Bioprinting has gained significant attention for creating biomimetic tissue constructs with potential to be used in biomedical applications such as drug screening or regenerative medicine. Ideally, biomaterials used for three-dimensional (3D) bioprinting should match the mechanical, hydrostatic, bioelectric, and physicochemical properties of the native tissues. However, many materials with these tissue-like properties are not compatible with printing techniques without modifying their compositions. In addition, integration of cell-laden biomaterials with bioprinting methodologies that preserve their physicochemical properties remains a challenge. In this work, a biocompatible conductive hydrogel composed of gelatin methacryloyl (GelMA) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was synthesized and bioprinted to form complex, 3D cell-laden structures. The biofabricated conductive hydrogels were formed by an initial crosslinking step of the PEDOT:PSS with bivalent calcium ions and a secondary photopolymerization step with visible light to crosslink the GelMA component. These modifications enabled tuning the mechanical properties of the hydrogels, with Young's moduli ranging from ∼40−150 kPa, as well as tunable conductivity by varying the concentration of PEDOT:PSS. In addition, the hydrogels degraded in vivo with no substantial inflammatory responses as demonstrated by haematoxylin and eosin (H&E) and immunofluorescent staining of subcutaneously implanted samples in Wistar rats. The parameters for forming a slurry of microgel particles to support 3D bioprinting of the engineered cell-laden hydrogel were optimized to form constructs with improved resolution. High cytocompatibility and cell spreading were demonstrated in both wet-spinning and 3D bioprinting of cell-laden hydrogels with the new conductive hydrogel-based bioink and printing methodology. The synergy of an advanced fabrication method and conductive hydrogel presented here is promising for engineering complex conductive and cell-laden structures.

Receptor-mediated drug delivery presents an opportunity to enhance therapeutic efficiency by accumulating drug within the tissue of interest and reducing undesired, off-target effects. In cancer, receptor overexpression is a platform for binding and inhibiting pathways that shape biodistribution, toxicity, cell binding and uptake, and therapeutic function. This review will identify tumor-targeted drug delivery vehicles and receptors that show promise for clinical translation based on quantitative in vitro and in vivo data. The authors describe the rationale to engineer a targeted drug delivery vehicle based on the ligand, chemical conjugation method, and type of drug delivery vehicle. Recent advances in multivalent targeting and ligand organization on tumor accumulation are discussed. Revolutionizing receptor-mediated drug delivery may be leveraged in the therapeutic delivery of chemotherapy, gene editing tools, and epigenetic drugs.in the site of interest. This is clinically important as reaching a therapeutic dosage locally and reducing systemic toxicity can be life-threatening or life-saving events for cancer patients.The design of targeted DDVs can be optimized by altering the size, shape, material, ligand, and ligand orientation. For systemic delivery, spherical DDVs less than 200 nm in diameter are standard, which is balanced by the trade off between surface area and volume ratio. DDVs are prepared from biomaterials based on the size, hydrophobicity, and ideal release of the drug. There are a diverse range of ligand candidates for DDV functionalization, including monoclonal antibodies (mAbs), peptides, oligosaccharides, small molecules, and aptamers. [5] These ligands can be tethered to vehicles or conjugated directly to drugs by covalent (typically thiol or amide-based reactions, or "click" chemistry) or noncovalent attachment; the type of reaction is often based on the material of the DDV. [6] Multi-targeted and patterned DDVs improved cancer cell binding and the overall therapeutic benefit in vivo. The ideal DDV platform may be rationally designed by evaluating the drug, release mechanism, mode of delivery into the body, and target cells.Utilizing these approaches, targeted DDVs were successfully translated from the research setting into clinical use, or are currently in preclinical trials. [7] Liposomal based DDVs were approved for use in cancer therapy, treating fungal diseases, analgesics, photodynamic therapy, and viral vaccines. [8] Specifically, FDA approved liposomal drug formulations, such as Mepact, Maribo, and Epaxal were proven to be effective for the treatment of nonmetastatic osteosarcoma, acute lymphoblastic leukemia, and hepatitis A, respectively. [9] Many targeted DDVs in clinical use are utilized for the treatment of multiple cancer types, as there is often broad overlap in malignant receptor overexpression across various carcinogenic tissues (Figure 1). The widely successful drug Pembrolizumab (Keytruda), a humanized IgG4 isotype mAb that targets the programmed cell death (PD-1) rec...

Suturing peripheral nerve transections is the predominant therapeutic strategy for nerve repair. However, the use of sutures leads to scar tissue formation, hinders nerve regeneration, and prevents functional recovery. Fibrin-based adhesives have been widely used for nerve reconstruction, but their limited adhesive and mechanical strength and inability to promote nerve regeneration hamper their utility as a stand-alone intervention. To overcome these challenges, we engineered composite hydrogels that are neurosupportive and possess strong tissue adhesion. These composites were synthesized by photocrosslinking two naturally derived polymers, gelatin-methacryloyl (GelMA) and methacryloyl-substituted tropoelastin (MeTro). The engineered materials exhibited tunable mechanical properties by varying the GelMA/MeTro ratio. In addition, GelMA/MeTro hydrogels exhibited 15-fold higher adhesive strength to nerve tissue ex vivo compared to fibrin control. Furthermore, the composites were shown to support Schwann cell (SC) viability and proliferation, as well as neurite extension and glial cell participation in vitro, which are essential cellular components for nerve regeneration. Finally, subcutaneously implanted GelMA/MeTro hydrogels exhibited slower degradation in vivo compared with pure GelMA, indicating its potential to support the growth of slowly regenerating nerves. Thus, GelMA/MeTro composites may be used as clinically relevant biomaterials to regenerate nerves and reduce the need for microsurgical suturing during nerve reconstruction.

Here we report benchtop fabrication of multilayer thermoplastic organs-on-chips via laser cut and assembly of double sided adhesives. Biocompatibility was evaluated with Caco-2 cells and primary human intestinal organoids. Chips with Luer fluidic interfaces were economical ($2 per chip) and were fabricated in just hours without use of specialized bonding techniques. Compared with control static Transwell™ cultures, Caco-2 and organoids cultured on chips formed confluent monolayers expressing tight junctions with low permeability. Caco-2 cells on chip differentiated ~4 times faster compared to controls and produced mucus. To demonstrate the robustness of laser cut and assembly, we fabricated a dual membrane, tri-layer gut chip integrating 2D monolayers, 3D cell culture, and a basal flow chamber. As proof of concept, we co-cultured a human, differentiated monolayer and intact organoids in a chip with multi-layered contacting compartments. The epithelium exhibited 3D tissue structure and organoids formed in close proximity to the adjacent monolayer. The favorable features of thermoplastics, such as low gas and water vapor permeability, in addition to rapid, facile, and economical fabrication of multilayered devices, make laser cut and assembly an ideal fabrication technique for developing organs-on-chips and studying multicellular tissues.

Recent advancements in electronic materials and subsequent surface modifications have facilitated real-time measurements of cellular processes far beyond traditional passive recordings of neurons and muscle cells. Specifically, the functionalization of conductive materials with ligand-binding aptamers has permitted the utilization of traditional electronic materials for bioelectronic sensing. Further, microfabrication techniques have better allowed microfluidic devices to recapitulate the physiological and pathological conditions of complex tissues and organs in vitro or microphysiological systems (MPS). The convergence of these models with advances in biological/biomedical microelectromechanical systems (BioMEMS) instrumentation has rapidly bolstered a wide array of bioelectronic platforms for real-time cellular analytics. In this review, we provide an overview of the sensing techniques that are relevant to MPS development and highlight the different organ systems to integrate instrumentation for measurement and manipulation of cellular function. Special attention is given to how instrumented MPS can disrupt the drug development and fundamental mechanistic discovery processes.

Excitation-contraction (EC) coupling in the heart has, until recently, been solely accredited to 9 cardiomyocytes. The inherent complexities of the heart make it difficult to examine non-muscle 10 contributions to contraction in vivo, and conventional in vitro models fail to capture multiple 11 features and cellular heterogeneity of the myocardium. Here, we report on the development of a 12 3D cardiac µTissue to investigate changes in the cellular composition of native myocardium in 13 vitro. Cells are encapsulated within micropatterned gelatin-based hydrogels formed via visible 14 light photocrosslinking. This system enables spatial control of the microarchitecture, perturbation 15 of the cellular composition, and functional measures of EC coupling via video microscopy and a 16 custom algorithm to quantify beat frequency and degree of coordination. To demonstrate the 17 robustness of these tools and evaluate the impact of altered cell population densities on cardiac 18 µTissues, contractility and cell morphology were assessed with the inclusion of exogenous non-19 myelinating Schwann cells (SCs). Results demonstrate that the addition of exogenous SCs alter 20 cardiomyocyte EC, profoundly inhibiting the response to electrical pacing. Computational 21 modeling of connexin-mediated coupling suggests that SCs impact cardiomyocyte resting 22 Ischemic heart disease remains a leading cause of death worldwide. While pharmacological 1 interventions have improved life expectancy by mitigating key risk factors, therapeutic strategies 2 for repairing the damaged myocardium have yet to become the clinical standard (Björnson et al., 3 2016; Hashimoto et al., 2018). Following infarct, delivery of autologous cells, including 4 mesenchymal stem cells, cardiac stem cells, and endothelial progenitor cells, have yielded 5 promising results at the benchtop, but inconsistent benefits in clinical trials (Hatzistergos and 6

Tissue‐engineered models continue to experience challenges in delivering structural specificity, nutrient delivery, and heterogenous cellular components, especially for organ‐systems that require functional inputs/outputs and have high metabolic requirements, such as the heart. While soft lithography has provided a means to recapitulate complex architectures in the dish, it is plagued with a number of prohibitive shortcomings. Here, concepts from microfluidics, tissue engineering, and layer‐by‐layer fabrication are applied to develop reconfigurable, inexpensive microphysiological systems that facilitate discrete, 3D cell compartmentalization, and improved nutrient transport. This fabrication technique includes the use of the meniscus pinning effect, photocrosslinkable hydrogels, and a commercially available laser engraver to cut flow paths. The approach is low cost and robust in capabilities to design complex, multilayered systems with the inclusion of instrumentation for real‐time manipulation or measures of cell function. In a demonstration of the technology, the hierarchal 3D microenvironment of the cardiac sympathetic nervous system is replicated. Beat rate and neurite ingrowth are assessed on‐chip and quantification demonstrates that sympathetic‐cardiac coculture increases spontaneous beat rate, while drug‐induced increases in beating lead to greater sympathetic innervation. Importantly, these methods may be applied to other organ‐systems and have promise for future applications in drug screening, discovery, and personal medicine.

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