Biomedical subjects

R S Labow

Publications and source records attributed to R S Labow.

At least 37 records · Page 2Linked to original sources

PubMed1998

Differential synthesis of cholesterol esterase by monocyte-derived macrophages cultured on poly(ether or ester)-based poly(urethane)s.

Monocytes adherent to implanted biomaterials differentiate into macrophages while synthesizing large amounts of degradative enzymes, including cholesterol esterase (CE), which previously has been shown to degrade poly(urethane)s. Human peripheral blood monocytes were cultured on tissue culture grade polystyrene (PS), and two model poly(urethane)s were synthesized from (1) polycaprolactone (PCL) and (2) polytetramethylene oxide (PTMO), both with 2,4-toluene diisocyanate (TDI) and ethylene diamine (ED). The increase in CE and total protein per cell were measured on days 8 and 28 in culture and normalized to the DNA content per cell. At day 8 there consistently were fewer cells remaining on the PTMO-based polymer than on the PCL-based polymer or the PS (p < 0.05). When comparing day 28 to day 8, there was more CE activity and protein per cell on all materials. However, there was a disproportionate synthesis of CE per mg of total protein on PS and TDI/PCL/ED whereas on PTMO there was not. Significantly, there was more protein and CE per cell on PTMO than on PS or TDI/PCL/ED (p < 0.05). This in vitro model system of the chronic phase of inflammation has shown that it is possible to culture monocytes for a month and assess the material surface itself as a potent activator of the differentiation into macrophages without secondary stimulation. Since CE has been shown to degrade poly(ether and ester)-based poly(urethane)s, the differential production of this enzyme relative to the total protein on different surfaces may impact on the potential long-term biostability of an implanted material.

Biocompatible Materials↗

PubMed1998

The importance of sampling site in the measurement of whole-blood platelet flow cytometry.

PURPOSE: Flow cytometry is an emerging technology that may be of use in clarifying the defects of platelet function after cardiopulmonary bypass. However, the technique used for platelet sampling may affect results. The objective of this study was to evaluate the influence of the sampling site on the degree of expression of a variety of platelet-associated proteins. METHODS: Whole-blood flow cytometric assays for the detection of platelet glycoprotein (GP) Ib, guanosine monophosphate (GMP)-140, thrombospondin, activated GPIIb/IIIa, and platelet-associated factor (FXIIIa) were developed. These markers were then measured in samples taken simultaneously from a peripheral vein, radial artery, and the side port of the central venous catheter, in eight patients about to undergo surgery. RESULTS: When multiple samples from individual patients were assessed, the degree of activation with all of the activation assays (GMP-140, thrombospondin, activated GPIIb/IIIa, FXIIIa) was significantly greater in samples taken from the arterial catheter (p < 0.05) compared with the central venous catheter or the peripheral vein. The mean difference between sample sites was calculated in the study patients. Percent activation of FXIIIa from arterial blood was significantly greater than from the central vein and the peripheral vein (arterial-peripheral venous, 18.7 +/- 8.6; central venous-peripheral venous, 3.7 +/- 3.6; p = 0.005). There was no site-related difference in detected expression of platelet GPIb. CONCLUSION: The site of platelet sampling significantly affects the degree of activation detected by flow cytometry. To approximate results that would be obtained from peripheral blood, samples should be taken from the side port of the central venous catheter and not from the arterial catheter in patients studied during surgery.

Adult↗

PubMed1998

The effect of oxytocin on the contractile force of human atrial trabeculae.

UNLABELLED: We performed an in vitro examination of the inotropic effect of oxytocin, chlorobutanol, and their combination to assess the effect of these drugs on the contractile force of human atrial trabeculae. Right atrial tissue samples were obtained during cardiac surgery with cardiopulmonary bypass. Trabeculae of the atrial appendage were dissected and mounted on muscle stands in a modified Krebs-Henseleit buffer bath. This isometric atrial trabecula preparation was subjected to a cumulative pharmacological protocol of either pure oxytocin, pure chlorobutanol, or a combination of the two drugs until no further change occurred in either developed force or resting force of the atrial trabeculae. A "no drug" buffer solution was used to assess the effect of time on the natural decay of the atrial preparation. The relative developed force of oxytocin plus chlorobutanol solution and pure chlorobutanol were similar in magnitude and lower than that in control experiments (P < 0.001) Pure oxytocin did not change the contractile force of atrial tissue. We conclude that pure oxytocin does not have a cardiodepressive effect in this human atrial preparation. Chlorobutanol has a negative inotropic effect, which is of a magnitude similar to a combined solution of chlorobutanol and oxytocin. Therefore, chlorobutanol added as a preservative to the commercial synthetic oxytocin solution may contribute to hypotension observed in patients after an intravenous bolus injection. IMPLICATIONS: We obtained specimens of heart tissue from patients undergoing cardiac surgery and conducted a laboratory study of the effects of oxytocin and its preservative (chlorobutanol) on these tissue samples. Chlorobutanol decreased the ability of the heart to contract, while as pure oxytocin had no effect. This explains why maternal blood pressure may decrease and provides impetus to produce oxytocin with another, safer preservative.

Adult↗

PubMed1998

Papaverine solutions cause loss of viability of endothelial cells.

OBJECTIVE: The optimal composition of the solution used for irrigation of saphenous veins used for cardiac surgery may influence ultimate graft patency due to potential injurious effects on the vein endothelium of some of the solution constituents. EXPERIMENTAL DESIGN: The viability of cultured saphenous vein endothelial cells was assessed after incubation of saphenous vein endothelial cells with solutions containing saline, saline with papaverine (0.15 M NaCl, 32.5 mg/mL papaverine), culture medium and buffered saline solution (Plasma-Lyte-A). RESULTS: Cell viability was significantly decreased after one hour incubation with solutions containing saline with papaverine (24.4+/-9.4%) as compared to culture medium and buffered saline solutions (medium 100%, Plasma-Lyte-A 86.8+/-6.90%). Loss of viability was directly related to the length of exposure of the cultured cells to papaverine. Morphologic changes of cells incubated with saline: papaverine were also seen including cell retraction and nuclear pyknosis. The cells exposed to medium recovered 100% viability whereas by 4 hours only 22% of the saline: papaverine cells were viable, and by 3 days this viability had fallen to 7.7%. CONCLUSIONS: Loss of viability was shown in cultured saphenous vein endothelial cells exposed to saline solutions containing papaverine, whereas no difference was found between culture medium, saline and balanced salt solutions. Cell death was directly related to the length of exposure of the cells to papaverine. Further, after short- and long-term recovery periods, there was little recovery of cell viability. Although papaverine is a potent vasodilator, exposure to this compound may compromise long-term viability of graft endothelial cells.

Cell Death↗

PubMed1997

High-performance liquid chromatographic separation and tandem mass spectrometric identification of breakdown products associated with the biological hydrolysis of a biomedical polyurethane.

As part of ongoing investigations into the biological degradation of biomaterials, methods have been developed to isolate and chemically analyze polymer biodegradation products. The use of these methods can provide information on the biodegradation product profiles and yield concentration levels for the isolated products. The latter information is required to assess the toxicological nature of biomaterials and their related degradation products. In this study a model biomedical polyurethane was synthesized with toluene diisocyanate, polyester diol and ethylene diamine, and then incubated at 37 degrees C in a biological solution containing enzyme. The biodegradation products were isolated from the in vitro system and prepared for HPLC analysis, by using a combination of ultrafiltration, freeze drying and liquid-solid extraction. The ultrafiltration and the liquid-solid extraction effectively removed protein contamination. The separation of more than 20 degradation products, with gradient HPLC, was optimized using a photodiode array detector. The separated degradation products were identified using a tandem mass spectrometer. The model polyurethane was labeled with 14C in different segments, in order to assist in confirming the efficiency of the sample preparation and isolation methods. A detection limit of 2 ng was found. No toluene diamine - a suspected human carcinogen associated with some medical implants - could be found in the test samples. This represents a significant finding since the amount of this injected sample actually contained a total of 28 microg of degradation products isolated from the incubation medium.

Biocompatible Materials↗

PubMed1997

Biodegradation of a poly(ester)urea-urethane by cholesterol esterase: isolation and identification of principal biodegradation products.

Synthesized poly(ester)urea-urethanes with 14C-labeled toluene diisocyanate or 14C-labeled chain extender ethylene diamine were incubated with cholesterol esterase in a phosphate buffer solution at 37 degrees C. A number of biodegradation products, generated at the level of 2.8 micrograms/cm2 of polymer surface area, were isolated from this simulated physiologic system. Individual products were obtained by separation with reversed-phase high-performance liquid chromatography. The two different radiolabels were used to assist in the identification of degradation products from hard- and soft-segment domains. Approximately 20 degradation products were isolated; however, toluene diamine (TDA) was not detected from the chromatographic separation. Two principal products were identified by tandem mass spectrometry. Both products are TDA derivatives (secondary aromatic diamine) substituted with end units of the polyester segment at N and N' positions of TDA. The absence of free TDA suggests that there could be a stabilization of urethane and urea linkages within the toluene diisocyanate (TDI) segments of the polyurethanes. For TDI-synthesized polymers, this finding raises awareness to the potential biological importance of degradation products other than TDA, particularly to their interaction with surrounding cells.

Biocompatible Materials↗

PubMed1997

Use of surface-modifying macromolecules to enhance the biostability of segmented polyurethanes.

Polyurethanes are widely used as biomaterials for medical implants because of their excellent mechanical properties and moderate biocompatibility. However, the demand for more bioresistant and biocompatible polyurethanes to meet the needs of long-term implant devices still remains an important issue. Since most biological interactions with materials occur at the interface, a significant number of studies for improving the biocompatibility of polyurethanes have concentrated on surface modification. It is well known that additives used in polymeric materials as processing aids, mold releasing agents, antioxidants, etc., migrate to the surface and change the surface properties of the material. Under certain conditions polymeric additives may also migrate toward surfaces. This study describes two fluorine-containing, surface-modifying macromolecules (SMMs) that have been evaluated for their ability to inhibit polyurethane degradation. These materials actively migrate to the upper surface of a material film when they are mixed with a base polymeric materia. Contact angle measurements for the mixture of SMM with base polyurethane indicate that the surface becomes more hydrophobic after adding the SMMs, while X-ray photoelectron spectroscopy analysis shows an enrichment of fluorine on the polymer surfaces. Differential scanning calorimetry thermograms indicate that the micro-structure, as defined by the thermal transitions of the base polymer, are not altered by the addition of SMMs. Enzyme-induced biodegradation tests exhibit a significant reduction of polyurethane degradation in the presence of these surface-resident materials. The results indicate that the SMMs have the potential to resist hydrolytic degradation mediated by lysosomal enzymes while generating a surface chemistry on the native elastomer which is similar in nature to that of a fluoropolymer, e.g., Teflon.

Absorptiometry, Photon↗

PubMed1997

The effect of hard segment size on the hydrolytic stability of polyether-urea-urethanes when exposed to cholesterol esterase.

Previous studies have shown that both polyester and polyether-based polyurea-urethanes are susceptible to cleavage by hydrolytic enzymes. Furthermore, it has been hypothesized that the degree of hard segment micro-domain formation in polyurethane materials, as well as its structure, influences the ability of enzymes to degrade the polymers. The current study has investigated a series of segmented polyether-urea-urethanes synthesized with the same reagents but having different hard segment content. Using these materials, the relationship between the formation of hard segment domains and the hydrolysis of urea/urethane groups was specifically addressed. Both differential scanning calorimetry and X-ray photo-electron spectroscopy data indicated that the three materials differed significantly in the extent of hard segment domain formation and the nature of the chemical groups located in the top 10 nm of the surface. Biodegradation studies showed a strong dependence on hard segment domain formation and indicated that the polymer containing the highest number of hydrolytically labile urea and urethane bonds exhibited the least degradation. The ability of a polyurethane material to form hard segment micro-domains may contribute to the formation of a protective structure for the hydrolysable hard segment linkages located within the micro-domains.

Biocompatible Materials↗

PubMed1997

Tissue factor expression by cells used for sodding of prosthetic vascular grafts.

Sodding of vascular grafts involves coating the biomaterial with cells prepared from collagenase-digested fat tissue after removal of the adipocytes by centrifugation. The goal of this study was to investigate the staining characteristics of the sodding cells as well as their ability to express the procoagulant protein tissue factor, and to compare these findings to those found with extensively purified microvascular endothelial cells (MEC) prepared from similar tissue. Sodding cells and MEC, isolated using immunomagnetic separation with anti-PECAM antibodies, were prepared from liposuction material and endothelial-specific staining was compared. The expression of tissue factor on these cells was examined using both an ELISA and a chromogenic assay to assess the rate of generation of factor Xa. Sodding cells expressed significantly more tissue factor than the unstimulated MEC in which the expression was undetectable (sodding cells 2466 +/- 830 pg/mL, P < 0.05). There was no further increase in tissue factor expression in the sodding cells with stimulation with lipopolysaccharide (LPS); however, purified MEC expressed significantly more tissue factor after exposure to LPS (1247 +/- 356 pg/mL, P < 0.05). These results were confirmed by the determination of procoagulant activity of the cells whereby the procoagulant activity on unstimulated MEC was significantly less than that found after stimulation of these cells, and it was also less than stimulated and unstimulated sodding cells (absorbance at 405 nm: 0.423 +/- 0.125, unstimulated MEC; 1.000 +/- 0.438, stimulated MEC; 1.129 +/- 0.396, unstimulated sodding cells; 1.171 +/- 0.254, stimulated sodding cells, P < 0.05). Staining of these two cells types also demonstrated significant uptake of acetylated LDL (Ac-LDL) in the purified MEC which was essentially absent in the sodding cells. Further, vWf staining was found to a greater degree in the purified MEC than in the sodding cells. These experiments demonstrated that the cells prepared for cell sodding express large amounts of tissue factor. The sodding cells do not stain for antigens known to be specific for endothelial cells, whereas MEC do and therefore the concentration of endothelial cells in the sodding cells is small. The significance of the tissue factor expression on the surface of sodded grafts is not yet known.

Antibody Specificity↗

PubMed1997

Application of macromolecular additives to reduce the hydrolytic degradation of polyurethanes by lysosomal enzymes.

Of the various polymers used in medical devices, polyurethanes have been relatively successful because of their acceptable mechanical and biological properties. However, over the past decade, increasing concerns have arisen in relation to long-term biostability of polyurethanes when exposed to the harsh environment of the human body. Lysosomal enzymes released from inflammatory cells have been proposed to be important mediators in the degradation of biomedical polyurethanes. In order to increase the biostability of polyurethanes to lysosomal enzymes, a series of surface-modifying macromolecules (SMMs) were synthesized in this work and then combined into a base polyurethane to reduce the material's susceptibility to hydrolysis. X-ray photoelectron spectroscopy (XPS) studies showed that the SMMs were enriched within the upper 10 nm of the surface. In vitro biodegradation test results indicated that the degradation of a polyester-urea-urethane could be inhibited by the new SMM surface. It was also found that different SMM formulations provided varying degrees of inhibition against the biodegradation of the polyester-urea-urethane. Certain formulations of the SMMs were shown to be physically incompatible with the polyurethane and distorted surface morphology to the extent that biodegradation was enhanced.

Biodegradation, Environmental↗

PubMed1997

The effect of phospholipids on the biodegradation of polyurethanes by lysosomal enzymes.

Although biodegradation of model poly(ester-urethane)s and poly(ether-urethane)s has been demonstrated using a single enzyme system (cholesterol esterase (CE) in vitro, in vivo biodegradation most likely involves many processes acting together. In this study, the physical (film vs textured surface) and chemical (poly(urethane)s containing polycaprolactone (PCL) vs poly(tetramethylene oxide) (PTMO)) nature of the materials as well as the products of enzymatic reactions known to occur during the inflammatory response (CE and phospholipase A2 (PLA)) were assessed for their effects on poly(urethane) (PU) biodegradation in vitro. A mixed micelle (phosphatidylcholine (PC):lysoPC (LPC):oleic acid (OA): 2:1:1) significantly increased the release of radiolabelled products from a C-labelled poly(ester-urethane) (TDI/PCL/ED) caused by CE. This effect was further enhanced when this material was cast as a textured surface. A model poly(ether-urethane) showed no significant enhancement of CE-mediated hydrolysis in the presence of phospholipids and their breakdown products whether cast as a film or a textured surface. PLA caused a small but significant release of radiolabel from TDI/PCL/ED which was enhanced in the presence of its substrate, PC, and a mixture of PC with its breakdown products, LPC and OA. Based on the results of this study, it may be possible to hypothesize that during the inflammatory response when PLA is activated, enhancement of the biodegradation of a PU could occur by direct action of PLA on the poly(ester-urethane) and by stimulation of CE due to the formation of LPC and OA occurring when PLA hydrolyses PC, its natural substrate

Biocompatible Materials↗

PubMed1996

Elastase-induced hydrolysis of synthetic solid substrates: poly(ester-urea-urethane) and poly(ether-urea-urethane).

Human neutrophil elastase (HNE) and porcine pancreatic elastase (PPE) were incubated with two radiolabelled model poly(urethane), a poly(ester-urea-urethane) containing [14C]toluene diisocyanate ([14C]TDI), poly(caprolactone)(PCL) and ethylenediamine (ED), and a poly(ether-urea-urethane) containing [14C]TDI, poly(tetramethylene oxide) (PTMO) and ED. Ten-fold more radioactive carbon was released when PPE was incubated with [14C]TDI/PCL/ED than when HNE was used. The PPE-induced radioactive carbon release was significantly reduced by a specific elastase inhibitor. Ten-fold less radioactive carbon was released when [14C]TDI/PTMO/ED was incubated with PPE as compared to [14C]TDI/PCL/ED. Since neutrophils, which contain elastolytic activity, are present during the inflammatory response, the stability of biomaterials used in implanted devices may be affected.

Animals↗

PubMed1995

Neutrophil-mediated degradation of segmented polyurethanes.

The biostability of polyurethanes was evaluated using a human neutrophil cell culture. The polymers were synthesized with 14C radiolabelled components incorporated into the polyurethane chain and the amount of radiolabel released during exposure to cells and medium was used as a marker for material degradation. The effect of diisocyanate, soft segment and chain extender chemistry on the susceptibility of polymer degradation was examined. All polymers showed a release of material into the tissue culture medium which was unrelated to the cells. A significant cell-dependent release of radiolabel-containing material was found from one of the polymers (a polyester urea-urethane, TDI/PCL/ED) which increased linearly up to 96 h. The polyether-containing polyurethanes showed no significant cell-mediated degradation under similar conditions as measured by radiolabel release. Scanning electron microscopy (SEM) showed that the cells adhered to the different polyurethanes. However, no effect of neutrophils on polymer structure could be detected by this technique. The cellular response to each polymer was evaluated by measuring release of elastase-like activity (ELA) into the tissue culture media. After 24h TDI/PCL/ED showed the highest levels of ELA in the tissue culture medium. When TDI/PCL/ED was incubated with commercial elastase in vitro, a significant release of radiolabel was found which was comparable to the amount of radiolabelled material released from this polymer in contact with the neutrophils in culture. No significant amount of radiolabel was released from the corresponding polyether material (TDI/PTMO/ED) under similar conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Biodegradation, Environmental↗

PubMed1995

The role of magnesium in myocardial preservation.

The purpose of this review is to look at the role of magnesium in the formation of preservation and reperfusion solutions for the ischaemic heart. Preservation of the heart during cardiac surgery procedures, including cardiac transplantation, can be divided into distinct phases: arrest, cold storage in the case of transplantation, global ischaemia during implantation or cardiac surgery procedures, followed by reperfusion when the heart is rewarmed and restarted. Although the magnesium ion can play a significant role in myocardial protection, it is important to recognize the different types of protection required during these different phases of surgical procedures. The rationale for the inclusion of magnesium in cardioplegic solutions is threefold: (i) for its negative inotropic effect; (ii) to prevent ischaemia-induced magnesium loss; (iii) to influence cellular ionic movements. Preservation temperature as well as the concentration of other ionic constituents present in the preservation solution alter the effects of magnesium. Results obtained from animal models suggest that elevated magnesium (16 mM) is beneficial to the hypothermic preservation of hearts with extracellular type solutions, especially when calcium is elevated in the solution formulation. Research has shown that the amplitude of the inotropic effect of magnesium varies from one species to another so that the beneficial effect of magnesium is inferior in the less sensitive species. Using the human atrial trabecular preparation as a model for myocardial preservation, we have assessed the effects of elevated magnesium on the recovery of developed force, both for long-term preservation (24 h) during hypothermic arrest (4 degrees C) and for reperfusion during rewarming of the trabeculae. No clear pattern emerged when the ratio of calcium to magnesium was altered in St Thomas' I and II solutions used for the storage. However, when the atrial trabecular preparation was rewarmed in a Krebs Henseleit buffer containing an elevated level of magnesium (16 mM), a greater number of trabeculae reached a greater developed force and had higher levels of energetic metabolites than when the magnesium in the Krebs Henseleit buffer was 1.2 mM. Several studies have suggested that an elevated magnesium prevents calcium overload by competing with this ion at the membrane, and reduces the workload, while ATP reserves and ion homoeostasis are re-established. The role of the magnesium ion in hypothermic preservation of the human myocardium is still not clear after many clinical and experimental studies and requires further investigation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1995

Preservation of cell organelles during storage of human atrial tissue in the University of Wisconsin solution.

AIM OF THE STUDY: The University of Wisconsin storage solution (UW) (E.I. du Pont de Nemours, Wilmington, DE) has been successful in extending the storage period using some model systems of donor heart preservation for cardiac transplantation. The ability of UW to preserve human cardiac cell organelle (sarcoplasmic reticulum, mitochondria and sarcolemmal) membrane composition (enzyme activity, protein, cholesterol and phospholipid content) was compared to St. Thomas's Hospital Solution (ST) and saline. METHODS: Human atrial appendages were stored at 4 degrees C for 24 h in saline, ST or UW or not stored (controls) and the cell organelles isolated. Each fraction was assayed for enzyme activity (mitochondria: azide sensitive Ca2+ ATPase, cytochrome C oxidase; sarcolemmal membrane: Na+K+ ATPase, p-nitrophenylphosphatase; sarcoplasmic reticulum: CA2+ uptake, Ca2+ ATPase, NADPH cytochrome C reductase), protein, cholesterol and phospholipid content. RESULTS: "Protein yield" proved to be the most sensitive marker for cell organelle preservation. Only the sarcolemmal membrane showed no decrease in either enzyme activities of "protein yield" after storage in saline, ST or UW. Mitochondria showed no decrease in enzyme activities but a decrease in "protein yield" after storage in all 3 solutions. The "protein yield" of sarcoplasmic reticulum was significantly reduced after storage in UW, saline and ST. No correlation could be drawn between cholesterol and phospholipid content and the preservation of cell organelle function. CONCLUSIONS: It is possible to distinguish between the ability of solutions to preserve the membrane composition of human cardiac tissue during hypothermic storage. Using simple assays to assess preservation provides preliminary screening for a superior solution which can then be used in more complicated transplantation models to more fully assess cardiac function.

Adenosine↗

PubMed1995

Assessment of the cytotoxicity of the photosensitizing drug BPD verteporfin using human vascular smooth muscle cells in culture.

Photosensitizing drugs are selectively taken up by lipid-rich lesions such as atheromatous plaque which when exposed to light render the drugs cytotoxic. However, skin photosensitivity which persists for many weeks is a significant side effect. We investigated the cytotoxicity of a new photosensitizing drug, the benzoporphyrin derivative BPD verteporfin (Quadra Logic Technologies), which does not have this deleterious side effect. Vascular smooth muscle cells (VSMC) from normal human mammary and diseased human coronary arteries were grown in culture from explants and characterized with respect to their growth rates. The sensitivity to BPD with and without light was assessed by measuring viability after treatment. The lethal dose of drug for 50% viability loss (LD50) for BPD with light was approximately 12.5 ng/ml for mammary artery, with 52 +/- 8% cell survival (n = 6). The coronary artery VSMC from all patient sources, although differing significantly in growth rate, had a survival of 44 +/- 6% (n = 12) at the same concentration of BPD used for the mammary artery SMC (p = NS). Our results established the LD50 for BPD using human arterial sources of SMC and showed that the growth rates of the cells did not affect the cytotoxicity of the drug.

Cell Survival↗

PubMed1994

Biodegradation evaluation of polyether and polyester-urethanes with oxidative and hydrolytic enzymes.

Enzyme-induced liberation of components from seven different radiolabeled polyurethanes was monitored by radiolabel counting of the incubation solutions and product isolation by high performance liquid chromatography (HPLC). The polyurethanes were selected to reflect variations in the hard-segment chemistry, soft-segment chemistry, and polyurethane hydrophilicity resulting from combinations of hydrophobic/hydrophilic soft segments. All materials were characterized using electron spectroscopy for chemical analysis, differential scanning calorimetry, size exclusion chromatography, and Fourier transform infrared spectroscopy. The material surfaces were examined both before and after incubation with enzyme and control solutions using scanning electron microscopy. Biodegradation assays were carried out at 37 degrees C using cholesterol esterase (CE) and horseradish peroxidase (HRP) under optimal pH conditions for each enzyme. The hydrolytic enzyme (CE) was effective in releasing degradation products that contained hard-segment components from some of the polyurethanes. HPLC analysis of products for a polyesterurethane synthesized with toluene diisocyanate (TDI) suggested that the bulk of the incorporated radiolabeled TDI was still covalently bonded within the cleaved chain segments of the original polymer and was not released as pure toluene diamine (TDA). The data suggest that urethane linkages in the soft-segment domains of phase separated polyetherurea-urethanes may be more prone to cleavage by CE than are the urea/urethane groups in the hard-segment domains. This could be related to the nature of the hard-segment domain structures. The oxidative enzyme (HRP) was not able to induce liberation of radiolabeled segments from either the polyether or polyester-based polyurethanes.

Biocompatible Materials↗

PubMed1994

The enzymatic hydrolysis of a synthetic biomembrane: a new substrate for cholesterol and carboxyl esterases.

With the introduction of artificial implant devices, a new host of biomembrane-like structures have been introduced into the bio-media made up of the synthetic matrix, adsorbed proteins and lipids. Lysosomal hydrolases, e.g. cholesterol esterase (CE), are implicated during the tissue response near the tissue-implant interface. The enzymatic attack on a radiolabelled 'hybrid biomembrane', a polyester-urethane (PUU-CAP), was investigated using two esterases. Membrane stability was monitored by release of radiolabelled molecules. Although some radioactivity was released by buffer controls, upon the addition of CE, a burst of radiolabel release occurred which was due to an enzymatic reaction that could be saturated and inhibited by the specific esterase inhibitor, phenylmethylsulfonylfluoride. Carboxyl esterase (CXE) incubation with PUU-CAP caused less radiolabel release than CE which was similar to the latter's activity when common nitrophenyl ester substrates were used. When a factorial analysis was performed, it was found that side chain length for the common substrates was twice more important for CE, than CXE activity. This would suggest that CE activity is greater for substrates which have spacer segments between potential ester-carbonyl cleavage sites and the rigid ring structure.

Biocompatible Materials↗