Dr. Hadi Mohammadi

Interview: Dr. Hadi Mohammadi on next generation of prosthetic heart valves, biomaterials, and life-like simulation models  

Dr. Hadi Mohammadi leads the The Heart Valve Performance Laboratory (HVPL) at the University of British Columbia, Okanagan, and is a mechanical (biomedical) engineer with hands-on experience in the design of many engineering structures and medical devices through various projects that he has been involved in over the past few years. Dr. Hadi took time recently to answer questions for Rob Fraser, ViVitro Labs Application Manager.

Please tell us about your current work

Our main focus is on the design and fabrication of the next generation of prosthetic heart valves. We work closely with cardiac surgeons and cardiologists, such as Dr. Guy Fradet and Dr. Frank Halperin, at Kelowna General Hospital’s Cardiothoracic Surgery Program. We are developing biomaterials needed to construct prosthetic valves for both the mitral and aortic positions and have been revolutionizing their mechanical design as applied in both surgical and transcatheter valves for adult and infant sizes.

How is the work going?

The horizon looks promising…

We have developed the Apex Valve (AV) which represents the next generation of bileaflet mechanical heart valves. The proposed design has the potential to be revolutionary in the area of heart valve prostheses, and may replace all conventional mechanical and bioprosthetic valves currently available on the market. The large central opening of the proposed design provides a greatly increased EOA (effective orifice area), making it ideal for miniaturization (<15 mm) and pediatric patients. The design also disperses the forces generated from the opening and closing motions away from the hinges, and onto the housing, reducing the risk of mechanical failure. This is essential for enduring the increased loads anticipated by the faster heart rates associated with children (up to 220 bpm during strenuous activity) in comparison to adults.

Soft Robotic Prosthesis

Soft Robotic Prosthesis

For the first time, we are applying the concept of soft robotics; devices that do not contain any ridged supports, to the design of polymer heart valve prostheses. Soft robots are meant to be devices that are deformable along their entire body. The actuation of these robots occurs with a fluid, either air or a liquid, channeled into specifically designed chambers that produce motion when they are pressurized and depressurized. Using this concept, the opening and closing of the leaflets, the size of the housing, and the effective orifice area of the valve are all related to aortic and ventricular pressures. In the opening phase, the annulus of the valve is forced to expand radially. This valve addresses the major hemodynamic complications linked with particularly small -sized bioprosthetic valves and seems to be vital in the design of the next generation of valves.

We recently developed a novel, one-piece, tricuspid percutaneous valve, consisting of leaflets made entirely from the hydrogel, polyvinyl alcohol (PVA) cryogel, reinforced by bacterial cellulose (BC) natural nanocomposite. This valve is attached to a nitinol basket. One of the significant advantages of this valve is that the entire structure of the valve, including the leaflets, is indeed one-piece. This provides the valve the ability to be temporarily compressed into a small sheath that can be inserted into the chest cavity through a keyhole incision. This property is well suited for the replacement of heart valves by means of closed-chest surgery which is thought to improve patient outcomes.

What are the reactions to this work?

We have industrial partners who are interested in the technology. Angeleno Medical Inc. (US) and Ebbtides Medical Inc. (Canada) along with Mitacs Canada are our main supporters. Nonetheless, we are still in the midst of our journey and great news is yet to come!

What else is happening in your lab?

Another major research program in my lab is the design and development of realistic platforms for the simulation of reconstructive cardiovascular surgeries. It is essential for us to study and develop more lifelike simulation tools for health care students and workers.  Patient outcomes are drastically affected by the level of care they receive from healthcare workers who may not have had realistic training.  It is widely understood that some patients will receive less than adequate care from newer practitioners or poorly trained ones.  The lack of skin/vasculature simulation technology available today is also cited as a reason for poor patient outcomes.  Several studies have proven this void is substantially affecting the level of patient care.

Improve the level of care: It is essential to further explore simulation for healthcare students and workers.  Current materials are not realistic. This forces students and workers to create their own materials in an attempt to mimic human skin and vasculature to practice what they will need to do in real life situations.  This is not ideal and has led to students practicing the placement of needles into the vasculature on each other and themselves.  Some healthcare schools have had to ban such practices from a legal and ethical standpoint.  There is a considerable need to offer a safe and viable solution to students and current healthcare workers.

Reduce healthcare costs through simulation:  Teaching healthcare workers with more advanced and lifelike simulated skin and vasculature will improve their efficiency as they enter into practice.  This efficiency will reduce the cost of healthcare by improving the pace and accuracy of palpating for vasculature, setting IV lines, administering anesthetic, and properly placing cannula for ECMO, just to cite a few examples.  With less adverse events because of better trained practitioners, there will be less hospital time for patients, resulting in a direct savings to the public health care system.

Working in hospitals and operating rooms for over 10 years, we have come to understand these issues.  Our company partner, ebbtides medical, now in its fifth year of operations, has been collaborating with HVPL on this issue for over 5 years now.  Through their proprietary hydrogel product line, we have established an opportunity to address the training challenges faced by healthcare workers.  We are very much into developing lifelike skin and vasculature to assist healthcare students and new practitioners in simulating real life-like simulation models.

Has ViVitro Labs helped you with this work?

I have been working with ViVitro Labs colleagues and friends since I was a PhD student at the University of Western Ontario (Dr. Wankei Wan was my PhD advisor and I learned a lot from him). Our recent in-vitro testing was performed by my good colleague and friend, Lawrence Scotten, the former founder of ViVitro Systems. He performed the tests on his Leonardo apparatus. “ViVitro labs is home for us” is the easiest way that I can say it!

What are your plans for the future?

We are a group of passionate and highly motivated scholars, and we want to make a significant change in the area of heart valve prostheses.

The Apex valve will be fabricated at a scale for pediatric use (<15 mm diameter) for evaluation. The valve will be evaluated at a range of loads simulating the heart of a child. Evaluating the Apex valve at increased loads (up to 220 bpm) will showcase the feasibility of utilizing the valve for pediatric applications. With the increased cyclic loading at the leaflet free edge under pediatric conditions, “continued micro trauma” will be evaluated to determine if new issues arise from this novel design.

Another application of the Apex valve would be towards the first-ever mechanical percutaneous (transcatheter) valve. For patients turned away for open heart surgery due to age, frailty and comorbid factors, a percutaneous valve option is essential, however the valve is hindered with poor performance and longevity after implantation. The durability of percutaneous bioprosthetic heart valves is an area of interest due to the possibility of the leaflet damage during the crimping process, expansion, or non-circular opening of the valve resulting changes to the valve hemodynamics. The Apex valve design could lend itself well to percutaneous application, providing similar hemodynamics to that of a bioprosthetic valve, but with the longevity and durability of an MHV. …the horizon looks promising!

Do you have advice for our readers?

Just one! Great ideas change the world! …and it can be yours!

Read Dr. Hadi Mohammadi’s publications citing ViVitro Labs equipment.

Read about other Cardiovascular Pioneers here.

Images courtesy of HVPL UBC Okanagan 

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