3D-printed hand exoskeletons enhance rehabilitation

Hand mobility is often impaired after accidents, strokes, or congenital conditions. Exoskeletons, designed as supportive external frameworks, offer assistance by guiding movements of the wrist and fingers. For successful rehabilitation, the devices must be light, compact, and individually adapted - otherwise, they risk becoming impractical for everyday use.

Fraunhofer IWU uses parametric CAD modeling and selective laser sintering (SLS) in 3D printing to create hand exoskeletons tailored to patients. A digital 3D scan captures the hand’s unique shape and proportions, ensuring precise fit. This approach allows:

• accurate reproduction of hand anatomy,
• flexibility for future adjustments,
• efficient production of patient-specific devices.

In addition to anatomical fit, the drive system is critical. Grip strength varies widely between patients, especially children and female patients. A heavy device would place unnecessary strain on users.

Alina Carabello, PhD candidate at Fraunhofer IWU and research associate at Chemnitz University of Technology, has designed a drive system that combines a bidirectional stepper motor with shape memory alloy (SMA) wires. The concept uses two artificial tendons that the motor precisely controls to enable both flexion and extension of the hand and fingers. Through the contraction and relaxation of the SMA wires, the system achieves finely graded and safe movement patterns.

The mechanism integrates gears, levers, and SMA wires. When current passes through an SMA wire, it contracts, driving the gear system to flex or extend the fingers. On cooling, the wire returns to its original length, supported by springs or an opposing SMA wire. This creates repeatable and smooth motion sequences that ensure both precision and comfort.

Fraunhofer IWU emphasizes the importance of individualized solutions in medical technology. Standardized assistive devices often fail to account for patient differences in size, weight, age, or physical condition. The hand exoskeleton aims to address these gaps by providing tailored therapy for tendon injuries, stroke rehabilitation, and paralysis treatment.

Therapists often face time constraints, limiting how frequently exercises can be supervised. With the Fraunhofer IWU exoskeleton, patients can train more independently, ensuring continuous movement therapy while reducing the workload of healthcare professionals.

COMPAMED-tradefair.com; Source: Fraunhofer IWU