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J R De Wijn

Publications and source records attributed to J R De Wijn.

8 recordsLinked to original sources
PubMed1998

Preparation of bioactive microporous titanium surface by a new two-step chemical treatment.

Microporous oxide layers allowing fast deposition of calcium phosphate layers (CPLs) were formed on commercially pure titanium (c.p.Ti) after the application of a newly developed two-step chemical treatment. The micropores were of submicrometre size. The two-step treatment was carried out by etching c.p.Ti samples with HCl and H2SO4 first and then treating them in boiling 0.2 N NaOH solution at 140 degrees C for 5 h. Conformal CPLs, about 20 microm thick, were deposited on the two-step treated c.p.Ti surface by means of a two-day immersion in an in vitro supersaturated calcification solution. The CPL was characterized to be mainly composed of two sublayers, i.e. an outside loose octacalcium phosphate crystal sublayer and an inside dense carbonated apatite sublayer. A scratching test indicated that the apatite sublayer was strongly bonded to the c.p.Ti substrate. Moreover, it was observed that the untreated or single-step treated c.p.Ti surfaces are not only morphologically different from one another but significantly different from the two-step treated one, in that no precipitation was observed on them up to 14 d immersion in the same calcification solution. It is indicated that the two-step chemical treatment is a simple and easily controllable method to prepare bioactive titanium surfaces and subsequently to induce the rapid precipitation of conformal and adherent CPL from in vitro supersaturated calcification solutions.

Journal Article↗
PubMed1997

A simple method to prepare calcium phosphate coatings on Ti6Al4V.

A two-step chemical treatment followed by immersion in a supersaturated calcification solution (SCS) was found to be a simple way to prepare calcium phosphate (Ca-P) coatings on Ti6Al4V. The Ca-P deposition on the treated metallic surfaces could be accelerated by employing a pre-calcification (Pre-Ca) procedure prior to immersion in SCS. The two-step treatment was performed by etching the metallic plates with a mixture of HCl and H2SO4 followed by ageing in boiling diluted NaOH solution at 140 degrees C. Pre-Ca was carried out by incubating the two-step treated plates in Na2HPO4 solution and then in saturated Ca(OH)2 solution. The formation of a bioactive microporous surface oxide layer on Ti6Al4V by the two-step treatment was most probably responsible for the induction of Ca-P precipitation. The deposition rates and compositions of Ca-P coatings in two different SCSs were investigated by means of scanning electron microscopy, X-ray diffraction and infrared spectrophotometry.

Journal Article↗
PubMed1976

Poly(methyl methacrylate)--aqueous phase blends: in situ curing porous materials.

A potential implant material has been developed which combines the advantages of curing in situ and an open porous structure. This paper deals with synthesis and characterization of the material, which is a modification of the well-known acrylic bone cements. Some early results of animal experiments are mentioned.

Biocompatible Materials↗
PubMed1975

Dimensional behavior of curing bone cement masses.

The curing of bone cements is accompanied by release of polymerization heat and, hence, by a temperature rise of the curing cement mass. This temperature rise causes expansion of enclosed air bubbles and evaporation of the volatile monomer. An overall expansion of 3 to 5 vol % has been mentioned in the literature. It has often been stated that this expansion favours the fixation of metal endoprostheses in the marrow cavity of bone. To check for the influence of this expansion on linear dimensions of the cured cement mass we filled stainless steel cylinders with a precision bore of 22,000 +/- 0,005 mm and a length of 120 mm with bone cement. After curing of the cement in a environment of 37 degrees C the resulting cement rod was released from the cylinder and the diameter of the rod was measured at 37 degrees C. The influence of the "foaming effect" on the transverse dimensions of the rods was studied by curing the cement at 37 degrees C and 2 atm air pressure in a high-pressure-vessel. This method of curing eliminates porosity in the cement almost completely, so that curing shrinkage is to be expected rather than expansion of the cement mass. The results indicate that a volumetric expansion of the cement during curing of cylindrical rods in laboratory experiments, can be accompanied by a linear diametrical shrinkage of the cement mass. The explanation of this phenomenon is to be sought in the fact that the volumetric expansion takes place at a time when the cement is still plastic; by the formation of gas bubbles, the cement is forced in longitudinal direction into the cylinder and when the temperature of the mass has passed through a maximum, the cooling of the cement mass results in a thermal shrinkage of approximately 0.4% linearly. Extrapolating this laboratory result to clinical situation one might doubt whether the overall expansion of bone cements during curing will result in a permanent positive pressure on the walls of marrow cavity and whether it will contribute to a better fixation of endoprostheses than in the case of a, still hypothetical, nonporous cement.

Bone Cements↗
PubMedDate not supplied

The effect of heating by microwave irradiation and by conventional heating on the aldehyde concentration in aqueous glutaraldehyde solutions.

The effect of short time heating of aqueous solutions of glutaraldehyde (GA) on relative aldehyde concentration was determined using spectrophotometric analysis. Because free monomeric GA absorbs U.V. light at 280 nm, whereas the alpha, beta polymeric forms absorb at 235 nm, the purity of GA solutions can be expressed as the ratio: A 235 nm/A 280 nm (purification index, P.I.). Heating of 4 ml aliquots of 0.85% distilled aqueous GA solution resulted in an increase of the absorption at 280 nm which is correlated positively with temperature. No increase of absorption at 235 nm was found when solutions were kept at 40 degrees C for several hours. The increase of absorption at 280 nm is caused by a rapid decyclization of hemiacetals producing an increase in free aldehyde concentration. No major differences in absorption were found between the solutions heated by microwave and by conventional heating. However, because microwave irradiation is known to produce an homogeneous rise in temperature, especially in bulky samples, it is expected that the results of fixation procedures will improve by the combined effect of higher temperature and enhanced diffusion rates of the fixating species.

Aldehydes↗