Harsh Sliding Wear of a Zirconia Ball against a-C:H Coated CoCrMo Disc in Hyaluronic Gel

The a-C:H (amorphous carbon-hydrogen) films belong to the family of DLC (diamond-like carbon) coatings. The a-C:H coating was deposited on medical grade CoCrMo substrates by plasma-assisted chemical vapor deposition (PA-CVD) using benzene as gaseous precursor. Benzene offers an aromatic structure, which affects the a-C:H properties after plasma decomposition. A zirconia ball was sliding at two different frequencies, 50 Hz or 1Hz, against the uncoated and a-C:H coated CoCrMo. The frequency of 1 Hz is typical for human movement during fast walking. The harsh sliding conditions with a normal load of 100 N and 50 Hz frequency simulate extreme overloading of the biomedical sliding partners. It gives insight into the failure mechanisms. The wear tests were carried out in laboratory air (dry, RH: 15.6%) or using hyaluronic gel as lubricant. The hyaluronic gel acts as an effective intermediate medium. It adheres very well to both, a-C:H coating and zirconia. No wear was evident on the ZrO2 ball at 1 Hz and 100 N. Minor wear traces were observed on the a-C:H coating only. A wear coefficient of 0.16 × 10−6 mm3/N·m were calculated for a-C:H coated CoCrMo after ZrO2 ball sliding with 1 Hz and 100 N in hyaluronic gel. This is two orders of magnitude lower in comparison to dry sliding of ZrO2 ball against DLC coated CoCrMo with 1 Hz. The coefficient of friction (COF) remained below 0.09 until the hyaluronic gel starts to lose viscosity. This finding pronounces the importance of a proper homogeneous lubrication during operation of the biomedical joints. For extreme harsh tribological loading like sudden jumps of a patient with artificial joints, the application of an intermediate layer before a-C:H coating needs further evaluation

Effect of fullerene C60 thermal and tribomechanical loading on Raman signals

Fullerene C60 powder was loaded by 1 N normal force and exposed to sliding under different frequencies for 15 min. It is shown that the velocity of the sliding movement determines the stability of the fullerene C60 powder. At slow velocity of movement with a frequency of 1 Hz under 1 N normal force, the fullerene C60 structure remains undamaged after 15 min sliding. On the contrary, high sliding velocities of 10 Hz and 50 Hz affected fragmentation of the fullerene C60, which resulted in a reduction of the coefficient of friction (COF). During sliding with 1 Hz, the friction reached the highest level with an average COF of 0.59 ± 0.03. The faster relative motion under 1 N normal force gave a lower average COF with 0.39 ± 0.03. The initial fullerene C60 powder formed a thick compressed layer in the tribomechanical loaded zone. As proven by Raman spectroscopy, operating the tribomechanical sliding test at 50 Hz stimulated the re-attraction of fresh C60 fullerene island onto the fragmented layer from outside of the loaded powder regions. The COF was increasing again up to 0.44 ± 0.04 for 1 N normal force and 50 Hz frequency. The fragmentation and decomposition of fullerene C60 with increasing sliding velocity is attributed to thermal heating up during fast relative movement. Raman spectra of the tribomechanical loaded fullerene C60 are compared with Raman spectra from slowly heated up C60 in air and with Raman spectra of laser irradiated fullerene C60

Hybrid Bone Substitute Containing Tricalcium Phosphate and Silver Modified Hydroxyapatite–Methylcellulose Granules

Despite years of extensive research, achieving the optimal properties for calcium phosphate-based biomaterials remains an ongoing challenge. Recently, ‘biomicroconcretes’ systems consisting of setting-phase-forming bone cement matrix and aggregates (granules/microspheres) have been developed and studied. However, further investigations are necessary to clarify the complex interplay between the synthesis, structure, and properties of these materials. This article focusses on the development and potential applications of hybrid biomaterials based on alpha-tricalcium phosphate (αTCP), hydroxyapatite (HA) and methylcellulose (MC) modified with silver (0.1 wt.% or 1.0 wt.%). The study presents the synthesis and characterization of silver-modified hybrid granules and seeks to determine the possibility and efficiency of incorporating these hybrid granules into αTCP-based biomicroconcretes. The αTCP and hydroxyapatite provide structural integrity and osteoconductivity, the presence of silver imparts antimicrobial properties, and MC allows for the self-assembling of granules. This combination creates an ideal environment for bone regeneration, while it potentially may prevent bacterial colonization and infection. The material’s chemical and phase composition, setting times, compressive strength, microstructure, chemical stability, and bioactive potential in simulated body fluid are systematically investigated. The results of the setting time measurements showed that both the size and the composition of granules (especially the hybrid nature) have an impact on the setting process of biomicroconcretes. The addition of silver resulted in prolonged setting times compared to the unmodified materials. Developed biomicroconcretes, despite exhibiting lower compressive strength compared to traditional calcium phosphate cements, fall within the range of human cancellous bone and demonstrate chemical stability and bioactive potential, indicating their suitability for bone substitution and regeneration. Further in vitro studies and in vivo assessments are needed to check the potential of these biomaterials in clinical applications

Special Issue Paper Diamond-like carbon coatings with Ca-O-incorporation for improved biological acceptance

Abstract. Diamond-like carbon (DLC) coatings were modified by doping the thin films with Ca-O compounds. Raman spectroscopy indicates growth of sp 2 -hybridised, ordered regions in size and/or number within the amorphous carbon-hydrogen network as a result of the Ca-O-incorporation. CaCO 3 was identified by X-ray induced photoelectron spectroscopy. Proliferation and morphology of L929 mouse fibroblasts reveal improved biocompatibility of Ca-O-modified DLC

Optimierung der Belastbarkeit und Biokompatibilitaet von Knochenersatzwerkstoffen durch angepasste Verstaerkung mit C-, Al_2O_3- und SiO_2-Fasern Schlussbericht

SIGLEAvailable from TIB Hannover: F03B579 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

Processing and Wear Behaviour of 3D Printed PLA Reinforced with Biogenic Carbon

For the first time, biocarbon reinforced polylactide (PLA) filaments were available for the 3D printing. Biocarbon is the carbon obtained from trees, plants, and soils to naturally absorb and store carbon dioxide from the atmosphere. One of the most important features is renewability. Because of this, it has been decided to reinforce PLA with biocarbon to obtain 100% recyclable material. Although PLA has been used in 3D printing for a long time, more applications like housings or structural interior of automobiles or other vehicles can be realised, if the mechanical and tribological properties are improved. Because the new PLA/biocarbon reinforced composites are degradable, they can be used as soil improvement after end of life as a structural material. The filaments were produced by compounding the biocarbon with polylactide granulate. Biocarbon was produced by pyrolysis of wheat stems at 800°C. The biomass were collected from different regions in Germany, Europe. As shown by Raman spectroscopy, the in-plane crystallite size of pyrolysed wheat stems from different regions is almost similar and amounts to 2.35 ±0.02 nm. Biocarbon particles were successfully integrated into the polylactide. Filaments of 1.75 mm diameter were produced for 3D (3-dimensional) printing. Filaments with 5 vol.-%, 15 vol.-%, and 30 vol.-% biocarbon were extruded. The fused deposition modelling (FDM) printing process was slightly hindered at higher biocarbon loading. Based on optical and scanning electron microscopy, a very homogeneous particle distribution can be observed. Single carbon particles stick out of the filament surface, which may be a reason for enhanced nozzle wear during 3D printing. Friction is more stable for 30 vol.-% reinforced PLA in comparison to unreinforced PLA and composites with lower particle fraction. This effect could be caused by some topographical effects due to void generation at the surface of PLA with 30 vol.-% biocarbon. In general, the tribological resistance increases with higher volume fraction of biocarbon