Biomedical subjects

J A Jansen

Publications and source records attributed to J A Jansen.

At least 91 records · Page 5Linked to original sources

PubMed2000

Early spreading events of fibroblasts on microgrooved substrates.

We investigated the "contact guidance" phenomenon, shortly after cell attachment. For this purpose polystyrene substrates were produced, either smooth, or equipped with micogrooves (depth 0.5 micrometer, width 1-10 micrometer). On these substrates, fibroblasts were cultured for 15, 30, 45, 60, 120, or 240 min. Subsequently, they were studied with light microscopy, scanning electron microscopy, confocal laser scanning microscopy, and digital image analysis. Up to 1 h, cell attachment on the grooved substrates was impaired. Further, cells oriented to the direction of the microgrooves. This orientation was established fastest on the narrow grooves. After 30 min, cells showed abundant membrane extensions in all directions. Well-formed actin filaments were not present in the cell body at timepoints before 4 h. Furthermore, cells on smooth surfaces exhibited less filaments. The addition of cytochalasin-B only caused a delay of cell attachment and spreading. From these experiments, we conclude that a well-formed cellular actin cytoskeleton is no prerequisite for the occurrence of contact guidance. Actin microfilaments in the lamellipodia, and the interplay between the lamellipodium and extracellular matrix molecules seem to be the determining factor in the establishment of contact guidance.

Actins↗

PubMed2000

Wound healing around bone-anchored percutaneous devices in experimental diabetes mellitus.

The objective of this investigation was to study the influence of impaired wound healing on the tissue response to bone-anchored percutaneous devices. For this reason, diabetes mellitus was induced in rabbits with alloxan. Untreated rabbits were used as controls. Skin-penetrating titanium implants were inserted in the tibial bone of diabetic and healthy animals. The enossal part of half of the implants was provided with a thin magnetron-sputtered calcium-phosphate coating. The soft-tissue and bone response was evaluated clinically, histologically, and histomorphometrically. We did not observe more infectious complications in diabetic animals. Furthermore, histological analysis revealed no differences in soft-tissue response between diabetic and healthy animals. A close bone-implant contact was observed for all implants. Nevertheless, the density of cortical bone around the implants was clearly lower in diabetic animals compared with control animals. In control rabbits, but not diabetic animals, coated implants showed more downgrowth of bone into the marrow cavity than uncoated ones. In general, diabetes mellitus was shown to have no adverse effect on the clinical performance of the percutaneous devices. We think that this is due to the good fixation of the implants in diabetic as well as control animals. Therefore, we conclude that the presence of impaired healing in chronic health disorders like diabetes is no contra-indication for the anchorage of percutaneous implants in cortical bone.

Animals↗

PubMed2000

The influence of impaired wound healing on the tissue reaction to percutaneous devices using titanium fiber mesh anchorage.

The objective of this investigation was to study the influence of impaired wound healing on the soft-tissue response to percutaneous devices using titanium fiber mesh anchorage. For this reason, diabetes mellitus was induced in rabbits with alloxan. Untreated rabbits were used as controls. Two implant types were inserted subcutaneously: two-stage percutaneous devices as well as separate titanium fiber mesh sheets. The soft-tissue response to both implants was assessed by clinical, histologic, and histomorphometric evaluation. Clinically, we observed a higher number of infectious complications around percutaneous implants in diabetic animals. Histologic and histomorphometric analyses revealed that severe diabetes effected matrix maturation and delayed neovascularization (p<0.05). We also observed higher numbers of inflammatory cells in the mesh porosity of percutaneous implants in severely diabetic animals (p = 0.09). Our results indicate that severe, uncontrolled diabetes negatively influences the maturity and neovascularization of connective tissue inside the fiber mesh porosity. The higher number of infectious complications in diabetic animals suggests that the presence of impaired healing conditions facilitates infection around skin penetrating devices.

Animals↗

PubMed2000

Bone formation in calcium-phosphate-coated titanium mesh.

The osteogenic activity of porous titanium fiber mesh and calcium phosphate (Ca-P)-coated titanium fiber mesh loaded with cultured syngeneic osteogenic cells was compared in a syngeneic rat ectopic assay model. In 30 syngeneic rats, (Ca-P)-coated and non-coated porous titanium implants were subcutaneously placed either without or loaded with cultured rat bone marrow (RBM) cells. Fluorochrome bone markers were injected at 2, 4, and 6 weeks. The rats were sacrificed, and the implants were retrieved at 2, 4, and 8 weeks post-operatively. Histological analysis demonstrated that none of the (Ca-P)-coated and non-coated meshes alone supported bone formation at any time period. In RBM-loaded implants, bone formation started at 2 weeks. At 4 weeks, bone formation increased. However, at 8 weeks bone formation was absent in the non-coated titanium implants, while it had remained in the (Ca-P)-coated titanium implants. Also, in (Ca-P)-coated implants more bone was formed than in non-coated samples. In general, osteogenesis was characterized by the occurrence of multiple spheres in the porosity of the mesh. The accumulation sequence of the fluorochrome markers showed that the newly formed bone was deposited in a centrifugal manner starting at the center of a pore. Our results show that the combination of Ti-mesh with RBM cells can indeed generate bone formation. Further, our results confirm that a thin Ca-P coating can have a beneficial effect on the bone-generating properties of a scaffold material.

Animals↗

PubMed2000

Biocompatibility evaluation of sol-gel coatings for subcutaneously implantable glucose sensors.

The objective of the current investigation is to determine the soft-tissue biocompatibility of sol-gel matrices which can be used to optimize the properties of implantable glucose sensors. The biocompatibility of sol-gel matrices with heparin, dextran sulphate, Nafion, polyethylene glycol, and polystyrene sulphonate was examined in vitro in simulated body fluid and with cell culture experiments using human dermal fibroblasts. Finally, an in vivo study was performed. Therefore, sol-gel coated polystyrene discs were inserted subcutaneously in the back of rabbits. After 4 and 12 weeks, the implants with surrounding tissue were retrieved and processed histologically. In simulated body fluid, the formation of a granular calcium phosphate precipitate was observed. Cell proliferation on polyethylene glycol, Nafion, and heparin coated substrates was comparable to control samples and significantly higher than on dextran sulphate and polystyrene sulphate coated substrates. Light microscopic evaluation of the retrieved in vivo samples showed a fair tissue reaction to all materials. Histomorphometric analysis demonstrated that there were no differences in tissue response to the different sol-gel coatings. In conclusion, sol-gel matrices exhibit a fair biocompatibility both in vitro and in vivo. These results will form the basis for further research into the real merits of sol-gel coatings in optimizing the properties of subcutaneously implantable glucose sensors.

Animals↗

PubMed2000

Microgrooved silicone subcutaneous implants in guinea pigs.

Cell-substratum interactions are of fundamental importance for the reaction of body tissues to surgically implanted foreign materials. In our study we investigated the influence of 2 microm wide microgrooves, with various depths (0.5-6 microm), on capsule formation around subcutaneous silicone implants, in an animal experiment. Silicone sheets with microtexture were glued around silicone tubes. These implants were placed subcutaneously in eight guinea pigs for 10 weeks. The implanted tubes were removed including all surrounding tissues, and processed for light microscopy and subsequent histomorphometrical evaluation. All removed implants were surrounded by a thin fibrous capsule, and it was observed that this capsule was separated from the implants by a thin, single layer of mono- and multinucleated phagocytotic cells. In histomorphometry no significant differences were seen in relation to the reaction towards the various textures. We conclude that microtextures do not have an effect on the morphological characteristics of capsule formation around silicone implants in soft tissue.

Animals↗

PubMed2000

A percutaneous device to study glucose kinetics in subcutaneous tissue fluid.

In the current study subcutaneous glucose kinetics were investigated in tissue fluid collected with a percutaneous device (PD). PDs containing a subcutaneous tissue chamber were implanted subcutaneously in New Zealand white rabbits. Sintered titanium fiber mesh sheets were used for subcutaneous anchorage of the PD. The bottom of the subcutaneous tissue chamber was either covered with a titanium fiber mesh sheet, a cellulose acetate membrane, or left uncovered. Subcutaneous glucose kinetics were determined after injection of octreotide and glucagon. The tissue reaction to the implants was evaluated histologically. No dynamic relationship was observed between glycaemia and subcutaneous tissue fluid glucose for all membrane covered devices. Histological evaluation showed that the presence of a seroma cavity in combination with obstruction of the membrane prevented adjustment of the subcutaneous glucose concentration in response to changes in glycaemia. In the uncovered devices, on the other hand, changes in glycaemia were reflected in subcutaneous tissue fluid. Our results prove that it is possible to measure changes in the glucose concentration in subcutaneous tissue fluid collected with a percutaneous device. Therefore, we conclude that a percutaneous device has an application as model to study the in vivo performance of implantable glucose sensors. The use of porous membranes in such devices has to be avoided.

Journal Article↗

PubMed2000

Effect of surface roughness and calcium phosphate coating on the implant/bone response.

The influence of surface roughness and calcium phosphate (Ca-P) coating on the bone response of titanium implants was investigated. Four types of titanium implants, i.e. as-machined, grit blasted, as-machined with Ca-P sputter coating, and grit blasted with Ca-P sputter coating, were prepared. The Ca-P sputter-coating, produced by using the RF magnetron sputter technique, was rapid heat-treated with infrared radiation at 600 degrees C. These implants were inserted into the left and right femoral condyles and the left and right tibial diaphyses of the rabbits. After implantation periods of 2 and 12 weeks, the bone-implant interface was evaluated histologically and histomorphometrically. Histological evaluation revealed no new bone formation around different implant materials after 2 weeks of implantation. After 12 weeks, bone healing was almost completed. For both tibial and femoral implants, Ca-P coated implants always showed a higher amount of bone contact than either of the non-coated implants. On the other hand, surface roughness improved only the response to implants inserted into the tibial diaphysis. On the basis of these findings, we concluded that 1) deposition of a sputtered Ca-P coating on an implant has a beneficial effect on the bone response to this implant during the healing phase, and 2) besides implant surface conditions the bone response is also determined by local implant site conditions.

Aluminum Oxide↗

PubMed2000

A mechanical evaluation of TiO2-gritblasted and Ca-P magnetron sputter coated implants placed into the trabecular bone of the goat: Part 1.

The influence of Ca-P magnetron sputter coated implants on the mechanical anchorage was evaluated in a goat model. Therefore, uncoated and coated screw designed commercially pure titanium TiO2-blasted implants were inserted into the trabecular bone of the femoral condyles of 12 goats. The thicknesses of the coatings were 0.1 micron (CaP-0.1), 1.0 micron (CaP-1) and 4.0 microns (CaP-4). In addition, uncoated TiO2-blasted implants (Ti) were used as control. Evaluation of the interface strength and appearance, using torque test and scanning electron microscopy, was done at implantation periods of 6 and 12 weeks. Although, especially at 6 weeks of implantation, the Ca-P coated implants showed higher failure torque values than the TiO2 blasted implants, the observed differences for type of implant and evaluation period were not significant (P > 0.1). SEM evaluation showed that all implants with failure values of more than 100 N conducted bone growth into their screw threads. In addition, we observed that the fracture plane for the CaP-4 implants was situated at the coating-implant interface or inside the coating. For the CaP-1 and CaP-0.1 the fracture line could not be determined definitely. For the Ti implants, the fracture torque testing resulted in failure at the bone-implant interface. Therefore, we conclude that all implants resulted in a good bonding strength with the surrounding bone. The sputtered Ca-P coatings seemed to improve the initial fixation of the TiO2 blasted implants.

Animals↗

PubMed2000

A histological evaluation of TiO2-gritblasted and Ca-P magnetron sputter coated implants placed into the trabecular bone of the goat: Part 2.

The aim of this study was to investigate the synergetic influence of surface topography and chemical composition of oral implant materials on bone response. For the experiment screw designed implants were used. The implants were grit-blasted with TiO2 particles. The implants were left uncoated (Ti) or provided with three different amorphous/crystalline Ca-P magnetron sputter coatings, resp. 0.1 micron (CaP-0.1), 1 micron (CaP-1) and 4 microns (CaP-4), in thickness. The implants were inserted in the medial femoral condyles of 12 goats. Each femur received 2 implants. After implantation periods of 6 and 12 weeks the implants were retrieved and prepared for histological and histomorphometrical evaluation (bone contact and bone mass). The light microscopy revealed that bone response to CaP-4 and CaP-1 implants was similar. For example, after 12 weeks, screw threads were almost completely covered with bone. In contrast to CaP-0.1 and Ti implants, where bone apposition was less pronounced. Histomorphometry demonstrated that the bone-to-implant contact for the CaP-1 and CaP-4 implants was significantly higher (P < 0.05) than for the CaP-0.1 and Ti implants. This difference existed already after 6 weeks and was even enhanced after 12 weeks. The bone mass measurements revealed that only at 12 weeks CaP-4 implants had significantly more bone contact inside the screw threads than non-coated Ti-implants (P < 0.05). Supported by our findings, we conclude that the additional application of a 1-4 microns thick Ca-P magnetron sputter coating can further improve the healing response to surface roughened oral implants placed into trabecular bone.

Analysis of Variance↗

PubMed2000

Effect of microgrooved poly-l-lactic (PLA) surfaces on proliferation, cytoskeletal organization, and mineralized matrix formation of rat bone marrow cells.

Previous experiments showed that microgrooved substrate surfaces can influence the in vitro behavior of osteoblast-like rat bone marrow (RBM) cells. Cellular morphology and matrix deposition can be directed by substrate chemistry and topography. RBM cells cultured on poly-l-lactic acid (PLA) exhibit increased mineralization and alkaline phosphatase activity compared to polystyrene substrates. Consequently, the purpose of the present in vitro study is to further evaluate the behavior of RBM cells on microgrooved (groove depth 0.5 to 1.5 microns, groove and ridge width 1 to 10 microns) polystyrene (PS) and PLA surfaces. Besides grooved, also smooth control surfaces were made. Our results confirmed that microtextured surfaces are capable of influencing the behavior of the osteoblast-like RBM cells in vitro. Microtopography did not influence the RBM proliferation rate, or cellular actin organization. However, confocal laser scanning microscopy showed that cellular attachment is dependent on the applied material. Also clear differences were found between textured PS and PLA, with regard to the calcium content. We therefore conclude, that the application of microtextures could possibly influence the bone regeneration around biodegradable PLA devices.

Absorbable Implants↗

PubMed2000

Influence of transforming growth factor-beta3 on fibrous capsule formation around microgrooved subcutaneous implants in vivo.

Previous studies have shown that addition of transforming growth factor-beta3 (TGF-beta3) is capable of reducing scar tissue formation in skin defects. Therefore, we examined whether TGF-beta3 can also influence the organization of a fibrous capsule around implants in vivo. For this reason, 24 silicone implants with microgrooves with a groove depth of 1.0 microm and a ridge and groove width of 10.0 microm were made and loaded with human recombinant TGF-beta3 (0, 5, 50, and 250 ng). An in vitro release enzyme-linked immunosorbent assay (ELISA) test was done with another 10 implants to estimate the amount of TGF released from the implants. The implants were inserted subcutaneously in the backs of 6 guinea pigs. Each animal received four implants, which were left in place for 10 weeks. At the end of the implantation time, the implants were retrieved, embedded, and processed for histology. Histomorphometrical measurements were done on the capsule formation and the implant-cell interface quality and quantity. The results showed a fibrous capsule of 15 microm up to 50 microm thickness around all implants. There were no significant differences between the TGF-beta3-loaded implants or the controls. Frequently, inflammatory cells were present in the capsule. The implant-tissue interface was on average between 5 and 15 microm thick and consisted mostly out of one or two layers of macrophages or foreign body giant cells. Statistical analysis again showed no significant differences between the various TGF-beta3-coated implants and controls. Finally, we concluded that a microtextured surface can indeed be used for the release of TGF-beta3. On the other hand, this did not result in major differences in wound healing between implants loaded with 5, 50, or 250 ng of TGF-beta3 and controls.

Animals↗

PubMed2000

Biting and chewing in overdentures, full dentures, and natural dentitions.

It has been suggested that the provision of dental implants can improve the oral function of subjects with severely resorbed mandibles, possibly restoring function to the level experienced by satisfied wearers of conventional complete dentures. Nevertheless, a quantitative comparison has never been made and can be drawn from the literature only with difficulty, since studies differ greatly in methodology. To make such a comparison, we measured bite force and chewing efficiency by using identical methods in subjects with overdentures, complete full dentures, and natural dentitions. Our results indicated that bite forces achieved with overdentures on dental implants were between those achieved with artificial and natural dentitions. Chewing efficiency was significantly greater than that of subjects with full dentures (low mandible), but was still lower than that of subjects with full dentures (high mandible) and overdentures on bare roots. Differences in the height of the mandible revealed significant differences in chewing efficiency between the two full-denture groups. Furthermore, subjects with a shortened dental arch exerted bite forces similar to those of subjects with a complete-natural dentition, but their chewing efficiency was limited due to the reduced occlusal area. For all groups combined, a significant correlation was found between maximum bite force and chewing efficiency. Nearly half of the variation in chewing efficiency was explained by bite force alone.

Adult↗

PubMed2000

The effects of selected drugs on the in vitro protein binding of repaglinide in human plasma.

This study investigated plasma protein binding by the novel oral hypoglycemic agent, repaglinide, and assessed the influence of other protein-bound drugs upon this process. Varying concentrations of [3H]-repaglinide (0.01 to 100 micrograms/ml) were incubated in solutions of plasma proteins (human serum albumin, HSA; alpha 1-acid glycoprotein, AAGP), or human plasma in the absence or presence of several test drugs. Protein binding was assessed using an ultrafiltration technique. At all concentrations tested, the mean binding of repaglinide in plasma was 98.5%, binding to HSA averaged 98.6%, and the binding to AAGP was saturable and remained below 50%. Warfarin 10 micrograms/ml, furosemide 0.2 microgram/ml, and tolbutamide 100 micrograms/ml, significantly reduced in vitro binding of repaglinide at 1 and 100 micrograms/ml versus control (p < 0.05), producing an 18-36% increase in free repaglinide. No reduction was found using 0.1 microgram/ml repaglinide. Diazepam, glibenclamide and nicardipine hydrochloride had no significant effects on the in vitro protein binding of repaglinide. These data suggest that the binding of repaglinide to HSA in human plasma has potential clinical significance, and that within the therapeutic range for repaglinide, the presence of the test drugs has no clinically relevant effects on repaglinide binding to plasma proteins.

Adsorption↗

PubMed1999

Biological and migrational characteristics of transponders implanted into beagle dogs.

Ninety transponders (microchips), 45 made of bioglass, 30 made of acid-etched bioglass, and 15 made of bioglass and provided with a polypropylene cap, were inserted into 15 dogs in six different locations: on the left and right side of the head, and on the left and right shoulders, both cranial and caudal to the dorsum. The transponders were left in place for 16 weeks, during which their position was determined by means of an electronic reader and radiographs, and they were then retrieved and examined histologically. A clinical evaluation revealed that about half of the transponders inserted in all the shoulder locations had migrated to some extent, whereas the transponders in the head location had hardly moved. There were no differences in the extent of migration between the different types of transponders. Histological analysis showed that almost all the transponders were surrounded by a thin fibrous capsule with no sign of any gross inflammatory reaction.

Animal Identification Systems↗

PubMed1999

Attachment of fibroblasts on smooth and microgrooved polystyrene.

In this study rat dermal fibroblasts (RDFs) were cultured on smooth or microgrooved (1-20 microm wide, 0.5-5.4 microm deep) substrates. Polystyrene microgrooved substrates were produced by solvent casting on molds that had been produced by photolithographic techniques. We investigated the attachment of RDFs with various analytical techniques. Light microscopy and image analysis showed that RDFs were oriented on most microgrooves. The rate of orientation effectively was increased by an increase of groove depth. An analysis of confluent layers of RDF showed that at confluency microgrooves were able to support greater numbers of cells. However, the largest numbers of cells were not found on the narrowest and deepest microgrooves even though such microgrooves have the largest total surface and induce the strongest alignment. Interference reflection microscopy (IRM) showed that the RDFs form focal adhesions where the cell membrane is only 10 nm from the substrate. IRM also showed that RDFs follow the contours of shallow and wide microgrooves but bridge the grooves on deeper and narrower ones. This could explain why such grooves are not able to increase the numerical cell adhesion to a greater degree. The absence of contact between cells and the bottom of the grooves is a very important factor in establishing contact guidance.

Algorithms↗

PubMed1999

Contact guidance of rat fibroblasts on various implant materials.

Providing a substrate surface with micrometer-sized parallel grooves influences the behavior of cells growing on such substrates in vitro. Cells elongate in the direction of the groove and migrate guided by the grooves. It has been suggested that cellular alignment on microgrooves is predominantly dependent on groove dimensions and that surface chemical variation of the substrate material has little effect. Therefore we seeded primary rat dermal fibroblasts (RDF) on smooth and microgrooved (groove width 1-10 microm, depth 0.5 microm) polystyrene (PS), poly-L-lactic acid (PLA), silicone (SIL), and titanium (Ti) substrates. The production process was found to be more accurate for PS and PLA than for SIL and Ti substrates. A proliferation study, scanning electron microscopy, confocal laser scanning microscopy, and transmission electron microscopy revealed differences between RDF behavior on the materials. Our conclusions are (1) the accuracy of microtexture production by casting depends greatly on the material used; (2) even if no sharp discontinuities are present, microtextures still are potent tools for inducing contact guidance; and (3) besides surface texture, surface chemistry has a definitive influence on cell morphology.

Animals↗

PubMed1999

The effect of poly-L-lactic acid with parallel surface micro groove on osteoblast-like cells in vitro.

In this study we evaluated the behavior of rat bone marrow (RBM) cells on microgrooved poly-L-lactic acid (PLA) and polystyrene (PS) surfaces. The applied groove depth was 0.5, 1.0 or 1.5 microns, with a groove and ridge width of 1, 2, 5 or 10 microns. Scanning electron microscopical examination showed that a collagen-rich mineralized layer of extracellular matrix (ECM) was deposited. Alignment of the cells and matrix to the surface grooves was observed as described before. Quantitative evaluation, using a tetracycline labeling assay, revealed that more mineralized ECM was formed on the PLA than on the PS. Further, PLA surfaces with a groove depth of 1.0 micron and groove widths of 1 and 2 microns induced most mineralized ECM. Finally, alkaline phosphatase activity was also higher on most microgrooved PLA surfaces, compared with the other materials. On the basis of these observations, we concluded that microtextured surfaces are able to influence the differentiation of osteoblast-like cells and the deposition of mineralized matrix. Probably, this phenomenon can be used to increase the bone regeneration around oral implants.

Alkaline Phosphatase↗