Two-Photon Polymerized Shape Memory Microfibers: A New Mechanical Characterization Method in Liquid.

Two-photon polymerization (TPP) has been widely used to create 3D micro- and nanoscale scaffolds for biological and mechanobiological studies, which often require the mechanical characterization of the TPP fabricated structures. To satisfy physiological requirements, most of the mechanical characterizations need to be conducted in liquid. However, previous characterizations of TPP fabricated structures were all conducted in air due to the limitation of conventional micro- and nanoscale mechanical testing methods. In this study, we report a new experimental method for testing the mechanical properties of TPP-printed microfibers in liquid. The experiments show that the mechanical behaviors of the microfibers tested in liquid are significantly different from those tested in air. By controlling the TPP writing parameters, the mechanical properties of the microfibers can be tailored over a wide range to meet a variety of mechanobiology applications. In addition, it is found that, in water, the plasticly deformed microfibers can return to their pre-deformed shape after tensile strain is released. The shape recovery time is dependent on the size of microfibers. The experimental method represents a significant advancement in mechanical testing of TPP fabricated structures and may help release the full potential of TPP fabricated 3D tissue scaffold for mechanobiological studies.

3D Printed Stem-Cell Derived Neural Progenitors Generate Spinal Cord Scaffolds.

A bioengineered spinal cord is fabricated via extrusion-based multi-material 3D bioprinting, in which clusters of induced pluripotent stem cell (iPSC)-derived spinal neuronal progenitor cells (sNPCs) and oligodendrocyte progenitor cells (OPCs) are placed in precise positions within 3D printed biocompatible scaffolds during assembly. The location of a cluster of cells, of a single type or multiple types, is controlled using a point-dispensing printing method with a 200 µm center-to-center spacing within 150 µm wide channels. The bioprinted sNPCs differentiate and extend axons throughout microscale scaffold channels, and the activity of these neuronal networks is confirmed by physiological spontaneous calcium flux studies. Successful bioprinting of OPCs in combination with sNPCs demonstrates a multicellular neural tissue engineering approach, where the ability to direct the patterning and combination of transplanted neuronal and glial cells can be beneficial in rebuilding functional axonal connections across areas of central nervous system (CNS) tissue damage. This platform can be used to prepare novel biomimetic, hydrogel-based scaffolds modeling complex CNS tissue architecture in vitro and harnessed to develop new clinical approaches to treat neurological diseases, including spinal cord injury.

3D Printed Programmable Release Capsules.

The development of methods for achieving precise spatiotemporal control over chemical and biomolecular gradients could enable significant advances in areas such as synthetic tissue engineering, biotic-abiotic interfaces, and bionanotechnology. Living organisms guide tissue development through highly orchestrated gradients of biomolecules that direct cell growth, migration, and differentiation. While numerous methods have been developed to manipulate and implement biomolecular gradients, integrating gradients into multiplexed, three-dimensional (3D) matrices remains a critical challenge. Here we present a method to 3D print stimuli-responsive core/shell capsules for programmable release of multiplexed gradients within hydrogel matrices. These capsules are composed of an aqueous core, which can be formulated to maintain the activity of payload biomolecules, and a poly(lactic-co-glycolic) acid (PLGA, an FDA approved polymer) shell. Importantly, the shell can be loaded with plasmonic gold nanorods (AuNRs), which permits selective rupturing of the capsule when irradiated with a laser wavelength specifically determined by the lengths of the nanorods. This precise control over space, time, and selectivity allows for the ability to pattern 2D and 3D multiplexed arrays of enzyme-loaded capsules along with tunable laser-triggered rupture and release of active enzymes into a hydrogel ambient. The advantages of this 3D printing-based method include (1) highly monodisperse capsules, (2) efficient encapsulation of biomolecular payloads, (3) precise spatial patterning of capsule arrays, (4) "on the fly" programmable reconfiguration of gradients, and (5) versatility for incorporation in hierarchical architectures. Indeed, 3D printing of programmable release capsules may represent a powerful new tool to enable spatiotemporal control over biomolecular gradients.

3D Printed Anatomical Nerve Regeneration Pathways.

An imaging-coupled 3D printing methodology for the design, optimization, and fabrication of a customized nerve repair technology for complex injuries is presented. The custom scaffolds are deterministically fabricated via a microextrusion printing principle which enables the simultaneous incorporation of anatomical geometries, biomimetic physical cues, and spatially controlled biochemical gradients in a one-pot 3D manufacturing approach.

Highly Sensitive Electro-Plasmonic Switches Based on Fivefold Stellate Polyhedral Gold Nanoparticles.

Electron-photon coupling in metal nanostructures has raised a new trend for active plasmonic switch devices in both fundamental understanding and technological applications. However, low sensitivity switches with an on/off ratio less than 5 have restricted applications. In this work, an electrically modulated plasmonic switch based on a surface-enhanced Raman spectroscopy (SERS) system with a single fivefold stellate polyhedral gold nanoparticle (FSPAuNP) is reported. The reversible switch of the SERS signal shows high sensitivity with an on/off ratio larger than 30. Such a high on/off ratio arises primarily from the plasmonic resonance shift of the FSPAuNP with the incident laser due to the altered free electron density on the nanoparticle under an applied electrochemical potential. This highly sensitive electro-plasmonic switch may enable further development of plasmonic devices.

Bioengineered tunable memristor based on protein nanocage.

Bioengineered protein-based nanodevices with tunable and reproducible memristive performance are fabricated by combining the unique high loading capacity of Archaeoglobus fulgidus ferritin with OWL-generated nanogaps. By tuning the iron amount inside ferritin, the ON/OFF ratio of conductance switching can be modulated accordingly. Higher molecular loading exhibits better memristive performance owing to the higher electrochemical activity of the ferric complex core.

Optoelectronics of organic nanofibers formed by co-assembly of porphyrin and perylenediimide.

Organic nanofibers are formed by simple ionic co-assembly of positively charged porphyrin (electron donor) and negatively charged perylenediimide (electron acceptor) derivatives in aqueous solution. Two kinds of electron transfer routes between electron donor and electron acceptor under light excitation in nanofibers are confirmed by DFT calculations and experimental data.

Desmosomal Cadherin Tension Loss in Pemphigus Vulgaris Mediated by the Inhibition of Active RhoA at Cell-Cell Adhesions.

Binding of autoantibodies to keratinocyte surface antigens, primarily desmoglein 3 (Dsg3) of the desmosomal complex, leads to the dissociation of cell-cell adhesion in the blistering disorder pemphigus vulgaris (PV). After the initial disassembly of desmosomes, cell-cell adhesions actively remodel in association with the cytoskeleton and focal adhesions. Growing evidence highlights the role of adhesion mechanics and mechanotransduction at cell-cell adhesions in this remodeling process, as their active participation may direct autoimmune pathogenicity. However, a large part of the biophysical transformations after antibody binding remains underexplored. Specifically, it is unclear how tension in desmosomes and cell-cell adhesions changes in response to antibodies, and how the altered tensional states translate to cellular responses. Here, we showed a tension loss at Dsg3 using fluorescence resonance energy transfer (FRET)-based tension sensors, a tension loss at the entire cell-cell adhesion, and a potentially compensatory increase in junctional traction force at cell-extracellular matrix adhesions after PV antibody binding. Further, our data indicate that this tension loss is mediated by the inhibition of RhoA at cell-cell contacts, and the extent of RhoA inhibition may be crucial in determining the severity of pathogenicity among different PV antibodies. More importantly, this tension loss can be partially restored by altering actomyosin based cell contractility. Collectively, these findings provide previously unattainable details in our understanding of the mechanisms that govern cell-cell interactions under physiological and autoimmune conditions, which may open the window to entirely new therapeutics aimed at restoring physiological balance to tension dynamics that regulates the maintenance of cell-cell adhesion.

Gold nanotip array for ultrasensitive electrochemical sensing and spectroscopic monitoring.

A gold nanotip array platform with a combination of ultrasensitive electrochemical sensing and spectroscopic monitoring capability is reported. Adenosine triphosphate is detected down to 1 pM according to the impedance changes in response to aptamer-specific binding. Furthermore, the local molecular information can be monitored at the individual plasmonic nanotips, and hence provide the capability for a better understanding of complex biological processes.

Spatially Guided Construction of Multilayered Epidermal Models Recapturing Structural Hierarchy and Cell-Cell Junctions.

A current challenge in three-dimensional (3D) bioprinting of skin equivalents is to recreate the distinct basal and suprabasal layers and to promote their direct interactions. Such a structural arrangement is essential to establish 3D stratified epidermis disease models, such as for the autoimmune skin disease pemphigus vulgaris (PV), which targets the cell-cell junctions at the interface of the basal and suprabasal layers. Inspired by epithelial regeneration in wound healing, we develop a method that combines 3D bioprinting and spatially guided self-reorganization of keratinocytes to recapture the fine structural hierarchy that lies in the deep layers of the epidermis. Here, keratinocyte-laden fibrin hydrogels are bioprinted to create geographical cues, guiding dynamic self-reorganization of cells through collective migration, keratinocyte differentiation and vertical expansion. This process results in a region of self-organized multilayers (SOMs) that contain the basal to suprabasal transition, marked by the expressed levels of different types of keratins that indicate differentiation. Finally, we demonstrate the reconstructed skin tissue as an in vitro platform to study the pathogenic effects of PV and observe a significant difference in cell-cell junction dissociation from PV antibodies in different epidermis layers, indicating their applications in the preclinical test of possible therapies.

Electric communication between the inner part of a cell and an electrode: the way to look inside a cell.

A strategy to assemble cells on a solid support surface, here the surface of a gold electrode, is developed by transfecting cells with thiolated DNA molecules which have been immobilized on the gold electrode surface in advance. This strategy to assemble cells can present a general and convenient method for cell assembly on a solid support surface. What is more interesting, since efficient electric communication via the thiolated DNA between the electroactive species inside the cells and the substrate electrode can be achieved, an approach to "look" into the inner part of the cells is proposed. For the test in this work, one drug, kaempferol, and one dye molecule, methylene blue, inside the cells have been detected by the commonly used electrochemical method linear scan voltammetry, and satisfactory results have been obtained.

Conformational transitions of immobilized DNA chains driven by pH with electrochemical output.

A pH-driven DNA sway rod is prepared by immobilizing thiolated DNA, mercaptohexanol, and cysteine on a gold electrode surface. As pH changes around the pI of cysteine, contrary electrostatic effect is produced between the negative DNA and amphoteric cysteine, which actuates reversible conformational transitions, such as sway of the DNA molecules, rodlike chain-to-globule, and so forth. The nanoscale motion can be detected by commonly used electrochemical technique and reversible electrochemical signal may be observed.

3D Bioprinted In Vitro Metastatic Models via Reconstruction of Tumor Microenvironments.

The development of 3D in vitro models capable of recapitulating native tumor microenvironments could improve the translatability of potential anticancer drugs and treatments. Here, 3D bioprinting techniques are used to build tumor constructs via precise placement of living cells, functional biomaterials, and programmable release capsules. This enables the spatiotemporal control of signaling molecular gradients, thereby dynamically modulating cellular behaviors at a local level. Vascularized tumor models are created to mimic key steps of cancer dissemination (invasion, intravasation, and angiogenesis), based on guided migration of tumor cells and endothelial cells in the context of stromal cells and growth factors. The utility of the metastatic models for drug screening is demonstrated by evaluating the anticancer efficacy of immunotoxins. These 3D vascularized tumor tissues provide a proof-of-concept platform to i) fundamentally explore the molecular mechanisms of tumor progression and metastasis, and ii) preclinically identify therapeutic agents and screen anticancer drugs.

Electrochemical approach to detect apoptosis.

This paper reports an electrochemical approach for detection of apoptosis. Here we prepare a gold electrode modified with a helix peptide ferrocene (Fc)-GDGDEVDGC. Fc is used as an electroactive reporter and the peptide as a recognition and cleavage site of caspase-3, which is a special proteinase to apoptosis. Results show that this method may sensitively and specifically detect apoptotic cells with signal decline of 85%. This approach is different from the previous methods for apoptosis detection, because it does not need any fluorescent materials, expensive biological instruments, or complicated procedures.

The electron transfer reactivity of kaempferol and its interaction with amino acid residues.

In this work, the electron transfer reactivity of kaempferol was studied and the interaction in vivo between kaempferol and protein was simulated. Dimethylsulfoxide (DMSO) as an aprotic solvent was employed to simulate the specific environment. Various residues of amino acids were used to study the effect of the amino acids in the active site of protein on the electron transfer reactivity of kaempferol. Experimental results revealed that the redox activity of kaempferol was different in aprotic medium DMSO from that in water, and a new redox process was further found. Of all the residues tested, nitrogenous nucleophile, for example, imidazole, was observed to be able to facilitate the electron transfer of kaempferol, and the mechanism was also proposed. This work might provide a simple model to study the electron transfer reactivity of some small active organic molecules, especially medicines, in specific environment, which might approach a more accurate understanding of the activity of some medicines in vivo.

Apoferritin as a bionanomaterial to facilitate the electron transfer reactivity of hemoglobin and the catalytic activity towards hydrogen peroxide.

In this report, apoferritin as a stable bionanomaterial was modified with hemoglobin on pyrolytic graphite electrode. Rapid electron transfer reactions of hemoglobin were achieved with the help of apoferritin in a large pH range. Moreover, hemoglobin as an enzyme exhibits fine electrocatalytic activity towards the reaction of hydrogen peroxide, and a wide concentration range of linear relationship between the reduction peak current and the concentration of hydrogen peroxide has been obtained with a higher upper detection limit, which may be further developed for a hydrogen peroxide biosensor. Therefore, a new property of apoferritin is explored, in which apoferritin works as a bionanomaterial to be an accelerant of the electron transfer of Hb and a stabilizer to retain the catalytic ability of the protein under mal-condition.

3D Printed Polymer Photodetectors.

Extrusion-based 3D printing, an emerging technology, has been previously used in the comprehensive fabrication of light-emitting diodes using various functional inks, without cleanrooms or conventional microfabrication techniques. Here, polymer-based photodetectors exhibiting high performance are fully 3D printed and thoroughly characterized. A semiconducting polymer ink is printed and optimized for the active layer of the photodetector, achieving an external quantum efficiency of 25.3%, which is comparable to that of microfabricated counterparts and yet created solely via a one-pot custom built 3D-printing tool housed under ambient conditions. The devices are integrated into image sensing arrays with high sensitivity and wide field of view, by 3D printing interconnected photodetectors directly on flexible substrates and hemispherical surfaces. This approach is further extended to create integrated multifunctional devices consisting of optically coupled photodetectors and light-emitting diodes, demonstrating for the first time the multifunctional integration of multiple semiconducting device types which are fully 3D printed on a single platform. The 3D-printed optoelectronic devices are made without conventional microfabrication facilities, allowing for flexibility in the design and manufacturing of next-generation wearable and 3D-structured optoelectronics, and validating the potential of 3D printing to achieve high-performance integrated active electronic materials and devices.

3D Printed Organ Models with Physical Properties of Tissue and Integrated Sensors.

The design and development of novel methodologies and customized materials to fabricate patient-specific 3D printed organ models with integrated sensing capabilities could yield advances in smart surgical aids for preoperative planning and rehearsal. Here, we demonstrate 3D printed prostate models with physical properties of tissue and integrated soft electronic sensors using custom-formulated polymeric inks. The models show high quantitative fidelity in static and dynamic mechanical properties, optical characteristics, and anatomical geometries to patient tissues and organs. The models offer tissue-mimicking tactile sensation and behavior and thus can be used for the prediction of organ physical behavior under deformation. The prediction results show good agreement with values obtained from simulations. The models also allow the application of surgical and diagnostic tools to their surface and inner channels. Finally, via the conformal integration of 3D printed soft electronic sensors, pressure applied to the models with surgical tools can be quantitatively measured.