Cover Story

Materials

The Importance Of Proper Material Selection In The Medical Device Development Process
(With Special Reference To Thermoplastic Polyurethanes)

Material Selection Process : Manufacturers Now Looking Outside

A company with expertise in material selection will often be able to help a manufacturer with the right selection of materials and processes, as well as help optimize its design to make it more manufacturing friendly, without sacrificing the most critical functional property of the device. It might offer a variety of processes under one roof, advice on material selection.

Material Consideration Often Overlooked In The Design Or Manufacturing Process

In the late 1980s to early 1990s, it was most of the time, compared to the last decade when it has become much less and as industry has become more familiar and comfortable with newer polymers and their versatility. Still about 10 percent to 20 percent of the time OEMs overlook material considerations. There are one or two out of 10 cases where we see a material mismatch, especially from new start-up companies where they have good mechanical or bio engineers but lack material science knowledge or insight.

What If A Company Has Made Material Selection An Afterthought?

Manufacturing issues in terms of bonding or cracking after sterilization.

Depending on economic considerations and long-term cost effectiveness, there can be one of three options: modify the surface with secondary treatments and/or primers, formulate it with more stabilizers or other additives, and/or replace it with a more compatible material.

Significant advances that have been made to thermoplastic polyurethanes in the medical device arena?

Many, with some more visible than others, like :

• Polycarbonate-based soft segment to enhance short-term or initial biostability compared to polyether backbone

• Hydrophilic grades of PUs which have high MVTR and can absorb up to 70 percent by weight, suitable for drug delivery applications

• Combination of silicone and polyurethanes to enhance surface property

• UV cross-linkable polyurethane for non-compliant/compliant combination film properties

• Low set, high elongation, rubber-like thermoplastic urethane for urethane stretch fiber

• Optically clear urethanes

• High flex modulus polyurethanes at >180,000 PSI at RT

• Polyurethane gloves and condoms now commercially available

• Softer TPUs at lower than 80 Shore A hardness

• Specialty additive formulations to make it easier to process and more stable against heat, UV, and hydrolytic degradation

How will thermoplastic polyurethanes evolve in the next few years?

1. Still more rubber-like properties—lower durometer, higher elongation, lower set, yet tough.

2. More work with nanoparticle-filled urethanes.

3. More development in cross-linkable technology and water swellable for drug delivery applications.

4. Better barrier properties and lower permeability of 02, CO2, and N2 gases.

5. Shape-memory polyurethanes with multiple Tg.