Intervertebral disc regeneration using platelet‑rich plasma‑containing bone marrow‑derived mesenchymal stem cells: A preliminary investigation

Current Therapeutic Strategies of Intervertebral Disc Regenerative Medicine

Intervertebral disc degeneration (IDD) is one of the most frequent causes of low back pain. No treatment is currently available to delay the progression of IDD. Conservative treatment or surgical interventions is only used to target the symptoms of IDD rather than treat the underlying cause. Currently, numerous potential therapeutic strategies are available, including molecular therapy, gene therapy, and cell therapy. However, the hostile environment of degenerated discs is a major problem that has hindered the clinical applicability of such approaches. In this regard, the design of drugs using alternative delivery systems (macro-, micro-, and nano-sized particles) may resolve this problem. These can protect and deliver biomolecules along with helping to improve the therapeutic effect of drugs via concentrating, protecting, and prolonging their presence in the degenerated disc. This review summarizes the research progress of diagnosis and the current options for treating IDD.

Orthobiologic Management Options for Degenerative Disc Disease

Degenerative disc disease (DDD) is a pervasive condition that limits quality of life and burdens economies worldwide. Conventional pharmacological treatments primarily aimed at slowing the progression of degeneration have demonstrated limited long-term efficacy and often do not address the underlying causes of the disease. On the other hand, orthobiologics are regenerative agents derived from the patient's own tissue and represent a promising emerging therapy for degenerative disc disease. This review comprehensively outlines the pathophysiology of DDD, highlighting the inadequacies of existing pharmacological therapies and detailing the potential of orthobiologic approaches. It explores advanced tools such as platelet-rich plasma and mesenchymal stem cells, providing a historical overview of their development within regenerative medicine, from foundational in vitro studies to preclinical animal models. Moreover, the manuscript delves into clinical trials that assess the effectiveness of these therapies in managing DDD. While the current clinical evidence is promising, it remains insufficient for routine clinical adoption due to limitations in study designs. The review emphasizes the need for further research to optimize these therapies for consistent and effective clinical outcomes, potentially revolutionizing the management of DDD and offering renewed hope for patients.

The Clinical Efficacy of Platelet-Rich Plasma Injection Therapy versus Different Control Groups for Chronic Low Back Pain: A Network Meta-Analysis of Randomized Controlled Trials

Objective

Low back pain is one of the main causes of disability in the world. Although regenerative medicine may represent breakthroughs in the management of low back pain, its use remains controversial. Therefore, we conducted a meta-analysis to evaluate the clinical efficacy of platelet-rich plasma (PRP) injection therapy versus different control groups for chronic low back pain during 4 weeks, 3 months, and 6 months.

Methods

Different electronic databases were searched for randomized controlled trials up to August 2023. Mean changes from baseline in pain and Oswestry Disability Index (ODI) scores at 4 weeks, 3 months, and 6 months and standard deviations of outcome were recorded.

Results

Four articles with 154 cases were finally included in this meta-analysis. After 4 weeks, corticosteroid (CS) was the optimal treatment option for chronic low back pain in terms of improvement in pain and disability index (surface under the cumulative ranking curve [SUCRA]=71.3%, SUCRA=57.8%, respectively). After 3 months, radiofrequency (RF) emerged as the best therapy in pain (SUCRA=100%) and disability index (SUCRA=98.5%), followed by PRP (SUCRA=62.3%, SUCRA=64.3%, respectively), CS (SUCRA=24.6%, SUCRA=25.9%, respectively) and lidocaine (SUCRA=13.1%, SUCRA=11.3%, respectively). At 6 months, RF was most likely to be the best treatment in pain (SUCRA=94.9%) and disability index (SUCRA=77.3%), followed by PRP (SUCRA=71.2%, SUCRA=79.6%, respectively). However, compared with the last follow-up, there was a slight downward trend in improvement pain and disability index with RF, while PRP was still an upward trend.

Conclusion

This study demonstrated better short-term improvement of chronic low back pain with CS after 4 weeks. PRP and RF improvement effects matched, but follow-up of at least 6 months showed that PRP seemed to be more advantageous in improvement in disability indices. Considering the limitations of this study, these conclusions still need to be verified by more comparative RCTs and a longer follow-up period.

Systematic Review of Platelet-Rich Plasma for Low Back Pain

BACKGROUND

Low back pain (LBP) has a high economic burden and is strongly related to the degenerative process of the spine, especially in the intervertebral disc and of the facet joints. Numerous treatment modalities have been proposed for the management of LBP, and the use of platelet-rich plasma (PRP) has emerged as an innovative therapeutic option for degenerative disease of the spine. The present study aims to evaluate the efficacy of PRP injections in managing low back pain.

METHODS

We conducted a systematic review in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations, a registered at PROSPERO Systematic Reviews Platform, under number CRD42021268491. The PubMed, Web of Science, and Scopus databases were searched to identify relevant articles, along with hand searching to identify gray literature articles, with no language restrictions. Randomized clinical trials (RCTs), nonrandomized trials (NRTs), and case series (CSs) with more than 10 patients were considered eligible. The quality assessment and the risk of bias of the randomized clinical trials were evaluated using the RoB II tool. An evaluation of the description of the preparation methods was performed using an adapted version of the MIBO checklist.

RESULTS

An electronic database search resulted in 2324 articles, and after the exclusion of noneligible articles, 13 RCTs and 27 NRTs or CSs were analyzed. Of the 13 RCTs, 11 found favorable results in comparison to the control group in pain and disability, one showed no superiority to the control group, and one was discontinued because of the lack of therapeutic effect at eight-week evaluation. Description of the PRP preparation techniques were found in almost all papers. The overall risk of bias was considered high in 2 papers and low in 11. An adapted MIBO checklist showed a 72.7% compliance rate in the selected areas.

CONCLUSIONS

In this systematic review, we analyzed articles from English, Spanish and Russian language, from large databases and grey literature. PRP was in general an effective and safe treatment for degenerative LPB. Positive results were found in almost studies, a small number of adverse events were related, the risk of bias of the RCTs was low. Based on the evaluation of the included studies, we graded as level II the quality of the evidence supporting the use of PRP in LBP. Large-scale, multicenter RCTs are still needed to confirm these findings.

The Potency of Platelet-Rich Plasma for Chronic Low Back Pain: A Systematic Review and Metaanalysis of Randomized Controlled Trial

Low back pain is one of the leading causes of disability in the world. Regenerative medicine can be one of the novel treatment breakthroughs in patients with low back pain, yet its use is still debatable. We performed a systematic evaluation and meta-analysis to determine the efficacy of platelet-rich plasma (PRP) treatment for patients with chronic low back pain. Comprehensive database searches were performed in four databases. This study was conducted and reported based on the Preferred Reporting Items for Systematic Reviews and Meta-analyses Guideline and registered to PROSPERO. We included and examined randomized controlled trials that looked into research employing PRP for patients with chronic low back pain. Outcomes of interest include clinical enhancement of pain, which is demonstrated in pain scores. Three studies were included comprising 138 patients with chronic low back pain. After 1, 3, and 6 months after injection, there was a substantial reduction in the pain score difference between the PRP and control groups, demonstrating PRP's superiority over the control group in the treatment of chronic low back pain. PRP injection significantly enhances chronic low back pain in the first, third, and sixth months after injection compared to controls.

Application of platelet-rich plasma in spinal surgery

With the aging of the population and changes in lifestyle, the incidence of spine-related diseases is increasing, which has become a major global public health problem; this results in a huge economic burden on the family and society. Spinal diseases and complications can lead to loss of motor, sensory, and autonomic functions. Therefore, it is necessary to identify effective treatment strategies. Currently, the treatment of spine-related diseases includes conservative, surgical, and minimally invasive interventional therapies. However, these treatment methods have several drawbacks such as drug tolerance and dependence, adjacent spondylosis, secondary surgery, infection, nerve injury, dural rupture, nonunion, and pseudoarthrosis. Further, it is more challenging to promote the regeneration of the interstitial disc and restore its biomechanical properties. Therefore, clinicians urgently need to identify methods that can limit disease progression or cure diseases at the etiological level. Platelet-rich plasma (PRP), a platelet-rich form of plasma extracted from venous blood, is a blood-derived product. Alpha granules contain a large number of cytokines, such as platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), epidermal growth factor, platelet factor 4 (PF-4), insulin-like growth factor-1 (IGF-1), and transforming growth factor-β (TGF-β). These growth factors allow stem cell proliferation and angiogenesis, promote bone regeneration, improve the local microenvironment, and enhance tissue regeneration capacity and functional recovery. This review describes the application of PRP in the treatment of spine-related diseases and discusses the clinical application of PRP in spinal surgery.

Evaluation of the Efficacy of Stem Cell Therapy in Animal Models of Intervertebral Disc Degeneration Based on Imaging Indicators: A Systematic Review and Meta-Analysis

Objective

The purpose of this study is to make a systematic review of the therapeutic effect of stem cells in animal models of disc degeneration from an imaging point of view.

Methods

Data were extracted by searching electronic databases for RCTs that met the inclusion criteria. Data analysis was performed using RevMan 5.3 and STATA 15.1 software. This meta-analysis was registered with INPLASY, registration number INPLASY202240148.

Results

A total of 34 studies were included, covering four species of animals, rabbits, sheep, rats, and mice, with a total of 1163 intervertebral discs. In terms of DHI, the efficacy of stem cell group in rabbits (P < 0.001), mice (P < 0.001), sheep (P < 0.001), and rats (P = 0.001) was better than that in control group. In terms of disc height, the efficacy of stem cell group in rats (P < 0.001) was better than that in control group, while in sheep (P = 0.355), there was no statistical difference between two groups. In terms of MRI index, the efficacy of stem cell group in rats (P < 0.001), mice (P < 0.001), and rabbits (P = 0.016) was better than that in control group. In terms of MRI signal score, the efficacy of stem cell group in rabbits (P < 0.001) was better than that of control group. In terms of T2 signal intensity, stem cell group was more effective than control group in rabbits (P < 0.001), mice (P < 0.001), and rats (P = 0.003).

Conclusion

Stem cell therapy can improve intervertebral disc-related imaging parameters in animal models of disc degeneration, indicating that stem cell therapy has a repairing effect on intervertebral discs. However, given the heterogeneity and limitations of this study, this conclusion still needs to be tested by a large number of studies.

Sod2 and catalase improve pathological conditions of intervertebral disc degeneration by modifying human adipose-derived mesenchymal stem cells

OBJECTIVE

To investigate if the modification of human adipose-derived mesenchymal stem cells (hADSCs) by the antioxidants superoxide dismutase 2 (Sod2) and catalase (Cat) can attenuate the pathological conditions of intervertebral disc degeneration (IVD).

METHODS

In vitro, MTT assay and qRT-PCR was used to detect cell proliferation and gene expressions in hADSCs transduced with Ad-null (an adenovirus vector containing no transgene expression cassette), Ad-Sod2 (recombinant adenovirus Sod2) and Ad-Cat. IVD mouse models were generated by needle puncture and treated with hADSCs with/without Ad-null/Ad-Sod2/Ad-Cat. X-ray evaluation, magnetic resonance imaging (MRI) analysis, histological analysis, immunohistochemistry, Western blots, ELISAs and qRT-PCR were performed.

RESULTS

hADSCs transduced with Ad-Sod2 and Ad-Cat showed enhanced cell proliferation with the upregulation of SOX9, ACAN, and COL2. In vivo, IVD mice injected with hADSCs showed increased disc height index, MRI index and mean T2 intensities, as well as the attenuated histologic grading of the annulus fibrosus (AF) and NP accompanied by the upregulation of GAG and COL2, which were further improved in the Ad-Sod2 hADSC + IVD and Ad-Cat hADSC + IVD groups. Furthermore, the increased expression of IL-1β, IL-6 and TNF-α was reduced in IVD mice injected with hADSCs. Compared with the hADSC + IVD group, the Ad-Sod2 hADSC/Ad-Cat hADSC + IVD groups had lower expression of pro-inflammatory factors.

CONCLUSION

Modification of hADSCs by the antioxidants Sod2 and Cat improved the pathological condition of intervertebral disc tissues with increased GAG and COL2 expression, as well as reduced inflammation, thereby demonstrating a therapeutic effect in IVD.

Effect of Platelet-Rich Plasma on Intervertebral Disc Degeneration In Vivo and In Vitro: A Critical Review

Intervertebral disc degeneration (IDD) is a globally occurring disease that represents a significant cause of socioeconomic problems. Currently, the main method for treating IDD is surgery, including discectomy and vertebral fusion. Several in vitro experiments demonstrated that platelet-rich plasma (PRP) could stimulate cell proliferation and extracellular matrix regeneration. Additionally, in vivo experiments have proven that PRP injection could restore intervertebral disc height. Clinical studies demonstrated that PRP injection could significantly relieve patient pain. However, further studies are still required to clarify the roles of PRP in IDD prevention and treatment. This review is aimed at summarizing and critically analyzing the current evidence regarding IDD treatment with PRP.

Intradiscal Delivery of Anabolic Growth Factors and a Metalloproteinase Inhibitor in a Rabbit Acute Lumbar Disc Injury Model

BACKGROUND

The purpose of our study was to examine the effect of controlled delivery of TGF-β₃, BMP-4, and TIMP-2 with a biocompatible biopolymer, chitosan, on an acutely injured intervertebral disc (IVD) in a rabbit model.

METHODS

After conducting an in vitro analysis of the chondrogenic capacity of the biomolecule cocktail use (ie, TGF-β₃, BMP-4, and TIMP-2) and confirming stem cell viability in chitosan hydrogel, 15 New Zealand white rabbits underwent a lateral approach of the L1 to L4 IVDs. In each rabbit, the L2 to L3 IVD was left pristine, whereas the L1 to L2 and the L3 to L4 IVDs in each rabbit underwent nucleotomy via a 25-G needle, and the animal was subsequently randomized to no further treatment (defect only), chitosan alone, Chitosan + TGF-β₃ + BMP-4, or chitosan + TGF-β₃ + BMP-4 + TIMP-2. At 6 weeks after injury and intervention, the rabbits were killed and spines harvested to undergo quantitative T2 magnetic resonance imaging (MRI) and subsequent histologic analysis.

RESULTS

In the in vitro analysis, cells treated with experimental media containing TGF-β₃, BMP-4, and TIMP-2 exhibited staining indicative of GAG production and began to exhibit a chondrocytic morphology. Quantitative T2 MRI mapping demonstrates that discs treated with chitosan, chitosan containing TGF-β₃ and BMP-4, or chitosan containing TGF-β₃, BMP-4, and TIMP-2 had consistently higher T2 relaxation times compared with defect-only discs. When the T2 relaxation times of each treatment group and defect-only discs were normalized to the healthy control disc, it was found that the T2 relaxation time of discs treated with chitosan containing TGF-β₃ and BMP-4 and discs treated with chitosan containing TGF-β₃, BMP-4, and TIMP-2 were significantly greater compared with defect-only discs (P = .048 and P = .013, respectively). Histologically, animals that received chitosan only, or chitosan with TGF-β₃ and BMP-4, showed a significantly higher intensity of Safranin-O staining (P = .016 and P = .02, respectively) compared with control discs, whereas the difference in staining intensity in animals that received chitosan loaded with TGF-β₃, BMP-4, and TIMP-2 failed to achieve significance (P = .161).

CONCLUSIONS

A combination of chitosan, TGF-β₃, and BMP-4 was effective at promoting regeneration in an acute disc injury rabbit model, whereas TIMP-2 did not have a significant effect.

Use of Platelet-Rich Plasma in Treating Low Back Pain: A Review of the Current Literature

Low back pain (LBP) is a common problem encountered by physicians. It is a considerable cause of morbidity and socioeconomic loss and is one of the most expensive musculoskeletal disorders. Conventional treatments include bed rest, analgesics, therapeutic exercises, lumbar or caudal epidural corticosteroids, and surgery. Several new biological therapies are being investigated for use in LBP and one of these is platelet-rich plasma (PRP). In this article, we summarize the current literature published on PRP concerning its composition, classification, and application in LBP. We believe our review will prove useful to clinicians and academics alike, interested in new developing therapies for LBP.

Efficacy of Platelet-Rich Plasma Containing Xenogenic Adipose Tissue-Derived Stromal Cells on Restoring Intervertebral Disc Degeneration: A Preclinical Study in a Rabbit Model

Objective

Platelet-rich plasma (PRP) containing multiple growth factors is a promising strategy for disc degeneration. Thus, this study hypothesizes that the combination of PRP and adipose tissue-derived stromal cells (ADSCs) may repair degenerative disc more effectively than using each one of them alone.

Methods

The model of early intervertebral disc degeneration was induced by annular puncture in the New Zealand rabbit. Autologous PRP was extracted from fresh arterial blood by using two centrifugation techniques. ADSC was offered by the Center for Clinic Stem Cell Research. Four weeks after the first experiment, PRP or ADSCs or a combination of PRP and ADSCs was injected into the punctured intervertebral disc. Four weeks later, disc height and signal intensity on T2-weighted magnetic resonance imaging (MRI) were assessed.

Results

One month after puncture, we detected relatively narrow discs and lower signal intensity in MRI T2-weighted images. At four weeks after injection, the PRP-ADSC group statistically significantly restored discs, compared with PRP, ADSCs, or negative control group.

Conclusions

The combination of PRP and ADSCs shows an effective potential to restore degenerated intervertebral discs in the rabbit.

In Vitro Evaluation of Proliferation and Migration Behaviour of Human Bone Marrow-Derived Mesenchymal Stem Cells in Presence of Platelet-Rich Plasma

Objective

To access the effects of platelet-rich plasma (PRP) on the behaviour of human bone marrow-derived mesenchymal stem cells (hBMSCs), including proliferation and migration.

Methods

PRP was diluted with DMEM/F12, resulting in concentrations of 1%, 2%, and 5%. The proliferation of hBMSCs was examined by 2 methods: cell-number counting with the haemocytometer method and the colony-forming unit-fibroblast (CFU-F) assay. Cell migration was evaluated using the scratch wound healing (SWH) assay; after that, the recorded digital images were analysed by the Image-Analysis J 1.51j8 software to compare the cell-free areas between groups after 0, 24, and 48 hours.

Results

hBMSCs cultured in DMEM/F12 at PRP concentrations of 1%, 2%, and 5% were all able to proliferate and migrate. In the 5% PRP group, hBMSCs proliferated greatly with a significantly higher cell number than reported for all other groups on days 5, 7, and 9. CFU-Fs were observed in all groups, except for the negative control group. The SWH assay demonstrated that hBMSCs cultured in 2% and 5% PRP almost filled the artificial wound scratch and significantly migrated more than those of all other groups at both 24 h and 48 h.

Conclusion

This study indicated that, due to the significant enhancement of cell proliferation and migration, 5% PRP might be the optimal concentration that should be used to promote the potential of hBMSCs in wound healing.

Platelet-rich plasma in the management of chronic low back pain: a critical review

Low back pain (LBP) is now regarded as the first cause of disability worldwide and should be a priority for future research on prevention and therapy. Intervertebral disc (IVD) degeneration is an important pathogenesis of LBP. Platelet-rich plasma (PRP) is an autologous blood concentrate that contains a natural concentration of autologous growth factors and cytokines and is currently widely used in the clinical setting for tissue regeneration and repair. PRP has great potential to stimulate cell proliferation and metabolic activity of IVD cells in vitro. Several animal studies have shown that the injection of PRP into degenerated IVDs is effective in restoring structural changes (IVD height) and improving the matrix integrity of degenerated IVDs as evaluated by magnetic resonance imaging (MRI) and histology. The results of this basic research have shown the great possibility that PRP has significant biological effects for tissue repair to counteract IVD degeneration. Clinical studies for evaluating the effects of the injection of PRP into degenerated IVDs for patients with discogenic LBP have been reviewed. Although there was only one double-blind randomized controlled trial, all the studies reported that PRP was safe and effective in reducing back pain. While the clinical evidence of tissue repair of IVDs by PRP treatment is currently lacking, there is a great possibility that the application of PRP has the potential to lead to a feasible intradiscal therapy for the treatment of degenerative disc diseases. Further large-scale studies may be required to confirm the clinical evidence of PRP for the treatment of discogenic LBP.

The Differential Effects of Leukocyte-Containing and Pure Platelet-Rich Plasma on Nucleus Pulposus-Derived Mesenchymal Stem Cells: Implications for the Clinical Treatment of Intervertebral Disc Degeneration

Background

Platelet-rich plasma (PRP) is a promising strategy for intervertebral disc degeneration. However, the potential harmful effects of leukocytes in PRP on nucleus pulposus-derived mesenchymal stem cells (NPMSCs) have seldom been studied. This study aimed at comparatively evaluating effects of pure platelet-rich plasma (P-PRP) and leukocyte-containing platelet-rich plasma (L-PRP) on rabbit NPMSCs in vitro.

Methods

NPMSCs isolated from rabbit NP tissues were treated with L-PRP or P-PRP in vitro, and then cell proliferation and expression of stem cell markers, proinflammatory cytokines (TNF-α, IL-1β), production of ECM (extracellular matrix-related protein), and NF-κB p65 protein were validated by CCK-8 assay, real-time polymerase chain reaction, enzyme-linked immunosorbent assay, immunofluorescence, and western blot respectively.

Results

NPMSCs differentiate into nucleus pulposus-like cells after treatment of PRPs (P-PRP and L-PRP), and NPMSCs exhibited maximum proliferation at a 10% PRP dose. L-PRP had observably higher concentration of leukocytes, TNF-α, and IL-1β than P-PRP. Furthermore, compared to P-PRP, L-PRP induced the differentiated NPMSCs to upregulate the expression of TNF-α and IL-1β, enhanced activation of the NF-κB pathway, increased the expression of MMP-1 and MMP-13, and produced less ECM in differentiated NPMSCs.

Conclusions

Both P-PRP and L-PRP can induce the proliferation and NP-differentiation of NPMSCs. Compared to L-PRP, P-PRP can avoid the activation of the NF-κB pathway, thus reducing the inflammatory and catabolic responses.

Biologic therapies to enhance intervertebral disc repair

Degenerative disc disease is a progressive, chronic disorder with strong association to pain, where the dysregulated tissue environment signals disc cells, thereby leading to a low inflammatory process and slow extracellular matrix degradation and fibrosis in a perpetual vicious cycle, generating a structural and functional failure of intervertebral disc joint (IVDJ). Among current biologic therapies, there is an emerging minimally invasive strategy that consists of infiltrating plasma rich in growth factors, a safe and efficacious therapeutic approach for other musculoskeletal degenerative conditions. This review summarizes the homeostasis and degeneration of IVDJ, discusses some results on basic science and therapeutic use of platelet-rich plasma products and advances an alternative minimally invasive biologic therapy in IVDJ degeneration and chronic back pain.

Efficacy of Platelet-Rich Plasma in Retarding Intervertebral Disc Degeneration: A Meta-Analysis of Animal Studies

Objectives

Several animal studies have demonstrated the positive effects of platelet-rich plasma (PRP) on disc degeneration retardation. The present meta-analysis was to verify the efficacy of PRP in retarding disc degeneration in animal.

Methods

Relevant studies were identified and evaluated according to our inclusion and exclusion criteria. The standardized mean difference (SMD) and related 95% confidence interval (95% CI) were estimated to assess PRP efficiency.

Results

In total, eleven studies were included in this meta-analysis. Significant differences were found in the PRP treatment group, which showed increased disc height (SMD = 2.66, 95% CI: 1.86, 3.47, p = 0.000), increased MRI T2 signal intensity (SMD = −3.29, 95% CI: −4.44, −2.13, p = 0.000), and decreased histological degeneration grade (SMD = −4.28, 95% CI: −5.26, −3.30, p = 0.000). However, no significant increase in collagen II expression was found (SMD = 25389.74, 95% CI: −27585.72, 78365.21, p = 0.348). Apart from the subgroup analysis of the disc height based on animal species (pig) and disc degeneration model (chymopapain induction), other subgroup analysis based on animal species (rabbit and rat), study design, disc degeneration model, and follow-up period demonstrated that PRP treatment can significantly restore disc height and increase MRI T2 signal intensity.

Conclusions

PRP treatment is potentially effective in restoring disc height of rodent rabbit and rat, reducing histological degeneration grade, and increasing MRI T2 image signal. PRP injection may be promising therapy for retarding disc degeneration.

Application of platelet-rich plasma with stem cells in bone and periodontal tissue engineering

Presently, there is a high paucity of bone grafts in the United States and worldwide. Regenerating bone is of prime concern due to the current demand of bone grafts and the increasing number of diseases causing bone loss. Autogenous bone is the present gold standard of bone regeneration. However, disadvantages like donor site morbidity and its decreased availability limit its use. Even allografts and synthetic grafting materials have their own limitations. As certain specific stem cells can be directed to differentiate into an osteoblastic lineage in the presence of growth factors (GFs), it makes stem cells the ideal agents for bone regeneration. Furthermore, platelet-rich plasma (PRP), which can be easily isolated from whole blood, is often used for bone regeneration, wound healing and bone defect repair. When stem cells are combined with PRP in the presence of GFs, they are able to promote osteogenesis. This review provides in-depth knowledge regarding the use of stem cells and PRP in vitro, in vivo and their application in clinical studies in the future.

Stem Cell Delivery With Polymer Hydrogel for Treatment of Intervertebral Disc Degeneration: From 3D Culture to Design of the Delivery Device for Minimally Invasive Therapy

Nucleus pulposus (NP) tissue damage can induce detrimental mechanical strain on the biomechanical performance of intervertebral discs (IVDs), causing subsequent disc degeneration. A novel, photocurable, injectable, synthetic polymer hydrogel (pHEMA-co-APMA grafted with PAA) has already demonstrated success in encapsulating and differentiating human mesenchymal stem cells (hMSCs) toward an NP phenotype during hypoxic conditions. After demonstration of promising results in our previous work, in this study we have further investigated the inclusion of mechanical stimulation and its impact on hMSC differentiation toward an NP phenotype through the characterization of matrix markers such as SOX-9, aggrecan, and collagen II. Furthermore, investigations were undertaken in order to approximate delivery parameters for an injection delivery device, which could be used to transport hMSCs suspended in hydrogel into the IVD. hMSC-laden hydrogel solutions were injected through various needle gauge sizes in order to determine its impact on postinjection cell viability and IVD tissue penetration. Interpretation of these data informed the design of a potential minimally invasive injection device, which could successfully inject hMSCs encapsulated in a UV-curable polymer into NP, prior to photo-cross-linking in situ.