Logo for University of Iowa Health Care This logo represents the University of Iowa Health Care

Ryan Horne, M5G



MSTP Learning Community: McCowen

MSTP Entry Date:  June 13, 2016

PhD Program:

Chemical & Biochemical Engineering


C. Allan Guymon, PhD

Lab Website Lab Profile

Zwitterionic Coatings Reduce Bacterial Adhesion to Silastic Surfaces


Introduction: Implantable medical devices, including cochlear implants (CI), must resist bacterial attachment and colonization on the device surface or risk device loss. Zwitterionic polymer systems have shown promise as anti-fouling materials, yet are practical only as coatings on sturdier materials. Here we explore the use of zwitterionic systems to provide a low-fouling surface coating on silastic materials that serve as housing/carrier for CI devices. The zwitterionic polymers, sulfobetaine methacrylate (SBMA) and carboxybetaine methacrylate (CBMA), were UV-photografted to silastic to form an antibacterial hydrogel coating. Hydroxyethyl methacrylate (HEMA) was  used as a low-fouling control. Zwitterionic coated and uncoated silastic samples were then exposed to two bacterial contaminants, Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis), in vitro and in vivo to evaluate the antifouling properties of the coatings.

Methods: GFP-expressing S. aureus and S. epidermidis were cultured on silastic surfaces that were coated with CBMA or SBMA or remained uncoated. After 24 and 48 hours epifluorescent microscopy was used to count attached bacteria. The experiment was repeated under dry conditions by spraying bacterial suspension onto dry samples. To assess the effect of the coatings on bacterial adhesion in vivo, adult rats were divided into four groups: 1) uncoated silastic implanted subcutaneously, 2) uncoated silastic implanted transcutaneously, 3) CBMA coated-silastic implanted subcutaneously, and 4) CBMA coated-silastic implanted transcutaneously. GFP-expressing S. aureus was then injected around each polymer implant. Serial live, quantitative imaging of the GFP signal was obtained 0, 3, 7, 14 and 21 days following bacterial innoculation. At 21 days, the implants were removed and attached bacteria were scored with epifluorescent microscopy. Colony counts were also performed to verify the viability of attached bacteria.

Results: CBMA coatings significantly reduced bacterial adhesion to silastic in vitro under wet and dry conditions. SBMA coatings exhibited mixed results, with reduction of bacterial adhesion under some conditions, but not others. Uncoated silastic and HEMA developed large numbers of attached bacteria. Significantly fewer bacterial counts and colonies were found on CBMA-coated implants in vivo compared to uncoated implants. While biofilms developed on uncoated silastic after 3 weeks in vivo, they did not appear to form on CBMA-coated implants.

Conclusion: CBMA and SBMA polymers applied as a UV photopolymerizable coating to silastic surfaces resist bacterial adhesion. CBMA is superior to SBMA. CBMA coatings on silastic could reduce the rate of bacterial infection, a difficult complication following cochlear implantation.


2018 - Carver's Got Talent 1st place for original piano solo

Individual Funding Awards:

05/10/2021 - 05/09/2024
F30 DC019274 - (National Institute on Deafness & other Communication Disorders)
Reducing Infection & Plugging of Tympanostomy Tubes Through Zwitterionic Thin Films


2015 - BS, Chemical Engineering - Brigham Young University


ORCiD:  0000-0002-6526-001X

Shen N, Cheng E, Whitley JW, Horne RR, Leigh B, Xu L, Jones BD, Guymon CA, Hansen MR. Photograftable Zwitterionic Coatings Prevent Staphylococcus aureus and Staphylococcus epidermidis Adhesion to PDMS Surfaces. ACS Appl Bio Mater. 2021 Feb 15;4(2):1283-1293. doi: 10.1021/acsabm.0c01147. Epub 2021 Jan 22. PMID: 35014480.

Bennion DM, Horne R, Peel A, Reineke P, Henslee A, Kaufmann C, Guymon CA, Hansen MR. Zwitterionic Photografted Coatings of Cochlear Implant Biomaterials Reduce Friction and Insertion Forces. Otol Neurotol. 2021 Dec 1;42(10):1476-1483. doi: 10.1097/MAO.0000000000003288. PubMed PMID: 34310554; PubMed Central PMCID: PMC8595522.

Jensen MJ, Peel A, Horne R, Chamberlain J, Xu L, Hansen MR, Guymon CA. Antifouling and Mechanical Properties of Photografted Zwitterionic Hydrogel Thin-Film Coatings Depend on the Cross-Link Density. ACS Biomater Sci Eng. 2021 Sep 13;7(9):4494-4502. doi: 10.1021/acsbiomaterials.1c00852. Epub 2021 Aug 4. PubMed PMID: 34347419; PubMed Central PMCID: PMC8441969.