Splint Mechanics

Any voluntary flexion of the finger lengthens the actuators. Each of them offers a counteracting force, whose modulus F is the sum of a passive component (elastic recovery) and an active component (electrically induced). Simple calculations adopting a linear elastic model for the elastomer (in the hypothesis of sufficiently small strains, e.g. up to 10%), lead to the following total force generated by the iV parallel actuators  

The mechanical comphance, C, of the considered system can be defined as coincident with that of the N parallel actuators, that is the ratio between the actuator lengthening and the voltage dependent applied force  

The aim of this chapter is to show how C can be electrically modulated, for any given L — Lo, through a variation of F according to a regulation of the driving voltage V. 

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The S. and C. composition varies, according to whether it it to be used for paralfined or sulphured splints, or for waxed threids. The ordinary composition is as follows —6 parts of phosphorus sesquisulj de, 34 parts of potassium chlorate, 6 parts of tine oxide (zinc white), 6 parts of red ochre, 6 parts of powdered glass, 6 parts of glue, and 34 parts of water. It is easy, by manipulation, to make these matches either more or less inflammable. The mechanical processes are much the tame as in the manufacture of phosphorous matches. 

The polymer can be spun into an elastic yam of very fine denier. It is also claimed to exhibit good mechanical properties for molding and compares favorably with commercial polyesters and nylons. Also, polycaprolactone was reported to be used in some medical applications in biodegradable surgical sutures and postoperative support pins and splints. Similar uses are also found for two other polyesters, poly (lactic acid) and poly(glycolic acid). The two polymers form from their cyclic dimers by cationic ring-opening polymerizations with the aid of Lewis acids ... 

Undisplaced fractures can be treated with a period of splinting in a cylinder cast or brace. However, as with all intraarticular fractures, any displaced patellar fracture requires open reduction and internal fixation. Displacement of more than 3 mm is not acceptable and may disrupt the extensor mechanism (Sponseller and Beaty 1996). 

To obtain a simple analytical description of the basic mechanics (in static condition) that are behind this application, consider a splint equipped with N parallel actuators (where N has to be defined according to the problem constraints, as specified in the following). Figure 24.6 presents a schematization of the system, by showing a rotation a of a finger around an axis crossing a fulcrum O. 

Bonnaire, F. (1994). Mechanical dynamic ankle passive motion for physical prevention of thrombosis changes in hemodynamics in the lower pressure system with new dynamic splints. 97 366-71. 

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