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 significant challenges—including high cost, large form factor, high power consumption, and complex integration—which severely limit their application in portable and 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 provides a detailed explanation of the key technology underlying this breakthrough: the central role of aerosol jet printing (AJP) in the manufacturing process.

Background

Haptic interfaces serve as a crucial bridge in human–machine interaction, delivering direct and natural tactile feedback. While traditional electronic haptic devices, such as vibration motors and pressure sensors, perform well in certain applications, they often suffer from the following limitations:

• Large volume, making high density and miniaturization difficult to achieve

• High power consumption limits battery life.

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

• Non-intuitive,单一 stimulation methods make it difficult to simulate complex tactile sensations.

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

Innovative Solution

The research team has proposed a novel “thermo-pneumatic” haptic display technology, the core principle of which is to use microheating elements—such as localized heating with conductive ink—to heat the air within microcavities, causing it to expand and generate a specific mechanical pressure that acts on the skin, thereby creating 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) to fabricate fine conductive traces and heating elements;

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

• Conductive connection: wires are connected to electronic components using silver conductive materials;

• Thermal insulation layer and support: A PDMS film is introduced as an elastic isolation layer to protect the sensitive structure.

These materials, through rational design and optimization, ensure the equipment’s excellent reliability and durability.

2) Manufacturing Process

• Employing aerosol jet printing (AJP) technology to precisely deposit conductive ink onto flexible substrates, thereby fabricating microheaters.

• Defining the micro-air-cavity structure using techniques such as laser cutting;

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

• Final assembly is performed on a flexible, elastic soft substrate (such as finger patches or gloves).

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 that is easy to integrate into equipment such as gloves and finger patches.

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

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

However, the key to realizing such complex microstructural precision manufacturing lies in high-resolution, miniaturized fabrication processes—precisely the domain where AJP technology shines.

Specific Application Process of AJP in Tactile Display Manufacturing

In this study, AJP primarily accomplished the following key steps:

01 Printing of Ultra-Fine Conductive Paths

AJP is used to directly jet silver nanoparticle ink onto Kapton film, thereby forming microheating coils with a line width of 55 μm and a thickness of approximately 2 μm.

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

02 High-Precision Resistance Value Setting

By adjusting inkjet printing parameters—such as jetting speed, air-flow ratio, and ink concentration—the width and thickness of the conductive traces can be controlled, 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, followed by UV laser cutting on Kapton to create a “hole” structure for the 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

Enhance the adhesion between Kapton and PDMS through plasma treatment to ensure 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 suitable for mass production.

Relevant electronic components, such as micro-resistors and sensors, can be co-fabricated on flexible PCBs to create a highly integrated, monolithic tactile array.

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

Illustrated Guide

Figure 1. Overview of thermo-pneumatic haptic display technology. a: Thermo-pneumatic actuation strategies for activating the display unit and b: haptic display architecture; c: Schematic illustration of the fabrication process used to manufacture the display; d: Optical image of the first prototype developed, which consists of resistive elements directly printed on a Kapton film, with perforated Kapton spacers and a top PDMS active membrane, using silver-nanoparticle ink; e: High-resolution image of the serpentine resistor, with an enlarged view of a single printed trace, and f: the corresponding confocal profilometry image. g: Distribution map of printed-line thickness, corresponding to the dashed line in f, with a maximum thickness of approximately 2.4 µm.

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

Figure 3. Advanced prototyping and displacement characteristics.

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

Figure 5. Wearable haptic display demonstration conducted with human subjects. a Schematic diagram of the control system, whose main components include an operational amplifier for closed-loop control via the MAX4210 power monitor and a wireless communication system; b The complete wearable platform, comprising an integrated electronic board mounted within a wristband and a haptic display attached to the user’s fingertip; c An example of the three test steps used for voluntary subjects, along with their corresponding modes; d Four of the six dots on the haptic display are sequentially activated to reproduce the Braille character “T” (each dot is activated for 500 milliseconds, with an activation signal of 10 milliseconds at 10 Hz), and a thermal image of the “T” pattern is generated by merging four thermal images, one corresponding to each activated dot; e and f Percentage of correct responses on average among 10 subjects in the two-point recognition test and the dynamic pattern recognition test, with average success rates of 82% and 85%, respectively; g Confusion matrix for Braille character recognition at a nominal peak power of 840 milliwatts, with a success rate of 83%.

Using aerosol jet printing (AJP), the team is able to deposit conductive traces with a line width of approximately 55 micrometers on flexible substrates such as Kapton film, enabling high-resolution array configurations and laying the technical foundation for high-precision, high-density tactile displays. Moreover, the non-contact nature of AJP and its compatibility with multiple materials facilitate the integration of complex structures, thereby promoting overall device lightweighting and structural compactness.

In summary, aerosol jet printing (AJP) technology plays an irreplaceable role in advancing the miniaturization and flexibility of electronic manufacturing, providing robust technical support for the development of future intelligent, portable, and low-power haptic interfaces. The innovative applications of this approach not only highlight its advantages in microelectronic fabrication but also usher in a new era of flexible electronics integrated with micromechanical systems, thereby laying a solid foundation for the widespread adoption of smart wearable devices.

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