Table 1.

Current problems and future perspectives of surface modifications.

Type of surface modification	Problems	Future perspectives
Heparin-bonded (HBC)	Ionic binding: heparin leach and tendency of oxygenator to swell and occlude. Does not obviate need for systemic anticoagulation.	HBC using covalent bonding are reported to not have leaching of heparin
Nitric oxide (NO)-releasing	First generation (MAHMA/NO): Entire molecule leaching releasing nitrosamines into the blood. Second generation (silica-based): - DACA-SR/NO: Delay in NO release time and required thickening of the coating to provide an adequate reservoir of NO not practical for clinical use. - Silica/NO: NO reservoir depletion over 24 hours due to circuit raceway delamination. Third generation (DBHD/NO): fibrinogen consumption. NO releasing properties are destroyed at high temperatures thus impractical for standard tubing production through extrusion. NO releasing surfaces have a finite reservoir which is depleted after about 4 weeks.	Surface modification strategy that avoids NO leaching is successful with DBHD/NO. The molecule remains in the organic phase of the polymer. Addition of topcoat with direct thrombin inhibitor prevents fibrinogen consumption. In addition antibacterial properties of NO will suppress biofilm formation. NO-release is controlled by modulating the pH within the polymer and threshold flux of NO required to inhibit platelet activation can be finessed. While argatroban prevents fibrinogen adhesion/consumption. Alternative method of manufacture either by mandrel dip coating or cold extrusion to retain the biomimetic properties. Thus an NO compound that allows close control of NO release, no leaching and maintains durability. Using endogenous NO reservoirs from NO donors as alternative biomimetic surfaces (metal-organic frameworks; nanotechnology) is an option to a finite reservoir of NO release.
Omniphobic surfaces	Undergoing research with coating for medical devices that needs to yet be tested in extracorporeal circuits.	Develop a non-adhesive, anti-thrombogenic surface for extracorporeal circuits that will suppress biofilm formation, and will reduce the need for systemic anticoagulation.
Endothelialization	In vitro: - Completion of endothelialization can take months to years. - Tenuous process with long culture times and cannot be implemented in emergency cases. - Risk of contamination and infection - Cost ineffective and limited to facilities with the ability to do it. In vivo: - Low endothelial cell proliferation activity.	Create the ideal artificial surface that will enhance endothelial progenitor cells function and adhesion and inhibit thrombogenesis. Customize long term respiratory and cardiac support devices to the patient by seeding the devices with the patient's endothelial cells. Would obviate the need for aggressive anticoagulation if any.