Platelet-rich plasma (PRP) has been used for different applications in human and veterinary medicine. Many studies have shown promising therapeutic effects of PRP; however, there are still many controversies regarding its composition, properties, and clinical efficacy. The aim of this study was to evaluate the influence of different platelet concentrations on the rheological properties and growth factor (GF) release profile of PRP-gels. In addition, the viability of incorporated bone marrow-derived human mesenchymal stem cells (MSCs) was investigated. PRP (containing 1000 × 10(3), 2000 × 10(3), and 10,000 × 10(3) platelets/μL) was prepared from human platelet concentrates. Platelet activation and gelification were achieved by addition of human thrombin. Viscoelastic properties of PRP-gels were evaluated by rheological studies. The release of GFs and inflammatory proteins was measured using a membrane-based protein array and enzyme-linked immunosorbent assay. MSC viability and proliferation in PRP-gels were assessed over 7 days by cell viability staining. Cell proliferation was examined using DNA quantification. Regardless of the platelet content, all tested PRP-gels showed effective cross-linking. A positive correlation between protein release and the platelet concentration was observed at all time points. Among the detected proteins, the chemokine CCL5 was the most abundant. The greatest release appeared within the first 4 h after gelification. MSCs could be successfully cultured in PRP-gels over 7 days, with the highest cell viability and DNA content found in PRP-gels with 1000 × 10(3) platelets/μL. The results of this study suggest that PRP-gels represent a suitable carrier for both cell and GF delivery for tissue engineering. Notably, a platelet concentration of 1000 × 10(3) platelets/μL appeared to provide the most favorable environment for MSCs. Thus, the platelet concentration is an important consideration for the clinical application of PRP-gels.

Pericyte recruitment is essential for the stability of newly formed vessels. It was also suggested that pericytes represent common ancestor cells giving rise to mesenchymal stem cells (MSCs) in the adult. Here, we systematically investigated pericytes and MSCs from different human tissues in terms of their angiogenic and multilineage differentiation potential in vitro in order to assess the suitability of the different cell types for the regeneration of vascularised tissues. Magnetic-activated cell sorting (MACS ® ) was used to enrich CD34-CD146+ pericytes from adipose tissue (AT) and bone marrow (BM). The multilineage potential of pericytes was assessed by testing their capability to differentiate towards osteogenic, adipogenic and chondrogenic lineage in vitro. Pericytes and endothelial cells were co-seeded on Matrigel™ and the formation of tube-like structures was examined to study the angiogenic potential of pericytes. MSCs from AT and BM were used as controls. CD34-CD146+ cells were successfully enriched from AT and BM. Only BM-derived cells exhibited trilineage differentiation potential. ATderived cells displayed poor chondrogenic differentiation upon stimulation with transforming growth factor-β1. Interestingly, osteogenic differentiation was more efficient in AT-PC and BM-PC compared to the respective full MSC population. Matrigel™ assays revealed that pericytes from all tissues integrated into tube-like structures. We show that MACS ® -enriched pericytes from BM and AT have the potential to regenerate tissues of different mesenchymal lineages and support neovascularisation. MACS ® represents a simple enrichment strategy of cells, which is of particular interest for clinical application. Finally, our results suggest that the regenerative potential of pericytes depends on their tissue origin, which is an important consideration for future studies.