Search PubMed⌕ Search

Biomedical subjects

J Feijen

Publications and source records attributed to J Feijen.

At least 127 records · Page 7Linked to original sources
PubMed1991

Synthesis of poly(hydroxypropylglutamine-prazosin carbamate) and release studies.

Prazosin, an antihypertensive drug with postsynaptic alpha 1-adrenergic blocking activity, has been coupled to poly-N5-(3-hydroxypropyl-L-glutamine) (PHPG) via a carbamate linkage. PHPG was activated by p-nitrophenyl chloroformate and then reacted with prazosin to form p(HPG-prazosin carbamate) conjugate. Drug loading was 23.9% (w/w). Activated polymer and conjugates were characterized by infrared spectroscopy and differential scanning calorimetry. In vitro studies proceeded in pH 7.4 isotonic phosphate-buffered saline solution. Prazosin was released at a rate of 0.92 mg/day/100 mg conjugate from p(HPG-prazosin carbamate) particles. In vivo studies were performed with New Zealand White rabbits. P(HPG-prazosin carbamate) conjugate particles (100 mg) were suspended in 2 ml saline and injected subcutaneously into both flanks of rabbits. P(HPG-prazosin carbamate) conjugates, following an initial burst, demonstrated a nearly constant plasma prazosin concentration profile above 2 ng/ml, which was maintained for 10 days.

Animals↗
PubMed1991

Secretory IgA adsorption and oral streptococcal adhesion to human enamel and artificial solid substrata with various surface free energies.

In this paper, secretory IgA adsorption from a single component sIgA solution and from human whole saliva onto human enamel and artificial solid substrata with various surface free energies was studied as a function of time. ELISA indicated that screening or displacement of adsorbed sIgA by other salivary proteins occurred only on low surface free energy substrata, not on high surface free energy substrata such as enamel. In addition, the adhesion of three oral streptococcal strains (Streptococcus mitis BMS, S. sanguis 12, and S. mutans NS), also having widely different surface free energies, to sIgA-coated surfaces was studied. The adhesion of all three streptococcal strains was significantly reduced in the presence of a sIgA coating. However, ranking the adhesion data with respect to the various substrata revealed a similar order to that in the case of uncoated substrata, indicating that substratum properties were at least partly transferred by the adsorbed protein film to the interface with adhering micro-organisms. For S. sanguis 12 and S. mitis BMS, adhesion decreased proportionally with the amounts of sIgA detected by ELISA, but for S. mutans NS such relations with the amounts of sIgA detected on the protein-coated substrata were not found. Thus, for S. mutans NS a specific antibody effect seems to exist in addition to a non-specific protein effect like that observed for S. sanguis 12 and S. mitis BMS.

Adsorption↗
PubMed1991

Protein adsorption from plasma onto poly(n-alkyl methacrylate) surfaces.

Protein adsorption of human serum albumin (HSA), human fibrinogen (Fg), human immunoglobulin G (IgG), high density lipoprotein (HDL) and high molecular weight kininogen (HMWK) from plasma onto poly (n-alkyl methacrylate) (PAMA) surfaces was measured using a semi-quantitative enzyme-immunoassay. Adsorption was investigated for PAMA(n = 1) (n is the number of C-atoms in the n-alkyl side chain), PAMA(n = 8) and PAMA(n = 18). PAMA(n = 1) has a relatively hydrophilic surface as compared to the more hydrophobic PAMA(n = 8) surface. Both polymers have surface chains which do not reorient after contact with water. The PAMA(n = 18) surface is relatively hydrophobic but in this case polymer surface chains and segments are able to reorient after contact with water. Protein adsorption was measured both as a function of time and as a function of the plasma dilution. If adsorption from plasma was measured as a function of time no exchange of proteins could be observed. The amount of adsorbed protein was always larger in the case of the hydrophobic PAMA(n = 8) as compared to PAMAS(n = 1 and 18), probably due to hydrophobic interactions between the proteins and the PAMA(n = 8) surface. At high plasma concentration relatively large amounts of HDL adsorb onto PAMA(n = 8), indicating that this lipoprotein preferentially adsorbs onto this surface.

Adsorption↗
PubMed1991

Adherence of coagulase-negative staphylococci onto polyethylene catheters in vitro and in vivo: a study on the influence of various plasma proteins.

Bacterial adherence on PE catheters inserted into the carotid artery of rabbits was assessed at 5, 30, and 240 min after injection with bacteria of five coagulase-negative staphylococci (CN Staph). These studies revealed that CN Staph adhere onto PE catheters 5 min after injection with bacteria. At 240 min after injection with bacteria almost all catheters were sterile, indicating that initially adherent bacteria on PE catheters disappear with time. EM studies revealed high numbers of platelets and leukocytes and many fibrin deposits on the surface of the PE catheter. In addition, the adherence of the five test strains on PE catheters was determined in vitro. In these in vitro studies the bacteria and catheters were pretreated with either fibrinogen, fibronectin, albumin or citrated whole plasma or the liquid adherence medium was supplemented with these proteins or the adherence assay was done in citrated whole plasma. The presence of proteins in the adherence medium or pretreatment of the catheter or bacteria with either fibronectin, albumin or whole citrated plasma markedly inhibited bacterial adherence. In contrast, pretreatment of bacteria or both bacteria and catheters with fibrinogen enhanced bacterial adherence suggesting the presence of ligands for fibrinogen on the cell surface of CN Staph.

Animals↗
PubMed1990

Poly(dimethylsiloxane)-poly(ethylene oxide)-heparin block copolymers. II: Surface characterization and in vitro assessments.

Amphiphilic block copolymers containing poly(dimethylsiloxane), poly(ethylene oxide), as well as heparin-coated glass beads and tubes were evaluated for the amounts and activities of surface-immobilized heparin. Because the amphiphilic copolymer system is thermodynamically predicted to demonstrate low-energy phase enrichment on the surfaces of air-cast films, studies were also undertaken to understand the in vitro results. Solvent-cast copolymer films have a heterogeneous microphase-separated structure according to transmission electron micrographs. Wilhelmy plate contact angle analysis indicates significant surface restructuring occurs upon hydration. Attenuated total reflectance infrared spectroscopy studies of the desiccated and hydrated films at two different sampling depths show compositional heterogeneity as a function of depth, as well as near surface restructuring allowing surface enrichment of the high-energy segments following contact with water. Significant concentrations of heparin are detected on the surface of these coatings by toluidine blue assays. In addition, a portion of the surface-bound heparin maintains its original bioactivity as determined by recalcification times, thrombin times, and Factor Xa assays. These substrates were also tested for platelet adhesion and activation reactions in vitro using polymer-coated beads in rabbit platelet-rich plasma. Heparinized polymers promoted low levels of platelet adhesion and serotonin release. Surface concentrations of heparin from bioactivity assays were then correlated with platelet adhesion and the extent of platelet release to assess the efficacy of this heparin-immobilized copolymer as a blood-compatible material or coating.

Animals↗
PubMed1990

Enzymatic activity toward poly(L-lactic acid) implants.

Tissue reactions toward biodegradable poly(L-lactic acid) implants were monitored by studying the activity pattern of seven enzymes as a function of time: alkaline phosphatase, acid phosphatase, alpha-naphthylacetyl esterase, beta-glucuronidase, ATP-ase, NADH-reductase, and lactate dehydrogenase. Cell types were identified by their specific enzyme patterns, their morphology and location. Special attention was paid to the enzyme patterns of macrophages, fibroblasts and polymorphonuclear granulocytes (PMNs), being involved in foreign body reactions or inflammatory responses. One day after implantation, an influx of neutrophilic and eosinophilic granulocytes was observed, coinciding with activity of alkaline phosphatase (PMN's) and beta-glucuronidase (eosinophils). From day 3 on, macrophages containing ATP-ase, acid phosphatase and esterase could be observed. From day 7 on, lactate dehydrogenase, the enzyme normally involved in the conversion of lactic acid, and its coenzyme NADH-reductase were observed in macrophages and fibroblasts. These two enzymes demonstrated more activity than expected on basis of wound-healing reactions upon implantation of a nonbiodegradable, inert biomaterial (as, e.g., Teflon). It is concluded that the biodegradable poly (L-lactic acid) used in these implantation studies is tissue compatible, and evokes a foreign body reaction with minor macrophage and giant cell activity, as observed during this 3-week implantation period. Most enzyme patterns were simply due to a wound-healing reaction. The slightly increased levels of LDH and NADH suggest the release of lactic acid from the implant, and thus confirms the biodegradable nature of this polymer.

Animals↗
PubMed1990

In vitro degradation of glycine/DL-lactic acid copolymers.

The in vitro degradation of glycine-DL-lactic acid copolymers was studied as a function of the composition. These polydepsipeptides were prepared by ring-opening copolymerization of 6-methyl-2,5-morpholinedione and DL-lactide. The degradation of discs of the copolymers was performed in a phosphate buffer at pH 7.4 and 37 degrees C. The decrease in molecular weight and weight was determined until complete weight loss had occurred. Poly(DL-lactide) was used as a reference material. All (co)-polymers show an immediate decrease in molecular weight, whereas the weight remains almost unchanged during a longer period of time. Decrease in weight started earlier as the glycine content of the co-polymer increased. The lactic acid content of the residual material increased during the weight loss showing a higher solubility of polymer fragments with a relatively high content of glycine residues. From the hydrolysis constants it was concluded that the degradation was best described by hydrolysis of ester bonds via a bulk erosion process, autocatalyzed by the generated carboxylic acid end groups. The rate constants varied from 4-7 X 10(-2) (day-1) for all (co)polymers. All (co)polymers show an increase in the molecular weight distribution upon weight loss.

Biocompatible Materials↗
PubMed1990

Synthesis and characterization of poly(dimethylsiloxane)-poly(ethylene oxide)-heparin CBABC type block copolymers.

Heparin and poly(ethylene oxide) were coupled to a central anchoring block of poly(dimethylsiloxane) in order to investigate its blood compatible properties. Diamino telechelic poly(dimethylsiloxane) (PDMS-(NH2)2, Mw = 20,000) was first modified to isocyanate functionalities using toluene 2,4-diisocyanate. This modified PDMS was then coupled to diamino-telechelic poly(ethylene oxide) (PEO-(NH2)2, Mw = 2000, 4000, 6000) to create BAB type copolymers having terminal free amino groups. These amino groups were covalently coupled to heparin containing terminal aldehyde groups using sodium cyanoborohydride to yield a bioactive, CBABC type block copolymer. The physical characterization of these copolymers was performed with IR, NMR, sulphur elemental analysis, Wilhelmy plate contact angle, and differential scanning calorimetry (DSC). CBABC block copolymer surfaces demonstrated heparin bioactivity in in vitro evaluation, and improved nonthrombogenic properties during ex vivo A-A shunt experiments.

Animals↗
PubMed1989

In vivo and in vitro degradation of glycine/DL-lactic acid copolymers.

A series of copolymers of glycine and DL-lactic acid with various compositions was synthesized and their in vivo and in vitro degradation behavior was studied. For the in vivo examination, discs of the copolymer films were subcutaneously implanted in rats. The in vitro studies were carried out in phosphate buffer at pH = 7.4 and 37 degrees C. The decrease in molecular weight, the loss of weight, and the tissue reactions of the different copolymers were determined after 2, 5, and 10 weeks. Poly(DL-lactic acid) was used as reference material. The in vivo and in vitro degradation behavior of the polymers was comparable. The decrease of molecular weight of the copolymers and poly(DL-lactic acid) in time was similar. The weight loss for copolymers with a higher mole fraction of glycine units started earlier. The copolymer with the highest content of glycine units disappeared completely within 10 weeks both in vivo and in vitro. The poly(DL-lactic acid) implant lost only 25% weight over the same period. Tissue reactions against all materials started with an acute inflammatory reaction caused by the trauma of implantation, followed by wound-healing processes, ending in a very mild foreign body reaction for the poly(DL-lactic acid) and a more excessive macrophage mediated foreign body reaction for the glycine/DL-lactic acid copolymers. The tissue reaction was more severe for polymers having a higher rate of degradation.

Animals↗
PubMed1989

Adhesion and spreading of cultured endothelial cells on modified and unmodified poly (ethylene terephthalate): a morphological study.

The in vitro adhesion and spreading of human endothelial cells (HEC) on hydrophobic poly(ethylene terephthalate) (PETP) and moderately wettable tissue culture poly(ethylene terephthalate) (TCPETP) were studied with light microscopy and electron microscopy. Numbers of HEC adhering on TCPETP were always higher than those found on PETP. When cells were seeded in the presence of serum, extensive cell spreading on both PETP and TCPETP was observed after the first 30 min. Thereafter, spread cells appeared to withdraw from the PETP surface, resulting in irregularly shaped cells. Complete cell spreading occurred on TCPETP. Complete cell spreading also occurred on PETP and TCPETP when HEC had first been seeded from phosphate buffer solution and serum was supplied after 30 min. Furthermore, HEC spread on both PETP and TCPETP when the surfaces were precoated with protein(s), which promotes cell adhesion. However, when plasma was used for the coating, spread cells did not proliferate in a monolayer pattern. This study shows that TCPETP is, in general, a better surface for adhesion and proliferation of HEC than is PETP, suggesting that vascular prostheses with a TCPETP-like surface will perform better in vivo than prostheses made of PETP.

Blood↗
PubMed1988

Poly(dimethylsiloxane)-poly(ethylene oxide)-heparin block copolymers. I. Synthesis and characterization.

Amphiphilic block copolymers containing poly(dimethylsiloxane), poly(ethylene oxide), and heparin (PDMS-PEO-Hep) have been prepared via a series of coupling reactions using functionalized prepolymers, diisocyanates, and derivatized heparins. All intermediate steps of the synthesis yield quantifiable products with reactive end-groups, while the final products demonstrate bioactive, covalently bound heparin moieties. Due to the solvent systems required, commercial sodium heparin was converted to its benzyltrimethyl ammonium salt to enhance its solubility. The same procedure was applied to heparin degraded by nitrous acid in order to covalently couple it in solutions with the semitelechelic copolymers. As might be expected, this derivatization reduces the apparent bioactivity of the heparin. However, preliminary findings suggest that the bioactivity can be restored by reforming the heparin sodium salt.

Biocompatible Materials↗
PubMed1988

Biodegradable hollow fibres for the controlled release of drugs.

Biodegradable hollow fibres of poly-L-lactic acid (PLLA) filled with a suspension of the contraceptive hormone levonorgestrel in castor oil were implanted subcutaneously in rats to study the rate of drug release, rate of biodegradation and tissue reaction caused by the implant. The in vivo drug release was compared with the release in vitro using different release media. Fibres, disinfected with alcohol showed a zero-order release, both in vitro and in vivo, for over 6 months. Fibres, either gamma-sterilized or disinfected with alcohol were harvested at time intervals ranging from 1 d to 6 months after implantation. Molecular weights of PLLA, tensile strengths, and remaining amounts of drug were determined as a function of time. The tissue reaction can be described as a very moderate foreign body reaction with the initial presence of macrophages, which are gradually replaced by fibroblasts which form a collagen capsule. Molecular weight determinations of PLLA showed a decrease from an initial Mw of 1.59 X 10(5) to 5.5 X 10(4) in 4 months (after alcohol sterilization). A gradual decrease in fibre strength with time was observed which did not significantly impair the release rate of levonorgestrel.

Animals↗
PubMed1988

Deposition of endothelial fibronectin on polymeric surfaces.

Cellular fibronectin is deposited on tissue culture polystyrene during the adhesion and spreading of cultured human endothelial cells (HEC). Following the seeding of HEC upon this polymer, larger amounts of fibronectin are deposited as both cell density and incubation time increase. Our results indicate that the ability to deposit cellular fibronectin onto a polymeric surface is a condition for the spreading and proliferation of HEC.

Adsorption↗
PubMed1988

Morphometric study of myocardial changes during doxorubicin-induced cardiomyopathy in mice.

Doxorubicin (DOX) is one of the most effective anti-cancer drugs in oncology, but may cause a cumulative dose-dependent cardiomyopathy in a number of cancer patients. The effect of DOX on the heart was studied in mice treated with i.v. injections of 2 mg/kg by measuring morphometric parameters, including nuclear index (number of non-myocytes/number of myocyte nuclei), reticulin index (reticulin area/number of myocyte transsections), nuclear transsectional area, myocyte transsectional area, capillary index (number of capillaries/number of myocyte transsections) and capillary transsectional area. The highest significant difference between control mice and DOX-treated mice was observed immediately after the 12th dose of DOX except for the two capillary parameters. The highest level of significance for these two parameters was obtained 12 weeks after the end of DOX treatment. In contrast to the observations in rats, mice did not develop a nephrotic syndrome during treatment with DOX. The morphometric analysis of myocardial changes in mice, as a quantitative and objective method, seems to be a good model for comparative studies on cardiomyopathy induced by anthracycline analogues.

Animals↗
PubMed1988

Smooth muscle cell seeding in biodegradable grafts in rats: a new method to enhance the process of arterial wall regeneration.

In this study a smooth muscle cell seeding technique was developed and evaluated in biodegradable vascular grafts in rats. Cultured smooth muscle cells (3.5 to 5 X 10(6) in 0.1 ml whole blood) were seeded by means of a one-step preclotting technique in microporous, compliant, biodegradable vascular grafts (internal diameter 1.3 mm, length 1 cm; n = 16). Four seeded grafts as well as four nonseeded preclotted control grafts were histologically evaluated immediately after seeding and on preclotting; the other seeded grafts (n = 12) as well as nonseeded preclotted control grafts (n = 12) were implanted into the abdominal aorta of rats and were evaluated after 2 hours (n = 4), 2 days (n = 4), and 1 week (n = 4) with regard to the process of arterial wall regeneration. All grafts, except one seeded graft harvested at 1 week, were patent. All nonseeded control grafts showed no (at 2 hours and at 2 days) or limited (at 1 week) smooth muscle cell ingrowth. Of the 11 patent seeded grafts three also showed poor or limited neomedia development, probably because of improper preclotting. However, eight of the 11 patent seeded grafts showed fast and uniform noemedia development (clearly discernible at 2 days). Moreover, in two patent 1-week seeded grafts there were neomedia comparable in thickness and architecture (circularly arranged smooth muscle cells) to that of normal rat media, and a neointima had already lined 30% to 40% of the lumen. These results clearly demonstrate that smooth muscle cell seeding in biodegradable grafts is feasible and indicate that this seeding can enhance the process of arterial wall regeneration in these grafts.

Animals↗
PubMed1987

Standardization of heparins by means of high performance liquid chromatography equipped with a low angle laser light scattering detector.

This study shows that HPLC-LALLS (high performance liquid chromatography with a light-scattering detector) is a convenient and reliable method for the characterization of standard heparin samples, provided that polyelectrolyte artefacts are suppressed by a suitable dialysis procedure. The method has been successfully applied to the assessment of calibrated relations like the Mark-Houwink relation and the calibration curve of gel permeation chromatography. Furthermore, this study confirms that gel permeation chromatography for heparins cannot be calibrated with dextranes or polyethyleneglycols, but in addition to this well known fact it is shown that even the universal (hydrodynamic volume) calibration procedure does not work. Moreover, in addition to the familiar conclusion that heparins should be calibrated with heparins, it is shown that calibrated relations are valid only when the calibration has been made with heparin samples of the same origin (i.e. same tissue source, same animal source, and same purification scheme).

Animals↗