Use of platelet lysate for bone regeneration-are we ready for clinical translation?

Current techniques to improve bone regeneration following trauma or tumour resection involve the use of autograft bone or its substitutes supplemented with osteoinductive growth factors and/or osteogenic cells such as mesenchymal stem cells(MSCs).Although MSCs are most commonly grown in media containing fetal calf serum,human platelet lysate(PL) offers an effective alternative.Bone marrow- derived MSCs grown in PLcontaining media display faster proliferation whilst maintaining good osteogenic differentiation capacity.Limited pre-clinical investigations using PL-expanded MSCs seeded onto osteoconductive scaffolds indicate good potential of such constructs to repair bone in vivo.In an alternative approach,nude PL-coated scaffolds without seeded MSCs have been proposed as novel regenerative medicine devices.Even though methods to coat scaffolds with PL vary,in vitro studies suggest that PL allows for MSC adhesion,migration and differentiation inside these scaffolds.Increased new bone formation and vascularisation in comparison to uncoated scaffolds have also been observed in vivo.This review outlines the state-of-the-art research in the field of PL for ex vivo MSC expansion and in vivo bone regeneration.To minimise inconsistency between the studies,further work is required towards standardisation of PL preparation in terms of the starting material,platelet concentration,leukocyte depletion,and the method of platelet lysis.PL quality control procedures and its "potency" assessment are urgently needed,which could include measurements of key growth and attachment factors important for MSC maintenance and differentiation.Furthermore,different PL formulations could be tailor-made for specific bone repair indications.Such measures would undoubtedly speed up clinical translation of PL-based treatments for bone regeneration.

Synovial mesenchymal stem cells in vivo:Potential key players for joint regeneration

Unlike bone marrow(BM)mesenchymal stem cells(MSCs),whose in vivo identity has been actively explored in recent years,the biology of MSCs in the synovium remains poorly understood.Synovial MSCs may be of great importance to rheumatology and orthopedics because of the direct proximity and accessibility of the synovium to cartilage,ligament,and meniscus.Their excellent chondrogenic capabilities and suggested transit through the synovial fluid,giving unhindered access to the joint surface,further support a pivotal role for synovial MSCs in homeostatic joint repair.This review highlights several unresolved issues pertaining to synovial MSC isolation,topography,and their relationship with pericytes,synovial fibroblasts,and synovial fluid MSCs.Critically reviewing published data on synovial MSCs,we also draw from our experience of exploring the in vivo biology of MSCs in the BM to highlight key differences.Extending our knowledge of synovial MSCs in vivo could lead to novel therapeutic strategies for arthritic diseases.