Biomedical subjects

I Molenaar

Publications and source records attributed to I Molenaar.

At least 19 recordsLinked to original sources

PubMed1995

Aggressive fibromatosis (non-familial desmoid tumour): therapeutic problems and the role of adjuvant radiotherapy.

Aggressive fibromatosis is a rare soft tissue tumour with a high tendency to local recurrence, even after apparently adequate resection. Wide local excision with a margin of at least 3 cm, depending on the anatomical location, should be performed to improve rates of recurrent disease. There is no consensus concerning the role of radiotherapy in the treatment of these lesions. The clinical findings of 39 cases diagnosed between 1972 and 1991 were reviewed retrospectively. Local control was effected in 19 of 32 patients treated with surgery alone after a median (range) follow-up of 72 (18-236) months. There were 40 cases of recurrent fibromatosis in 15 patients. Local control was obtained in 13 of 14 patients who received radiotherapy using a wide-field technique and doses of more than 50 Gy over a period of 5 weeks after marginal or incomplete resection of primary or recurrent lesions (P < 0.001). The results suggest that in a selected group of patients with aggressive fibromatosis radiotherapy may effectively achieve control of residual disease after surgery without marked disfigurement and loss of function.

Adult↗

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↗

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↗

PubMed1989

Evaporative water loss and epidermis regeneration in partial-thickness wounds dressed with a fluid-retaining versus a clot-inducing wound covering in guinea pigs.

The effects of a new high vapour permeable poly-(ether urethane) (PEU) wound covering on evaporative water loss (EWL) and epidermis regeneration in partial-thickness wounds in guinea pigs were investigated and compared with an occlusive wound covering (OpSite) and air-exposed controls. It was also assessed whether the EWL reflected the phases of epidermis regeneration. In PEU-covered wounds, the initially raised EWL of 100 gm-2h-1 decreased in four days to 30 gm-2h-1, the same level as in occluded wounds. In control wounds this level was only reached after seven days, reflecting slower epidermis regeneration. The results showed that triphasic EWL behaviour corresponded to the sequence of wound healing. There was (1) a constant raised EWL until epidermal resurfacing is complete, (2) a fast EWL decrease during parakeratotic keratinization, and (3) a gradual normalization of the EWL during maturation of the stratum corneum. In wounds covered with OpSite this phasic EWL behaviour did not occur, owing to forced reduction because of the relatively impermeable covering. It was concluded that the PEU wound covering has an ideal water vapour permeance of 22.2 gm-2h-1 kPa-1, as can be seen in the accelerated epidermis regeneration and fast EWL reduction in partial thickness wounds in guinea pigs.

Animals↗

PubMed1988

Malignant hemangiopericytoma in three kindred members of one family.

Three cases of malignant hemangiopericytoma in one family are reported. To our knowledge familial occurrence of malignant hemangiopericytoma has not been described before. Two of these lesions occurred in the head and neck region and one case presented as an intraabdominal tumor. Consanguinity of the parents seems to be likely, suggesting an autosomal recessive mode of inheritance in our family, whereas the similarity in age of onset in these three patients was apparent.

Adult↗

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

New method to assess the water vapour permeance of wound coverings.

A new method for assessing the permeability to water vapour of wound coverings is presented, using the evaporimeter developed by Nilsson. This new method combines the water vapour transmission rate (WVTR) and the vapour pressure difference across a wound covering in one absolute measure: the water vapour permeance (WVP). The WVP of a wound covering is the steady flow (g) of water vapour per unit (m2) area of surface in unit (h) time induced by unit (kPa) vapour pressure difference, g.m-2.h-1.kPa-1. Since the WVP of a wound covering is a more accurate measure for the permeability than the WVTR is, it facilitates the prediction of the water exchange of a wound covering in clinical situations.

Bandages↗

PubMed1988

A clot-inducing wound covering with high vapor permeability: enhancing effects on epidermal wound healing in partial-thickness wounds in guinea pigs.

Although the use of an occlusive wound covering accelerates the reepithelialization of a partial-thickness wound, it has the disadvantage of leading to wound exudate accumulation. The effect of an experimental polyetherurethane (PEU) wound covering with a high vapor permeability was compared with an occlusive wound covering (OpSite covering) and air exposure with respect to the rate of reepithelialization, eventual epidermal thickness, and scab thickness in 122 partial-thickness wounds in guinea pigs. The percentage of reepithelialization on day 2 was 85% in wounds covered with the permeable PEU membrane, whereas it was 66% and 35%, respectively, in wounds covered with the occlusive covering or exposed to air. The epidermal thickness did not differ among the three types of treatment. The scab thickness, however, was maximal in the uncovered air-exposed wounds. We conclude that epidermal wound healing is accelerated when the PEU wound covering is used. This wound-healing-promotion effect is apparently due to the high water vapor permeability of PEU, which induces clotting of the wound exudate, and subsequent jellifying of the clot layer.

Animals↗

PubMed1987

Long-term biologic fate of neoarteries regenerated in microporous, compliant, biodegradable, small-caliber vascular grafts in rats.

Microporous, compliant, biodegradable vascular grafts prepared from a mixture of polyurethane [( PU], 95% weight) and poly-L-lactide [( PLLA] 5% weight) can function as temporary scaffolds for the regeneration of the arterial wall of small-caliber arteries. The purpose of this study was to determine the long-term biologic fate of these neoarteries that were regenerated in PU/PLLA vascular grafts. The PU/PLLA vascular grafts (1.5 mm internal diameter [ID]) were implanted into the abdominal aortas of rats (N = 8) and were evaluated 1 year after implantation by means of macroscopic inspection, light microscopy, and electron microscopy. All implants were patent; three implants were normally shaped, two were slightly dilated (+/- 10% of the original ID), and three implants were aneurysmal. Arterial pulsations were reduced but still visible in the normally shaped implants and absent in the other implants. In all implants, the neointima was complete. The neomedia varied among the implants: In the normally shaped implants, smooth muscle cells were predominantly circularly arranged as in normal arterial tissue; in the other implants, smooth muscle cells were predominantly longitudinally arranged. The neoadventitia showed a completely fragmented graft lattice, which was organized by fibrohistiocytic tissue. These results suggest that the pattern of arrangement of smooth muscle cells in the neomedia determines the ultimate biologic fate of neoarteries regenerated in microporous, compliant, biodegradable vascular grafts. Only those neoarteries with predominantly circularly arranged smooth muscle cells in the neomedia were able to function normally as an arterial substitute for a 1-year period after implantation into the rat abdominal aorta.

Aortic Dissection↗

PubMed1987

Sequential studies of arterial wall regeneration in microporous, compliant, biodegradable small-caliber vascular grafts in rats.

Microporous, compliant, biodegradable vascular grafts prepared from a mixture of polyurethane (95% weight) and poly-L-lactic acid (5% weight) can function as a temporary scaffold for the regeneration of the arterial wall in small-caliber arteries. This study was undertaken to document the sequential events leading to this regeneration. Therefore, polyurethane/poly-L-lactic acid vascular grafts were implanted into the abdominal aorta of rats (N = 28) and were harvested at regular intervals from 1 hour up to 12 weeks after implantation. The implants were evaluated by means of light and electron microscopy. At each time of harvesting, the implants were patent and showed arterial pulsations. No stenosis or dilatation was observed. Endothelial cells grew from the adjacent aortic intima across the anastomoses, from day 6 onward, to form an almost complete neointima after 6 weeks of implantation. Smooth muscle cells also grew from the adjacent aortic media over the graft lattice through the platelet-fibrin coagulum from day 6 onward. The smooth muscle cells, predominantly longitudinally arranged at week 6, but also circularly arranged in some areas at week 12, formed a neomedia in which elastic laminae regenerated. Polymorphonuclear leukocytes and monocytes initially invaded the graft lattices. Fibroblasts, histiocytes, and capillaries grew from the perigraft tissue into the polyurethane/poly-L-lactic acid lattices from day 6 onward, which resulted in the formation of a neoadventitia. The polyurethane/poly-L-lactic acid lattices started to disintegrate from day 12 onward. The regenerative processes in the disintegrating polyurethane/poly-L-lactic acid grafts resulted in the formation of neoarteries, which were of sufficient strength, compliance, and thromboresistance to function as small-caliber arterial substitutes.

Animals↗

PubMed1986

Segmental uterine horn replacement in the rat using a biodegradable microporous synthetic tube.

To investigate the possible use of a biodegradable microporous synthetic tube for fallopian tube replacement, polyetherurethane/poly-L-lactide (PU/PLLA) grafts in the uterine horn of the rat were studied and their patency and healing characteristics compared with those of nonbiodegradable polytetrafluoroethylene (PTFE; Teflon) grafts as well as with those of reanastomosed uterine horns. Regarding the healing characteristics, the PU/PLLA grafts were superior to the PTFE graft, as was indicated by the regeneration of endometrium and the extensive perigraft tissue ingrowth. However, the graft/uterine anastomoses of the PU/PLLA and PTFE grafts became obstructed by a plug of mucosal folds, all reanastomosed, uterine horns in the control experiments remaining open. In conclusion, although biodegradable microporous PU/PLLA uterine horn grafts have better healing characteristics than PTFE grafts, they easily obstruct at the graft/uterine junction. Mucosal suturing and/or the use of splints may contribute to the feasibility of biodegradable microporous artificial fallopian tubes in tubal surgery.

Animals↗

PubMed1985

Regeneration of the arterial wall in microporous, compliant, biodegradable vascular grafts after implantation into the rat abdominal aorta. Ultrastructural observations.

The ultrastructure of a new type of vascular graft, prepared from a mixture of polyurethane (95 weight %) and poly-L-lactic acid (5 weight %), was examined six weeks after implantation into the abdominal aorta of rats. These microporous, compliant, biodegradable, vascular grafts function as temporary scaffolds for the regeneration of the arterial wall. Smooth muscle cells, covering the grafts, regenerated a neo-media underneath an almost completely regenerated endothelial layer (neo-intima). These smooth muscle cells varied in morphology from normal smooth muscle cells to myofibroblasts. They were surrounded by elastic laminae and collagen fibers. Macrophages, epithelioid cells, multinucleated giant cells, fibroblasts and capillaries were present in the disintegrating graft lattices. The epithelioid cells and multinucleated giant cells engulfed polymer particles of the disintegrating grafts. The regeneration of the endothelial and smooth muscle cells is similar to the natural response of arterial tissue upon injury. The presence of macrophages, epithelioid cells, multinucleated giant cells, fibroblasts and capillaries in the graft lattices resembles the natural response of tissue against foreign body implants. Both of these responses result in the formation of a neo-artery that possesses sufficient strength, compliance and thromboresistance to function as a small caliber arterial substitute.

Animals↗

PubMed1985

Arterial wall regeneration in small-caliber vascular grafts in rats. Neoendothelial healing and prostacyclin production.

Clinically available synthetic graft materials frequently fail when used as a small-caliber arterial substitute. Therefore, we developed a new type of graft material, prepared from a mixture of polyurethane and poly-L-lactic acid, to be used as a scaffold for the regeneration of the arterial wall. In this study microporous, compliant, biodegradable polyurethane/poly-L-lactic acid grafts (n = 16) and polytetrafluoroethylene grafts (n = 16) were implanted in the rat abdominal aorta and evaluated 3, 6, and 12 weeks after implantation. First, we evaluated the extent of neoendothelial healing (n = 8) by means of light microscopy and scanning electron microscopy. Next, we studied the ability of the neoendothelial cells to produce prostacyclin (n = 8) by means of bioassay for prostacyclin and radioimmunoassay for its stable hydrolysis product, 6-oxo-prostaglandin F1 alpha. There were no significant differences between the two graft types in the amount of prostacyclin production per unit graft area covered with neoendothelium, and this amount was the same as for normal endothelium. However, the polytetrafluoroethylene grafts showed incomplete neoendothelial healing, even after 12 weeks of implantation, in contrast to the polyurethane/poly-L-lactic acid grafts. The better healing characteristics of the polyurethane/poly-L-lactic acid grafts ensured the fast development of a complete neoarterial wall, possessing strength, compliance, and thromboresistance equivalent to normal arterial wall tissue. These results demonstrate that arterial wall tissue regeneration in polyurethane/poly-L-lactic acid grafts may open new perspectives in the field of arterial reconstructive surgery.

Animals↗

PubMed1984

Radiation-induced structural changes in membrane proteins of human erythrocytes and ghosts and the relation to cellular morphology.

Isolated human erythrocytes and ghosts were irradiated with X-rays under different experimental conditions. The effect of the radiation treatment was examined with regard to the structure of membrane proteins as well as to the morphology of whole cells and ghosts. From sodium dodecyl sulphate/polyacrylamide gel electrophoresis it is concluded that spectrin (band 1 and 2) is the most radiosensitive of the membrane proteins examined. X-irradiation of cells and ghosts induced covalent cross-linking of a small fraction of membrane proteins. In the protein aggregates thus formed spectrin was found to be the major component. Molecular disulphide (-SS-) bridges seemed to account for part of the cross-links observed. Some nondisulphide cross-links were also found, especially when ghosts were irradiated. Significant amounts of spectrin aggregates were formed during post-irradiation incubation at 37 degrees C but not at 4 degrees C. In the intact cell a transformation in shape from discocyte to echinocyte accompanied the process of post-irradiation spectrin aggregation. The characteristics of both processes, such as their reversibility with adenosine, point to a metabolic involvement. It is shown that there is no causal relationship between the two phenomena observed. The possible cause of the post-irradiation effects and the parallelism with similar processes in nonirradiated metabolically depleted cells is discussed.

Electrophoresis, Polyacrylamide Gel↗

PubMed1983

Some applications of scanning electron microscopy for the study of biopsies in central nervous system pathology.

The present report describes SEM observations on a variety of subjects, such as the walls of cerebral ventricles under pathological circumstances (hydrocephalus) as well as the surface morphology of abnormal cavities like arachnoid cysts and subdural hematomas. In the human specimens with hydrocephalus the changes consisted of degeneration of ependymal cilia, progressing to denudation of the ependyma while rupture of the ependymal layer was also seen. In experimental animals where the hydrocephalus was induced by agents (presumably irritant to the tissue), the presence of reactive supraependymal cells was observed next to the manifestations of ependymal degeneration. With the SEM the wall of arachnoid cysts showed numerous microvilli of stubby appearance with interspersed projections of diverse shape in the individual cases. SEM may aid in the diagnosis of arachnoid cysts, particularly in differentiating them from traumatic leptomeningeal cysts.

Animals↗

PubMed1981

The permeability of the blood-brain barrier in acute hypertension. Comparison of an endogenous and exogenous protein tracer.

Experimental acute hypertension in male Wistar rats was produced by metaraminol infusion to systemic blood pressure levels of 190-210 mm Hg. After 20 sec or 30 min the animals were killed by perfusion fixation with 8% formaldehyde perfusion. The barrier passage of exogenous HRP (75 mg i.v.) given 10 min before killing (5 rats) and the passage of endogenous anti-HRP antibodies of the IgG class (8 rats, produced by antigenic stimulation beforehand) were compared electron microscopically by semiquantitation of tracer location in unstained ultrathin sections. Five rats served as controls. The number of tracer-filled vesicles was consistently lower in anti-HRP rats than in HRP rats: not only during acute hypertension but also in the controls. The penetration of both tracers into the basement membrane and brain parenchyma, however, was comparable. Anti-HRP was more prominent in the endothelial cytoplasm. Vesicular transport and penetration through the plasma membrane with diffuse cytoplasmic passage tend to be the most likely transport mechanisms, the former for HRP and the latter for the antibody.

Animals↗

PubMed1981

Human brain in tissue cultures. VI. Presence of glial fibrillary acidic protein in subcultivated human fetal brain cells as demonstrated by immunofluorescent and immunoperoxidase staining.

Glial fibrillary acidic protein (GFAP) was present in cell cultures derived from human fetal brain tissue as determined by indirect immunofluorescence (IF) and immunoperoxidase (IP) staining using rabbit anti-human GFAP antisera. The IF and IP techniques were comparable in localizing the cytoplasmic distribution and the frequent perinuclear concentration of GFAP in brain cells. The horseradish peroxidase technique was more sensitive and a 1:20-1:40 dilution of anti-GFAP serum could be applied in the initial step of the peroxidase staining as compared to a 1:10 dilution of anti-GFAP serum for IF staining. Sequential studies of subcultivated human fetal brain cell lines by these techniques indicated that some brain cell lines become GFAP-negative rapidly, whereas other cell lines remain GFAP-positive for no less than ten subcultivations in vitro. GFA protein was never present in any PML-SV40-transformed human brain cells.

Animals↗