Bioadhesion tissues

Also, PVA hydrogels evidenced a very good behaviour in contact with skin and other tissues, mucosa, or blood. PVA exhibits a bioadhesive nature, shape-memory properties, avoid the protein adsorption onto the gel surface and is biocompatible. 

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. 

The adsorption theory states that the bioadhesive bond formed between an adhesive substrate and tissue or mucosae is due to van der Waals interactions, hydrogen bonds, and related forces. Alternatively, when mucus or saliva are interacting with a solid dosage form, the molecules of the liquid are adsorbed on the solid surface. This is an exothermic process. The free energy of adsorption is given by Eq. (1). 

Peppas, N.A., and Buri, P., Surface, interfacial and molecular aspects of polymer bioadhesion on soft tissue, J. Control. Rel., 2 257-275 (1985). 

Chickering, D.E.lll, Jacob, J.S., and Mathiowitz, E., Bioadhesive microspheres. 2. Characterization and evaluation of bioadhesion involving hard, bioerodible polymers and soft tissue. Reactive Polymers, 25 189-206 (1995). 

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. 

It is possible to study cilia beat frequency and drug interaction with mucus independently using models such as tissue explants or cultures of ciliated cells or purified mucus preparations. However, these are not able to provide information about mucociliary transport rates. For such studies, a model incorporating the integrated cilia and mucus components is required such as the frog palate. Drugs, preservatives and absorption enhancers, and bioadhesive formulations have been extensively studied in this model [9]. 

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]. 

Some of the most promising data on gastroretentive delivery systems using bioadhesion have resulted from the use of acrylate-based as well as chitosan-based polymers. Poly(acrylates) have been shown to have significant mucoadhesive properties in contact with intestinal mucosal tissues.104 122 135 Longer et al.136 demonstrated successful reduction in the... 

Li H, Song J-H, Park J-S, Han K (2003) Polyethylene glycol-coated liposomes for oral delivery of recombinant human epidermal growth factor. Int J Pharm 258(1-2) 11-19 Liu L, Fishman ML, Hicks KB, Kende M (2005) Interaction of various pectin formulations with porcine colonic tissues. Biomaterials 26 5907-5916 Longer MA, Ch ng HS, Robinson JR (1985) Bioadhesive polymers as platforms for oral controlled drug delivery III Oral delivery of chlorothiazide using a bioadhesive polymer. J Pharm Sci 74 406-411... 

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

Dry vagina the bioadhesive gel can hydrate vaginal tissue for 3-4 days after a single application. Tissue hydration is caused by an increased blood flow, thus increasing transudation of vaginal fluid though the intercellular channels of the vaginal epithelium. 

Spermicide-antiviral the polymer appears to be an effective delivery system for the spermicidal/antiviral agent nonoxynol-9. By its ability to adhere to vaginal tissue while retaining nonoxynol-9 in its gel structure, it is an excellent extended effect spermicide. As an antiviral, nonoxynol-9 can only kill free HIV and is not noticeably active when the virus is within a lymphocyte. In contrast, the bioadhesive gel containing nonoxynol-9 attaches to lymphocytes and maintains sufficient contact time to allow the nonoxynol-9 surfactant to disrupt the cell wall, thus eliminating the lymphocyte and killing the vims within. This suggests that the polymer may be useful in the prophylaxis of AIDS and the treatment of other sexually transmitted diseases. 

Muller, R. H., and Heinemann, S. (1989), Surface modeling of microparticles as parenteral systems with high tissue affinity, in Bioadhesion-Possibilities and Future Trends, Wissenschaftliche Verlagsgesellschaft, Stuttgart, pp. 202-214. 

Poly(alkyl-cyanoacrylates) As poly(alkyl-cyanoacrylates) form strong bonds with polar substrates including the skin and living tissues, they exhibit bioadhesive properties. These polymers are synthesized by free-radical, anionic, or zwitterionic polymerization. As detailed in a recent review, poly(alkyl-cyanoacrylate) nanoparticles are prepared by emulsion polymerization, interfacial polymerization, nanoprecipitation, and emulsion-solvent evaporation methods [102],... 

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. 

Woolfson, A. D., McCafferty, D. F., McCarron, P. A., and Price, FI. (1995), A bioadhesive patch cervical drug delivery system for the administration of 5-fluorouracil to cervical tissue, J. Controlled Release, 35,49-58. 

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