Plymouth-based medical technology startup Urotronic has raised $20 million in its effort to invent a better way to treat urethral problems.

A joint venture of Hillhouse Capital and Mayo Clinic called HM Ventures led the $20 million strategic funding round to support the continued development of Urotronic's Optilume device.

Urotronic is doing pivotal clinical testing of its balloon-dilation system in the U.S. to treat a narrowed urethra, which makes it difficult or painful to urinate because of a buildup of scar tissue. Such scar tissue can be caused by infections or trauma to the urethra, past medical procedures, sexually transmitted conditions or having surgery on the prostate gland.

The company is also running a clinical trial in the Dominican Republic and Panama looking at treating moderate to severe symptoms of BPH, or benign prostatic hyperplasia, which is an enlargement of the prostate gland that can block the flow of urine. BPH is a fast-growing condition that causes moderate to severe symptoms in about one-third of men by age 60, according to the Mayo Clinic.

Urotronic's Optilume system is similar to the drug-coated medical balloons on the market used in blocked blood vessels. For patients with urethral strictures, the Optilume is inserted into the urethra and precisely inflated to reopen the canal from the bladder. The process of doing so creates tiny cracks in the tissue, which allow an anti-inflammatory drug called paclitaxel to seep deep into the tissue and create a therapeutic effect.

The idea is to create a longer-lasting therapy; conventional treatments are sometimes followed by the need for another procedure. The Optilume treatment can be done in an outpatient medical visit, making it applicable to parts of the world where access to health care is a challenge.

The $20 million raised by Urotronic will be used to expand the company's staff and manufacturing space and to complete the clinical trials to gain regulatory approval to sell the device, a news release on the Series B round says.

"This technology is very disruptive, and the end beneficiary is going to be the patients," said Doug Kohrs, a veteran Twin Cities med-tech entrepreneur who sits on Urotronic's board of directors. "Urotronic has embarked on an approach to treating BPH and strictures that no one else has ever taken."