Kārlis-Agris Gross

Selection of the Implant and Coating Materials for Optimized Performance by Means of Nanoindentation

Mechanical compatibility between a coating and a substrate is important for the longevity of implant materials. While previous studies have utilized the entire coating for analysis of mechanical compatibility of the surface, this study focuses on the nanoindentation of a uniformly thermally sprayed splat. Hydroxyapatite was thermally sprayed to create a homogeneous deposit density, as confirmed by microRaman spectroscopy, of amorphous calcium phosphate. Substrates were commercially pure Ti, Ti-6Al-4V, Co-Cr alloy and stainless steel. Nanoindentation revealed that splats deposited on the different metals have similar hardness and elastic modulus values of 4.2 ± 0.2 GPa and 80 ± 3 GPa, respectively. The mechanical properties were affected by the substrate type more than residual stresses, which were found to be low. It is recommended that amorphous calcium phosphate is annealed to relieve the quenching stress or that appropriate temperature histories are chosen to relax the stress created in cooling the coating assembly.

In Vitro Characterization Perspectives Using Fourier Transform Infrared Photoacoustic Spectroscopy (FTIR-PAS) and Diffuse Reflectance Infrared Spectroscopy (DRIFT)

The activity of antibacterial material is conventionally estimated by using an indirect method – a bacteria suspension is inoculated onto a surface, and then the bacteria are collected from the surface and examined as to whether they can form colonies on the agar plate. In the present study, the presence of bacteria was examined by direct detection. Our study is based on FTIR-PAS with an interferometer cantilever detector. Our work discusses the possibility of identifying and distinguishing the presence of different bacteria (Staphylococcus epidermidis and Pseudomonas aeruginosa) and the possibility to evaluate the crystallization processes on the pressed calcium phosphate surface.

An Ice Track Equipped with Optical Sensors for Determining the Influence of Experimental Conditions on the Sliding Velocity

Abstract The ability to slide on ice has previously focused on the measurement of friction coefficient rather than the actual sliding velocity that is affected by it. The performance can only be directly measured by the sliding velocity, and therefore the objective was to design and setup a facility to measure velo-city, and determine how experimental conditions affect it. Optical sensors were placed on an angled ice track to provide sliding velocity measurements along three sections and the velocity for the total sliding distance. Experimental conditions included the surface roughness, ambient temperature and load. The effect of roughness was best reported with a Criterion of Contact that showed a similar sliding velocity for metal blocks abraded with sand paper smoother than 600 grit. Searching for the effect of temperature, the highest sliding velocity coincided with the previously reported lowest coefficient of ice friction. Load showed the greatest velocity increase at temperatures closer to the ice melting point suggesting that in such conditions metal block overcame friction forces more easily than in solid friction. Further research needs to be conducted on a longer ice track, with larger metal surfaces, heavier loads and higher velocities to determine how laboratory experiments can predict real-life situations.

Thermokinetic Investigation of the Drying Conditions on Amorphous Calcium Phosphate

The present work investigated dried calcium phosphate powders which still retain an amorphous or poorly crystalline structure under a variety of conditions. In previous studies, freeze-drying was found to be the optimum drying condition. However, several publications, as well as our previous studies, have shown that calcium phosphate amorphous, or a poorly crystalline structure, can retain their structure even if the samples are dried immediately after synthesis up to 200°C. In our study, we used the thermokinetic studies FTIR and XRD and showed that the samples are amorphous, or poorly crystalline, but were unable to answer the questions: Is there a difference between the differently dried amorphous calcium phosphates What are the optimum drying conditions under which the amorphous calcium phosphate (ACP) structure loses the physically bounded water, but still retains the chemically bounded water