H. K. Koerten

Reactions of cells at implant surfaces

The surface of implants is an important parameter in host-implant integration. Several strategies can be used to obtain integration, such as the application of grooves or pores at the implant surface. Most of these surface alterations, however, will lead to an increase of total implant surface area which might influence the inflammatory response to an implant. As far as integration with bone is concerned several biomaterials have been successful in mimicking this material, by having similar crystals at their surface (calcium phosphate ceramics) or by containing a certain amount of calcium and phosphorus. Polyactive, a poly(ethylene oxide)-poly(butylene terephthalate) segmented copolymer, also possesses favourable integration properties with bone, but initially lacks calcium and phosphorus. It is proposed that the application of hydrogels as biomaterial may add a new dimension to integration capacity.

In vivo degradation of processed dermal sheep collagen evaluated with transmission electron microscopy

The in vivo degradation of hexamethylenediisocyanate-tanned dermal sheep collagen was studied with transmission electron microscopy. Discs of hexamethylenediisocyanate-tanned dermal sheep collagen were subcutaneously implanted in rats. Both an intra- and an extracellular route of degradation could be distinguished. In addition to normal components of a typical foreign body reaction, remarkable phenomena, such as locally deviant neutrophil morphology, infiltration of basophil-like cells, indications of foreign body multinucleate giant cells formed from different cell types, aluminium silicate accumulations and calcium phosphate depositions, were observed. Foreign body multinucleate giant cells intracellularly degraded hexamethylenediisocyanate-tanned dermal sheep collagen after internalization. Both internalized and cellularly enveloped hexamethylenediisocyanate-tanned dermal sheep collagen degraded by the detachment of fibrils. Another extracellular route of degradation was characterized by calcium phosphate depositions in large bundles of hexamethylenediisocyanate-tanned dermal sheep collagen. From 6 wk, the hexamethylenediisocyanate-tanned dermal sheep collagen implant was replaced by rat connective tissue, which was subsequently also degraded. After 15 wk, the presence of basophil-like foreign body multinucleated giant cells containing aluminium/silicon-crystalline accumulations still persisted. These phenomena were related to the specific nature of the material used and suggest cytotoxicity. They emphasize the need for detailed evaluation at the ultrastructural level of newly developed biomaterials before they can be used for medical applications.

Some characteristics of hydroxylapatite powder particles after plasma spraying

We have studied the particles of hydroxylapatite (HA) powder, the particles after plasma spraying, their distribution on substrate surface and their condition after transfer through the plasma torch. Mean particle size of HA powders was as follows: HA-A: 3.8 microm, HA-B 88.2 microm. The area of HA coating after plasma spraying, when the torch had a constant position against the substrate surface, shows two characteristic zones: the central part of coating formed mainly from deformed particles and the marginal part of coating with small non-deformed particles. These small non-deformed particles can be found in all zones of the coating and together with greater non-deformed particles and partially deformed particles will unfavourably affect the adhesive and cohesive strength of the coating and its porosity. The maximum diameter of the molten (spherical) particles in the conditions of Ar + H2 plasma, output P = 24 kW was: DA = 25 microm (HA-A) and DB = 65 microm (HA-B). The intervals of dimensions in which most of molten particles occurred were HA-A: 0-15 microm (98%), HA-B: 5-35 microm (84%). From comparison of HA-A and HA-B powders it can be concluded that the transport of HA-A powder was not continuous, the amount of molten HA-A particles was considerably greater (90%) than that of HA-B powder (63%). Phase decomposition and also solubility of HA-A powder (at in vitro tests) was greater. If we consider transport of particles, their melting, splitting and spraying efficiency, the suitable size of HA powder particles for the given spraying conditions is somewhere between the size of HA-A and HA-B particles--let us say--in the interval from 20 to 60 microm.

Biocompatibility of wear-resistant coatings in orthopaedic surgery in vitro testing with human fibroblast cell cultures

The in vitro biocompatibility of six wear-resistant coatings that were devised as an alternative to polyethylene in resurfacing hip arthroplasties was assessed. The coatings were applied on glass-cover slips via the chemical vapour deposition (CVD) and physical vapour deposition (PVD) methods. Testing was performed in human fibroblast cultures and toxicity was evaluated by use of total cell surface quantitation, light and scanning electron microscopy. Multiple cracks were observed in the tungstenhydrogencarbide (WCH) and chromiumcarbide (CrC) coatings immediately after adding the growth medium. These surface alterations were not related to the presence of fibroblasts. Because of these surface changes, the general biocompatibility of WCH and CrC could not be assessed. Chromiumoxide (Cr2O3) caused severe alterations in cellular morphology followed by significant cytotoxicity. Alumina (Al2O3), titaniumnitride (TiN) and titaniumcarbide (TiC) coatings caused no adverse effects on cells in culture. The fibroblasts showed a rapid and logarithmically stable growth curve on these three materials. They merit further investigation as a wear-resistant coating for orthopaedic implants.

The use of vibratome sections for the ruthenium tetroxide protocol: a key for optimal visualization of epidermal lipid bilayers of the entire human stratum corneum in transmission electron microscopy.

In this paper we describe a preparative procedure which allows maximal visualization of all lipid bilayers in the human stratum corneum (SC). We used 50‐μm‐thick vibratome sections of paraformaldehyde/glutaraldehyde‐fixed human skin. The sections were post‐fixed in 1% osmium tetroxide and 0.5% ruthenium tetroxide. The vibratome sections were dehydrated only in 70% ethanol in order to prevent dissolution of the lipids. u2003Lipid bilayers, including the alternating electron‐dense and electron‐lucent lamellae, were visible between all cell layers of the SC. In addition, this preparative procedure also appeared to be excellent for the ultrastructural preservation of lamellar bodies.

Cellular reaction on the intraperitoneal injection of four types of polylactide particulates

Four types of polylactide particulates, P-L-LA 100, 250, 550 KD and a P-DL-LA 400 KD were injected into the peritoneal cavity of mice. The inflammatory reaction showed an increase in cell number (mainly neutrophilic granulocytes) up to 48 h after which the cell numbers decreased below the control (phosphate-buffered saline). All four polylactide particulates aggregated and intermingled with inflammatory cells. The aggregates remained throughout the investigation period of 6 months. Quantitative measurements showed that standardization of the particle form and size is essential. From this study and other experiments in which calcium phosphates and asbestos were injected intraperitoneally, it is concluded that the inflammatory response observed in the peritoneal cavity is related to the type of material injected and probably to form and size of the individual particles, but not to molecular weight.

The effect of biological environment on the surface of titanium and plasma-sprayed layer of hydroxylapatite.

The solubility of titanium samples with different surface coatings, i.e., hydroxylapatite (HA) powders, a two-layer coating of ZrO5+HA on a titanium substrate in solution and of tooth implants after long-term functioning in the human organism, was studied. A minimum difference in solubility of titanium samples with different surface finishes (polished or grit blasted) was established. For the HA powders and coatings, the lowest solubility was observed with a coarse-grained HA–B powder and a coating made of that powder. Clinical tests of tooth implants after long implantation times were performed. A titanium implant (implantation 12 y), a titanium implant with a two-layer coating of ZrO5+HA–A (implantation time 4 y) and a titanium implant with a two-layer coating of Al5O3+3% TiO2)+ HA–A (implantation time 6 y) were studied. The results show that the titanium surface and HA–A layers were dissolved. Nevertheless, after 6 y implantation, total removal of HA–A coating from that part of implant set into the bone, was not observed.

Analysis of primary bone formation in porous alumina: a fluorescence and scanning electron microscopic study of marrow cell induced osteogenesis.

Porous alumina ceramics alone and combined with rat marrow cells were implanted subcutaneously in the back of syngeneic Fischer rats. Fluorochrome-labeling was performed post operatively and the ceramics were harvested 6 and 8 weeks after implantation. Undecalcified sections of the implants were observed under fluorescence microscopy and the de novo bone-ceramic interfacial areas were analyzed by a scanning electron microscope equipped with an electron probe microanalyzer. Alumina ceramics alone did not show any bone formation, while all marrow cell loaded ceramics showed new bone formation 6 and 8 weeks after implantation. Bone formation was first observed in the center of the pores and proceeded in a centrifugal direction, leading to contact with the ceramic. These results suggest that bone marrow cells have inherent osteogenic capacity and in the pore region of alumina ceramics progression of the osteogenesis causes the dissipation of intervening fibrous tissue between the de novo bone and alumina ceramic surface.

Biodegradation-Dependent Trace Element Accumulation: A Study on Calcium Phosphate Ceramics and Polymers

Rontgen microanalysis revealed the accumulation of trace elements such as silicon, titanium, aluminum, iron, and chromium in electron-dense inclusion bodies in the cytoplasm of phagocytes associated with the implantation of a tricalcium phosphate ceramic, EstaneR polyether urethane, HPOE/PBT copolymer or polypropylene oxide into the rat middle ear. The constituent element magnesium was found as well. In only one case did hydroxyapatite implanted in the human middle ear give rise to the presence of these elements in phagocyte cytoplasm, and trace element accumulation at the implantation site was not found for SilasticR implants.