C. P. A. T. Klein

Bonding of bone to apatite-coated implants

Implants of solid sintered hydroxyapatite form very tight bonds with living bone, but are susceptible to fatigue failure. This problem can be overcome by using plasma-sprayed apatite coatings on titanium implants. A very strong bond is formed between bone and this composite material; this was studied in canine bone with plug implants, avoiding any mechanical retention. Mechanical testing showed an interface shear strength at six weeks of 49 MPa with a maximum of 64 MPa after six months. There was histological evidence of direct bonding between the apatite coating and living bone while uncoated control plugs were easily extracted. The results indicate that apatite-coated implants can form a chemical fixation with a strength comparable to that of cortical bone itself. This fixation is far stronger than that provided by current cemented or uncemented fixation techniques.

A Simple Method for Preparing Thin (10 μm) Histological Sections of Undecalcified Plastic Embedded Bone with Implants

A simple method for preparing undecalcified thin sections of bone with implants has been developed. After exposing a surface of bone and implant in a plastic block by sawing thick sections, the surface is stained prior to making a thin section. A glass coverslip is affixed with a thin layer of cement to the stained surface to stabilize the tissue and implant during sectioning. A mixture of glycerine and water is used as a coolant and lubricant. The orientation in situ is preserved allowing demonstration of bone architecture and cells, and the tissue-implant interface.

In vivo study of calcium phosphate cements: implantation of an α-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.

Studies of the solubility of different calcium phosphate ceramic particles in vitro

In vitro solubility tests of hydroxyapatite, tetracalcium phosphate or tricalcium phosphate particles were performed in lactate, citrate, Gomoris or Michaelis buffer with pH 6.2 or 7.2 and in aqua destillata. The results showed that in general the solubility decreased in the order tetracalcium phosphate greater than tricalcium phosphate greater than hydroxyapatite, except for lactate or citrate buffer where the solubility order was tetracalcium phosphate = tricalcium phosphate greater than hydroxyapatite. The influence of the specific buffer used is much larger than either pH or specific calcium phosphate salt tested. The pH stability of lactate buffer and aqua destillata is very low, the other buffer solvents had a rather stable pH value.

Long-term in vivo study of plasma-sprayed coatings on titanium alloys of tetracalcium phosphate, hydroxyapatite and α-tricalcium phosphate

Abstract In order to study the interaction of calcium phosphate coatings with bone tissue, coated titanium plugs of standard size were implanted in dog femora. The bone bonding and bone formation of hydroxyapatite, α-tricalcium phosphate (α-TCP) and tetracalcium phosphate plasma-sprayed coatings were evaluated by mechanical push-out tests and histological observations after 3, 5, 15 and 28 months of implantation. During this time all coating types degraded. α-TCP showed the most significant degradation after 3 months of implantation. Hydroxyapatite and tetracalcium phosphate showed significant signs of degradation after about 5 months of implantation. All coatings showed a small increase in bone bonding after 5 months of implantation. In general, all types of implants showed similar bone response, some bone contact and several remodelling lacunae along the surfaces after long-term implantation.

Morphology and composition of nanograde calcium phosphate needle-like crystals formed by simple hydrothermal treatment

Nanograde calcium phosphate needle-like crystals are prepared from wet synthesized Ca−P precipitates by simple hydrothermal treatment at 140°C and 0.3 MPa for 2 h. The morphology of these crystals is observed by transmission electron microscopy (TEM). The phase composition is tested through X-ray diffractometer (XRD) and infrared spectroscopy (IR). It is found that the morphology of these crystals is related to the activity or fresh degree of the starting Ca−P precipitates and the added fluorine ions, but is not greatly influenced by the Ca/P ratio of the precipitates. These crystals with a Ca/P ratio between 1.67 and 1.5 show a poorly crystallized apatite structure at room temperature and a biphasic (HA+β−TCP) structure at 1100°C, corresponding to their Ca/P ratio. It is demonstrated that these nonstoichiometric apatite crystals contain lattice-bound water which could play an important role in the formation of bone apatite. The similarity in morphology and composition between these needle-like crystals and the apatite crystals in bone provides a possibility to make a bone-like implant consisting of these needle-like crystals and collagen, etc.

Bone tissue response to biodegradable polymers used for intra medullary fracture fixation: A long-term in vivo study in sheep femora

Since the degradability of the synthetic polymers used for fracture fixation is still unclear, a research project with biodegradable interlocking nails with a longterm implantation period has been started. In 21 female sheep a complete mid-shaft osteotomy of the left femur was performed to mimic a fracture of the femoral shaft. For the fixation, an intramedullary stainless-steel interlocking nail, a PLA rod or a PLA/PGA rod was used. After 30 months of implantation the histological results of these three materials were examined. In contrast to most reports the degradation rate of both polymers was much lower than the suggested ultimate period of two years. Even the tissue response was more pronounced than expected and this reaction can imply certain risks for repulsion. One can conclude that the volume quantity of polymeric implant in the bony tissue must be reduced if possible to avoid severe foreign body responses. The immunologic responses and the clinical consequences need more studies. The degradation behavior of the polymer is still not under control.

Preparation and characterization of nanograde osteoapatite-like rod crystals

In this paper, nanograde osteoapatite-like rod crystals are made from wet synthesized calcium phosphate precipitates by hydrothermal treatment at 140°C under 0.3 MPa pressure for 2 h. The morphology, crystal structure, crystallinity and phase composition of these nanograde rod crystals are similar to those of thin apatite crystals in bony tissues of the body. This analogy provides an opportunity in the near future to build bone-like substitutes which consist of the nanograde rod crystals and special organic matrices and cells.

Evaluation of hydroxylapatite/poly(l-lactide) composites: physico-chemical properties

The aim of this in vitro study was to examine the physico-chemical behaviour of hydroxylapatite/poly(l-lactide) (HA/PLLA) composites in solution tests. The polymer PLLA, the composites 30 wt% HA/PLLA (C30) and 50 wt% HA/PLLA (C50) and a one-side HA-coated PLLA (HAcP) were evaluated. Rectangular specimens were incubated in various acellular aqueous buffer solutions [citrate, Gomoris and phosphate-buffered saline (PBS)] up to 24 weeks. Data for cumulative release of calcium, phosphate and l-lactate release in solutions containing C30 or C50 showed linear patterns. Release data for solutions containing HAcP combined with scanning micrographs, X-ray microanalysis and X-ray diffraction patterns of the specimens in time showed that the plasma-sprayed HA coating on PLLA dissolves significantly, progressively in the first weeks and almost completely within the tested period of 24 weeks in vitro. A precipitate of scaly crystallites (calcium phosphates) was observed at the HA coating-PBS interface. After 24 weeks incubation all materials were still above their initial weight, indicating that swelling still exceeded dissolution. Application of C30, C50 and HAcP as implant materials seems interesting where initial stabilization through bone bonding is needed or where the linear release of constituents is a requirement. HAcP has the advantage that the HA coating acts as a hydrolysis barrier and consequently delays the degradation of PLLA in vitro.

Calcium phosphate cement: in vitro and in vivo studies of the α-tricalcium phosphate-dicalcium phosphate dibasic-tetracalcium phosphate monoxide system

In this paper, calcium phosphate cement consisting of α-tricalcium phosphate (α-TCP), dicalcium phosphate dibasic (DCPD) and tetracalcium phosphate monoxide (TeCP) was investigated in vitro and in vivo. Measurements of compressive strength against soaking time in simulated body fluid (SBF) showed a rapid increase of the hardness for the first 7 days. The gained strength was retained up to 1 year and the maximal mean value was 94.7 (±14.4) MPa. X-ray diffraction (XRD) and scanning electron microscopy (SEM) presented precipitates of hydroxyapatite (HA) after mixing, also after soaking in SBF and after implantation in rat subcutaneous tissues. However, the conversion to HA happened in different ways between in vitro and in vivo exposures. Histologic examinations showed that the cement causes the same reactions at the interface with surrounding soft tissues as HA. The authors consider the cement to be a promising material as a bone substitute, bone cement or dental material, however, further studies in a paste form and in bone tissue environments are necessary.