Wednesday, 23 July 2014
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Orthopaedic stem cell concentrator

Partners: University of Southampton Medical School; Southampton University Hospitals NHS Trust (Southampton General Hospital, Department of Trauma and Orthopaedics) and Smith and Nephew

Stem cells, with their ability to transform into any specialised cell, represent an important potential for medicine. They are at the focus of the emerging field known as regenerative medicine, in which damaged tissues are repaired by the body itself rather than by being patched with grafts of donated or transplanted tissues, or with synthetic materials designed to approach the properties of biological tissue.

It’s a method which is still fraught with difficulties, however, and one of these is obtaining the stem cells in the right condition to maxmise their effectiveness. For example, there is growing evidence that stem cells contained within bone marrow are particularly effective at repairing damaged skeletal tissue, as they are capable of transforming into bone and cartilage tissues. But the samples of bone marrow from which the stem cells are derived — known as aspirate — also contain a large proportion of blood, and the stem cells are most effective when administered in a concentrated or enriched form. The difficulty of obtaining stem cells in this form has held back the development of these techniques, despite their theoretical promise.

Medical equipment manufacturer Smith & Nephew has set out to tackle this problem in collaboration with the University of Southampton and the Southampton University Hospital NHS Trust, developing a small, simple, single-shot device to concentrate bone marrow samples for regenerative surgery. The collaboration with the hospital was vital, explained orthopaedic registrar and research fellow James Smith, who was involved with the project, because it allowed the team to be certain that they developed a device which would provide the correct material under the right conditions — the sterile field of an operating theatre.

concept

Concept sketches for the stem cell concentrator

‘Stem cells can turn into any sort of cell, but bone marrow stem cells are more likely to turn into skeletal tissue,’ Smith said. ‘Working on this kind of problem is the raison d’etre of the Bone and Joint Group at the hospital.’

With the field of regenerative medicine in its infancy, there is relatively little equipment available to enrich stem cell samples. The concentrator devices on the market at the moment are large, bulky machines that work on the same principle as a centrifuge, but their size means that they can’t be used in the operating theatre.

‘That’s a problem for this type of therapy,’ Smith explained. ‘Ideally, you want to remove a sample of bone marrow aspirate, enrich the stem cells, and reimplant them into the patient as part of the same operation, under the same anaesthetic. Some of the people who would benefit from this kind of therapy are elderly, and you want to reduce the risk as much as possible. With these large machines, you have to take the sample outside the sterile area of the theatre and away from the surgeon’s viewpoint to process it; that can take some time.’

Moreover, these machines are expensive — around £10,000 for the device itself, plus extra for consumables for each separate enrichment. ‘It can become very costly.’

The ideal answer would be a compact device which carried out the enrichment quickly, within the operating theatre. ‘In crude terms, what we want is something small, cheap and quick,’ Smith said. ‘And it’s a bonus if it’s disposable as well, so there’s no risk of sample contamination or patient mix-up.’

concept2

Concept design showing some of the features which needed to be incorporated into the device

Smith & Nephew’s team, led by project manager Stephen Curran, developed a device which works using a technology called acoustic wave filtration. The device contains a membrane with a closely-controlled porosity, which is vibrated with a frequency in the acoustic region. The combination of pore size and vibration frequency, combined with reduced pressure on the opposite side of the membrane to the aspirate injection chamber, allows all of the cells in the sample apart from the stem cells to pass through the membrane, retaining the stem cells on the membrane itself. ‘We’re still in the prototype phase at the moment, but we’d expect the production model to produce an enriched sample in about 15 minutes,’ Smith said.

prototype

The final form of the stem cell concentrator is a single-use device which can process a sample within the sterile environment of an operating theatre in about 15min

Curran’s team gave their prototypes to the clinical team in the Bone and Joint Unit, which had access to samples of bone marrow from different categories of patient and could work with orthopaedic surgeons and their theatre teams to ensure that the device could be coordinated with the procedures of an operation. ‘When you want to regenerate bone in trauma patients, they’re often quite young, and getting bone marrow from them is quite easy; the marrow is thin and easy to process,’ Smith said. ‘But when you’re looking at revision hip replacements, where you remove a loose hip prosthesis from a femur and you want to regenerate bone around a new one, we’re looking at older patients, often in their 70s and 80s, and we’d find that the marrow is more viscous and has a lower concentration of stem cells, making it more difficult to process.’

The form and design of the device, with simple ports for injection of aspirate and collection of concentrate, was very close to what was needed in theatre, Smith said; the clinical team’s main contribution was to fine-tune the thickness, density and porosity of the membrane.

The device has particular promise in three types of surgery, the researchers say. In trauma, or bone breakage, there is a ten percent chance that fractures will fail to heal using traditional setting methods; identifying the fractures most likely to fail to heal and treating them with stem cells would reduce the need for further operations on troublesome breaks. In spinal fusion in the elderly, one in five cases do not heal properly; again, stem cell treatment could improve this. Finally, in cases of cartilage focal defect, a condition often seen in athletes where the cartilage of the knee tears, implantation of stem cells could help regrow the cartilage.

‘We’re currently working on a condition called avascular necrosis, where the head of the femur loses its blood supply — which can happen for a number of reasons — and the bone starts to break down,’ Smith said. ‘We’ve found that injecting enriched stem cells into that area, along with a bone graft or a substitute, can actually improve the shape of the femoral head and prevent it from collapsing further, while also regenerating some of the lost bone. So we do know that this technique works. This device will help us obtain the enriched stem cells more easily and in a better form, and it’ll help us to perfect the technique.’

Orthopaedic work such as this is only the start, according to Smith & Nephew. Once practice is established in this area, the company hopes that it will also find applications in soft tissue surgery, including cardiovascular applications, and even in veterinary surgery. ‘Not only will it improve patient treatment, but the cost of such treatment will be reduced, relieving currently overwhelmed healthcare services from some financial burden,’ it said.

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