Biodispensing techniques have been widely applied in biofabrication processes to deliver cell suspensions and biomaterials to create cell-seeded constructs. Under identical operating conditions,two types of dispensing needles—tapered and cylindrical—can result in different flow rates of material and different cell damage percent induced by the mechanical forces. In this work, mathematical models of both flow rate and cell damage percent in biodispensing systems using tapered and cylindrical needles, respectively, were developed, and experiments were carried out to verify the effectiveness of the developed models. Both simulations and experiments show tapered needles produce much higher flow rates under the same pressure conditions than cylindrical needles. Use of a lower pressure in a tapered needle can therefore achieve the same flow rate as that in a cylindrical needle. At equivalent flow rates, cell damage in a tapered needle is lower than that in a cylindrical one. Both Schwann cells and 3T3 fibroblasts, which have been widely used in tissue engineering, were used to validate the cell damage models. Application of the developed models to specify the influence of process parameters, including needle geometry and air pressure, on the flow rate and cell damage percent represents a significant advance for biofabrication processes.The models can be used to optimize process parameters to preserve cell viability and achieve the desired cell distribution in dispensing-based biofabrication.

Surface wrinkled particles are ubiquitous in nature and present in different sizes and shapes, such as plant pollens and peppercorn seeds. These natural wrinkles provide the particles with advanced functions to survive and thrive in nature. In this work, by combining flow lithography and plasma treatment, we have developed a simple method that can rapidly create wrinkled non-spherical particles, mimicking the surface textures in nature. Due to the oxygen inhibition in flow lithography, the non-spherical particles synthesized in a microfluidic channel are covered by a partially cured polymer (PCP) layer. When exposed to plasma treatment, this PCP layer rapidly buckles, forming surface-wrinkled particles. We designed and fabricated various particles with desired shapes and sizes. The surfaces of these shapes were tuned to created wrinkle morphologies by controlling UV exposure time and the washing process. We further demonstrated that wrinkles on the particles significantly promoted cell attachment without any chemical modification, potentially providing a new route for cell attachment for various biomedical applications.

Emerging biomanufacturing processes involve incorporation of living cells into various processes and systems by employing different cell manipulation techniques. Among them, biodispensing, in which the cell suspension is extruded via a fine needle under pressurized air, is a promising technique because of its high efficiency. Cells in this process are continually subjected to mechanical forces and may be damaged if the force or manipulation time exceeds certain levels. Modeling cell injury incurred in these processes is lacking in the literature. This article presents a method to quantify the force-induced cell damage in the biodispensing process. This method consists of two steps: first is to establish cell damage laws to relate cell damage to hydrostatic pressure/shear stress; and the second is to represent the process-induced forces experienced by cells during the biodispensing process and apply the established cell damage law to represent the percentage of cell damage. Schwann cells and 3T3 fibroblasts were used to validate the model and the comparisons of experimental and simulation results show the effectiveness of the method presented in this article.

surfaces and may not be applicable to fabrication of 3D wrinkled surfaces. The fi rst strategy may introduce local stress concentrations on 3D surface as the substrate is globally stretched and thus may form undesired wrinkles on the surface. The second one has the potential to create wrinkles on curved surfaces, but it generates wrinkles on the surfaces without 3D spatial control. [ 35,36 ] Methods that can facilely make 3D microstructured surfaces with tunable and controllable wrinkles are still not available, essentially limiting their applications to planar surface. Given the distinctive morphology of wrinkles and its proven functional roles in various 2D applications, creation of artifi cial 3D wrinkled surfaces, mimicking the diverse morphologies of wrinkles on nonplanar surfaces appearing in nature, may offer enhanced surface platforms and extend current 2D applications into a new dimension.Here, we demonstrate the formation of spatially tunable and controllable wrinkles on 2D/3D microstructured surfaces. In this microfabrication, fi rst we use photolithography to create polymeric 3D features with conformal partially-cured-polymer (PCP) layers by applying precisely controlled UV exposure. By projecting UV light via a photomask, we polymerize a prepolymer solution of poly(ethylene glycol) diacrylate (PEG-DA) in between a glass substrate and a PDMS slit channel ( Figure S1, Supporting Information) to create the 2D and 3D surfaces. The initial presence of oxygen in the prepolymer solution inhibits the polymerization until the oxygen is gradually depleted by the UV-initiated free radicals. [ 37 ] Because of the continuous diffusion of oxygen from the surrounding environment via the PDMS while no oxygen has penetrated from the glass, nonuniform polymerization across the channel height occurs and a PCP layer is created. The polymerization starts from the glass side and grows with a partially cured outer layer where the oxygen is being consumed by the UV-initiated free radicals (see the simulation of the polymerization progress in Figure S2, Supporting Information). When the UV is turned off, the polymerization stops and a photomask-defi ned 2D/3D microstructure is formed with a cured-body (foundation) and a PCP layer. This PCP layer is comprised of a semi-crosslinked PEG polymer network and uncured monomers trapped inside the network. The layer thickness is determined by the UV exposure time ( Figure S2, Supporting Information). After applying the photolithography, we gently rinse the sample to remove the uncured monomers, while retain those monomers trapped in the PCP layer. Finally, we treat the sample surface with plasma to create 2D/3D wrinkled microstructures (see Experimental Section). The charged ions of the plasma crosslink the PCP layer and slightly modify its mechanical properties, turning the PCP layer into a thin crust. Moreover, the continuous plasma also expands the thin crust, thus introduces in-plane compressive stresses in the Surface wrinkles are ubiquitous in nature and are used as a strategy ...

Biofabrication technologies involve the incorporation of living cells into various bioproducts by employing different cell manipulation techniques. Among them, bioprinting, delivering cell suspension through a fine needle under pressurized air, has been widely used because of its capability of precise process control. In the cell-printing process of bioprinting, cells are exposed to fluid stresses due to the velocity gradient in the fine needle. If the stresses exceed a certain level, the cell membrane may be overstretched, leading to membrane failure and thus causing mechanical cell damage. Modeling the mechanical cell damage in the bioprinting process is a challenging task due to the complex fluid flow and cell deformation involved. This paper introduces a novel method based on computational fluid dynamics (CFD) to represent the mechanical cell damage in the bioprinting process using a conical needle. Specifically, the cell deformation and movement during the cell-fluid interaction processes were represented by the immersed boundary method (IBM). A strain energy density (SED)-based cell damage criterion was developed and used to determine cell damage. Experiments were performed by using 3T3 fibroblasts and the results agree well with the proposed model.