Additively manufactured patient specific cranioplasty implants with antibiotic modifications
Cranioplasty is the secondary surgery done to restore the skull defect after the previous surgery of decompressive craniectomy (i.e., Brain decompression). Poly-methyl-methacrylate (PMMA) is widely used for cranioplasty implants as it has better long-term outcome. The procedure is performed through in situ forming approach where the reagents are mixed to initiate the radical polymerization of PMMA and used to repair the skull directly. Despite PMMA having better long-term outcomes, the heat and shrinkage due to the polymerization process as well as the release of unreacted monomers causes problems such as local tissue burn. In addition to this, it is difficult to disinfect the newly formed implant properly thus infection has complicated the outcome of this procedure with a significant rate of graft infection of more than 10%. These infections are caused by strains of bacteria such as Staphylococcus epidermidis or Staphylococcus aureus which are found in indwelling foreign devices. Therefore, if the prosthetic can be additively manufactured (i.e., 3D print) prior to the surgery it will shorten the duration of the exposed wound and thus reduces the risk of infection. Moreover, if the prosthetic has antibacterial properties, then it can overcome the drawback from the lack of deep disinfection and thus reduce the risk of infection caused by the bacteria indwelling on the surface of the implant. This research will investigate the possible chemical modifications of PMMA, the 3D printing parameters of the chemically modified PMMA implants and the antibacterial properties of these implants. For this research 10 g of powdered PMMA will be sulfonated using 100 mL of concentrated sulfuric acid and stirred for 2 hours. After which the degree of sulfonation and cation exchange capacity will be determined by a titration test. In the unlikely event that the cation exchange capacity and degree of sulfonation is not at an acceptable level then sulfonation process will be repeated with an extra one hour until acceptable results are obtained. The sulfonated PMMA will then be 3D printed into samples using an extrusion type machine and is expected to not deviate significantly from the 3D printing parameters of standard PMMA. During this trial the optimal 3D printing parameters such as the bed temperature and filament feeding rate will be identified. Finally, the sulfonated PMMA will be attached to antibacterial agents which are gentamicin and silver ions by immersing the sulfonated PMMA samples in aqueous solution of gentamicin sulphate and aqueous solution of silver nitrate solution respectively for 30 minutes. The final trial will be then zone inhibition test by using Staphylococcus epidermidis and Staphylococcus aureus. The test will be carried out on the following samples; chemically modified PMMA with silver ions, chemically modified PMMA with gentamicin, standard PMMA and one agar will have no samples. It is expected that the PMMA implants modified with antibacterial agents will display strong resistance to bacterial growth. Thus, will show bigger inhibition zones. In the end this research will determine if the additively manufactured implant with antibacterial modifications can inhibit bacterial growth better the standard implants.