Bone Tissue Response to Porous and Functionalized Titanium and Silica Based Coatings

Background: Topography and presence of bio-mimetic coatings are known to improve osseointegration. The objective of this study was to evaluate the bone regeneration potential of porous and osteogenic coatings. Methodology: Six-implants [Control (CTR); porous titanium coatings (T1, T2); thickened titanium (Ti) dioxide layer (TiO2); Amorphous Microporous Silica (AMS) and Bio-active Glass (BAG)] were implanted randomly in tibiae of 20-New Zealand white rabbits. The animals were sacrificed after 2 or 4 weeks. The samples were analyzed histologically and histomorphometrically. In the initial bone-free areas (bone regeneration areas (BRAs)), the bone area fraction (BAF) was evaluated in the whole cavity (500 mm, BAF-500), in the implant vicinity (100 mm, BAF-100) and further away (100–500 mm, BAF-400) from the implant. Bone-to-implant contact (BIC-BAA) was measured in the areas where the implants were installed in contact to the host bone (bone adaptation areas (BAAs)) to understand and compare the bone adaptation. Mixed models were used for statistical analysis. Principal Findings: After 2 weeks, the differences in BAF-500 for different surfaces were not significant (p.0.05). After 4 weeks, a higher BAF-500 was observed for BAG than CTR. BAF-100 for AMS was higher than BAG and BAF-400 for BAG was higher than CTR and AMS. For T1 and AMS, the bone regeneration was faster in the 100-mm compared to the 400-mm zone. BIC-BAA for AMS and BAG was lower after 4 than 2 weeks. After 4 weeks, BIC-BAA for BAG was lower than AMS and CTR. Conclusions: BAG is highly osteogenic at a distance from the implant. The porous titanium coatings didn’t stimulate bone regeneration but allowed bone growth into the pores. Although AMS didn’t stimulate higher bone response, it has a potential of faster bone growth in the vicinity compared to further away from the surface. BIC-BAA data were inconclusive to understand the bone adaptation.status: publishe

Existence of a Tribo-Modified Surface Layer on SBR Elastomers: Balance Between Formation and Wear of the Modified Layer

In most of the tribological contacts, the composition and tribological properties of the original interface will change during use. The tribo-films, with modified properties compared to the bulk, are dynamic structures that play a significant role in friction. The existence of a tribo-modified surface layer and its importance on the overall friction of elastomers has been shown both theoretically and experimentally before. The characteristics of the modified surface layer deserve specific attention since the tribological properties of elastomers in contact with a rough counter-surface are determined by these modified surfaces together with the properties of bulk of the material. Both the formation of the modified layer and the break down (wear) of it are of importance in determining the existence and thickness of the tribo-modified layer. In this study, the importance of the wear is emphasized by comparing two styrene butadiene rubber-based elastomers in contact with a granite sphere. A current status of perception of the removal and the stability of the modified surface layers on rubbers is introduced as well as experimental work related to this matter and discussion within literature. Pin-on-disk friction tests are performed on two SBR-based samples in contact with a granite sphere under controlled environmental conditions to form the modified surface layer. Although the hysteresis part of the friction force which has a minor contribution in the overall friction is not markedly different, the total measured friction coefficient differs significantly. Mechanical changes both inside and outside the wear track are determined by atomic force microscope nano-indentations at different timescales to examine the modified surface layer on the test samples. The specific wear rates of the two tribo-systems are compared, and the existence of the modified surface layer, the different measured friction coefficient and the running-in distances toward steady-state friction are explained considering different wear rates. A conceptual model is presented, correlating the energy input into the tribo-system and the existence of a modified surface layer

Additive manufacturing of a novel alpha titanium alloy from commercially pure titanium with minor addition of Mo₂C

In this study, a fully dense and crack-free alpha titanium alloy was fabricated using selective laser melting (SLM) of commercially pure titanium (CP Ti) blended with 1 vol.% micrometre-sized Mo₂C powder. The microstructure and mechanical properties of the fabricated Ti alloy were systematically investigated. It was found that the fabricated Ti alloy consisted of both alpha (α) and beta (β) phases and exhibited a nest-like inhomogeneous microstructure with graded local phase formation, composition and crystallographic texture. This novel microstructure was formed through melting and rapid solidification of CP Ti and Mo₂C during SLM, assisted by the high laser absorptivity and resultant high temperature rise of the Mo₂C powder. The fabricated Ti alloy exhibited higher tensile strength (∼1250 ± 50 MPa) and improved ductility (elongation ∼17 ± 1%) when compared to CP Ti fabricated using the same SLM process. The underlying reasons were mainly attributed to (i) the nest-like inhomogeneous microstructure consisting of fine grained α-Ti and β-Ti, (ii) the overall solid solution strengthening of the Ti matrix by interstitial C, and (iii) the high dislocation density in the Ti matrix arising from the mismatch between α-Ti and β-Ti phases. This study not only provides a fundamental knowledge about the modification of CP Ti with minor addition of secondary particles through SLM but also provides insight into the fabrication of inhomogeneous Ti alloys with graded microstructure and local composition through SLM for enhanced mechanical properties.status: publishe

A novel phenotype in N-glycosylation disorders: Gillessen-Kaesbach-Nishimura skeletal dysplasia due to pathogenic variants in ALG9.

A rare lethal autosomal recessive syndrome with skeletal dysplasia, polycystic kidneys and multiple malformations was first described by Gillessen-Kaesbach et al and subsequently by Nishimura et al. The skeletal features uniformly comprise a round pelvis, mesomelic shortening of the upper limbs and defective ossification of the cervical spine. We studied two unrelated families including three affected fetuses with Gillessen-Kaesbach-Nishimura syndrome using whole-exome and Sanger sequencing, comparative genome hybridization and homozygosity mapping. All affected patients were shown to have a novel homozygous splice variant NM_024740.2: c.1173+2T>A in the ALG9 gene, encoding alpha-1,2-mannosyltransferase, involved in the formation of the lipid-linked oligosaccharide precursor of N-glycosylation. RNA analysis demonstrated skipping of exon 10, leading to shorter RNA. Mass spectrometric analysis showed an increase in monoglycosylated transferrin as compared with control tissues, confirming that this is a congenital disorder of glycosylation (CDG). Only three liveborn children with ALG9-CDG have been previously reported, all with missense variants. All three suffered from intellectual disability, muscular hypotonia, microcephaly and renal cysts, but none had skeletal dysplasia. Our study shows that some pathogenic variants in ALG9 can present as a lethal skeletal dysplasia with visceral malformations as the most severe phenotype. The skeletal features overlap with that previously reported for ALG3- and ALG12-CDG, suggesting that this subset of glycosylation disorders constitutes a new diagnostic group of skeletal dysplasias.European Journal of Human Genetics advance online publication, 13 May 2015; doi:10.1038/ejhg.2015.91