Biology subjects

Geffert, Z. J.

Publications and source records attributed to Geffert, Z. J..

6 recordsLinked to original sources

bioRxiv2026

Shaping hydrogel bioinks into 3D, multiscale, perfusable models using multimodal printing

Despite technological advances, the fabrication of multiscale, multi-material, and topologically complex 3D structures using soft hydrogel bioinks remains a challenge due to the inherent trade-offs between print size/resolution, bioink properties, and design complexity. In this work, we combine additive (macroscale) digital light projection (DLP) mode with subtractive (microscale) two-photon ablation (TPA) mode with multi-material exchange capability. We identify ideal hydrogel bioink formulations that are compatible with both DLP and TPA modes of processing. Technical challenges related to multimodal fabrication such as alignment of multiscale topologies to facilitate seamless media perfusion, soft-hard multi-material printing to facilitate handling of mechanically weak hydrogel constructs, and hydrogel swelling during printing, were resolved. To highlight the novelty of this hybrid platform, we fabricated centimeter-scale bioink constructs with embedded microscale perfusable topologies that cannot be achieved by isolated use of either DLP or TPA modes. This includes simpler microfluidic chips with independently perfusable microchannels to more complex 3D constructs with embedded, multiscale, perfusable dual-fluidic circuits that mimic the alveoli-capillary interface, or microfluidic chips with endothelialized microchannels. The unique ability of this multimodal platform to mimic in vivo-like multiscale complexities can be potentially used to develop next-generation organ-on-chips.

bioengineering↗

bioRxiv2025

3D osteocyte networks under Pulsatile Unidirectional Fluid Flow Stimuli (PUFFS)

Although osteocytes are known to play a key role in skeletal mechano-adaptation, few in vitro models have investigated how pulsatile mechanical stimuli influence the properties of 3D osteocyte networks. Here we design and develop a microfluidic based in vitro model to study 3D osteocyte networks cultured under Pulsatile Unidirectional Fluid Flow Stimuli (PUFFS). Digital light projection stereolithography was used to design and fabricate a three-chambered PDMS microfluidic chip. Model osteocytes (murine MLO-Y4) were encapsulated in collagen matrix within the chip to form self-assembled three-dimensional (3D) cell networks. Daily stimulus in the form of PUFFS was then applied for upto 21 days. A combination of experiments, computational simulation and analytical modeling was used to characterize the mechanical environment experienced by embedded cells during PUFFS. Viability, morphology, cell-connectivity, expression of key proteins, and gene expression, and real-time calcium signaling within 3D osteocyte networks were characterized at select time-points and compared to static conditions. Results show that PUFFS stimulation at 0.33 and 1.66 Hz can initiate mechanotransduction via calcium signals that are propagated across the network of collagen encapsulated osteocytes via Cx43 junctions. Furthermore, osteocytes cultured in these devices maintain expression of several key osteocyte genes for up to 21d. Taken together, this model can potentially serve as a testbed to study how 3D osteocyte networks respond to dynamic mechanical stimulation relevant to skeletal tissues.

bioengineering↗

bioRxiv2024

Multipath projection stereolithography (MPS) for 3D printing microfluidic devices

Although many lab-on-chip applications require inch-sized devices with microscale feature resolution, achieving this via current 3D printing methods remains challenging due to inherent tradeoffs between print resolution, design complexity, and build sizes. Inspired by microscopes that can switch objectives to achieve multiscale imaging, we report a new optical printer coined as Multipath Projection Stereolithography (MPS) specifically designed for printing microfluidic devices. MPS is designed to switch between high-resolution (1xmode, [~]10{micro}m) and low-resolution (3x mode, [~]30{micro}m) optical paths to generate centimeter sized constructs (3cm x 6cm) with a feature resolution of [~]10{micro}m. Illumination and projection systems were designed, resin formulations were optimized, and slicing software was integrated with hardware with the goal of ease of use. Using a test-case of micromixers, we show user-defined CAD models can be directly input to an automated slicing software to define printing of low-resolution features via the 3x mode with embedded microscale fins via 1x mode. A new computational model, validated using experimental results, was used to simulate various fin designs and experiments were conducted to verify simulated mixing efficiencies. New 3D out-of-plane micromixer designs were simulated and tested. To show broad applications of MPS, multi-chambered chips and microfluidic devices with microtraps were also printed. Overall, MPS can be a new fabrication tool to rapidly print a range of lab-on-chip applications.

bioinformatics↗

bioRxiv2023

Droplet bioprinting of acellular and cell-laden structures at high-resolutions

Advances in Digital Light Processing (DLP) based (bio) printers have made printing of intricate structures at high resolution possible using a wide range of photosensitive bioinks. A typical setup of a DLP bioprinter includes a vat or reservoir filled with liquid bioink, which presents challenges in terms of cost associated with bioink synthesis, high waste, and gravity-induced cell settling, contaminations, or variation in bioink viscosity during the printing process. Here, we report a vat-free, low-volume, waste-free droplet bioprinting method capable of rapidly printing 3D soft structures at high resolution using model bioinks. A multiphase many-body dissipative particle dynamics (mDPD) model was developed to simulate the dynamic process of droplet-based DLP printing and elucidate the roles of surface wettability and bioink viscosity. Process variables such as light intensity, photo-initiator concentration, and bioink formulations were optimized to print 3D soft structures ([~]0.4 to 3 kPa) with an XY resolution of 38 {+/-} 1.5 m and Z resolution of 237{+/-}5.4 m. To demonstrate its versatility, droplet bioprinting was used to print a range of acellular 3D structures such as a lattice cube, a Mayan pyramid, a heart-shaped structure, and a microfluidic chip with endothelialized channels. Droplet bioprinting, performed using model C3H/10T1/2 cells, exhibited high viability (90%) and cell spreading. Additionally, microfluidic devices with internal channel network lined with endothelial cells showed robust monolayer formation while osteoblast-laden constructs showed mineral deposition upon osteogenic induction. Overall, droplet bioprinting could be a low-cost, no-waste, easy-to-use, method to make customized bioprinted constructs for a range of biomedical applications.

bioengineering↗

bioRxiv2023

Meniscus-enabled Projection Stereolithography (MAPS)

Light-based additive manufacturing methods have been widely used to print high-resolution 3D structures for applications in tissue engineering, soft robotics, photonics, and microfluidics, among others. Despite this progress, multi-material printing with these methods remains challenging due to constraints associated with hardware modifications, control systems, cross-contaminations, waste, and resin properties. Here, we report a new printing platform coined Meniscus-enabled Projection Stereolithography (MAPS), a vat-free method that relies on generating and maintaining a resin meniscus between a crosslinked structure and bottom window and to print lateral, vertical, discrete, or gradient multi-material 3D structures with little-to-no cross-contamination or waste. We also show that MAPS is compatible with a wide range of resins and can print complex multi-material 3D structures without requiring specialized hardware, software, or complex washing protocols. MAPSs ability to print structures with microscale variations in mechanical stiffness, opacity, surface energy, cell densities, and magnetic properties provides a generic method to make advanced materials for a broad range of applications.

bioengineering↗

bioRxiv2023

Printing double network tough hydrogels using Temperature-Controlled Projection Stereolithography (TOPS)

We report a new method to shape double-network (DN) hydrogels into customized microscale 3D structures that exhibit superior mechanical properties in both tension and compression. A one-pot prepolymer formulation containing photo-cross-linkable acrylamide and thermo-reversible sol-gel {kappa}-carrageenan with a suitable crosslinker, and photo-initiator/absorbers are optimized. A new TOPS system is utilized to photo-polymerize the primary acrylamide network into a 3D structure above the sol-gel transition of {kappa}-carrageenan (80{degrees}C), while cooling down generates the secondary physical {kappa}-carrageenan network to realize tough DN hydrogel structures. 3D structures, printed with high lateral (37m) and vertical (180m) resolutions and superior 3D design freedoms (internal voids), exhibit ultimate stress and strain of 200 kPa and 2400% respectively under tension, and simultaneously exhibit high compression stress of 15 MPa with a strain of 95%, both with high recovery rates. The roles of swelling, necking, self-healing, cyclic loading, dehydration, and rehydration on the mechanical properties of printed structures are also investigated. To demonstrate the potential of this technology to make mechanically reconfigurable flexible devices, we print an axicon lens and show that a Bessel beam can be dynamically tuned via user-defined tensile stretching of the device. This technique can be broadly applied to other hydrogels to make novel smart multifunctional devices for a range of applications.

bioengineering↗