Saturday, September 17, 2016

Polyurethane in Prosthesis

Polyurethane in Prosthesis

Polyurethane has been finding wide usage in many of biomedical and therapeutic applications. One such application is prosthesis. Prosthesis means artificial replacement for a missing limb. Most widely used prosthesis for rehabilitation includes feet, legs, arms and hands.  Others include dental , facial and heart valve etc.  Correctly made prosthesis has proven a major enabler to many people globally. What could have been better fitting example than the recently held Paralympic events at Rio? In fact some of the Olympic records were beaten at Paralympic events this year.
Like many Indians, my early introduction to prosthesis was to famous Jaipur foot. As the name suggests these are below knee prosthetic which before the era of globalization has helped in rehabilitation of many people including soldiers, accident victims and polio patients. Low cost and custom-made products have been two most attractive features of Jaipur Foot. Over the years technological developments have aided the transformation of earlier wood-rubber based products to combination of metals with polyethylene, polyurethane.  

Various forms of Jaipur Foot []

Light weight, strength, flexibility, non-abrasiveness, durability, antimicrobial properties and soft to tissues – these are some of the common desirable properties of the prosthetic. However depending upon the final application, multiple complexities get added.  Further each prosthetics has to be designed as per the life style, physical characteristics of the individual.  Hence most prosthetics require multiple types of materials for the fabrications. Polymers have become choice of materials for prosthetic application due to properties like high strength, non-corrosive nature, light weight, impact strength, toughness, flexibility etc.  Use of low weight reinforcing fillers has added another dimension to make light weight and stronger part. Carbon fiber has been introduced few years ago due to its strength at very low loadings in the composite form.
In addition to the material development, designing has also evolved tremendously in the prosthetics development. This year, Paralympic participants have used 3D-printed prosthetics. Introduction of better mechanical designs through use of electrical signalling and robotics have improved the functionality of prosthetics in recent years.
Polyurethane has been used in prosthetic applications for its shock absorption capacity to reduce vibrations. Due to its availability in a very soft form, polyurethane has been used along with silicone as a liner material. Polyurethane foam has been used as a cushioning material for its ability to distribute pressure evenly.  

                        Application of polyurethane in prosthetic foot (]

In addition, features like easy fabrication, wear resistance, resilience, high strength to weight ratio, easy to clean, ability to withstand weight of the person without disintegration make polyurethane foam an ideal choice of material in prosthetic.  Other applications include inserts, leg sleeve, grip pads for hand prosthetic, as a matrix in carbon fiber based composite for foot prosthetic, as a elastomer for designing socket and polyurethane adhesive to glue various parts.

Thursday, July 7, 2016

3D Printing

In the series of recent innovation waves ( nanocomposites, graphenes, carbon nanotubes etc) where the whole academic and industry research teams seem to be chasing the same dream materials at the same time, 3D printing has stood up to the challenge of showing commercial success in terms of innovative products albeit it is still in the initial phase of growth.
Decades back , small industrial parts like gaskets, flanges were carved out of the cast rods made of sintered PTFE, PEEK , PEI like materials leading to the waste of materials during processing. 3D printing has changed the scenario where the material is dispensed through the extruder to make parts from very small to large dimensions. The beauty of this technology is you can make any intricate part. Early limitation on traditional materials like PLA, ABS has been given away to introduction of newer materials even of high processing temperatures like PEEK, polyarylamide by additive manufacturers. Recently fiber reinforced materials based on carbon fibers  have been launched by Arevo (  to make stronger parts.
Polyurethane is a relatively new entrant (since 2013) as an additive in 3D printing technology. Both flexible and rigid polyurethane are used for 3D printing to make various products like soft toys, gaskets, parts for robotics, prostheses,running shoes etc. With polyurethane, one can choose materials of desired shore hardness.There have been attempts to fabricate polyurethane foam using 3D printing technology.