 3200 patients were managed using bone or ligament fixation devices made of self-reinforced (matrix and fibres of the same polymer) bioabsorbable alpha-hydroxy polyesters. The devices used included cylindrical rods, screws, tacks, plugs, arrows, and wires. The most common indication for the use of bioabsorbable implants was the displaced malleolar fracture of the ankle. Transphyseal fixation with small-diameter, mainly polyglycolide pins was used in children. The postoperative clinical course was uneventful in more than 90% of the patients. The complications included bacterial wound infection in 4% and failure of fixation in 4%. In one-fifth of the latter cases, however, re-operation was not necessary. The occurrence of non-infectious foreign-body reactions two to three months postoperatively has been observed in 2% of the patients operated in the last few years with polyglycolide implants but none of the patients managed with polylactide implants. This inflammatory tissue response often required aspiration with a needle but did not influence the functional or radiologic result of the treatment. Owing to the biodegradability of these internal fixation devices, implant removal procedures were avoided. This results in financial benefits and psychological advantages. Bioabsorbable implants can also be used in open fractures and infection operations.

Absorbable Implants↗

PubMed2003

Surface properties of and cell adhesion onto allylamine-plasma-coated polyethylenterephtalat membranes.

Allylamine was plasma polymerised onto a polyester (PET) membrane to obtain a surface with good cell adhesive properties. Samples were coated using a microwave plasma source operating at different process parameters. The effect of process parameters on the physical, and chemical properties of plasma-polymerised-allylamine (PPAa) was evaluated by studying elemental composition, amine concentration, wettability, and surface morphology. A relatively high amine concentration was measured (up to 50 nmol/cm2). In parallel, nitrogen enrichment was observed after exposure to high-energetic plasma. Irrespective of the treatment conditions, oxygen was incorporated into the polymer structure. PPAa surfaces were found to be more hydrophilic than PET. The wettability of the samples increased with increasing amine concentration. Pictures from scanning electron microscopy indicated that homogeneous pinhole-free PPAa layers were deposited on PET membranes, without a significant change of permeability. In vitro evaluation of biocompatibility was carried out by studying human skin fibroblast interaction with surfaces. Cell attachment and viability on PPAa layers were found to be more intensive than on the control PET, based on the higher metabolic activity of adhering cells, but also on morphological criteria including overall cell morphology.

Allylamine↗

PubMed2003

Reduced mouse fibroblast cell growth by increased hydrophilicity of microbial polyhydroxyalkanoates via hyaluronan coating.

The mouse fibroblast cell line L929 was inoculated on 3D scaffolds of microbial polyesters, namely polyhydroxybutyrate (PHB) and poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) to evaluate their in vitro biocompatibility. It was found that both polyhydroxyalkanoates (PHA) subjected to lipase treatment and hyaluronan (HA) coating decreased the contact angle of water to the material surface approximately 30%, meaning an increased hydrophilicity on the PHA surface. At the same time, both the lipase treatment and the HA coating smoothened the PHA surface. After the lipase treatment or HA coating, the ratio of PHA hydrophilic groups including hydroxyl and carboxyl to carbonyl of PHA was approximately 1:1 or 2:1. Cells grown on scaffolds treated with lipase were approximately 4 x 10(5)/ml, twice in number of the control. However, PHA scaffolds coated with HA were observed with a 40% decrease in cell growth compared with that of the control. HA coating reduced the cell attachment and proliferation on PHA although the materials had increased hydrophilicity. In comparison, lipase treatment promoted the cell growth on PHA although the treatment did not lead to better hydrophilicity compared with HA coating. It appeared that an appropriate combination of hydrophilicity and hydrophobicity was important for the biocompatibility of PHBHHx, especially for the growth of L929 cells on the surface of this material. This may have instructive significance for biomaterial selection and design.

Animals↗

PubMed2004

Novel micro-crosslinked poly(organophosphazenes) with improved mechanical properties and controllable degradation rate as potential biodegradable matrix.

As biodegradable materials, linear polyphosphazenes undergo rapid hydrolysis degradation but exhibit poor mechanical properties. Blending with biodegradable polyesters or inorganic particles strengthen their mechanical properties but give rise to slower degradation rate. To balance the mechanical properties and the degradation rate, micro-crosslinked polyphosphazenes were synthesized in this study. Their glass transition temperatures, mechanical properties, and in vitro degradation behavior were investigated. 2-hydroxyethyl methacrylate (HEMA) was firstly attached to the side chain along with glycine ethyl ester to prepare co-substituted poly(organophosphazene) with pendant ethenyl substituents. The co-substituted poly(organophosphazene) was blended with HEMA or acrylic acid (AA) followed by a free radical polymerization to prepare micro-crosslinked poly(organophosphazenes). The resulting crosslinked polymers showed two separate glass transition temperatures depending on the HEMA or AA feed. Incorporation of crosslinking affected the mechanical properties positively. Crosslinked poly(organophosphazenes) showed an approximately 11-17 fold increase in terms of modulus of elasticity when compared to the linear counterpart. In vitro degradation tests indicated that HEMA-crosslinked polymers hydrolyzed at a retarded rate while AA-crosslinked polymers hydrolyzed at a moderate rate compared to linear polymers.

Biocompatible Materials↗

PubMed1997

Nanotechnology for biomaterials engineering: structural characterization of amphiphilic polymeric nanoparticles by 1H NMR spectroscopy.

Nanoparticles composed of diblock poly(D,L-lactide-co-glycolide)-poly(ethylene glycol) (PLGA-PEG) or a branched, multiblock PLA-(PEG)3 were prepared by the single emulsion technique. Results of previous studies of these nanoparticles suggested that their structure is of the core-corona type with a polyester core and an outer PEG coating. In the present study, 1H NMR spectroscopy was utilized to provide direct evidence of the structure of these nanoparticles suspended in an aqueous environment. The results confirm the existence of the core-corona structure under these conditions, and show that the PEG moieties extend out from the nanoparticle core into the aqueous environment, and exhibit chain mobility similar to that of PEG in solution.

Biocompatible Materials↗