33 / 2021-05-27 16:53:44

3D-PRINTING OF LOW SOLIDS NANOCELLULOSES FOR MULTIFUNCTIONAL APPLICATIONS

cellulose nanofibers; chitin nanofibers; emulsions; emulgel; direct ink writing

Direct ink writing (DIW), a novel technique for 3D printing of hydrogel-based materials, provides a programmable and customizable platform to engineer hierarchically organized constructs. The ink suitable for extrusion-based DIW must exhibit shear-thinning to enable efficient flow through the nozzles but demand fast recovery into objects with a sufficiently high yield stress and storage modulus to ensure shape retention and distortion-free geometries. Bio-based materials, including cellulose nanofibers (CNF) derived from wood and chitin nanofibers (ChNF) derived from crabs are ideally suited for increasing shear-thinning behavior, storage modulus and viscosity to the final inks. Herein, the ink formulation for DIW derived from single- and multiple-phase systems containing CNF are explored and summarized. For single-phase system, the printability and microstructure against drying of CNF with different surface properties were first studied and optimized. Then a biomaterial system incorporating TEMPO-CNF, poly(glycerol sebacate) and polypyrrole was designed and printed for the treatment of myocardial infarction. In the later endeavor, we designed a two-phase ink, namely emulsion-based ink for further increasing the printability of the inks at low solid content. An emulgel system incorporating CNF, PLA/chloroform, surfactants and alginate was firstly studied. The result proves that the addition of PLA solution as oil phase could obviously restrict the shrinkage and deformation after drying. In line with this effort, we further finetuned such emulgel system by mixing CNF/ChNF/PLA Pickering emulsions with CNF/PAA/silica hydrogels, aiming to print bionic 3D shapes with better fidelity. A skin-bearing architecture was formed by one-step DIW using our two-phase emulgel system, mainly due to separation of immiscible but metastable phases given the possibility of spontaneous phase-separation upon printing. The skin on the filaments was used not only as a protection to keep the integrity of the hierarchical structure and to improve the mechanical strength, but also to tune the diffusion and permeability of encapsulated cargos, enabling the regulation of transport and channeling to the outer environment. Our efforts demonstrate the efficiency and robustness of using 3D printing to design and construct novel materials with multifunctional applications.