Biomedical subjects

K de Groot

Publications and source records attributed to K de Groot.

At least 91 records · Page 5Linked to original sources

PubMed1997

Influence of substrate material and surface finishing on the morphology of the calcium-phosphate coating.

The formation of an apatite-like layer was achieved by immersing Ti-6A1-4V, Ti-Al-2.5Fe, and 316 L stainless-steel substrata in Hank's balanced salt solution (HBSS). The layer was characterized by surface analysis techniques, namely X-ray microanalysis and X-ray diffraction, and the morphology was observed by scanning electron microscopy and atomic force microscopy. The concentrations of Ca and P were monitored as a function of time. The morphology of the precipitate layer seems to be dependent both on the type of metal substrate and its surface finish. Polished Ti-6A1-4V and Ti-Al-2.5Fe surfaces exhibit a plate precipitate morphology, whereas rougher surfaces show scattered crystal-like precipitation. The results suggest that the layer produced by immersion of polished titanium alloys in HBSS is constituted by an amorphous apatite.

Alloys↗

PubMed1997

In vitro calcium phosphate formation on a natural composite material, bamboo.

A natural self-reinforced composite material, bamboo, is studied for the first time as a biomedical material. Its anatomical structure was investigated and its mechanical properties were measured and compared with those of some common bone-bonding or bone-repairing biomaterials. It is found that, among all kinds of biomaterials, bamboo has the closest modulus of elasticity to human long bone. The cytotoxicity of bamboo was tested using the agar overlay method before and after heat or chemical treatments. The results reveal that ethanol, methanol and toluene can remove toxic leachable components from bamboo to some extent through extraction. After grafting a polymer whose molecule includes poly(ethylene glycol), alpha,omega-di(aminopropyl)poly(ethylene glycol) 800 on bamboo, bamboo has the ability to form a calcium phosphate coating after being immersed in calcification solution (simulated body fluid and accelerated calcification solution). The characteristics and the morphology of the mineral formed on bamboo were studied by infrared spectroscopy and scanning electron microscopy.

Apatites↗

PubMed1997

In vivo study of calcium phosphate cements: implantation of an alpha-tricalcium phosphate/dicalcium phosphate dibasic/tetracalcium phosphate monoxide cement paste.

alpha-Tricalcium phosphate (alpha-TCP)/dicalcium phosphate dibasic (DCPD)/tetracalcium phosphate monoxide (TeCP) cement was implanted in paste form into soft tissue (rate subcutaneous sockets) and bone tissue (defects in rabbit mandibles) to evaluate the setting behaviour of the cement and tissue responses to the cement. A histological study of the soft tissue implants revealed thin fibrous capsule formation, the appearance of multinucleated giant cells on and close to the cement surface, and small clusters of the cement near the main part of the set cement which were formed by the migration of the paste while setting. X-ray diffraction (XRD) analysis of the implanted cement showed peaks for hydroxyapatite (HA) which increased as the implant period increased. Histology and microradiography of the bone tissue implants showed well-set cement without migration, active bone formation around the cement and direct bone union to it. However, the cement disappeared from the implant site in 4 of 16 specimens where intense bleeding seemed to wash away the implants while setting. From the results of the present study, we concluded that the cement is well tolerated, especially by bone tissue. This may be related to the fact that the cement sets producing HA. The cement is a promising material as a bone substitute; however, there is a problem of migration while setting in soft tissue and of exclusion from the bone defects by intense bleeding.

Animals↗

PubMed1997

Stability of radiofrequency magnetron sputtered calcium phosphate coatings under cyclically loaded conditions.

The stability of radiofrequency (RF) magnetron sputtered calcium phosphate was studied under cyclically loaded conditions. The coatings were deposited on titanium bars and tested in either dry or wet conditions X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and Fourier transform infrared (FTIR) spectroscopy were used to characterize the as-sputtered and tested coatings. XRD demonstrated that the amorphous structure after annealing at 650 C changed into a crystalline apatite structure. The residual stresses were determined by the XRD cos 2 i/i method. These residual film stresses were influenced by the coating conditions and the crystalline sputtered coating showed the presence of compressive stresses. SEM demonstrated that, after cyclic loading conditions in air, the crystalline sputter-coated Ti-6A1-4V bars showed a partial coating loss. Furthermore, in wet conditions (simulated body fluid) only the heat-treated sputter-coated bars appeared to be stable. On the other hand, the amorphous coating only showed signs of delamination in the more highly stressed regions, while in the less stressed regions a Ca-P precipitate was formed. On the basis of these results we conclude that calcium phosphate coatings subjected to cyclic loading conditions show an important difference in fatigue behaviour when tested in either dry or wet conditions.

Absorptiometry, Photon↗

PubMed1997

Hydrolysis and phase transition of alpha-tricalcium phosphate.

Increasing attention has been paid in recent years to alpha-tricalcium phosphate (alpha-TCP), which is used as the main constituent of calcium phosphate bioactive bone cements and biphasic calcium phosphate ceramics. Its hydrolysis and conversion into apatite phase may play an important role in new bone formation in vivo. In this experiment, alpha-TCP powder was made and immersed in deionized water. The morphology change and phase composition were analysed before and after immersion. Based on the results of hydrolysis, a formula for the converted apatite-TCP phase containing lattice water was put forward and a partial structural model along the hydroxyl column was proposed.

Biocompatible Materials↗

PubMed1997

Formation and characteristics of the apatite layer on plasma-sprayed hydroxyapatite coatings in simulated body fluid.

Plasma-sprayed hydroxyapatite (HA) coatings were incubated in simulated body fluids (SBFs) for different periods of time to investigate the nucleation and growth of apatite on their surface. The layer that formed was recognized as having similarities to bone apatite because it is poorly crystallized, non-stoichiometric or calcium deficient, and contains carbonate and magnesium. Scanning electron microscopy (SEM) and infrared spectroscopy (IR) were employed to investigate the morphological changes of the coating surface and the structure of the grown layer respectively. In the first few hours, calcium and phosphate ions dissolved from the coatings so as to increase their local supersaturation to a higher degree, thereafter followed by the nucleation and growth of apatite. The nucleation occurred firstly on the recessed regions, inside pores and cracks where the higher supersaturation was readily maintained. Only after 24 h incubation was a complete layer formed on the surface of the coating. There is no obvious interface between the grown layer and the underlying coating. Heat treatment in the air made the apatite transform into biphasic calcium phosphate of HA and tricalcium phosphate, with a blue colour because of trace manganese ions. The heat-treated HA coating showed no dissolution by SEM observation. This resulted in no precipitation on the surface. When SBF was used with two-fold higher ion concentrations, the apatite layer formed slowly in 72 h without dissolution of the coating surface. This may mean that the microenvironment with a sufficiently high degree of supersaturation of calcium and phosphate ions is crucial for apatite to nucleate and grow in SBF, while the HA crystalline structure is not critical in the nucleation process, as expected.

Apatites↗

PubMed1997

Histological and biomechanical analysis of bone and interface reactions around hydroxyapatite-coated intramedullary implants of different stiffness: a pilot study on the goat.

We hypothesized that reduced stem stiffness of orthopaedic implants contributes to a high risk of loosening, since interface stresses and relative motions may exceed a tolerable range. To study this hypothesis, three types of load-bearing implant with different stiffnesses were inserted into the tibia of the goat. Histological analysis was performed of bone repair after insertion of the implant, bone ingrowth, interface disruption and loosening. A finite element model of the configuration provided the quantitative range of interface stresses and relative motions for the present experiment. The implants were made out of stainless steel, hollow titanium and a thin titanium core covered with a polyacetal coating. The stiffness ratios of these implants were approximately 10:4:1, respectively. All implants were coated with a layer of hydroxyapatite (HA) in order to minimize the possible biological effects of the different implant materials. Irrespective of the type of implant, there was a repair phase that lasted 6-12 weeks. The stiff implants functioned well. Large areas of bone bonding to the HA layer were found after the repair phase at 12 weeks postoperatively. After 24 weeks, some signs of loosening were observed. More loosening occurred with the hollow titanium and polyacetal implants, mainly during the repair phase. Three hollow titanium and three polyacetal coated implants survived this period, and were killed after 24 weeks. The integrity of the HA layer at the bone-implant interface of the titanium implants was good. In the polyacetal implants, the repair reaction of the cortical bone was incomplete. Bone ingrowth into HA was largely lacking. In conclusion, we found significant differences in the repair and interface reactions around implants of different stiffness. Stiff implants showed favourable initial interface conditions for bone ingrowth. Intermediate and flexible implants provoked unfavourable interface conditions for initial bone ingrowth. The finite element study showed that the flexible stems produce larger micromotions and higher interface stresses at the bone-prosthesis interface than the stiff stems, indicating an explanation for the histological findings.

Acetals↗

PubMed1997

Fast precipitation of calcium phosphate layers on titanium induced by simple chemical treatments.

A simple two-step chemical treatment, i.e. etching with HCl and H2SO4 followed by immersion in boiling dilute NaOH solution, has been developed by our group to prepare bioactive microporous titanium surfaces allowing fast deposition of a calcium phosphate layer (CPL) from an in vitro supersaturated calcification solution (SCS). In this work, a precalcification (Pre-Ca) procedure was applied by soaking the two-step treated titanium in Na2HPO4 and then saturated Ca(OH)2 solution before immersion in SCS to accelerate further the CPL precipitation. The treated titanium surfaces with Pre-Ca were characterized after 1, 2, 4, 8 and 16 h of immersion in SCS by means of scanning electron microscopy together with energy dispersive X-ray analysis, X-ray diffraction and infrared absorption analysis. It was observed that the CPL precipitation rate with Pre-Ca averaged 1 microm h-1, twice as fast as without Pre-Ca. No precipitation was observed on untreated titanium with Pre-Ca up to day 14 of immersion in the SCS.

Calcium Hydroxide↗

PubMed1997

XPS characterization of surface films formed on surface-modified implant materials after cell culture.

Nitrogen ion-implanted Ti-6Al-4V, Ti-5Al-2.5Fe and 316 L stainless steel and nitrogen or carbon sputter-coated samples were inoculated with rat bone marrow. The interface between the cell layer and the substrata was studied by X-ray photo-electron spectrometry and observed by scanning electron microscopy (SEM). Ca and P were detected on all materials after in vitro cell culture. Titanium appears to be present mainly in the form of TiO2.

Journal Article↗

PubMed1997

In-vitro apatite formation on phosphorylated bamboo.

Natural self-reinforced composite, bamboo, was surface modified by phosphorylation with urea-H3PO4 and NaOH-H3PO4 methods; then precalcification was performed by immersing samples in saturated Ca(OH)2 solution. After that, calcium phosphate can be formed on the surface of bamboo samples in calcification media: simulated body fluid (1.5 SBF) and accelerated calcification solution (ACS). Experimental results reveal that pre-calcification is an inevitable step for the formation of calcium phosphate. The calcium phosphate formed in 1.5 SBF was identified by thin-film X-ray diffraction as apatite which was not well crystallized. Compared with the urea-H3PO4 method, the NaOH-H3PO4 method has the advantages of quicker and continuous apatite formation and stronger adhesive between apatite and bamboo.

Journal Article↗

PubMed1997

Calcium phosphate formation induced on silica in bamboo.

The effect of in vitro induction of calcium phosphate on bamboo surfaces is reported for the first time. Bamboo is studied for biomaterial application due to its elasticity modulus being closer to human bone than other biomaterials. Following an earlier study of cytotoxicity and precipitation of apatite on ground tissue and vascular bundles of bamboo, the composition and function of the minerals in bamboo, especially silica, are considered in the present work. It is found that in both outer and inner surfaces of bamboo culm, there exists some silica. Bamboo elicits an inert response when soaked directly in calcification solution. After the rind of bamboo is treated with sodium hydroxide solution, the silica underneath can induce precipitation of calcium phosphate in an ambient environment. Furthermore, by subsequent grafting with polyethylene glycol (PEG 1000), calcium phosphate induction of bamboo rind can be improved, depending on the concentration of NaOH solution and treatment time. Heat treatment of bamboo can remove the organic materials around the minerals in bamboo, allowing the calcification behaviour of the silica-containing inorganic phase of bamboo in aqueous solution to be studied.

Journal Article↗

PubMed1997

A survey on dental care and oral implantology in Beijing, China.

In this article, we present a survey on dental care and oral implantology in Beijing, China. The Chinese population comprises 1.2 billion or about 20% of the world's population. This survey shows: (i) there is a well-developed dental system in China, mostly operated by the Chinese government; (ii) in Beijing, there are 1328 dentists and oral surgeons and 515 special dental nurses working in dental departments of hospitals; (iii) about 2 million new patients visit the dentist every year; (iv) oral implantology is a new technology for the Chinese dentist and oral surgeon, as shown by the finding that in 1992, only 384 persons were treated with oral implants in a few hospitals in Beijing; however, most hospitals are interested in performing oral implantology in the near future; (v) imported implants are too expensive for Chinese patients, and therefore good qualified domestic implants and cheaper imported implants have a great market potential.

China↗

PubMed1996

Integrity and thermal decomposition of apatite in coatings influenced by underlying titanium during plasma spraying and post-heat-treatment.

The integrity and thermal decomposition of calcium apatite are influenced by the underlying titanium during plasma-spraying deposition, especially at the apatite/titanium interface. The destruction of apatite at the interface is governed by substrate temperature, titanium catalysis, and its reaction with titanium dioxide produced from oxidation of titanium in the plasma gas. The apatite in the outer layer of coatings is affected mainly by the substrate temperature and can keep its integrity with a suitable plasma-spraying procedure to minimize the increase of substrate temperature. The heat treatment of the coatings in vacuum results in the decomposition of apatite to alpha-tricalcium phosphate (alpha-TCP) and tetracalcium phosphate monoxide (TCPM) with the increase of intensity approaching the interface, which roughens the surface of the coatings. In the air-heat treatment, oxidation of titanium produces a thickened, dense rutile layer at the interface which prevents titanium atoms from diffusing into the coatings and inhibits the titanium-catalyzed decomposition of apatite. The apatite adjacent to the rutile layer reacts moderately with rutile to produce calcium titanate (CaTiO3), alpha- and beta-TCP, while the apatite in the outer layer, separated from the rutile layer, maintains its integrity without decomposition even in a prolonged air-heat treatment. The retention of apatite integrity leads to a decreased surface roughness of the coating.

Biocompatible Materials↗

PubMed1996

Characterization of silane-treated hydroxyapatite powders for use as filler in biodegradable composites.

Hydroxyapatite (HA) powder was treated with different silane adhesion promoters, to optimize its performance as a filler in polymer composites. The silane coupling agents investigated possessed vinyl, methacryloxy, primary amine, secondary amine, and diamine functionality. The different coatings were evaluated with respect to their influence on ionic exchange. X-ray photoelectron spectroscopy revealed the presence of a few monolayers thin silane films on HA powder. Silane coupling agents were able to bond chemically on the HA surface because a thin coating remained after washing of the powder with water. The water stability of this bond was evaluated by successive extractions and was judged limited, especially in the case of the hydrophilic aminosilanes. Zeta-potential measurements indicated the "transparency" of the coatings for ionic transport, that was corroborated by two in vitro dissolution studies, in Gomori's Tris-maleate buffer, and in simulated body fluid. However, aminosilane coatings could delay the release of calcium and phosphate ions during the first 2 days of immersion of treated HA powder in Gomori's buffer.

Biocompatible Materials↗

PubMed1996

Therapy for the maintenance of remission in sixty-five patients with generalized Wegener's granulomatosis. Methotrexate versus trimethoprim/sulfamethoxazole.

OBJECTIVE: To compare the efficacy of low-dose intravenous (IV) methotrexate (MTX; 0.3 mg/kg once weekly), both with and without concomitant prednisone, versus daily oral trimethoprim/sulfamethoxazole (T/S; 160 mg of trimethoprim + 800 mg of sulfamethoxazole twice a day), with and without prednisone, in maintaining remission in patients with generalized Wegener's granulomatosis (WG). METHODS: In this study, 65 patients with generalized WG whose disease had entered remission with cyclophosphamide (CYC) and prednisone therapy were started on one of the following remission-maintenance regimens: MTX alone (group A; n = 22), T/S alone (group B; n = 24), MTX plus concomitant prednisone (group C; n = 11), and T/S plus concomitant prednisone (group D; n = 8). Clinical, radiographic, and seroimmunologic data were evaluated to assess the efficacy of the 4 regimens and to seek possible predictive factors concerning outcome in each group. RESULTS: Partial or complete remission was maintained in 86% of the patients in group A, but in only 58% of those in group B (P < 0.05). In group C, 91% of patients remained in remission, which is in sharp contrast to group D, in which all patients experienced a relapse after a median of 14.5 months (P < 0.005). Side effects occurred twice as often with MTX (n = 12) as with T/S (n = 6) treatment and could usually be resolved by supplemental folinic acid. Two patients taking MTX and 3 patients taking T/S were withdrawn from the study medication because of side effects. In none of the patients were the adverse effects life threatening. No statistically significant factors predictive of poor outcome emerged in any group. CONCLUSION: Low-dose MTX was found to be superior to T/S for the safe and effective maintenance of remission in patients with generalized WG. The use of concomitant prednisone was not associated with a worse outcome with MTX treatment. Since T/S, especially with concomitant prednisone, seemed to increase the chance of relapse, neither T/S alone nor T/S plus prednisone can be recommended for the maintenance of remission in patients with generalized WG.

Adolescent↗

PubMed1995

In vivo calcium phosphate formation induced by sol-gel-prepared silica.

Implantation with plugs made of a porous sol-gel-prepared silica into the femurs of goats demonstrated that a calcium phosphate was formed both on the silica plugs and within the pores inside the silica plugs 12 weeks postoperatively. This observation indicates that a highly hydrated silica surface is effectively catalytic for calcium phosphate nucleation. Calcification can be triggered in physiologic solution under stimulation of the silica gel. A high level of silicon in the uncalcified osteoid region of young bone is thus thought to provide a number of SiOH groups for initiating calcium phosphate formation. Our results provide some information about the mechanism of calcium phosphate mineralization in higher animals. We believe that heterogeneous nucleation of apatite can be induced from metastable calcium phosphate solutions including physiologic fluids on those specific surfaces of materials, where there are abundant acidic OH groups.

Animals↗

PubMed1995

Osteogenesis in muscle with composite graft of hydroxyapatite and autogenous calvarial periosteum: a preliminary report.

To investigate the bone forming activity of composite grafts of hydroxyapatite (HA) and autogenous calvarial periosteum, porous HA rods with or without the periosteum were implanted into the back muscle of white rabbits. They were harvested 3 and 6 months after implantation and studied histologically and microradiographically. Bone formation in the pores of HA occurred in three out of four composite implants of the 3 month group, and four out of five implants of the 6 month group. The two specimens without bone formation revealed irregular calcified tissue outside the HA implant. No formation of bone and calcified tissue took place in any of the specimens with HA alone. These results indicate the potential of this new experimental system of ectopic osteogenesis and offer the possibility of a new improved bone graft consisting of HA and autogenous periosteum.

Animals↗

PubMed1995

Effect of sintering temperature on silica gels and their bone bonding ability.

Silica gels gave rise to apatite precipitation onto their surface depending on the sintering temperature. Silica gels prepared at different sintering temperatures were studied in vivo in cortical bone for their bone bonding ability in relation to their apatite precipitation. From the results we conclude that the sintering temperature influenced the stability of the material. Sintering at the lower temperatures of 400 and 600 degrees C allow the silica gels to be degraded more easily, while gels treated at 900 and 1000 degrees C were more stable. The more stable gels showed some bone bonding, while the degraded gels evoked a high cellular reaction of giant cells and lymphocytes.

Animals↗