Encapsulation of Mesenchymal Stem Cells in GAG-Chitosan Polyelectrolyte Microcapsules Using a Novel Electrospraying Technique: Investigating Capsule Morphology and Cell Viability

Progress in regenerative medicine requires development of versatile tools for the scalable assembly of engineered tissues. Polyelectrolyte microcapsules are once such tool capable of facilitating handling, differentiation, and assembly of cell-based tissue modules. For many anticipated applications of this technology, large scale production of uniformly sized capsules under 300 microns in diameter is essential. In this study, an electrospray encapsulation apparatus was developed for the encapsulation of rat bone marrow mesenchymal stem cells (rbMSC) on a large scale. Due to the uniformity and high production rate of the technique, the microcapsules can be later used in modular tissue engineering and 3D printing based tissue assembly methods. The core solution consisted of rbMSC’s suspended in a solution of 4 wt% chondroitin sulfate A (CSA) plus 1.5 wt% carboxymethyl cellulose (CMC). This solution was then electrosprayed into stirred chitosan solution (0.6 wt%) using voltages in the range 5-15 kV. Ionic complexation between oppositely charged polymers formed a polyelectrolyte complex membrane at the interface of the electrosprayed droplets and chitosan solution. In order to optimize the capsule production method, the effects of voltage, needle diameter, and distance to chitosan surface was investigated experimentally, and analyzed using Design Expert ® software. It was seen that by increasing the voltage capsule size could be decreased, but beyond a value, the standard deviation increased drastically. The same trend was observed for decreasing the needle diameter. Upon optimization of the three parameters, it was noted that with 12.2 kV, 30 G needle diameter and a 32-mm separation distance to the chitosan solution surface, the microcapsules formed had the lowest standard deviation and highest uniformity. The capsules formed were in the range of 280 µm to 450 µm. Cell viability was evaluated using Calcein AM and Ethydium homodimer and was found to be above 80%, which is in agreement with other microencapsulation techniques. These results suggest that electrospraying is a highly efficient, versatile, and highly scalable approach to the encapsulation of MSCs for subsequent use in modular tissue engineering and regenerative medicine applications.