State of the art of Additive Manufacturing for polymeric medical implants

Abstract

Additive Manufacturing (AM) commonly known as 3D printing has found many applications in the automotive, aerospace and medical industries. The flexibility to fabricate 3D objects of any complexity displayed by AM technologies such as Selective Laser Sintering (SLS), Stereolithography (SLA), Fused Deposition Modeling (FDM), PolyJet printing and electrospinning, has been used to improve the lives of many patients through the provision of polymeric implants, scaffolds and devices for drug delivery. The common limitation of such applications is the biocompatibility of the AM material with the human body and systems. An ideal non degradable implant would not invoke an inflammatory or toxic response whereas for a degradable implant, the degradants must also be metabolized in the body after fulfilling its purpose, thus leaving no trace. Furthermore, inertness, weight similar to human bone or even lighter, capability to generate no artifacts on Computer Tomography (CT) and Magnetic Resonance Imaging (MRI) scans, sufficient strength to resist functional stresses for load bearing implants, low and no thermal conductivity, easy sterilization and low cost of manufacturing are the desired characteristics for the acceptance of the use of an implant in a human body. Metallic and ceramic implants have been extensively used for medical implants. However the possible need for a second surgery to remove metallic implants, the stress shielding effect, the radio-opacity of the metal and long-term presence of metallic ions in vivo are major disadvantages of metallic implants which can be overcome by the use of their counterparts manufactured from polymeric materials. Building on the already established AM powder based technologies; a transition from micro to nanosized powder particles to improve the mechanical properties of SLS polymeric implants is a new trend of development. The optimum ratio of Hydroxyapatite (HA) to polymer composites and the establishment of measuring standards to meet the requirement of a medical implant are the actual challenges of AM for polymeric medical implants.