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The objective of this research is to develop a novel, multi-material additive manufacturing technique for fabricating laminated polymer nancomposite structures that have characteristic length-scales in the tens of millimeters range. The 3D printing technology presented in this paper combines the conventional inkjet-based printing of ultraviolet (UV) curable polymers with the deposition of either aligned or random nano-scale fiber mats, in between each printed layer. The fibers are first generated using an electrospinning process that produces the roll of fibers. These fibers are then transferred to the part being manufactured using a stamping operation. The process has been proven to manufacture multi-material laminated nanocomposites having different 3D geometries. The dimensional accuracy of the parts is seen to be a function of the interaction between the different UV-curable polymer inks. In general, the addition of the nanofibers in the form of laminates is seen to improve the mechanical properties of the material, with the Young’s modulus and the ultimate breaking stress showing the most improvement. The pinning and deflection of micro-cracks by the nano-scale fiber mats has been identified to be the underlying mechanism responsible for these improved mechanical properties. The thermogravimetric analysis reveals that these improvements in the mechanical properties are obtained without drastically altering the thermal degradation pattern of the base polymer.

The objective of this research is to develop a novel, multimaterial additive manufacturing technique for fabricating laminated polymer nanocomposite structures that have characteristic length-scales in the tens of millimeters range. The three-dimensional (3D) printing technology presented in this paper combines the conventional inkjet-based printing of ultraviolet (UV) curable polymers with the deposition of either aligned or random nanoscale fiber mats, in between each printed layer. The fibers are first generated using an electrospinning process that produces the roll of fibers. These fibers are then transferred to the part being manufactured using a stamping operation. The process has been proven to manufacture multimaterial laminated nanocomposites having different 3D geometries. The dimensional accuracy of the parts is seen to be a function of the interaction between the different UV-curable polymer inks. In general, the addition of the nanofibers in the form of laminates is seen to improve the mechanical properties of the material, with the Young’s modulus and the ultimate breaking stress showing the most improvement. The pinning and deflection of microcracks by the nanoscale fiber mats has been identified to be the underlying mechanism responsible for these improved mechanical properties. The thermogravimetric analysis (TGA) reveals that these improvements in the mechanical properties are obtained without drastically altering the thermal degradation pattern of the base polymer.

The extracellular matrix (ECM) is known to play an important role in the health of cells and tissues. Not only are chemical signals transmitted via bonds and tightly controlled diffusion, but the structure of the ECM also provides important physical signaling for the cells attached to it. The structure is composed of a mesh of fibrous proteins, such as collagen, embedded in a hydrated gel matrix of glycosaminoglycans. To study cell behavior with respect to the combined morphology and mechanics of such matrices is not currently possible with the types of 3D cell culture matrices available. Most of the cell culture matrices are single-phase bio- or polymeric hydrogels. Therefore, here we developed a continuous hybrid manufacturing process to make fiber-reinforced composite hydrogels. A far field electrospinning process was used to deposit the fibrous component with the aid of guiding electrodes; and a gravity-assisted, droplet-based system controlled the rate of addition of the cell-laden hydrogel component. The addition of the fibrous component slightly increased the elastic modulus of the pure hydrogel. The cells that were embedded into the fiber-reinforced hydrogels were viable for 8 days. The cells were randomly placed in the matrix such that some had no contact to the fibers and others were initially in proximity to fibers. The cells with no contact to fibers grew into spheroidal clusters within the hydrogel, and those in proximity to the fibers spread out and grew along the fibers showing that the fiber-reinforced hydrogels are able to control cell behavior with morphological cues.

This work demonstrates a general strategy for introducing remarkable changes in matrix organization and, consequently, functional properties of bacterial cellulose (BC). BC-producing cells were induced, using a well-defined atomized droplet nutrient delivery (ADND) system, to form pellicles with a regular layered morphology that persists throughout the mat depth. In contrast, the morphology of mats formed by conventional static medium nutrient delivery (SMND) is irregular with no distinguishable pattern. ADND also resulted in larger meso-scale average pore sizes but did not alter the fibril diameter (∼70 nm) and crystallinity index (92−95%). The specific modulus and specific tensile strength of ADND mats are higher than those of SMND mats. This is due to the regularity of dense layers that are present in ADND mats that are able to sustain tensile loads, when applied parallel to these layers. The density of BC films prepared by ADND is 1.63-fold lower than that of the SMND BC film. Consequently, the water contents (g/g) of ADND-and SMND-prepared BC mats are 263 ± 8.85 and 99.6 ± 2.04, respectively. A model that rationalizes differences in mat morphology resulting from these nutrient delivery methods based on nutrient and oxygen concentration gradients is proposed. This work raises questions as to the extent that ADND can be used to fine-tune the matrix morphology and how the resulting lower density mats will alter the diffusion of actives from the films to wound sites and increase the ability of cells to infiltrate the matrix during tissue engineering.