Research & Development
Case Study – Magnetic Eye Implant
Carrs have been working with the medical industry for nearly 10 years.
Capable of laser welding materials such as titanium and high-grade stainless steel with huge accuracy makes CWT the first choice for companies to weld products from surgical instruments to orthopaedic implants.
Laser welding has a reduced heat input, decreasing risk of distortion and alteration to essential properties of the material.
Working within the medical industry presents multiple challenges, one of which is ensuring materials used are not biologically reactive. Another common issue to overcome when working with medical equipment such as implants is the size which provides very little tolerance for error.
Medical industry standards mean margin for error is much smaller than other industries as this can lead to further medical issues for the patient. These constraints make laser welding the best option for several applications, down to as little as 0.01 mm accuracy becomes achievable. In addition to this is the ability to control heat transfer and being able to work with medical grade metals such as grade 2 titanium.
THE CONTEXT AND CHALLENGE
PROJECT BACKGROUND AND DESCRIPTION
Having a great deal of experience in the medical industry attracts a wide range of clients to work with Carrs to solve any issues they encounter and to attempt to make their vision a reality.
In this instance a client came to Carrs while trying to combat a medical condition called ‘Persistent Nystagmus’. Persistent nystagmus is an abnormal rhythmic oscillation of the eyes that is estimated to occur in 0.24% of the population. Nystagmus effects a person’s ability to control eye movements, having a substantial impact on quality of life.
Many drugs have been evaluated but no generally effective pharmacologic treatment exists. This is largely down to the diversity of the potential causes of nystagmus, meaning no single agent could conceivably target the cause. Due to the nature of this condition an implant that would provide an intermediate force without direct contact was required to ensure normal eye movement was unaffected.
Currently, the only practical means of achieving an action at a distance is permanent, rare earth magnets that have enough magnetic force while remaining an implantable size. These parameters led to the concept of a two-part permanent magnetic implant. The force produced by the magnets dampens ocular oscillation, while leaving a full range of movement, essential for normal eye functionality.
The ocular magnet was a cylinder 3mm in diameter and 1mm in length, and the orbital magnet was a cylinder 3.73mm in diameter and 2mm in length. Because permanent magnetic materials are biologically reactive, each part needed to be encased in grade 2 titanium, with laser welded joints.
When welding parts with magnetic components having precise control of heat transfer is crucial. Magnets have what’s called a Curie point, this is when magnetic materials undergo a drastic change in magnetic field (around 571°C). As this implant relies on the force generated between the two magnets, the pull force of the magnet must stay the same.
PROJECT GOALS AND OBJECTIVES
The main objective with this project was to ensure the magnet was fully sealed inside of the titanium casing as the magnets used are biologically reactive and could cause problems to the patient. Another crucial part of this project was control of the temperature changes of the magnet during the welding process, as demagnetisation occurs after a certain temperature is reached. Excess material added through the welding process was also a concern as the nature of this project required a very small final product and the addition of material would affect this.
THE PROCESS AND INSIGHT
The technology chosen for this application was pulsed laser welding for its accuracy, low overall temperature rise and the ability to weld very small parts. The technology also allowed to build up a small surface using the same grade of filler material as the base metal and, therefore, ensure that a fully sealed weld was achieved.
Every magnetic implant underwent an inspection before and after the welding operation where their charge was measured. This step was crucial to assure that the welding operation was, not only safe to use around said magnets, but also to ensure that the optimal magnetic charge would be available to the patients in need.
Pulsed laser welding allied with Titanium grade 2 filler wire allowed Carrs to achieve the required characteristics and positively improve the lives of several people.
CWT were able to meet the requirements of the client, successfully welding the titanium casing, encapsulating the magnet in a biologically safe casing. This success led to the implant meeting the required standard to be able to be tested in the patient.
After recovery from surgery, the patient reported that the oscillopsia (where objects in someone’s visual field appear to oscillate) had improved, especially on the downgaze. His visual acuity scores also improved, the parameters of which have remained stable over 4 years of follow-up checks. These improvements in vision were paralleled by real life impact: the patient was able to return to part-time work, and daily functions such as reading and watching television improved substantially as well as no discernible impact on shirts of gaze or on functional range of eye movement over 4 years.
Working with the medical industry is very important to Carrs. Successfully meeting the client’s requirements allows for a significant improvement in the patient’s quality of life. Knowing that we helped contribute to this makes us eager to work with companies in the medical field to help contribute to future patient’s quality of life.
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