title: Development of a 3D printable maxillofacial silicone: Part I. Optimization of polydimethylsiloxane chains and cross-linker concentration.
abstract: BACKGROUND
  Conventionally, maxillofacial prostheses are fabricated by hand carving the missing anatomic defect in wax and creating a mold into which pigmented silicone elastomer is placed. Digital technologies such as computer numerical control (CNC) milling and 3-dimensional (3D) printing have been used to prepare molds directly or indirectly into which a biocompatible pigmented silicone elastomer is placed.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to develop a silicone elastomer by varying composition that could eventually be 3D printed directly without a mold to create facial/body prostheses.
  
  
  METHODS
  The silicone was composed of polydimethylsiloxane (PDMS), filler, catalyst, and cross-linker. Four types of base silicone polymers were prepared with different PDMS molecular weight combinations with long, medium, and short chain length PDMS. The effect of the cross-linker (2.5% to 12.5%) content in these bases was assessed for the effect upon the mechanical properties of the elastomer. Ten readings were made for each formulation, and differences in the means were evaluated with a 2-way ANOVA (α=.05).
  
  
  RESULTS
  Variations in silicone composition resulted in hardness from 6.8 to 28.5 durometer, tensile strength from 0.720 to 3.524 kNm-1and tear strength from 0.954 to 8.484 MPa. Significant differences were observed among all formulations (P<.05). These formulations have mechanical properties comparable with the commercial silicones currently used for the fabrication of facial prostheses. The formulation with 5% cross-linker content and high content of long-chain PDMS chains with optimum mechanical properties was chosen for further development.
  
  
  CONCLUSIONS
  The optimum combination of mechanical properties implies the use of one of these formulations for further evaluation in a 3D printer capable of actively mixing and extruding 2-component, room temperature vulcanization silicone.
authors.affiliation: Doctoral student, Academic Centre for Reconstructive Science, King's College London, Guy's Hospital, London, United Kingdom.
authors.forename: Swati K
authors.initials: SK
authors.lastname: Jindal
authors.affiliation: Visiting Professor, School of Oral and Dental Sciences, University of Bristol, Bristol, United Kingdom.
authors.forename: Martyn
authors.initials: M
authors.lastname: Sherriff
authors.affiliation: Professor, School of Dentistry, Cardiff University, Heath Park, Cardiff, United Kingdom.
authors.forename: Mark G
authors.initials: MG
authors.lastname: Waters
authors.affiliation: Reader/Consultant, Academic Centre for Reconstructive Science, King's College London, Guy's Hospital, London, United Kingdom. Electronic address: trevor.coward@kcl.ac.uk.
authors.forename: Trevor J
authors.initials: TJ
authors.lastname: Coward
mesh_terms: D001672:Biocompatible Materials / Q000627:therapeutic use; D003432:Cross-Linking Reagents / Q000008:administration & dosage / Q000627:therapeutic use; D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D006801:Humans; D008447:Maxillofacial Prosthesis; D058105:Polymerization; D066330:Printing, Three-Dimensional; D011474:Prosthesis Design / Q000379:methods; D012828:Silicones / Q000627:therapeutic use
chemical_list: D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D004129:Dimethylpolysiloxanes; D012828:Silicones; C013830:baysilon