Application of PDMS in Robotic Electronic Skin

2026/02/27 0

I. Characteristics of Conductive Films and Adaptability to Electronic Skin

Conductive films with a resistance of 100–200 kΩ fall into the medium-resistance category, whose core advantage lies in the balance between resistance sensitivity and stability:

Compared with low-resistance conductive films (close to 0 kΩ), films in this range show a more significant response to minor deformations, meeting the precise sensing requirements of electronic skin for physical stimuli such as pressure and stretching (based on the piezoresistive effect, where the relative resistance change is linearly related to strain).

In contrast to high-resistance materials (>500 kΩ), they feature lower signal transmission loss and stronger anti-interference capability, minimizing the impact of ambient humidity and temperature on sensing accuracy, making them especially suitable for long-term wearable applications.

In terms of material compatibility, conductive films within this resistance range can be fabricated via PDMS membrane modification, achieving both flexibility and biocompatibility with no irritation upon contact with human skin.

II. Core Preparation Processes and Technical Key Points

The key to realizing conductive films of 100–200 kΩ is the precise control of conductive network density. Mainstream processes include:

Laser-Induced Vapor Deposition

Using copper-containing nanomaterials (e.g., copper oxide nanoparticles, copper hydroxide) and a mixed gas atmosphere (reducing gas + inert gas + carbon-source gas), graphene-encapsulated copper conductive particles are generated under laser irradiation and deposited into a conductive film via gas-jet spraying.

By adjusting laser power and gas ratio, the packing density of conductive particles can be accurately controlled to tune the resistance to 100–200 kΩ, with excellent conductivity uniformity (no agglomeration).

Low-Temperature Solution Process

Silver nanowires (AgNWs) or carbon nanotubes (CNTs) serve as conductive fillers dispersed in a polymer solution, coated onto flexible substrates via spin-coating, spray-coating, etc., and dried at 60–100 °C to form a conductive network.

By controlling filler concentration (e.g., AgNWs at 0.5–1.2 mg/mL), the target resistance range can be stably obtained. This method features low cost and suitability for large-scale production; the relative resistance change remains < 5% after 1000 bending cycles.

Composite Conductive Hydrogel Method

Conductive particles such as carbon black (CB) and reduced graphene oxide (rGO) are dispersed in a hydrogel matrix, and continuous conductive pathways are constructed by adjusting the particle loading (5%–10%).

Such conductive films combine adhesiveness and flexibility, with resistance precisely controllable at 150–200 kΩ, ideal for skin-adherent health-monitoring sensors.

III. Typical Application Scenarios and Technical Breakthroughs

1. Flexible Pressure-Sensing Electronic Skin

Applications: Tactile feedback for humanoid robots, smart prosthetics, wearable health devices (e.g., sleep monitoring mats, plantar pressure analysis insoles).

Technical advantages:

Conductive films in this resistance range enable a pressure sensing span of 0.0005–40 kPa, with a gauge factor (GF) of 10–50 and fast response time, allowing accurate recognition of varying pressure levels such as fingertip pressing and limb contact.

For example, electronic skin based on a CNT–TPU composite conductive film maintains stable performance after 11,000 pressing cycles, with resistance fluctuation < 3%.

Innovation direction:

Integration with interlocked micro-dome arrays can further enhance sensitivity (e.g., Sₚ = 184.82 kPa⁻¹), suitable for fine-operation feedback in minimally invasive surgical robots.

2. Human Health Monitoring Systems

Respiration monitoring:

Ultra-thin conductive films (near 0 μm thickness) of 100–200 kΩ are integrated into chest-mounted sensors. Resistance changes caused by thoracic expansion during respiration enable real-time monitoring of respiratory rate and depth, with clinical applications in diagnosing sleep apnea syndrome and monitoring duration exceeding 6.5 hours.
ECG signal acquisition:

Tight adhesion between conductive films and skin captures weak surface electrocardiogram signals. The resistance range matches the input impedance of signal-acquisition circuits, supporting wireless transmission (>20 m). Hydrogel-based conductive films offer an adhesion strength of 9.9 kPa, resisting detachment during movement.

3. VR/AR Human–Computer Interaction

Flexible tactile gloves based on these conductive films detect resistance changes induced by finger bending and grasping, transmitting gesture signals to VR devices. Combined with electromagnetic actuators, they provide tactile feedback at a low power consumption of only 1.75 mW, enabling users to perceive the shape and hardness of virtual objects.

Transparent conductive films (transmittance >85%) can be integrated into AR spectacle lenses for simultaneous touch control and biosignal acquisition, with stable resistance ensuring signal consistency during long-term use.

IV. Technical Challenges and Future Prospects

Currently, 100–200 kΩ conductive films for electronic skin face two major challenges:

Environmental stability:

High-humidity environments (e.g., sweating, showering) may cause moisture absorption and swelling, leading to resistance drift of 10%–15%. Optimization via fluoride encapsulation or hydrophobic coatings is required.
Large-scale uniformity:

During large-area fabrication (>100 cm²), uneven distribution of conductive particles can result in resistance deviation of ±20%. Improved coating uniformity control in roll-to-roll processing is needed.

Future development directions:

Development of self-healing conductive films: Introduce dynamic covalent bonds or hydrogen bonds to achieve autonomous resistance recovery after mechanical damage (recovery rate >90%).
Multi-sensing integration: Combine pressure, temperature, and humidity sensing in a single 100–200 kΩ conductive film, distinguishing multiple signals via different resistance responses.
Low-power optimization: Integrate flexible integrated circuits to reduce power consumption of signal-acquisition circuits (mW level) and extend the battery life of wearable devices.