Techniques for Molding Plastic Over a TLSO Foam Model
May 2021 Issue
The orthotics department at The Ottawa Hospital Rehabilitation Centre has been using a 3D scanner and modification software to scan scoliosis patients. We have been experimenting with the best practice for molding polypro plastic over the foam models for fabrication of TLSOs. I recently put the question of what techniques other facilities have tried on the OANDP-L listserv and added the responses to our experimentations.
The responses from practitioners working specifically with TLSO foam molds could be generalized as follows:
Layup of two layers of Tubifast, which we wet, and then wring out as much excess moisture as possible, then two layers of thin nylon sprayed with silicon. Plastic is then molded directly over this. Nil issues with shrinkage or nylon sticking and a smooth finish. Bleed the suction off to 20psi on larger models/thicker plastics after a vacuum seal is gained.
One nylon stocking over the carving (dry), then two damp Ottobock cotton stockinettes (623T1) This is the only stockinette that we have found that works well. Then one FeatherStretch (dry). Let the moisture leave the cotton stockinette until it is just damp to the touch, never wet. Pull your plastic, get a good vacuum, and as soon as the plastic starts to change color (cool), turn off the vacuum and remove the molded brace from the vacuum tube. Leave it overnight and then cut off as normal.
Put a thin coating of plaster over the foam model, buff this smooth, put two layers of thin stockinette over the cast and pull 1/8-inch copoly over this as our definitive brace.
In our department we have had success with our own method of wrapping the model in cling wrap, applying one layer of FeatherStretch, then molding 3mm polypro to seal the model. Next, we cut off the top and bottom ends of the plastic, apply one layer of FeatherStretch, and mold the definitive brace. Both layers of plastic are cut off the model at the same time and the edges finished before separating the two layers. Don't cut any windows in the brace until both layers of plastic are separated.
Another of our attempts came as close as we got to one of the listserv responses. We used two wet Accu-Cast layers over the foam model, and then two dry FeatherStretch layers. The 4mm polypro was heated and maintained at 200 degrees C (390 degrees F). Once the plastic was molded, it was wrapped in towels to slow the cooling process. The difference in our method was that we used Accu-Cast instead of Tubifast or Ottobock stockinettes, because we didn't have those kinds of stockinettes. The inner surface finish was acceptable, but not as smooth as our first method.
We have been using our method of molding a 3mm polypro spacer over the model since it reliably provides the best inner surface finish, but it does waste more material.
Through this experience we have learned that there are many methods for molding plastic over foam, and each facility develops or uses the method that works best for them. I hope this article has been helpful in choosing the most effective method for your circumstances.
Rajiv Kalsi, CO(c), practices at The Ottawa Hospital Rehabilitation Centre, Canada. To see a chart of the TLSO fabrication methods and results, he can be contacted at email@example.com.