The big picture: The bespoke machine makes large models that show the prosthetic in place
Tucked away in a hospital in a leafy city most famous for its cathedral is a small company that is forging ahead in using additive manufacturing technology for medical applications. The company is Replica 3DM, which started out just over two years ago after managing director Matthew Sherry approached Salisbury District Hospital with the idea of setting up an operation that could provide additive manufacturing techniques not just for that location but for the NHS in general.
Within a few months of starting up, the company – which is jointly owned by external parties including Sherry and the hospital – began to push out its services to other NHS Trusts in the South West of England, and is intent on establishing a national presence, he says.
Sherry’s background is in computer science, but he encountered additive techniques in an industrial context and saw their potential for medical applications, so he convinced an orthopaedic surgeon friend to get involved in the venture with him.
The company has just three employees including Sherry, and operates three additive manufacturing machines. The other two employees are technicians who can process computer tomography (CT) data from a patient’s body scan, so that it can be converted into an industry standard format stl file of a body part – usually an area of bone – that can be printed by one of the machines.
The conversion process is fairly straightforward, says Sherry: “There are a number of software packages available to do that.” However, to refine the capabilities of the open-source program used by the company, he has written some bespoke software. The more rigorously the scan data can be processed to isolate the bone from the surrounding soft tissue, the more accurate the final model will be. “It is all about ‘thresholding’,” he says.
The hardware involved comprises two Objet additive machines – an Objet24 and an Objet30 Pro – from system vendor Stratasys plus a third bespoke device built to Sherry’s specification. He says that the Objet machines, which are based on a polyjet technique that is an adaptation of inkjet technology, are easy to use and do not involve a thermal process.
The bespoke device, in contrast, uses an extrusion technique in which a filament of polymer material is heated to around 190ºC. It also features an unusually large bed on which the parts are formed, which allows model dimensions to reach 0.6m in each of the X, Y and Z axes, says Sherry.
The main difference in the way the machines can be applied is in the degree of resolution they can attain, he says. The bespoke machine prints in layers about 100 micrometres thick, whereas the Objet machines can achieve much finer resolutions in the range 14-28μm. So the bespoke machine might be used to make what Sherry terms large “aesthetic models”, where the aim is to give an overall impression of how a prosthetic part might look when fitted. The Objet machine would be used to model just the immediate area to which a part would be fitted, to ensure a first-time perfect fit when surgery is carried out. Modelling a whole skull, for example, on one of the Objet machines would be just too expensive.
The main value of additive manufacturing in a medical context is that it allows surgeons to carry out beforehand what would otherwise be in-theatre procedures, he says. This preparation saves time and therefore money, but also has a therapeutic value in that it minimises the length of time for which a patient needs to be anaesthetised.
The most common body part that the company prints is a cancerous mandible, says Sherry. The surgeon can cut away from the model the parts representing the tumour, leaving an exact representation of the bone ready for fitting a titanium prosthetic plate. A technician can then shape the plate so that it is ready for immediate fitting in the operating theatre as soon as the tumour is removed.
Previously, the surgeon would have had to move between the patient and a workstation, bending the plate bit by bit until the right shape was achieved. In addition, because there is no need to create extra space in which to work at the fitting process, the surgeon can make smaller incisions on the patient – thereby reducing post-operative recovery time.
Although cases will vary, Sherry estimates at least 30 minutes could be shaved off in-theatre time. With operating theatres costing around £60 a minute and the model costing just £180, the potential financial savings are considerable.
Chain reaction: Titanium prosthetics used after tumour removal provide an exact fit
Another procedure that can benefit from additive manufacturing is facial reconstruction. Sherry says the technique helps with planning the operation, and with determining the optimal positioning for the jigs and templates involved. One area of the skull that lends itself to the use of the additive technique is the eye socket, he says. If a socket is damaged, then its counterpart can be scanned and ‘mirrored’ in software to enable the fashioning of a template that will be an exact match.
The technique is catching on, and Replica 3DM is seeing the benefits. In the company’s first 12 months, it made about 100 models, and in the following comparable period 200, says Sherry. But since the summer of this year, output has increased to “two to three models a day”.
The methodology that supports that rate of production is a mix of manual and automated procedures. The actual model build by the machines is a ‘lights out’, overnight procedure, with perhaps three models being made simultaneously on the same machine, says Sherry. He says the technology has proved highly reliable. “We have only had one bad run in two years and that was due to a programming error,” he says.
The manual procedures that follow the automated run involve the removal of ‘support material’ around the model and may require no more than breaking the material off by hand – though a jetwash or sodium hydroxide bath might also be required. A key factor in how much manual work is involved is the geometrical complexity. Something relatively simple such as a mandible might be cleaned up in just 10 minutes, whereas a complex object such as a complete skull might take as much as 30 minutes.
The company is not the first to use additive manufacturing in a medical environment. The technique has been extensively used in, for instance, maxillofacial surgery for at least a decade, and surgeons who operate in that field are familiar with its capabilities.
Nevertheless, there are areas where the technique’s potential seems to be under-appreciated, including orthopaedics and in ear, nose and throat (ENT) surgery. In ENT, one opportunity is the manufacture of nasal septum buttons to plug holes between the adjoining nasal cavities, says Sherry. The conventional approach involves trimming standard units costing about £500 each to fit, whereas using CT data to make a mould on an additive machine would cost about £50, with a small further outlay to enable a technician to use it to make a custom part – a process that takes about 15 minutes, he says.
As for the future, one type of additive manufacture that might increase in the medical field is laser sintering of metal powders to make prostheses directly, says Sherry. Another is the manufacture of models of soft tissue parts. “We have already made an aorta,” he says.
Such plans show the extent to which a technology that made its debut producing prototypes of industrial components is now enhancing surgical procedures –
and helping to improve the subsequent quality of life for the patients involved.
Perfect fit: A cranioplasty infill model is typically used to help plan reconstructive surgery for skull damage