Bioadhesion phenomenon

The different theories that have been proposed to explain the bioadhesion phenomenon are hereafter summarized. The design of bioadhesive drug delivery systems should take into account the mechanisms on which the bioadhesion phenomenon is based. An insight into bioadhesion theories could help formulators to design bioadhesive drug delivery systems with optimal performances. 

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. 

Takayama K, Hirata M, Machida Y et al (1990) Effect of interpolymer complex formation on bioadhesive property and drug release phenomenon of compressed tablet consisting of chitosan and sodium hyaluronate. Chem Pharm Bull 38 1993-1997... 

Thus, protein adsorption and cell adhesion occur for various reasons and in different appearances. When surfaces of living systems are involved, specific recognition mechanisms undoubtedly play crucial roles. Nevertheless, since we are dealing with a rather general phenomenon, it is likely that these specific interactions are superimposed on a generic interaction mechanism. Bioadhesion and adsorption is very complicated from a physical chemical point of view. Interfacial tensions, wetting and electrical properties of the surfaces are prominently involved. 

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 ... 

Bioadhesion can be defined as the process by which a natural or a synthetic polymer can adhere to a biological substrate. When the biological substrate is a mucosal layer, the phenomenon is known as mucoadhesion. The substrate possessing bioadhesive property can help in devising a delivery system capable of delivering a bioactive agent for a prolonged period of time at a specific delivery site. 

FTIR spectroscopy has proven to be particularly useful in gaining an understanding of the biocompatibility phenomenon. It is believed [746, 841, 856, 857] that protein adsorption is the initial step in the interaction of blood with implanted biomaterials, followed by adhesion of cells and subsequent tissue attachment. This implies that the substrate surface characteristics influence the process, which was confirmed by ATR studies of albumin adsorption on calcium phosphate bioceramics and titanium [763] and segmented polyurethane [764], albumin and fibrinogen on acetylated and unmodified cellulose [765, 766], poly(acrylic acid)-mucin bioadhesion [767], polyurethane-blood contact surfaces [768], and other proteins on poly(ester)urethane [769], polystyrene [767, 771] and poly(octadecyl methacrylate) [771] and by IRRAS study of adsorption of proteins on Cu [858]. Another branch of IR spectroscopic studies of protein adsorption relates to microbial adhesion (Section 7.8.3). 

One of the most relevant, if not the most relevant, coUoidal and interfacial phenomenon in life sciences is bioadhesion, that is, the joining together of surfaces of which at least one is of biological nature. Usually, bioadhesion involves the association of a biological cell (including bacterial cells) with the surface of a living or an inanimate substratum. In the special case where the adhesion is between particles of comparable size, it may be referred to as aggregation, and adhesion at a gas-liquid interface is also called flotation. 

In the introductory part of this chapter, it is mentioned that in various systems and applications, bioadhesion is an unwanted phenomenon. Different strategies may be taken to prevent or suppress (microbial) cell adhesion and biofilm formation. Coating the surface with antimicrobial agents such as silver nanoparticles may have some effect. However, the hazard of release of such toxic particles in the body, product, or enviromnent puts severe restrictions on their use. Furthermore, prophylactic supply of antibiotics to treat biomaterials associated infections is in most cases highly unsuccessful, because in biofilms bacteria tend to be resistant against antibiotics. 

Bioadhesion can present the following mechanisms a wetting or swelling phenomenon (intimate contact between a bioadhesive and a membrane) and/or an interpenetration phenomenon (penetration of the bioadhesive into the tissue or into the surface... 

Bioadhesion as an Interface Phenomenon in Biocompatibility of Implant Materials , D. F. Williams, Editor, Pitman (Med), London... 

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