Protein adsorption
The adsorption of larger biomolecules such as proteins is of high physiological relevance, and as such they adsorb with different mechanisms than their molecular or atomic analogs.
By knowing how these factors affect protein adsorption, they can then be manipulated by machining, alloying, and other engineering techniques to select for the most optimal performance in biomedical or physiological applications.
[2] Taking this a step further, implantable devices can be coated with a bioactive material to encourage adsorption of specific proteins, fibrous capsule formation, and wound healing.
The adhesion properties of proteins to non-biological surfaces greatly influences whether or not cells can indirectly attach to them via scaffolds.
Surgical tools can be designed to be sterilized more easily so that proteins do not remain adsorbed to a surface, risking cross-contamination.
[3] Some devices are intended to interact with the internal body environment such as sensors or drug-delivery vehicles, and protein adsorption would hinder their effectiveness.
Each amino acid has a side chain that gains or loses charge depending on the pH of the surrounding environment, as well as its own individual polar/nonpolar qualities.
In terms of surface chemistry, protein adsorption is a critical phenomenon that describes the aggregation of these molecules on the exterior of a material.
Larger proteins are more likely to adsorb and remain attached to a surface due to the higher number of contact sites between amino acids and the surface (Figure 1).The fundamental idea behind spontaneous protein adsorption is that adsorption occurs when more energy is released than gained according to Gibbs law of free energy.
[6] In order for proteins to adsorb, they must first come into contact with the surface through one or more of these major transport mechanisms: diffusion, thermal convection, bulk flow, or a combination thereof.
These effects are short-range because of the high di-electric constant of water, however, once the protein is close to a charged surface, electrostatic coupling becomes the dominant force.
During a folding and association process, peptide and amino acid groups exchange hydrogen bonds with water.
[12][13] Ionic strength determines the Debye length that correlates with the damping distance of the electric potential of a fixed charge in an electrolyte.
In multi-protein system attraction between molecules can occur, whereas in single-protein solutions intermolecular repulsive interactions dominate.
Γp = Δcp V/Atot where: This method also requires a high surface area material such as particulate and beaded adsorbents.
This technique requires planar, reflecting surfaces, preferably quartz, silicon or silica, and a strong change in refractive index upon protein adsorption.
This technique is based on the excitation of surface plasmons, longitudinal electromagnetic waves originated at the interface between metals and dielectrics.
In addition to the adsorption studies, QCM-D also provides information regarding elastic moduli, viscosity, and conformational changes [17] Optical waveguide lightmode spectroscopy (OWLS) is a device that relies on a thin-film optical waveguide, enclosing a discrete number of guided electromagnetic waves.
[18] This intermolecular force is relatively strong, and gives rise to the repeated crystalline orientation of atoms, also referred to as its lattice system.
This state of higher energy is unfavorable, and the surface atoms will try to reduce it by binding to available reactive molecules.
[5] In terms of biomedical engineering applications, micromachining techniques are often used to increase protein adhesion to implants in the hopes of shortening recovery time.
Grit-blasting, a method analogous to sand blasting, and chemical etching have proven to be successful surface roughening techniques that promote the long-term stability of titanium implants.
As the chain grows by the addition of mers, the chemical and physical properties of the material are dictated by the molecular structure of the monomer.
These conformational changes can affect protein interaction with ligands, substrates, and antigens which are dependent on the orientation of the binding site of interest.
In addition to the essentials of mechanics and geometry, a suitable scaffold construct will possess surface properties that are optimized for the attachment and migration of the cell types of particular interest.
As a result, much research has gone into investigating natural polymers that can be tailored, through processing methodology, toward specific design criteria.
Chitosan is currently one of the most widely used polymers as it is very similar to naturally occurring glycosaminoglycan (GAGs) and it is degradable by human enzymes.
[28] Chitosan is a linear polysaccharide containing linked chitin-derived residues and is widely studied as a biomaterial due to its high compatibility with numerous proteins in the body.
Chitosan is cationic and thus electrostatically reacts with numerous proteoglycans, anionic GAGs, and other molecules possessing a negative charge.
Since many cytokines and growth factors are linked to GAG, scaffolds with the chitosan-GAG complexes are able to retain these proteins secreted by the adhered cells.
