The remarkable progress in additive manufacturing has promoted the design of architected materials with mechanical properties that go beyond those of conventional solids. Their realization, however, leads to architectures with process-induced defects that can jeopardize mechanical and functional performance. In this work, we investigate experimentally and numerically as-manufactured defects in Ti–6Al–4V octet truss lattice materials fabricated with selective laser melting. Four sets of as-manufactured defects, including surface, microstructural, morphological, and material property imperfections, are characterized experimentally at given locations and orientations. Within the characterized defects, material property and morphological defects are quantified statistically using a combination of atomic force microscopy and micro–computed tomography to generate representative models that incorporate individual defects and their combination. The models are used to assess the sensitivity to as-manufactured defects. Then, the study is expanded by tuning defects amplitude to elucidate the role of the magnitude of as-designed defects on the mechanical properties of the lattice material.

Prevascularized medical devices can improve cell therapy. Such devices may replace whole organ transplantation with hosting only the necessary therapeutic cells. We have developed a noninvasive optical technology to study the vascularization into such medical devices. In our technique, oxygen partial pressure within a device is monitored by Oxygen Sensitive Tubes (OSTs), comprising oxygen permeable silicone tubing with inner luminal surfaces coated by an oxygen-sensitive porphyrin dye. OSTs were placed within a PDMS device and transplanted into the subcutaneous space of athymic nude mice. An optical probe placed over the skin excites the OSTs with a pulse of light and detects the luminescent lifetime of emitted light, which is uniquely related to oxygen partial pressure. Furthermore, we developed a Dynamic Inhalation Gas Test (DIGT) to determine the oxygen transport rate between the microvasculature and the device. DIGT works by monitoring oxygen partial pressure in a device following a step change in inhaled-gas oxygen content. We report DIGT oxygen dynamics measured intermittently over eight weeks. Our study shows DIGT dynamics are unique to each implant, supporting the important role of the host tissue response in the availability of oxygen over time.

Triply Periodic Minimal Surfaces (TPMS) possess locally minimized surface area under the constraint of periodic boundary conditions. Different families of surfaces were obtained with different topologies satisfying such conditions. Examples of such families include Primitive (P), Gyroid (G) and Diamond (D) surfaces. From a purely mathematical subject, TPMS have been recently found in materials science as optimal geometries for structural applications. Proposed by Mackay and Terrones in 1991, schwarzites are 3D crystalline porous carbon nanocrystals exhibiting a TPMS-like surface topology. Although their complex topology poses serious limitations on their synthesis with conventional nanoscale fabrication methods, such as Chemical Vapour Deposition (CVD), schwarzites can be fabricated by Additive Manufacturing (AM) techniques, such as 3D Printing. In this work, we used an optimized atomic model of a schwarzite structure from the D family (D8bal) to generate a surface mesh that was subsequently used for 3D-printing through Fused Deposition Modelling (FDM). This D schwarzite was 3D-printed with thermoplastic PolyLactic Acid (PLA) polymer filaments. Mechanical properties under uniaxial compression were investigated for both the atomic model and the 3D-printed one. Fully atomistic Molecular Dynamics (MD) simulations were also carried out to investigate the uniaxial compression behavior of the D8bal atomic model. Mechanical testings were performed on the 3D-printed schwarzite where the deformation mechanisms were found to be similar to those observed in MD simulations. These results are suggestive of a scale-independent mechanical behavior that is dominated by structural topology.

Scaffolds based on two different geometries were constructed by additive manufacturing: one based on a triply periodic minimal surface, the Schwarz D surface, and the other based on a rectangular geometry with orthogonal through-holes. For construction of the scaffolds, two different materials were used: polylactic acid (PLA) in filament form and alumina in printable paste form. The structure of the resulting scaffolds was characterized via X-ray diffraction and scanning electron microscopy, and cell proliferation was assessed for each geometry and material, using fluorescence microscopy and DNA quantification via NanoDrop. Additive manufacturing allowed us to obtain scaffolds with the assessed materials while guaranteeing the interconnectivity of the pores in each one. The curved surfaces constructed with PLA were more favorable for cell attachment and proliferation of the CHO-K1 cell line.

Bamboo is a natural composite and one of the most efficient structures in nature because of the relationship of mechanical properties with its microstructural features. This research presents the 3D characterization of the reinforcement bundles of a branching nodal region of bamboo, through high-resolution X-ray microtomography (µCT). µCT was used to characterize a sample regarding the volume, relative density, and porosity of parenchyma and sclerenchyma tissues, and the resulting data were used to estimate their constitutive properties. A nonlinear finite element analysis (FEA) was performed based on a discretized model of the µCT to the limiting compressive load. Secondary bundles presented an interweaved arrangement into the primary vascular elements that distribute axial compressive stresses into new branches. Our findings suggest that the foam-like behavior of the parenchyma, the sclerenchyma thickening above the nodal zone, and the nodal vascular branching are ways for bamboo to protect important tissues from mechanical stress by allocating axial loads. In addition, such mechanism could be applied in the design of biomimetic structures with selective load-bearing capabilities.

3D printing has been shown to be a robust and inexpensive manufacturing tool for a range of applications within biomedical science. Here we report the design and fabrication of a 3D printer-enabled microfluidic device used to generate cell-laden hydrogel microspheres of tunable sizes. An inverse mold was printed using a 3D printer, and replica molding was used to fabricate a PDMS microfluidic device. Intersecting channel geometry was used to generate perfluorodecalin oil-coated gelatin methacrylate (GelMA) microspheres of varying sizes (35–250 μm diameters). Process parameters such as viscosity profile and UV cross-linking times were determined for a range of GelMA concentrations (7–15% w/v). Empirical relationships between flow rates of GelMA and oil phases, microspheres size, and associated swelling properties were determined. For cell experiments, GelMA was mixed with human osteosarcoma Saos-2 cells, to generate cell-laden GelMA microspheres with high long-term viability. This simple, inexpensive method does not require the use of traditional cleanroom facilities and when combined with the appropriate flow setup is robust enough to yield tunable cell-laden hydrogel microspheres for potential tissue engineering applications.

3D microarchitected metamaterials exhibit unique, desirable properties influenced by their small length scales and architected layout, unachievable by their solid counterparts and random cellular configurations. However, few of them can be used in high-temperature applications, which could benefit significantly from their ultra-lightweight, ultrastiff properties. Existing high-temperature ceramic materials are often heavy and difficult to process into complex, microscale features. Inspired by this limitation, we fabricated polymer-derived ceramic metamaterials with controlled solid strut size varying from 10-µm scale to a few millimeters with relative densities ranging from as low as 1 to 22%. We found that these high-temperature architected ceramics of identical 3D topologies exhibit size-dependent strength influenced by both strut diameter and strut length. Weibull theory is utilized to map this dependency with varying single strut volumes. These observations demonstrate the structural benefits of increasing feature resolution in additive manufacturing of ceramic materials. Through capitalizing upon the reduction of unit strut volumes within the architecture, high-temperature ceramics could achieve high specific strength with only fraction of the weight of their solid counterparts.

Direct ink writing of silicone elastomers enables printing with precise control of porosity and mechanical properties of ordered cellular solids, suitable for shock absorption and stress mitigation applications. With the ability to manipulate structure and feedstock stiffness, the design space becomes challenging to parse to obtain a solution producing a desired mechanical response. Here, we derive an analytical design approach for a specific architecture. Results from finite element simulations and quasi-static mechanical tests of two different parallel strand architectures were analyzed to understand the structure-property relationships under uniaxial compression. Combining effective stiffness-density scaling with least squares optimization of the stress responses yielded general response curves parameterized by resin modulus and strand spacing. An analytical expression of these curves serves as a reduced order model, which, when optimized, provides a rapid design capability for filament-based 3D printed structures. As a demonstration, the optimal design of a face-centered tetragonal architecture is computed that satisfies prescribed minimum and maximum load constraints.

A kinetic model for ECM decellularization with Trypsin and Deoxycholic Acid as reactants in a batch system has been developed. The decellularization mechanism has been analysed by solving a series of ordinary differential equations relating heterogeneous reaction kinetics at the solid/liquid interface to mass transfer of reactant and products. In order to remove the Deoxyribonucleic acid (DNA) of porcine, special emphasis has been given to the surface area for regulating the depth and amount of the penetration of the reagent, the numerical analysis thereof, and the corresponding experiment were carried out. The effect of chemical reaction order, rate constants and mass transfer coefficients on the overall decellularization rate has been analysed and discussed.

Two α-alumina + YSZ samples were prepared by sintering for 3 h one at 1500 °C and the other at 1700 °C. The samples were then converted to Na-β″-alumina + YSZ by vapor phase conversion. Characterization techniques such as X-ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopy in addition to dimensional geometrical changes reveal the evolution of slight anisotropy in these samples during conversion. This results in an electrical conductivity anisotropy factor of about 5.5 and 1.8 for samples sintered at 1500 °C and 1700 °C, respectively. In all samples, the higher ionic conductivity was measured across the sample thickness as opposed to parallel to the disc faces. The ionic conductivity measurements show the conductivity of about 0.15 S/cm and 0.07 S/cm at 300 °C for samples sintered at 1500 °C and 1700 °C, respectively. The larger anisotropy in samples sintered at 1500 °C is explained by the higher aspect ratio of grains in this sample and by different Na concentrations.

New closed-form analytical equations for volume fractions and surface-area-to-volume ratios for architected lattice cellular materials are derived. Prior approximate equations which erroneously over count overlapping volumes and the associated surface area are commonly used in the literature. These equations are found to have up to 184% error for volume fraction calculations for hollow lattices and 211% error for surface-area-to-volume ratio calculations, thus necessitating computational methods to arrive at accurate geometric properties for cellular lattice materials. This work derives new equations which are accurate to better than 1% for both volume fraction and surface-area-to-volume ratio as compared to the computational models. These new equations for cellular lattice materials are applicable to both pyramidal and tetrahedral unit cells as well as to both hollow and solid lattice members. By eliminating the need for numerical models to compute accurate volume fractions and surface-area-to-volume ratios of architected cellular materials, these new analytical equations will enable accurate yet computationally efficient optimization of the physical properties of architected cellular materials.

Nanoporous metallic foams with high surface area and novel functional behavior are positioned to stimulate new multifunctional and metamaterial applications. However, there are fundamental challenges in achieving uniform nanopores and tailorable morphology. Emerging templating methods offer a wide range of applicable metallic species while enhancing control of pore morphology, uniformity, and interconnectivity. Here, a critical review of nanoporous metal fabrication is presented, with focus on templating methods utilizing nanoporous polymeric templates. Metals are introduced into percolative nanochannels of sacrificial templates by deposition, and subsequent removal of templates yields ordered nanoporous metals. We introduce approaches for preparing nanoporous templates, including utilizing block copolymer self-assembly that yields periodic gyroid networks. While metallization of templates by electrodeposition has been demonstrated, electroless deposition permits uniform deposition by many metallic species and infiltration of narrow pores. Examples of nanoporous metals with uniform pore sizes below 50 nm fabricated by templating methods are examined.

Inspired by sea sponges, porous Al2O3/starch composite sponges were designed and fabricated as a new controlled release system enabling mechano-triggered logic delivery of molecules. Results of material characterization indicate that the all the composite sponges had a high macro-porosity of >80%, and dehydrated sponges revealed favorable pore structure for drug loading and retaining. The composite sponges have moisture-dependent mechanical properties and samples with appropriate moisture contents revealed high resilience and mechanical robustness under cyclic deformation. Based on the unique mechanical properties of the composite sponge, mechanically modulated, nano-gram precision delivery of model molecules was achieved in an AND logic manner gated by both moisture and compressive strain.

Extrusion-based bioprinting (EBP) is limited by loss of pattern fidelity when printing on wet substrates. This can be overcome using aqueous two-phase systems (ATPSs) as novel ink formulations for EBP. In this study, optimal concentrations of ATPS “inks” were determined and used to pattern human epidermal keratinocyte (HEK001) colonies on a wet substrate for promoting epidermal growth. Four equilibrated and non-equilibrated ATPS formulations were tested for stable ATPS formation and uniform cell patterning. We identified an optimal formulation that produced stable droplets on a standard tissue culture plate coated with PEG. This process was also tested on an acellular dermal matrix (DermGENTM ) to evaluate biopattern fidelity on a tissue matrix. Cell proliferation and formation of adherens junctions between cells were analyzed by immunocytochemistry. Non-equilibrated 5.0% PEG and 5.0% DEX solutions formed tighter colonies than equilibrated solutions containing identical total polymer concentrations. Cells patterned in colonies displayed higher cell viability and increased formation of E-cadherin junctions compared to non-patterned cells. Finally, when the cells were patterned on DermGENTM , discrete cell colonies were observed. This suggests that ATPS EBP holds promise for biopatterning epidermal keratinocyte cells to improve skin tissue engineering.

The three-dimensional (3D) culture of neural cells in extracellular matrix (ECM) gels holds promise for modeling neurodegenerative diseases and pre-clinical evaluation of novel therapeutics. However, most current strategies for fabricating 3D neural cell cultures are not well suited to automated production and analysis. Here, we present a facile, replicable, 3D cell culture system that is compatible with standard laboratory equipment and high-throughput workflows. This system uses aqueous two-phase systems (ATPSs) to confine small volumes (5 and 10 μl) of a commonly used ECM hydrogel (Matrigel) into thin, discrete layers, enabling highly-uniform production of 3D neural cell cultures in a 96-well plate format. These 3D neural cell cultures can be readily analyzed by epifluorescence microscopy and microplate reader. Our preliminary results show that many common polymers used in ATPSs interfere with Matrigel gelation and instead form fibrous precipitates. However, 0.5% hydroxypropyl methylcellulose (HPMC) and 2.5% dextran 10 kDa (D10) were observed to retain Matrigel integrity and had minimal impact on cell viability. This novel system offers a promising yet accessible platform for high-throughput fabrication of 3D neural tissues using readily available and cost-effective materials.

Liposome reinforced by adding cholesterol was synthesized using the dipalmitoyl-phosphatidylcholine (DPPC). Phase stability of the phospholipid bilayers was examined by FT-IR spectroscopy. The reinforced liposomes filled with ultrapure water or physiological saline were observed by the conventional TEM equipped with a mass spectrometer. It was confirmed that the liposomes filled with water or saline solution were stable in the vacuum at room temperature. However, during electron irradiation, water molecules escaped gradually, and a single crystal of rock salt precipitated in the liposome.

Chlorella is a green, photosynthetic single-celled genus of algae. It can be 3D printed as a suspension in sodium alginate and gelled with calcium solutions. We have made “log pile” structures with channels between the gel lines to allow easy transport of nutrients and products. Under white light and immersed in solutions of bicarbonate and phosphate and urea “plant food” the algae multiply with the gel and produce oxygen at a rate comparable to that reported for suspensions of Chlorella. The system is stable for one or two weeks at least. In principle this can be extended to other plant tissues but there are concerns relating to bacterial and fungal infection and toxicity of the gel components. In addition a tougher gel is needed if this was to be converted to a practical bioreactor system.

Mimicking the resilience offered by hard biomaterials, such as mollusk shells and beaks, has been among the most sought-after engineering pursuits. Technological advances in fabrication methods have provided pathways for using different materials to create architected structural metamaterials with hierarchy and length scales similar to those found in nature. Inspiration from nature has led to the creation of structural metamaterials, or nanolattices, with enhanced mechanical properties caused by hierarchical ordering at various length scales, ranging from angstroms and nanometers for the material microstructure to microns and millimeters for the macroscale architecture. The inherent periodicity and high surface-area-to-volume ratios of nanolattices make them useful for a variety of applications, including photonics, photovoltaics, phononics, and electrochemical systems. This article provides an overview of current three-dimensional architected metamaterials, including their fabrication methods, properties, applications, and limitations.

This work presents a strategy to perform ex-vivo cell-drug interaction studies through electro-kinetically assisted drug delivery system. Here, we present a novel technique to electro-kinetically control the vesicles carrying drug to deliver to pre-determined locations. In order to achieve efficient targeted drug delivery, effect of electrokinetic attractive and repulsive forces on liposomes and target cells were studied and presented. The device consists of a simple bifurcated microfluidic chamber and microelectrodes that assist in carrying the liposomes to the target location. To test the prototype, fully grown human embryonic kidney cell lines (HEK 293) and trypsin as test drug was used. External electrical signal with voltages less than of 5 V peak-to-peak (Vpp) for cells and 10 Vpp for liposomes were applied over a spectrum of frequencies to study the effect of electrokinetic forces. Through this label-free method, we were able to study loading and unloading efficiency of the drug without altering the natural properties of the liposomes and target cells. In this study, characterization and performance comparison studies for two different types of materials (HEK cells and liposomes) were performed. We were able to achieve an overall efficiency of approximately 85%. Various electrical parameters such as applied voltage, frequency and conductivity were manipulated to study the drug-cell interaction. This electrokinetic based method will be highly applicable in understanding the effect on drugs on cell populations ex vivo.

Biological cells are major building blocks of tissues and organs of living organisms. These cells are also being used as biomarkers for diagnosis and sources for regenerative medicine. To better understand and even regulate diverse activities of cells, materials capable of interacting with cells have been designed by integrating various material chemistry, characterization, and processing techniques. These materials are often integrated with various nano- and microscale engineering devices. In this article, we provide an overview of materials for biological modulation, sensing, and imaging and also discuss opportunities for the future development of multifunctional materials for sensing and therapies.