Effect of constant strain rate, composed of varying amplitude and frequency, of early loading on peri-implant bone (re)modelling.

AIM: Examine the effect of varying components of strain rate -- amplitude versus frequency -- while maintaining a constant strain rate of early controlled mechanical loading on implant stability, peri-implant bone mass and bone-to-implant contact. MATERIAL AND METHODS: Three groups of guinea-pigs received TiO2 -blasted implants in both tibiae. One week after installation test implants were loaded 5 days/week during 4 weeks. The contra-lateral implants were the unloaded controls. Strain rate was kept constant (1600 micro epsilon/s), while amplitude and frequency were varied per group. Implant stability was followed by resonance frequency analysis. Animals were sacrificed, and ground sections were prepared to rate bone-to-implant contact and bone mass. RESULTS: All implants (n=78) integrated uneventfully. A significant positive effect (p=0.03) of early loading on bone mass was observed in the distal medullar cavity. A significant difference in bone mass between test and control implants was evidenced between the groups (p=0.03 and 0.04). A significant increase in implant stability and bone-to-implant contact could not be shown. CONCLUSIONS: Early controlled stimulation of peri-implant bone is related to amplitude/frequency and not to strain rate as such, considering a constant stimulation time. An increase of bone mass around early-loaded implants was shown. This cortical bone model is most sensitive to low-frequency/high-amplitude stimulation.

A new titanium fiber mesh-cuffed peritoneal dialysis catheter: evaluation and comparison with a Dacron-cuffed tenckhoff catheter in goats.

OBJECTIVE: We report the development of a new peritoneal dialysis catheter. The purpose of the current study was to evaluate tissue response to this catheter. DESIGN: In our catheter design, the catheter's cuffs are made from sintered titanium fiber mesh instead of the common Dacron material. The catheters were implanted in goats. During the study period, the catheter exit sites were observed once every 2 weeks. After 14 weeks, the catheters and surrounding tissues were processed for histology and analyzed. RESULTS: We observed that catheters with titanium cuffs performed significantly better, compared with a commercial catheter design. Histology showed that titanium fibers evoked a lesser inflammatory response compared with Dacron fibers. In addition, the capsule surrounding the titanium cuff was significantly thinner. CONCLUSIONS: Supported by the obtained results, we conclude that the use of Dacron velour for anchorage of percutaneous catheters has to be reconsidered. Titanium fiber mesh has a great potential for application in percutaneous catheters.

Effect of microgrooved poly-l-lactic (PLA) surfaces on proliferation, cytoskeletal organization, and mineralized matrix formation of rat bone marrow cells.

Previous experiments showed that microgrooved substrate surfaces can influence the in vitro behavior of osteoblast-like rat bone marrow (RBM) cells. Cellular morphology and matrix deposition can be directed by substrate chemistry and topography. RBM cells cultured on poly-l-lactic acid (PLA) exhibit increased mineralization and alkaline phosphatase activity compared to polystyrene substrates. Consequently, the purpose of the present in vitro study is to further evaluate the behavior of RBM cells on microgrooved (groove depth 0.5 to 1.5 microns, groove and ridge width 1 to 10 microns) polystyrene (PS) and PLA surfaces. Besides grooved, also smooth control surfaces were made. Our results confirmed that microtextured surfaces are capable of influencing the behavior of the osteoblast-like RBM cells in vitro. Microtopography did not influence the RBM proliferation rate, or cellular actin organization. However, confocal laser scanning microscopy showed that cellular attachment is dependent on the applied material. Also clear differences were found between textured PS and PLA, with regard to the calcium content. We therefore conclude, that the application of microtextures could possibly influence the bone regeneration around biodegradable PLA devices.

Phenotypic transformation of normal rat kidney fibroblasts by endothelin-1. Different mode of action from lysophosphatidic acid, bradykinin, and prostaglandin f2alpha.

In the present study, we compared the effects of endothelin (ET)-1 on cell proliferation and second messenger induction in normal rat kidney (NRK) fibroblasts, with those of other activators of G-protein-coupled receptors such as prostaglandin (PG)-F2alpha, bradykinin (BK), and lysophosphatidic acid (LPA). LPA is mitogenic by itself, while the other factors require the presence of EGF. In density-arrested NRK cells, ET-1 and LPA induce phenotypic transformation rapidly, with similar kinetics as retinoic acid (RA) and transforming growth factor (TGF)-beta, while BK and PGF2alpha only do so with delayed kinetics. ET-1 and PGF2alpha are strong inducers of anchorage-independent growth, with a similar level of induction as TGFbeta, in contrast to LPA and BK. When investigating the second messenger generation, we found that ET-1 is the strongest activator of arachidonic acid release and phosphatidylinositol diphosphate hydrolysis. Only in the case of ET-1 the cell depolarization is not reversible upon removal of the factor. Similarly, only the ET-1-induced transient enhancement of intracellular calcium concentration is paralleled by both homologous and heterologous desensitization. In conclusion, these data show that ET-1 is a potent inducer of second messengers and phenotypic transformation in NRK cells, with characteristics that clearly differ from those of other activators of G-protein-coupled receptors, most likely as a result of prolonged receptor activation.