Sacrificial Scaffold Research Articles

Direct Laser Writing Photonic Crystal Hydrogels with a Supramolecular Sacrificial Scaffold.

Photonic crystal hydrogels (PCHs), with smart stimulus-responsive abilities, have been widely exploited as colorimetric sensors for years. However, the current fabrication technologies are mostly applicable to produce PCHs with simple geometries at the sub-millimeter scale, limiting the introduction of structural design into PCH sensors as well as the accompanied advanced applications. This paper reports the microfabrication of three-dimensional (3D) PCHs with the help of supramolecular agarose PCH as a sacrificial scaffold by two-photon lithography (TPL). The supramolecular PCHs, formulated with SiO2 colloidal nanoparticles and agarose aqueous solutions, show bright structural color and are degradable upon short-time dimethyl sulfoxide treatment. Leveraging the supramolecular PCH as a sacrificial scaffold, PCHs with precise 3D geometries can be fabricated in an economical and efficient way. This work demonstrates the application of such a strategy in the creation of structural-designed PCH mechanical microsensors that have not been explored before.

Sacrificial scaffold-assisted direct ink writing of engineered aortic valve prostheses

Heart valve disease has become a serious global health problem, which calls for numerous implantable prosthetic valves to fulfill the broader needs of patients. Although current three-dimensional (3D) bioprinting approaches can be used to manufacture customized valve prostheses, they still have some complications, such as limited biocompatibility, constrained structural complexity, and difficulty to make heterogeneous constructs, to name a few. To overcome these challenges, a sacrificial scaffold-assisted direct ink writing approach has been explored and proposed in this work, in which a sacrificial scaffold is printed to temporarily support sinus wall and overhanging leaflets of an aortic valve prosthesis that can be removed easily and mildly without causing any potential damages to the valve prosthesis. The bioinks, composed of alginate, gelatin, and nanoclay, used to print heterogenous valve prostheses have been designed in terms of rheological/mechanical properties and filament formability. The sacrificial ink made from Pluronic F127 has been developed by evaluating rheological behavior and gel temperature. After investigating the effects of operating conditions, complex 3D structures and homogenous/heterogenous aortic valve prostheses have been successfully printed. Lastly, numerical simulation and cycling experiments have been performed to validate the function of the printed valve prostheses as one-way valves.

Engineering 3D‐Architected Gyroid MXene Scaffolds for Ultrasensitive Micromechanical Sensing

A novel piezoresistive sensor based on ultralight 3D MXene scaffold (3DMS) is developed by a facile and architecturally versatile method using additively manufactured, polymer‐based gyroidal triply periodic minimal surface (TPMS) as the initial sacrificial scaffold. A neat MXene scaffold with the gyroidal TPMS structure is prepared by dip coating MXene sheets onto 3D‐printed polymeric Gyroid lattices, followed by thermal treatment. 3DMS exhibits a high compressive strength of 27.18 kPa and a thermal conductivity of 0.3454 W m−1 K−1. The thermal conductivity of the MXene layer in the 3D structure can reach up to 23.88 Wm−1 K−1, which demonstrates that 3DMS has high versatility for all‐in‐one applications, such as thermal insulation, sensors, and energy storage. The 3DMS developed herein combines the high electrical conductivity of MXene (Ti3C2Tx), intricacy of the gyroidal structure, as well as high porosity, offering a promising platform for high‐performance sensors. In addition, the piezoresistive sensor shows extremely high sensitivity (134.48 kPa−1), good response time (477 ms) and recovery time (402 ms), and improvable durability, validating its potentials for measuring pressure distribution in various engineering devices.

Development of Cell-Derived Matrices for Three-Dimensional In Vitro Cancer Cell Models.

Most morphogenetic and pathological processes are driven by cells responding to the surrounding matrix, such as its composition, architecture, and mechanical properties. Despite increasing evidence for the role of extracellular matrix (ECM) in tissue and disease development, many in vitro substitutes still fail to effectively mimic the native microenvironment. We established a novel method to produce macroscale (>1 cm) mesenchymal cell-derived matrices (CDMs) aimed to mimic the fibrotic tumor microenvironment surrounding epithelial cancer cells. CDMs are produced by human adipose mesenchymal stem cells cultured in sacrificial 3D scaffold templates of fibronectin-coated poly-lactic acid microcarriers (MCs) in the presence of macromolecular crowders. We showed that decellularized CDMs closely mimic the fibrillar protein composition, architecture, and mechanical properties of human fibrotic ECM from cancer masses. CDMs had highly reproducible composition made of collagen types I and III and fibronectin ECM with tunable mechanical properties. Moreover, decellularized and MC-free CDMs were successfully repopulated with cancer cells throughout their 3D structure, and following chemotherapeutic treatment, cancer cells showed greater doxorubicin resistance compared to 3D culture in collagen hydrogels. Collectively, these results support the use of CDMs as a reproducible and tunable tool for developing 3D in vitro cancer models.

Scalable synthesis, characterization and testing of 3D architected gyroid graphene lattices from additively manufactured templates

We have developed a novel, facile and architecturally versatile fabrication method for specially designed cellular graphene lattices using additively manufactured polymer-based gyroidal triply periodic minimal surface (TPMS) as the initial sacrificial scaffold. Three-dimensional (3D)-printed templates of the polymeric gyroid lattices were coated with a mixture of graphene oxide (GO) and hydrazine solution via the hydrothermal process, followed by drying and thermal etching of the polymer scaffold, which resulted in a neat reduced GO (rGO) lattice of the gyroidal TPMS structure. Scanning electron microscopy and micro-computed tomography were used to evaluate the morphology and size of the 3D rGO architectures, while a Raman response at 1360[Formula: see text]cm[Formula: see text] (D peak), 1589[Formula: see text]cm[Formula: see text] (G peak) and 2696[Formula: see text]cm[Formula: see text] (2D peak) verified the presence of rGO. Thermo–electro–mechanical properties of rGO gyroid lattices of different densities were characterized where the highest Young’s modulus recorded was 351[Formula: see text]kPa for a sample with a density of 45.9[Formula: see text]mg[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text]. The rGO gyroid lattice exhibits an electrical conductivity of 1.07[Formula: see text]S[Formula: see text][Formula: see text][Formula: see text]m[Formula: see text] and high thermal insulation property with a thermal conductivity of 0.102[Formula: see text]W[Formula: see text][Formula: see text][Formula: see text]m[Formula: see text][Formula: see text]K[Formula: see text]. It is demonstrated that the hydrothermal-assisted fabrication process is adaptable for different lattice architectures based on 3D-printed scaffolds and thus has wide functional applications.

Injectable Therapeutic Organoids Using Sacrificial Hydrogels

SummaryOrganoids are becoming widespread in drug-screening technologies but have been used sparingly for cell therapy as current approaches for producing self-organized cell clusters lack scalability or reproducibility in size and cellular organization. We introduce a method of using hydrogels as sacrificial scaffolds, which allow cells to form self-organized clusters followed by gentle release, resulting in highly reproducible multicellular structures on a large scale. We demonstrated this strategy for endothelial cells and mesenchymal stem cells to self-organize into blood-vessel units, which were injected into mice, and rapidly formed perfusing vasculature. Moreover, in a mouse model of peripheral artery disease, intramuscular injections of blood-vessel units resulted in rapid restoration of vascular perfusion within seven days. As cell therapy transforms into a new class of therapeutic modality, this simple method—by making use of the dynamic nature of hydrogels—could offer high yields of self-organized multicellular aggregates with reproducible sizes and cellular architectures.

Biofabrication of valentine-shaped heart with a composite hydrogel and sacrificial material.

3D bioprinting represents a potential solution for organs regeneration, however, the production of complex tissues and organs that are in large size, randomly shaped, hollow, and contain integrated pre-vascularization still faces multiple challenges. This study aimed to test the feasibility of our 3D printing scheme for the manufacturing of micro-fluid channel networks complex three-dimensional tissue structures. The reverse engineering software was used to design the CAD model and polyvinyl alcohol (PVA) was used as the sacrificial material to print the sacrificial stent use the bioprinter nozzle 1. Hydrogel composite H9c2 and human umbilical vein endothelial cells (HUVECs) were mixed with sodium alginate, agarose solution and platelet-rich plasma (PRP) as cellular bioink, which was extruded through nozzle 2 to deposit the internal pores of the sacrificial scaffold. The scaffold dissolved, change to a flexible, hollow and micro-fluid channel networks complex structure. The 3D-bioprinting technology can construct a micro-fluid channel networks valentine heart with a self-defined height and hollow in suitable mechanical properties. The cells proliferate and maintain their biological properties within the printed constructs. This study demonstrates that valentine heart-like constructs can be fabricated with 3D bioprinting using sacrificial and hydrogel materials.

The 3D CoNi alloy particles embedded in N-doped porous carbon foams for high-performance microwave absorbers

The 3D CoNi alloy particles embedded N-doped porous carbon (CoNi@PRM-NC) foam with open reticular structures and high-performance microwave absorption are prepared by the novel sponge-templated strategy that uses melamine foam as a sacrificial scaffold and supporting template, phenolic resol as a carbon precursor and cobalt nickel nitrate as a magnetic particle precursor. It is worth noting that the surface of the skeleton has a large amount of honeycomb-like pores without add any pore formers and surfactants. After adding cobalt nickel metal particles, all three materials exhibit the enhanced electromagnetic wave absorption. By contrast, 3D CoNi@PRM-NC performs best, with the minimum reflection loss values of −56 dB at 17.8 GHz when the thickness is 1.7 mm. Meanwhile, an ultrabroad bandwidth of 11.9 GHz (6.1–18 GHz) at the thickness range of 1–5 mm is also obtained. The excellent microwave absorption performance of these materials is ascribed to the multiple scatterings caused by 3D conductive foam structure, large attenuation as well as the balanced impedance match between dielectric loss and magnetic loss. This strategy might open an avenue to large-scale synthesization of various porous carbon-magnetic metal composites which can be a promising candidate for high-performance microwave absorber.

Freestanding hierarchical vascular structures engineered from ice

The ability to engineer a synthetic hierarchical vascular network is one of the most demanding and unaddressed challenges in tissue engineering and regenerative medicine. A material that is both structurally rigid and biocompatible is needed to fabricate freestanding hierarchical vascular structures with defined dimensions and geometry. This is particularly important for creating commercially viable and easily suturable synthetic vasculature. Here, we present the surprising discovery that ice is a versatile material which satisfies these requirements. We demonstrate utilizing ice as a sacrificial scaffold, onto which a diverse range of materials were coated, including tropoelastin, polycaprolactone (PCL), silk, and polydimethylsiloxane (PDMS). We present ice facilitating the fabrication of freestanding hierarchical vascular structures with variable lumen dimensions, and validate the vascular application of these vessels by demonstrating their mechanical tunability, biocompatibility, and permeability to nutrient diffusion. This adaptable technology delivers engineered synthetic vasculature and has potential wider applications encompassing tissue engineering bespoke structures.

Metal Organic Framework-Templated Chemiresistor: Sensing Type Transition from P-to-N Using Hollow Metal Oxide Polyhedron via Galvanic Replacement.

Facile synthesis of porous nanobuilding blocks with high surface area and uniform catalyst functionalization has always been regarded as an essential requirement for the development of highly sensitive and selective chemical sensors. Metal-organic frameworks (MOFs) are considered as one of the most ideal templates due to their ability to encapsulate ultrasmall catalytic nanoparticles (NPs) in microporous MOF structures in addition to easy removal of the sacrificial MOF scaffold by calcination. Here, we introduce a MOFs derived n-type SnO2 (n-SnO2) sensing layer with hollow polyhedron structures, obtained from p-n transition of MOF-templated p-type Co3O4 (p-Co3O4) hollow cubes during galvanic replacement reaction (GRR). In addition, the Pd NPs encapsulated in MOF and residual Co3O4 clusters partially remained after GRR led to uniform functionalization of efficient cocatalysts (PdO NPs and p-Co3O4 islands) on the porous and hollow polyhedron SnO2 structures. Due to high gas accessibility through the meso- and macrosized pores in MOF-templated oxides and effective modulation of electron depletion layer assisted by the creation of numerous p-n junctions, the GRR-treated SnO2 structures exhibited 21.9-fold higher acetone response (Rair/Rgas = 22.8 @ 5 ppm acetone, 90%RH) compared to MOF-templated p-Co3O4 hollow structures. To the best of our knowledge, the selectivity and response amplitudes reported here for the detection of acetone are superior to those MOF derived metal oxide sensing layers reported so far. Our results demonstrate that highly active MOF-derived sensing layers can be achieved via p-n semiconducting phase transition, driven by a simple and versatile GRR process combined with MOF templating route.

Hollow amphiphilic crosslinked nanocapsules from sacrificial silica nanoparticle templates and their application as dispersants for oil spill remediation

Hollow nanocapsules were constructed using a sacrificial silica scaffold to produce novel oil remediation agents.

Three-Dimensional Single Gyroid Photonic Crystals with a Mid-Infrared Bandgap

A gyroid structure is a distinct morphology that is triply periodic and consists of minimal isosurfaces containing no straight lines. We have designed and synthesized amorphous silicon (a-Si) mid-infrared gyroid photonic crystals that exhibit a complete bandgap in infrared spectroscopy measurements. Photonic crystals were synthesized by deposition of a-Si/Al2O3 coatings onto a sacrificial polymer scaffold defined by two-photon lithography. We observed a 100% reflectance at 7.5 μm for single gyroids with a unit cell size of 4.5 μm, in agreement with the photonic bandgap position predicted from full-wave electromagnetic simulations, whereas the observed reflection peak shifted to 8 μm for a 5.5 μm unit cell size. This approach represents a simulation-fabrication-characterization platform to realize three-dimensional gyroid photonic crystals with well-defined dimensions in real space and tailored properties in momentum space.

Synthesis of Cu2O nanoparticle films at room temperature for solar water splitting

A Cu2O nanoparticle film using ZnO nanorods as a sacrificial scaffold was fabricated near 23°C, for applications in photoelectrochemical (PEC) water splitting. Three chemical solutions were utilized to convert ZnO nanorods to a Cu2O nanoparticle film – solutions of CuCl2 and NaOH, NaBH4 and NaOH, respectively. The structural evolution from ZnO through Cu(OH)2 and metallic Cu to Cu2O phase was analyzed at each stage with X-ray diffraction and X-ray absorption spectra. The energy bandgap was deduced from IPCE; the concentration of carriers and flat-band of a Cu2O nanoparticle film were obtained from a Mott-Schottky plot. Significantly, the Cu2O nanoparticle film exhibited a useful PEC response to water oxidation. This nanostructure synthesized with no energy requirement can not only illustrate a great prospect for solar generation of hydrogen but also offer a blueprint for the future design of photocatalysts.

Indirect additive manufacturing as an elegant tool for the production of self-supporting low density gelatin scaffolds.

The present work describes for the first time the production of self-supporting low gelatin density (<10w/v%) porous scaffolds using methacrylamide-modified gelatin as an extracellular matrix mimicking component. As porous scaffolds starting from low gelatin concentrations cannot be realized with the conventional additive manufacturing techniquesin the abscence of additives, we applied an indirect fused deposition modelling approach. To realize this, we have printed a sacrificial polyester scaffold which supported the hydrogel material during UV crosslinking, thereby preventing hydrogel structure collapse. After complete curing, the polyester scaffold was selectively dissolved leaving behind a porous, interconnective low density gelatin scaffold. Scaffold structural analysis indicated the success of the selected indirect additive manufacturing approach. Physico-chemical testing revealed scaffold properties (mechanical, degradation, swelling) to depend on the applied gelatin concentration and methacrylamide content. Preliminary biocompatibility studies revealed the cell-interactive and biocompatible properties of the materials developed.

Radially organized pillars in TiO2 and in TiO2/C microspheres: Synthesis, characterization and photocatalytic tests

► Synthesis of porous microspheres via template processes. ► Two kinds of materials: (1) porous core–shell C/TiO 2 and (2) pure TiO 2 mesoporous microspheres. ► The structure of the TiO 2 phase is constituted by cemented anatase and rutile nanoparticles. ► By changing the temperature of treatment, tunable anatase/rutile composition is obtained. ► Materials exhibit high activity in the photocatalytic oxidation of NO. Porous TiO 2 microspheres with robust texture and high photoactivity were prepared by inflowing a TiO 2 precursor in the confined space of polystyrene-co-divinyl benzene (PS-co-DVB) polymer, working as sacrificial scaffold. The impregnated polymer spheres, upon thermal treatments under N 2 , N 2 /air or pure air flow at temperatures in the 400–500 °C interval, are transformed into porous microspheres. Depending on the gas flow composition, the obtained microspheres are constituted by porous carbon, hybrid core–shell C/TiO 2 or of cemented TiO 2 nanoparticles assembled in elongated pillars. The composition of pure TiO 2 microspheres ranges from pure anatase (400 °C) to the prevailing rutile phase (>475–500 °C). All samples have been extensively characterized by means of SEM/AFM microscopes, N 2 -volumetric porosimetry, XRD and UV–vis analyses. The photodegradation of NO has been used to check the photocatalytic activity of the TiO 2 materials. It is concluded that they exhibit higher photoactivity than the classical benchmark material (Degussa P25). This property together with porous character of the microspheres, the tunable anatase–rutile ratio and the high crystallinity makes these microspheres very interesting materials for applications in photocatalysis. From a physical point of view, the large axial pores and the columnar nature of the spheres can produce the entrapment of the light into the material.

Nanoporous carbon template from surface reconstruction in block copolymer thin film

Fine tuning of the orientation and lateral ordering of block copolymer microdomains is essential to their application as templates for the fabrication of nanostructures. Also, a process must be robust, simple, rapid, and not disruptive. In addition, the fabrication of ultrathin and nanoscale carbon template from self assembled copolymer is still a challenging task in the field of materials science. Here, a simple way for the fabrication of carbon nanoporous template via block copolymer surface reconstruction is described. A thin film of poly(styrene- b-4-vinylpyridine) showing micelle structure was spin casted from toluene solution on carbon precursor film poly(acrylonitrile- b-methyl methacrylate) as a sacrificial scaffold for the formation of nanoporous carbon template. The preferential solvation of the vinylpyridine block with an alcohol resulted in a surface reconstruction that leads to the formation of nanoporous film. Subsequent reactive ion etching and thermal treatment generated nanoporous and robust carbon template.

Kilogram-scale synthesis of ordered mesoporous carbons and their electrochemical performance

An efficient post-cure approach has been demonstrated for the kilogram-scale synthesis of high-quality ordered mesoporous carbons (OMC) by using triblock copolymer Pluronic F127 as a template, phenolic resol as a carbon precursor and polyurethane foam as a sacrificial scaffold through an organic–organic self-assembly. The effects of the concentration and the loading amount of resol on the mesostructure of the carbons are systematically investigated. The small-angle X-ray scattering, nitrogen sorption and transmission electron microscopy results reveal that the resultant OMC in kilogram-scale quantities possesses high surface area (∼690 m 2 g −1), large pore volume (∼0.45 cm 3 g −1) and uniform, large pore size (∼4.5 nm) as well as thick pore walls (∼6.5 nm). The OMC exhibits good electrochemical performance of about 130 F g −1 in KOH electrolyte.

Facile Synthesis of Hierarchical Alumina Monoliths with Tubular Macropores and Ordered Mesoporous Walls

Abstract A facile approach of evaporation-induced self-assembly plus coating was developed using nonwoven fabrics (NF) as a sacrificial scaffold, leading to the acquisition of hierarchically macro/mesoporous alumina monolith. The macropores templated by NF show a tubular structure of about 10 µm in channel diameter. The monolith is composed of ordered mesostructured wall with large-sized mesopores and high thermal stability. The regularity of the mesopores can be maintained up to 900 °C, even after the amorphous Al2O3 transforms to crystalline structure (γ-Al2O3). This facile route can be extended to the preparation of other hierarchically macro/mesoporous monoliths such as TiO2, ZrO2, ZnO, et al.

Artificial Black Opal Fabricated from Nanoporous Carbon Spheres

A nanocasting method via chemical vapor deposition of acetonitrile was successfully employed to fabricate porous carbon colloidal crystal using colloidal crystal from monodispersed mesoporous silica spheres (MMSS) as a sacrificial scaffold. The mesostructure as well as periodic arrays within (111) plane of MMSS were replicated for the carbon colloidal crystal (black opal) with the length scale in the centimeter range. Brilliant iridescent colors were clearly observed for the first time on the black carbon colloidal crystal fabricated from porous carbon spheres, and they changed dramatically in accordance with the observation angle, like natural black opals. Reflection spectra measurements based on 2D surface diffraction and Bragg diffraction in the mirror mode were conducted for the fabricated carbon periodic arrays. The periodicity in the (111) plane as well as in the direction perpendicular to the (111) plane of the colloidal crystal was evaluated by comparing the results obtained from these two measurements. It was found that the periodicity in the direction perpendicular to the (111) surface is not high for the obtained black carbon opal. On the other hand, the relationship between the incident angles and the peak wavelengths of the reflection spectra, collected in the condition where the incident light and the reflected light pass through in the same direction, is governed by an approximation based on 2D surface diffraction. The results imply that the origin of the iridescent colors on the fabricated black carbon opal is derived from the periodicity not in the direction perpendicular to the (111) plane but within the (111) plane.

Polycaprolactone coated porous tricalcium phosphate scaffolds for controlled release of protein for tissue engineering.

Polycaprolactone (PCL) was coated on porous tricalcium phosphate (TCP) scaffolds to achieve controlled protein delivery. Porous TCP scaffolds were fabricated using reticulated polyurethane foam as sacrificial scaffold with a porosity of 70-90 vol %. PCL was coated on sintered porous TCP scaffolds by dipping-drying process. The compressive strength of TCP scaffolds increased significantly after PCL coating. The highest strength of 2.41 MPa at a porosity of 70% was obtained for the TCP scaffold coated with 5% PCL solution. Model protein bovine serum albumin (BSA) was encapsulated efficiently within the PCL coating. The amount of BSA encapsulation was controlled by varying proteins' composition in the PCL coating. The FTIR analysis confirmed that BSA retained its structural conformation and did not show significant denaturization during PCL coating. The release kinetics in phosphate buffer solution indicated that the protein release was controlled and sustained, and primarily dependant on protein concentration encapsulated in the PCL coating.