Learn definition and principles of bioadhesion with theories. Bioadhesion is a process where biological molecules adhere to one another.
What is Bioadhesion?
In novel drug delivery, the term bioadhesion define as a process where a drug carrier make attachment to a specific biological system.
Principles of bioadhesion
In chemistry, the molecules should bind across the interface for adhesion through the following bonds:
1) Ionic Bonds: These strong bonds are formed when two oppositely charged ions attach to each other through electrostatic interactions (e.g., in a salt crystal).
2) Covalent Bonds: Here strong bonds form when electron pairs are shared between atoms.
3) Hydrogen Bonds: These bonds are generally weaker than ionic or covalent bonds. Here hydrogen (positively charged) atom is binds to electronegative atoms like oxygen or nitrogen.
4) Van der Waals Bonds: These are some of the weaker forms of interaction. They arise from dipole-dipole attractions and dispersion forces.
5) Hydrophobic Bonds (Hydrophobic Effect): These are also some of the weakest interactions. This occur when non-polar groups attach in an aqueous solution. Water molecules near non-polar groups form hydrogen bonded structures and also minimizes system entropy. This water molecules also increase the tendency for non-polar groups to stick together.
What are the theories of bioadhesion?
The process of bioadhesive can be complex. It involves more than one of the following theories,
1) Wetting theory:
This theory is applied to liquid systems and takes into account surface and interfacial energies. It involves the ability of a liquid to spontaneously spread on a surface as a pre-requisite for adhesion development.
2) Electronic theory:
As per this theory, electron transfer occurs across contacting adhering surfaces due to differences in their electronic structure. This results in the formation of an electrical double layer, which is adhered to the interface due to attractive forces.
3) Adsorption theory:
This theory defines the attachment of adhesives due to hydrogen bonds and Van der Waal forces. These forces mainly contribute to the adhesive interaction. As per the chemisorption theory (a subsection of adsorption theory) it is an interaction across the interface occurs due to strong covalent bonds.
4) Diffusion theory:
This theory defines the inter diffusion of polymer chains across an adhesive interface driven by concentration gradients. This is affected by the available molecular chain lengths, the compatibility of two polymers and their mobilities. The diffusion coefficient and the contact time influence the depth of inter penetration. If the penetration depth is sufficient, a semi-permanent adhesive bond is formed.
5) Mechanical theory:
As per this theory, adhesion arises from an interlocking of a liquid adhesive (on setting) into irregularities on a rough surface. Rough surfaces also provide an increased surface area for interaction along with an enhanced viscoelastic and plastic dissipation of energy during joint failure, which are important in the adhesion process.
6) Fracture Theory:
This theory relates the adhesive strength to the forces required for detaching the two involved surfaces after adhesion. This theory assumes that the failure of adhesive bond occurs at the interface. However, failure occurs at the weakest component, which is a cohesive failure within one of the adhering surfaces.
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