Microparticles for controlled growth differentiation factor 6 delivery to direct adipose stem cell-based nucleus pulposus regeneration

Stem cell therapy for degenerative disc disease: Bridging the gap between preclinical promise and clinical potential

Stem cell therapy has gained attention in the field of regenerative medicine due to its potential to restore damaged tissue. This article focuses on the application of stem cell therapy for treating spinal pathologies, particularly intervertebral disc degeneration. Disc degeneration is a major cause of low back pain and is characterized by changes in the matrix and inflammation. Animal studies have demonstrated that the implantation of mesenchymal stem cells (MSCs) yields promising results, including increased disc height, improved hydration, and reduced inflammation. However, the number of clinical trials remains limited, necessitating further research to optimize MSCs therapy. Although preclinical studies offer valuable insights, caution is needed when extrapolating these findings to clinical practice. Stem cell therapy still faces multiple challenges, such as the durability and survival of MSCs upon implantation, uncertain pathways to discogenic differentiation, and the adverse impact of a harsh microenvironment on cell survival. The avascular nature of the intervertebral disc and dynamic loading conditions also affect the adaptation of transplanted cells. Despite these obstacles, stem cell therapy holds promise as a potential treatment for disc degeneration, and ongoing research aims to fill the current gap in conclusive data.

Transcriptomic profiling reveals key early response genes during GDF6-mediated differentiation of human adipose-derived stem cells to nucleus pulposus cells

Background

Stem cell-based therapies show promise as a means of repairing the degenerate intervertebral disc, with growth factors often used alongside cells to help direct differentiation toward a nucleus pulposus (NP)-like phenotype. We previously demonstrated adipose-derived stem cell (ASC) differentiation with GDF6 as optimal for generating NP-like cells through evaluating end-stage differentiation parameters. Here we conducted a time-resolved transcriptomic characterization of ASCs response to GDF6 stimulation to understand the early drivers of differentiation to NP-like cells.

Methods

Human ASCs were treated with recombinant human GDF6 for 2, 6, and 12 h. RNA sequencing and detailed bioinformatic analysis were used to assess differential gene expression, gene ontology (GO), and transcription factor involvement during early differentiation. Quantitative polymerase chain reaction (qPCR) was used to validate RNA sequencing findings and inhibitors used to interrogate Smad and Erk signaling pathways, as well as identify primary and secondary response genes.

Results

The transcriptomic response of ASCs to GDF6 stimulation was time-resolved and highly structured, with "cell differentiation" "developmental processes," and "response to stimulus" identified as key biological process GO terms. The transcription factor ERG1 was identified as a key early response gene. Temporal cluster analysis of differentiation genes identified positive regulation NP cell differentiation, as well as inhibition of osteogenesis and adipogenesis. A role for Smad and Erk signaling in the regulation of GDF6-induced early gene expression response was observed and both primary and secondary response genes were identified.

Conclusions

This study identifies a multifactorial early gene response that contributes to lineage commitment, with the identification of a number of potentially useful early markers of differentiation of ASCs to NP cells. This detailed insight into the molecular processes in response to GDF6 stimulation of ASCs is important for the development of an efficient and efficacious cell-based therapy for intervertebral disc degeneration-associated back pain.

A new strategy for intervertebral disc regeneration: The synergistic potential of mesenchymal stem cells and their extracellular vesicles with hydrogel scaffolds

Intervertebral disc degeneration (IDD) is a disease that severely affects spinal health and is prevalent worldwide. Mesenchymal stem cells (MSCs) and their derived extracellular vesicles (EVs) have regenerative potential and have emerged as promising therapeutic tools for treating degenerative discs. However, challenges such as the harsh microenvironment of degenerated intervertebral discs and EVs' limited stability and efficacy have hindered their clinical application. In recent years, hydrogels have attracted much attention in the field of IDD therapy because they can mimic the physiologic microenvironment of the disc and provide a potential solution by providing a suitable growth environment for MSCs and EVs. This review introduced the biological properties of MSCs and their derived EVs, summarized the research on the application of MSCs and EVs in IDD, summarized the current clinical trial studies of MSCs and EVs, and also explored the mechanism of action of MSCs and EVs in intervertebral discs. In addition, plenty of research elaborated on the mechanism of action of different classified hydrogels in tissue engineering, the synergistic effect of MSCs and EVs in promoting intervertebral disc regeneration, and their wide application in treating IDD. Finally, the challenges and problems still faced by hydrogel-loaded MSCs and EVs in the treatment of IDD are summarized, and potential solutions are proposed. This paper outlines the synergistic effects of MSCs and EVs in treating IDD in combination with hydrogels and aims to provide theoretical references for future related studies.

Reviving Intervertebral Discs: Treating Degeneration Using Advanced Delivery Systems

Intervertebral disc degeneration (IVDD) is commonly associated with many spinal problems, such as low back pain, and significantly impacts a patient's quality of life. However, current treatments for IVDD, which include conservative and surgical methods, are limited in their ability to fully address degeneration. To combat IVDD, delivery-system-based therapy has received extensive attention from researchers. These delivery systems can effectively deliver therapeutic agents for IVDD, overcoming the limitations of these agents, reducing leakage and increasing local concentration to inhibit IVDD or promote intervertebral disc (IVD) regeneration. This review first briefly introduces the structure and function of the IVD, and the related pathophysiology of IVDD. Subsequently, the roles of drug-based and bioactive-substance-based delivery systems in IVDD are highlighted. The former includes natural source drugs, nonsteroidal anti-inflammatory drugs, steroid medications, and other small molecular drugs. The latter includes chemokines, growth factors, interleukin, and platelet-rich plasma. Additionally, gene-based and cell-based delivery systems are briefly involved. Finally, the limitations and future development of the combination of therapeutic agents and delivery systems in the treatment of IVDD are discussed, providing insights for future research.

Decellularized nucleus pulposus matrix/chitosan hybrid hydrogel combined with nucleus pulposus stem cells and GDF5-loaded microspheres for intervertebral disc degeneration prevention

BACKGROUND

Intervertebral disc degeneration (IDD) is considered an important pathological basis for spinal degenerative diseases. Tissue engineering is a powerful therapeutic strategy that can effectively restore the normal biological properties of disc units. In this study, hydrogels loaded with growth/differentiation factor 5 (GDF5) and stem cells were combined to provide an effective strategy for nucleus pulposus regeneration.

METHODS

Nucleus pulposus stem cells (NPSCs) were obtained by low-density inoculation and culture, and their stem cell characteristics were verified by flow cytometry and a tri-lineage-induced differentiation experiment. A decellularized nucleus pulposus matrix (DNPM) and chitosan hybrid hydrogel was prepared, and GDF5-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres were incorporated into the hydrogels to obtain a composite hydrogels with GDF5-loaded microspheres. Taking bone marrow mesenchymal stem cells (BMSCs) as a reference, the effect of composite hydrogels with GDF5-loaded microspheres on the chondrogenic differentiation of NPSCs was evaluated. A model of intervertebral disc degeneration induced by acupuncture on the tail of rats was constructed, and the repair effect of composite hydrogels with GDF5-loaded microspheres combined with NPSCs on IDD was observed.

RESULTS

Stem cell phenotype identification, stemness gene expression and tri-lineage-induced differentiation confirmed that NPSCs had characteristics similar to those of BMSCs. The rat DNPM and chitosan hybrid hydrogels had good mechanical properties, and the GDF5-loaded microspheres sustainably released GDF5. NPSCs grew normally in the composite hydrogels and gradually expressed a chondrocyte phenotype. Animal experiments showed that the composite hydrogels with GDF5-loaded microspheres combined with NPSCs effectively promoted nucleus pulposus regeneration and that the effect of the hydrogels on the repair of IDD was significantly better than that of BMSCs.

CONCLUSION

GDF5-loaded microspheres combined with DNPM/chitosan composite hydrogels can effectively promote the differentiation of NPSCs into nucleus pulposus-like cells and effectively preventIDD.

A Review: Methodologies to Promote the Differentiation of Mesenchymal Stem Cells for the Regeneration of Intervertebral Disc Cells Following Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration (IDD), a highly prevalent pathological condition worldwide, is widely associated with back pain. Treatments available compensate for the impaired function of the degenerated IVD but typically have incomplete resolutions because of their adverse complications. Therefore, fundamental regenerative treatments need exploration. Mesenchymal stem cell (MSC) therapy has been recognized as a mainstream research objective by the World Health Organization and was consequently studied by various research groups. Implanted MSCs exert anti-inflammatory, anti-apoptotic, and anti-pyroptotic effects and promote extracellular component production, as well as differentiation into IVD cells themselves. Hence, the ultimate goal of MSC therapy is to recover IVD cells and consequently regenerate the extracellular matrix of degenerated IVDs. Notably, in addition to MSC implantation, healthy nucleus pulposus (NP) cells (NPCs) have been implanted to regenerate NP, which is currently undergoing clinical trials. NPC-derived exosomes have been investigated for their ability to differentiate MSCs from NPC-like phenotypes. A stable and economical source of IVD cells may include allogeneic MSCs from the cell bank for differentiation into IVD cells. Therefore, multiple alternative therapeutic options should be considered if a refined protocol for the differentiation of MSCs into IVD cells is established. In this study, we comprehensively reviewed the molecules, scaffolds, and environmental factors that facilitate the differentiation of MSCs into IVD cells for regenerative therapies for IDD.

Codelivery of TGF-β1 and anti-miR-141 by PLGA microspheres inhibits progression of intervertebral disc degeneration

BACKGROUND

Cervical and lumbar pain is usually caused by degeneration of the nucleus pulposus (NP). As a powerful therapeutic strategy, tissue engineering can effectively restore the normal biological properties of the spinal unit. Previous studies suggested that poly(lactic-co-glycolic acid) (PLGA) microspheres are effective carriers of cells and biomolecules in NP tissue engineering. This study aims to explore the therapeutic effect of PLGA microspheres coloaded with transforming growth factor-β1 (TGF-β1) and anti-miR-141 on intervertebral disc degeneration (IDD).

METHODS

PLGA microspheres were characterized by scanning electron microscopy, a laser particle size analyzer, and laser confocal microscopy. The in vitro release rate of biomolecules from the microspheres was analyzed by reversed-phase high-performance liquid chromatography and agarose gel electrophoresis. The rat NP cells (NPCs) treated with the solutions released from microspheres for different lengths of time were assigned to a control group (Ctrl), an empty PLGA microsphere group (Mock microsphere, MS), a TGF-β1-loaded PLGA microsphere group (TMS), an anti-miR-141-loaded PLGA microsphere group (AMS), and an anti-miR-141 + TGF-β1-loaded PLGA microsphere group (ATMS). The proliferation and apoptosis of NPCs were observed by alamar blue and flow cytometry. The gene and protein expression of cartilage markers COL2A1 and ACAN were observed by RT-qPCR and Western blot. The rat model of IDD was established by tail puncture. Rats were divided into a control group (Ctrl), a mock operation group (Mock), a TGF-β1 microsphere group (TMS), an anti-miR-141 microsphere group (AMS), and an anti-miR-141 + TGF-β1 microsphere group (ATMS). The degree of rat tail IDD was assessed in each group through magnetic resonance imaging (MRI), safranin O-fast green staining, immunohistochemistry, and Western blotting.

RESULTS

PLGA microspheres were stably coloaded and could sustainably release TGF-β1 and anti-miR-141. The results of in vitro cell experiments showed that the release solution of PLGA microspheres significantly enhanced the proliferation of NPCs without inducing their apoptosis and significantly upregulated cartilage markers in NPCs. The effect of microspheres was greater in the ATMS group than that in the TMS group and AMS group. In vivo experiments showed that IDD could be effectively inhibited and reversed by adding microspheres coloaded with TGF-β1 and/or anti-miR-141, and the effect was greatest in the ATMS group.

CONCLUSION

PLGA microspheres coloaded with TGF-β1 and anti-miR-141 can reverse IDD by inhibiting the degeneration of NPCs.

Precision medicine strategies for spinal degenerative diseases: Injectable biomaterials with in situ repair and regeneration

As the population ages, spinal degeneration seriously affects quality of life in middle-aged and elderly patients, and prevention and treatment remain challenging for clinical surgeons. In recent years, biomaterials-based injectable therapeutics have attracted much attention for spinal degeneration treatment due to their minimally invasive features and ability to perform precise repair of irregular defects. However, the precise design and functional control of bioactive injectable biomaterials for efficient spinal degeneration treatment remains a challenge. Although many injectable biomaterials have been reported for the treatment of spinal degeneration, there are few reviews on the advances and effects of injectable biomaterials for spinal degeneration treatment. This work reviews the current status of the design and fabrication of injectable biomaterials, including hydrogels, bone cements and scaffolds, microspheres and nanomaterials, and the current progress in applications for treating spinal degeneration. Additionally, registered clinical trials were also summarized and key challenges and clinical translational prospects for injectable materials for the treatment of spinal degenerative diseases are discussed.

Application of single and cooperative different delivery systems for the treatment of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration (IDD) is the most universal pathogenesis of low back pain (LBP), a prevalent and costly medical problem across the world. Persistent low back pain can seriously affect a patient's quality of life and even lead to disability. Furthermore, the corresponding medical expenses create a serious economic burden to both individuals and society. Intervertebral disc degeneration is commonly thought to be related to age, injury, obesity, genetic susceptibility, and other risk factors. Nonetheless, its specific pathological process has not been completely elucidated; the current mainstream view considers that this condition arises from the interaction of multiple mechanisms. With the development of medical concepts and technology, clinicians and scientists tend to intervene in the early or middle stages of intervertebral disc degeneration to avoid further aggravation. However, with the aid of modern delivery systems, it is now possible to intervene in the process of intervertebral disc at the cellular and molecular levels. This review aims to provide an overview of the main mechanisms associated with intervertebral disc degeneration and the delivery systems that can help us to improve the efficacy of intervertebral disc degeneration treatment.

New Hope for Treating Intervertebral Disc Degeneration: Microsphere-Based Delivery System

Intervertebral disc (IVD) degeneration (IVDD) has been considered the dominant factor in low back pain (LBP), and its etiological mechanisms are complex and not yet fully elucidated. To date, the treatment of IVDD has mainly focused on relieving clinical symptoms and cannot fundamentally solve the problem. Recently, a novel microsphere-based therapeutic strategy has held promise for IVD regeneration and has yielded encouraging results with in vitro experiments and animal models. With excellent injectability, biocompatibility, and biodegradability, this microsphere carrier allows for targeted delivery and controlled release of drugs, gene regulatory sequences, and other bioactive substances and supports cell implantation and directed differentiation, aiming to improve the disease state of IVD at the source. This review discusses the possible mechanisms of IVDD and the limitations of current therapies, focusing on the application of microsphere delivery systems in IVDD, including targeted delivery of active substances and drugs, cellular therapy, and gene therapy, and attempts to provide a new understanding for the treatment of IVDD.

Droplet microfluidic devices for organized stem cell differentiation into germ cells: capabilities and challenges

Demystifying the mechanisms that underlie germline development and gamete production is critical for expanding advanced therapies for infertile couples who cannot benefit from current infertility treatments. However, the low number of germ cells, particularly in the early stages of development, represents a serious challenge in obtaining sufficient materials required for research purposes. In this regard, pluripotent stem cells (PSCs) have provided an opportunity for producing an unlimited source of germ cells in vitro. Achieving this ambition is highly dependent on accurate stem cell niche reconstitution which is achievable through applying advanced cell engineering approaches. Recently, hydrogel microparticles (HMPs), as either microcarriers or microcapsules, have shown promising potential in providing an excellent 3-dimensional (3D) biomimetic microenvironment alongside the systematic bioactive agent delivery. In this review, recent studies of utilizing various HMP-based cell engineering strategies for appropriate niche reconstitution and efficient in vitro differentiation are highlighted with a special focus on the capabilities of droplet-based microfluidic (DBM) technology. We believe that a deep understanding of the current limitations and potentials of the DBM systems in integration with stem cell biology provides a bright future for germ cell research.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12551-021-00907-5.

New hope for intervertebral disc degeneration: bone marrow mesenchymal stem cells and exosomes derived from bone marrow mesenchymal stem cell transplantation

Bone marrow mesenchymal stem cells (BMSCs), multidirectional cells with self-renewal capacity, can differentiate into many cell types and play essential roles in tissue healing and regenerative medicine. Cell experiments and in vivo research in animal models have shown that BMSCs can repair degenerative discs by promoting cell proliferation and expressing extracellular matrix (ECM) components, such as type II collagen and protein-polysaccharides. Delaying or reversing the intervertebral disc (IVD) degeneration (IDD) process at an etiological level may be an effective strategy. However, despite increasingly in-depth research, some deficiencies in cell transplantation timing and strategy remain, preventing the clinical application of cell transplantation. Exosomes exhibit the characteristics of the mother cells from which they were secreted and can inhibit nucleus pulposus (NP) cell (NPC) apoptosis and delay IDD through intercellular communication. Furthermore, the use of exosomes effectively avoids problems associated with cell transplantation, such as immune rejection. This manuscript introduces almost all of the BMSCs and exosomes derived from BMSCs (BMSCs-Exos) described in the IDD literature. Many challenges regarding the use of cell transplantation and therapeutic exosome intervention for IDD remain to be overcome.

Applications of Functionalized Hydrogels in the Regeneration of the Intervertebral Disc

Intervertebral disc degeneration (IDD) is caused by genetics, aging, and environmental factors and is one of the leading causes of low back pain. The treatment of IDD presents many challenges. Hydrogels are biomaterials that possess properties similar to those of the natural extracellular matrix and have significant potential in the field of regenerative medicine. Hydrogels with various functional qualities have recently been used to repair and regenerate diseased intervertebral discs. Here, we review the mechanisms of intervertebral disc homeostasis and degeneration and then discuss the applications of hydrogel-mediated repair and intervertebral disc regeneration. The classification of artificial hydrogels and natural hydrogels is then briefly introduced, followed by an update on the development of functional hydrogels, which include noncellular therapeutic hydrogels, cellular therapeutic hydrogel scaffolds, responsive hydrogels, and multifunctional hydrogels. The challenges faced and future developments of the hydrogels used in IDD are discussed as they further promote their clinical translation.

Role of the Wnt pathway in the formation, development, and degeneration of intervertebral discs

Intervertebral disc degeneration (IVDD) is an age-related degenerative disease that is the main cause of low back pain. It seriously affects the quality of life of patients and places a heavy economic burden on families and society. The Wnt pathway plays an important role in the growth, development, and degeneration of intervertebral discs (IVDs). In the embryonic stage, the Wnt pathway participates in the growth and development of IVD by promoting the transformation of progenitor cells into notochord cells and the extension of the notochord. However, the activation of the Wnt pathway after birth promotes IVD cell senescence, apoptosis, and degradation of the extracellular matrix and induces the production of inflammatory factors, thereby accelerating the IVDD process. This article reviews the relationship between the Wnt pathway and IVD, emphasizing its influence on IVD growth, development, and degeneration. Targeting this pathway may become an effective strategy for the treatment of IVDD.

Multiscale Regulation of the Intervertebral Disc: Achievements in Experimental, In Silico, and Regenerative Research

Intervertebral disc (IVD) degeneration is a major risk factor of low back pain. It is defined by a progressive loss of the IVD structure and functionality, leading to severe impairments with restricted treatment options due to the highly demanding mechanical exposure of the IVD. Degenerative changes in the IVD usually increase with age but at an accelerated rate in some individuals. To understand the initiation and progression of this disease, it is crucial to identify key top-down and bottom-up regulations' processes, across the cell, tissue, and organ levels, in health and disease. Owing to unremitting investigation of experimental research, the comprehension of detailed cell signaling pathways and their effect on matrix turnover significantly rose. Likewise, in silico research substantially contributed to a holistic understanding of spatiotemporal effects and complex, multifactorial interactions within the IVD. Together with important achievements in the research of biomaterials, manifold promising approaches for regenerative treatment options were presented over the last years. This review provides an integrative analysis of the current knowledge about (1) the multiscale function and regulation of the IVD in health and disease, (2) the possible regenerative strategies, and (3) the in silico models that shall eventually support the development of advanced therapies.

Regenerative Response of Degenerate Human Nucleus Pulposus Cells to GDF6 Stimulation

Growth differentiation factor (GDF) family members have been implicated in the development and maintenance of healthy nucleus pulposus (NP) tissue, making them promising therapeutic candidates for treatment of intervertebral disc (IVD) degeneration and associated back pain. GDF6 has been shown to promote discogenic differentiation of mesenchymal stem cells, but its effect on NP cells remains largely unknown. Our aim was to investigate GDF6 signalling in adult human NP cells derived from degenerate tissue and determine the signal transduction pathways critical for GDF6-mediated phenotypic changes and tissue homeostatic mechanisms. This study demonstrates maintained expression of GDF6 receptors in human NP and annulus fibrosus (AF) cells across a range of degeneration grades at gene and protein level. We observed an anabolic response in NP cells treated with recombinant GDF6 (increased expression of matrix and NP-phenotypic markers; increased glycosaminoglycan production; no change in catabolic enzyme expression), and identified the signalling pathways involved in these responses (SMAD1/5/8 and ERK1/2 phosphorylation, validated by blocking studies). These findings suggest that GDF6 promotes a healthy disc tissue phenotype in degenerate NP cells through SMAD-dependent and -independent (ERK1/2) mechanisms, which is important for development of GDF6 therapeutic strategies for treatment of degenerate discs.

High BMPR2 expression leads to enhanced SMAD1/5/8 signalling and GDF6 responsiveness in human adipose-derived stem cells: implications for stem cell therapies for intervertebral disc degeneration

Stem cell–based regenerative strategies are promising for intervertebral disc degeneration. Stimulation of bone-marrow- and adipose-derived multipotent stem cells with recombinant human growth differentiation factor 6 (rhGDF6) promotes anabolic nucleus pulposus like phenotypes. In comparison to mesenchymal stem cells, adipose-derived multipotent stem cells exhibit greater NP-marker gene expression and proteoglycan-rich matrix production. To understand these response differences, we investigated bone morphogenetic protein receptor profiles in donor-matched human mesenchymal stem cells and adipose-derived multipotent stem cells, determined differences in rhGDF6 signalling and their importance in NP-like differentiation between cell populations. Bone morphogenetic protein receptor expression in mesenchymal stem cells and adipose-derived multipotent stem cells revealed elevated and less variable expression of BMPR2 in adipose-derived multipotent stem cells, which corresponded with increased downstream pathway activation (SMAD1/5/8, ERK1/2). Inhibitor studies demonstrated SMAD1/5/8 signalling was required for rhGDF6-induced nucleus-pulposus-like adipose-derived multipotent stem cell differentiation, while ERK1/2 contributed significantly to critical nucleus pulposus gene expression, aggrecan and type II collagen production. These data inform cell regenerative therapeutic choices for intervertebral disc degeneration regeneration and identify further potential optimisation targets.

Microparticles for controlled growth differentiation factor 6 delivery to direct adipose stem cell-based nucleus pulposus regeneration

Currently, there is no effective long‐term treatment for intervertebral disc (IVD) degeneration, making it an attractive candidate for regenerative therapies. Hydrogel delivery of adipose stem cells (ASCs) in combination with controlled release of bioactive molecules is a promising approach to halt IVD degeneration and promote regeneration. Growth differentiation factor 6 (GDF6) can induce ASC differentiation into anabolic nucleus pulposus (NP) cells and hence holds promise for IVD regeneration. Here, we optimised design of novel poly(DL‐lactic acid‐co‐glycolic acid) (PLGA)–polyethylene glycol–PLGA microparticles to control GDF6 delivery and investigated effect of released GDF6 on human ASCs differentiation to NP cells. Recombinant human (rh)GDF6 was loaded into microparticles and total protein and rhGDF6 release assessed. The effect of microparticle loading density on distribution and gel formation was investigated through scanning electron microscopy. ASC differentiation to NP cells was examined after 14 days in hydrogel culture by quantitative polymerase chain reaction, histological, and immunohistochemical staining in normoxic and IVD‐like hypoxic conditions. RhGDF6 microparticles were distributed throughout gels without disrupting gelation and controlled rhGDF6 release over 14 days. Released GDF6 significantly induced NP differentiation of ASCs, with expression comparable with or exceeding media supplemented rhGDF6. Microparticle‐delivered rhGDF6 also up‐regulated sulphated glycosaminoglycan and aggrecan secretion in comparison with controls. In hypoxia, microparticle‐delivered rhGDF6 continued to effectively induce NP gene expression and aggrecan production. This study demonstrates the effective encapsulation and controlled delivery of rhGDF6, which maintained its activity and induced ASC differentiation to NP cells and synthesis of an NP‐like matrix suggesting suitability of microparticles for controlled growth factor release in regenerative strategies for treatment of IVD degeneration.