Improved synthesis and in vitro characterization of chitosan–thioethylamidine conjugate

Kafedjiiski, Krum; Hoffer, Martin; Werle, Martin; Bernkop‐Schnürch, Andreas

doi:10.1016/j.biomaterials.2005.05.075

Cited by 60 publications

(45 citation statements)

References 21 publications

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“…Typical examples of polymeric thiomers include the following conjugates: poly(acrylic acid)/cystein, [95] chitosan/N-acetylcystein, [96] alginate/cystein, [97] chitosan/thioglycolic acid [98] and chitosan/thioethylamidine. [99] The mucoadhesive properties of polymeric thiomers have been extensively studied by Bernkop-Schnurch and coworkers. [49,94] They established that these polymers are capable of forming covalent bonds (disulfide bridges) with cysteinrich sub-domains of mucus glycoproteins either via thiol/ disulfide exchange reactions or through a simple oxidation of free thiol groups ( Figure 10).…”

Section: Polymeric Thiomersmentioning

confidence: 99%

Advances in Mucoadhesion and Mucoadhesive Polymers

Khutoryanskiy

2010

Macromolecular Bioscience

531

421

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Mucoadhesion is the ability of materials to adhere to mucosal membranes in the human body and provide a temporary retention. This property has been widely used to develop polymeric dosage forms for buccal, oral, nasal, ocular and vaginal drug delivery. Excellent mucoadhesive properties are typical for hydrophilic polymers possessing charged groups and/or non-ionic functional groups capable of forming hydrogen bonds with mucosal surfaces. This feature article considers recent advances in the study of mucoadhesion and mucoadhesive polymers. It provides an overview on the structure of mucosal membranes, properties of mucus gels and the nature of mucoadhesion. It describes the most common methods to evaluate mucoadhesive properties of various dosage forms and discusses the main classes of mucoadhesives.

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Section: Polymeric Thiomersmentioning

confidence: 99%

Advances in Mucoadhesion and Mucoadhesive Polymers

Khutoryanskiy

2010

Macromolecular Bioscience

531

421

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“…The reaction mixture is stirred and incubated at room temperature for several hours. Finally, this is dialyzed to remove unbound reagents and lyophilized [26]. The initial reason for the introduction of thiol groups was based on the hypothesis that these thiol groups would form disulfide bonds with the thiol groups of the mucus, consequently leading to high mucoadhesive properties [20,27].…”

Section: Synthesis Of Thiolated Chitosansmentioning

confidence: 99%

Chitosan and Thiolated Chitosan

Sarti

Bernkop‐Schnürch

2011

Advances in Polymer Science

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Thiolated chitosans constitute an integral part of designated "thiomers", which are thiolated polymers widely investigated for non-invasive drug delivery. In brief, thiomers display thiol-group-bearing ligands on their polymer backbone. Through thiol/disulfide exchange reactions and/or a simple oxidation process, disulfide bonds are formed between such polymers and the cysteine-rich subdomains of mucus glycoproteins, thus building up the mucus gel layer. Most chemical modifications of chitosan are performed at the free amino groups of the glucosamine units. So far, the alkyl thiomers chitosan-cysteine, chitosan-thiobutylamidine, chitosan-thioglycolic acid, chitosan-N-acetylcysteine, and chitosan-thioethylamidine and the aryl thiomers chitosan-6-mercaptonicotinic acid and chitosan-4-mercaptobenzoic acid have been generated. Due to the immobilization of thiol groups on the chitosan backbone, its mucoadhesive, permeation enhancing, in situ gelling, efflux pump inhibitory, and controlled drug release properties are improved. The great benefits of this new generation of chitosans in comparison to the corresponding unmodified polymers has been verified via numerous in vivo studies on various mucosal membranes. A proof of concept for oral, nasal and buccal drug delivery is provided. This chapter includes an overview of the mechanism of adhesion and the design of thiomers as well as of delivery systems comprising thiolated chitosans and their in vivo performance.

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“…Furthermore, the pH of the solution has a great impact as the higher the pH the more rapid and to a higher extent the oxidation of thiol groups proceed. This oxidation behaviour can be explained by the pKa of the thiol moieties and by the stearic factors (Kafedjiiski et al 2006). On the one hand, disulphide bonds are responsible for the stability of chitosan microand nanoparticles and on the other hand free thiol groups are essential for improved mucoadhesive and permeation enhancing properties (Bernkop-Schnürch et al 2006a).…”

Section: Preparation Of Nanoparticles Via High Pressure Homogenizermentioning

confidence: 99%

Preparation and evaluation of thiomer nanoparticles via high pressure homogenization

Hoyer¹,

Schlocker²,

Greindl³

et al. 2010

Journal of Microencapsulation

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The aim of this study was to establish and evaluate a high pressure homogenization method for the preparation of thiomer nanoparticles. Particles were formulated by incorporation of the model protein horseradish peroxidase in chitosan-glutathione (Ch-GSH) and poly(acrylic acid)-glutathione (PAA-GSH) via co-precipitation followed by air jet milling. The resulting microparticles were suspended in distilled water using an Ultraturax and subsequently micronized by high pressure homogenization. Finally, resulting particles were evaluated regarding size distribution, shape, zeta potential, drug load, protein activity and release behaviour. The mean particle size after 30 cycles with a pressure of 1500 bar was 538 +/- 94 nm for particles consisting of Ch-GSH and 638 +/- 94 nm for particles consisting of PAA-GSH. Nanoparticles of Ch-GSH had a positive zeta-potential of +1.03 mv, whereas nanoparticles from PAA-GSH had a negative zeta potential of -6.21 mv. The maximum protein load for nanoparticles based on Ch-GSH and based on PAA-GSH was 45 +/- 2% and 37 +/- %, respectively. The release profile of nanoparticles followed a first order release kinetic. Thiolated nanoparticles prepared by a high pressure homogenization technique were shown to be stable and provide controlled drug release characteristics. The preparation method described here might be a useful tool for a more upscaled production of nanoparticulate drug delivery systems.

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Improved synthesis and in vitro characterization of chitosan–thioethylamidine conjugate

Cited by 60 publications

References 21 publications

Advances in Mucoadhesion and Mucoadhesive Polymers

Advances in Mucoadhesion and Mucoadhesive Polymers

Chitosan and Thiolated Chitosan

Preparation and evaluation of thiomer nanoparticles via high pressure homogenization

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