Biological Evaluation of Human Degenerated Nucleus Pulposus Cells in Functionalized Self-Assembling Peptide Nanofiber Hydrogel Scaffold

Nucleus pulposus (NP) tissue engineering has been proposed as a novel biological treatment for early-stage intervertebral disc degeneration. In this study, a novel functional self-assembling peptide PKP was first designed by linking the short functional motif of bone morphogenetic protein-7 (BMP7) to the C-terminal of RADA16-I, and another new functional self-assembling peptide was obtained by mixing RKP with RADA16-I. Then, the bio-compatibilities and bioactivities of RKP and RAD-RKP for human degenerated nucleus pulposus cells (hNPCs) were studied in vitro. Atomic force microscopy and scanning electron microscopy (SEM) confirmed that both RKP and RAD-RKP could self-assemble into three-dimensional (3D) nanofiber hydrogel scaffolds in a culture medium at 37 degrees C. After the hNPCs were cultured in 3D scaffolds, both RKP and RAD-RKP exhibited reliable attachment and extremely low cytotoxicities (<14%), which were verified by SEM and cytotoxity assays, respectively. Our results also showed that the functional-based scaffolds could increase the proliferation and migration of hNPCs after 7 days compared with culture plates and pure RADA16-I. Quantitative real-time polymerase chain reaction demonstrated that the expressions of collagen II alpha 1, Sox-9, and aggrecan were upregulated, while collagen I alpha 1 was down-regulated by functional-based scaffolds after 28 days. Furthermore, we also confirmed that RAD-RKP exhibited a higher hNPC proliferation, migration, and expression of Sox-9 and aggrecan compared with pure RKP. Therefore, the results of this study indicated that the BMP7 short motif-designed functional self-assembling peptide nanofiber hydrogels could be used as excellent scaffolds in NP tissue engineering, and RAD-RKP might have further potential application in human mild degenerated NP tissue regeneration.