Surface Modification and Functionalization

BOC Sciences can select the right PEG or PEGylate substance for the materials provided according to the customer's needs, and carry out PEG modification and functionalization services with high quality.

Biomedical materials are mainly in contact with blood, tissues or organs, and there are always some biological reactions between the interfaces, such as the adsorption of plasma proteins and the formation of a thrombus. Therefore, the biomedical materials used to manufacture artificial hearts and artificial blood vessels must have excellent blood compatibility. As well known, polyethylene glycol (PEG) is an excellent hydrophilic polymer and has good blood compatibility. Its coating process on the biomedical materials for modification and functionalization has been widely accepted by the medical industry.

Why PEG?

Polyethylene glycol (PEG) is a kind of linear or branched polyether derived from ring-opening polymerization of epoxyethane. In spite of being a high molecular polymer, PEG possesses some excellent properties such as strong polarity and the resulting hydrophilicity and water-solubility. Due to its excellent hydrophilicity, PEG can make the material have a lower friction coefficient in the wet state, while in the dry state there is no different from ordinary materials, which can improve the mobility of the material and reduce the probability of adhesion to the tissue. On the other hand, the polymer chain of hydrated-PEG can affect the microscopic dynamic environment of the interface between blood and material, and reduce the interaction between plasma protein and material, thus PEG has good blood compatibility and can be used to modify various biomedical materials. In addition, because PEG can be soluble in many different organic solvents, such as dimethylformamide (DMF), tetrahydrofuran (THF), etc., it is easy to process PEG coating on the surface of medical devices by dipping or spraying.

Methods for Surface Modification and Functionalization

There are several approaches to modify the surface of biomedical materials: physical adsorption, surface grafting reactions and surface polymerization.

  • Physical adsorption
  • Physical adsorption is the most traditional strategy, taking advantages of simple operation, relatively few control conditions and low experiment threshold. Physical adsorption is the force between the adsorbed fluid molecules and the solid surface molecules, which is also called Van der Waals force. This is a reversible process. When the gravitational force between the molecules on the solid surface and the gas or liquid molecules is greater than that inside the gas or liquid, the molecules of the gas or liquid will be adsorbed on the solid surface. Although this method is simple, it still faces the problems of low adsorption strength and unstable of formed layer. Consequently, this strategy of surface modification is suitable for the cases that do not require bigger amount and higher adsorption strength PEG on the surface, or that the substrates have strong adsorption capacity.

  • Surface grafting
  • Diagram of PEG silane coupling reaction for surface grafting
    Fig. 1 Diagram of PEG-silane coupling reaction for surface grafting. (Chinese Journal of Analytical Chemistry, 2013, 3(41): 445-453.)

    Surface grafting strategy is available for surface modification only when both the substrate surface and PEG terminal have reaction activity. For silicon and other silicon-based substrates, PEG-silane coupling reaction is an ideal method. Grafted polymers chains can be securely bonded on the substrates by the high strength Si-O bonds even in tough environment. Moreover, click chemistry is also suitable for the surface modification process due to its characteristics and advantages of mild and controllable reaction conditions, as well as its high yield. Through surface grafting strategy, the grafted bonds are stable enough so that the modified materials will become more durable, and the types of grafted PEGs can be easily chosen or synthesized in advance. However, it is hard to precisely calculate the surface grafting density and know if it meets with the requirements for application.

  • Surface polymerization
  • Surface polymerization procedure and further bio application based on PEG derivatives
    Fig. 2 Surface polymerization procedure and further bio-application based on PEG derivatives. (Chinese Journal of Analytical Chemistry, 2013, 3(41): 445-453.)

    Surface polymerization is a strategy that the macromolecules grow on the substrate surfaces by polymerization using the appropriated monomers and reagents. In this method, surface-initiated free radical polymerization is usually adopted, and commonly used methods for generation of free radicals involve ozone pretreatment, plasma treatment, ultraviolet irradiation and etc. Surface polymerization is an efficient PEG surface modification strategy with high surface grafting density. In addition, it is more versatile which allows various of substrates with different properties and structures to be constructed. The procedures, however, are relatively complex, and the original regularity of surfaces is difficult to be maintained.

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Reference

  1. Xiao X F, Jiang X Q, et al. Surface modification of poly ethylene glycol to resist nonspecific adsorption of proteins. Chinese Journal of Analytical Chemistry, 2013, 3(41): 445-453.

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