TABLE 2.

Various biomaterials used in IVD regeneration and their key findings.

Biomaterial	Crosslinker	Composition	Model	Mechanism of action	Analysis and result	Ref
HA with type II collagen	4S-Star PEG	Weight ratio HA to collagen II: 1:9 and 4.5:9	In vitro	Mimics the NP microenvironment, supporting human Wharton’s Jelly -MSC viability and differentiation through its biocompatible, stable, and degradable 3D matrix	Significantly higher swelling capacity in HA/collagen II 4.5:9 compared to HA/COLII 1:9. Both formulations reached stability in an aqueous solution from day 21 up to 1 month of incubation at 37°C. Degradation analysis with type II collagenase demonstrated a time-dependent increase in the degradation percentage for both formulations	Mohd Isa et al. (2023)
		Weight ratio HA to collagen II 1:9 Induction TGF-β3	In Vitro		Human Wharton jelly-derived mesenchymal stem cells in hydrogel differentiated into NP-like cells with increased SOX-9, while 2D culture led to fibroblastic-like cells. Viability improved over time, indicating hydrogel biocompatibility
Collagen cryogel	1-ethyl-3-(3-dimethylaminopropyl-carbodiimide hydrochloride/N-hydroxy-succinimide	Acidic Collagen (4wt%, pH 4.0) Induction TGF-β3	In vitro	Restores disc structure, retains water, and promotes regeneration, relieving pain and maintaining IVD integrity	Alginate shape memory and collagen cryogel demonstrated similar physical properties in terms of water absorption, compressive properties and shape memorability	Koo et al. (2023)
Alginate shape memory structure	CaCl2	Sodium Alginate (4 wt%) Induction TGF-β3		Absorbs water, changes shape in response to temperature or pH, and maintains mechanical properties. It promotes cell migration, proliferation, and matrix restoration
			In Vitro		Cells remained viable in both hydrogels, with higher activity in CG than A-SMS. CG also induced more efficient and uniform chondrogenic activity
		Scaffold Biomaterial with Hyaluronic Acid Scaffold Biomaterial Volume: 8ul HA Composition 1 w/v% in PBS, 15 μL	In Vivo		The CG group exhibited a higher withdrawal threshold, indicating reduced mechanical allodynia. MRI T2-weighted images showed better disc hydration in CG. Histology revealed greater NP area, cell number, and preserved disc structure. CG had lower histological grading scores, higher type II collagen and aggrecan, and lower type I collagen, suggesting enhanced extracellular matrix regulation. It also showed increased transcription factors Brachyury and Tie-2, indicating more NP cells. Additionally, CG downregulated proinflammatory cytokines, neurogenic factors, and catabolic enzymes, potentially reducing discogenic pain and preserving ECM.
Decellularized nucleus pulposus matrix (DNPM) and chitosan hybrid hydrogel	physical crosslinking	2.5% DNPM, 1.5% Chitosan in 3% acetic acid	In vitro	DNPM promotes nucleus pulposus regeneration by providing a biomimetic environment that supports cell adhesion, migration, and differentiation. The DNPM mimics the natural extracellular matrix, enhancing cell interaction, while the chitosan hydrogel serves as a biocompatible scaffold that facilitates sustained release of growth factors	SEM Analysis: Smooth, porous structure, good connectivity FITR: collagen and polysaccharides Compression: elastic, fails at ∼70% strain Rheology: Stable storage modulus, good elasticity. pH: Neutral (7.1–7.3), supports cell growth.	Ma et al. (2024)
		DNPM/chitosan hydrogel mixed with GDF5-loaded PLGA microspheres	In vitro	PLGA microspheres provide a controlled, sustained release of GDF5, which promotes chondrogenic differentiation of NP stem cells and supports the regeneration of NP.	SEM: uniform spherical GDF5 microspheres (50–160 μm, avg. 110 μm) Encapsulation efficiency: 75.1% Release: slow release, plateau at day 10 Degradation: 20% residual mass after 24 days
			In vitro		The composite hydrogel with GDF5-loaded microspheres enhanced chondrogenesis, with the nucleus pulposus stem cell showing the highest COL2A1 expression and secretion at 21 days
			In vivo		GDF5/CH + NPSC hydrogel showed the best IDD repair, with the highest MRI signal, mildest degeneration, and highest COL2A1 expression
Genipin-enhanced fibrin hydrogel combined with an engineered silk scaffold	Genipin	Fibrinogen, thrombin, genipin, DMSO. Fetal calf serum and ε-aminocaproic acid	In vitro	act as a crosslinked filler, fills the injury in the AF, while the silk scaffold provides additional support and structural integrity	Genipin combined with DMSO completely inhibited mitochondrial activity at all tested concentrations	Frauchiger et al. (2018)
			In ex vivo		No herniation in any loading condition, disc height not restored, matrix and DNA content similar to healthy control, and genipin safe in organ culture
Mucin-derived gels	Tetrazine and norbornene click chemistry	Bovine Submaxillary Mucin, Tetrazine-amine, Norbornene-amine, EDC, NHS, MES buffer, and PBS.	In vivo	Immune modulation and protection against immune infiltration	Prevent fibrous encapsulation and macrophage infiltration in the mouse model. In the rat tail IVD degeneration model, Muc-gel injection prevents degeneration for up to 24 weeks post-operation. Mechanistically, Muc-gels attenuate immune cell infiltration into the NP, protecting against immune attack following microdiscectomy	Wang et al. (2024c)
chitosan/PEG hydrogel	Dual crosslink: Schiff base reaction and photo-crosslinking	chitosan, PEG, methacrylic anhydride, lithium phenyl-2,4,6-trimethylbenzoylphosphinate, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride	In vitro	Rapid in situ seal at the defect site through photo-crosslinking and Schiff base reactions, providing mechanical support and physical plugging	Low cytotoxicity was observed when nucleus pulposus (NP) cells were cultured with the hydrogel	Huang et al. (2023)
			In vivo		Hydrogel sealed the IVD defect, reducing disc height loss and matrix degradation while preserving NP and AF structures in rat tail model
Electrospun biodegradable poly (ε-caprolactone) membranes	N/A	The membrane was produced in three different fibres diameters (thin, medium, and thick), prepared by electrospinning Poly (ε-caprolactone) dissolved in solvents such as chloroform and methanol	In vitro	Provide mechanical support in tissue engineering by forming a structural scaffold	Membranes exhibited increased crystallinity and ester bond degradation over time. The modulus increased in the first loading cycle, then varied with subsequent cycles based on strain and membrane type. The elastic range improved with strain, and the modulus was within the lower range of human annulus fibrosus tissue, showing potential for sealing damaged annulus fibrosus	Alexeev et al. (2021)
PVA with a polyvinyl pyrrolidone	sodium trimetaphosphate	PVA: polyvinyl pyrrolidone ratios of 1:1 and 1:3 were used	In vitro	The thixotropic, injectable 3D network forms a stable structure that remains injectable due to chemical cross-linking with trisodium trimetaphosphate	The 1:1 Polyvinyl alcohol- polyvinyl pyrrolidone scaffold showed favourable viscoelasticity, no cytotoxicity, and supported chondrocyte adhesion and proliferation, making it a promising NP replacement	Leone et al. (2019)
PEG with decellularized notochordal cell-derived matrix	PEG-diurethane	8-arm-PEG-vinyl sulfone, PEG-diurethane-dithiol crosslinker, and decellularized notochordal cell-derived matrix	In vitro	leveraging the regenerative properties of the decellularized matrix along with the mechanical tunability of PEG hydrogels	Tunable stiffness, sustained release of decellularized notochordal cell-derived matrix, and high viability of bone marrow stromal cells, but notochordal cells lost activity over time	Schmitz et al. (2023)