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Implants promote healing

Сase studies
15

Individualised, additively manufactured parts to replace cranial bones are conceivable.

Special resorbable implants are used in the form of screws or pins for the fixation of bones or tissue, for example. The advantage of this material, which is based on poly lactide (PLA), is that it biodegrades in the body after a defined time period. ARBURG and the company BIOVISION process a PLA material of this kind on electric ALLROUNDER A machines to produce bone pins, for example, for the medical sector.

One advantage of resorbable implants is self-evident: they don’t have to be re moved surgically once healing is complete. Moreover, the plastic granulate can be charged with anti-inflammatory agents to minimise rejection reactions. In order for the material to dissolve in the body at the correct time, selection of the material type is extremely important. One indicator of this is the so-called inherent viscosity (IV value). The lower this value is, the more the material is biodegraded.

Complex processing of PLA

“Owing to their toughness, the PLA plastics are complex to process and they require the appropriate injection moulding expertise,” explains Sven Kitzlinger from applications consulting for medical technology at ARBURG. “At a purchase price of several thousand euros a kilo, the material is rather expensive, as well as being sensitive to high temperatures and long dwell times. So there’s no scope for error during injection moulding.” High shearing during preparation would also damage the material and lead to premature biodegrading in the body.

Gentle material preparation

“For gentle material preparation and short dwell times, we therefore use a special 15-millimetre screw with widened flights and a chrome nitride (CrN) coating. This reliably prevents the formation of undesirable deposits and microfretting,” says Sven Kitzlinger.

ARBURG has decades of experience in medical technology and automation. The modular machines and turnkey solutions can be precisely tailored to the customers’ requirements; jointly with partners where appropriate.

At the Technology Days 2016,ARBURG demonstrated the processing of “Resomer L 210 S” from Evonik on an electric ALLROUNDER370 A. The clean-room machine, equipped with a stainless steel clamping unit meets the most stringent hygiene requirements in compliance with ISO13485 and according to the FDA requirements and GMP guidelines. An ISO 7 class clean-air module with ionisation above the clamping unit provides the necessary clean atmosphere during running production.“At a shot weight of less than one gram, use of our micro-injection module also makes sense,” adds Sven Kitzlinger. “It can optionally combine either an 18 or 15-millimetre screw for melting the material with an 8-millimetre screw for injection. This ensures gentle processing of the plastic according to the first-in, first-out principle and compensates for the disadvantages of pure piston injection.”

Implants can either be injection moulded or manufactured additively

BIOVISION from Ilmenau, Germany, specialises in the injection moulding of resorbable plastics. Using an ALLROUNDER 270 A machine and a micro-module, “PolyPIN®” bone pins with lengths between 25 and 60 millimetres are produced for use during the surgical fixation of fractures subjected to low biomechanical stresses. These implants are biodegraded after around two years.

A further interesting area of application is also the additive manufacturing of individualised implants, which can be designed precisely for the specific patient. The fact that medical PLA can also in principle be processed using the freeformer was already demonstrated by ARBURG at the Technology Days 2016.

Examples here included a facial and a cranial bone. Further investigations into this new field of applications are ongoing.

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