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

Abstract

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.

Evaluation of Marine Agarose Biomaterials for Tissue Engineering Applications

“…Although a detailed analysis of the molecular structure and pore size of each agarose type and concentration is in need, we could hypothesize that highly dense agaroses could not allow cells to easily migrate and spread within the biomaterial, thus preventing biodegradation and remodeling of this type of biomaterials in a short period of time. Again, the in vivo results support our hypothesis that the use of highly concentrated agaroses could be indicated in cases requiring long-term stability and low cellularity, such as the human intervertebral disk [41]. However, other tissues and organs with an abundant cell population requiring a progressive remodeling and biodegradation, such as the human skin and cornea [3,19,37], should use low concentrations of agarose.…”

Recent advances of hydrogel‐based biomaterials for intervertebral disc tissue treatment: A literature review

“…An example is that genipin, the crosslinker in the FibGen, may cause AF cells apoptosis by inhibiting integrin binding (Panebianco, DiStefano, Mui, Hom, & Iatridis, 2020). When cells are encapsulated, nutrient diffusion related to the pore size and osmolarity of hydrogels should be well designed in case to impede cell proliferation and matrix synthesis (Krouwels et al., 2018; P. Li et al., 2016; Nativel et al., 2018). Also, the importance of the degradation rate could not be ignored when designing the materials, because inappropriate degradation rate will either affect the homogeneity of the tissue or hinder matrix synthesis (Sridhar et al., 2017; Zhao et al., 2016).…”

“…When cells are encapsulated, nutrient diffusion related to the pore size and osmolarity of hydrogels should be well designed in case to impede cell proliferation and matrix synthesis (Krouwels et al, 2018;P. Li et al, 2016;Nativel et al, 2018).…”

Tissue Engineering Strategies for Intervertebral Disc Treatment Using Functional Polymers

“…To culture IVD cells especially nucleus pulpous cell in 3D scaffold, alginate hydrogel beads under pressured system were used [153,154]. In the pressure loading system, MSCs were cultured in the 3D alginate hydrogel using poly (ethylene glycol) diacrylate (PEGDA) microcryogels [155].…”