Heart-on-a-Chip Model of Epicardial-Myocardial Interaction in Ischemia Reperfusion Injury.

Epicardial cells (EPIs) form the outer layer of the heart and play an important role in development and disease. Current heart-on-a-chip platforms still do not fully mimic the native cardiac environment due to the absence of relevant cell types, such as EPIs. Here, using the Biowire II platform, engineered cardiac tissues with an epicardial outer layer and inner myocardial structure are constructed, and an image analysis approach is developed to track the EPI cell migration in a beating myocardial environment. Functional properties of EPI cardiac tissues improve over two weeks in culture. In conditions mimicking ischemia reperfusion injury (IRI), the EPI cardiac tissues experience less cell death and a lower impact on functional properties. EPI cell coverage is significantly reduced and more diffuse under normoxic conditions compared to the post-IRI conditions. Upon IRI, migration of EPI cells into the cardiac tissue interior is observed, with contributions to alpha smooth muscle actin positive cell population. Altogether, a novel heart-on-a-chip model is designed to incorporate EPIs through a formation process that mimics cardiac development, and this work demonstrates that EPI cardiac tissues respond to injury differently than epicardium-free controls, highlighting the importance of including EPIs in heart-on-a-chip constructs that aim to accurately mimic the cardiac environment.

Itaconate and citrate releasing polymer attenuates foreign body response in biofabricated cardiac patches.

Application of cardiac patches to the heart surface can be undertaken to provide support and facilitate regeneration of the damaged cardiac tissue following ischemic injury. Biomaterial composition is an important consideration in the design of cardiac patch materials as it governs host response to ultimately prevent the undesirable fibrotic response. Here, we investigate a novel patch material, poly (itaconate-co-citrate-co-octanediol) (PICO), in the context of cardiac implantation. Citric acid (CA) and itaconic acid (ITA), the molecular components of PICO, provided a level of protection for cardiac cells during ischemic reperfusion injury in vitro. Biofabricated PICO patches were shown to degrade in accelerated and hydrolytic conditions, with CA and ITA being released upon degradation. Furthermore, the host response to PICO patches after implantation on rat epicardium in vivo was explored and compared to two biocompatible cardiac patch materials, poly (octamethylene (anhydride) citrate) (POMaC) and poly (ethylene glycol) diacrylate (PEGDA). PICO patches resulted in less macrophage infiltration and lower foreign body giant cell reaction compared to the other materials, with corresponding reduction in smooth muscle actin-positive vessel infiltration into the implant region. Overall, this work demonstrates that PICO patches release CA and ITA upon degradation, both of which demonstrate cardioprotective effects on cardiac cells after ischemic injury, and that PICO patches generate a reduced inflammatory response upon implantation to the heart compared to other materials, signifying promise for use in cardiac patch applications.

High Throughput Omnidirectional Printing of Tubular Microstructures from Elastomeric Polymers.

Bioelastomers are extensively used in biomedical applications due to their desirable mechanical strength, tunable properties, and chemical versatility; however, three-dimensional (3D) printing bioelastomers into microscale structures has proven elusive. Herein, a high throughput omnidirectional printing approach via coaxial extrusion is described that fabricates perfusable elastomeric microtubes of unprecedently small inner diameter (350-550 µm) and wall thickness (40-60 µm). The versatility of this approach is shown through the printing of two different polymeric elastomers, followed by photocrosslinking and removal of the fugitive inner phase. Designed experiments are used to tune the microtube dimensions and stiffness to match that of native ex vivo rat vasculature. This approach affords the fabrication of multiple biomimetic shapes resembling cochlea and kidney glomerulus and affords facile, high-throughput generation of perfusable structures that can be seeded with endothelial cells for biomedical applications. Post-printing laser micromachining is performed to generate micro-sized holes (520 µm) in the tube wall to tune microstructure permeability. Importantly, for organ-on-a-chip applications, the described approach takes only 3.6 min to print microtubes (without microholes) over an entire 96-well plate device, in contrast to comparable hole-free structures that take between 1.5 and 6.5 days to fabricate using a manual 3D stamping approach.

Toward Hierarchical Assembly of Aligned Cell Sheets into a Conical Cardiac Ventricle Using Microfabricated Elastomers.

Despite current efforts in organ-on-chip engineering to construct miniature cardiac models, they often lack some physiological aspects of the heart, including fiber orientation. This motivates the development of bioartificial left ventricle models that mimic the myofiber orientation of the native ventricle. Herein, an approach relying on microfabricated elastomers that enables hierarchical assembly of 2D aligned cell sheets into a functional conical cardiac ventricle is described. Soft lithography and injection molding techniques are used to fabricate micro-grooves on an elastomeric polymer scaffold with three different orientations ranging from -60° to +60°, each on a separate trapezoidal construct. The width of the micro-grooves is optimized to direct the majority of cells along the groove direction and while periodic breaks are used to promote cell-cell contact. The scaffold is wrapped around a central mandrel to obtain a conical-shaped left ventricle model inspired by the size of a human left ventricle 19 weeks post-gestation. Rectangular micro-scale holes are incorporated to alleviate oxygen diffusional limitations within the 3D scaffold. Cardiomyocytes within the 3D left ventricle constructs showed high viability in all layers after 7 days of cultivation. The hierarchically assembled left ventricle also provided functional readouts such as calcium transients and ejection fraction.

Bioengineering strategies to control epithelial-to-mesenchymal transition for studies of cardiac development and disease.

Epithelial-to-mesenchymal transition (EMT) is a process that occurs in a wide range of tissues and environments, in response to numerous factors and conditions, and plays a critical role in development, disease, and regeneration. The process involves epithelia transitioning into a mobile state and becoming mesenchymal cells. The investigation of EMT processes has been important for understanding developmental biology and disease progression, enabling the advancement of treatment approaches for a variety of disorders such as cancer and myocardial infarction. More recently, tissue engineering efforts have also recognized the importance of controlling the EMT process. In this review, we provide an overview of the EMT process and the signaling pathways and factors that control it, followed by a discussion of bioengineering strategies to control EMT. Important biological, biomaterial, biochemical, and physical factors and properties that have been utilized to control EMT are described, as well as the studies that have investigated the modulation of EMT in tissue engineering and regenerative approaches in vivo, with a specific focus on the heart. Novel tools that can be used to characterize and assess EMT are discussed and finally, we close with a perspective on new bioengineering methods that have the potential to transform our ability to control EMT, ultimately leading to new therapies.

3D Printing of Vascular Tubes Using Bioelastomer Prepolymers by Freeform Reversible Embedding.

Bioelastomers have been extensively used in tissue engineering applications because of favorable mechanical stability, tunable properties, and chemical versatility. As these materials generally possess low elastic modulus and relatively long gelation time, it is challenging to 3D print them using traditional techniques. Instead, the field of 3D printing has focused preferentially on hydrogels and rigid polyester materials. To develop a versatile approach for 3D printing of elastomers, we used freeform reversible embedding of suspended prepolymers. A family of novel fast photocrosslinakble bioelastomer prepolymers were synthesized from dimethyl itaconate, 1,8-octanediol, and triethyl citrate. Tensile testing confirmed their elastic properties with Young's moduli in the range of 11-53 kPa. These materials supported cultivation of viable cells and enabled adhesion and proliferation of human umbilical vein endothelial cells. Tubular structures were created by embedding the 3D printed microtubes within a secondary hydrogel that served as a temporary support. Upon photocrosslinking and porogen leaching, the polymers were permeable to small molecules (TRITC-dextran). The polymer microtubes were assembled on the 96-well plates custom made by hot-embossing, as a tool to connect multiple organs-on-a-chip. The endothelialization of the tubes was performed to confirm that these microtubes can be utilized as vascular tubes to support parenchymal tissues seeded on them.

Method for the Fabrication of Elastomeric Polyester Scaffolds for Tissue Engineering and Minimally Invasive Delivery.

Using the methods described herein, we have demonstrated how scaffolds can be designed for a number of applications including tissue engineering, biomedical devices and injectable tissues. Details on the methods of polymerization and physical and chemical characterization of poly(octamethylene maleate (anhydride) citrate (POMaC) are described. Two POMaC polymer recipes with different monomer ratios of maleic anhydride and citric acid were synthesized and compared. Mechanical testing was performed on scaffolds of two distinct anisotropic designs to show how scaffold design influences the apparent elasticity in the long and short axis. POMaC scaffolds of various patterns and geometries were fabricated to demonstrate: (1) scaffold function can be determined by scaffold design (e.g., inherent shape-memory or self-assembling tubular structures), and (2) the soft lithography approach to fabricating biodegradable elastomers described here can be used to suit a number of different potential applications.

Organ-On-A-Chip Platforms: A Convergence of Advanced Materials, Cells, and Microscale Technologies.

Significant advances in biomaterials, stem cell biology, and microscale technologies have enabled the fabrication of biologically relevant tissues and organs. Such tissues and organs, referred to as organ-on-a-chip (OOC) platforms, have emerged as a powerful tool in tissue analysis and disease modeling for biological and pharmacological applications. A variety of biomaterials are used in tissue fabrication providing multiple biological, structural, and mechanical cues in the regulation of cell behavior and tissue morphogenesis. Cells derived from humans enable the fabrication of personalized OOC platforms. Microscale technologies are specifically helpful in providing physiological microenvironments for tissues and organs. In this review, biomaterials, cells, and microscale technologies are described as essential components to construct OOC platforms. The latest developments in OOC platforms (e.g., liver, skeletal muscle, cardiac, cancer, lung, skin, bone, and brain) are then discussed as functional tools in simulating human physiology and metabolism. Future perspectives and major challenges in the development of OOC platforms toward accelerating clinical studies of drug discovery are finally highlighted.

Multifunctional microbeads for drug delivery in TACE.

INTRODUCTION: Transarterial chemoembolization (TACE) is the standard treatment for unresectable intermediate-stage hepatocellular carcinoma (HCC). Microbeads used to embolize tumor vasculature have recently been designed to deliver a therapeutic drug to the tumor site. Increasing the functionality of microbeads for TACE has the potential to improve therapy by accomplishing multiple, beneficial tasks with one system. AREAS COVERED: Microbead functions beyond embolization and drug delivery that could be highly advantageous include detection and tracking with imaging, targeting, degradation, and the delivery of multiple therapeutics or combination therapies. This review covers the concepts of TACE for treatment of HCC, the need for controlled delivery systems and the use of drug-eluting beads. Shortcomings of the current technology and the current approaches to improve materials used as embolic microbeads are discussed. Relevant studies aimed to enhance microbead visibility, targetability, degradability, and the use of multiple therapeutics or combination therapies are reviewed. EXPERT OPINION: The incorporation of nanoparticles that possess desirable properties into the microbead matrix is a suitable method of creating multifunctional microbeads. The development of these 'nano-on-micro' systems is a promising approach to improve TACE therapy and may lead to improved treatment.