3D cell culture strategies have been developed to bridge the gap between 2D cell culture and animal studies in the past two decades since 3D culture approaches enable abundant cell-cell and cell-ECM interactions that closely mimic the in vivo cell milieu. Importantly, aggregate culture of stem cells shows promise for application in tissue engineering, where the aggregates can be used as building blocks for tissue regeneration.
However, control over stem cell differentiation within aggregates still remains challenging due to the inherent diffusion barrier for biological mediators (e.g. growth factors) throughout the 3D multicellular aggregates. Non-viral transfection approaches are an attractive approach to control stem cell fate, as it is possible to deliver genes encoding key biological mediators.
Although initial successes of cell transfection have been achieved on 2D culture systems using nanoparticulate vectors (e.g. liposomes, polyplexes), it is difficult to translate these delivery systems from 2D to 3D stem cell culture systems. The goal of this work was to develop a microparticle based gene delivery approach to transfect stem cells within multicellular aggregates with high efficiency and uniformity throughout the aggregates. We hypothesize that incorporation of plasmid DNA (pDNA) laden mineral coated microparticles (MCMs) into hMSC aggregates would enable efficient pDNA delivery to human mesenchymal stem cells (hMSC), resulting in efficient cell transfection within the 3D aggregates.
We show that the transfection efficiency increased 4-fold in the hMSC aggregates incorporated with pDNA bound MCMs when compared to standard protocols for non-viral transfection. The distribution of transfected cells was found to be homogenous throughout the stem cell aggregates. Finally, we used the microparticle approach to deliver a gene encoding the functional growth factor bone morphogenetic protein-2 (BMP-2) to induce osteogenic differentiation within the aggregates. The technology described herein may have utility as a tool to achieve scaffold-free 3D cell transfection with high efficiency and uniformity.