Multiscale embedded printing of engineered human tissue and organ equivalents.

Creating tissue and organ equivalents with intricate architectures and multiscale functional feature sizes is the first step toward the reconstruction of transplantable human tissues and organs. Existing embedded ink writing approaches are limited by achievable feature sizes ranging from hundreds of microns to tens of millimeters, which hinders their ability to accurately duplicate structures found in various human tissues and organs. In this study, a multiscale embedded printing (MSEP) strategy is developed, in which a stimuli-responsive yield-stress fluid is applied to facilitate the printing process. A dynamic layer height control method is developed to print the cornea with a smooth surface on the order of microns, which can effectively overcome the layered morphology in conventional extrusion-based three-dimensional bioprinting methods. Since the support bath is sensitive to temperature change, it can be easily removed after printing by tuning the ambient temperature, which facilitates the fabrication of human eyeballs with optic nerves and aortic heart valves with overhanging leaflets on the order of a few millimeters. The thermosensitivity of the support bath also enables the reconstruction of the full-scale human heart on the order of tens of centimeters by on-demand adding support bath materials during printing. The proposed MSEP demonstrates broader printable functional feature sizes ranging from microns to centimeters, providing a viable and reliable technical solution for tissue and organ printing in the future.

Scalable nanomanufacturing of holey graphene via chemical etching: an investigation into process mechanisms.

Graphene with in-plane nanoholes, named holey graphene, shows great potential in electrochemical applications due to its fast mass transport and improved electrochemical activity. Scalable nanomanufacturing of holey graphene is generally based on chemical etching using hydrogen peroxide to form through-the-thickness nanoholes on the basal plane of graphene. In this study, we probe into the fundamental mechanisms of nanohole formation under peroxide etching via an integrated experimental and computational effort. The research results show that the growth of nanoholes during the etching of graphene oxide is achieved by a three-stage reduction-oxidation-reduction procedure. First, it is demonstrated that vacancy defects are formed via a partial reduction-based pretreatment. Second, hydrogen peroxide reacts preferentially with the edge-sites of defect areas on graphene oxide sheets, leading to the formation of various oxygen-containing functional groups. Third, the carbon atoms around the defects are removed along with the neighboring carbon atoms via reduction. By advancing the understanding of process mechanisms, we further demonstrate an improved nanomanufacturing strategy, in which graphene oxide with a high density of defects is introduced for peroxide etching, leading to enhanced nanohole formation.

Bioinspired Manufacturing of Aerogels with Precisely Manipulated Surface Microstructure through Controlled Local Temperature Gradients.

The freeze casting process has been widely used for fabricating aerogels due to its versatile and environmentally friendly nature. This process offers a variety of tools to tailor the entire micropore morphology of the final product in a monolithic fashion through manipulation of the freezing kinetics and precursor suspension chemistry. However, aerogels with nonmonolithic micropore morphologies, having pores of various sizes located in certain regions of the aerogels, are highly desired by certain applications such as controlled drug-delivery, bone tissue engineering, extracellular simulation, selective liquid sorption, immobilized catalysts, and separators. Furthermore, aerogels composed of micropores with predesigned size, shape, and location can open up a new paradigm in aerogel design and lead to new applications. In this study, a general manufacturing approach is developed to control the size, shape, and location of the pores on the aerogel surface by applying a precise control on the local thermal conductivity of the substrate used in a unidirectional freeze casting process. With our method, we created patterned low and high thermal conductivity regions on the substrate by depositing patterned photoresist polymer features. The photoresist polymer has a much lower thermal conductivity, which resulted in lower cooling/freezing rates compared to the silicon substrate. Patterned thermal conductivity created a designed temperature profile yielding to local regions with faster and slower freezing rates. Essentially, we fabricated aerogels whose micropore morphology on their surface was a replica of the patterned substrates in terms of size and location of the micropores. Using the same substrates, we further showed the possibility of 3D printed aerogels with precisely controlled, surface micropore morphologies. To the best of our knowledge, this is the first study that reports aerogels having micropore morphologies (e.g., size, shape, and location) that are precisely controlled through locally controlled thermal conductivity of the substrates.

Laser shock-based platform for controllable forming of nanowires.

One-dimensional nanomaterials have attracted a great deal of research interest in the past few decades due to their unique mechanical, electrical, and optical properties. Changing the shape of nanowires (NWs) is both challenging and crucial to change the property and open wide functions of NWs, such as strain engineering, electronic transport, mechanical properties, band structure, and quantum properties, etc. Here we report a scalable strategy to conduct cutting, bending, and periodic straining of NWs by making use of laser shock pressure. Three-dimensional shaping of silver NWs is demonstrated, during which the Ag NWs exhibit very good ductility (strain-to-failure reaches 110%). Meanwhile, the high electrical conductivity of Ag NWs could retain well under controlled laser shock pressure. The microstructure observation indicates that the main deformation mechanism in Ag NWs under dynamic loading is formation of twinning and stacking fault, while dislocation motion and pile-up is less obvious. This method could be applied to semiconductor NWs as well.

Direction-tunable nanotwins in copper nanowires by laser-assisted electrochemical deposition.

Nanotwins can improve mechanical strength and maintain high electrical conductivity in metallic nanowires. We demonstrated a method of pulsed-laser-assisted electrodeposition, which could form dense nanotwins with tunable directions in copper nanowires of uniform sizes. Transmission electron microscopy characterization showed with a growth potential of -0:2 V, nanotwins tend to align along the longitudinal direction of the nanowires, whereas at a larger potential of -0:8 V, nanotwins of {111}g/<112> type perpendicular to the longitudinal direction of the wire were formed. The two types of nanotwins were investigated by comparing the microstructures under different electrochemical conditions and laser irradiation energies. Two different mechanisms are proposed­annealing twins and growth twins.

Aligned electrospun ZnO nanofibers for simple and sensitive ultraviolet nanosensors.

The current of uni-axially aligned electrospun ZnO nanofibers is modulated reversibly under UV irradiation, with the sensitivity of the UV nanosensors depending on the surface coating of the nanofibers, due to the effect on the photo-generated current.

Preparation, characterization, and encapsulation/release studies of a composite nanofiber mat electrospun from an emulsion containing poly (lactic-co-glycolic acid).

The aim of this study was to investigate the preparation, characterization, and encapsulation/release performance of an electrospun composite nanofiber mat. The hypothesis was that the composite nanofiber mat with nano-scaled drug particles impregnated in biocompatible and biodegradable polymer nanofibers can serve as an innovative type of tissue engineering scaffold with desired and controllable drug encapsulation/release properties. To test the hypothesis, the composite nanofiber mat electrospun from an emulsion consisting of poly (lactic-co-glycolic acid) (PLGA) Rhodamine B (a model compound to simulate drugs), sorbitan monooleate (Span-80, a non-ionic emulsifier/surfactant that is presumably non-toxic/safe for cell-growth), chloroform, DMF, and distilled water was prepared and characterized; and the Rhodamine B encapsulation/release profile in phosphate buffered saline (pH = 7.4) was recorded and analyzed. For comparison purposes, two additional nanofiber mats electrospun from (1) a solution containing PLGA and Rhodamine B, and (2) a solution containing PLGA, Rhodamine B, and Span-80 were also prepared and assessed as the control samples. The results indicated that the composite nanofiber mat electrospun from the emulsion had the most desired and controllable Rhodamine B encapsulation/release profile and the excellent morphological sustainability; thus, it could be utilized as both a drug encapsulation/release vehicle and a tissue engineering scaffold.

Fabrication and evaluation of Bis-GMA/TEGDMA dental resins/composites containing nano fibrillar silicate.

OBJECTIVE: To investigate the reinforcement of Bis-GMA/TEGDMA dental resins (without conventional glass filler) and composites (with conventional glass filler) with various mass fractions of nano fibrillar silicate (FS). METHODS: Three dispersion methods were studied to separate the silanized FS as nano-scaled single crystals and uniformly distribute them into dental matrices. The photo-curing behaviors of the Bis-GMA/TEGDMA/FS resins were monitored in situ by RT-NIR to study the photopolymerization rate and the vinyl double bond conversion. Mechanical properties (flexural strength, elastic modulus and work-of-fracture) of the nano FS reinforced resins/composites were tested, and analysis of variance (ANOVA) was used for the statistical analysis of the acquired data. The morphology of nano FS and the representative fracture surfaces of its reinforced resins/composites were examined by SEM/TEM. RESULTS: Impregnation of small mass fractions (1% and 2.5%) of nano FS into Bis-GMA/TEGDMA (50/50 mass ratio) dental resins/composites improved the mechanical properties substantially. Larger mass fraction of impregnation (7.5%), however, did not further improve the mechanical properties (one way ANOVA, P>0.05) and may even reduce the mechanical properties. The high degree of separation and uniform distribution of nano FS into dental resins/composites was a challenge. Impregnation of nano FS into dental resins/composites could result in two opposite effects: a reinforcing effect due to the highly separated and uniformly distributed nano FS single crystals, or a weakening effect due to the formation of FS agglomerates/particles. SIGNIFICANCE: Uniform distribution of highly separated nano FS single crystals into dental resins/composites could significantly improve the mechanical properties of the resins/composites.

Bis-GMA/TEGDMA Dental Composites Reinforced with Electrospun Nylon 6 Nanocomposite Nanofibers Containing Highly Aligned Fibrillar Silicate Single Crystals.

The objective of this research was to study the reinforcement of electrospun nylon 6/fibrillar silicate nanocomposite nanofibers on Bis-GMA/TEGDMA dental composites. The hypothesis was that the uniform distribution of nano-scaled and highly aligned fibrillar silicate single crystals into electrospun nylon 6 nanofibers would improve the mechanical properties of the resulting nanocomposite nanofibers, and would lead to the effective reinforcement of dental composites. The nylon 6/fibrillar silicate nanocomposite nanofibers were crystalline, structurally oriented and had an average diameter of approximately 250 nm. To relatively well distribute nanofibers in dental composites, the nanofiber containing composite powders with a particle structure similar to that in interpenetration networks were prepared first, and then used to make the dental composites. The results indicated that small mass fractions (1 % and 2 %) of nanofiber impregnation improved the mechanical properties substantially, while larger mass factions (4 % and 8 %) of nanofiber impregnation resulted in less desired mechanical properties.