(Nanowerk Spotlight) The ability to control a material’s properties at the nanoscale underlies many remarkable structures in nature. Seashells achieve their strength through precise arrangements of calcium carbonate and proteins at scales of billionths of meters. Creating artificial materials with similar levels of control would enable dramatic improvements in everything from structural materials to medical devices, but manufacturing limitations have prevented such precision.
Current 3D printing techniques can create complex structures, but they can only control material properties – like strength and flexibility – down to scales of about 100 to 320 micrometers. This limitation prevents engineers from replicating the sophisticated structural arrangements found in natural materials that give them their exceptional properties.
Researchers at the University of Sydney have now developed a manufacturing technique that achieves a 130-fold improvement in the precision of mechanical property modulation compared to previous methods. Their method creates stable structures where mechanical properties can transition from rigid to flexible over distances of just 770 nanometers.
The advance relies on a new printing material that maintains consistent volume regardless of its mechanical properties. Traditional materials typically expand or contract differently based on their rigidity, which causes structural failure at small scales. The research team solved this by developing a specialized polymer mixture containing precisely balanced rigid and flexible components. The material uses two different forms of a polymer that respond differently to water, and when combined with specific chemical additives such as an enzymatic oxidase system, it ensures stability during and after printing. This system actively reduces oxygen inhibition during polymerization, improving print resolution and structural integrity.
To control the printing process, the researchers developed software called OpenScribe that translates desired mechanical properties into optimized laser parameters during printing. The system varies the laser energy delivered—higher energy creates stiffer material, while lower energy produces more flexible sections. Additionally, hatch volume—the spacing of laser paths—further fine-tunes mechanical properties, allowing for precise control of elasticity at the nanoscale.
Voxelating material properties without structural deformation. a) A material with voxelated properties, wherein color represents voxels of arbitrary material properties – inset shows the transition between material properties b) A photoresist for 3Dprinting materials with nanovoxelated elastic modulus. The photoresist uses DMSO as a solvent for its high solvency, with hydroxypropyl-methyl cellulose to enhance viscosity, and an enzymatic oxidase system of glucose and glucose oxidase, reducing oxidative inhibition. Photopolymerization is initiated by the photoinitiator BAPO, polymerizing the hydrophilic (PEGDA575) and hydrophobic (PEGDA250) prepolymers. c) Additional developments include the OpenScribe software for defining objects with complex voxelated properties, and biocompatibility of the photoresist via the incorporation of biomolecules with free cysteine residues into the photoresist can enable specific biofunctionalities., i.e., laminin at 50 μgmL endows the capacity for human induced pluripotent stem cells to attach to the hydrogel. d)Workflow for measuring the swelling properties of the printed hydrogel: printed arrays are imaged using confocal microscopy to measure their swelling ratio, defined as their deviation from the ideal shape following water immersion. Example images show prints with swelling ratios ranging from 0.55 to 1.09. e) Swelling ratio as a function of PEGDA575 to PEGDA250 ratios. Different markers indicate varying total PEG concentrations (40%, 60%, 80%, 100%), galvo acceleration (1, 5, 10 μm s−2), and scan velocities (10, 20, 50, 100 mm s−1). Violin plots showing the distribution of swelling ratio data projected onto individual parameters, with overlaid box-plot showing mean, 1st/3rd quartile lines, and limits. Each plot represents a singleparameter projection of the multi-dimensional parameter space. (Image: Reprinted from DOI:10.1002/adma.202416262, CC BY) (click on image to enlarge)
The team demonstrated their technique by printing complex three-dimensional lattice structures that integrated stiff and flexible regions without structural defects. These structures maintained their integrity even when exposed to water, proving the stability of the new material system. The researchers confirmed their results using atomic force microscopy (AFM) force spectroscopy, which mapped the local elasticity of the printed structures and validated the nanoscale mechanical transitions.
The precision achieved by this method approaches the scale at which natural materials create their exceptional properties. This advance enables the development of new materials that could combine seemingly contradictory properties – like the strength of ceramics with the flexibility of rubber – in single structures.
The implications extend beyond structural materials. The technique could improve heat management in electronics by creating materials with precisely controlled thermal properties. In medical applications, it could enable devices that better match the mechanical properties of biological tissues. For electronics manufacturing, it offers the possibility of three-dimensional circuit boards that pack more components into smaller spaces.
The researchers have published their software as open source, providing other scientists the tools to build on this advance. Their technique establishes a foundation for creating materials with precisely controlled properties at the nanoscale, potentially enabling a new generation of engineered materials that rival nature’s most sophisticated designs.
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