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Objectives: Lung remains the least-utilized solid organ for transplantation. Efforts to recover donor lungs with reversible injuries using ex vivo perfusion systems are limited to<24 hours of support. Here, we demonstrate the feasibility of extending normothermic extracorporeal lung support to 4 days using crosscirculation with conscious swine.Methods: A swine behavioral training program and custom enclosure were developed to enable multiday cross-circulation between extracorporeal lungs and recipient swine. Lungs were ventilated and perfused in a normothermic chamber for 4 days. Longitudinal analyses of extracorporeal lungs (ie, functional assessments, multiscale imaging, cytokine quantification, and cellular assays) and recipient swine (eg, vital signs and blood and tissue analyses) were performed.

The advent of successful solid organ transplantation is undoubtedly among the most significant medical achievements of the 20th century. Despite advances in the field of transplantation since its inception over 50 years ago, our approach to donor organ preservation outside of the body remains unchanged. Recently, attempts have been made to replace static cold storage with more sophisticated ex vivo machine perfusion. Rather than cooling the organ on ice to slow metabolic processes, machine perfusion aims to support normal metabolic function in a near-physiologic environment and to provide a platform on which the organ can be evaluated, preserved, and recovered. Ex vivo machine perfusion devices have demonstrated early success with respect to transplant outcomes in heart, lung, and liver, with perfusion times limited to several hours. The continued development of more advanced perfusion systems is likely to extend the duration of ex vivo organ support to days or even weeks, and enable recovery of initially unsuitable donor organs. In this review, we discuss recent clinical and pre-clinical studies, state-of-the-art organ preservation technologies, existing limitations, and a perspective on future developments.

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Biomaterial drug delivery systems (DDS) can be used to regulate growth factor release and combat the limited intrinsic regeneration capabilities of central nervous system (CNS) tissue following injury and disease. Of particular interest are systems that aid in oligodendrocyte regeneration, as oligodendrocytes generate myelin which surrounds neuronal axons and helps transmit signals throughout the CNS. Oligodendrocyte precursor cells (OPCs) are found in small numbers in the adult CNS, but are unable to effectively differentiate following CNS injury. Delivery of signaling molecules can initiate a favorable OPC response, such as proliferation or differentiation. Here, we investigate the delivery of one such molecule, platelet derived growth factor-AA (PDGF-AA), from poly(lactic-co-glycolic) acid microparticles to OPCs in a 3D polyethylene glycol-based hydrogel. The goal of this DDS was to better understand the relationship between PDGF-AA release kinetics and OPC fate. The system approximates native brain tissue stiffness, while incorporating PDGF-AA under seven different delivery scenarios. Within this DDS, supply of PDGF-AA followed by PDGF-AA withdrawal caused OPCs to upregulate gene expression of myelin basic protein (MBP) by factors of 1.6-9.2, whereas continuous supply of PDGF-AA caused OPCs to remain proliferative. At the protein expression level, we observed an upregulation in O1, a marker for mature oligodendrocytes. Together, these results show that burst release followed by withdrawal of PDGF-AA from a hydrogel DDS stimulates survival, proliferation, and differentiation of OPCs in vitro. Our results could inform the development of improved neural regeneration strategies that incorporate delivery of PDGF-AA to the injured CNS. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2402-2411, 2018.

Gastrointestinal disease burden continues to rise in the United States and worldwide. The development of bioengineering strategies to model gut injury or disease and to re-establish functional gut tissue could expand therapeutic options and improve clinical outcomes. Current approaches leverage a rapidly evolving gut bioengineering toolkit aimed at: (i) de-novo generation of gut-like tissues at multiple scales for microtissue models or implantable grafts, and (ii) regeneration of functional gut in vivo. Although significant progress has been made in intestinal organoid cultures and engineered tissues, development of predictive in-vitro models and effective regenerative therapies remains challenging. In this review, we survey emerging bioengineering tools and recent methodological advances to identify future opportunities and challenges in gut bioengineering for disease modeling and regenerative medicine.

Recent synergistic advances in organ-on-chip and tissue engineering technologies offer opportunities to create in vitro-grown tissue or organ constructs that can faithfully recapitulate their in vivo counterparts. Such in vitro...

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