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Abstract Synthetically modified proteins, such as gelatin methacryloyl (GelMA), are growing in popularity for bioprinting and biofabrication. GelMA is a photocurable macromer that can rapidly form hydrogels, while also presenting bioactive peptide sequences for cellular adhesion and proliferation. The mechanical properties of GelMA are highly tunable by modifying the degree of substitution via synthesis conditions, though the effects of source material and thermal gelation have not been comprehensively characterized for lower concentration gels. Herein, the effects of animal source and processing sequence are investigated on scaffold mechanical properties. Hydrogels of 4–6 wt% are characterized. Depending on the temperature at crosslinking, the storage moduli for GelMA derived from pigs, cows, and cold‐water fish range from 723 to 7340 Pa, 516 to 3484 Pa, and 294 to 464 Pa, respectively. The maximum storage moduli are achieved only by coordinated physical gelation and chemical crosslinking. In this method, the classic thermo‐reversible gelation of gelatin occurs when GelMA is cooled below a thermal transition temperature, which is subsequently “locked in” by chemical crosslinking via photocuring. The effects of coordinated physical gelation and chemical crosslinking are demonstrated by precise photopatterning of cell‐laden microstructures, inducing different cellular behavior depending on the selected mechanical properties of GelMA. 

Blood coagulation is a highly regulated injury response that features polymerization of fibrin fibers to prevent the passage of blood from a damaged vascular endothelium. A growing body of research seeks to monitor coagulation in microfluidic systems but fails to capture coagulation as a response to disruption of the vascular endothelium. Here we present a device that allows compression injury of a defined segment of a microfluidic vascular endothelium and the assessment of coagulation at the injury site. This pressure injury-on-a-chip (PINCH) device allows visualization of coagulation as the accumulation of fluorescent fibrin at injury sites. Quantification of fluorescent fibrin levels upstream of and at injury sites confirm that pre-treating vascular endothelium with fluid shear stress helps capture coagulation as an injury response. We leverage the PINCH devices to demonstrate the limited coagulation response of type A hemophiliacs and evaluate the performance of hemostatic microparticles and fibrinolytic nanoparticles. Our findings and the straightforward fabrication of the PINCH devices make it a promising choice for additional screening of hemostatic therapeutics. 

Microphysiological systems (MPS) incorporate physiologically relevant microanatomy, mechanics, and cells to mimic tissue function. Reproducible and standardized in vitro models of tissue barriers, such as the blood-tissue interface (BTI), are critical for next-generation MPS applications in research and industry. Many models of the BTI are limited by the need for semipermeable membranes, use of homogenous cell populations, or 2D culture. These factors limit the relevant endothelial-epithelial contact and 3D transport, which would best mimic the BTI. Current models are also difficult to assemble, requiring precise alignment and layering of components. The work reported herein details the engineering of a BTI-on-a-chip (BTI Chip) that addresses current disadvantages by demonstrating a single layer, membrane-free design. Laminar flow profiles, photocurable hydrogel scaffolds, and human cell lines were used to construct a BTI Chip that juxtaposes an endothelium in direct contact with a 3D engineered tissue. A biomaterial composite, gelatin methacryloyl and 8-arm polyethylene glycol thiol, was used for in situ fabrication of a tissue structure within a Y-shaped microfluidic device. To produce the BTI, a laminar flow profile was achieved by flowing a photocurable precursor solution alongside phosphate buffered saline. Immediately after stopping flow, the scaffold underwent polymerization through a rapid exposure to UV light (<300 mJ/cm2). After scaffold formation, blood vessel endothelial cells were introduced and allowed to adhere directly to the 3D tissue scaffold, without barriers or phase guides. Fabrication of the BTI Chip was demonstrated in both an epithelial tissue model and blood-brain barrier (BBB) model. In the epithelial model, scaffolds were seeded with human dermal fibroblasts. For the BBB models, scaffolds were seeded with the immortalized glial cell line, SVGP12. The BTI Chip microanatomy was analyzed post facto by immunohistochemistry, showing the uniform production of a patent endothelium juxtaposed with a 3D engineered tissue. Fluorescent tracer molecules were used to characterize the permeability of the BTI Chip. The BTI Chips were challenged with an efflux pump inhibitor, cyclosporine A, to assess physiological function and endothelial cell activation. Operation of physiologically relevant BTI Chips and a novel means for high-throughput MPS generation was demonstrated, enabling future development for drug candidate screening and fundamental biological investigations. 

Most affinity-based biosensors are designed to be single-use devices, based on the measurement of irreversible binding events, which makes longitudinal monitoring resource-intensive, and typically prohibits the measurement of analyte fluctuations over time using the same device. Selective reversal of biorecognition events, i.e., regeneration, may enable repeated and longitudinal use of affinity-based biosensors; however, typical regeneration methods utilize additional chemical reagents, requiring longer processing times and increasing the likelihood of operator error. The development of a “solid-state” regeneration method provides significant value for extending the utility of affinity-based biosensors, such as electrochemical immunosensors and aptasensors. Herein, we report the characterization of a method for electronically controlling pH without additional reagents. Palladium was used to induce pH swings in aqueous electrolytes and buffers by application of an electric potential. The developed system was able to affect acidic and basic pH changes of ± 4. The efficacy of this method was further demonstrated by reversing common affinity-binding complexes and compared to conventional glycine-based regeneration. 

Gene therapies have shown great promise for the potential treatment of a broad range of diseases. Adeno-associated viruses (AAVs) are popular gene vectors because of their ability to target specific tissues, and they have demonstrated high transduction efficiencies in multiple neurological targets. While these therapeutics hold great promise, their biomanufacturing has limited potential cost-reduction and more widespread adoption. Herein, we report the preliminary development of an immunosensor for measuring the titer of adeno-associated virus 2 (AAV2), which may be deployed for rapid quantification of product yield during AAV biomanufacturing. We functionalized an interdigitated electrode array with anti-AAV2 antibodies, and electrochemical impedance spectroscopy was employed to investigate the response to AAV2 titer. A Faradaic sensing principle was utilized, in which the charge transfer resistance (Rct) of an electrochemical reporter was monitored after capture of AAV2 on the surface of the sensor. A linear response was measured over titers 1012 - 1013 capsids/mL. 

A new microphysiological system allows precise control and monitoring of oxygen levels at the cell surface to study the impact of hypoxia. Hypoxia pushes human intestinal stem cells (hISCs) into a dormant but reversible proliferative state and primes hISCs to respond to a subset of interleukins that rescues hISC activity. 

Herein, a 60-electrode array is fabricated down the length of a microchamber for analysis of a microphysiological system. The electrode array is fabricated by standard photolithographic, metallization, and etching techniques. Permutations of 2-wire impedance measurements (10 Hz to 1 MHz) are made along the length of the microchannel using a multiplexer, Gamry potentiostat, and custom Labview code. An impedance "heat map" is created via custom algorithms. Spatial resolution and mapping capabilities are exhibited using conductive NaCl solutions and 2D cell culture. 

Wound healing is a multivariate process involving the coordinated response of numerous proteins and cell types. Accordingly, biomedical research has seen an increased adoption of the use of in vitro wound healing assays with complexity beyond that offered by traditional well-plate constructs. These microphysiological systems (MPS) seek to recapitulate one or more physiological features of the in vivo microenvironment, while retaining the analytical capacity of more reductionist assays. Design efforts to achieve relevant wound healing physiology include the use of dynamic perfusion over static culture, the incorporation of multiple cell types, the arrangement of cells in three dimensions, the addition of biomechanically and biochemically relevant hydrogels, and combinations thereof. This review provides a brief overview of the wound healing process and in vivo assays, and we critically review the current state of MPS and supporting technologies for modelling and studying wound healing. We distinguish between MPS that seek to inform a particular phase of wound healing, and constructs that have the potential to inform multiple phases of wound healing. This distinction is a product of whether analysis of a particular process is prioritized, or a particular physiology is prioritized, during design. Material selection is emphasized throughout, and relevant fabrication techniques discussed.