Material Properties Self-reinforcement of three dimensionally printed polymethyl methacrylate J. Suwanprateeb * , W. Suvannapruk, R. Sanngam National Metal and Materials Technology Center,114 Paholyothin Road, Klong 1, Klongluang, Pathumthani 12120, Thailand article info Article history: Received 24 March 2008 Accepted 5 May 2008 Keywords: Polymethyl methacrylate Self-reinforcement Three dimensional printing Mechanical properties Medical abstract This study shows the use of heat-cured MMA/PMMA liquid mixture, varying from 0% to 12% PMMA, as reinforcing phases to enhance the mechanical properties of three dimen- sionally printed polymethyl methacrylate based specimens by means of infiltration. It was observed that this self-reinforcement could increase flexural properties of the samples significantly, up to a factor of 5 for flexural modulus and a factor of 27 for flexural strength. Degree of reinforcement depended on the amount of initial binder content in the as-fabricated green 3DP specimens and the ratio of MMA:PMMA in the reinforcing mix- ture. Decreasing initial binder content in the green specimens increased the efficiency of reinforcement. This is related to the increased amount of initial porosity in the green 3DP specimens with decreased binder content which the reinforcing infiltrant can diffuse into. The MMA/PMMA infiltrant liquid containing less than 10% of PMMA was able to dif- fuse and reinforce the structure. Greater amounts of PMMA than this level yielded high viscosity fluid which hardly flowed through the specimens. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Three dimensional printing (3DP) is one type of free- form fabrication technology that additively builds three di- mensional parts by using an inkjet printhead to jet a liquid media to bind a powder together layer by layer. This ap- proach allows complex physical structures to be fabricated rapidly and accurately, without limitation, using graphical data in a computer. In the case of medical implant fabrica- tion, implants can be designed digitally to fit the host site and aesthetically corrected for the individual patient prior to the surgery. The 3DP models are then fabricated and employed as patterns for the desired implants to create sil- icone or plaster moulds for further casting of biomedical materials [1–3]. This two-step process is normally done due to the fact that the raw materials for a three dimen- sional printing machine are not designed for medical appli- cations. If the biomedical materials could be fabricated directly from a machine, the steps of generating moulds are omitted and extra cost of moulds is saved. In addition, the risk of model damage from handling during the casting step could be reduced [4,5]. It was shown previously that polymethyl methacrylate could be mixed with binders and used as raw materials for direct fabrication by three dimensional printing machine [6,7]. However, due to the nature of 3DP processing technology in which the particles are lightly packed and bonded by an adhesive binder, pores are normally present in the as-fabricated green samples. This leads to low strength parts that may be suitable as im- plants for low load bearing structure. In order to be used in greater load bearing area, methods to improve mechanical properties should be explored. Reinforcing by Bis-GMA based acrylate resin was previously studied and it was found that this could enhance the mechanical properties of the samples significantly [8]. However, acrylate mono- mer was reported to be more toxic than methyl methacry- late monomer [9,10]. If the curing is not done properly, the residual Bis-GMA monomer might cause greater tissue toxicity. This study was, therefore, aimed to use heat-cured * Corresponding author. Tel.: þ66 2564 6500; fax: þ66 2564 6501. E-mail address: jintamai@mtec.or.th (J. Suwanprateeb). Contents lists available at ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest 0142-9418/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2008.05.001 Polymer Testing 27 (2008) 711–716