CTS Innovation: The promise of tissue engineering for heart valve replacement and repair

Both technologies rely on the concept of matrix infiltration by autologous cells after implantation in order to create a living mimic of the patient’s own tissues.

CardioCel is a highly treated, bovine pericardium-derived, decellularized collagen matrix. It showed significant resistance to calcification in mitral and pulmonary implants in a juvenile sheep model as reported by Dr. Christian P. Brizard at Royal Children’s Hospital, Melbourne, and his colleagues (J Thorac Cardiovasc Surg. 2014 Dec;148[6]:3194-201). These investigators replaced the posterior leaflet of the mitral valve and one of the pulmonary valve cusps with patches in 10-month-old ewes. They compared the use of CardioCel in six ewes to a control group of four ewes repaired with autologous pericardium that was treated intraoperatively with glutaraldehyde, which is the standard default used at their institution for more than 2 decades as the best material for valve repair in their pediatric patients.

^{Courtesy of JTCVS/American Association for Thoracic Surgery}

In controls ([A] mitral [C] pulmonary), outer layers are made of new collagen I, are much less dense than the patch, and contain collegen III (green). In CardioCel ([B] mitral, [D] pulmonary) outer layers are very dense, thin, and exclusively collagen I.

The primary end points of the study were thickening and calcium content. They found that all animals survived with normal valve echocardiography until sacrifice at 7 months. They reported that the bovine pericardium patches allowed accurate valve repair at both systemic and pulmonary pressure with preserved mechanical properties and more-controlled healing and without calcification as compared with the controls. (Calcification is a known major risk factor for the eventual failure of bioprosthetic valves.) Additionally, the bovine pericardium patched valves showed the in vivo development of dense but thin cellularized outer layers of mature collagen I, compared with the controls, which had outer layers that were much less dense and showed the presence of immature collagen III.

In another case of valvular use of the CardioCel material, at the recent American Association for Thoracic Surgery Mitral Conclave 2015, M. Bonnie Ghosh-Dastidar, Ph.D., and her colleagues from the Royal Brompton Hospital, London, reported on a severely ill patient with significant mitral regurgitation and an infected mitral valve with large vegetations on the anterior leaflets. The infected tissue was resected and a large patch of CardioCel bovine pericardium was used to reconstruct the leaflets. Postoperative assessment showed a competent mitral valve with good area of leaflet coaptation, according to Dr. Ghosh-Dastidar.

In his invited commentary on the animal-model research by Dr. Brizard, Dr. Niv Ad, director of cardiac surgery research at Inova Heart and Vascular Institute, Falls Church, Va., said that despite the promise of the CardioCel patches, there were a number of alternative approaches being investigated. “Other engineered materials currently being study include processes such as lyophilization, which has shown promising results in reducing inflammation. Another proposed approach is the use of decellularized vessels and patches with the promise of normal remodeling and growth, such as extracellular matrix and its potential for tissue regeneration.”

Dr. Ad also stated that, “the key bioengineering challenge is to determine how biologic, structural, and mechanical factors interact and function in vivo. The understanding of these factors will prove critical to the development of a clinically viable tissue-engineered heart valve,” (J Thorac Cardiovasc Surg. 2014 Dec;148[6]:3202-3).

^{Courtesy of JTCVS/American Association for Thoracic Surgery}

Patient with annular decalcification and leaflet repair: A. Decalcification; B. Annular reconstruction with ECM bioscaffold; C. Leaflet reattached and neochordae implanted; D. Completed mitral valve.

An example of the use of extracellular matrix material referred to by Dr. Ad is the CorMatrix ECM, which is an extracellular matrix material derived from porcine small-intestinal submucosa, processed and decellularized.

Dr. Marc W. Gerdisch and his colleagues from the Franciscan St. Francis Heart Center, Indianapolis, reported on the results of treating 19 patients with mitral valve disease using the CorMatrix patch material for partial or subtotal leaflet repair or extension. There were three deaths unrelated to the repair and no instances of perioperative or late stroke. Two patients with a history of cancer and cancer therapy experienced failure of the initial repair, requiring reintervention. However, the other mitral valve repair patients continued to show good valvular function and no calcification on echocardiographic follow-up of 4 days to 48 months (Thorac Cardiovasc Surg. 2014 Oct;148[4]:1370-8).

And in 2015, CorMatrix Cardiovascular announced FDA approval of an investigational device exemption for an early feasibility study of their CorMatrix ECM Tricuspid Heart Valve in up to 15 patients at 5 U.S. centers (NCT02397668). Indications are for the surgical management of tricuspid valve disease not amenable to annuloplasty or repair, including tricuspid valve disease secondary to congenital heart disease in pediatric patients and adult endocarditis patients. The CorMatrix ECM Tricuspid Valve is a flexible, unstented valve acting as a 3‐D scaffold designed to function immediately as a prosthetic, but one constructed to permit native cellular infiltration and remodeling.