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At least 1,153 records · Page 64Linked to original sources

PubMed1984

The influence of environmental aging upon the loadbearing properties of polyurethane foams.

The effects of environmental exposure upon the loadbearing properties of nine polyurethane foams commonly used for wheelchair cushion construction were studied. Test pieces with and without a stretch cloth cover were aged in the open air at Houston over the period April 26 to October 31, 1982. The indentation resistance of each piece was measured initially and at frequent intervals during the exposure period. Resistance changes between covered and uncovered specimens were not found to be significant. All foams displayed a sharp rise in indentation resistance within the first 2 weeks of aging followed by a gradual decrease to an average 68 percent of the initial value over a 6-month period. These hardness changes were found to be strongly correlated with the density, thickness, and initial indentation resistance of the test pieces. Foams of maximum density and minimum practicable indentation resistance are recommended for wheelchair cushion construction to minimize the adverse effects of environmental aging upon the support properties of these devices.

Environmental Exposure↗

PubMedDate not supplied

A fibrous polyurethane microvascular prosthesis. Morphological evaluation of the neo-intima.

A fibrous polyurethane microvascular prosthesis with an inner diameter of 1.5 mm was implanted to replace the rat aorta between the left renal artery and the bifurcation of the aorta. Twenty-four implantations, using three different lengths (0.5; 1; 1.5 cm), were carried out. Rats were sacrificed 3, 6, 9 and 12 weeks after implantation. Only 1 prosthesis was occluded (probably due to a technical error). Grafts were already lined with a neo-intima by the third week, irrespective of their length. Different shapes of endothelial cells were recognized. It appeared that cells arise and migrate from the aortic stumps into the prosthesis, since the neo-intima is thicker in the anastomotic area than in the middle of the graft. The well-defined neo-intima consisted of several layers of smooth muscle cells embedded in a glycoprotein matrix and covered by a very flat continuous endothelium. The structure of the prosthesis allowed anchoring of the lining cells. Migration of cells through the wall of the prosthesis was not observed. At those places in the prosthesis where fibres had fused together to form flat areas the neo-intima became torn by the contraction of the myofibroblasts. This was because the cells had evidently failed to become anchored to the prosthetic wall. The neo-intima retained the ability of immediate repair of small defects which develop occasionally on the non-fibrous areas of the luminal surface of the prosthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

The endothelialization process of a fibrous polyurethane microvascular prosthesis after implantation in the abdominal aorta of the rat. A scanning electron microscopic study.

The endothelialization process of a fibrous microvascular polyurethane prosthesis (inner diameter 1.6 mm) was studied by scanning electron microscopy. Forty-seven prostheses (1 cm) were implanted into the abdominal aorta of rats between the left renal artery and the bifurcation. Specimens were taken on day 1, 3, 5, 7, 10, 14, 18, 21 and 25, as well as 6 and 9 months after implantation, to evaluate immediate and delayed response and complications. The patency rate of the implants was 91.2%. After an initial recovery period of five days, endothelial cells started to migrate onto the inner surface of the prosthesis with a velocity of approximately 0.3 mm per day, resulting in a completely endothelialized prosthesis at day 21. A smooth continuous inner lining was achieved. A difference in growth pattern between the proximal and distal growth zone was observed, and may be attributed to the direction of the blood flow through the prosthesis. The endothelial cells advanced in a close arrangement. No cells were seen to settle and grow in between the two growth zones on the fibrin layer. If no immediate complications occur, the endothelialization process (21 days) proceeds uneventfully and no late complications are observed. Though it may be argued that the new cells lack some authentic endothelial features, this study indicates that they are at least of endothelial orgin, and behave morphologically like endothelial cells. It can be concluded that the adequate texture of the prosthesis and the cell anchoring, in combination with both an optimal surgical performance and blood flow, ensure that the microvascular prostheses are rapidly endothelialized and retain high patency rates over long periods of time.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

Reduced thrombogenic characteristics of expanded polytetrafluoroethylene and polyurethane arterial grafts after heparin bonding.

The effect of bonding of heparin, via a glutaraldehyde-stabilized ionic complex, on the early thrombogenicity of polyurethane (PU) and expanded polytetrafluoroethylene (PTFE) (Gore-tex) as well as covalent bonding of heparin on PTFE was studied in vivo. Grafts 6 cm long and 4 mm in diameter were placed in the carotid arteries of sheep and perfused for 4 hours at 25 ml/min in order to accelerate thrombus formation. The thrombogenicity was determined by calculation of the percent of the luminal surface free of thrombus and patency. In addition, 32P-labelled platelet accumulation was determined in some of the grafts. The stabilized ionic bonding of heparin significantly reduced the early thrombogenicity of PU but had little effect on PTFE grafts; but the thrombogenicity of the latter was markedly decreased following covalent bonding of heparin. A regional distribution of platelet accumulation was found with the distal anastomoses showing the highest platelet deposition. By choice of an appropriate method of heparinization, a significant reduction of the thrombogenicity of PU and PTFE grafts was achieved.

Animals↗

PubMed1980

[Short-term study of a new kind of polyurethane-based fixative (Bayer) on monkeys and pigs].

A new kind of material for cementing dental castings, on polyurethan basis was experimentally tested on a monkey and on a pig and compared at short range (7 days) according to "Recommended standard practices for biological evaluation of dental materials" (ADA, 1975). Dentin and pulp compatibility was investigated, using a phosphate cement (Duraphos) for comparison. The results showed no difference in biocompatibility between the two materials nor between the endodontic tissue of the species.

Animals↗

PubMed1983

Surgical wound management with adhesive polyurethane membrane: a preferred method for routine usage.

The author gives an account of his experience of the use in some 1600 patients of adhesive polyurethane membrane, marketed as Op-site, both for skin closure and wound dressing, in combination, as a routine method of surgical wound management in a wide variety of surgical operations. The technique of utilising this method is described in detail, as also are the advantages for patients, nursing and medical staff.

Adhesives↗

PubMedDate not supplied

[Acid phosphatase activity in rabbit kidneys after implantation of different polyurethanes].

Activity of acid phosphatase was determined in rabbit kidneys under subcapsular implantation of polyester-based polyurethane films (A-10) and films (D-1) containing the links of L-phenylalanyl-L-serine dipeptide in the main chain of the polymer. Optimal conditions are chosen for detecting activity of this enzyme in homogenates and in the lysosome enriched fraction of rabbit kidneys with L-glycerophosphate used as a substrate. Activity of acid phosphatase under the A-10 specimen implantation increases on the 7th and 14th day and later (during a year) does not differ from the normal level. Under the D-1 spectrum implantation the acid phosphatase activity remains increased for a longer period--up to one month. It is possibly due to the fact, that this polymer contains dipeptide fragments and is subjected to a more intensive enzymic destruction than the A-10 specimen.

Acid Phosphatase↗

PubMed1978

Effect of polyurethane morphology on blood coagulation.

A series of polyurethanes based on the hard segment MDI and soft segment PTMG were synthesized. The molecular weight of the PTMG was 730, 1000, and 2000, and ethylene diamine was used as chain extender. The fabrication process was varied so as to achieve the maximum disorder (nonequilibrium state) and maximum order, fully annealed. It was demostrated that the "quenched" non-equilibrium state reduces the rate of activation of the intrinsic systems, factor XII pathway, when compared to the fully annealed state. Platelet attachment is primarily affected by phase separation.

Blood Coagulation↗

PubMed1982

[Occupational exposure of workers to vapors of p,p'-diphenylmethane diisocyanate used in the production of building materials filled with polyurethane foam].

The building elements filled with polyurethane foam produced in Poland are called "Obornicka plate". The authors investigated the concentrations of p, p-diisocyanodiphenylmethane (MDI) vapours at workplaces and found considerably excessed TLV values. This would call for a prompt introduction of technological prophylaxis in the production of "Obornicka plate".

Air Pollutants↗

PubMed1982

Platelet-compatible hydrophilic segmented polyurethanes from polyethylene glycols and cyclohexane diisocyanate.

A new type of segmented polyurethane (SPU) was synthesized from alpha, omega polyethylene oxide diols (PEG) of MW varying from 600 to 4500, by end capping with 1,4 trans cyclohexane diisocyanate (CHDI) and chain extending with ethylene diamine (ED) in toluene with dibutyl tin dilaurate as catalyst. These SPU are cast as films and coatings from hexafluroisopropanol (HFIP). Depending on PEG MW, these SPU swell two- to tenfold in water. Examined by an in vitro platelet retention test, these SPU are more bland (platelet retention -rho around 0.05) than most other polymers, whereas an alternating copolymer of CHDI and ED shows -rho around 0.80 (very active); x-ray photoelectron spectroscopy shows that the surfaces of these SPU to a depth of about 40 Ao are nearly pure PEO, unlike SPU synthesized from aromatic diisocyanates TDI and MDI.

Biocompatible Materials↗

PubMedDate not supplied

Inhalation studies with polyurethane foam dust in relation to respiratory tract carcinogenesis.

Male and female Sprague-Dawley rats were exposed to freshly generated polyurethane foam dusts, in concentrations averaging 8.65 mg/m3 air, for 6 hours daily 5 days a week over a period of 12 weeks. For comparison the same numbers of rats were exposed to titanium dioxide (TiO2) (15.95 mg/m3 air), which is a known inert dust, and to air alone, as controls for the same exposure period. This exposure caused no noticeable changes in appearance, behavior, or body weight. The average lifespan values were within the normal range. A high tumor rate was seen in all groups, with no significant differences among the groups. No indications of a carcinogenic effect of the inhaled dusts on the respiratory tract could be established. The numerous tumors found in the different organs and groups were of a spontaneous nature. The observed lung-reactions are discussed.

Animals↗

PubMed1994

[Experience of a double Malecot polyurethane intraurethral catheter in patients with dysuria].

We reviewed our experience of using double Malecot polyurethane intraurethral catheters (IUC). Ten patients with dysuria were treated between April 1991 and April 1993. Seven patients with benign prostatic hypertrophy (BPH) were judged as in a high risk group for operation. The three other patients had neurogenic bladder (two had underactive bladder and 1 had overactive bladder). Under local anesthesia, 150 ml of 0.1% Povidone iodine solution was infused into the bladder through a Nelaton catheter. Under guidance by ultrasonography, an IUC was placed into the bladder neck and posterior urethra using the specially designed introduction set. An long-term follow up of the BPH patients, two IUCs were removed for operation and one was exchanged for an indwelling catheter because of deterioration in general condition. In the neurogenic bladder patients, all IUC were removed because of the increase of residual urine, formation of a pseudourethra, or dislocation into the bladder. Side effects were observed in 6 patients such as, urethral bleeding and stone formation in the stent. Erosion and bleeding tendency in the urethral mucosa were shown in the prolonged duration cases. We conclude that a urethral stent is an effective devise for a high risk patient with benign prostatic hypertrophy but we must keep each patient under strict observation for complications during IUC placement.

Aged↗

PubMed1993

[Experience with polyurethane intraurethral stents in aged patients].

A double Malecot-like 16F, polyurethane intraurethral catheter (IUC) was inserted 39 times in 25 patients between 68 and 91 years old (mean +/- SD: 77.5 +/- 5.5 years). Most of them were unfit for surgery because of severe illness or advanced age. All patients except 1 had either an indwelling catheter or a residual urine volume > 50ml at their first visit. The remaining one suffered from prostatic cancer and complained of pollakisuria and urinary incontinence. His symptoms were controlled well after ICU insertion and anticholinergic therapy. Twenty-nine insertions in 17 patients were considered successful, and the patients with successfully inserted stents voided without residual urine. Nine of 21 patients needed to take anticholinergic drugs. The mean duration of IUC use was 113 days in successful cases. In 9 out of 17 patients with an indwelling IUC for more than 112 days, the catheter became blocked by stones or clots. Therefore, we consider that the device should be changed after 110-120 days. Ten insertions failed for the following reasons: malposition, inappropriate IUC length, spontaneous migration to the bladder in patients with a short prostatic urethra, urinary retention due to underactive detrusor, and total incontinence and bleeding from prostatic cancer.

Aged↗

PubMedDate not supplied

Polyurethane and silicone: myths and misconceptions.

Silicone elastomer has been the standard by which other catheter materials have been judged. In the past ten years, technical advances in polymer research have provided the medical manufacturer with a wide variety of new materials for catheter manufacture. Thermoplastic polyurethane has shown great promise as an alternative to silicone for vascular catheters. This article examines the basic properties of the two materials and describes the findings in the literature that show comparable biocompatibility properties for both materials.

Catheters, Indwelling↗

PubMedDate not supplied

Work place challenge: spirometric response in polyurethane (isocyanate) paint workers.

In industrialised countries, isocyanate is probably the most common cause of occupational asthma. The present study was conducted to see the effect on FEV1 in workers who were directly exposed to isocyanate. One hundred and fourteen workers of a rail coach factory who were involved in polyurethane paint spray were studied. Spirometry was done three times, first before starting the work, at two hours and then 6-8 hours after finishing the work to see immediate, late and dual responses. Positive response was considered when there was fall of 20% or more in forced expiratory volume in 1 second (FEV1) from base line. Sixteen per cent of the workers exposed to isocyanate developed immediate reaction, 10% developed late reaction and 6% developed dual reaction. Non-smokers were more prone to develop late and dual responses.

Adolescent↗

PubMedDate not supplied

Cuffed polyurethane catheter for ambulatory infusional chemotherapy.

This article describes the technique for inserting cuffed polyurethane catheters under local anaesthesia. A very low complication rate is seen with these catheters and patients tolerate the catheters and Cadd infusional pumps for continuous chemotherapy very well.

Ambulatory Care↗

PubMed1994

A new three-dimensional culture system for hepatocytes using reticulated polyurethane.

Poly-N-para-vinylbenzyl-lactonamide (PVLA)-coated reticulated polyurethane (PVLA-RPU) has been employed for the long-term maintenance of primary rat hepatocyte cultures. After 3 days of incubation of 2 x 10(7) hepatocytes/cm3 embedded in PVLA-RPU discs and kept in culture medium, most cells showed typical hepatocyte morphology, with some bile canaliculus-like intercellular spaces among the hepatocytes on examination with scanning and transmission electron microscopy. The cells were attached to the surface of the PVLA-RPU and formed multicellular spheroids in the reticulated pores. The hepatocytes maintained various liver-specific functions such as albumin secretion, ammonium metabolism, urea synthesis and gluconeogenesis, and they were viable. The liver-specific functions could be maintained for more than 1 month when the cells were kept in the rats' peritoneal cavities. This new system may be useful as a bioreactor for an artificial liver.

Albumins↗

PubMedDate not supplied

Development of a hybrid artificial pancreas with a dense polyurethane membrane.

We have synthesized a series of strong, elastomeric polyurethaneureas and have used them to fabricate non-porous film and hollow fiber membranes. The solvent cast membranes are non cytotoxic, angiogenic, and permeable to gases, nutrients, secretagogues, and cell products via purely concentration driven transport. Permeability to water, glucose, and protein increases monotonically with membrane water absorption above a threshold value. Water absorption increases with soft segment hydrophilicity, soft segment molecular weight, and soft segment volume fraction of the (dry) segmented polyurethanes. Cell lines (RAJI and MOPC-31C) and primary cells (porcine islets) contained within our membranes have been maintained in culture for up to 6 months with nutrients supplied only by the external media. Cells within membrane devices were protected from immune rejection when implanted into murine hosts. Simple, compact devices containing porcine islets restored normoglycemia and near normal response to glucose tolerance tests in diabetic mice for at least 2 months. Explants had a high degree of vascularization adjacent to the membrane, with little or no fibrous tissue. These properties, and the material's ability to support cell function and protect xenogeneic cells from immunologic rejection, suggest that it would be useful in the construction of hybrid artificial organs and in in vitro cell culture.

Animals↗