Effect of 20 µm thin ceramic coatings of hydroxyapatite, bioglass, GB14 and Beta-Tricalciumphosphate with copper on the biomechanical stability of femoral implants.

In the present work, we test four thin coatings for titanium implants, namely, bioglass, GB14, Beta-Tricalciumphosphate (ß-TCP) and hydroxyapatite (HA) with and without incorporated copper ions for their osteointegrative capacity. A rabbit drill hole model for time intervals up to 24 weeks was used in this study. Implant fixation was evaluated by measuring shear strength of the implant/bone interface. Quantitative histological analysis was performed for the measurements of bone contact area. Implants with and without copper ions were compared after 24 weeks. Thin coatings of GB14, HA or TCP on titanium implants demonstrated high shear strength during the entire test period of up to 24 weeks. Results confirmed osteointegrative properties of the coatings and did not reveal any negative effect of copper ions on osteointegration. The integration of copper in degradable osteoconductive coatings with a thickness of approx. 20 µm represents a promising method of achieving antibacterial shielding during the entire period of bone healing while at the same time improving osteointegration of the implants.

A Method for the Evaluation of Early Osseointegration of Implant Materials Ex Vivo: Human Bone Organ Model.

In the present work, an ex vivo organ model using human bone (explant) was developed for the evaluation of the initial osseointegration behavior of implant materials. The model was tested with additive manufactured Ti6Al4V test substrates with different 3D geometries. Explants were obtained from patients who underwent total knee replacement surgery. The tibial plateaus were used within 24 h after surgery to harvest bone cylinders (BC) from the anterior side using hollow burrs. The BCs were brought into contact with the test substrate and inserted into an agarose mold, then covered with cell culture media and subjected to the external load of 500 g. Incubation was performed for 28 days. After 28d the test substrate was removed for further analysis. Cells grown out BC onto substrate were immunostained with DAPI and with an antibody against Collagen-I and alkaline phosphatase (ALP) for visualization and cell counting. We show that cells stayed alive for up to 28d in our organ model. The geometry of test substrates influences the number of cells grown onto substrate from BCs. The model presented here can be used for testing implant materials as an alternative for in vitro tests and animal models.

Alendronate Release from UHMWPE-Based Biomaterials in Relation to Particle Size of the GUR Powder for Manufacturing.

Ultra-high molecular weight polyethylene (UHMWPE) is widely used in endoprosthetics and has been the subject of countless studies. This project investigates the dependence of alendronate (AL) release on the molecular weight of the UHMWPE used (GUR1020 and GUR1050). A 0.5 wt% AL was added to the UHMWPE during the production of the moldings. In addition to the 14-day release tests, biocompatibility tests such as live dead assay, cell proliferation assay (WST) and Lactate dehydrogenase test (LDH) with MG-63 cells as well as a tensile test according to DIN EN ISO 527 were carried out. The released AL concentration was determined by HPLC. A continuous release of the AL was observed over the entire period of 2 weeks. In addition, a correlation between molar mass and AL release was demonstrated. The GUR1020 showed a release four times higher than the GUR1050. Both materials have no negative influence on the proliferation of MG-63 cells. This was also confirmed in the live/dead assay by the increase in cell count. No cytotoxicity was detected in the LDH test. The addition of 0.5 wt% AL increased the elongation at break for GUR1020 by 23% and for GUR1050 by 49%. It was demonstrated that the choice of UHMWPE has an influence on the release of AL. The particle size in particular has a strong influence on the release behavior.

Viscoelasticity and histology of the human cartilage in healthy and degenerated conditions of the knee.

BACKGROUND: There are many studies on osteoarthritis, but only a few studies deal with human arthrosis, comparing the mechanical properties of healthy and diseased samples. In most of these studies, only isolated areas of the tibia are examined. There is currently only one study investigating the complete mapping of cartilage tissue but not the difference between instantaneous modulus (IM) in healthy and diseased samples. The aim of this study is to investigate the relationship between the biomechanical and histological changes of articular cartilage in the pathogenesis of osteoarthritis. METHODS: The study compared 25 tibiae with medial gonarthrosis and 13 healthy controls. The IM was determined by automated indentation mapping using a Mach-1 V500css testing machine. A grid was projected over the sample and stored so that all measurements could be taken at the same positions (100 ± 29 positions across the tibiae). This grid was then used to perform the thickness measurement using the needle method. Samples were then taken for histological examinations using a hollow milling machine. Then Giemsa and Safranin O staining were performed. In order to determine the degree of arthrosis according to histological criteria, the assessment was made with regard to Osteoarthritis Research Society International (OARSI) and AHO scores. RESULTS: A significant difference (p < 0.05) could be observed in the measured IM between the controls with 3.43 ± 0.36 MPa and the samples with 2.09 ± 0.18 MPa. In addition, there was a significant difference in IM in terms of meniscus-covered and meniscus-uncovered areas. The difference in cartilage thickness between 2.25 ± 0.11 mm controls and 2.0 ± 0.07 mm samples was highly significant with p < 0.001. With regard to the OARSI and AHO scores, the samples differed significantly from the controls. The OARSI and AHO scores showed a significant difference between meniscus-covered and meniscus-uncovered areas. CONCLUSIONS: The controls showed significantly better viscoelastic behavior than the arthrotic samples in the measured IM. The measured biomechanical values showed a direct correlation between histological changes and altered biomechanics in gonarthrosis.

Inversely 3D-Printed ß-TCP Scaffolds for Bone Replacement.

The aim of this study was to predefine the pore structure of ß-tricalcium phosphate (ß-TCP) scaffolds with different macro pore sizes (500, 750, and 1000 µm), to characterize ß-TCP scaffolds, and to investigate the growth behavior of cells within these scaffolds. The lead structures for directional bone growth (sacrificial structures) were produced from polylactide (PLA) using the fused deposition modeling techniques. The molds were then filled with ß-TCP slurry and sintered at 1250 °C, whereby the lead structures (voids) were burnt out. The scaffolds were mechanically characterized (native and after incubation in simulated body fluid (SBF) for 28 d). In addition, biocompatibility was investigated by live/dead, cell proliferation and lactate dehydrogenase assays. The scaffolds with a strand spacing of 500 µm showed the highest compressive strength, both untreated (3.4 ± 0.2 MPa) and treated with simulated body fluid (2.8 ± 0.2 MPa). The simulated body fluid reduced the stability of the samples to 82% (500), 62% (750) and 56% (1000). The strand spacing and the powder properties of the samples were decisive factors for stability. The fact that ß-TCP is a biocompatible material is confirmed by the experiments. No lactate dehydrogenase activity of the cells was measured, which means that no cytotoxicity of the material could be detected. In addition, the proliferation rate of all three sizes increased steadily over the test days until saturation. The cells were largely adhered to or within the scaffolds and did not migrate through the scaffolds to the bottom of the cell culture plate. The cells showed increased growth, not only on the outer surface (e.g., 500: 36 ± 33 vital cells/mm² after three days, 180 ± 33 cells/mm² after seven days, and 308 ± 69 cells/mm² after 10 days), but also on the inner surface of the samples (e.g., 750: 49 ± 17 vital cells/mm² after three days, 200 ± 84 cells/mm² after seven days, and 218 ± 99 living cells/mm² after 10 days). This means that the inverse 3D printing method is very suitable for the presetting of the pore structure and for the ingrowth of the cells. The experiments on which this work is based have shown that the fused deposition modeling process with subsequent slip casting and sintering is well suited for the production of scaffolds for bone replacement.

Carbon-Fibre-Reinforced SiC Composite (C/SiSiC) as an Alternative Material for Endoprosthesis: Fabrication, Mechanical and In-Vitro Biological Properties.

Particle-induced periprosthetic osteolysis and subsequent aseptic implant loosening are a major cause of compromising the long-term results of total joint replacements. To date, no implant has been able to mirror radically the tribological factors (friction/lubrication/wear) of in vivo tribological pairings. Carbon-Fibre Reinforced SiC-Composites (C/SiSiC), a material primarily developed for brake technology, has the opportunity to fulfil this requirement. Until now, the material itself has not been used in medicine. The aim of this investigation was to test the suitability of C/SiSiC ceramics as a new material for bearing couples in endoprosthetics. After the preparation of the composites flexural strength was determined as well as the Young's-modulus and the coefficient of friction. To investigate in vitro biological properties, MG 63 and primary human osteoblasts were cultured on C/SiSiC composites. To review the proliferation, the cytotoxicity standardized tests were used. The cell morphology was observed by light microscopy, ESEM, confocal and 3D-laserscanning microscopy. C/SiSiC possesses a high resistance to wear. Cells exhibited no significant alterations in morphology. Vitality was not impaired by contact with the ceramic composite. There was no higher cytotoxicity to observe. Regarding these results, C/SiSiC ceramics seem to be biologically and mechanically appropriate for orthopaedic applications.