example of mucoadhesive polymer
Answers
Explanation:
The mucoadhesive polymers used for the ocular delivery include thiolated poly(acrylic acid), poloxamer, celluloseacetoph- thalate, methyl cellulose, hydroxy ethyl cellulose, poly(amidoamine) dendrimers, poly(dimethyl siloxane) and poly(vinyl pyrrolidone) [55–57].
Answer:
The phenomena of bioadhesion occurs by a complex mechanism. T. date, six theories have been proposed which can improve our understanding for the phenomena
of adhesion and can also be extended to explain the mechanism of bioadhesion. The
theories include: (i) the electronic theory, (ii) the wetting theory, (iii) the adsorption
theory, (iv) the diffusion theory, (v) the mechanical theory and (vi) the cohesive
theory. The electronic theory proposes transfer of electrons amongst the surfaces
resulting in the formation of an electrical double layer thereby giving rise to attractive forces. The wetting theory postulates that if the contact angle of liquids on
the substrate surface is lower, then there is a greater affinity for the liquid to the
substrate surface. If two such substrate surfaces are brought in contact with each
other in the presence of the liquid, the liquid may act as an adhesive amongst the
substrate surfaces. The adsorption theory proposes the presence of intermolecular
forces, viz., hydrogen bonding and Van der Waals forces, for the adhesive interaction amongst the substrate surfaces. The diffusion theory assumes the diffusion of
the polymer chains, present on the substrate surfaces, across the adhesive interface
thereby forming a networked structure. The mechanical theory explains the diffusion of the liquid adhesives into the micro-cracks and irregularities present on the
substrate surface thereby forming an interlocked structure which gives rise to adhesion. The cohesive theory proposes that the phenomena of bioadhesion are mainly
due to the intermolecular interactions amongst like-molecules [24, 25].
Based on the above theories, the process of bioadhesion can be broadly classified into two categories, namely chemical (electronic and adsorption theories) and
physical (wetting, diffusion and cohesive theory) methods [26, 27]. The process
of adhesion may be divided into two stages. During the first stage (also known as
contact stage), wetting of mucoadhesive polymer and mucous membrane occurs
followed by the consolidation stage, where the physico-chemical interactions prevail [28, 29].
As mentioned above, bioadhesion may take place either by physical or by chemical interactions. These interactions can be further classified as hydrogen bonds, Van
der Waals force and hydrophobic bonds which are considered as physical interactions while the formation of ionic and covalent bonds are categorized as chemical
interactions. Hydrogen bonds are formed due to the interaction of the electronegative and electropositive atoms though there is no actual transfer of electrons. An
example of this kind of interaction is the formation of a gelled structure when aqueous solutions of poly(vinyl alcohol) and glycine are mixed. Van der Waals forces are
either due to presence of the dipole–dipole interactions in polar molecules or due to
the dispersion forces amongst non-polar substrates. Hydrophobic bonds are formed
due to the interaction of the non-polar groups when the polymers are dispersed in an aqueos solution
Explanation:
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