Cell loading of open-porous SLM-generated metal implants with mesenchymal stem cells for optimized tissue recovery and tissue regeneration

Status:

completed 12/2013

Aims:

Selective Laser Meltiung (SLM) allows the fabrication of highly porous implant geometries which could hardly be produced or not at all by conventional processes. Additionally, so called "tailor-made" individual implants can be produced. It was the purpose of this research project to determine optimal features of porous metallic SLM implants as carriers for autologous mesenchymal stem cells (such as cell viability, cell adherence, cell proliferation, cell differentiation).

Activities/Methods:

SLM samples (cylinder, 8 mm diameter, 5 mm height) made from Ti6Al4V ELI (Alpha Beta Titan alloy with vanadium and aluminium "Extra Low Interstitials") were fabricated by SLM-Solutions (Lübeck, Germany). Three different given pore sizes (0.5, 0.8 and 1.1 mm) and three different geometries (starcross, dodecahedron, fccz) were combined among each other (maximal porosity 90%). Sample analysis was performed by light microscopy and scanning electron microscopy (SEM). After fabrication pore sizes were reduced up to 200 μm due to adherent powder particles. Despite intensive washings (8 x ethanol, 2 x distilled water) a pore size related particle release was measured. The size distribution of these spheric particles was between 1 μm and 80 μm with maxima of 50 μm. The release increased with decreasing pore size and increasing porosity. The load capacity of the samples was determined by uniaxial load tests. The maximal strain for a first irreversible deformation by compression was higher than the functional failure strain of human vertebral bodies with except for highly porous dodecahedron structures (0.8 and 1.1 mm pore size).

Results:

Cell biological analyses revealed adherence of human mesenchymal stem cells (hMSC) at all sample types (calcein-AM fluorescence microscopy, SEM) incl. the internal area. Comparison of geometries showed optimal adherence at dodecahedron as well as at starcross types. A cell colonization of internal surfaces of the samples was possible. Cellular cytotoxic reactions towards the material were not observed (PI stain, LDH). The number of adherent cells was increased with decreasing pore size. A previous coating of the samples with fibronectin did not lead to an increase in cell adherence. Adherent cells proliferated on the struts of the porous samples. A colonization of the samples by hMSC embedded in gelled human plasma (plasma clot) resulted in consistant cellular distribution also within the sample pores but induced a decrease in cell viability within the samples’ center. After adherence and proliferation on samples or after lysis of the plasma clot matrix the osteogenic capacity of hMSC was preserved.

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