Low back pain (LBP) can significantly reduce the quality of life of patients, and has a considerable economic and social impact worldwide. It is commonly associated with disc degeneration, even though many people with degenerate discs are asymptomatic. Degenerate disc disease (DDD), is thus a common term for intervertebral disc (IVD) degeneration associated with LBP. Degeneration is thought to lead to LBP because of nerve ingrowth into the degenerate disc, inflammation, or because degradation of extracellular matrix (ECM) alters spinal biomechanics inappropriately. Thus, while the objectives of some interventions for LBP are to control pain intensity, other interventions aim to deal with the consequences of disc degeneration through stabilizing the disc surgically, by inserting artificial discs or by repairing the disc biologically and preventing progressive IVD degeneration. Despite tremendous research efforts, treatment of LBP through the use of regenerative interventions aiming to repair the IVD is still controversial. The use of mesenchymal stem cells for IVD regeneration in a patient‐based case will be discussed by an ensemble of clinicians and researchers.

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Background: Platelet-rich plasma (PRP) refers to an enriched platelet suspension in plasma. In addition to the clinical application of PRP in the context of various orthopedic diseases and beyond, PRP and platelet lysate (PL) have been in focus in the field of tissue engineering. In this review, we discuss the application of PRP as a cell culture supplement and as part of tissue engineering strategies, particularly emphasizing current hurdles and ambiguities regarding the efficacy of PRP in these approaches. Summary: As a putative autologous replacement for animal-derived supplements such as fetal calf serum (FCS), PRP has been applied as cell culture supplement for the expansion of stem and progenitor cells for tissue engineering applications and cell therapies. Attributed to the high content of growth factors in platelets, PRP has been shown to promote cell growth, which was mostly superior to standard cultures supplemented with FCS, while the differentiation capacity of progenitor cells seems not to be affected. However, it was also suggested that cultivation of cells with PRP significantly alters the protein expression profile in cells in comparison to FCS, indicating that the influence of PRP on cell behavior should be thoroughly investigated. Moreover, different PRP preparation methods and donor variations have to be considered for the use of PRP under good manufacturing practice conditions. PRP has been used for various tissue engineering applications in the context of bone, cartilage, skin, and soft tissue repair, where most studies were conducted in the field of bone tissue engineering. These approaches take either advantage of the release of chemoattractive, angiogenic, proliferative, and putatively pro-regenerative growth factors from PRP, and/or the hydrogel properties of activated PRP, making it suitable as a cell delivery vehicle. In many of these studies, PRP is combined with biomaterials, cells, and in some cases recombinant growth factors. Although the experimental design often does not allow conclusions on the pro-regenerative effect of PRP itself, most publications report beneficial effects if PRP is added to the tissue-engineered construct. Furthermore, it was demonstrated that the release of growth factors from PRP may be tailored and controlled when PRP is combined with materials able to capture growth factors. Key Messages: Platelet-derived preparations such as PRP and PL represent a promising source of autologous growth factors, which may be applied as cell culture supplement or to promote regeneration in tissue-engineered constructs. Furthermore, activated PRP is a promising candidate as an autologous cell carrier. However, the studies investigating PRP in these contexts often show conflicting results, which most likely can be attributed to the lack of standardized preparation methods, particularly with regard to the platelet content and donor variation of PRP. Ultimately, the use of PRP has to be tailored for the individual application.

BackgroundTreatment of meniscus tears within the avascular region represents a significant challenge, particularly in a situation of early osteoarthritis. Cell-based tissue engineering approaches have shown promising results. However, studies have not found a consensus on the appropriate autologous cell source in a clinical situation, specifically in a challenging degenerative environment. The present study sought to evaluate the appropriate cell source for autologous meniscal repair in a demanding setting of early osteoarthritis.MethodsA rabbit model was used to test autologous meniscal repair. Bone marrow and medial menisci were harvested 4 weeks prior to surgery. Bone marrow-derived mesenchymal stem cells (MSCs) and meniscal cells were isolated, expanded, and seeded onto collagen-hyaluronan scaffolds before implantation. A punch defect model was performed on the lateral meniscus and then a cell-seeded scaffold was press-fit into the defect. Following 6 or 12 weeks, gross joint morphology and OARSI grade were assessed, and menisci were harvested for macroscopic, histological, and immunohistochemical evaluation using a validated meniscus scoring system. In conjunction, human meniscal cells isolated from non-repairable bucket handle tears and human MSCs were expanded and, using the pellet culture model, assessed for their meniscus-like potential in a translational setting through collagen type I and II immunostaining, collagen type II enzyme-linked immunosorbent assay (ELISA), and gene expression analysis.ResultsAfter resections of the medial menisci, all knees showed early osteoarthritic changes (average OARSI grade 3.1). However, successful repair of meniscus punch defects was performed using either meniscal cells or MSCs. Gross joint assessment demonstrated donor site morbidity for meniscal cell treatment. Furthermore, human MSCs had significantly increased collagen type II gene expression and production compared to meniscal cells (p < 0.05).ConclusionsThe regenerative potential of the meniscus by an autologous cell-based tissue engineering approach was shown even in a challenging setting of early osteoarthritis. Autologous MSCs and meniscal cells were found to have improved meniscal healing in an animal model, thus demonstrating their feasibility in a clinical setting. However, donor site morbidity, reduced availability, and reduced chondrogenic differentiation of human meniscal cells from debris of meniscal tears favors autologous MSCs for clinical use for cell-based meniscus regeneration.

The endogenous healing potential of avascular meniscal lesions is poor. Up to now, partial meniscectomy is still the treatment of choice for meniscal lesions within the avascular area. However, the large loss of meniscus substance predisposes the knee for osteoarthritic changes. Tissue engineering techniques for the replacement of such lesions could be a promising alternative treatment option. Thus, a polyurethane scaffold, which is already in clinical use, loaded with mesenchymal stromal cells, was analyzed for the repair of critical meniscus defects in the avascular zone. Large, approximately 7 mm broad meniscus lesions affecting both the avascular and vascular area of the lateral rabbit meniscus were treated with polyurethane scaffolds either loaded or unloaded with mesenchymal stromal cells. Menisci were harvested at 6 and 12 weeks after initial surgery. Both cell-free and cell-loaded approaches led to well-integrated and stable meniscus-like repair tissue. However, an accelerated healing was achieved by the application of mesenchymal stromal cells. Dense vascularization was detected throughout the repair tissue of both treatment groups. Overall, the polyurethane scaffold seems to promote the vessel ingrowth. The application of mesenchymal stromal cells has the potential to speed up the healing process.