Decreased tissue factor expression with increased CD11b upregulation on elastin-based biomaterial coatings.

Elastin-like polypeptide (ELP) coatings have been shown to have non-thrombogenic properties both in vitro and in vivo. In this work, we expand our understanding of this phenomenon by investigating the interaction of these coatings with leukocytes. Citrated whole blood was exposed to a shear rate of 300 s-1 for 2 hours at 37 °C on ELP1- and ELP4-coated polyethylene terephthalate (Mylar™) surfaces in a cone and plate device. Scanning electron microscopy and flow cytometry were used to measure leukocyte activation and platelet-leukocyte aggregation in response to the ELP1 and ELP4 coatings on the surface and in the bulk, respectively. Surface analysis showed little leukocyte activity on the surface of uncoated positive controls. Both the tissue factor (TF) expression (indicative of leukocyte activation) and CD61 expression (indicative of platelet-leukocyte aggregates), in the bulk were decreased by 40% and 20%, respectively, with the ELP coating of Mylar™, while a two- to three-fold increase in CD11b upregulation (indicative of leukocyte activation) for ELP1 and ELP4 was determined. Two of three bulk markers indicated that ELP-coated Mylar™ decreased the leukocyte response compared to the uncoated Mylar™, while the third, CD11b, indicated an increase in leukocyte response to the ELP coatings.

Platelet Adhesion and Fibrinogen Accretion on a Family of Elastin-Like Polypeptides.

Previous work in our laboratory showed the potential of using a human recombinant elastin-like polypeptide (ELP) as a thromboresistant coating. In this work we investigate the use of three particular ELPs (ELP1, ELP2 and ELP4), that differ by molecular weight and number of repeating hydrophobic and cross-linking domains, as coatings to improve blood-contacting properties. All three ELPs were passively adsorbed on Mylar surfaces. Differences in water contact angle and surface concentration were found among the three ELP coatings, with the shortest polypeptide, ELP1, being the most hydrophilic and abundant on the surface (55°, 0.76 µg/cm(2)), followed by ELP2 (55°, 0.35 µg/cm(2)) and ELP4, the longest of the three (66°, 0.25 µg/cm(2)), respectively. The blood interactions of the ELP coatings were investigated by measuring fibrinogen adsorption and platelet adhesion in whole blood under laminar flow in a cone and plate viscometer configuration. In general, platelet adhesion to the ELP-coated surfaces was found to correlate with fibrinogen adsorption. Decreases in fibrinogen accretion and platelet adhesion were observed for ELP-coated compared to uncoated surfaces. The magnitude of the decreases was found to depend on the ELP sequence length, with ELP4 exhibiting the lowest levels of fibrinogen adsorption and platelet adhesion at 43 ± 24 ng/cm(2) and 113 ± 77 platelets/mm(2), respectively.

Adipose tissue engineering in vivo with adipose-derived stem cells on naturally derived scaffolds.

Placental decellular matrix (PDM) and PDM combined with cross-linked hyaluronan (XLHA) scaffolds, seeded with primary human adipose-derived stem cells (ASC), were investigated in a subcutaneous athymic mouse model. The in vivo response at 3 and 8 weeks was characterized using histological and immunohistochemical staining. Fibrous capsule formation was assessed and the relative number of adipocytes in each scaffold was quantified. Undifferentiated ASC were localized using immunostaining for human vimentin. Unilocular and multilocular adipocytes were identified by intracellular lipid accumulation. Staining for murine CD31 assessed implant vascularization. Both scaffolds macroscopically maintained their three-dimensional volume and supported mature adipocyte populations in vivo. There was evidence of implant integration and a host contribution to the adipogenic response. The results suggested that incorporating the XLHA had a positive effect in terms of angiogenesis and adipogenesis. Overall, the PDM and PDM with XLHA scaffolds showed great promise for adipose tissue regeneration.

Polyurethane films seeded with embryonic stem cell-derived cardiomyocytes for use in cardiac tissue engineering applications.

Cardiomyocytes are terminally differentiated cells and therefore unable to regenerate heart tissue after infarction. The successful engraftment of various cell types resulting in improved cardiac function has been reported, however methods for improving the delivery of donor cells to the infarct site still need to be developed. The use of bioengineered cardiac grafts has been suggested to replace infarcted myocardium and enhance cardiac function. In this study, we cultured embryonic stem (ES) cell-derived cardiomyocytes on thin polyurethane (PU) films. The films were coated with gelatin, laminin or collagen IV in order to encourage cell adhesion. Constructs were examined for 30 days after seeding. Cells cultured on laminin and collagen IV, exhibited preferential attachment, as assessed by cellular counts, and viability assays. These surfaces also resulted in a greater number of contracting films compared to controls. A degradable elastomer seeded with embryonic stem cell-derived cardiomyocytes may hold potential for the repair of damaged heart tissue.

Understanding the biodegradation of polyurethanes: from classical implants to tissue engineering materials.

After almost half a century of use in the health field, polyurethanes (PUs) remain one of the most popular group of biomaterials applied for medical devices. Their popularity has been sustained as a direct result of their segmented block copolymeric character, which endows them with a wide range of versatility in terms of tailoring their physical properties, blood and tissue compatibility, and more recently their biodegradation character. While they became recognized in the 1970s and 1980s as the blood contacting material of choice in a wide range of cardiovascular devices their application in long-term implants fell under scrutiny with the failure of pacemaker leads and breast implant coatings containing PUs in the late 1980s. During the next decade PUs became extensively researched for their relative sensitivity to biodegradation and the desire to further understand the biological mechanisms for in vivo biodegradation. The advent of molecular biology into mainstream biomedical engineering permitted the probing of molecular pathways leading to the biodegradation of these materials. Knowledge gained throughout the 1990s has not only yielded novel PUs that contribute to the enhancement of biostability for in vivo long-term applications, but has also been translated to form a new class of bioresorbable materials with all the versatility of PUs in terms of physical properties but now with a more integrative nature in terms of biocompatibility. The current review will briefly survey the literature, which initially identified the problem of PU degradation in vivo and the subsequent studies that have led to the field's further understanding of the biological processes mediating the breakdown. An overview of research emerging on PUs sought for use in combination (drug + polymer) products and tissue regeneration applications will then be presented.

Adverse drug reactions in elderly patients.

Many studies from around the world show a correlation between increasing age and adverse drug reaction (ADR) rate, at least for some medical conditions. More than 80% of ADRs causing admission or occurring in hospital are type A (dose-related) in nature, and thus predictable from the known pharmacology of the drug and therefore potentially avoidable. Frail elderly patients appear to be particularly at risk of ADRs and this group is also likely to be receiving several medicines. The toxicity of some drug combinations may sometimes be synergistic and be greater than the sum of the risks of toxicity of either agent used alone. In order to recognize and to prevent ADRs (including drug interactions), good communication is crucial, and prescribers should develop an effective therapeutic partnership with the patient and with fellow health professionals. Undergraduate and postgraduate education in evidence-based therapeutics is also vitally important. The use of computer-based decision support systems (CDSS) and electronic prescribing should be encouraged, and when problems do occur, health professionals need to be aware of their professional responsibility to report suspected adverse drug events (ADEs) and ADRs. "Rational" or "obligatory" polypharmacy is becoming a legitimate practice as increasing numbers of individuals live longer and the range of available therapeutic options for many medical conditions increases. The clear risk of ADRs in this situation should be considered in the context that dose-related failure of existing therapy to manage the condition adequately may be one of the most important reasons for admission of the elderly to hospital. Thus, age itself should not be used as a reason for withholding adequate doses of effective therapies.

Acellularization of human placenta with preservation of the basement membrane: a potential matrix for tissue engineering.

Basement membrane directs cell migration, cell adherence, and tissue organization in vivo. These qualities would be advantageous in tissue engineering, during which repopulation of scaffolds by functional cells is a common problem. The purpose of this study was to expose human term placenta to a chemical acellularization protocol using the isolated cotyledon perfusion technique to develop an acellular scaffold rich in extracellular matrix components for tissue engineering applications. The processed blocks of tissue demonstrated no cellular material on histologic examination. Periodic acid-Schiff staining, type IV collagen labeling, and transmission electron microscopy demonstrated preservation of the extracellular matrix and basement membrane. Maintenance of the extracellular matrix architecture was seen on scanning electron microscopy. Placenta-derived acellular matrix is a potential volume scaffold for tissue engineering. It is rich in extracellular matrix, has a complex architecture of vascular channels, and has unique donor opportunities.

Elastomeric biodegradable polyurethane blends for soft tissue applications.

Four biodegradable polyurethane blends were made from segmented polyurethanes that contain amino acid-based chain extender and diisocyanate groups. The soft segments of these parent polyurethanes were either polyethylene oxide (PEO) or polycaprolactone (PCL) diols. The blends were developed to investigate the effect of varying soft segment compositions on the overall morphological, mechanical, and degradative properties of the materials, with a view to producing a family of materials with a wide range of properties. The highly hydrophilic PEO material was incorporated to increase the blend's susceptibility to degradation, while the PCL polyurethane was selected to provide higher moduli and percent elongations (strains) than the PEO parent materials can achieve. All four blends were determined to be semi-crystalline, elastomeric materials that possess similarly shaped stress-strain curves to that of the PCL-based parent polyurethane. As the percent composition of PEO polyurethane within the blend increased, the material became weaker and less extensible. The blends demonstrated rapid initial degradation in buffer followed by significantly slower, prolonged degradation, likely corresponding to an initial loss of primarily PEO-containing polymer, followed by the slower degradation of the PCL polyurethane. All four blends were successfully formed into three-dimensional porous scaffolds utilizing solvent casting/particulate leaching methods. Since these new blends possess a range of mechanical and degradation properties and can be shaped into three-dimensional objects, these materials may hold potential for use in soft tissue engineering scaffold applications.

22 week assessment of bladder acellular matrix as a bladder augmentation material in a porcine model.

Previous studies on the reconstruction of porcine bladder using bladder acellular matrix allograft (BAMA) have indicated positive preliminary results with respect to graft shrinkage and cellular repopulation. The current study was conducted to investigate the feasibility of using BAMA in a similar model of bladder reconstruction out to longer time frames (22 weeks). At predetermined time points, the macroscopic, histological and mechanical properties of explanted native and BAMA tissues were evaluated and compared. Macroscopically, contracture of the BAMA was observed. The peripheral regions of the grafts experienced extensive cellular repopulation. Towards the centre however, all grafts were consistently devoid of organized smooth muscle bundles and a well-developed urothelium. An alteration in both the amount and organization of collagen was also observed within this region. Significant differences (p < 0.05) in the rupture strain and the elastic modulus of the BAMA compared to native bladder tissue appear to correlate with macroscopic graft contracture as well as the fibroproliferative tissue response of the matrix.

Self-aggregation characteristics of recombinantly expressed human elastin polypeptides.

Elastin is an extracellular matrix protein found in tissues requiring extensibility and elastic recoil. Monomeric elastin has the ability to aggregate into fibrillar structures in vitro, and has been suggested to participate in the organization of its own assembly into a polymeric matrix in vivo. Although hydrophobic sequences in elastin have been suggested to be involved in this process of self-organization, the contributions of specific hydrophobic and crosslinking domains to the propensity of elastin to self-assemble have received less attention. We have used a series of defined, recombinant human elastin polypeptides to investigate the factors contributing to elastin self-assembly. In general, coacervation temperature of these polypeptides, used as a measure of their propensity to self-assemble, was influenced both by salt concentration and polypeptide concentration. In addition, hydrophobic domains appeared to be essential for the ability of these polypeptides to self-assemble. However, neither overall molecular mass, number of hydrophobic domains nor general hydropathy of the polypeptides provided a complete explanation for differences in coacervation temperature, suggesting that the specific nature of the sequences of these hydrophobic domains are an important determinant of the ability of elastin polypeptides to self-assemble.

Giardia in older people.

CASE REPORTS: We report two cases of giardiasis in elderly women. Neither patient had been abroad recently and neither had diarrhoea at the time of diagnosis. In the first case, an extensive gastrointestinal cancer work-up was carried out before the diagnosis was made. CONCLUSION: It is important to consider possible infective causes in older patients who have anaemia and weight loss.

In vitro degradation and erosion of degradable, segmented polyurethanes containing an amino acid-based chain extender.

In vitro degradation and erosion of novel, degradable segmented polyurethanes containing a phenylalanine diester chain extender were investigated by exposing the polymers to buffer. chymotrypsin, and trypsin solutions for up to 28 days. Polyurethane degradation and erosion were monitored by gravimetry, scanning electron microscopy (SEM), and gel permeation chromatography (GPC) and compared to a control polyurethane. Polyurethanes were synthesized using two different soft segments (polycaprolactone diol and polyethylene oxide) of variable molecular weight. Inclusion of the phenylalanine-based chain extender resulted in an increased susceptibility to enzyme-mediated, but not buffer-mediated, erosion in comparison to the control polyurethane. SEM analysis indicated that enzyme-mediated erosion proceeded via a surface-limited mechanism resulting in a progressive removal of material from the surface inwards with time. The magnitude of degradation and erosion was highly variable and was dependent on soft segment type and molecular weight. The range of degradation rates, as well as physicochemical properties, makes these polyurethanes potentially useful for a wide range of biomedical applications.

The effect of community-acquired pneumonia on plasma esterases in older people.

INTRODUCTION: Pneumonia is a major cause of morbidity and mortality in older people. The poor outcome of older pneumonia patients despite treatment is still not understood. OBJECTIVE: The aim of this study was to examine the effect of community-acquired pneumonia on enzymes of drug metabolism in older people. METHODS: Fifteen patients (median age 67 years) with a clinical and radiological diagnosis of community-acquired pneumonia and 14 healthy volunteers matched for age and gender (median age 75 years) were recruited. Plasma activities of benzoylcholinesterase, butyrylcholinesterase, acetylcholinesterase and aspirin esterase were determined spectrophotometrically at three time points in pneumonia patients--within 24 h of admission to hospital, 2 days later and 10 days later. Monocyte aryl hydrocarbon hydroxylase (AHH) activity was determined spectrofluorimetrically at the same time points. Enzyme activities were measured at one time point in healthy controls. RESULTS: Mean plasma benzoylcholinesterase activity was significantly lower in pneumonia patients on admission to hospital (mean +/- SEM 848 +/- 100) and after 10 days of treatment (mean +/- SEM 925 +/- 114) than in healthy controls (mean +/- SEM 1333 +/- 84, P < 0.05). Similarly, plasma acetylcholinesterase activity was significantly lower in pneumonia patients on admission (P = 0.007) and after 10 days of treatment (P = 0.01) than in controls. Butyrylcholinesterase activity was lower in pneumonia patients on admission (P = 0.029) than in healthy controls, but improved slightly after treatment so there was no longer a significant difference at 10 days compared with controls (P = 0.077). In contrast there were no significant differences in plasma aspirin esterase activity or induced monocyte AHH activity between pneumonia patients and healthy controls. The activities of benzoylcholinesterase (r = -0.536, P = 0.04), butyrylcholinesterase (r = -0.638, P = 0.01), acetylcholinesterase (r = -0.583, P = 0.022) and aspirin esterase (r = -0.624, P = 0.013) correlated inversely with the British Thoracic Society pneumonia poor prognostic index. CONCLUSION: The activities of several esterases are reduced in older pneumonia patients. Other enzymes including aspirin esterase and induced monocyte AHH activity are unaltered in pneumonia. There was a significant inverse relationship between the activities of all esterases studied and the British Thoracic Society pneumonia poor prognostic index.

Relationship between age and plasma esterases.

INTRODUCTION: the older population is the most medicated. Despite high drug usage, older people are generally excluded from the research underpinning new drug development. This means that drugs are prescribed to older people with very little understanding of how they are likely to metabolize them. More research is needed to investigate the possible effects of ageing on the biotransformation of drugs. We therefore undertook a cross-sectional study examining the effect of age on the activities of benzoylcholinesterase, butyrylcholinesterase, acetylcholinesterase and aspirin esterase. METHODS: we measured the activities of benzoylcholinesterase and butyrylcholinesterase in 70 healthy volunteers aged 18-85 years. We measured the activities of acetylcholinesterase and aspirin esterase in 43 healthy volunteers aged 18-85 years. We determined plasma activities of benzoylcholinesterase, butyrylcholinesterase, acetylcholinesterase and aspirin esterase spectrophotometrically. RESULTS: we found no correlation between the activities of any of the enzymes measured and advancing age. CONCLUSION: age per se is not associated with reductions in the activities of esterase enzymes.

Older adults, diabetes mellitus and visual acuity: a community-based case-control study.

MAIN OBJECTIVES: to screen for impaired distance visual acuity in older adults living at home, both with and without diabetes mellitus to determine whether diabetes increases the likelihood of visual impairment and to identify associated factors. DESIGN: case-control study. SETTINGS: three districts of Wales: North Clwyd, Powys and South Glamorgan, with assessments in subjects' homes. SUBJECTS: 385 with diabetes mellitus and 385 age- and sex-matched controls. MAIN OUTCOME MEASURES: visual acuity measures, short form (SF)-36 quality of life scores RESULTS: we observed impairment of visual acuity in 40% of those with diabetes mellitus and 31% of controls. Diabetes was associated with an increased risk of visual impairment [odds ratio 1.50 (95% confidence interval 1.09-2.05), P = 0.013]. The pinhole test identified uncorrected refractive error in 11% of the 63 patients with diabetes and 12% of the 49 controls who wore glasses, and in 51% of the 91 patients and 84% of the 69 controls who did not wear glasses (P < 0.001). Increasing age (P < 0.001) and female sex (P = 0.014) were significantly associated with visual impairment in both groups, whilst history of foot ulceration (P = 0.001), duration of diabetes (P = 0.018) and treatment with insulin (P < 0.001) were significantly associated with visual impairment in subjects with diabetes. We observed a significant association between impaired visual acuity and five domains of the SF-36 (physical and social functioning, mental health, vitality, and health perceptions; P < 0.01 in each case). CONCLUSION: older adults living at home have a high prevalence of uncorrected visual impairment. Diabetes mellitus is associated with significantly increased risk of visual loss. This impairment is associated with detriments in health-related quality of life. We recommend earlier use of optometry services and assessment of visual acuity by clinicians.

Acellular bladder matrix allografts in the regeneration of functional bladders: evaluation of large-segment (> 24 cm) substitution in a porcine model.

OBJECTIVES: To evaluate the use of a large-segment (> 24 cm2) bladder substitution with porcine bladder acellular matrix allograft (BAMA) in a large animal model. Materials and methods Bladders were harvested from pigs at the time of necropsy and subjected to detergent and enzymatic extractions to render them acellular. The BAMA produced had the surgical handling and suture-retaining properties of normal bladder tissue. Six pigs had BAMA segments implanted under general anaesthesia, through a low midline abdominal incision and after partial cystectomy. The defect was repaired with a BAMA patch (mean size 43.88 cm2, range 12-72), with no urinary diversion. Two animals each were then killed at 9, 16 and 30 days and the bladders explanted. The native bladder and BAMA patch were analysed morphometrically to evaluate cellular re-population and matrix re-organization. RESULTS: All animals survived surgery; there were no urinary leaks and no stones detected in any of the bladders. At 9 days there was a diffuse infiltration with acute inflammatory cells, but no areas of necrosis. There were isolated areas of smooth muscle cell (SMC) infiltration of the BAMA. At 16 days the luminal surface was lined with a single layer of urothelium, there was stromal infiltration with disorganized SMC and angiogenesis, with mature vessels in the BAMA patch. At 30 days the urothelium was multilayered with organizing groups of SMCs and angiogenesis. The highest cell density was at the periphery of the repopulated BAMA patch, decreasing towards the centre. CONCLUSIONS: The implantation of large patches of BAMA is technically feasible and may prove to be a viable surgical alternative to bladder augmentation with intestinal segments. The advantages of BAMA include the potential for complete and functional regeneration of a bladder substitute. This model provides a tool with which to obtain a better understanding of the cellular and molecular aspects of matrix re-population.

Gastric acid suppression does not promote clostridial diarrhoea in the elderly.

Gastric acid prevents bacterial colonization of the stomach and suppression of its secretion might predispose to Clostridium difficile (CD) diarrhoea. We retrospectively studied elderly patients admitted to medical wards of an acute hospital to determine whether the incidence of CD diarrhoea was greater among those previously treated with gastric acid suppressants. From records of stool CD toxin tests undertaken in 1995 and 1996, we found 126 cases with positive results, and selected 126 controls with negative results. Information about pre-morbid illness, predisposing factors for CD and medication received in the preceding 16 weeks was obtained from case-notes. A greater number of CD positive cases had received antibiotics such as Cefuroxime, ciprofloxacin or macrolides with or without metronidazole, were more severely disabled, required assistance for feeding, or had hypoalbuminaemia before the onset of diarrhoea. A greater number of controls had received lactulose, suggesting either that its laxative effect resembled CD infection prompting frequent stool tests, or that it offered protection against CD in this group. Both groups were similar for the use of proton-pump inhibitors or H2-receptor antagonists, suggesting that susceptible elderly patients are not more likely to develop CD diarrhoea after receiving gastric acid suppression therapy.

Plasma esterase activities in young and old patients undergoing open inguinal hernia repair.

Previous research has shown substantial decrements in enzymes of drug metabolism (esterases) in older patients following fracture neck of femur and hip replacement surgery. The main aim of this study was to examine the effect of open inguinal hernia repair on the activities of four plasma esterases in old and young patients. Seventeen older patients (mean age+/-S.E.M. was 67.6+/-1.8) and 12 young patients (mean age+/-S.E.M. was 38+/-3.3) undergoing open hernia repair for clinical reasons were recruited. The activities of plasma benzoylcholinesterase, butyrylcholinesterase, acetylcholinesterase, and aspirin esterase were determined spectrophotometrically, before the operation, 1 day post operatively and 1 week later. There was no significant effect of hernia repair surgery on any of the four enzymes measured in young or old patients. Neither was there any significant difference in enzyme activity between young and old at any of the three time points. Hernia repair surgery is not associated with decrements in enzymes of drug metabolism in man. This contrasts with the previous findings in hip replacement surgery.

Plasmin degradation of fibrin coatings on synthetic polymer substrates.

The goal of this research was to evaluate the in vitro stability of fibrin coatings on polymeric materials in the presence of plasmin. Factor XIIIa-crosslinked and noncrosslinked fibrin layers were coated on three different polyurethane substrates: Corethane, Tegaderm, and a biodegradable polyurethane, PCL/HDI/Phe. Degradation assays indicated that crosslinking the fibrin coatings enhanced the stability of the coatings on both Tegaderm and PCL/HDI/Phe; however, the persistence of the coating on the woven Corethane was not influenced by crosslinking. Degradation assay results also showed that the fibrin coating on the Corethane was significantly less stable than the fibrin coatings on the Tegaderm and PCL/HDI/Phe films. The chromogenic substrate assay data showed crosslinking did not affect the specific plasmin activity on the coatings; therefore, the increased stability resulting from crosslinking was not achieved through a reduction of fibrinolysis. The plasmin activity on the coated Corethane samples was much greater than that on either of the coated flat wound dressing materials. The large surface area of Corethane, a porous woven vascular graft material, may have had a direct influence on the fibrinolysis of its coatings by providing a large number of tissue-type plasminogen activator (tPA) binding sites. A thin, crosslinked, fibrin-coated polyurethane provides a theoretically attractive biomaterial for use in a wound dressing application and should be subject to ongoing research.