Date Published: June 21, 2019
Publisher: Public Library of Science
Author(s): Clara R. Correia, Maryam Ghasemzadeh-Hasankolaei, João F. Mano, Kim Hamad-Schifferli.
Cell encapsulation is a widely used technique in the field of Tissue Engineering and Regenerative Medicine (TERM). However, for the particular case of liquefied compartmentalised systems, only a limited number of studies have been reported in the literature. We have been exploring a unique cell encapsulation system composed by liquefied and multilayered capsules. This system transfigured the concept of 3D scaffolds for TERM, and was already successfully applied for bone and cartilage regeneration. Due to a number of appealing features, we envisage that it can be applied in many other fields, including in advanced therapies or as disease models for drug discovery. In this review, we intend to highlight the advantages of this new system, while discussing the methodology, and sharing the protocol optimization and results. The different liquefied systems for cell encapsulation reported in the literature will be also discussed, considering the different encapsulation matrixes as core templates, the types of membranes, and the core liquefaction treatments.
Cell encapsulation is a very promising method for the treatment of different endocrine diseases, including diabetes, liver and kidney failure. There are also advantages in using this methodology in Tissue Engineering and Regenerative Medicine (TERM), including mediation of undesired acute immune responses, while offering a three-dimensional (3D) environment essential for anchorage dependent cells . In the particular case of liquefied cell encapsulation systems, a possible strategy to build the encapsulation membrane is through the Layer-by-Layer (LbL) technique, which has been proposed to process materials for a variety of biomedical applications . It is a simple, low cost, and cell-friendly method which can be performed under mild conditions using different pairs-interactions . Moreover, LbL is a very versatile technique which allows us to produce membranes with desired permeability according to the number and composition of the layers deposited, while allowing to increase the applicability of the system by endowing nanoparticles  or lipids and viruses  into the multilayers.
We tested the influence of different EHDA parameters on the diameter of the alginate microgels, which serve as templates for the production of the liquefied capsules discussed above. We varied the applied voltage (5, 7, and 10 kV), the flow rate (30, 40, and 50 mL.h-1), the needle diameter (18, 22, and 26 G), the distance between the needle and the collector (6, 8, and 10 cm), the presence/absence of microparticles, and the alginate concentration (1.5, 2, and 2.5% w/v). The parameters 7 kV, 50 mL.h-1, 22 G, 8 cm, presence of microparticles, and 2.5% w/v of alginate were kept constant for each parameter evaluation. Of note, the different parameters were all tested in the presence of a stable Tailor cone-jet mode. Results are summarized in Figs 2 and 3, and discussed individually in the following subsections.
EHDA is a very versatile technology with many advantages for cell encapsulation, particularly in terms of the reproducibility of the processed microsize hydrogels. Given its simplicity and high yield when compared to other techniques, such as microfluidics, this method has shown to be a reliable technique to produce hydrogels in different size ranges and with controlled morphology and homogeneity. Therefore, we envision that its promising and increasing prominence in the TERM field will continue to flourish.