Functional coatings are applied to improve resistance of implants like artificial heart valves or coronary stents against various impacts in the human body. One problem is the formation of biofilms on the implant surface, which limits communication of the implant with the surrounding area and might induce inflammatory reactions. In addition, nature of the implant material can promote the formation of blood clots, which leads to blocked arteries.
Research aims for new and better coatings, to further improve implants. Thereby, chitosan is a highly promising candidate to overcome short and long-term complications of implants in contact with blood.
In May 2017, 284 articles about chitosan and chitosan derivatives were published. Most articles were published by the International Journal of Biological Macromolecules (10 articles), followed by AAPS PharmaSciTech (6) and Biosensors and Bioelectronics (3). Germany can be found under the top 5 countries, which published chitosan-related articles in May 2017.
Table: List of countries, which published the highest number of chitosan-related articels in May 2017. Source: www.gopubmed.org
In the following, we want to present two interesting publications about the application of chitosan as coating for implants to prevent biofouling and blood clot formation.
Polymer Brush-Functionalized Chitosan Hydrogels as Antifouling Implant Coatings
Buzzacchera I., Vorobii M., Kostina N. Y. et al. Biomacromolecules. Epub May 2017. doi: 10.1021/acs.biomac.7b00516
The application of implantable sensor devices for health monitoring is becoming reality. Embedding of such implants into chitosan hydrogels allows an optimal integration into the surrounding tissue. However, fouling on the implant surface is still a major problem. Deposition of proteins from blood or interstitial fluids negatively affects the sensor sensitivity, as the sensor needs to communicate with the surrounding tissue.
The study presents a strategy to refine chitosan hydrogels by the grafting of polymer brushes to achieve anti-fouling properties. Polymer brushes of oligo(ethylene glycol) methyl ether methacrylate (MeOEGMA) or 2-hydroxyethyl methacrylate (HEMA) were grown on spin-coated chitosan (100−300 kDa, degree of deacetylation ≥ 90%) applied on silicon wafers. Functionalization was conducted using photoinduced single electron transfer living radical polymerization. Hemocompatibility was tested by adding platelets and leukocytes to the surface.
- coatings were hydrophilic
- reached thickness: 180 nm (30 min polymerization)
- reduced protein fouling
- elimination of platelet activation
- inhibition of leukocyte adhesion
- Poly(MeOEGMA) brush increased swelling of chitosan hydrogel in buffer
- Poly(HEMA) proceeded also inside the chitosan hydrogel
Conclusion: The authors from the Netherlands, Germany and the Czech Republic successfully applied antifouling polymer brushes on chitosan hydrogels. The coatings had a high surface uniformity and were hydrophilic. The desired functions of the coating were fulfilled, anti-fouling coatings prevented platelet activation and leukocyte adhesion. Thus new and already existing medical implants could be improved with polymer brush coatings.
Sulfonated chitosan and dopamine based coatings for metallic implants in contact with blood
Campelo C. S., Chevallier P., Vaz J. M., Vieira R. S. et al. Materials Science and Engineering C, 72 682-691, March 2017. doi: 10.1016/j.msec.2016.11.133
Researchers from Canada and Brazil investigated a stainless steel surface coated with sulfonated chitosan. They applied dopamine and PEG as anchors for native and sulfonated chitosan. To create a successful blood-interacting device, the material surface needs to reduce platelets adhesion and delay the clot formation. In addition, the coating should reduce the calcification process.
Results for the sulfonated chitosan coating compared to native chitosan coating:
- Higher roughness and hydrophilicity
- Limited platelet activation
- Inhibition of clot formation
- Minimal calcification
Conclusion: The sulfonated chitosan coatings fulfilled the desired characteristics. Therefore, those coatings have a great potential to improve implants in their interaction with blood.