Weightbearing ovine osteochondral defects heal with inadequate subchondral bone plate restoration: implications regarding osteochondral autograft harvesting

PURPOSE: It is unknown what causes donor site morbidity following the osteochondral autograft transfer procedure or how donor sites heal. Contact pressure and edge loading at donor sites may play a role in the healing process. It was hypothesized that an artificially created osteochondral defect in a weightbearing area of an ovine femoral condyle will cause osseous bridging of the defect from the upper edges, resulting in incomplete and irregular repair of the subchondral bone plate. METHODS: To simulate edge loading, large osteochondral defects were created in the most unfavourable weightbearing area of 24 ovine femoral condyles. After killing at 3 and 6 months, osteochondral defects were histologically and histomorphometrically evaluated with specific attention to subchondral bone healing and subchondral bone plate restoration. RESULTS: Osteochondral defect healing showed progressive osseous defect bridging by sclerotic circumferential bone apposition. Unfilled area decreased significantly from 3 to 6 months (P = 0.004), whereas bone content increased (n.s.). Complete but irregular subchondral bone plate restoration occurred in ten animals. In fourteen animals, an incomplete subchondral bone plate was found. Further common findings included cavitary lesion formation, degenerative cartilage changes and cartilage and subchondral bone collapse. CONCLUSIONS: Osteochondral defect healing starts with subchondral bone plate restoration. However, after 6 months, incomplete or irregular subchondral bone plate restoration and subsequent failure of osteochondral defect closure is common. Graft harvesting in the osteochondral autograft transfer procedure must be viewed critically, as similar changes are also present in humans. LEVEL OF EVIDENCE: Prognostic study, Level III

A multiscale experimental analysis of mechanical properties and deformation behavior of sintered copper–silicon carbide composites enhanced by high‑pressure torsion

Experiments were conducted to investigate, within the framework of a multiscale approach, the mechanical enhancement, deformation and damage behavior of copper–silicon carbide composites (Cu–SiC) fabricated by spark plasma sintering (SPS) and the combination of SPS with high-pressure torsion (HPT). The mechanical properties of the metal–matrix composites were determined at three different length scales corresponding to the macroscopic, micro- and nanoscale. Small punch testing was employed to evaluate the strength of composites at the macroscopic scale. Detailed analysis of microstructure evolution related to SPS and HPT, sample deformation and failure of fractured specimens was conducted using scanning and transmission electron microscopy. A microstructural study revealed changes in the damage behavior for samples processed by HPT and an explanation for this behavior was provided by mechanical testing performed at the micro- and nanoscale. The strength of copper samples and the metal–ceramic interface was determined by microtensile testing and the hardness of each composite component, corresponding to the metal matrix, metal–ceramic interface, and ceramic reinforcement, was measured using nano-indentation. The results confirm the advantageous effect of large plastic deformation on the mechanical properties of Cu–SiC composites and demonstrate the impact on these separate components on the deformation and damage type

Suspended manufacture of biological structures

We present a novel method of extrusion-based ALM for the production of cell-laden strucutres from low viscosity polymers. The traditional planar print bed is replaced with a bed of micoparticulate fluid gel. During the extrusion process, the fluid gel is displaced whilst providing a support strucutre for the low viscosity material allowing manufacture of relatively complex geometries. The extruded structure can then be easily removed from this self-healing fluid bed. For this study, a bi-layered cell-seeded construct was produced to model the osteochondral junction. Osteochondral plugs were produced by the addition of chondrocytes and osteoblasts to 1.5%w/v gellan and 1.5%w/v gellan-5% nano-hydroxyapatite respectively. The consecutive extrusion of these two solutions into the fluid bed followed by further ionic crosslinking produced the bi-layered construct that was implant into a femoral condyle defect in vitro. Cell viability following extrusion was confirmed using calcein AM/PI live/dead staining showing excellent viability. Constructs were then sectioned, and qRT-PCR was performed, showing a native collagen phenotype across the construct with evidence of matrix markers in the cartilage-like region which were also identified using fluroescent-IHC. Constructs were also tested for their bulk relaxation properties. Addition of nano-hydroxyapatite in the bone-like region resulted in a faster, more elastic relaxation than gellan alone, something that has previously been reported to favour osteogenic differentiation. We have demonstrated the efficacy of suspended manufacturing to maintain viability and phenotype of two populations of human primary cells in a single construct thus emulating the structure of the osteochondral junction. Please click Additional Files below to see the full abstract

Effect of spark plasma sintering and high-pressure torsion on the microstructural and mechanical properties of a Cu–SiC composite

This investigation examines the problem of homogenization in metal matrix composites (MMCs) and the methods of increasing their strength using severe plastic deformation (SPD). In this research MMCs of pure copper and silicon carbide were synthesized by spark plasma sintering (SPS) and then further processed via highpressure torsion (HPT). The microstructures in the sintered and in the deformed materials were investigated using Scanning Electron Microscopy (SEM) and Scanning Transmission Electron Microscopy (STEM). The mechanical properties were evaluated in microhardness tests and in tensile testing. The thermal conductivity of the composites was measured with the use of a laser pulse technique. Microstructural analysis revealed that HPT processing leads to an improved densification of the SPS-produced composites with significant grain refinement in the copper matrix and with fragmentation of the SiC particles and their homogeneous distribution in the copper matrix. The HPT processing of Cu and the Cu-SiC samples enhanced their mechanical properties at the expense of limiting their plasticity. Processing by HPT also had a major influence on the thermal conductivity of materials. It is demonstrated that the deformed samples exhibit higher thermal conductivity than the initial coarse-grained samples