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.

Deepak Kumar,Christina Lenardi,Alex Lyness,Nicholas R. Forsyth,Yang Liu,Irini Gerges

doi:10.3727/096368916x692618

Abstract

Nucleus pulposus (NP) tissue damage can induce detrimental mechanical strain on the biomechanical performance of intervertebral discs (IVDs), 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) toward 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 toward 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 determine its impact on postinjection cell viability and IVD tissue penetration. Interpretation of these 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 photo-cross-linking in situ.

Highlights

Biomechanical and pathohistological structure changes occur in the degenerated intervertebral disc (IVD)
Further insights were examined in terms of specifying the power and impact of each of the stimulating parameters individually on the differentiation process of human mesenchymal stem cells (hMSCs) toward an nucleus pulposus (NP) cell-like phenotype
PCR analysis revealed that the 3D culture of hMSCs within the hydrogel under hypoxic conditions triggered the differentiation of hMSCs toward an NP celllike phenotype (Fig. 1)

Summary

Introduction

Biomechanical and pathohistological structure changes occur in the degenerated intervertebral disc (IVD). When considering an acellular or tissue engineering therapy for IVD, several factors must be considered, including extracellular matrix architecture, hydrated tissue matrix, hypoxic nature, and the mechanical stresses and strains imposed upon the nucleus pulposus (NP) tissue. For this reason, hydrogels are an ideal and popular choice, as they are able to offer a hydrated environment, they have the ability to mimic native fibrillar structure, and are biocompatible[1,2]. Photocurable hydrogels display additional benefits, including fine-tuning mechanical properties and swelling behavior, short reaction times, minimal heating, and minimally invasive delivery. Only a single study exists that has displayed the successful use of a photocurable polyethyelene glycol diacrylate hydrogel to encapsulate and differentiate mesenchymal stem cells (MSCs) toward NP-like cells, proven by the positive expression of typical NP matrix proteins (aggrecan and collagen II)[3]

Methods

Results

Conclusion