Chitosan and Derivatives for Biopharmaceutical Use: Mucoadhesive Properties

Chitosan-Based Systems for Biopharmaceuticals: Delivery, Targeting and Polymer Therapeutics

Volumn , Issue , 2012, Pages 159-180

  Leithner, Katharina ^a   Bernkop Schnürch, Andreas ^a  

^a UNIVERSITY OF INNSBRUCK   (Austria)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 84884907235     PISSN: None     EISSN: None     Source Type: Book    
DOI: 10.1002/9781119962977.ch10     Document Type: Chapter

References (111)

1. Gu, J.M., Robinson, J.R. and Leung, S.H. (1988) Binding of acrylic polymers to mucin/epithelial surfaces: structureproperty relationships. Crit. Rev. Ther. Drug Carrier Syst., 5, 21-67.
2. Streubel, A., Siepmann, J. and Bodmeier, R. (2006) Gastroretentive drug delivery systems. Expert Opin. Drug Deliv., 3, 217-233.
3. 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. (Tokyo), 38, 1993-1997.
4. Bernkop-Schnürch, A., Hornof, M. and Guggi, D. (2004) Thiolated chitosans. Eur. J. Pharm. Biopharm., 57, 9-17.
5. Leitner, V.M., Walker, G.F. and Bernkop-Schnürch, A. (2003) Thiolated polymers: evidence for the formation of disulphide bonds with mucus glycoproteins. Eur. J. Pharm. Biopharm., 56, 207-214.
6. Illum, L., Farraj, N.F. and Davis, S.S. (1994) Chitosan as a novel nasal delivery system for peptide drugs. Pharm. Res., 11, 1186-1189.
7. Schipper, N.G., Varum, K.M. and Artursson, P. (1996) Chitosans as absorption enhancers for poorly absorbable drugs. 1: Influence of molecular weight and degree of acetylation on drug transport across human intestinal epithelial (Caco-2) cells. Pharm. Res., 13, 1686-1692.
8. van der Lubben, I.M., Verhoef, J.C., Borchard, G. and Junginger, H.E. (2001) Chitosan and its derivatives in mucosal drug and vaccine delivery. Eur. J. Pharm. Sci., 14, 201-207.
9. Lai, W.F. and Lin, M.C. (2009) Nucleic acid delivery with chitosan and its derivatives. J. Control. Release, 134, 158-168.
10. Werle, M., Takeuchi, H. and Bernkop-Schnürch, A. (2009) Modified chitosans for oral drug delivery. J. Pharm. Sci., 98, 1643-1656.
11. Amidi, M., Mastrobattista, E., Jiskoot, W. and Hennink, W.E. (2010) Chitosan-based delivery systems for protein therapeutics and antigens. Adv. Drug Deliv. Rev., 62, 59-82.
12. Harding, S.E., Davis, S.S., Deacon, M.P. and Fiebrig, I. (1999) Biopolymer mucoadhesives. Biotechnol. Genet. Eng. Rev., 16, 41-86.
13. Kerss, S., Allen, A. and Garner,A. (1982)Asimple method for measuring thickness of the mucus gel layer adherent to rat, frog and human gastric mucosa: influence of feeding, prostaglandin, N-acetylcysteine and other agents. Clin. Sci. (Lond.), 63, 187-195.
14. Allen, A., Cunliffe,W.J., Pearson, J.P. and Venables, C.W. (1990) The adherent gastric mucus gel barrier in man and changes in peptic ulceration. J. Intern. Med. Suppl., 732, 83-90.
15. Sonju, T., Christensen, T.B., Kornstad, L. and Rolla, G. (1974) Electron microscopy, carbohydrate analyses and biological activities of the proteins adsorbed in two hours to tooth surfaces in vivo. Caries Res., 8, 113-122.
16. Smart, J.D. (2005) The basics and underlying mechanisms of mucoadhesion. Adv. Drug Deliv. Rev., 57, 1556-1568.
17. Peppas, N.A. and Sahlin, J.J. (1996) Hydrogels as mucoadhesive and bioadhesive materials: a review. Biomaterials, 17, 1553-1561.
18. Ahuja, A., Khar, R.K. and Ali, J. (1997) Mucoadhesive drug delivery systems. Drug Dev. Ind. Pharm., 23, 489-515.
19. Andrews, G.P., Laverty, T.P. and Jones, D.S. (2009) Mucoadhesive polymeric platforms for controlled drug delivery. Eur. J. Pharm. Biopharm., 71, 505-518.
20. Wu, S. (1982) Polymer Interface and Adhesion, Marcel Dekker, New York.
21. Smart, J.D. (1999) The role of water movement and polymer hydration in mucoadhesion, in Bioadhesive Drug Delivery Systems: Fundamentals, Novel Approaches and Development (eds E. Mathiowitz, D.E. Chickering III and C.-M. Lehr), Marcel Dekker, New York.
22. Rinaudo, M., Auzely, R., Vallin, C. and Mullagaliev, I. (2005) Specific interactions in modified chitosan systems. Biomacromolecules, 6, 2396-2407.
23. Bernkop-Schnürch, A. (2000) Chitosan and its derivatives: potential excipients for peroral peptide delivery systems. Int. J. Pharm., 194, 1-13.
24. He, P., Davis, S.S. and Illum, L. (1998) In vitro evaluation of the mucoadhesive properties of chitosan microspheres. Int. J. Pharm., 166, 75-88.
25. Sogias, I.A.,Williams, A.C. and Khutoryanskiy,V.V. (2008) Why is chitosan mucoadhesive? Biomacromolecules, 9, 1837-1842.
26. Arai, K., Kinumaki, T. and Fujita, T. (1968) Toxicity of chitosan. Bull. Tokai Reg. Fish Lab., 43, 89-94.
27. Illum, L. (1998) Chitosan and its use as a pharmaceutical excipient. Pharm. Res., 15, 1326-1331.
28. Roller, S. and Covill, N. (1999) The antifungal properties of chitosan in laboratory media and apple juice. Int. J. Food Microbiol., 47, 67-77.
29. Rhoades, J. and Roller, S. (2000) Antimicrobial actions of degraded and native chitosan against spoilage organisms in laboratory media and foods. Appl. Environ. Microbiol., 66, 80-86.
30. Anandan, R., Nair, P.G. and Mathew, S. (2004) Anti-ulcerogenic effect of chitin and chitosan on mucosal antioxidant defence system in HCl-ethanol-induced ulcer in rats. J. Pharm. Pharmacol., 56, 265-269.
31. Bernkop-Schnürch, A., Brandt, U.-M. and Clausen, A. (1999) Synthese und in vitro evaluierung von chitosan-cystein konjugaten. Sci. Pharm., 67, 197-208.
32. Bernkop-Schnürch, A., Hornof, M. and Zoidl, T. (2003) Thiolated polymers-thiomers: synthesis and in vitro evaluation of chitosan-2-iminothiolane conjugates. Int. J. Pharm, 260, 229-237.
33. Kast, C.E. and Bernkop-Schnürch, A. (2001) Thiolated polymers-thiomers: development and in vitro evaluation of chitosan-thioglycolic acid conjugates. Biomaterials, 22, 2345-2352.
34. Hornof, M.D., Kast, C.E. and Bernkop-Schnürch, A. (2003) In vitro evaluation of the viscoelastic properties of chitosan-thioglycolic acid conjugates. Eur. J. Pharm. Biopharm., 55, 185-190.
35. Bernkop-Schnürch, A. and Hopf, T.E. (2001) Synthesis and in vitro evaluation of chitosan-thioglycolic acid conjugates. Sci. Pharm., 69, 109-118.
36. Schmitz, T., Hombach, J. and Bernkop-Schnürch, A. (2008) Chitosan-N-acetyl cysteine conjugates: in vitro evaluation of permeation enhancing and P-glycoprotein inhibiting properties. Drug Deliv., 15, 245-252.
37. Kafedjiiski, K., Krauland, A.H., Hoffer, M.H. and Bernkop-Schnürch, A. (2005) Synthesis and in vitro evaluation of a novel thiolated chitosan. Biomaterials, 26, 819-826.
38. Kafedjiiski, K., Föger, F., Werle, M. and Bernkop-Schnürch, B. (2005) Synthesis and in vitro evaluation of a novel chitosan-glutathione conjugate. Pharm. Res, 22, 1480-1488.
39. Millotti, G., Samberger, C., Fröhlich, E., and Bernkop-Schnürch, A. (2009) Chitosan-graft-6-mercaptonicotinic acid: synthesis, characterization, and biocompatibility. Biomacromolecules, 10, 3023-3027.
40. Millotti, G., Samberger, C., Fröhlich, E. et al. (2010) Chitosan-4-mercaptobenzoic acid: synthesis and characterization of a novel thiolated chitosan. J. Mater. Chem., 20, 2432-2440.
41. Kafedjiiski, K., Hoffer, M., Werle, M. and Bernkop-Schnürch, A. (2006) Improved synthesis and in vitro characterization of chitosan-thioethylamidine conjugate. Biomaterials, 27, 127-135.
42. Ellman, G.L. (1958) A colorimetric method for determining low concentrations of mercaptans. Arch. Biochem. Biophys., 74, 443-450.
43. Habeeb, A.F. (1973) A sensitive method for localization of disulfide containing peptides in column effluents. Anal. Biochem., 56, 60-65.
44. Leitner, V.M., Walker, G.F. and Bernkop-Schnürch, A. (2003) Thiolated polymers: evidence for the formation of disulphide bonds with mucus glycoproteins. Eur. J. Pharm. Biopharm., 56, 207-214.
45. Roldo, M., Hornof, M., Caliceti, P. and Bernkop-Schnürch, A. (2004) Mucoadhesive thiolated chitosans as platforms for oral controlled drug delivery: synthesis and in vitro evaluation. Eur. J. Pharm. Biopharm, 57, 115-121.
46. Sakloetsakun, D., Perera, G., Hombach, J. et al. (2010) The impact of vehicles on the mucoadhesive properties of orally administrated nanoparticles: a case study with chitosan-4-thiobutylamidine conjugate. AAPS PharmSciTech., 11, 1185-1192.
47. Millotti, G., Perera, G., Vigl, C. et al. (2010) Novel thiolated chitosan tablets for oral insulin delivery: in vivo evaluation. Unpublished work, University of Innsbruck.
48. Bernkop-Schnürch, A. (1999) Polymer/inhibitor conjugates-a promising strategy to overcome the enzymatic barrier to perorally administered (poly)peptide drugs? STP Pharma Sci., 9, 83-92.
49. Inoue, K., Yamaguchi, T., Shinbaru, R. et al. (1996) Adsorption behaviors of some complexane types of chemically modified chitosan for metal ions, in Advances in Chitin Science, vol. I (eds A. Domard, C. Jeauniaux, R. Muzzarelli and G. Roberts), Jacques AndrÉ Publisher, Lyon.
50. Bernkop-Schnürch, A. and Krajicek, M.E. (1998) Mucoadhesive polymers as platforms for peroral peptide delivery and absorption: synthesis and evaluation of different chitosan-EDTA conjugates. J. Control. Release, 50, 215-223.
51. Bernkop-Schnürch, A. and Freudl, J. (1999) Comparative in vitro study of different chitosan-complexing agent conjugates. Pharmazie, 54, 369-371.
52. Bernkop-Schnürch, A., Paikl, C. and Valenta, C. (1997) Novel bioadhesive chitosan-EDTA conjugate protects leucine enkephalin from degradation by aminopeptidase N. Pharm. Res., 14, 917-922.
53. Loretz, B., Föger, F.,Werle, M. and Bernkop-Schnürch, A. (2006) Oral gene delivery: strategies to improve stability of pDNA towards intestinal digestion. J. Drug Target., 14, 311-319.
54. Loretz, B. and Bernkop-Schnürch, A. (2006) In vitro evaluation of chitosan-EDTA conjugate polyplexes as a nanoparticulate gene delivery system. AAPS J., 8, E756-E764.
55. KotzÉ, A.F., Luessen, H.L., de Boer, A.G. et al. (1999) Chitosan for enhanced intestinal permeability: prospects for derivatives soluble in neutral and basic environments. Eur. J. Pharm. Sci., 7, 145-151.
56. KotzÉ, A.F., Luessen, H.L., Thanou, M.M. et al. (1999) Chitosan and chitosan derivatives as absorption enhancers for peptide drugs, in Bioadhesive Drug Delivery Systems: Fundamentals, Novel Approaches and Development (eds E. Mathiowitz, D.E. Chickering III and C.-M. Lehr), Marcel Dekker, New York.
57. Sieval, A.B., Thanou, M., KotzÉ, A.F. et al. (1998) Preparation and NMR characterization of highly substituted N-trimethyl chitosan chloride. Carbohydr. Polym., 36, 157-165.
58. Mourya, V. and Inamdar, N. (2009) Trimethyl chitosan and its applications in drug delivery. J. Mater. Sci. Mater. Med., 20, 1057-1079.
59. KotzÉ, A.F., Luessen, H.L., de Leeuw, B.J. et al. (1997) N-trimethyl chitosan chloride as a potential absorption enhancer across mucosal surfaces: in vitro evaluation in intestinal epithelial cells (Caco-2). Pharm. Res., 14, 1197-1202.
60. Jintapattanakit, A., Mao, S., Kissel, T. and Junyaprasert, V.B. (2008) Physicochemical properties and biocompatibility of N-trimethyl chitosan: effect of quaternization and dimethylation. Eur. J. Pharm. Biopharm., 70, 563-571.
61. Snyman, D., Hamman, J.H. and KotzÉ, A.F. (2003) Evaluation of the mucoadhesive properties of N-trimethyl chitosan chloride. Drug Dev. Ind. Pharm., 29, 61-69.
62. Cardile, V., Frasca, G., Rizza, L. et al. (2008) Improved adhesion to mucosal cells of water-soluble chitosan tetraalkylammonium salts. Int. J. Pharm., 362, 88-92.
63. Snyman, D., Hamman, J.H., KotzÉ, J.S. et al. (2002) The relationship between the absolute molecular weight and the degree of quaternisation of N-trimethyl chitosan chloride. Carbohydr. Polym., 50, 145-150.
64. Sandri, G., Rossi, S., Bonferoni, M.C. et al. (2005) Buccal penetration enhancement properties of N-trimethyl chitosan: influence of quaternization degree on absorption of a high molecular weight molecule. Int. J. Pharm., 297, 146-155.
65. Thanou, M.,Verhoef, J.C. and Junginger, H.E. (2001) Chitosan and its derivatives as intestinal absorption enhancers. Adv. Drug Deliv. Rev., 50, S91-S101.
66. Haffejee, N., du Plessis, J., Muller, D.G. et al. (2001) Intranasal toxicity of selected absorption enhancers. Pharmazie, 56, 882-888.
67. Thanou, M., Nihot, M.T., Jansen, M. et al. (2001) Mono-N-carboxymethyl chitosan (MCC), a polyampholytic chitosan derivative, enhances the intestinal absorption of low molecular weight heparin across intestinal epithelia in vitro and in vivo. J. Pharm. Sci., 90, 38-46.
68. Thanou, M., Henderson, S., Kydonieus, A. and Elson, C. (2007) N-sulfonato-N,O-carboxymethylchitosan: a novel polymeric absorption enhancer for the oral delivery of macromolecules. J. Control. Release, 117, 171-178.
69. Desbrieres, J., Martinez, C. and Rinaudo, M. (1996) Hydrophobic derivatives of chitosan: characterization and rheological behaviour. Int. J. Biol. Macromol., 19, 21-28.
70. Thongborisute, J., Takeuchi, H., Yamamoto, H. and Kawashima, Y. (2006) Properties of liposomes coated with hydrophobically modified chitosan in oral liposomal drug delivery. Pharmazie, 61, 106-111.
71. Le Tien, C., Lacroix, M., Ispas-Szabo, P. and Mateescu, M.-A. (2003) N-acylated chitosan: hydrophobic matrices for controlled drug release. J. Control. Release, 93, 1-13.
72. Zhang, M., Li, X.H., Gong, Y.D. et al. (2002) Properties and biocompatibility of chitosan films modified by blending with PEG. Biomaterials, 23, 2641-2648.
73. Prego, C., Torres, D., Fernandez-Megia, E. et al. (2006) Chitosan-PEG nanocapsules as new carriers for oral peptide delivery: effect of chitosan pegylation degree. J. Control. Release, 111, 299-308.
74. Jintapattanakit, A., Junyaprasert, V.B. and Kissel, T. (2009) The role of mucoadhesion of trimethyl chitosan and PEGylated trimethyl chitosan nanocomplexes in insulin uptake. J. Pharm. Sci., 98, 4818-4830.
75. Royer, G.P. and Anantharmaiah, G.M. (1979) Peptide-synthesis in water and the use of immobilized carboxypeptidase-Y for deprotection. J. Am. Chem. Soc., 101, 3394-3396.
76. Aiedeh, K. and Taha, M.O. (1999) Synthesis of chitosan succinate and chitosan phthalate and their evaluation as suggested matrices in orally administered, colon-specific drug delivery systems. Arch. Pharm. (Weinheim), 332, 103-107.
77. Ubaidulla, U., Khar, R.K., Ahmad, F.J. et al. (2007) Development and characterization of chitosan succinate microspheres for the improved oral bioavailability of insulin. J. Pharm. Sci., 96, 3010-3023.
78. Ubaidulla, U., Khar, R.K., Ahmad, F.J. and Tripathi, P. (2009) Optimization of chitosan succinate and chitosan phthalate microspheres for oral delivery of insulin using response surface methodology. Pharm. Dev. Technol., 14, 96-105.
79. Jacobs, C., Kayser, O. and Muller, R.H. (2001) Production and characterisation of mucoadhesive nanosuspensions for the formulation of bupravaquone. Int. J. Pharm., 214, 3-7.
80. Remunan-Lopez, C., Portero, A., Lemos, M. et al. (2000) Chitosan microspheres for the specific delivery of amoxycillin to the gastric cavity. STP Pharma Sci., 10, 69-76.
81. Takeuchi, H.,Yamamoto, H., Niwa, T. et al. (1996) Enteral absorption of insulin in rats from mucoadhesive chitosancoated liposomes. Pharm. Res., 13, 896-901.
82. Luessen, H.L., de Leeuw, B.J., Langemeyer, M.W. et al. (1996) Mucoadhesive polymers in peroral peptide drug delivery. VI. Carbomer and chitosan improve the intestinal absorption of the peptide drug buserelin in vivo. Pharm. Res., 13, 1668-1672.
83. Thanou, M., Florea, B.I., Langemeyer, M.W.E. et al. (2000) N-trimethylated chitosan chloride (TMC) improves the intestinal permeation of the peptide drug buserelin in vitro (Caco-2 cells) and in vivo (rats). Pharm. Res., 17, 27-31.
84. Thanou, M., Verhoef, J.C., Marbach, P. and Junginger, H.E. (2000) Intestinal absorption of octreotide: N-trimethyl chitosan chloride (TMC) ameliorates the permeability and absorption properties of the somatostatin analogue in vitro and in vivo. J. Pharm. Sci., 89, 951-957.
85. Thanou, M., Verhoef, J.C., Verheijden, J.H.M. and Junginger, H.E. (2001) Intestinal absorption of octreotide using trimethyl chitosan chloride: studies in pigs. Pharm. Res., 18, 823-828.
86. Bernkop-Schnürch, A., Pinter, Y., Guggi, D. et al. (2005) The use of thiolated polymers as carrier matrix in oral peptide delivery-proof of concept. J. Control. Release, 106, 26-33.
87. Clausen, A.E., Kast, C.E. and Bernkop-Schnürch, A. (2002) The role of glutathione in the permeation enhancing effect of thiolated polymers. Pharm. Res., 19, 602-608.
88. Krauland, A.H., Guggi, D. and Bernkop-Schnürch, A. (2004) Oral insulin delivery: the potential of thiolated chitosan-insulin tablets on non-diabetic rats. J. Control. Release., 95, 547-555.
89. Foger, F., Schmitz, T. and Bernkop-Schnürch, A. (2006) In vivo evaluation of an oral delivery system for P-gp substrates based on thiolated chitosan. Biomaterials, 27, 4250-4255.
90. Martien, R., Loretz, B., Thaler, M. et al. (2007) Chitosan-thioglycolic acid conjugate: an alternative carrier for oral nonviral gene delivery? J. Biomed. Mater. Res. A, 82, 1-9.
91. Wu, Z.H., Ping, Q.N., Lei, X.M. et al. (2005) Effects of the liposomes coated by chitosan and its derivatives on the gastrointestinal transit of insulin. Yao Xue Xue Bao, 40, 618-622.
92. Dodane, V. and Vilivalam, V.D. (1998) Pharmaceutical applications of chitosan. Pharm. Sci. Technol. Today, 1, 246-253.
93. Soane, R.J., Frier, M., Perkins, A.C. et al. (1999) Evaluation of the clearance characteristics of bioadhesive systems in humans. Int. J. Pharm., 178, 55-65.
94. Illum, L. (2003) Nasal drug delivery-possibilities, problems and solutions. J. Control. Release, 87, 187-198.
95. Luppi, B., Bigucci, F., Cerchiara, T. and Zecchi, V. (2010) Chitosan-based hydrogels for nasal drug delivery: from inserts to nanoparticles. Expert Opin. Drug Deliv., 7, 811-828.
96. Illum, L.,Watts, P., Fisher, A.N. et al. (2000) Novel chitosan-based delivery systems for the nasal administration of a LHRH-analogue. STP Pharma Sci., 10, 89-94.
97. Krauland, A.H., Guggi, D. and Bernkop-Schnürch, A. (2006) Thiolated chitosan microparticles: a vehicle for nasal peptide drug delivery. Int. J. Pharm., 307, 270-277.
98. Bernkop-Schnürch, A., Guggi, D. and Pinter, Y. (2004) Thiolated chitosans: development and in vitro evaluation of a mucoadhesive, permeation enhancing oral drug delivery system. J. Control. Release, 94, 177-186.
99. Jintapattanakit, A., Peungvicha, P., Sailasuta, A. et al. (2010) Nasal absorption and local tissue reaction of insulin nanocomplexes of trimethyl chitosan derivatives in rats. J. Pharm. Pharmacol., 62, 583-591.
100. SayIn, B., Somavarapu, S., Li, X.W. et al. (2009) TMC-MCC (N-trimethyl chitosan-mono-N-carboxymethyl chitosan) nanocomplexes for mucosal delivery of vaccines. Eur. J. Pharm. Sci., 38, 362-369.
101. Harris, D. and Robinson, J.R. (1992) Drug delivery via the mucous-membranes of the oral cavity. J. Pharm. Sci., 81, 1-10.
102. Nagai, T. and Machida, Y. (1993) Buccal delivery systems using hydrogels. Adv. Drug Deliv. Rev., 11, 179-191.
103. Giunchedi, P., Juliano, C., Gavini, E. et al. (2002) Formulation and in vivo evaluation of chlorhexidine buccal tablets prepared using drug-loaded chitosan microspheres. Eur. J. Pharm. Biopharm., 53, 233-239.
104. Langoth, N., Kahlbacher, H., Schoffmann, G. et al. (2006) Thiolated chitosans: design and in vivo evaluation of a mucoadhesive buccal peptide drug delivery system. Pharm. Res., 23, 573-579.
105. Kafedjiiski, K., Krauland, A.H., Hoffer, M.H. and Bernkop-Schnürch, A. (2005) Synthesis and in vitro evaluation of a novel thiolated chitosan. Biomaterials, 26, 819-826.
106. Werle, M. and Hoffer, M. (2006) Glutathione and thiolated chitosan inhibit multidrug resistance P-glycoprotein activity in excised small intestine. J. Control. Release, 111, 41-46.
107. Guggi, D., Krauland, A.H. and Bernkop-Schnürch, A. (2003) Systemic peptide delivery via the stomach: in vivo evaluation of an oral dosage form for salmon calcitonin. J. Control. Release, 92, 125-135.
108. Guggi, D., Kast, C.E. and Bernkop-Schnürch, A. (2003) In vivo evaluation of an oral salmon calcitonin-delivery system based on a thiolated chitosan carrier matrix. Pharm. Res., 20, 1989-1994.
109. Werle, M., Loretz, B., Entstrasser,D. and Föger, F. (2007) Design and evaluation of a chitosan-aprotinin conjugate for the peroral delivery of therapeutic peptides and proteins susceptible to enzymatic degradation. J. Drug Target., 15, 327-333.
110. Jintapattanakit, A., Junyaprasert, V.B., Mao, S. et al. (2007) Peroral delivery of insulin using chitosan derivatives: a comparative study of polyelectrolyte nanocomplexes and nanoparticles. Int. J. Pharm., 342, 240-249.
111. Bernkop-Schnürch, A. and Paikl, C. (1998) Chitosan-conjugates with acidic chelate-complex forming agents, European Patent WO 09831712A2.