Bioadhesion biological

The electronic theory is based on the assumption that the mucoadhesive hydrogel and the target biological tissue have different electronic structures. When two materials come into contact with each other, electron transfer occurs, causing the formation of a double layer of electrical charge at the bioadhesive-biological interface. The bioadhesive force is believed to be due to attractive forces across this electrical double layer. 

Chitosan acetate and lactate salt films have been tested as wound-healing materials. Mechanical, bioadhesive and biological evaluation of the films were carried out. The results were compared to Omiderm . Chitosan lactate exhibited a lower tensile strength, however, it was more flexible and bioadhesive than chitosan acetate. Chitosan lactate and Omiderm did not cause any allergic reactions in contrast, chitosan acetate produced skin irritation clearly due to the anion. Nevertheless, no sign of toxicity was encountered when the extracts of three preparations were administered parenterally [244]. 

Additionally, the fracture energy for a zero extension rate can be defined as the bioadhesion work to the initial surface between the bioadhesive material (in a form of a tablet or disk) and the biological support of a surface Aq, which allows for calculation of the fracture energy (e) using Eq. (8). 

The term bioadhesion ean be defined as the ability of a material (synthetic or natural) to stick (adhere) to a biological tissue for extended periods of time [27]. The phenomenon of bioadhesion can be visualized as a two-step process. The first step involves the initial contaet between polymer and the biological tissue. The second step is the formation of seeondary bonds due to noncovalent interactions. The strength of bioadhesion (expressed as the foree of detachment) for a novel oligosaccharide gum Hakea Gibbosa) contained in a buccal tablet developed by Alur et al. [28,29]... 

Bioadhesive formulations and microsphere delivery systems in particular have attracted much attention. As drug formulations are usually rapidly removed from the site of deposition by the mucociliary clearance, increasing the retention time of drug in the nasal cavity via bioadhesion can increase bioavailability [28], Bioadhesion may be defined as the ability of a material (synthetic or biological) to adhere to a biological tissue for an extended period of time. When applied to a mucous membrane, a bioadhesive polymer may adhere primarily to the mucus layer or epithelial cell surface in a phenomenon known as mucoadhesion [29,30]. The bioadhesive properties of a wide range of materials have been evaluated over the last decade. 

The term bioadhesion refers to any bond formed between two biological surfaces or to a bond between a biological and a synthetic surface [44]. In the case of bioadhesive drug delivery systems, the term bioadhesion is typically used to describe the adhesion between polymers, either synthetic... 

Two steps have been described in adhesive bond formation (1) intimate contact of the mucoadhesive agent and of mucus or mucosa consequent to wetting and (2) formation of physical or chemical bonds between the biological substrate and the mucoadhesive agent, preceded, in the case of polymeric materials, by interpenetration and diffusion between the bioadhesive and the mucin glycoprotein. 

A confirmation of the soundness of electronic theory was derived from a recent study, performed by Bogotaj et al. [46], They measured the zeta potential of different polymer dispersions and mucosal homogenates and found a correlation between such a parameter and the force necessary to detach a polymer dispersion from the biological substrate. The adsorption theory states that the bioadhesive bond is due to van der Waals interactions, hydrogen bonds, and other related weak interactions [44],... 

The wetting theory is applicable to liquid bioadhesive systems. According to this theory, the ability of a bioadhesive material to spread and determine an intimate contact with the biological substrate plays a major role in bond formation [44], This theory uses interfacial tensions to predict spreading and, in turn, bioadhesion. In the past, the surface energy of both bioadhesive materials and tissues or mucus have been extensively studied to predict the bioadhesive performance [47-49]. 

Artificial membranes soaked in animal mucin dispersions or animal model mucosae are used as biological substrates. Another apparatus proposed for in vitro measurements of bioadhesive properties of liquid formulations (polymer solutions or pessaries upon melting) consists of a thermostated inclined plane over which a mucosal membrane or a mucin film is layered. This test measures, as a function of time, the amount of formulation that after contact with the biological substrate, drops on a microbalance placed under the inclined plane [86] (Figure 22.3). 

Bioadhesives (sometimes also termed mucoadhesives) adhere to biological substrates such as mucus or tissue. Bioadhesives are proposed to influence dmg bioavailability by ... 

Bioadhesion is an interfacial phenomenon in which a synthetic or natural polymer becomes attached to a biological substrate by means of interfacial forces. If it involves mucin or mucous-covered membrane, the narrow term mucoadhesion is employed. Bioadhesion has been used to enhance bioavailability of dmgs via various other routes including oral (Section 6.7.1), transmucosal (Section 1.123) and vaginal (Section 11.7.6). Bioadhesion may offer several unique features ... 

Mucoadhesive Polymers Bioadhesion refers to the attachment of a drug molecule or a delivery system to a specific biological tissue by means of interfacial forces. If the surface of the tissue is covered by a mucin film, as is the case for the external globe, it is more commonly referred to as mucoadhesion. 

Zaman, M. McAlhster, M. Martini, L.G. Lawrence, M.J. The physicochemical and biological factors influencing bioadhesion. Pharm. Tech. Eur. 1999, 11 (8-Biopharm. 

Adhesion between a surface of a hydrophilic polymer, or a surface to which a hydrophilic polymer has been grafted or adsorbed, and a biological surface arises from interactions between the polymer chains and the macromolecules on the mucosal surface. From Fig. 8.23(a) it is clear that to achieve maximum adhesion there should be maximum interaction between the polymer chains of the bioadhesive (A) and the mucus (B). The charge on the molecules will be important, and for two anionic polymers maximum interaction will occur when they are not charged. Penetration and association must be balanced. Table 8.5 shows the adhesive performance of a... 

---