Focal adhesion signaling affects regeneration by human nucleus pulposus cells in collagen- but not carbohydrate-based hydrogels

Ion elemental-optimized layered double hydroxide nanoparticles promote chondrogenic differentiation and intervertebral disc regeneration of mesenchymal stem cells through focal adhesion signaling pathway

Chronic low back pain and dyskinesia caused by intervertebral disc degeneration (IDD) are seriously aggravated and become more prevalent with age. Current clinical treatments do not restore the biological structure and inherent function of the disc. The emergence of tissue engineering and regenerative medicine has provided new insights into the treatment of IDD. We synthesized biocompatible layered double hydroxide (LDH) nanoparticles and optimized their ion elemental compositions to promote chondrogenic differentiation of human umbilical cord mesenchymal stem cells (hUC-MSCs). The chondrogenic differentiation of LDH-treated MSCs was validated using Alcian blue staining, qPCR, and immunofluorescence analyses. LDH-pretreated hUC-MSCs were differentiated prior to transplantation into the degenerative site of a needle puncture IDD rat model. Repair and regeneration evaluated using X-ray, magnetic resonance imaging, and tissue immunostaining 4–12 weeks after transplantation showed recovery of the disc space height and integrated tissue structure. Transcriptome sequencing revealed significant regulatory roles of the extracellular matrix (ECM) and integrin receptors of focal adhesion signaling pathway in enhancing chondrogenic differentiation and thus prompting tissue regeneration. The construction of ion-specific LDH nanomaterials for in situ intervertebral disc regeneration through the focal adhesion signaling pathway provides theoretical basis for clinical transformation in IDD treatment.

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LDH nanoparticles with different elemental compositions are constructed to optimize the chondrogenic differentiation of hUC-MSCs.

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Optimized-LDH pretreated hUC-MSCs transplantation show recovery of disc space height and integrated tissue structure.

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ECM and focal adhesion signaling pathway play significant roles in LDH-promoted cell differentiation and tissue regeneration.

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Ion-specific optimizing LDH provides theoretical basis for clinical transformation on IDD treatment.

The enhanced generation of motor neurons from mESCs by MgAl layered double hydroxide nanoparticles

The committed differentiation of stem cells into neurons is a promising therapeutic strategy for neurological diseases. Predifferentiation of transplanted stem cells into neural precursors could enhance their utilization and control the direction of differentiation. Embryonic stem cells with totipotency can differentiate into specific nerve cells under appropriate external induction conditions. Layered double hydroxide (LDH) nanoparticles have been proven to regulate the pluripotency of mouse ESCs (mESCs), and LDH could be used as carrier in neural stem cells for nerve regeneration. Hence, we sought to study the effects of LDH without loaded factors on mESCs neurogenesis in this work. A series of characteristics analyses indicated the successful construction of LDH nanoparticles. LDH nanoparticles that may adhere to the cell membranes had insignificant effect on cell proliferation and apoptosis. The enhanced differentiation of mESCs into motor neurons by LDH was systematically validated by immunofluorescent staining, quantitative real-time PCR analysis and western blot analysis. In addition, transcriptome sequencing analysis and mechanism verification elucidated the significant regulatory roles of focal adhesion signaling pathway in the enhanced mESCs neurogenesis by LDH. Taken together, the functional validation of inorganic LDH nanoparticles promoting motor neurons differentiation provide a novel strategy and therapeutic prospect for the clinical transition of neural regeneration.

Curcumin encapsulated polylactic acid nanoparticles embedded in alginate/gelatin bioinks for in situ immunoregulation: Characterization and biological assessment

Curcumin is a known naturally occurring anti-inflammatory agent derived from turmeric, and it is commonly used as a herbal food supplement. Here, in order to overcome the inherent hydrophobicity of curcumin (Cur), polylactic acid (PLA) nanoparticles (NPs) were synthesised using a solvent evaporation, and an oil-in-water emulsion method used to encapsulate curcumin. Polymeric NPs also offer the ability to control rate of drug release. The newly synthesised NPs were analysed using a scanning electron microscope (SEM), where results show the NPs range from 50 to 250 nm. NPs containing graded amounts of curcumin (0 %, 0.5 %, and 2 %) were added to cultures of NIH3T3 fibroblast cells for cytotoxicity evaluation using the Alamar Blue assay. Then, the curcumin NPs were incorporated into an alginate/gelatin solution, prior to crosslinking using a calcium chloride solution (200 nM). These hydrogels were then characterised with respect to their chemical, mechanical and rheological properties. Following hydrogel optimization, hydrogels loaded with NP containing 2 % curcumin were selected as a candidate as a bioink for three-dimensional (3D) printing. The biological assessment for these bioinks/hydrogels were conducted using THP-1 cells, a human monocytic cell line. Cell viability and immunomodulation were evaluated using lactate dehydrogenase (LHD) and a tumour necrosis factor alpha (TNF-α) enzyme-linked immunosorbent (ELISA) assay, respectively. Results show that the hydrogels were cytocompatible and supressed the production of TNF-α. These bioactive hydrogels are printable, supress immune cell activation and inflammation showing immense potential for the fabrication of tissue engineering constructs.

The Added Value of the “Co” in Co-Culture Systems in Research on Osteoarthritis Pathology and Treatment Development

Osteoarthritis (OA) is a highly prevalent disease and a major health burden. Its development and progression are influenced by factors such as age, obesity or joint overuse. As a whole organ disease OA affects not only cartilage, bone and synovium but also ligaments, fatty or nervous tissue surrounding the joint. These joint tissues interact with each other and understanding this interaction is important in developing novel treatments. To incorporate and study these interactions in OA research, several co-culture models have evolved. They combine two or more cell types or tissues and investigate the influence of amongst others inflammatory or degenerative stimuli seen in OA. This review focuses on co-cultures and the differential processes occurring in a given tissue or cell as a consequence of being combined with another joint cell type or tissue, and/or the extent to which a co-culture mimics the in vivo processes. Most co-culture models depart from synovial lining and cartilage culture, but also fat pad and bone have been included. Not all of the models appear to reflect the postulated in vivo OA pathophysiology, although some of the discrepancies may indicate current assumptions on this process are not entirely valid. Systematic analysis of the mutual influence the separate compartments in a given model exert on each other and validation against in vivo or ex vivo observation is still largely lacking and would increase their added value as in vitro OA models.

Comprehensive Profile Analysis of Differentially Expressed circRNAs in Glucose Deprivation-Induced Human Nucleus Pulposus Cell Degeneration

Nucleus pulposus (NP) is the core substance to maintain the homeostasis of intervertebral disc and stability of biomechanics. The insufficient supply of nutrition (especially glucose) is an important factor that leads to the degeneration of NP cells. circRNAs play an important role in the process of intervertebral disc degeneration (IDD) by regulating the functions of NP cells. However, glucose deprivation-related circRNAs and their functions in IDD have not been reported. In this study, the differentially expressed circRNAs in NP cells after 0, 6, 12, and 24 h of glucose deprivation culture were detected by a microarray assay. Besides, time series clustering analysis by STEM software obtained the differentially up- and downregulated circRNAs during glucose deficiency. Then, the main functions and pathways of up- and downregulated circRNAs were predicted by the functional enrichment analysis. By constructing the circRNA-miRNA regulatory network, the potential mechanisms of the most differentially expressed circRNAs were predicted. In addition, according to in vitro validation, circ_0075062 was upregulated in degenerating NP tissues and glucose deprivation-induced NP cell degeneration. Based on Sanger sequencing and RNase tolerance assay, circ_0075062 was the circular transcript. Interfering with circ_0075062 expression could potentially alleviate the imbalance of extracellular matrix (ECM) synthesis and degradation in the NP cells induced by glucose deprivation. Together, these findings help us gain a comprehensive understanding of the underlying mechanisms of IDD, and circ_0075062 may be a promising therapeutic target of IDD.

6-deoxy-aminocellulose derivatives embedded soft gelatin methacryloyl (GelMA) hydrogels for improved wound healing applications: In vitro and in vivo studies

Hydrogels were prepared by mixing protein and carbohydrate-based biopolymers to increase the mechanical properties and efficient cell adhesion and proliferation for wound healing applications. Microcrystalline cellulose (MCC) and its 6-deoxy-aminocellulose derivatives (6-deoxy-6-hydrazide Cellulose (Cell-Hyd), 6-deoxy-6-diethylamide Cellulose (Cell-DEA), and 6-deoxy-6-diethyltriamide Cellulose (Cell-DETA)) were embedded in methacrylated gelatin (GelMA). GelMA and 6-deoxy-aminocellulose derivatives were synthesized and characterized by spectroscopic techniques. MCC and cellulose derivatives embedded GelMA gels were characterized by FTIR, SEM and Tensile mechanical testing. SEM images revealed that, porosity of the amine MCC incorporated GelMA was decreased compared to GelMA and MCC incorporated GelMA. Tensile strain of GelMA 61.30% at break was increased to 64.3% in case of GelMA/Cell-HYD. In vitro cytocompatibility and cell proliferation using NIH-3T3 cell lines showed cell density trend on scaffold as GelMA/Cell-DETA>GelMA/Cell-Hyd > GelMA. Scratch assay for wound healing revealed that GelMA/Cell-DETA showed complete wound closure, while GelMA/Cell-Hyd and GelMA exhibited 85.7%, and 66.1% wound healing, respectively in 8 h. In vivo tests on rats revealed that GelMA/Cell-DETA exhibited 98% wound closure on day 9, whereas GelMA/Cell-Hyd exhibited 97.7% and GelMA 66.1% wound healing on day 14. Our findings revealed that GelMA embedded amine MCC derivatives hydrogels can be applied for achieving accelerated wound healing.

Differential Production of Cartilage ECM in 3D Agarose Constructs by Equine Articular Cartilage Progenitor Cells and Mesenchymal Stromal Cells

Identification of articular cartilage progenitor cells (ACPCs) has opened up new opportunities for cartilage repair. These cells may be used as alternatives for or in combination with mesenchymal stromal cells (MSCs) in cartilage engineering. However, their potential needs to be further investigated, since only a few studies have compared ACPCs and MSCs when cultured in hydrogels. Therefore, in this study, we compared chondrogenic differentiation of equine ACPCs and MSCs in agarose constructs as monocultures and as zonally layered co-cultures under both normoxic and hypoxic conditions. ACPCs and MSCs exhibited distinctly differential production of the cartilaginous extracellular matrix (ECM). For ACPC constructs, markedly higher glycosaminoglycan (GAG) contents were determined by histological and quantitative biochemical evaluation, both in normoxia and hypoxia. Differential GAG production was also reflected in layered co-culture constructs. For both cell types, similar staining for type II collagen was detected. However, distinctly weaker staining for undesired type I collagen was observed in the ACPC constructs. For ACPCs, only very low alkaline phosphatase (ALP) activity, a marker of terminal differentiation, was determined, in stark contrast to what was found for MSCs. This study underscores the potential of ACPCs as a promising cell source for cartilage engineering.

Control of adhesive ligand density for modulation of nucleus pulposus cell phenotype

Cells of the nucleus pulposus have been observed to undergo a shift from their notochordal-like juvenile phenotype to a more fibroblast-like state with age and maturation. It has been demonstrated that culture of degenerative adult human nucleus pulposus cells upon soft (<1 kPa) full length laminin-containing hydrogel substrates promotes increased levels of a panel of markers associated with the juvenile nucleus pulposus cell phenotype. In the current work, we observed an ability to use soft polymeric substrates functionalized with short laminin-mimetic peptide sequences to recapitulate the behaviors elicited by soft, full-length laminin containing materials. Furthermore, our work suggests an ability to mimic features of soft systems through control of peptide density upon stiffer substrates. Specifically, results suggest that stiffer polymer-peptide hydrogel substrates can be used to promote the expression of a more juvenile-like phenotype for cells of the nucleus pulposus by reducing adhesive ligand presentation. Here we show how polymer stiffness combined with adhesive ligand presentation can be controlled to be supportive of nucleus pulposus cell phenotype and biosynthesis.

Cell-Laden Agarose-Collagen Composite Hydrogels for Mechanotransduction Studies

The increasing investigation of cellular mechanotransduction mechanisms requires biomaterials combining biofunctionality and suitable mechanical properties. Agarose is a standard biomaterial for cartilage and intervertebral disc mechanobiology studies, but lacks adhesion motifs and the necessary cell-matrix interaction for mechanotransduction. Here, collagen type I was blended at two concentrations (2 and 4.5 mg/mL) with agarose 2% wt/vol. The composite hydrogels were characterized in terms of structural homogeneity, rheological properties and size stability. Nucleus pulposus (NP) cell viability, proliferation, morphology, gene expression, GAG production, adhesion and mechanotransduction ability were further tested. Blended hydrogels presented a homogenous network of the two polymers. While the addition of 4.5 mg/mL collagen significantly decreased the storage modulus and increased the loss modulus of the gels, blended gels containing 2 mg/mL collagen displayed similar mechanical properties to agarose. Hydrogel size was conserved over 21 days for all agarose-based gels. Embedded cells were viable (>80%) and presented reduced proliferation and a round morphology typical of NP cells in vivo. Gene expression of collagen types I and II and aggrecan significantly increased in blended hydrogels from day 1 to 7, further resulting in a significantly superior GAG/DNA ratio compared to agarose gels at day 7. Agarose-collagen hydrogels not only promoted cell adhesion, contrary to agarose gels, but also showed a 5.36-fold higher focal adhesion kinase phosphorylation (pFAK/β-tubulin) when not compressed, and increased pFAK/FAK values 10 min after compression. Agarose-collagen thus outperforms agarose, mimics native tissues constituted of non-fibrillar matrix and collagens, and allows exploring complex loading in a highly reproducible system.

Intensified Stiffness and Photodynamic Provocation in a Collagen-Based Composite Hydrogel Drive Chondrogenesis

Directed differentiation of bone-marrow-derived stem cells (BMSCs) toward chondrogenesis has served as a predominant method for cartilage repair but suffers from poor oriented differentiation tendency and low differentiation efficiency. To overcome these two obstacles, an injectable composite hydrogel that consists of collagen hydrogels serving as the scaffold support to accommodate BMSCs and cadmium selenide (CdSe) quantum dots (QDs) is constructed. The introduction of CdSe QDs considerably strengthens the stiffness of the collagen hydrogels via mutual crosslinking using a natural crosslinker (i.e., genipin), which simultaneously triggers photodynamic provocation (PDP) to produce reactive oxygen species (ROS). Experimental results demonstrate that the intensified stiffness and augmented ROS production can synergistically promote the proliferation of BMSCs, induce cartilage-specific gene expression and increase secretion of glycosaminoglycan. As a result, this approach can facilitate the directed differentiation of BMSCs toward chondrogenesis and accelerate cartilage regeneration in cartilage defect repair, which routes through activation of the TGF-β/SMAD and mTOR signaling pathways, respectively. Thus, this synergistic strategy based on increased stiffness and PDP-mediated ROS production provides a general and instructive approach for developing alternative materials applicable for cartilage repair.

Anatomical meniscus construct with zone specific biochemical composition and structural organization

A PCL/hydrogel construct that would mimic the structural organization, biochemistry and anatomy of meniscus was engineered. The compressive (380 ± 40 kPa) and tensile modulus (18.2 ± 0.9 MPa) of the PCL scaffolds were increased significantly when constructs were printed with a shifted design and circumferential strands mimicking the collagen organization in native tissue (p < 0.05). Presence of circumferentially aligned PCL strands also led to elongation and alignment of the human fibrochondrocytes. Gene expression of the cells in agarose (Ag), gelatin methacrylate (GelMA), and GelMA-Ag hydrogels was significantly higher than that of cells on the PCL scaffolds after a 21-day culture. GelMA exhibited the highest level of collagen type I (COL1A2) mRNA expression, while GelMA-Ag exhibited the highest level of aggrecan (AGG) expression (p < 0.001, compared to PCL). GelMA and GelMA-Ag exhibited a high level of collagen type II (COL2A1) expression (p < 0.05, compared to PCL). Anatomical scaffolds with circumferential PCL strands were impregnated with cell-loaded GelMA in the periphery and GelMA-Ag in the inner region. GelMA and GelMA-Ag hydrogels enhanced the production of COL 1 and COL 2 proteins after a 6-week culture (p < 0.05). COL 1 expression increased gradually towards the outer periphery, while COL 2 expression decreased. We were thus able to engineer an anatomical meniscus with a cartilage-like inner region and fibrocartilage-like outer region.

Profiling and bioinformatics analysis of differentially expressed circular RNAs in human intervertebral disc degeneration

The functional changes of nucleus pulposus (NP) cells are considered to be the initiating factors of intervertebral disc degeneration (IDD), and the differentially expressed circRNAs in NP cells may play an important role in the process of IDD. To identify circular RNAs (circRNAs) associated with human IDD, we isolated the NP cells from human degenerated and non-degenerated intervertebral disc and identified NP cells by microscopy and cell proliferation. CircRNA microarray expression profiles were obtained from NP cells of degenerated and non-degenerated intervertebral disc and further validated by quantitative reverse transcription PCR (qRT-PCR). The expression data were analyzed by bioinformatics. Microarray analysis identified 7294 circRNAs differentially expressed in degenerated human IDD NP cells. Among them, 3724 circRNAs were up-regulated and 3570 circRNAs were down-regulated by more than 2 folds. After validating by qRT-PCR, we predicted the possible miRNAs of the top dysregulated circRNAs using TargetScan, and miRanda. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the most modulated circRNAs regulate the viability, degradation, apoptosis and oxidative stress in NP cells, and the possible mechanism underlying IDD was discussed. These results revealed that circRNAs may play a role in IDD and might be a promising candidate molecular target for gene therapy.

Oxidized alginate hydrogels with the GHK peptide enhance cord blood mesenchymal stem cell osteogenesis: A paradigm for metabolomics-based evaluation of biomaterial design

Oxidized alginate hydrogels are appealing alternatives to natural alginate due to their favourable biodegradability profiles and capacity to self-crosslink with amine containing molecules facilitating functionalization with extracellular matrix cues, which enable modulation of stem cell fate, achieve highly viable 3-D cultures, and promote cell growth. Stem cell metabolism is at the core of cellular fate (proliferation, differentiation, death) and metabolomics provides global metabolic signatures representative of cellular status, being able to accurately identify the quality of stem cell differentiation. Herein, umbilical cord blood mesenchymal stem cells (UCB MSCs) were encapsulated in novel oxidized alginate hydrogels functionalized with the glycine-histidine-lysine (GHK) peptide and differentiated towards the osteoblastic lineage. The ADA-GHK hydrogels significantly improved osteogenic differentiation compared to gelatin-containing control hydrogels, as demonstrated by gene expression, alkaline phosphatase activity and bone extracellular matrix deposition. Metabolomics revealed the high degree of metabolic heterogeneity in the gelatin-containing control hydrogels, captured the enhanced osteogenic differentiation in the ADA-GHK hydrogels, confirmed the similar metabolism between differentiated cells and primary osteoblasts, and elucidated the metabolic mechanism responsible for the function of GHK. Our results suggest a novel paradigm for metabolomics-guided biomaterial design and robust stem cell bioprocessing. STATEMENT OF SIGNIFICANCE: Producing high quality engineered bone grafts is important for the treatment of critical sized bone defects. Robust and sensitive techniques are required for quality assessment of tissue-engineered constructs, which result to the selection of optimal biomaterials for bone graft development. Herein, we present a new use of metabolomics signatures in guiding the development of novel oxidised alginate-based hydrogels with umbilical cord blood mesenchymal stem cells and the glycine-histidine-lysine peptide, demonstrating that GHK induces stem cell osteogenic differentiation. Metabolomics signatures captured the enhanced osteogenesis in GHK hydrogels, confirmed the metabolic similarity between differentiated cells and primary osteoblasts, and elucidated the metabolic mechanism responsible for the function of GHK. In conclusion, our results suggest a new paradigm of metabolomics-driven design of biomaterials.

A 3D printed PCL/hydrogel construct with zone-specific biochemical composition mimicking that of the meniscus

Engineering the meniscus is challenging due to its bizonal structure; the tissue is cartilaginous at the inner portion and fibrous at the outer portion. Here, we constructed an artificial meniscus mimicking the biochemical organization of the native tissue by 3D printing a meniscus shaped PCL scaffold and then impregnating it with agarose (Ag) and gelatin methacrylate (GelMA) hydrogels in the inner and outer regions, respectively. After incubating the constructs loaded with porcine fibrochondrocytes for 8 weeks, we demonstrated that presence of Ag enhanced glycosaminoglycan (GAG) production by about 4 fold (p < 0.001), while GelMA enhanced collagen production by about 50 fold (p < 0.001). In order to mimic the physiological loading environment, meniscus shaped PCL/hydrogel constructs were dynamically stimulated at strain levels gradually increasing from the outer region (2% of initial thickness) towards the inner region (10%). Incorporation of hydrogels protected the cells from the mechanical damage caused by dynamic stress. Dynamic stimulation resulted in increased ratio of collagen type II (COL 2) in the Ag-impregnated inner region (from 50% to 60% of total collagen), and increased ratio of collagen type I (COL 1) in the GelMA-impregnated outer region (from 60% to 70%). We were able to engineer a meniscus, which is cartilage-like at the inner portion and fibrocartilage-like at the outer portion. Our construct has a potential for use as a substitute for total meniscus replacement.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

Osteoinductive Agents-Incorporated Three-Dimensional Biphasic Polymer Scaffold for Synergistic Bone Regeneration

Large-scale bone defects are difficult to be regenerated entirely in the clinical practice. Bone tissue engineering has drawn more attention as an alternative to bone grafting owing to its convenience and flexibility. However, the low bioactivity of scaffolds and adverse effects of growth factors have hindered its practical application. Herein, the properties of poly(lactic-co-glycolic acid) (PLGA) scaffold, including hydrophilicity and mechanical strength, were improved by a gelatin coating incorporated with two small molecules, alendronate (ALD) and naringin (NG). Interestingly, these two drugs demonstrated a synergistic effect for the repair of rat calvarial defect, as ALD had an inhibitory impact on osteoclast activity and NG had an osteogenic effect on mesenchymal stem cells. From the results of histopathological staining and microcomputed tomography, the PLGA scaffold incorporated with gelatin, ALD, and NG (PLGA+Gelatin/ALD/NG) almost completely repaired the rat calvarial defect with physiological integrity at 16 weeks. In all, this biphasic scaffold can be a promising alternative to the conventional scaffold for clinical application.

Hydrogels of agarose, and methacrylated gelatin and hyaluronic acid are more supportive for in vitro meniscus regeneration than three dimensional printed polycaprolactone scaffolds

In this study, porcine fibrochondrocyte-seeded agarose, methacrylated gelatin (GelMA), methacrylated hyaluronic acid (MeHA) and GelMA-MeHA blend hydrogels, and 3D printed PCL scaffolds were tested under dynamic compression for potential meniscal regeneration in vitro. Cell-carrying hydrogels produced higher levels of extracellular matrix (ECM) components after a 35-day incubation than the 3D printed PCL. Cells on GelMA exhibited strong cell adhesion (evidenced with intense paxillin staining) and dendritic cell morphology, and produced an order of magnitude higher level of collagen (p < 0.05) than other materials. On the other hand, cells in agarose exhibited low cell adhesion and round cell morphology, and produced higher levels of glycosaminoglycans (GAGs) (p < 0.05) than other materials. A low level of ECM production and a high level of cell proliferation were observed on the 3D printed PCL. Dynamic compression at 10% strain enhanced GAG production in agarose (p < 0.05), and collagen production in GelMA. These results show that hydrogels have a higher potential for meniscal regeneration than the 3D printed PCL, and depending on the material used, fibrochondrocytes could be directed to proliferate or produce cartilaginous or fibrocartilaginous ECM. Agarose and MeHA could be used for the regeneration of the inner region of meniscus, while GelMA for the outer region.

Comparing Hydrogels for Human Nucleus Pulposus Regeneration: Role of Osmolarity During Expansion

Hydrogels can facilitate nucleus pulposus (NP) regeneration, either for clinical application or research into mechanisms of regeneration. However, many different hydrogels and culture conditions for human degenerated NP have been employed, making literature data difficult to compare. Therefore, we compared six different hydrogels of natural polymers and investigated the role of serum in the medium and of osmolarity during expansion or redifferentiation in an attempt to provide comparators for future studies. Human NP cells of Thompson grade III discs were cultured in alginate, agarose, fibrin, type II collagen, gelatin methacryloyl (gelMA), and hyaluronic acid-poly(ethylene glycol) hydrogels. Medium containing fetal bovine serum and a serum-free (SF) medium were compared in agarose, gelMA, and type II collagen hydrogels. Isolation and expansion of NP cells in low compared to high osmolarity medium were performed before culture in agarose and type II collagen hydrogels in media of varying osmolarity. NP cells in agarose produced the highest amounts of proteoglycans, followed by cells in type II collagen hydrogels. The absence of serum reduced the total amount of proteoglycans produced by the cells, although incorporation efficiency was higher in type II collagen hydrogels in the absence than in the presence of serum. Isolation and expansion of NP cells in high osmolarity medium improved proteoglycan production during culture in hydrogels, but variation in osmolarity during redifferentiation did not have any effect. Agarose hydrogels seem to be the best option for in vitro culture of human NP cells, but for clinical application, type II collagen hydrogels may be better because, as opposed to agarose, it degrades in time. Although culture in SF medium reduces the amount of proteoglycans produced during redifferentiation culture, isolating and expanding the cells in high osmolarity medium can largely compensate for this loss.