Stem cell delivery with polymer hydrogel for treatment of intervertebral disc degeneration: from 3D culture to design of the delivery device for minimally invasive therapy

Nucleus pulposus (NP) tissue damage can induce detrimental mechanical strain on the biomechanical performance of intervertebral disc (IVD) causing subsequent disc degeneration. A novel, photocurable, injectable, synthetic polymer hydrogel (pHEMA-co-APMA grafted with PAA) has already demonstrated success in encapsulating and differentiating human mesenchymal stem cells (hMSCs) towards an NP phenotype during hypoxic conditions. After demonstration of promising results in our previous work, in this study, we have further investigated the inclusion of mechanical stimulation and its impact on hMSC differentiation towards an NP phenotype through the characterization of matrix markers such as SOX-9, Aggrecan and Collagen II. Furthermore, investigations were undertaken in order to approximate delivery parameters for an injection delivery device, which could be used to transport hMSCs suspended in hydrogel into the IVD. hMSC laden hydrogel solutions were injected through various needle gauge sizes in order to deter its impact on postinjection cell viability and IVD tissue penetration. Interpretation of this data informed the design of a potential minimally invasive injection device, which could successfully inject hMSCs encapsulated in a UV curable polymer into NP, prior to photocrosslinking in situ.