Reticulated polyurethane foam has been a workhorse for a range of medical tasks because of its good tensile and elongation properties. “Its tear resistance, for example, allows fabricating it into almost any configuration by shaping, stitching, cementing, and other techniques,” says Thomas Myers, an engineer and national sales manager for Crest Foam Industries Inc., Moonachie, N.J. (crestfoam.com). “The foam works well in medical devices because it can carry additives that improve its antimicrobial performance.”

The foam is a thin membrane of polyurethane encapsulating a network of open cells. “Reticulation, a proprietary process that uses heat and pressure, removes the membranes for a completely open-pore foam with a skeletal structure through which fluids and gasses easily pass. The foam can be made with pore sizes ranging from 4 to 100 pores/in., void volumes of up to 98%, and surface areas up to 2,000 ft²/ft³. Pore size can be precisely governed for permeability control and design flexibility, as well as an aesthetic appearance when needed,” adds Myers.

“The foam's characteristics work well in medical tasks involving filtration, absorption, wiping, and padding. Using it as a cushion that breathes makes slings and braces more comfortable. And the foam can be washed. But those characteristics are almost common knowledge,” says Myers. What designers might not know about it makes it more interesting. For instance:

• Manipulating the foam changes its properties. For instance, compressing it improves its nonlinting filtration qualities and imparts a circuitous flow path with more impingement surfaces to trap particulates. Compressing the foam also improves its breathability, wicking, capillary action, and strength. Reticulated felted (compressed) foam is used in blood filters for analysis and research applications. The felted foam comes in densities from 3 to 20 lb/ft³. Higher densities filter out smaller particles.

• Reticulated foam can be coated to break bubbles in blood caused by oxygenation. “Heart-lung machines, for example, use the material to aid in oxygenation. A machine froths the blood, channels it through the center of a reticulated foam pocket, then forces it through the foam cells. A surface coating applied by the machine manufacturer to the foam coalesces the froth back into a liquid,” he says.

• Reticulated foam filters with fine pores are used in nebulizers, ventilators, oxygen concentrators, and air compressors as a moisture evaporative medium and filter. Compressed reticulated-foam felt has smaller pore sizes for finer filtration.

• Reticulated foams protect surgical instruments several ways. Before steam sterilization, each instrument is individually placed in a reticulated-foam bag which lets steam penetrate while preventing instruments from contacting each other. In addition, the hydrophobic foam wicks liquids away from the instruments.

• The foam can be impregnated with several useful liquids. For instance, impregnating EKG pads made of a fine-pore reticulated foam with a conductive gel removes a work step for busy health care personnel. The gel improves electrical contact with the patient's skin.

Reticulated and non-reticulated foams are used as hand-scrub sponges by surgeons. The sponges can be filled with a steroid soap or used separately with traditional soap.

Fine-cell reticulated foam has also been used to fashion artificial legs. The foam is contoured to the shape of a leg and hollowed out. The load-bearing prosthesis device is then inserted, and the foam is covered with a stocking or washable flesh-colored film.