Electrowriting of silk fibroin: Towards 3D fabrication for tissue engineering applications

Abstract

Electrowriting (EW) successfully combines the principles of two widely studied biofabrication techniques; 3D printing and electrospinning, and is capable of producing complex architectures, with submicron resolutions. However, the EW process so far is limited mainly to thermoplastic polymers of synthetic origin such as poly ε-caprolactone. Herein we demonstrate the EW of silk fibroin (SF) on an in-house build setup to identify the compatibility of water-based SF ink with EW. More specifically, we optimized the SF ink composition and investigated the effect of EW process parameters including ink concentration, collector translation speed, applied voltage, and distance between nozzle and collector on filament orientation and diameter. During SF ink preparation, control over the silk degumming process and ink concentration enabled modulation of rheology and surface tension properties of SF inks. We envision that the EW of hydrophilic SF will offer a new class of material structures with biological properties akin to natural systems.

Cryo-Electrohydrodynamic Jetting of Aqueous Silk Fibroin Solutions

“…Given the low evaporation rate of water and its implications on fiber solidification, cooling the substrate was deemed the most viable option to solidify the jet. There are several approaches to generate frozen substrates, , and here we used a Peltier device due to its capacity to precisely control temperature based on an applied current. For the collector, a potted Peltier (TE technology, model HP-127–1.4–1.15–71) was placed in contact with a custom-made copper block (5 mm thick and 60 mm square), which served as the printing collector (Figure b,d).…”

“…Additionally, EHD instabilities linked to electrospinning significantly impact fiber deposition leading to random fiber accumulation. , Various studies have endeavored to mitigate EHD instabilities in aqueous solutions for precise fiber positioning and reliable jet solidification . These efforts encompass the use of viscous solutions, such as silk fibroin (SF)/polyethylene glycol (PEO: 600,000–1,000,000 Da) hydrogels, highly concentrated silk aqueous solutions (∼30 wt %/wt), and fast solidification systems like UV photo-cross-linking or liquid nitrogen-driven cryogenic systems. , However, achieving the same level of jet stability as MEW without resorting to complex systems, undesirable additives, and organic solvents remains a significant challenge. , …”

“…SF, a protein extracted from the silkworm cocoon, was selected as the proof-of-concept polymer due to its versatility, , including its wide use in biomedical applications, − and specific physical-chemical characteristics, such as water solubility, ability to become water-stable through secondary treatments, and unique mechanical properties. The control of both solution molecular entanglements and solidification dynamics by increasing the SF concentration, and freezing the jet upon contact with the collector, proved crucial in achieving stable jetting with favorable printing outcomes. , Furthermore, the used 3D system to conduct the research is compatible with MEWron project, which aims to make the MEW and EHD processing more accessible . The design and implementation of all the 3D system components are fully available in the manuscript.…”

“…23,24 However, achieving the same level of jet stability as MEW without resorting to complex systems, undesirable additives, and organic solvents remains a significant challenge. 3,22 In our study, we attain a high degree of control over jetting by combining the printing stability provided by viscous water solutions, in conjunction with a system that enables high printing speeds and accuracy, and collector temperatures down to −35 °C. SF, a protein extracted from the silkworm cocoon, was selected as the proof-of-concept polymer due to its versatility, 25,26 including its wide use in biomedical applications, 27−29 and specific physical-chemical characteristics, such as water solubility, ability to become water-stable through secondary treatments, 30 and unique mechanical properties.…”

Materials Design Innovations in Optimizing Cellular Behavior on Melt Electrowritten (MEW) Scaffolds

“…Several studies have explored the optimization of water-based electrowriting parameters such as voltage, flow rate, and concentration of the ink solution. Researchers have investigated various natural polymeric materials, including gelatin, [73,74] silk fibroin (SF) [75][76][77][78] alginate, and collagen, and for their suitability in water-based electrowriting. Synthetic polymers like polyvinyl alcohol (PVA), [79,80] have also been investigated, and these studies often focus on achieving specific mechanical and biological properties for the resulting fibers or structures.…”