Yong, Ling Xin
(2022)
Development of Fungal Anti-Attachment Inks for 3D Printed Medical Devices.
PhD thesis, University of Nottingham.
Abstract
Fungal infections of medical devices caused by Candida albicans alone have resulted in up to 50 % mortality. Utilisation of fungal-resistant polymer could reduce mortality rate and reduce complications in patient’s health from frequent changes of medical devices. At present, Polydimethylsiloxane (PDMS) is commonly used due to its biocompatibility, excellent temperature and chemical resistance, and its good mechanical and moulding properties. However, in many of its biomedical applications such as voice prostheses and urinary catheters, PDMS can attract yeasts that form biofilms which trigger infections in device users. This is especially so for indwelling voice prostheses as there are currently no commercially available antimicrobial options and the device must be changed every few months.
Fungal biofilm resistant polymers can be incorporated to medical devices simply by dip coating or via additive manufacturing (AM) processes. AM is a manufacturing method that deposits material layer by layer, this method would be especially advantageous for low volume manufacturing and/ or customization. With medical technology advancements progressing towards catering to personalised treatment for individual patients, customization of medical devices with AM technique would be highly desirable. This work evaluates acrylate and methacrylate as ultraviolet (UV) curing polymers in AM processes - stereolithography (SLA) and material jetting. These processes are known to offer a high level of resolution and are also suitable for building smaller parts such as medical devices.
In this work, nine selected polymers with mixed resistance against fungal attachment were used to develop a high throughput screening (HTS) method for discovering fungal anti-attachment polymers. With the developed method, selected polymers were mixed in different ratios and cured under UV, forming copolymers. From the HTS of 30 copolymers, 19 out of 30 copolymers were identified to exhibit reduced C. albicans attachment <25 %. These copolymers were predicted with the Flory-Fox equation to have a wide varying range of glass transition temperature (Tg), and this widens the options for fungal-resistant polymers available for use in the medical industry.
Out of the 19 copolymers, Triethylene glycol methyl ether methacrylate (TEGMA) and (R)-α-Acryloyloxy-β,β-dimethyl-γ-butyrolactone (AODMBA) copolymer in the ratio of 40:60 was found to be the most suitable ratio for material jetting. Concurrently, TEGMA:AODMBA40:60 was also thermally synthesised into a copolymer for dip coating process. The application of this copolymer was then demonstrated by printing a voice prosthesis flap used by patients who have undergone a laryngectomy.
This inkjet-printed TEGMA:AODMBA40:60 copolymer was found to have a Tg of 13.6°C, which is within the targeted Tg range for a flexible medical device. While TEGMA:AODMBA40:60 could be inkjet-printed and dip-coated, curability was compromised, and the resolution of the printed part did not capture the finer details. Further modification of the copolymer ink formulation was performed by exploiting acrylate alternatives with similar structures, replacing of monomer with oligomers and inclusion of hyperbranched tripropylene glycol diacrylate (HBP-TPGDA) to improve the ink’s functionality. Finetuning of the formulation with the above methods was able to improve the printing resolution, a significant improvement was found especially when using similar acrylate alternatives of methacrylate monomers and incorporation of hyperbranched polymers as an additive. However, more work has to be done to study this formulation adjustment in detail and its effect on the end properties.
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