Development of injectable cell delivery systems for high accuracy cell therapy applications

Cell-based therapeutic interventions are being developed for a variety of clinical indications, including irreversible retinal pathologies and stroke. Numerous cell therapy procedures use injection-based administration to deliver high density cell preparations, either systemically or directly. The mode of delivery of fragile cells can compromise treatment efficacy, which is dependent on cell viability and functionality post-injection. Reviewing current literature, there is a lack of comprehensive testing of the effects of injection-based cell delivery on the various parameters of cell function. This study investigated the effects of the administration process on a range of cell characteristics, and aimed to answer critical questions regarding possible reasons for failure to deliver a sufficient numbers of viable cells. Biomaterial-assisted cell delivery was also investigated to determine improvement of cell recovery and possible influence on cell fate. \ud \ud Primary human mesenchymal stem cells (hMSCs) and Swiss mouse embryonic fibroblast cell line (NIH 3T3) suspensions were drawn up into 100 μL Hamilton syringes with 30- and 34G needles. They were then ejected at rates ranging from 10-300 μL/min. A comprehensive toolset was employed to assess the effects of various injection parameters, including ejection rate and needle size. Cell dose recovery, viability, apoptosis, senescence and other parameters of cellular health were evaluated using various standard and multiplex assays. Trilineage differentiation potential of ejected hMSCs was also assessed. Moreover, various injectable cell carriers were explored in terms of improvement of cell recovery and potential influence on differentiation capacity.\ud \ud Ejections at slower flow rates resulted in a significantly lower percentage of dose delivered as viable cells, with ejections at 300 μL/min showing the maximum percentage of hMSCs dose delivered at 77.6 ± 11.7%. Lower cell numbers delivered at slower ejection rates were mainly attributed to cell retention within the delivery device. Normalised caspase-3/7 activity measurements ejected at 10 μL/min were also significantly higher than control. Quantification of differentiation of ejected hMSCs revealed that both ejection rate and cell carrier employed may exert an effect on differentiation capacity. The use of biomaterials as cell carriers significantly improved cell recovery. Ejection of hMSCs in gelatin solution resulted in 87.5 ± 14% of the cell dose being delivered as viable cells, in comparison with 32.2 ± 19% of the dose ejected in phosphate buffered saline (PBS) at 10 μL/min. \ud \ud This study shows that ejection rate, needle size and cell carrier have a significant impact on the percentage of cell dose delivered as viable cells, cellular health and differentiation potential post-ejection. Optimal delivery strategies for injectable cell-based therapeutics are required to enhance their efficacy and reproducibility. This study emphasises the importance of careful consideration of administration protocols, according to the nature of the administered cells and cellular responses post-ejection. The combination of the investigated factors, among others, may also influence the fate of stem cells injected, thereby affecting the success of cell-based therapies