(L-459) Investigation of biomedical device sterilization methods on hydrogel viability

Introduction:: Hip implants are one of the most common joint replacement procedures done in the United States. Bacteria tends to grow on the surface of the implant, leading to infection. Synovial fluid surrounds the hip implant and the pH fluctuates in the presence of infection. A pH-sensitive hydrogel inserted into the casing of an implant can be used to measure presence of infection in the joint.1 When bacteria is present, the pH lowers and the hydrogel shrinks. To detect shrinkage, a pinning wire and Tantalum bead are placed at opposite ends of the hydrogel, which creates an x-ray visualized sensor (X-VIS) that can be seen on a routine X-ray image. The main focus of this particular study is to investigate how the hydrogel formulation reacts to changes in pH before and after several sterilization techniques. The techniques include autoclave sterilization, ETO sterilization, and UV rays. The results allow us to recommend the most effective and efficient sterilization approach for the device.


Materials and Methods:: In this study, three standard sterilization methods were assessed in order to determine their effect on a pH sensitive hydrogel. Circular samples of hydrogel were placed into a PBS buffer solution at pH 6, allowed to come to equilibrium, and then measured using two methods. The hydrogel samples were weighed and photographed from above and from the side. ImageJ was then used to determine the diameter and height of each hydrogel sample so that the volume could be calculated. The hydrogel samples were then placed into a PBS buffer at pH 8 and allowed to come to equilibrium before being measured again. Once a full reversibility test was completed, three sets of hydrogel samples were sterilized using the following methods: autoclaved using the liquid cycle for 3 hours, ETO sterilized using a 12 hour cycle, and UV sterilized for 30 minutes. The above procedure was then repeated in order to determine behavioral differences between pre- and post- sterilization hydrogel samples.


Results, Conclusions, and Discussions:: Results and Discussion



The graph (Figure 1) is a visual representation of the average change in hydrogel diameter with respect to its initial dimension throughout two cycles of pH change. As indicated by the results, each sterilization method has a small effect on the measurement viability of the hydrogel. Post sterilization, the hydrogel response follows approximately the same curve as unsterilized hydrogels. It appears that the ETO sterilized hydrogels may have a bit of a slower response in high pH environments, though their response mimics that of the unsterilized hydrogels when placed in lower pH. This difference may be explained due to operating time that was unaccounted for, as the ETO trial was the first trial run in this study. It should also be noted that the samples used for the unsterilized hydrogel measurements were subject to the same conditions as the UV sterilized samples for simplicity; though controlled, the conditions may have varied slightly. Further investigation is needed to verify hydrogel viability following ETO sterilization, though none of the three methods appear to entirely disrupt the responsivity of the hydrogels to changes in pH.



Conclusion



The hydrogel pH sensor is an integral feature of our device intended to detect infection in a hip implant. Prior to implantation, the hydrogel must be sterilized. When deciding on a sterilization protocol for our device, it is essential to ensure the technique does not affect the viability of the sensor. In this study, we explored the effect of ETO, UV, and autoclave sterilization methods. The response of the hydrogels following UV and autoclave sterilization closely mimicked the unsterilized hydrogel response, while further investigation may be needed to verify the response of the hydrogel following ETO sterilization. To continue this research it is planned to investigate the effect of these sterilization methods on the ball and pinning wire hydrogel model used in the device, as well the effect of sterilization on the device as a whole.




Acknowledgements (Optional): : We would like to thank the Clemson University Department of Bioengineering as well as the Clemson Creative Inquiry Program for making this research possible. We would also like to thank Dr. John D. DesJardins, Dr. Jeffrey Anker, and Rong Wang for their mentorship throughout this project.

References (Optional): : 1. Wijayaratna, U. N., Kiridena, S. D., Adams, J. D., Behrend, C. J., Anker, J. N., Synovial Fluid pH Sensor for Early Detection of Prosthetic Hip Infections. Adv. Funct. Mater. 2021, 31, 2104124. https://doi.org/10.1002/adfm.202104124