I. Core Research Summary

• Directly Formed Conductive Sensing Circuitry on a Bandage Substrate

Using commercially available Opsite flexible adhesive dressings as the substrate, an aerosol‑based technique precisely prints silver nanoparticle strain gauges with a 200 μm linewidth, thereby avoiding the high cost of advanced flexible films. The dressing features a medical‑grade adhesive that allows for direct application to the skin.

• Localized laser sintering to protect the high-temperature‑sensitive bandage substrate.

The decomposition temperature of the PU bandage is only 225°C, whereas conventional thermal curing above 150°C would cause it to melt and degrade. The 780 nm femtosecond laser selectively heats only the silver nanolayer, keeping the overall substrate temperature well below the thermal damage threshold; after sintering, the silver film exhibits a sheet resistance as low as 0.2 Ω/□.

• Excellent tensile and bending sensing performance

The bandage substrate exhibits a maximum tensile strain of 400%, while the sensor can accommodate up to 150% deformation. Even with a bending radius of 1 cm, it maintains a significant resistive response; after 700 cycles of repeated bending, only a minor change in resistance is observed, and the signal reliably distinguishes between different wrist flexion angles.

• Adjustable Multilayer Film Molding Process

By adjusting the number of printing passes to 4, 6, 8, or 10, the thickness of the silver film can be precisely controlled. A six-pass printing process combined with a laser scanning speed of 70 mm/s achieves an optimal balance between electrical conductivity and mechanical stretchability, yielding a crack-free coating with excellent adhesion; tape‑peel tests confirm that the film remains intact.

• Human-body wearable real-world usability

Directly adhered to the wrist, the capture joint detects flexion and extension; at a 45° bend, the resistance rises steadily, and upon release, it rapidly returns to its original state. The average response time is approximately 492 ms, enabling real-time acquisition of limb motion signals and supporting home‑based rehabilitation monitoring.

II. Complete Preparation Process and Process Advantages for Aerosol Spraying

(1) Complete Manufacturing Process for Bandage Sensors

• Medical-grade PU bandages are smoothly adhered to a PET carrier sheet, with surface pretreatment enhancing ink wettability.
• Dilute silver nanoparticle conductive ink, apply strain‑gauge patterns via aerosol ultrasonic atomization with CNC printing, and pre‑dry the substrate at 70°C.
• 780 nm femtosecond fiber laser–based directional scanning sensing circuit, with localized photothermal sintering limited to the silver layer only;
• After cooling, the carrier substrate is peeled off, leaving the dressing base intact with its adhesiveness and breathability, thereby completing the fabrication of the wearable strain-sensing dressing.

(II) Five Core Process Advantages (Compared with Screen Printing, Inkjet, and Thermal Evaporation)

• Maskless micrometer-level precision printing, suitable for small dressing areas.

Aerosol beam‑focusing technology enables the fabrication of features as fine as 200 μm, allowing multiple strain‑gauge arrays to be patterned on the limited‑area surface of a patch—something that is difficult to achieve with screen printing for microscale, high‑precision sensing patterns.

• Low-temperature pre-drying combined with localized laser treatment—perfectly suited for heat-sensitive medical substrates.

The entire process avoids high‑temperature oven baking; only laser‑localized heating is used to activate the conductive layer, ensuring that the polyurethane dressing neither melts nor loses its medical adhesion, whereas conventional flexible substrates subjected to thermal processing would be rendered unusable.

• Thickness is precisely controllable, balancing electrical conductivity with tensile toughness.

The number of printing layers allows for flexible control of film thickness, enabling on-demand adaptation to applications requiring high electrical conductivity or large‑strain deformation. A single device can rapidly switch between sample parameters for iterative optimization.

• Extremely low consumable costs and low mass-production costs for single-use dressings.

Silver ink is deposited only in the sensing area, and the bandage substrate consists of off-the-shelf, cost-effective medical consumables, eliminating the need for custom‑made specialty electronic films. This makes it well suited for large‑scale production of consumer‑grade health‑care supplies.

• Conformal Deposition on Curved/Flexible Substrates

The bandage features embossed, breathable micro‑pores; aerosol droplets penetrate and adhere to the substrate surface, while the thin film exhibits strong anchoring, resisting delamination even under repeated stretching.

III. Five Key Technological Innovations

Innovation 1: A novel composite process combining aerosol deposition with localized laser sintering

Innovation 2: Low-cost medical bandages as integrated sensing substrates

Innovative Quantitative Optimization System for Laser Parameters 3

Innovative 4 High-Compatibility, Large-Deformation Silver Nanocomposite Sensing Film

Innovation 5: A Self-Adhesive, Non-Invasive Human Motion Monitoring Solution

IV. Existing Process Challenges and Corresponding Solutions for Overcoming Them

Challenge 1: Medical PU bandages exhibit extremely poor heat resistance; conventional high-temperature sintering causes them to melt and become scrap.

Challenge 2: Screen-printed and inkjet‑printed lines are rough, and they are highly prone to breakage and open circuits under significant stretching.

Challenge 3: Conventional printing films exhibit poor adhesion to the textured surface of embossed bandages, resulting in peeling upon water washing and stretching.

Challenge 4: Lack of standardized process parameters makes it difficult to rapidly match sintering conditions for different types of coatings.

Challenge 5: High-end flexible electronic films are expensive, preventing their widespread consumer adoption as disposable products.

V. Future Diversified Industrial Application Scenarios

1. Home-based rehabilitation monitoring sensor patch

2. Mass-market wearable disposable sensor dressings

3. Simple Monitoring of Children’s Physical Development

4. Daily Activity Monitoring for Chronic Diseases in Older Adults

5. Rapid Development of Low-Cost Flexible Sensor Prototypes in the Laboratory

Figure 1: The schematic illustrates the fabrication process for silver metallic conductive traces used in circuits, which are printed onto a bandage substrate and subsequently sintered using laser irradiation. The inset further details the necking process, during which silver nanoparticles aggregate into clusters, enabling the formation of a continuous thin film.

Figure 2: The schematic illustrates the laser sintering process of printed silver nanoparticles and the swelling phenomenon caused by the decomposition of organic additives. (a) A freshly printed, unsintered silver nanoparticle film; (b) a sintered metallic film formed under the first laser pulse; (c) swelling of the metallic film due to trapped gas.

Figure 3: (a) Film thickness and (b) resistance variation curves of silver films printed by aerosol jet deposition on the surface of a bandage under different numbers of printing passes; also shown are plots illustrating how the sheet resistance of the printed film varies with (c) laser scanning speed and (d) laser energy.

Figure 4: Scanning electron microscope (SEM) images show the surface topography of (a) the bandage substrate, (b) the aerosol-jet-printed silver film, and (c) the laser-sintered silver film. The micrographs illustrate the morphological evolution of the laser-sintered silver film at different laser scanning speeds: (d) 10 mm·s⁻¹, (e) 50 mm·s⁻¹, (f) 90 mm·s⁻¹, and (g) 130 mm·s⁻¹.

Figure 5: (a) TGA analysis; (b) Tensile test conducted to investigate the stretchability of the bandage substrate; (c) FTIR spectrum of the unsintered silver nanoparticle film; (d) XRD pattern of the laser-sintered silver nanoparticle film.

Figure 6: (a) Schematic of an strain sensor fabricated via aerosol jet printing on a bandage substrate; (b) Corresponding optical image of the printed silver nanoparticle conductive pathways. The sensor exhibits exceptional flexibility, enabling conformal coverage: it can bend to accommodate (c) a rod with a small radius and (d) the human wrist; (e) the sensor maintains normal functionality even under torsional–stretching deformation; (f) response curves of the functional strain gauge during elbow motion; (g) plot of impedance characteristics as a function of bending radius, used to determine the design margin of this strain sensor.

Figure 7: (a) Cyclic testing results of the aerosol-jet-printed strain sensor (700 cycles in total); (b) Corresponding scanning electron microscope (SEM) images showing cracks that developed in the printed silver film after 700 cycles; (c) Results from finite element method (FEM) simulations: on the left, the stress distribution within the printed strain gauge; on the right, the deformation of the substrate under 100% and 150% strain.