News from Manufacturers of Long Term Implantable Polymers
PEEK-OPTIMA Ultra Reinforced Promotes Optimal Clinical Outcomes by Addressing Persistent Challenges to Maximal Implantation Success
UK-based Invibio have written about how its carbon fibre reinforced brand of PEEK, PEEK-OPTIMA Ultra-Reinforced, an alternative to metal in implantable devices, is promoting optimal clinical outcomes by addressing “persistent challenges to maximal implantation success”. Invibio’s article is as follows. References are available on request.
The use of metal-based medical devices in trauma applications is the current gold standard in patient treatment for internal fracture fixation (fracture plates and intramedullary nails). Although quite effective the use of metal presents an ongoing challenge to long-term implantation success1, 2, 3, 4. Optimal clinical outcomes could benefit from improvement in persistent shortfalls associated with use of metals.
Challenges with metals: Chief among these shortfalls is implant failure, due to fatigue performance challenges and the high stiffness of metal. Cold welding and galvanic corrosion also present difficulties during the removal or revision of devices due to the inherent properties of metal. Another challenge is the poor imaging characteristics (radiopacity) of previous plate materials (which could contribute to improper placements that preclude appropriate fracture site coverage, obscured screw placements hampering optimal construct strength and stability, and masked imaging hindering healing assessment accuracy). There is a clear clinical need for non-metallic biomaterials that speed and enhance healing, enable dynamic loading, promote bone conservation, and improve fatigue performance and healing assessment.
A novel alternative to metal: Designed to the highly specific demands of trauma applications, Invibio’s PEEK-OPTIMA Ultra-Reinforced material combines the high performance material properties of PEEK-OPTIMA natural polymer with carbon-fibre reinforced strength (similar to that of metal, but with a bone-like modulus). Dynamic testing of trauma fixation devices demonstrates that PEEK-OPTIMA Ultra-Reinforced has a higher fatigue strength compared to titanium, while providing radiolucent properties that enable proper plate placement to assure appropriate fracture site coverage, precision screw placements to enable optimal construct strength and stability, and artifact free imaging for appropriate healing assessment during follow-up.
Compared to radiopaque implants made of metal, PEEK-OPTIMA Ultra-Reinforced implants allow for better bone fragment visualisation during image guided intraoperative fracture reduction procedures. Implant radiolucency also aids in post-operative visualisation of callus formation for improved healing assessment.
Invibio’s revolutionary, non-corrosive polymer also provides benefits that address the cold welding and galvanic corrosion issues that have plagued previous generations of trauma plates. No corrosion enables easier screw removal and promotes smoother device retrieval uneventful to the benefit of surgeon and patient.
Biologically inert and with low tissue adhesion, PEEK-OPTIMA Ultra-Reinforced reduces tissue adhesion to the implant, simplifies implant removal, and allows for greater conservation of the bone during surgical revision procedures. The inert nature of PEEK-OPTIMA Ultra-Reinforced additionally allows for sterilisation through all standard technologies, and is backed with almost 15 years of proven biocompatibility.
Manufacturing pathway: PEEK-OPTIMA Ultra-Reinforced brings the material characteristics and performance capabilities to address the issues and shortfalls associated with metal, while advancing surgical techniques and approaches, and optimising patient outcomes. Invibio is a true biomaterials solution provider and device partner offering the expert capabilities to deliver commercial PEEK-based trauma devices.
PEEK-OPTIMA Ultra-Reinforced meets the requirements of ISO10993 standards for long-term implantable medical devices and are included in the FDA master file. Testing demonstrated no evidence of cytotoxicity, systemic toxicity, irritation or macroscopic reaction response.
Solvay and Evonik Announce FDA Approvals of PEEK Spinal Cages
Polymer manufacturers Solvay Specialty Polymers, part of Belgian chemical company Solvay, and Evonik, based in Germany, have provided details of PEEK spinal implants approved for sale in the USA by the FDA.
The details from Solvay Specialty Polymers regard a device made from that company’s Zeniva brand of PEEK by Maxim Surgical, described by Solvay as a new designer and manufacturer of spinal implants based in Texas, USA.
Maxim Surgical has received 510(k) clearance for its new MaxFuse-C cervical interbody fusion system (see image) machined from Zeniva PEEK rods. Zeniva PEEK—part of Solvay’s line of Solviva biomaterials—is said to have a modulus very close to that of bone plus excellent toughness and fatigue resistance. The press release providing the information reported that the FDA clearance was based, in part, on Solvay’s master access file for Zeniva PEEK.
The MaxFuse-C cervical interbody fusion system is hollow so that bone can grow through the device, fusing the adjacent bony surfaces of the vertebrae. The cervical spacer for the spinal fusion market is Maxim Surgical’s first orthopaedic implant.
Evonik’s announcement, made at Medtec Europe in February 2013, is that the FDA has approved an implantable spinal cage made from its Vestakeep brand of PEEK. This is the first spinal cage to be made from Vestakeep to have been approved by the FDA. The associated pre-market notification 510(k) has been successfully issued and, according to Evonik, this will make it far easier in the future for medical device manufacturers looking to use Vestakeep to get approval.
Evonik describes Vestakeep PEEK as having good processability properties, lending itself well to injection moulding and cutting processes in production and supports freedom of design in the development of new implant technologies.
In general, PEEK offers numerous advantages over metals such as titanium for spinal implants. The material offers many important benefits including biocompatibility, chemical inertness, and a modulus of elasticity that is close to that of bone.
Solvay points out that, based on biocompatibility testing, Zeniva PEEK demonstrates no evidence of cytotoxicity, sensitisation, irritation, or acute systemic toxicity, and meets ASTM F2026, the standard specification for PEEK polymers for surgical implant applications. It also boasts high strength and stiffness and has radiolucent properties which enable x-ray procedures without interference.
The MaxFuse-C cervical interbody fusion system is machined from 16-mm and 20-mm diameter Zeniva PEEK rods. It is available in two footprints—15 mm x 13 mm and 17 mm x 14 mm in both neutral and six degree lordotic options—offering surgeons flexibility in meeting different patient anatomies. The system also provides a large graft window which facilitates a bigger graft volume for fusion. Maxim offers an easy-to-use single tray system which includes simplified instrumentation for all of their available implant options. Maxim plans to explore the future use of Zeniva PEEK in a range of other spinal fusion products.
“We’re excited about the commercial success of Zeniva PEEK in the orthopaedic implantable market,” said Shawn Shorrock, global healthcare market manager for Solvay Specialty Polymers. “The ongoing acceptance of Zeniva PEEK has validated our approach to the orthopaedic implant market and we’re encouraged by the momentum we’ve generated.”
MedShape Develops Shape Memory PEEK for Suture Anchors and Soft Tissue Fasteners
A US orthopaedic implantable device manufacturer, MedShape, has developed a proprietary shape memory PEEK material called Altera. The material is based on Solvay’s Zeniva PEEK.
The company has used Zeniva PEEK for two new products. The first, an anchor for sutures for tendon and ligament repair, is the Morphix anchor. The second is the ExoShape soft tissue fastener for reconstruction of the anterior cruciate ligament (ACL), one of the four major ligaments of the human knee.
MedShape is the first to develop and commercialise FDA-cleared devices manufactured from shape memory polymers. Using Zeniva PEEK as the base material, Altera reportedly allows devices to enter the target surgical site in a compact geometry and then be triggered to deploy with minimal mechanical force into the optimal geometry for fixation.
The Morphix suture anchor is injection-moulded. It is said to offer improved cyclic loading stability, which means less chance of the surgical repair failing during the healing process. The Morphix suture anchor deploys dynamic wings with a high bearing area into the cancellous bone beneath the cortical shelf for improved device fixation.
According to MedShape, active rehabilitation can cause anchor migration and loosening which may lead to clinical failure of the repair.
Furthermore, laboratory testing has reportedly shown that traditional anchor pullout can occur below 1,000 cycles at a load less than 50% of initial pullout strength. The Morphix suture anchor is said to respond positively to cyclic loading due to its dynamic geometry and stored shape memory strain. After implantation, cyclic loading stimulates the Morphix suture anchor to attain its permanent, fully open “zero-strain” state. This results in continued wing expansion and retention of initial pullout strength, according to the company.
The shape memory Morphix suture anchor is delivered pre-compressed in a low-profile geometry that inserts easily into the surgical site, utilising a simple and reproducible tap-in technique. It is available in diameters of 2.5 mm, 3.5 mm, 4.5 mm, and 5.5 mm and a range of suture and needle configurations.
The ExoShape soft tissue fastener is designed for fixation of the soft tissue graft on the tibial side of the knee joint in ACL reconstructions. It is said to offer unparalleled accuracy to ensure the most anatomic and stable reconstruction, strong fixation, complete graft protection, simplified insertion, and total biocompatibility. The ExoShape sheath is machined from 6 mm, 9 mm, and 13 mm Zeniva PEEK rod.
The ExoShape soft tissue fastener reportedly provides a straightforward, non-rotational insertion and expansion which eliminates “graft wrap” and preserves the preferred graft orientation. The graft bundles stay exactly where they’re placed, promoting a more anatomic reconstruction, according to Kathryn Smith, MedShape marketing manager.
Other fixation devices can drive the graft back up the tibial tunnel, introducing unwanted graft laxity. The ExoShape soft tissue fastener’s “closed force loop” design eliminates this problem by preventing retrograde force being applied to the graft, according to the company.
“We’ve been very pleased to work with MedShape as they develop improved approaches for orthopedic fixation devices,” said Shawn Shorrock, global healthcare market manager for Solvay Specialty Polymers. “The ongoing acceptance of Zeniva PEEK has validated our approach to the orthopaedic implant market and we’re encouraged by the momentum we’ve generated.”
The manufacturing site for Zeniva PEEK and other Solviva Biomaterials in Alpharetta, Georgia, USA, is ISO13485 registered and the relevant aspects of current Good Manufacturing Practices are also applied. Solvay says its biomaterial manufacturing processes are carefully validated and enhanced controls provide product traceability. In addition, all materials are tested in a lab accredited to ISO17025—the general requirements for the competence of testing and calibration laboratories.
Solvay Announces TranS1 VEO Interbody Fusion System Uses Spinal Implants Made of Solvay’s Zeniva PEEK
Another example of Solvay’s biomaterials being used in medical devices is in US minimally invasive spinal implant manufacturer TranS1’s VEO direct lateral access and interbody fusion system. The system incorporates a lumbar fusion cage implant made from Zeniva PEEK and a tubular retractor made of Solvay’s Radel polyphenylsulfone (PPSU) resin for radiolucency and the ability to withstand repeated steam sterilisation. TranS1’s VEO is a direct lateral fusion system for the lumbar spine. VEO’s interbody cage is made from rod stock offered in various sizes, including widths of 17 mm and 22 mm and lengths from 40 mm to 60 mm. The implant has a large centre channel to allow bone growth through the device, fusing the adjacent bony surfaces of the vertebrae.
The VEO direct lateral system is said to bring clear and direct visualisation to lateral fusion surgery. Through a combination of direct psoas visualisation and clear lateral fluoroscopic views, the system offers complete visualisation of the operative site. This approach was designed to help minimise iatrogenic trauma to the psoas muscle and the nerve plexus to help reduce the risk of post-operative complications.
The system offers a comprehensive portfolio of interbody implants in both parallel and lordotic angles to match various anatomical dimensions. The interbody implants contain five tantalum markers for precise fluoroscopic visualisation. The large centre channel is readily visualised and can be easily evaluated for progression of fusion.
“This is a perfect example of the value Solvay brings with its breadth of products, expanding the options for designers in terms of design flexibility and performance optimisation,” said Shawn Shorrock, global healthcare market manager for Solvay Specialty Polymers. “In addition, the ongoing acceptance of Zeniva PEEK has validated our approach to the spinal market and we’re encouraged by the momentum we’ve generated.”
Meanwhile, TranS1 was able to draw again on Solvay’s extensive product offering by using Radel PPSU for the tubular retractor that was designed to prevent soft tissue intrusion. The high-performance material reportedly provides superior strength, high thermal performance, chemical resistance, and the ability to withstand repeated steam sterilisation. The retractor is made from 50 mm diameter Radel PPSU rod stock in lengths of 100 mm, 120 mm, and 140 mm.
Call for Abstracts Involving Technical and Clinical Advances in Medical Grade UHMWPE for Orthopaedic Implants
The organisers of the sixth International UHMWPE Meeting—the University of Torino, the Implant Research Center of Drexel University and Exponent—are inviting authors to submit presentation proposals on advancements in medical grade ultra high molecular weight polyethylene (UHMWPE) technology and clinical joint replacement applications.
Engineers, scientists and clinicians from academia and industry are invited to present leading edge research during the said meeting on October 10-11, 2013, at the congress centre Unione Industriale in central Torino, Italy.
Sponsored by Ticona, the manufacturer of GUR implantable UHMWPE, the meeting will focus on clinical and retrieval studies of standard, crosslinked and stabilised UHMWPE. There will be a special emphasis on performance of thin acetabular liners and knee arthroplasty, advances in vitamin E and new antioxidant technologies for UHMWPE, structural composites and woven fibre applications of medical grade UHMWPE, and advances in biologic aspects of UHMWPE wear debris incorporating vitamin E.
Quadrant Provide Machining PPSU Guidelines
Jack Sharp, tooling manager at the US subsidiary of Quadrant EPP, a company which specialises in machined plastics, has written a guide on how to achieve the best machined finish for PPSU parts. The guide is as follows.
PPSU has virtually unlimited resistance to steam sterilisation making it ideal for medical devices which come in contact with the body or bodily fluids. This FDA and USP Class VI compliant material also withstands the rigours of repeated use and demonstrates high mechanical strength and stiffness. Today, various colours of PPSU are being used for orthopaedic trial implants and other surgical tools where size identification is required. Improper machining of critical-sized coloured PPSU components can result in poor surface finish, improper tolerances or parts that do not meet customer specifications—and ultimately affect your bottom line.
To achieve the best machined finish and ensure proper dimensional control for critical tolerance parts, the incoming material should be allowed to stabilise in the environment in which it will be machined for 24 hours. Correct tooling, feeds and speeds are critical and using a water-based coolant is highly recommended. For very tight tolerance work, roughly machine components to within 0.05-0.075 mm (0.020-0.030 inches) on all surfaces and leave the parts to rest for up to 48 hours to allow machined-in stress relief. Best results can be achieved with solid carbide, uncoated (polycrystalline diamond turning inserts work extremely well) cutting tools (two flute end mills and turning tools with 0.031-inch radius) because of their rigidity and long cutting life—although high speed cutters can be used.
Coated tooling is not recommended for use with PPSU as the cut will not be as sharp and may “pull” at the material rather than cutting. This may impart excess heat and material movement causing a loss of stability.
Whether turning, milling or drilling, process at the highest reasonable RPM and use a feed rate for roughing of 0.010 to 0.020 inches per revolution. For finishing, feed rates should be 0.003 to 0.007 inches per revolution. This high speed approach moves the cutting tool quickly across the material and keeps heat generation to a minimum.
Remember these are just guidelines or starting points and may not be the optimum conditions for all types of equipment and setups.