Bioresorbable polymers push new boundaries

Available for more than 40 years, bioresorbable polymers remain a focus of research in industry and academia, with some potentially groundbreaking developments in the pipeline. 

C.C. Chu, the Rebecca Q. Morgan '60 Professor at Cornell's College of Human Ecology, and Michiel Van Alst, director new business development and marketing at Purac Biomaterials, revealed some of the latest research at the Bioresorbable Polymer workshop held in advance of the recently completed MedTech Polymers Conference (Sept. 10-12; Hyatt Regency O'Hare; Chicago).

A new polymer family
Chu, who noted that bioresorbable polymers have been available since the 1970's, has been working with the unique materials at Cornell since 1978. Traditional absorbable polyesters are based on five different building blocks, Chu said, adding that advantages of the current materials include an established track record, stable quality, and reproducibility. One problem area, however, is in storage due to bulk hydrolytic degradation mode.

Chu's research team has been investigating family of amino acid-based polymeric biomaterials called polyester amides (PEA). Use an amino acid and a fatty diacid, the research team has uncovered at least 32,000 different combinations that allow them to custom design materials. The results display a broad range of characteristics, with polymers that go from hydrophilic to hydrophobic; have glass transition temperatures from 11 to 109°C; and exhibit semicrystalline to amorphous morphologies.

One material is currently being trialed as a coating for a drug eluting stent, and thus far shows a reduced inflammation response that could ultimately promote more natural healing. The coating is being trialed in New Zealand at this time, as part of a two-year international human trial.

Chu's goal in part is to be able to replace absorbable polyesters, which have been in use since the 1970's. Chu believes the technology is there biologically, but needs to get there mechanically.

In other work, Chu discussed a protein that would serve a dual purpose, acting as the delivery device and the drug. The technology has a patent would result in a product where the drug is the delivery vehicle.

Better bone healing through bioresorbables
Michiel van Alst, whose company produces bioresorbable polymers, offered attendees a brief history of the material, noting that its been available for 40 years as a wound closure technology applied in sutures, with 30 years in orthopedics, 25 years in controlled drug delivery, and a presence in cardio for 15 years. Within orthopedics, van Alst discussed a unique opportunity for specialized bioresorbable polymers.

Since metals are far stronger than bone, they don't promote bone healing when used in orthopedic applications. In fact, van Alst described how the bone can even get weaker, since the metal takes over the load and the tissue is not stimulated to grow, resulting in what's called stress healing.

"The solution is to combine a polymer with a ceramic," van Alst explained, for a composite that's stronger than bone, but not as strong as metal, and will break down over time, weakening as the bone strengthens.

To that end, Purac acquired FiberLive in August, a company that manufactures a silica-fiber reinforced composite. Bioglass fiber has a covalent bond with a coupling agent surface modifier, which has a covalent bond with a compatibilizer, which has a physical bond with a the polymer matrix. "The product is fully resorbable but stronger than bone," van Alst said. In vitro studies showed "no adverse results at all, so far so good."

In a release following the acquisition, Purac Managing Director Menno Lammers called the FiberLive technology a "game changer" for his company. "The FiberLive technology is the strongest fully resorbable material available for human implants, with strength up to 6 times higher than cortical bone, comparable to metal."