Biodegradable scaffold may spur wound healing

From left, Scott Guelcher, Jeffrey Davidson, Christopher Nelson and Craig Duvall showed that an enzyme-blocking molecule released by a biodegradable scaffold can enhance wound healing in a mouse model. (photo by Susan Urmy)

Biomedical and chemical engineers at Vanderbilt University, working with a pathologist, have constructed a sponge-like, biodegradable tissue “scaffold” that releases an enzyme-blocking molecule to indirectly activate endogenous pathways and enhance tissue regeneration and wound healing.

If further animal studies confirm the initial findings, the drug-containing scaffold could provide a new approach to healing chronic wounds, which afflict millions of patients with diabetes and other diseases and cost the U.S. health care system more than $25 billion a year, according to one estimate.

Small interfering ribonucleic acids (siRNAs) can block translation of messenger RNA into proteins, including enzymes that regulate the activity of transcription factors, as was done in this work. One of the biggest challenges is delivery — getting siRNA into the cell.

In their report, posted online Dec. 16 by the journal Advanced Materials, the researchers demonstrate they did this in a mouse model by “packaging” the siRNA in protective nanoparticles and embedding the particles in a porous polyester urethane scaffold.

The study was supported by National Institutes of Health (NIH) grants EB021750 and AR056138.

“This innovative approach and effective method for local siRNA delivery could have wide applications including diabetic wound healing, a significant and growing problem across the globe,” said Christine Kelley, division director in the National Institute of Biomedical Imaging and Bioengineering, part of the NIH.

The study was led by Craig Duvall, assistant professor of biomedical engineering, and biomedical engineering graduate student Christopher Nelson using scaffolding developed by Scott Guelcher, associate professor of chemical and biomolecular engineering.

The nanoparticles protected the siRNA from degradation, which would destroy its activity, and were optimized to ferry the siRNA into the correct intracellular compartment where its activity occurs. The scaffold, inserted into the wound, allowed sustained and “tunable” release of the siRNA nanoparticles for up to a month.

In this case, the siRNA blocked translation of an enzyme called PHD2 (prolyl hydroxylase domain 2), which inhibits the pro-angiogenic transcription factor Hif1-alpha (hypoxia inducible factor 1-alpha).

Hif1-alpha serves as an “alarm bell” for low oxygen, and triggers the expression of factors that spur the growth of blood vessels and can help heal the wound. That’s what the researchers showed – a three-fold increase in vascular volume in 33 days.

“These data convincingly demonstrate the regenerative potential of this platform, as formation of robust, mature vessels is one of the primary challenges of tissue regeneration,” they concluded.

As many as a quarter of people with diabetes will develop a diabetic foot ulcer, and a fifth of them will ultimately lose their limb as a result, said Jeffrey Davidson, professor of pathology, microbiology and immunology, who contributed to the study.

“The typical diabetic patient would be very pleased if you could close that persistent wound, prevent the infection and avoid amputation,” Davidson said. “The attractiveness of siRNAs as drugs is that they are very precise. They hit one very specific gene target.”

While studies in humans are at least five years away, Duvall said their “upstream” approach of manipulating transcription factor activity allows “a better orchestrated and holistic response” that could be applied to other challenges, such as generation of new cardiac tissue damaged by heart attack.

Other contributors to the paper were Arnold Kim, Elizabeth Adolph, Mukesh Gupta, Fang Yu and Kyle Hocking.