By Balaji Prabhu, Director Strategic Marketing, Medical Device Solutions, Evonik Health Care
Over the past decade, 3D printing innovations have redefined the possibilities in a number of industries, including automotive, consumer goods, aerospace, and healthcare. However, the adoption of 3D printing technologies for implantable medical devices has been relatively slow. This was largely due to challenges in sourcing the right biocompatible materials, validating processes, and meeting quality and regulatory requirements. Where innovations in medical devices for 3D printing have previously occurred, they have been largely limited to metal-based implants traditionally used for hip, knee and spine reconstruction applications.
While well-characterized bioresorbable polymers with sufficient strength and biocompatibility have now begun to replace metallic materials in traditional device applications, it has been difficult to process them into shapes such as filaments and powders that are compatible with established 3D printing technologies. For example, the use of polymers such as poly (L-lactide) or poly (caprolactone) with FFF (Fused Filament Fabrication) systems required a processing solution that enables patient-specific geometries and a bone-like, porous structure without sacrificing essential functional properties.
Cranio-maxillofacial (CMF) plates, which are used in operations for congenital or acquired defects of the skull and facial region, represented a particular gap in the market. It is important here that filament-based bioabsorbable polymers are able to maintain mechanical properties such as strength, durability, flexibility and the elimination of stress shielding during processing with FFF systems in order to ensure that each CMF board has a sufficiently high resolution and printed without defects.
FFF systems have long been considered an attractive way to produce bioresorbable CMF sheets that are tailored to the individual patient. This is because they are highly efficient in creating and consistently replicating parts with complex geometries. Parts manufactured by FFF in particular typically have a high compressive strength in the z-direction and attractive tensile properties in the xy-direction. In addition, they are not as complex and generally cheaper to buy and operate when compared to Selective Laser Sintering (SLS) systems.
Materials used with FFF systems typically must be designed for the continuous supply of spaghetti-like filament material from a spool through a moving, heated extruder die. The nozzle then prints the molten filament, layer by layer, into an end device. The layer height typically ranges from 0.05 mm to 0.3 mm with a tolerance of +/- 0.1 mm. However, until recently, GMP grade polymer filament was not available for bioresorbable devices.
As one of the world’s leading suppliers of biomaterials, Evonik recently met this unmet market need with the development of the RESOMER® filament line of standard and customer-specific bioresorbable polymers. Standard RESOMER® filament products are supplied in spools with a filament diameter of either 1.75 mm (standard) or 2.85 mm (customer-specific). To meet specific requirements for strength, modulus, flexibility and elongation properties, a range of filament qualities with compositions are available including poly (L-lactide), poly (L-lactide-co-glycolide), poly (caprolactone) and polydioxanone .
As with all RESOMER® products, all filament qualities are hydrolyzed in vivo and excreted via excretion routes. The degradation times of standard RESOMER® filament products are between less than six months and more than three years.
Many other mechanical properties can also be tailored precisely to the requirements of the target application. A number of additional customer-specific options are available under RESOMER Filament Select®, including mechanical properties, filament diameter, additives and sterilized filaments for point-of-care printing. They are also manufactured in ISO Class 8 clean rooms that conform to ISO 13485 and a robust global quality system.
In addition to RESOMER® filament, Evonik can supply customers of medical products with RESOMER® PrintPowder for 3D printing with SLS systems. A number of granulate-based RESOMER® products are also suitable for use with extrusion-based systems such as freeformers and bioplotters for the 3D printing of implants and frameworks for tissue engineering applications.
Evonik’s experienced technical team is available at the Medical Device Competence Center in Birmingham, Alabama, USA, to support medical device customers in the development, evaluation and 3D printing of their applications. The 3D printing services include material selection and development, prototype printing for feasibility, standardized sample printing, and development and optimization of printing processes using FFF or other systems. To arrange a free consultation or to request a sample, contact Evonik at firstname.lastname@example.org.