Design and direct metal laser sintering of replacement heart valves

Degenerative heart valve disease is a growing problem in the ageing populations of Europe and North America. Further, tens of millions of both young and old people experience valve failure from bacterial infections in low- and middle-income countries such as those in South Asia and Africa.

The current state of the art for the treatment of heart valve disease is rapidly moving towards transcatheter approaches, seeking to deploy replacement valves comprising frames that are laser cut from metallic tubes. However, to develop new valve concepts that can better address existing and emerging challenges globally, alternative manufacturing methods will likely be necessary. In response to this opportunity, we successfully conducted a preliminary pilot study involving additive manufacturing of valve frames using direct metal laser sintering (DMLS). In so doing, we have demonstrated the feasibility of 3D printing these type of thin strut structures.

Now, it is necessary to fundamentally optimise and assess the DMLS manufacturing process for replacement heart valve frames. World-leading facilities will be used for DMLS at both partner sites. A Concept Laser machine has been operated for over three years in the Engineering Design Manufacturing Centre at the University of Southampton and the Italian industry partner, Sisma, which actually manufactures its own high precision DMLS machines which will be used by specialists within the company. Consequently, Sisma will provide the necessary expertise in additive manufacturing, something that will be invaluable for the small, thin features of heart valve frames. Also, the project will significantly benefit from the Mu-Vis Imaging Centre at the University of Southampton in which high resolution scans of the frames will help to determine manufacturing precision, accuracy and quality.

Once the manufacturing process has been optimised, it will be used to manufacture and test two new frame concepts, both made possible by the additive nature of 3D printing. One of the frames will be based on patented intellectual property for a radially layered frame that produces zero change of length during deployment. The second frame will feature a concept that was devised in a Masters project at the University that came to an end in September 2018. This second concept aims to overcome the problems associated with the need to replace a previously deployed prosthetic valve that has started to fail. This can happen when prosthetic leaflets degenerate in similar ways to native valves. Currently, standard replacement valves are used in a procedure know as valve-in-valve which doesn't involve a device specifically designed for such redo procedures.

In addition to these engineering tasks, we have a strong focus on our pathway to impact, particularly in relation to the contrasting needs of heart valve patients in both developed and low- and middle-income countries.

At the end of the project, we will have (i) a detailed understanding of optimal settings for maximum precision, accuracy and structural integrity of metal sintered valve frames and (ii) developed two novel device concepts made possible by additive manufacturing one of which will be specifically designed for treating young patients across all territories of the world.

Heart valve disease in the UK, Europe and North America is characterised by
(i) significant and growing numbers of patients in ageing populations;
(ii) a traditional form of treatment called surgical valve replacement (SVR) involving open heart surgery;
(iii) increasing popularity of transcatheter valve replacement (TVR) methods.

The main type of TVR is transcatheter aortic valve implantation (TAVI). This is used to treat the most common form of degenerative heart valve disease known as aortic stenosis.

Even though TAVI devices are expensive at approximately $32,000, TAVI is experiencing double digit compound annual growth and it is becoming more cost-effective than SVR. There is a growing body of evidence to demonstrate the short and medium-term effectiveness of TAVI, but there is a lack of data for long-term performance such as durability.

In contrast to the developed parts of the world, heart valve disease in low- to middle-income countries is largely due to degeneration of valve leaflets following streptococcal throat infection. This is known as rheumatic heart valve disease (RHVD) and it affects tens of millions of patients. In these low- and middle-income countries
(i) both young and old people are vulnerable to RHVD;
(ii) there is low availability of treatment and cardiology expertise and
(iii) treatment, if available, is unaffordable for most patients.

Against this background, there is an opportunity to couple our inter-disciplinary design expertise, with additive manufacturing capabilities, to address the design challenges associated with emerging needs in
(i) valve-in-valve procedures for failing prosthesis;
(ii) dedicated redo-TAVI to overcome valve-in-valve shortcomings;
(iii) dedicated redo-TVR for the other valves, particularly in the mitral position;
(iv) making TVR devices more affordable and readily available in low- and middle-income countries.

New valve design concepts will also benefit patients who are adversely affected by sub-optimal device characteristics including
(i) length changes, or foreshortening, during deployment ;
(ii) valve distortion following deployment and
(iii) performance failings related to valve leakage, compromised electrical conduction and/or reduced orifice area.

So, the main beneficiaries of the proposed technologies will be the large and growing populations of patients with heart valve disease in both developed and developing parts of the world, the great majority of whom are untreated. Devices are very expensive and would not be affordable in low- and middle-income countries even if TVR procedures could be made more readily available. Most significantly, there is a growing expectation that widening TVR to younger and lower risk patients will generate a need for repeat procedures such as redo-TAVI and, in the longer term, redo-TVR. Dedicated redo-devices will overcome the key failings of current valve-in-valve procedures, particularly related to reduced orifice area, and provide young heart valve patients with greater life expectancy and quality of life.