2.2.1. Preparation of a 3D Printed Supporting Framework

An online computer-assisted design tool (Tinkercad, AUTODESK, San Rafael, CA, USA) was used to prepare a 3D stereolithographic design in STL (stereolithography) file format. As shown in Figure 1a, a typical framework contains an external thick skeletal structure with a thin internal lattice of crisscross elements used to create a luminal space. An opening injection port to one side allows access to the internal space. The design was uploaded to a computer-assisted 3D printer manufacturing system (Form 2, FormLabs, Somerville, MA, USA). The 3D printer uses a laser to cure solid isotropic parts from a liquid photopolymer resin. A biocompatible resin was used (EN-ISO 10993-1:2009/AC:2010, USP Class VI, Dental SG, FormLabs, Somerville, MA, USA). Removal of non-cured resin was achieved by post-fabrication washing in absolute ethanol for 15 min, as per the supplier's recommendation.

**Figure 1.** Schematic showing sacrificial core electrospinning capsule fabrication and use: (**a**) Images show the CAD 3D model of the supporting framework (frame). (**b**) Work flow showing the steps involved in device assembly, detailing supporting framework production, salt embedding, electrospinning and salt dissolution. (**c**) Electrospinning setup, highlighting how the salt aggregate contacting supporting frame was placed directly in front of the grounded collecting plate and rotated during fiber collection. (**d**) Loading of the electrospun capsule with cells for use in cell and tissue encapsulation applications, highlighting how the capsule allows free diffusion on nutrients, gases, cellular products and waste, whilst blocking access to immune cell penetration.
