# Medical Devices for Tremor Suppression: Current Status and Future Directions
## 4 Wearable Orthoses
### Semi-Active Suppression  
Several semi-active orthoses utilize magnetorheological (MR) fluids as a strategy to provide tremor suppression. MR fluids consist of magnetizable, microscopic particles dispersed in oil or water. Upon encountering a magnetic field, these particles experience attractive force, and the viscosity of the MR fluids increases, opposing the existing flow. This rheological property has been exploited in tremor suppression orthoses by varying magnetic field intensities to tune the resistance force for tremor suppression [106].  
The Double Viscous Beam (DVB) orthosis, positioned on the dorsal surface of the forearm, consists of a chamber of MR fluids and two shear plates to make up a passive actuator, applying mechanical loads for tremor suppression [107]. Compared to the previous approach [88], the DVB orthosis has an improved responsiveness to the viscous resistance as a result of the increased shear strength. This orthosis is coupled to a sensor and a controller to optimize the actuation performance.  
[PERSON] and colleagues developed a wearable orthosis that incorporated four MR dampers for the wrist flexion/extension and abduction/adduction, the elbow flexion/extension, and the forearm pronation/supination [108; 109; 110]. An estimation algorithm for tremor frequency and a controller were used to measure the amount of resistance force needed to counteract tremulous movements. The resistance force generated by the MR dampers depends on a piston-coil design.  
More recently, the MR damper-based soft exoskeleton for the tremor suppression (SETS) system was proposed to suppress tremor in the wrist [112]. Unlike previously designed semi-active orthoses, the SETS system equips a controllable flexible semi-active actuator that dynamically adapts to the motions of the wrist joint, providing tremor suppression in the wrist flexion/extension, abduction/adduction, rotation. This device also integrates passive suppression with two hyper-elastic blades, which suppress tremor in the wrist supination/pronation. The SETS system demonstrates potential clinical utility with its compatibility with the human wrist, real-time tunability based on tremor frequency, and lightweight design.  
The carbon fiber-based, lightweight orthosis developed by [PERSON] and [PERSON] is magnetically activated by an electromagnetic brake (EB) [113]. When the tremor frequency and joint angular displacement are detected by a sensor and potentiometer, respectively, a pulse width modulation signal is sent from the controller to produce a magnetic field, exciting the EB. In turn, the EB actuates the orthosis to generate a resistive force for tremor suppression. In comparison to electric motors such as the DC motor, EBs are capable of producing a higher force while consuming less power. In three healthy participants with simulated tremor motions, the use of the EB-based orthosis demonstrated an 88% tremor suppression [113].  
Apart from magnetically driven semi-active orthoses, [PERSON] and [PERSON] designed a pneumatically controlled hand cuff [114]. Similarly, this device is built along with an accelerometer that sends tremor frequency data to a controller. When the threshold is met, an air pump inflates the hand cuff, yielding a resistance force in a reciprocating, linear motion to suppress the tremor. Inflation and deflation of the hand cuff are enabled by two separate valves. The limited efficacy of this approach was observed in one patient with ET who experienced a 30% tremor suppression [114].