Bioprinting-assisted tissue assembly to generate organ substitutes at scale.

Various external cues can guide cellular behavior and maturation during developmental processes. Recent studies on bioprinting-assisted tissue engineering have considered this a practical, versatile, and flexible way to provide external cues to developing engineered tissues. An ensemble of multiple external cues can improve the speed and capability of morphogenesis. In this review, we discuss how bioprinting and biomaterials provide multiple guidance to generate micro-sized building blocks with specific shapes and also highlight their applications in tissue assembly toward volumetric tissue and organ generation. Furthermore, we discuss our perspectives on the future translation of bioprinting technologies integrated with artificial intelligence (AI) and robot-assisted apparatus to promote automation, standardization, and clinical translation of bioprinted tissues.

Microbiological contamination of fresh-cut produce in Korea.

This study evaluated the microbiological contamination of fresh-cut produce in Korea. A total of 108 fresh-cut vegetables and fruits were surveyed for the aerobic mesophilic (AM) count, aerobic psychrophilic (AP) count, total coliform, generic Escherichia coli, yeast and mold, and foodborne pathogens. AM counts ranged from 1.00 to 7.36 log CFU/g, and AP counts showed very similar results as AM counts. For total coliform and generic E. coli, 53.7% and 9.3% of the samples were detected, respectively. For foodborne pathogens, none of the samples were identified as E. coli O157:H7 or Salmonella spp. However, S. aureus and B. cereus was detected in 5.6% and 6.5% of the samples, respectively. Although the contamination level has varied widely, samples with high bacterial counts, such as julienned green onion, bell pepper, carrot, and mixed sprout, should be implemented with strict control measures.

Construction of 3D hierarchical tissue platforms for modeling diabetes.

Diabetes mellitus (DM) is one of the most serious systemic diseases worldwide, and the majority of DM patients face severe complications. However, many of underlying disease mechanisms related to these complications are difficult to understand with the use of currently available animal models. With the urgent need to fundamentally understand DM pathology, a variety of 3D biomimetic platforms have been generated by the convergence of biofabrication and tissue engineering strategies for the potent drug screening platform of pre-clinical research. Here, we suggest key requirements for the fabrication of physiomimetic tissue models in terms of recapitulating the cellular organization, creating native 3D microenvironmental niches for targeted tissue using biomaterials, and applying biofabrication technologies to implement tissue-specific geometries. We also provide an overview of various in vitro DM models, from a cellular level to complex living systems, which have been developed using various bioengineering approaches. Moreover, we aim to discuss the roadblocks facing in vitro tissue models and end with an outlook for future DM research.

A 3D bioprinted hybrid encapsulation system for delivery of human pluripotent stem cell-derived pancreatic islet-like aggregates.

Islet transplantation is a promising treatment for type 1 diabetes. However, treatment failure can result from loss of functional cells associated with cell dispersion, low viability, and severe immune response. To overcome these limitations, various islet encapsulation approaches have been introduced. Among them, macroencapsulation offers the advantages of delivering and retrieving a large volume of islets in one system. In this study, we developed a hybrid encapsulation system composed of a macroporous polymer capsule with stagger-type membrane and assemblable structure, and a nanoporous decellularized extracellular matrix (dECM) hydrogel containing pancreatic islet-like aggregates using 3D bioprinting technique. The outer part (macroporous polymer capsule) was designed to have an interconnected porous architecture, which allows insulin-producingß-cells encapsulated in the hybrid encapsulation system to maintain their cellular behaviors, including viability, cell proliferation, and insulin-producing function. The inner part (nanoporous dECM hydrogel), composed of the 3D biofabricated pancreatic islet-like aggregates, was simultaneously placed into the macroporous polymer capsule in one step. The developed hybrid encapsulation system exhibited biocompatibilityin vitroandin vivoin terms of M1 macrophage polarization. Furthermore, by controlling the printing parameters, we generated islet-like aggregates, improving cell viability and functionality. Moreover, the 3D bioprinted pancreatic islet-like aggregates exhibited structural maturation and functional enhancement associated with intercellular interaction occurring at theß-cell edges. In addition, we also investigated the therapeutic potential of a hybrid encapsulation system by integrating human pluripotent stem cell-derived insulin-producing cells, which are promising to overcome the donor shortage problem. In summary, these results demonstrated that the 3D bioprinting approach facilitates the fabrication of a hybrid islet encapsulation system with multiple materials and potentially improves the clinical outcomes by driving structural maturation and functional improvement of cells.

Pancreatic Tissue-Derived Extracellular Matrix Bioink for Printing 3D Cell-Laden Pancreatic Tissue Constructs.

The transplantation of pancreatic islets is a promising treatment for patients who suffer from type 1 diabetes accompanied by hypoglycemia and secondary complications. However, islet transplantation still has several limitations such as the low viability of transplanted islets due to poor islet engraftment and hostile environments. In addition, the insulin-producing cells differentiated from human pluripotent stem cells have limited ability to secrete sufficient hormones that can regulate the blood glucose level; therefore, improving the maturation by culturing cells with proper microenvironmental cues is strongly required. In this article, we elucidate protocols for preparing a pancreatic tissue-derived decellularized extracellular matrix (pdECM) bioink to provide a beneficial microenvironment that can increase glucose sensitivity of pancreatic islets, followed by describing the processes for generating 3D pancreatic tissue constructs using a microextrusion-based bioprinting technique.

3D cell printing of islet-laden pancreatic tissue-derived extracellular matrix bioink constructs for enhancing pancreatic functions.

Type 1 diabetes mellitus (T1DM) is a form of diabetes that inhibits or halts insulin production in the pancreas. Although various therapeutic options are applied in clinical settings, not all patients are treatable with such methods due to the instability of the T1DM or the unawareness of hypoglycemia. Islet transplantation using a tissue engineering-based approach may mark a clinical significance, but finding ways to increase the function of islets in 3D constructs is a major challenge. In this study, we suggest pancreatic tissue-derived extracellular matrix as a potential candidate to recapitulate the native microenvironment in transplantable 3D pancreatic tissues. Notably, insulin secretion and the maturation of insulin-producing cells derived from human pluripotent stem cells were highly up-regulated when cultured in pdECM bioink. In addition, co-culture with human umbilical vein-derived endothelial cells decreased the central necrosis of islets under 3D culture conditions. Through the convergence of 3D cell printing technology, we validated the possibility of fabricating 3D constructs of a therapeutically applicable transplant size that can potentially be an allogeneic source of islets, such as patient-induced pluripotent stem cell-derived insulin-producing cells.

A slanted-nanoaperture metal lens: subdiffraction-limited focusing of light in the intermediate field region.

Diffraction of light limits the resolution of beam focusing with conventional lenses, as dictated by the Abbe limit, that is, approximately half the wavelength. Numerous techniques have been explored to overcome this limit. One of the most intensively explored approaches is to design a lens that operates in the near-field region, that is, with a focal length on the order of 10 nm, where evanescent fields can carry and project large in-plane wave-vectors (greater than free-space wave-vectors) to a focal plane. From a practical perspective, however, the requirement of such an ultra-short focal length puts too much constraint, since much longer focal length is commonly desired for intermediate or far-field operation. Here we report a method to beat the Abbe limit while operating with focal length greater than wavelength λ. Our approach is to tailor the radiation patterns of nanoaperture transmission by tilting aperture axes away from the surface of a metal film such that each slanted aperture transmits a highly directed, tilt-oriented beam onto a common focal point carrying maximal in-plane wave-vector components. The proposed nanoaperture array lens was fabricated by forming tilted nanoslits in a Ag, Al, or Cr film. We demonstrate minimal spot size of λ/3 (210-nm or 110-nm full-width half-maximum at λ = 633 nm or 325 nm, respectively) with 1-4λ focal length in air, beating the Abbe limit.

Electrically-triggered micro-explosion in a graphene/SiO2/Si structure.

Electrically-triggered micro-explosions in a metal-insulator-semiconductor (MIS) structure can fragment/atomize analytes placed on it, offering an interesting application potential for chip-scale implementation of atomic emission spectroscopy (AES). We have investigated the mechanisms of micro-explosions occurring in a graphene/SiO2/Si (GOS) structure under a high-field pulsed voltage drive. Micro-explosions are found to occur more readily in inversion bias than in accumulation bias. Explosion damages in inversion-biased GOS differ significantly between n-Si and p-Si substrate cases: a highly localized, circular, protruding cone-shape melt of Si for the n-Si GOS case, whereas shallow, irregular, laterally-propagating trenches in SiO2/Si for the p-Si GOS case. These differing damage morphologies are explained by different carrier-multiplication processes: in the n-Si case, impact ionization propagates from SiO2 to Si, causing highly-localized melt explosions of Si in the depletion region, whereas in the p-Si case, from SiO2 towards graphene electrode, resulting in laterally wide-spread micro-explosions. These findings are expected to help optimize the GOS-based atomizer structure for low voltage, small-volume analyte, high sensitivity chip-scale emission spectroscopy.

Space charge neutralization by electron-transparent suspended graphene.

Graphene possesses many fascinating properties originating from the manifold potential for interactions at electronic, atomic, or molecular levels. Here we report measurement of electron transparency and hole charge induction response of a suspended graphene anode on top of a void channel formed in a SiO2/Si substrate. A two-dimensional (2D) electron gas induced at the oxide interface emits into air and makes a ballistic transport toward the suspended graphene. A small fraction (>~0.1%) of impinging electrons are captured at the edge of 2D hole system in graphene, demonstrating good transparency to very low energy (<3 eV) electrons. The hole charges induced in the suspended graphene anode have the effect of neutralizing the electron space charge in the void channel. This charge compensation dramatically enhances 2D electron gas emission at cathode to the level far surpassing the Child-Langmuir's space-charge-limited emission.

Nanofluidic preconcentration device in a straight microchannel using ion concentration polarization.

In this paper, we introduce a simple, straight microchannel design for a nanofluidic protein concentration device. Compared with concentration devices previously developed, the anode channel and cathode channel in this new concentration scheme are both integrated into a straight microchannel, with one inlet and one outlet. Most of the functions of a conventional two-channel concentration device can be achieved by this concentration device, and the efficiency of sample accumulation can be controlled by the dimension of the Nafion membrane. Also, the operating mechanism of this device was tested on various material combinations such as PDMS (polydimethyl-siloxane) channel-glass substrate and silicon channel-PDMS substrate. Using a combined PDMS-silicon device which was sealed reversibly without plasma bonding, surface based immunoassay for concentrator-enhanced detection of clinically relevant samples such as C-reactive protein (CRP) was demonstrated. As a result, it was possible to enhance the detection sensitivity of the immunoassay by more than 500 folds compared to the immunoassay without preconcentration process.