Another PhD from the department!

Sebastian Geißler has publicly defended his doctoral dissertation Surface functionalization of dental implants for improved biological response and reduced infection risk. Department of Biomaterials congratulates Sebastian on his great achievement!

The opponents Tautgirdas Ruzgas and Guruprakash Subbiahdoss did not let Sebastian Geißler get off too easy during his PhD defence.

Thesis summary

Missing teeth are often replaced by single-tooth implants or implant-supported prostheses. Titanium and titanium based alloys are the state-of-the-art material used for such implants. To ensure long-lasting functionality of dental implants in the human body, a healthy and stable connection between the titanium surface and the surrounding bone tissue is necessary. Colonization of the implant surface by bacteria can interfere with the establishment and maintenance of this connection. In this thesis, two different techniques were applied to modify the surfaces of titanium implant materials with the aim to enhance bone formation and reduce the infection risk around dental implants.

In the first part, the antibiotic doxycycline was coated on titanium surfaces by means of cathodic polarization. Although these doxycycline modified surfaces have previously shown potential to promote bone formation, the in vitro results of the present bacteria study revealed that the observed antibacterial properties of the coatings were only of short duration. In addition, the proposed involvement of a titanium hydride layer in the binding of doxycycline to the surfaces could not be confirmed, and the changes induced to the titanium surfaces were found not to be controllable.

Therefore, a different surface modification route was chosen in the second part of this study. Inspired by the various biological functions of naturally occurring polyphenols, an auto-oxidative process was used to coat titanium surfaces with the (poly)phenolic compounds tannic acid (TA) and pyrogallol (PG). Our QCM-D study revealed that multiple phases were involved in the coating deposition, and that a complex interplay of physical and chemical interactions is responsible for the coating formation. The effect of such (poly)phenol coatings with different thicknesses (few nanometers up to 75 nm) on osteoblasts and S. epidermidis was investigated in vitro. None of the coatings were toxic to osteoblasts. Even though thick coatings revealed anti-inflammatory potential, a delay in osteoblast maturation was observed. This effect was assigned to the release of phenolic compounds from the surfaces. The released compounds significantly interfered with the growth of planktonic bacteria. However, the coatings were not able to prevent biofilm formation on the surfaces.

Compared to cathodic polarization with doxycycline, TA and PG coatings represent a simple and versatile functionalization method which exhibit promising properties for implant applications. However, more studies have to be conducted to fully understand and improve these properties.

Read more about Sebastian's PhD project in English or på norsk.

We were all happy to raise our glasses to the newly baked doctor from our department.

Evaluation committee

  • Professor Tautgirdas Ruzgas, Department of Biomedical Science, Malmö University, Sweden
  • Postdoctoral Fellow Guruprakash Subbiahdoss, iNANO, Aarhus University, Denmark
  • Specialist Dentist Tanya Franzen, Institute of Clinical Dentistry, University of Oslo


Tags: Biomaterials, PhD defences, titanium, implants, polyphenols, Sebastian Geissler
Published Apr. 11, 2017 8:14 AM - Last modified Dec. 8, 2020 11:03 AM