Computer Controlled Rotational Moulding of liquid polymers for the manufacturing of elastomeric prosthetic interface liners.

Interface Liners play an important role in the comfort and health for prosthetic leg users. They fit over the residual limb and go between the limb and the socket (the socket is the shell that encases the limb and connects the user to the prosthesis. The liner is a protective cover made of a flexible, cushioning material. (typically silicone, polyurethane or co-polymer) Worn over the residual limb, it reduces movement and chafing between the skin and the socket. Liners are designed with specific characteristics to work with different suspension systems.



Current manufacturing methods utilise a cavity moulding technique where liquid not polymerised resin is gravity fed or pressure injected in a fixed volume cavity. The established liner manufacturers offer a considerable liner range with different sizes to accommodate for the diversity within the western amputee population. After curing of the liquid material, the moulds are separated and the product removed from the cavity. This process has a high quality consistency but the manufacturing of moulds is complex and expensive and therefore driving up the product costs. In addition, multiple cavities are needed when more than one material behaviour is required such as hard and soft areas.



An exciting and innovative manufacturing technique is the liquid rotational moulding process aiming at using standard injection-moulding polymer grades normally used in the manufacturing of interface liners. In this process, the 2 component polymer is injected into a single mould rotating around two axes. Rotational moulding in two axes has the advantage of producing hollow products. Previously, the inherent difficulty was in the production of objects with uniform thickness since the speed of the two primary axes are fixed and cannot be varied independently to take into account the changes in material properties such as its density and viscosity. With the advent of computers, it is now possible to control the thickness of the object accurately. This is made possible by creating an intelligent software which takes in the viscosity and density time variation of the polymer and using the flat plate withdrawal theory, computes the new speed for each axis. The relationship between rotational moulding parameters and polymeric material properties for a room temperature vulcanisation (RTV) silicone rubber system to produce liners is the focus of this project. In addition,

the single rotational mould approach will deliver, beside, off the shelf products a truly personalised capability for the manufacturing of bespoke multi material/behavioural liners.

The CDT students will help create solutions for amputees and people with debilitating conditions such as stroke and diabetes, reducing mortality and enabling them to live more satisfying, productive and fulfilling lives. These solutions, co-created with industry and people living with disabilities, will have direct economic and societal benefits. The principal beneficiaries are industry, P&O service delivery, people who need P&O devices, and society in general.
Industry
The novel methods, devices and processes co-created with users and industry will have a direct economic value to our industry partners (by the creation of IP, new products, and improved industry and academic links). Our CDT graduates will be the natural potential employees of our industry partners and for companies in the wider healthcare technology sector. This will help address the identified critical skills need and shortage leading to improvement in the UK's competitiveness in this rapidly developing and growing global market. The CDT outcomes will help UK businesses spread risk (because new developments are well founded) and more confidently enter new markets with highly skilled employees (CDT graduates).

P&O service delivery
Doctoral engineering graduates with clinical knowledge are needed to improve the deployment of advanced technologies in practice. Our main UK industry partner, Blatchford, stated: "As technology develops it will become easier for the end-user (the patient), but the providers (the clinicians) are going to need to have a higher level of engineering training, ideally to PhD level". The British Association of Prosthetists and Orthotists estimates that no more than ten practising P&O clinicians have a PhD in the UK. Long-term P&O clinical academic leadership will be substantially improved by the CDT supporting a select number of clinically qualified P&O professionals to gain doctorates.

Users
The innovation of devices, use of device and patient monitoring, and innovation approaches in LMIC should not only lead to improved care but also lower healthcare costs. Diabetes UK estimates that the total healthcare expenditure related to foot ulceration and amputation in diabetes was £1billion (2014-15), with 2/3 of this related to foot ulceration. Small innovations could lead to large cost savings if targeted at the right aspects of care (e.g. earlier adoption, and reducing device abandonment).
An ability to work is fundamental to a person's place in society and their sense of purpose and has a significant societal impact in all territories. This is perhaps greatest in LMIC where attitudes towards disability may still be maturing, and appropriate social care infrastructure is not always in place. In these cases, an ability to work is essential for survival.
Improved design approaches will impact on all users regardless of context, since the device solutions will better match local and individual user needs. Addressing issues related to prosthetic/orthotic device abandonment (e.g. cosmesis) and improved adherence should also lead to greater social participation. Improved device solutions will shift focus from what users "cannot do" to what they now "can do", and help progress attitudes towards acceptance of disability.
Societal
The majority of the global P&O users are of working age, and a key economic impact will be keeping users in work. The average age at amputation due to diabetes is just 52 in the USA but much younger in countries with less well-developed health care and trauma services (e.g. 38 in Iran). Diabetes UK reports that 35-50% of people are of working age at diagnosis and that there are around 70,000 foot ulcers in the UK, precursors to amputation. There is a similar concern for stroke survivors around a quarter of whom are of working age and are 2-3 times more likely to be out of work after eight years.