In fields such as smart wearables, virtual reality, and robotic interaction, haptic display technology is playing an increasingly vital role. However, conventional haptic displays often face numerous challenges—high costs, bulky form factors, substantial power consumption, and complex integration—which severely limit their applicability in portable, flexible devices. Recently, an innovative study has successfully developed a low‑voltage, wearable haptic display based on the “thermo‑pneumatic” principle, opening up new possibilities for future intelligent haptic interfaces. This article will provide a detailed explanation of the key technology behind it: the pivotal role of aerosol jet printing (AJP) in its fabrication.

Background

As an essential bridge in human–computer interaction, haptic interfaces provide direct, natural tactile feedback. Traditional electronic haptic devices, such as vibration motors or pressure sensors, perform well in certain applications but often suffer from the following limitations:

• Large in size, making high density and miniaturization difficult to achieve.

• High power consumption, resulting in limited battery life

• The control system is complex and difficult to flexibly integrate into flexible materials.

• Non-intuitive, single-mode stimulation makes it difficult to simulate complex tactile sensations.

Accordingly, developing a low-power, flexible, miniaturized tactile display solution that is easy to manufacture at scale has become a major focus in the industry.

Innovative Solution

The research team has proposed a novel “thermo‑aerodynamic” haptic display technology. At its core, this approach uses miniature heating elements—such as localized heating with conductive ink—to warm the air within microcavities, causing it to expand and generate mechanical pressure that is applied to the skin, thereby eliciting a tactile sensation. When the heating is turned off, the air cools and contracts, terminating the stimulation.

1) Material Selection

• Conductive materials: Silver nanoparticle ink (particle size 30–40 nm) is deposited using aerosol jet printing (AJP) technology to fabricate fine conductive traces and heating elements.

• Substrate material: Polyimide (Kapton) film, which is flexible and resistant to high temperatures;

• Conductive connection: The wire is connected to the electronic device via a silver conductive material.

• Adiabatic Layer and Support: A PDMS film is introduced as an elastic isolation layer to protect the sensitive structure.

These materials, through careful design and optimization, ensure that the equipment exhibits excellent reliability and durability.

2) Manufacturing Process

• Employing aerosol jet printing (AJP) technology, conductive ink is precisely deposited onto flexible substrates to fabricate microheaters.

• Define micro‑cavity structures using techniques such as laser cutting;

• Employing plasma‑assisted bonding technology to achieve encapsulation of multilayer structures;

• The final assembly is mounted on a flexible, elastic soft substrate (such as a finger patch or glove).

This type of manufacturing process is easily scalable and meets the requirements of industrial production.

3) The advantages of this plan are obvious:

• Low-voltage operation (can be achieved with just a few volts)

• Wearable, flexible design, easily integrated into equipment such as gloves and finger patches.

• Simple structure, with no complex fluid or gas storage piping, facilitating miniaturization and mass production.

• Achieve multi-point, multimodal tactile stimulation through intelligent control.

However, achieving such complex microstructural precision manufacturing hinges on high-resolution, miniaturized fabrication processes—precisely the domain where AJP technology shines.

The specific application process of AJP in haptic display manufacturing

In this study, AJP primarily carried out the following key steps:

01 Printing of Ultra-Fine Conductive Paths

Silver nanoparticle ink is directly jetted onto a Kapton film using AJP, forming miniature heating coils with a line width of 55 μm and a thickness of approximately 2 μm.

After high-temperature sintering, a micro‑resistor with excellent electrical conductivity and rapid response is formed, which is used for localized heating control.

02 High-Precision Resistance Value Setting

By adjusting the inkjet printing parameters—such as jetting speed, air‑flow ratio, and ink concentration—we can control the width and thickness of the conductive traces, thereby precisely tuning the resistance value to approximately 27 Ω.

This approach ensures heating efficiency and response time, facilitating rapid and precise pneumatic control.

03 Additive manufacturing with multilayer structures

First, the conductive traces are printed, and then UV laser ablation is performed on Kapton to create a “hole”‑like structure that forms an air cavity.

A thin layer of PDMS is sprayed onto the surface of the hole, forming an elastic membrane and an air-sealing structure that provides elastic support for gas expansion.

04 Packaging and Structural Assembly

Plasma treatment is employed to enhance the adhesion between Kapton and PDMS, ensuring a leak‑free seal.

After assembly, the entire structure is integrated onto a flexible substrate and subjected to fine-tuning and testing.

05 Potential for Mass Production

All critical processes can be implemented using industrially customized AJP equipment, making them well-suited for mass production.

Relevant electronic components, such as miniature resistors and sensors, can be fabricated concurrently on flexible PCBs, yielding a highly integrated, monolithic tactile array.

High-precision wire printing achieved via AJP significantly enhances the quality and uniformity of microstructures, providing a robust foundation for device reliability and response speed.

Image and Text Guide

Figure 1. Overview of thermo‑pneumatic haptic display technology: (a) the thermo‑pneumatic actuation strategy used to activate the display elements and the b haptic display architecture; (c) a schematic of the fabrication process for the display; (d) an optical image of the first prototype, which consists of resistive elements printed directly onto a Kapton film, with perforated Kapton spacers and a top PDMS active membrane; (e) a high‑resolution image of the serpentine resistor, with an enlarged view of a single printed trace, and (g) the corresponding confocal profilometry image. (h) A map of the printed line thickness distribution, corresponding to the dashed line in (g), with a maximum thickness of approximately 2.4 µm.

Figure 2. Thermoelectric properties of the first prototype of the tactile display.

Figure 3. Advanced prototyping and displacement characteristics.

Figure 4. Advanced characterization of prototype force‑response characteristics. a Repeatability of force application across devices. For five points selected from five different displays, time‑averaged force values are reported as mean (black line) and standard deviation (colored bands), corresponding to each activation signal tested. All experiments were conducted at an average power of 1 W (complete signals are presented in Supplementary Figure S9a); b,c Repeatability of force application across devices. The new prototype was characterized using the same metrics described in Figure 2 and in the “Device Characterization” section. d Force response to activation signals with varying pulse durations—sampling frequency 20 kHz, smoothed by a 4‑point moving average filter. e Peak‑to‑peak and average force responses for activation signals at 10 ms–10 Hz and 25 ms–1 Hz, over a power range from 100 to 1200 mW.

Figure 5. Demonstration of the wearable haptic display on human subjects. a Schematic of the control system, whose main components include an operational amplifier for closed-loop control via the MAX4210 power monitor and a wireless communication subsystem; b The complete wearable platform, integrating the electronic board into a wristband and incorporating a haptic display attached to the user’s fingertip; c An example of the three test steps performed on volunteer subjects, along with their corresponding modes; d Four of six points on the haptic display are sequentially activated to reproduce the Braille character “T” (each point is activated for 500 ms, with an activation signal of 10 ms at 10 Hz), and a thermal image of the “T” pattern is generated by merging four thermal images—one corresponding to each activated point; e, f The average percentage of correct responses among ten subjects in the two-point recognition test and the dynamic pattern recognition test, with mean success rates of 82% and 85%, respectively; g A confusion matrix for Braille character recognition at a nominal peak power of 840 mW, yielding a success rate of 83%.

Using aerosol jet printing (AJP) technology, the team can deposit conductive traces with a linewidth of approximately 55 micrometers onto flexible substrates such as Kapton film, enabling high‑resolution array layouts and providing the technical foundation for high‑precision, high‑density tactile displays. Moreover, the non‑contact nature of this technique and its compatibility with multiple materials facilitate the integration of complex structures, contributing to overall device lightweighting and structural compactness.

In summary, aerosol jet printing (AJP) technology plays an irreplaceable role in advancing miniaturized and flexible electronics manufacturing, providing robust technical support for the development of future smart, portable, and low‑energy tactile interfaces. The innovative applications of this approach not only highlight its advantages in microelectronic fabrication but also usher in a new era of integrated flexible electronics and micromechanics, laying a solid foundation for the widespread adoption of smart wearable devices.

Original article link: https://doi.org/10.1038/s41528-025-00426-3