The chapter will cover the fundamentals of product design principles for additive manufacturing in medical devices, with a key focus on orthopedic implants and related devices. The chapter will describe commonly used additive manufacturing processes for medical devices and orthopedics, key design considerations, and how they have opened up possibilities in healthcare. The chapter will detail the fundamentals of design principles, which are expanding the boundaries of rapid, meaningful innovation and positively impacting the innovation cycles of a wide range of industries. It will describe how topology optimization, with the help of computing power, is providing design engineers with the tools to accurately understand structure-functional relationships of designs and in the process re-imagine the biomedical designs of tomorrow.
TopIntroduction
Additive manufacturing is a general term for technologies which, based on a geometrical representation, creates physical objects by successive addition of material (ISO/ASTM 52900:2015). These technologies are used across applications in various industries such as healthcare, aerospace, architecture, automobiles, archaeology, consumer goods, toys, food and entertainment.
All definitions for terms and nomenclature associated with additive manufacturing technology used herein are according to ISO/ASTM 52900:2015.
Applications of additive manufacturing, also referred to as “3D printing”, span across multiple applications in both metallic materials and plastics. Common additive manufacturing techniques used for metallic materials include Laser Rapid Manufacture (LRM) or Direct Metal Laser Sintering (DMLS) and Electron beam Melting (EBM). Commonly used additive techniques for plastic materials are Fused Deposition Modeling (FDM), Material Jetting (MJ), Stereo-lithography (SLA), Multi Jet Fusion (MJF) and Selective Laser Sintering (SLS). Most additive manufacturing methods make use of one or more of the below principles:
- 1.
Vat photopolymerization: This is an additive manufacturing process in which a liquid photopolymer is selectively cured by light-activated polymerization in a vat1.
- 2.
Material extrusion: This is an additive manufacturing process in which a material is selectively extruded through a nozzle or orifice1.
- 3.
Material jetting: This is an additive manufacturing process in which droplets of a material are selectively deposited1.
- 4.
Binder jetting: This is an additive manufacturing process in which a binder liquid is deposited on layers of powdered materials, selectively joined together, and then followed by a densification process (Mostafaei et al., 2021).
- 5.
Powder bed fusion1: This is an additive manufacturing process in which thermal energy is used to selectively fuse regions of a powder bed.
Depending on the materials that each of these techniques can build, they are used for different types of applications across both product prototyping and large-scale manufacturing. For example, while FDM is widely used to prototype complex geometries out of relatively low-cost plastic materials within a short amount of time, SLS is more commonly used to manufacture more structurally sound parts with better surface finish over a longer build time. Figure 1 describes some of the common additive manufacturing technologies, their underlying principles and their material compatibility for different types of applications.
Figure 1.
Additive manufacturing technologies
In healthcare industry and research, both plastic and metal additive technologies are being rapidly adopted globally across multiple applications. The orthopedic implant industry has seen an explosion of additively manufactured prostheses over the last two decades, and currently is one of the highest commercial users of large-scale additive manufacturing.
Additively manufactured spinal cages are currently used to treat patients undergoing spinal fusions, 3D printed hip stems and acetabular cups are used to treat patients undergoing total and partial hip arthroplasty procedures, and additively manufactured femoral and tibial implants are being increasingly used to treat patients undergoing total and partial knee arthroplasty procedures.
There are several technical and financial advantages of shifting from traditional manufacturing techniques such as milling, forging, casting etc. to additive manufacturing, when it comes to fabricating orthopedic implants. Some key advantages are described below: