I. Core Research Summary

• Biomimetic Support-Free 3D Printing Principle

By mimicking the natural mechanism by which fog droplets condense into minerals in deserts, ultrasonic atomization generates silver nanodroplets, with a 3-mm nozzle enabling non‑contact deposition. A substrate maintained at a constant temperature of 90–110°C accelerates solvent evaporation; each new layer is deposited only after the preceding droplet has fully solidified, allowing for the fabrication of inclined three‑dimensional trusses without any support structures and achieving a stable growth critical angle of approximately 37°.

• Near‑dense, high length‑to‑diameter ratio micro‑truss fabrication

The individual truss members have diameters of 20–55 μm, with a maximum aspect ratio of 20:1; the overall microlattice porosity is tunable (9.5%–27%), and post-sintering, the internal nanopores within the struts are controllable. The structure features a three‑level hierarchical porous architecture—millimeter‑scale lattice pores, micrometer‑scale truss gaps, and nanoscale interparticle voids—spanning five orders of magnitude in size.

• Establish a comprehensive physical prediction model for sedimentation.

We derive formulas for the droplet evaporation half-life and the critical angle for stable growth, enabling precise prediction of the maximum printable tilt angle and the minimum substrate temperature control requirements. Experimental results closely match theoretical simulations, allowing direct application to upfront process design.

• Sintering-Driven Regulation of Hierarchical Porous Structures

Low-temperature, short-duration sintering preserves a large number of nanopores, while high-temperature, full densification yields nearly dense rods; by seamlessly switching between thermal and photonic sintering modes, one can tailor either porous or dense microstructures to meet the distinct requirements of energy storage and mechanical performance.

• Integrated verification of multiple types of functional prototypes

We have successfully fabricated stretchable spatially interconnected conductive wires, high‑aspect‑ratio helical microcolumns, biomimetic cellular scaffolds, and miniature heat‑dissipation arrays. Our microporous lattice‑structured lightweight materials exhibit an exceptionally high specific strength, opening up a new performance regime on the Ashby material chart.

II. Complete Process Flow for Aerosol-Based Point-Style 3D Printing

(1) Printing Procedure

• Silver nanoparticle ink formulation: 30–50 nm silver particles, deionized water, and ethylene glycol blended together; the mixture is subjected to roller milling for 12 hours to ensure thorough dispersion and prevent agglomeration.
• Plasma cleaning of alumina polishing substrates, with the workbench maintained at a constant temperature of 90–110°C.
• AJ300 ultrasonic atomization module, carrier gas 28 SCCM, sheath gas 40 SCCM, with a 100/150 μm ceramic nozzle;
• CAD-based layered spatial trajectory programming enables the print head to lift layer by layer, maintaining a constant 3 mm nozzle‑to‑substrate distance, while droplets are deposited in mid-air to form self-supporting structures.
• Post‑processing options: 200°C tubular furnace sintering / Xenon lamp–induced transient photon sintering;
• SEM was used to observe hierarchical porosity, and a universal testing machine was employed to perform mechanical calibration of lattice‑structured compression.

(II) Five Core Process Advantages (Compared with Two-Photon Polymerization, Template-Based Methods, and Extrusion-Based 3D Printing)

• Completely eliminate sacrificial molds and support structures.

It eliminates multiple process steps such as lithography, coating, and resist stripping, generates no chemically corrosive waste, is environmentally friendly and low-cost, and significantly shortens the sample preparation cycle.

• Integrated in-situ formation of hierarchical porosity

A single printing process simultaneously generates hierarchical pores spanning the nano-, micro-, and millimeter scales, eliminating the need for secondary etching to create porosity and perfectly meeting the high‑surface‑area requirements of catalysis and energy storage.

• Low‑damage, gentle forming; compatible with multi‑material nano‑slurries.

The entire process operates at low temperatures, accommodating metal, oxide, and conductive polymer nanoinks, thereby expanding the capabilities of composite micro‑array fabrication.

• Micrometer-level high-precision freeform surface three-dimensional structure

Stably fabricate 20-μm ultrafine lattice structures, enabling the printing of helices, inclined columns, and irregular biomimetic topologies; extrusion-based printing cannot produce large‑angle overhanging features.

• Digitally Rapidly Iterated Topology Structure

With a single click in CAD, modify the lattice cell size, truss diameter, and inclination angle, and complete eight sets of comparative specimens—octahedral and hexagonal—in a single day.

III. Five Core Technological Innovations of This Study

Innovation 1: Original technology for bio-inspired aerosol-point-based spatial 3D printing

Innovation 2: A Multi-Porous, Controllably Fabricated Hierarchical System Across Five Scales

Innovation 3: Droplet Evaporation – Physical Prediction Model for the Critical Angle

Innovation: Four Strategies for Controlling Sintered Porosity

Innovation: A Multifunctional, Integrated Microdevice Paradigm

IV. Current Industry Challenges and Corresponding Solutions for Overcoming Them

Challenge 1: Conventional microarrays rely on polymer templates, resulting in a complex demolding process and the generation of polluting waste liquids.

Challenge 2: Current fabrication processes can only produce hollow trusses, which exhibit poor densification of the members and weak mechanical properties.

Challenge 3: It is difficult to simultaneously achieve multi-scale composite porosity spanning nanoscale, microscale, and millimeter scale.

Challenge 4: Suspended, tilted microstructures are prone to collapse, and there are no established process parameters to guide their fabrication.

Challenge 5: A single device struggles to simultaneously accommodate both mechanical and electrochemical microdevices.

V. Future Diversified Industrial Application Scenarios

1. Biomimetic Scaffolds for Tissue Engineering

2 Micro‑lithium batteries / Supercapacitor three‑dimensional electrodes

3 Aerospace Lightweight Energy-Absorbing Metamaterials

4 Stretchable Interconnect Wires for Flexible Electronic Systems

5 Microfluidics and Miniature Optoelectronic Heat-Sink Arrays

6. General R&D Platform for Micro- and Nano-Manufacturing in Universities

Figure 1. Schematic analogy illustrating the natural growth process of desert roses and the fabrication of microstructures via three-dimensional nanoparticle assembly achieved through lattice‑based printing. (A) Shows the formation of a desert rose: under the high‑temperature conditions typical of desert climates, sulfur‑containing aerosols undergo condensation. The photograph of the desert rose is provided by O. Apostolidou (reproduced with permission). (B) Based on the principle illustrated in (A), we employ a method that combines sequential condensation, solvent evaporation, and sintering of nanoparticle ink droplets in three spatial dimensions to fabricate controllable three‑dimensional microarchitectures with hierarchical porous structures. Scanning electron microscopy (SEM) images reveal a petal‑like morphology (right panel), with truss‑unit diameters on the order of 40 μm.

Figure 2. Illustrates the physical model developed to investigate the stability and control of dot‑printing, along with its experimental validation. (A) A simplified free-body diagram of a critical droplet at the edge of a structure, together with the design of the experimental setup used to validate the model; (B) Predicted relationships between the growth angle and droplet radius at various measured dried‑droplet heights; (C) Numerical calculations based on evaporation rates that reveal how the half-life of microdroplets varies with substrate temperature; (D) Scanning electron microscope images showing a series of inclined pillars fabricated at different tilt angles, used to verify the model’s predictions. The magnified side view of the last inclined pillar indicates a critical angle—defined as the minimum angle between the pillar and the horizontal plane when assembled by this method—of 37°, in excellent agreement with the model’s prediction. Scale bar: 250 μm.

Figure 3. Lattice‑printed three‑dimensional microarchitectures with different network topologies. (A) An open‑cell octahedral microarchitecture, with truss members approximately 35 μm in diameter; scale bar = 50 μm. (B) A lattice‑fabricated microarchitecture combining octahedral and hexagonal motifs; scale bar = 50 μm. (C) Top views of the octahedral scaffold structure at various magnifications. (D) The truss‑member architecture of the 3D‑printed scaffold after adhesive debonding and nanoparticle sintering (with possible grain growth).

Figure 4. Combined application of dot‑printing technology and controlled sintering. The printed material is designed with a primary macroporous structure; during sintering, the coalescence of sintered nanoparticles gives rise to a secondary porous architecture, which can be suppressed before pore closure and grain growth occur. Scale bar: 100 nm.

Figure 5. Point-by-point printed hierarchical materials with three-dimensional microstructures, spanning more than five orders of magnitude in feature size. (A) Scanning electron microscope images at the millimeter scale showing octahedral and hexagonal microlattices (overall view); (B) High aspect-ratio truss units that constitute the sintered structural framework, forming the first layer of porous architecture; (C) Engineering surfaces of lattice truss units fabricated under different sintering process parameters, exhibiting porosity ranging from highly porous to nearly dense; (D) Final surface features and pore‑distribution morphologies corresponding to various sintering temperature profiles, revealing a spectrum of pore structures from the microscale to the nanoscale.

Figure 6 illustrates the versatility of nanoparticle architectures fabricated via inkjet printing across a range of applications. (A) A hierarchical porous scaffold and its porous surface morphology, suitable for tissue engineering and cell proliferation; (B) A stretchable spatial interconnect structure assembled between two micro‑LEDs. Scale bar: 100 µm; (C) Scanning electron microscope images of an array of cylindrical structures with varying diameters (35–100 µm) and heights (85–500 µm); (D) From left to right: four helical hollow columns with high aspect ratios forming a dome‑like structure, demonstrating the method’s flexibility in fabricating spatial interconnect architectures, along with a delicate silver interconnect featuring a thickness of 30 µm and an aspect ratio exceeding 20.