• Maria G. Bauer, Kjetil Baglo, Luca Reichert, Jan Torgersen, Oliver Lieleg

    Comparing the resilience of macromolecular coatings on medical-grade polyurethane foils

    Surfaces and Interfaces Volume 41, October 2023, 103231;

    Foils made from elastomeric polymers, such as polycarbonate-based polyurethane (PCU), can combine desirable properties including flexibility, durability, and compliance. Still, their usage is often limited by their strongly autohesive behavior. To overcome this issue, surface coatings can be applied. Here, dopamine-based (dopa) and carbodiimide-mediated (carbo) coatings are compared by assessing their tribological performance and surface properties after long-term sliding tests, and after storage or sterilization. Even though both coating strategies achieve very good lubricity, the dopa-coatings are less resilient than the carbo-coatings. Thus, for such applications where extended sample storage or sterilization is required, covalent coatings should be preferred.

  • P. Farjam, M. Luckabauer, E.G. de Vries, V.R. Rangel, E.E.G. Hekman, G.J. Verkerke, J. Rouwkema

    Bioactive calcium phosphate coatings applied to flexible poly(carbonate urethane) foils

    Surface and Coatings Technology Volume 470, 15 October 2023, 129838

    Long-term fixation of orthopaedic implants can be enhanced by tissue ingrowth techniques. As such, the deposition of a bioactive bone-like coating could be considered a promising method to facilitate the integration of implants onto bone tissue. In this study, we identified the optimized osteo-conductive Calcium Phosphate (CaP) coating parameters for deposition on PolyCarbonate-Urethane (PCU) foils. The oxygen plasma surface-activated PCU specimens were suspended in simulated body fluid (SBF) and supersaturated SBFs for 4 h, 8 h, 24 h, or 6 days at a temperature of 20 °C, 37 °C, or 50 °C. This resulted in semi-crystalline CaP coatings on a thin flexible foil via a one-step low-temperature aqueous technique. The deposited CaP coatings demonstrated high stability and remained intact upon bending deformation. According to the in vitro cell assessments, the conducted CaP coatings did not influence cell viability nor cell proliferation compared to the bare PCU substrate. In addition, the deposited CaP coatings enhanced the cell-mediated calcium deposition. All in all, this paper demonstrates a promising method to apply stable bioactive coatings to flexible PCU foils, which can be a promising strategy for the enhanced integration of PCU implants onto bone.

  • Maria G. Bauer, Oliver Lieleg

    Bio-Macromolecular Surface Coatings for Autohesive, Transparent, Elastomeric Foils

    Thin materials made from elastomeric polymers such as polydimethylsiloxane (PDMS) and polyurethane (PU) can be both, compliant and resilient. Their mechanical robustness and flexibility will make them great candidates for applications in the human body where space is limited and repeated deformations occur. Nonetheless, current medical applications of elastomeric foil-like products are mainly restricted to inflatable balloon parts of stents or intubation tubes. Here, a key limiting factor is the autohesive behavior of those foils, that is, their propensity to stick to themselves. This property impedes handling and processing and can also interfere with the designated tasks of such foils. To mitigate this undesired behavior, different bio-macromolecular coatings are applied here and assess their influence on the autohesive behavior, flexibility, and transparency of the materials. A non-covalent, dopamine-assisted coating approach is compared to a covalent coating strategy employing carbodiimide chemistry and investigated both, anionic and cationic macromolecules as top layers. The results show that especially the carbodiimide-mediated mucin coating can efficiently suppress the autohesive behavior of the foils while maintaining the flexibility and transparency of the material. Thus, such coatings can not only broaden the medical application range of foil-based elastomeric devices but may also prove beneficial for applications in soft robotics.


  • Theresa M.Lutz, Ceren Kimna, Angela Casini, Oliver Lieleg

    Bio-based and bio-inspired adhesives from animals and plants for biomedical applications

    Materials Today Bio Volume 13, January 2022, 100203.

    With the “many-headed” slime mold Physarum polycelphalum having been voted the unicellular organism of the year 2021 by the German Society of Protozoology, we are reminded that a large part of nature's huge variety of life forms is easily overlooked – both by the general public and researchers alike. Indeed, whereas several animals such as mussels or spiders have already inspired many scientists to create novel materials with glue-like properties, there is much more to discover in the flora and fauna. Here, we provide an overview of naturally occurring slimy substances with adhesive properties and categorize them in terms of the main chemical motifs that convey their stickiness, i.e., carbohydrate-, protein-, and glycoprotein-based biological glues. Furthermore, we highlight selected recent developments in the area of material design and functionalization that aim at making use of such biological compounds for novel applications in medicine – either by conjugating adhesive motifs found in nature to biological or synthetic macromolecules or by synthetically creating (multi-)functional materials, which combine adhesive properties with additional, problem-specific (and sometimes tunable) features.

  • Charles Burson-Thomas, Alexander Dickinson, Martin Browne

    Quantifying joint congruence with an elastic foundation

    Journal of Biomechanical Engineering, 144 (10), [101003]. (doi:10.1115/1.4054276); May 2022

    People’s finger joints come in different sizes and shapes. This affects the typical forces and pressures seen by the joint. It is thought that excess pressure in a joint increases the risk of developing osteoarthritis. Joint ‘congruence’ measures how conforming the two contacting surfaces within the joint are – a higher congruence means pressure is distributed over the whole joint, while a lower congruence means it is focussed over a smaller area, resulting in higher pressures. In knee joints, poor congruence can have the same effect as increasing the load on the joint considerably, making the person at risk of developing osteoarthritis. Current methodologies for measuring joint congruence have particular challenges that make using them tricky. In this paper, a new way of measuring joint congruence is presented. Using a computer simulation, it was possible to work out the congruence from 3D X-ray scans of 10 people’s thumb joints. It was found the congruence varied substantially between them, similar to the way it does in knees and other joints. The new method should be helpful for researchers who already work on computer simulations of joints, as it enables measurement of joint congruence with relative ease.


  • P.Farjam, E.E.G.Hekman, J.Rouwkema, G.J.Verkerke

    Bone fixation techniques for managing joint disorders and injuries: A review study

    Journal of the Mechanical Behavior of Biomedical Materials, Volume 126, February 2022, 104982 (available online 7 November 2021);

    The demand for utilizing new novel orthopedic implants and increasing the success rate of currently conducted orthopedic surgery is anticipated to raise for the foreseeable future. Importantly, In this article we aim to attract the attention of inventors, designers and surgeons to fixation techniques as they play a critical role in the overall success of treatment and surgery. The review on current novel anchoring systems that assure sufficient stability to implants will bring multiple advantages. One benefit would be modifying fixation methods currently being used in traditional reconstruction and replacement surgery to enhance stability and integration. In addition, this review potentially serves as a valuable source for designing fixation methods for novel future implants.

  • Bauer, Maria G., Reithmeir, Rosa, Lutz, Theresa M., Lieleg, Oliver

    Wetting behavior and stability of surface‐modified polyurethane materials

    Plasma Processes and Polymers, Volume 18, September 2021, 2100126; doi:10.1002/ppap.202100126

    Even though polyurethanes (PU) constitute a class of highly versatile and customizable polymeric materials, being able to modify their surface properties, for example, their wettability, without altering the composition of the bulk material would often be desirable. However, PU-based materials can be both rather diverse and resilient to chemical modification. Thus, in this study, three PU variants are subjected to three different treatments that aim at altering the wetting properties of the materials: We assess the feasibility of plasma treatment, dopamine incubation, and chemical etching, and evaluate the stability of the obtained surface modifications with regard to wet and dry storage, UV exposure, and application-specific properties such as lubricity and colonization with eukaryotic cells. The results obtained here can be used to achieve an additional customization of PU surfaces to tailor their behavior for selected applications where dedicated surface properties are required.