Chitosan-apatite composites: synthesis and properties

The aim of this short review was to discuss applications of a unique biopolymer chitosan in practical medicine, especially for bone tissue engineering. The article highlights the preparation and properties of innovative chitosan-based biomaterials such as CaP-chitosan (CS-CP)-composites and chitosan...

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Published in:Вiopolymers and Cell
Date:2016
Main Authors: Sukhodub, L.F., Sukhodub, L.B., Chorna, I.V.
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Language:English
Published: Інститут молекулярної біології і генетики НАН України 2016
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Online Access:https://nasplib.isofts.kiev.ua/handle/123456789/152817
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Cite this:Chitosan-apatite composites: synthesis and properties / L.F. Sukhodub, L.B. Sukhodub, I.V. Chorna // Вiopolymers and Cell. — 2016. — Т. 32, № 2. — С. 83-97. — Бібліогр.: 78 назв. — англ.

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Digital Library of Periodicals of National Academy of Sciences of Ukraine
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spelling Sukhodub, L.F.
Sukhodub, L.B.
Chorna, I.V.
2019-06-13T07:29:40Z
2019-06-13T07:29:40Z
2016
Chitosan-apatite composites: synthesis and properties / L.F. Sukhodub, L.B. Sukhodub, I.V. Chorna // Вiopolymers and Cell. — 2016. — Т. 32, № 2. — С. 83-97. — Бібліогр.: 78 назв. — англ.
0233-7657
DOI: http://dx.doi.org/10.7124/bc.000910
https://nasplib.isofts.kiev.ua/handle/123456789/152817
615.31:541.64:539.6:617-089.844:615.28
The aim of this short review was to discuss applications of a unique biopolymer chitosan in practical medicine, especially for bone tissue engineering. The article highlights the preparation and properties of innovative chitosan-based biomaterials such as CaP-chitosan (CS-CP)-composites and chitosan-alginate (CS-AG)-scaffolds. This paper takes a closer look at the physicochemical properties, spectral characteristics and chemical modifications of the chitosan molecule. The obtained chitosan-apatite composites were analysed using X-ray diffraction to verify the crystalline nature of their structures. It was observed that the addition of chitosan to the composite material reduces apatite crystallinity. Besides, an accent was made on antibacterial properties of chitosan, the use of chitosan nanoparticles to produce nanofibers and controlled drug delivery systems. Keywords: chitosan, hydroxyapatite, biocomposites, X-ray diffraction.
Мета цього короткого огляду – розгляд застосування унікального біополімеру хітозану в практичній медицині, особливо для інженерії кісткової тканини. Основне місце в статті відведено синтезу та властивостям інноваційних біоматеріалів на основі хітозану, таким як CaP-хітозан (CS-CP)-композити і хітозан-альгінатні (CS-AG)-скаффолди. У статті висвітлено фізико-хімічні властивості, спектральні характеристики і хімічні модифікації молекули хітозану. Отримані хітозан-апатитні композитні матеріали були проаналізовані з використанням методу рентгенівської дифракції для аналізу кристалічної природи їх структур. Було виявлено, що додавання хітозану до композитного матеріалу призводить до зниження кристалічності вихідного апатиту. Крім того, акцентовано увагу на антибактеріальні властивості хітозану, використанні наночастинок хітозану для отримання нановолокон і створенні системи контрольованої доставки ліків.
Цель этого краткого обзора – рассмотреть применения уникального биополимера хитозана в практической медицине, особенно для инженерии костной ткани. Основное место в статье отведено синтезу и свойствам инновационных биоматериалов на основе хитозана, таким как CaP-хитозан (CS-CP)-композиты и хитозан-альгинатные (CS-AG)-скаффолды. В статье освещены физико-химические свойства, спектральные характеристики и химические модификации молекулы хитозана. Полученные хитозан-апатитные композитные материалы были проанализированы с использованием метода рентгеновской дифракции для анализа кристаллической природы их структур. Было обнаружено, что добавление хитозана к композитному материалу приводило к снижению кристалличности исходного апатита. Кроме того, акцентировано внимание на антибактериальных свойствах хитозана, использовании наночастиц хитозана для получения нановолокон и создании систем контролируемой доставки лекарств.
We thank the Ukrainian Fundamental Foundation (project NU/7-2013) for funding our researches, Dr. V.G. Lugin from State technological university of Belarus for IR-studies of the apatite-biopolymer samples.
en
Інститут молекулярної біології і генетики НАН України
Вiopolymers and Cell
Reviews
Chitosan-apatite composites: synthesis and properties
Хітозан-апатитні композити: синтез і властивості
Хитозан-апатитные композиты: синтез и свойства
Article
published earlier
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
title Chitosan-apatite composites: synthesis and properties
spellingShingle Chitosan-apatite composites: synthesis and properties
Sukhodub, L.F.
Sukhodub, L.B.
Chorna, I.V.
Reviews
title_short Chitosan-apatite composites: synthesis and properties
title_full Chitosan-apatite composites: synthesis and properties
title_fullStr Chitosan-apatite composites: synthesis and properties
title_full_unstemmed Chitosan-apatite composites: synthesis and properties
title_sort chitosan-apatite composites: synthesis and properties
author Sukhodub, L.F.
Sukhodub, L.B.
Chorna, I.V.
author_facet Sukhodub, L.F.
Sukhodub, L.B.
Chorna, I.V.
topic Reviews
topic_facet Reviews
publishDate 2016
language English
container_title Вiopolymers and Cell
publisher Інститут молекулярної біології і генетики НАН України
format Article
title_alt Хітозан-апатитні композити: синтез і властивості
Хитозан-апатитные композиты: синтез и свойства
description The aim of this short review was to discuss applications of a unique biopolymer chitosan in practical medicine, especially for bone tissue engineering. The article highlights the preparation and properties of innovative chitosan-based biomaterials such as CaP-chitosan (CS-CP)-composites and chitosan-alginate (CS-AG)-scaffolds. This paper takes a closer look at the physicochemical properties, spectral characteristics and chemical modifications of the chitosan molecule. The obtained chitosan-apatite composites were analysed using X-ray diffraction to verify the crystalline nature of their structures. It was observed that the addition of chitosan to the composite material reduces apatite crystallinity. Besides, an accent was made on antibacterial properties of chitosan, the use of chitosan nanoparticles to produce nanofibers and controlled drug delivery systems. Keywords: chitosan, hydroxyapatite, biocomposites, X-ray diffraction. Мета цього короткого огляду – розгляд застосування унікального біополімеру хітозану в практичній медицині, особливо для інженерії кісткової тканини. Основне місце в статті відведено синтезу та властивостям інноваційних біоматеріалів на основі хітозану, таким як CaP-хітозан (CS-CP)-композити і хітозан-альгінатні (CS-AG)-скаффолди. У статті висвітлено фізико-хімічні властивості, спектральні характеристики і хімічні модифікації молекули хітозану. Отримані хітозан-апатитні композитні матеріали були проаналізовані з використанням методу рентгенівської дифракції для аналізу кристалічної природи їх структур. Було виявлено, що додавання хітозану до композитного матеріалу призводить до зниження кристалічності вихідного апатиту. Крім того, акцентовано увагу на антибактеріальні властивості хітозану, використанні наночастинок хітозану для отримання нановолокон і створенні системи контрольованої доставки ліків. Цель этого краткого обзора – рассмотреть применения уникального биополимера хитозана в практической медицине, особенно для инженерии костной ткани. Основное место в статье отведено синтезу и свойствам инновационных биоматериалов на основе хитозана, таким как CaP-хитозан (CS-CP)-композиты и хитозан-альгинатные (CS-AG)-скаффолды. В статье освещены физико-химические свойства, спектральные характеристики и химические модификации молекулы хитозана. Полученные хитозан-апатитные композитные материалы были проанализированы с использованием метода рентгеновской дифракции для анализа кристаллической природы их структур. Было обнаружено, что добавление хитозана к композитному материалу приводило к снижению кристалличности исходного апатита. Кроме того, акцентировано внимание на антибактериальных свойствах хитозана, использовании наночастиц хитозана для получения нановолокон и создании систем контролируемой доставки лекарств.
issn 0233-7657
url https://nasplib.isofts.kiev.ua/handle/123456789/152817
citation_txt Chitosan-apatite composites: synthesis and properties / L.F. Sukhodub, L.B. Sukhodub, I.V. Chorna // Вiopolymers and Cell. — 2016. — Т. 32, № 2. — С. 83-97. — Бібліогр.: 78 назв. — англ.
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fulltext 83 L. F. Sukhodub, L. B. Sukhodub, I. V. Chorna © 2016 L. F. Sukhodub et al.; Published by the Institute of Molecular Biology and Genetics, NAS of Ukraine on behalf of Biopolymers and Cell. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited UDC 615.31:541.64:539.6:617-089.844:615.28 Chitosan-apatite composites: synthesis and properties L. F. Sukhodub1, L. B. Sukhodub2, I. V. Chorna1 1 Sumy State University 2, Rymskogo-Korsakova., Sumy, Ukraine, 40007 2 Mechnikov Institute of Microbiology and Immunology NAMS of Ukraine 14, Pushkinska Str., Kharkiv, Ukraine, 61057 l_sukhodub@yahoo.com The aim of this short review was to discuss applications of a unique biopolymer chitosan in practical medicine, especially for bone tissue engineering. The article highlights the preparation and properties of innovative chi- tosan-based biomaterials such as CaP-chitosan (CS-CP)-composites and chitosan-alginate (CS-AG)-scaffolds. This paper takes a closer look at the physicochemical properties, spectral characteristics and chemical modifi- cations of the chitosan molecule. The obtained chitosan-apatite composites were analysed using X-ray diffrac- tion to verify the crystalline nature of their structures. It was observed that the addition of chitosan to the composite material reduces apatite crystallinity. Besides, an accent was made on antibacterial properties of chitosan, the use of chitosan nanoparticles to produce nanofibers and controlled drug delivery systems. K e y w o r d s: chitosan, hydroxyapatite, biocomposites, X-ray diffraction. Introduction Over the last years, chitosan (CS) has attracted a great interest of scientists as functional polymeric material because of its remarkable intrinsic proper- ties: biodegradability, biocompatibility, nontoxicity, antibacterial activity, mucoadhesive, analgesic and haemostatic properties [1–3]. Chitosan is a linear, semi-crystalline polysaccharide composed of (1→4)-2-acetamido-2-deoxy-β-D-glucan (N-acetyl D-glucosamine) and (1→4)-2-amino-2-deoxy-β-D- glucan (D-glucosamine) units [1, 4–6]. Chitosan can be easily obtained from a natural polymer chitin af- ter its partial deacetylation by chemical hydrolysis under severe alkaline conditions or by enzymatic hydrolysis [7, 8]. Chitosan is well tolerated by living tissues, including the skin, ocular membranes, the nasal epithelium. A low or no toxicity of chitosan compared with other natural polysaccharides has been demonstrated by in vivo toxicity studies [9]. Some studies showed that chitosan, as an immune adjuvant, could effectively promote the local im- mune response and enhance antigen presentation [10]. The combination of CS with different materi- als, such as hydroxyapatite (HA), is very promising, especially for orthopedics and traumatology [11]. All these features make chitosan an outstanding can- didate for biomedical applications. Physical and chemical properties of chitosan Chitosan as the product of partial deacetylation of chitin contains five types of active functional groups: primary amine groups at the C-2 position of each deacetylated structural unit, secondary amide groups, ether groups of polysaccharide main chain as well as both primary and secondary hydroxyl groups at the C-6 and C-3 positions, respectively (Fig. 1). The molecular weight (MW) of CS is in the range of 300 to 1 000 kDа and it depends on the source and the method used for obtaining CS. Degree of CS Reviews ISSN 1993-6842 (on-line); ISSN 0233-7657 (print) Biopolymers and Cell. 2016. Vol. 32. N 2. P 83–97 doi: http://dx.doi.org/10.7124/bc.000910 mailto:l_sukhodub@yahoo.com 84 L. F. Sukhodub, L. B. Sukhodub, I. V. Chorna deacetylation (DD) (N- acetylglucosamine / glucos- amine) may vary from 30 to 95 %. The higher DD of CS, the greater the quantity of protonated amino groups in the polymer and, correspondingly, the higher the amount of charge on the macromolecule. In crystalline form, CS is insoluble in aqueous solu- tions with pH > 7 whereas in dilute acids (pH < 6) it becomes soluble due to protonation of NH2- groups [5]. Chitosan’s primary amines confer impor- tant material properties. At low pH, the amines are protonated making chitosan a cationic polyelectro- lyte. In protonated form, the amines allow connection through electrostatic interactions [12]. Due to its amino groups, chitosan can form bonds with a wide variety of organic and inorganic molecules, such as lipids, proteins, DNA and some negatively charged synthetic polymers [13–16]. At high pH, the amines are deprotonated and chitosan undergoes a transition from a soluble cationic polyelectrolyte to an insolu- ble polymer. Insolubility of chitosan in water means that the intermolecular interactions between macro- molecules exceed the interactions in the system of “chitosan-water molecules”. Importantly, this pH-re- sponsive switch is near neutrality (chitosan’s appar- ent pKa has been reported to range between 6 and 7) [17, 18] suggesting chitosan as a biologically-derived A B Fig. 1. The structural formula of chitin (A) and chitosan (B) Fig. 2. Schematic representation of the metal-chitosan complexation [22] 85 Chitosan-apatite composites: synthesis and properties stimuli-responsive polymer for medical applications (e.g., injectable matrices) [19]. There are well known the nucleophilic properties of the amines that allow connections through covalent linkages that can be formed through a range of coupling chemistries [20]. Chitosan’s metal binding properties [21] allow con- nections through chelation mecha nisms. Fig. 2 illus- trates the structural chemical formula of two strands of chitosan and the “cross-linking” mechanism caused by the divalent metal ion [22]. Micro/nanoparticles and hydrogels are widely used in the design of chitosan-based therapeutic sys- tems [4]. The cationic nature of CS provides the electrostatic interaction with quantivalent linear an- ionic polysaccharides (glycosaminoglycans (GAG), proteoglycans etc.). This factor is very important be- cause of a large number of growth factors and other proteins bound to GAG, that is why the formation of GAG-CS complexes provides maintenance and ac- cumulation of these necessary biopolymers in vivo. Thus, chitosan based scaffolds deliver growth fac- tors in a controlled fashion to promote the in-growth and biosynthetic ability of chondrocytes [4]. Under the action of cellular enzymes, especially lysozyme, CS degraded depending on the degree of crystallini- ty and deacetylation [6]. Hence these properties must be necessarily taken into account at creating chitosan based implants. Also it should be noted that the CS hydrogel composite is able to form a porous structure using, for example, lyophilization techno- logy (“freeze-drying”). A pore size in the CS hydro- gel composite depends on speed of freezing. The degree of porosity and pore orientation significantly affect the mechanical properties of the implant. Another property of CS is its internal antibacterial ability [23–25]. Chitosan in bone tissue engineering Tissue engineering (TE) is an interdisciplinary area that contains both a basic knowledge of life sciences and engineering to create biologically compatible, biodegradable scaffolds (matrices) in different forms (powder, microcapsules, gels, films, etc.) for a wide use in nanomedicine. Systems for the controlled drug delivery by using chitosan and its derivatives are of huge interest [4]. Chitosan is widely used in bone tissue engineering because of its ability to pro- mote a cell growth and the formation of mineral ma- trix by osteoblasts [26]. Biocompatibility of chitosan minimizes the local inflammation, and its conver- sion into a porous structure contributes to osteocon- ductivity [27]. The Chitosan - Calcium Phosphate composites (CS-CP) were the subject of intensive study in the world [28–31]. CS-CP composites Biomaterials that mimic the structure and composi- tion of bone tissues at the nanoscale level are ex- tremely important for the development of bone tis- sue engineering applications [32]. CS-CP compo si- tes have certain advantages compared to other simi- lar structures. Thus, during the resorption, the degra- dation products of chitosan and calcium phosphate (calcium ions, phosphates, glycosamines, etc.) are naturally metabolized and do not induce the increas- ing calcium and phosphorus concentrations in urine, serum or internal organs. A composite material con- tains both the macro- and micropores and nano-sized crystals of HA. This promotes an increase in the re- active surface and material osteoconductive activity. Similar 3D-macroporous ceramics pierced by chito- san grid have better mechanical properties [33, 34]; therefore, there is a perspective of the CS-CP com- posites future use in the clinic. The main advantages of CS-CP biomaterials are: structural organization, which is close to the structure of natural bone, bio- compatibility, biodegradation, macro- and micropo- rosity, regulation of resorption rate, immobilization of drugs, antibacterial action, simplicity of flowsheet synthesis, low cost. Among a wide range of calcium phosphates hy- droxyapatite (HA), Ca10(PO4)6(OH)2 is a widely used material for biomedical application in dentistry and orthopedy due to the excellent bioactivity, bio- compatibility and osteoconductivity [31, 35]. However, the migration of HA powder from im- planted sites and bone defects is really a big prob- lem. Therefore, organic compounds in nanocompo- 86 L. F. Sukhodub, L. B. Sukhodub, I. V. Chorna sites are promising for improving weak mechanical properties of HA [36]. The CS-HA composites have been recently syn- thesized in our laboratory. For this aim the chitosan macromolecules ( MW 500 kDa, 200 kDa, 39 kDa) with DD 85 % were supplied by the “Bioprogress” (Moskow, Russia). Calcium acetate Ca(CH3COO)2, sodium dihydrogen phosphate NaH2PO4, and sodi- um hydroxide (NaOH) were of analytical grade and supplied by “Merck”. An influence of the chitosan’s molecular weight and various ways of the synthesis on obtaining the CS-HA composite structure have been studied. Calcium acetate was used as the 0.167 M solution in 1 % CH3COOH (first way of synthesis) or was added in solid state to chitosan so- lution in 1 % CH3COOH (second way of synthesis). By the first way of synthesis 0.8 g of chitosan powder with certain MW were added to 20 mL of the 0.167 M (CH3COO)2Ca stock solution in 1 w % CH3COOH. The final chitosan concentration in the reaction mixture was 0.4 w %. The calcium acetate– chitosan solution was stirred in a shaker (160 rpm) for 1.5 h at 37 ºC, then 20 mL of 0.1 M NaH2PO4 solution were added gradually to the above mixture. The pH value was adjusted to 11.8 by using 10 M NaOH solution. The obtained suspension was aged for 5 days at 22 ºC, then washed thoroughly with deionized water to pH 7.4. Finally, the precipitate was separated by centrifuging the suspension. For the analysis the product was dried at 37 oC and an- nealed for 1 h at 900 oC. The second way of synthesis was provided by addition of solid (CH3COO)2Ca (0.526 g) to the 20 mL of the 0.4 w % chitosan solu- tion in 1 % CH3COOH. The calcium acetate–chito- san solution was stirred in a shaker (160 rpm) for 1.5 h at 37 ºC, after which 20 mL of 0.1 M NaH2PO4 solution were added gradually to the above mixture. The pH value of solution (about 11.0) was corrected by using 10 M NaOH solution. A white precipitate was observed after the phosphate solution addition at both ways of synthesis. It was associated with the hydroxyapatite formation. Both suspensions were aged for 5 days at 22 ºC, then washed thoroughly with deionized water to obtain solution of pH 7.4. Finally, the precipitate was separated by centrifug- ing the suspension. For the analysis the product was dried at 37 oC and annealed for 1 h at 900 oC. The Obtained composites consisted of 80 w % of HA and 20 w % of CS. The crystallinity and structure of precipitates were examined using an X-ray diffractometer DRON-3 (“Burevestnik”, Russia) connected to a computer- aided system for the experiment control and data processing. The Ni-filtered CuKα radiation (wave- length 0.154 nm) with a conventional Bragg– Brentano θ-2θ geometry was used. The current and voltage of X-ray tube were 20 mA and 40 kV respec- tively. The samples were tested in a continuous mode in the range 10º to 60º at a rate 2.0 º/min with 2θ-angles. The samples phase composition was de- termined and crystallite size calculated. The average crystallite size (L) and strain (ε) were calculated in the [0 0 c] crystal direction using XRD data by Scherrer equation [37]. The crystalline phases were identified by comparing the experimental XRD pat- terns to the standards compiled by the Joint Committee on Powder Diffraction and Standards (JCPDS cards). The formation of crystalline HA phase occurs in both the presence and the absence of polymer, independently from chitosan MW and syn- thesis way. The existence of 2θ peaks at approxi- mately 26º, and 31.9º corresponding to the (002) and (211) diffraction planes confirms the formation of HA phase in products [36]. Taking into account the broadening of each peak in XRD spectra, mean crys- tallite sizes for examined samples were calculated using Scherrer equation and approximation method (Table 1). As can be assumed from the Table 1, 20 w % of chitosan in material composition did not decrease significantly crystallite sizes of HA-CS samples compared to HA sample. The changes in the polymer molecular weight and the way of synthesis had no observable effect on the peaks positions and/or their intensity. However, the strain in [0 0 c] direction in- creased for all HA-CS composite samples indicating significant defects in the hydroxyapatite crystal struc- ture caused by the presence of the polymer. 87 Chitosan-apatite composites: synthesis and properties To evaluate the functional groups of CS, HA and synthesized composite HA-CS (Fig. 3), the FTIR analysis was performed by the instrument “Thermo Nicolet Nexus 470 ESP” (Minsk Technological University, Belarus). The sample for spectral analy- sis was prepared in a traditional way: a small amount of the preparation (synthesized composite powder) was mixed with KBr in the ratio 1:200 in an agate mortar while grinding. From the obtained mixtures corresponding tablets were prepared in press-forms of stainless steel under hydraulic pressure. Transmission spectrum was obtained in the frequen- cy range of 400–5000 cm–1 with a spectral resolution of 0.125 cm–1. FTIR-spectrum of CS(c) shows characteristic peaks of amide I at 1651 cm−1 (–C=O stretching), amide III at 1378 cm–1 (C– N stretching coupled with NH in plane deformation), CH2 wagging cou- pled with OH in plane deformation at 1324 cm−1. The peak at 1598 cm–1 belongs to the bending vibra- Table 1. Structure characteristics of hydroxyapatite nanocrystals in dried at 37 °C HA-CS nanocomposites Sample Miller Indices Crystallite sizes by Scherrer, nm Approximation method Crystallite sizes, nm Strain, ∙103 HA (0 0 2) 22.8 22.8 0.003 (0 0 4) 22.8 HA / CS 500 (1) (0 0 2) 21.7 21.5 0.097 (0 0 4) 22 HA / CS 500 (2) (0 0 2) 19.6 21.4 0.71 (0 0 4) 18.2 HA / CS 200 (1) (0 0 2) 18.3 17.8 0.27 (0 0 4) 19 HA / CS 200 (2) (0 0 2) 19 18.4 0.32 (0 0 4) 19.7 HA / CS 39 (1) (0 0 2) 18.2 21.7 1.53 (0 0 4) 15.6 HA / CS 39 (2) (0 0 2) 21.6 20.7 0.342 (0 0 4) 22.6 Fig. 3. FTIR-spectra of a) HA-CS nanocomposite (down), b) HA, sintered at 900 ºC (middle), c) CS with MW 500 kDa (top) 88 L. F. Sukhodub, L. B. Sukhodub, I. V. Chorna tions of the N–H and C–N (amide II band). Peaks at 1430 belong to the N–H stretching of the amide and ether bonds [38]. The vibration band about 1029 cm−1 – 1077 cm−1 indicates the C–O stretching vibration in the primary and secondary hydroxyl groups in chitosan [39, 40], wide band (3429 cm–1) is attributed to –OH stretching and –NH2 asymmet- ric stretching vibrations [41], the peak at 2868 cm–1 is caused by –CH2-stretching vibrations [42]. FTIR-spectrum of CS (c) shows characteristic bands of amide I (the main contribution of C=O stretching) at 1651 cm–1 and amide II (the main con- tribution of N–H bending) together with N–H bend- ing vibration of primary amine groups at 1598 cm–1. Three bands at ~1450, 1430 and 1378 cm–1 belong to C-H asymmetric and symmetric bending vibrations of methyl and methylene groups. The band of –CH2- wagging coupled with -OH in plane deformation ap- pears at 1324 cm–1. Some vibration bands in a region of 1200–1000 cm–1 with the main peak at 1161 cm–1 indicate asymmetric and symmetric C–O–C and C–O stretching vibrations of CS ether and hydroxyl groups. The O–H and N–H stretching vibrations of hydroxyl, amide and amine groups of CS appear in FTIR spectrum by a wide band with maximum at 3429 cm–1, whereas C-H stretching of –CH2- and – CH3 groups is revealed by two overlapped bands at 2920 and 2862 cm–1. Pure HA (b) shows a vibration band around 3427 cm–1 and peak at 630 cm–1 corresponding to stretching vibration of the hydroxyl group [43]. The characteristic peaks at 576 cm–1, 604 cm–1, 961 cm–1, 1048 cm–1and 1090 cm–1 are due to the bending and stretching modes of P–O vibrations in the phosphate network [44, 45]. In the HA-CS spectrum (a) the protonation of chi- tosan amine functionalities is suggested by the pres- ence of the band, attributed to NH3 + groups, namely the bending vibration at 1475 cm−1. This is evidently conditioned by the formation of electrostatic bonds with HA. Also the low-frequency shift of the amide I band up to 1638 cm–1 is observed, thus pointing out the participation of carbonyls of CS amide groups in hydrogen bonding with hydroxyl groups of HA. It was observed the disappearance of the vibration band in HA-CS spectrum (a) at 1324 cm−1 that may indicate partial phosphorylation of hydroxyl groups in CS with the feather formation of calcium phos- phates. The wide band indicated the C–O–C and C–O stretching vibrations in the ether; the primary and secondary hydroxyl groups in CS spectrum (c) were present as the vibration band with peak at 1032 cm–1 in the spectrum of HA–CS (a). These changes may be attributed to the formation of hydro- gen bonds with participation of ether and/or –OH- groups in HA and CS. Additionally, the vibration bands at 960 cm–1 and 630 cm–1, belonging to the phosphate- and hydroxyl- groups in HA (b) were ab- sent in the HA–CS spectrum. All these facts confirm molecular interactions between CS and HA in the HA–CS composite. Chitosan-alginate-hydroxyapatite polyelec- trolyte composites The chitosan- and sodium alginate (AG)-based scaf- folds have been widely used as biomaterials in tissue engineering. Freeze-drying, also known as lyophili- zation, has been used for the fabrication of polymer- based hydrogels. The porous scaffolds composed of AG and CS have been fabricated by the formation of a polyelectrolyte complex (PEC) between macro- molecules of both polymers [46]. They perform a 3D-grid with uniformly distributed and intercon- nected pores. Two technologies of the scaffold for- mation are proposed in this paper. According to the first, the uncrosslinked alginate scaffold is formed from 4 w % AG solution using the “freeze-drying” technology. Next, it undergoes some crosslinking using 1 w % CaCl2. By the second technology, the alginate scaffold was immerged into 2 w % CS solu- tion or the CS-HA composite acetic acid aqueous solution. In this case the pores of the alginate scaf- folds were filled with chitosan solution. These sam- ples were frozen at –40 °C and lyophilized. Finally, the samples were additionally crosslinked with CaCl2 solution. Chitosan-alginate (CS-AG)-scaffolds exhibit bet- ter mechanical properties and thermostability than 89 Chitosan-apatite composites: synthesis and properties AG-scaffold, crosslinked with calcium ions only. The main reasons for the mechanical strength im- provement of crosslinked scaffold could be strong ionic interactions. In the Ca2+ crosslinked AG scaf- fold the mechanical strength is enhanced because Ca2+ is characterized by strong ionic interaction with COO- in an alginate chain. For CS-AG PEC scaffold the strong interaction exists between NH3 + groups in CS and COO- groups in alginate (Fig. 4). Additionally, a decrease of porosity for crosslinked scaffold is an- other factor enhancing the mechanical strength. Considering the participation of chitosan in PEC, it should be noted a series of studies of chitosan complexes with DNA, glycosaminoglycans, chon- droitin sulfate, hyaluronic acid, heparin, carboxy- methyl cellulose, pectin and proteins such as gelatin, albumin, collagen and keratin [47–52]. The stability of such complexes depends on the charge density, solvent, ionic strength, pH and temperature [46]. The Chitosan-, alginate- and hydroxyapatite-based scaffolds (with a ratio of 1:1:1) were recently syn- thesized in our laboratory using our own flowsheet. Such precursors were used for the synthesis: chito- san (MW 500 kDa, DD 80%, “Bioprogress”, Moscow), sodium alginate (E401), sodium hydro- gen phosphate (Na2HPO4) and calcium acetate (CH3COO)2Ca∙H2O (China). 500 ml of chitosan so- lution (2 g/l in 1 w % acetic acid) were gradually added to 0.1 M calcium acetate (100 ml); 1 g of so- dium alginate powder was dissolved in 0.1 M sodi- um hydrogen phosphate (60 ml). Two obtained solu- tions were mixed and stirred in a shaker (160 rpm) at 37 ºC for 5 h. pH was adjusted with 10 M NaOH solution to 11.0. Additionally the mixture was stirred by ultrasound, heated at 80 ºC for 10 min and aged for 48 h for the HA nucleation. The obtained product was washed with the deionized water to pH 7.0-7.4 with subsequent freezing and vacuum drying (“freeze-drying”) at –150 °C during 16 h. As a result, the porous HA-CS-AG-scaffold with a ratio of com- ponents 1:1:1 was obtained. The polymer amounts for the synthesis might be calculated to obtain the product with required component proportions. The cation-anionic interactions between macromolecules of CS and AG are the main driving force in the cre- ation and stabilization of the biopolymer scaf- folds [31]. X-ray structure analysis of apatite-biopoly- mer composites Recently the usage of materials in the form of hydro- gels has become increasingly popular. The structure of the polymer chains that form a three-dimensional net of gel enables immobilization and sufficient con- tent of water, biological fluids or drugs [53, 54]. We investigated the composite materials that consisted of the polymer matrix and inorganic filler and to some extent modeled a bone. As the polymer matrix, chitosan was used in the sample 1 and sodium algi- nate - in the sample 2. Fig. 4. Chemical structures of CS (top) and AG (down) and the scheme of their interaction 90 L. F. Sukhodub, L. B. Sukhodub, I. V. Chorna Sample N 1: HA–CS composite. The HA–CS composite was synthesized by wet chemistry. Two solutions were prepared for the synthesis: 1) 100 mL [of] 0.1 M CaCl2, pH was adjusted up to 11.0 by ad- dition of 10 M NaOH solution; 2) chitosan (MW 39 kDa) was dissolved in 100 ml of 0.06 M H3PO4 in the amount, which provides chitosan concentration in the final material from 10 to 40 w %. The second solution was added drop by drop to the first one fol- lowed with mixing and heating at 60 °C during 10 min. The pH value was adjusted by NaOH addi- tion to 7.4. After aging for 24 h the resulting suspen- sion was washed with distilled water and centri- fuged. The degree of moisture in the obtained gel ranged from 70 to 88 w %. The composition of sol- ids was: HA from 60 to 90 w %, CS from 10 to 40 w %. For analysis, the composites were dried at 37 °C and annealed for 1 h at 900 ºC . Sample N 2: HA–AG composite. Orthophosphoric acid H3PO4 (0.06 M), anhydrous calcium chloride CaCl2 (0.1 M), aqueous solution of sodium hydrox- ide NaOH (10 M) and sodium alginate (E401, MW 15 kDa, China) were used as starting materials for the HA-AG composite preparation. The composite mate- rial was synthesized by the “wet chemistry” method: 1) sodium alginate was dissolved in 100 ml of 0.06 M H3PO4 in the amount, which provides its content in the final material from 10 to 40 w % at 37 °C. This solution was added drop by drop to the calcium chlo- ride solution with vigorous stirring. After mixing the reactants, the suspension was treated with ultrasound. Then, pH value was adjusted with 10 M NaOH to 10.6 and the suspension was heated at 60 °C during 10 min. After aging within 10 days the precipitate was thoroughly washed with the deionized water; solids were separated by centrifugation and steril- ized. The degree of moisture in the obtained gel ranged from 70 to 88 w %. The composition of solids was: HA from 60 to 90 w %, AG from 10 to 40 w %. The obtained samples were dried at 37 °C and an- nealed for 1 h at 900 °C for further research. To evaluate the structure of samples – the lattice options (a, c), the average crystallite size (L, D) and microstrain ε – two methods were used and com- pared: X-Ray diffraction (XRD) and transmission electron microscopy (TEM; SELMI, Sumy, Ukraine) with the electron diffraction (ED). The obtained data are shown in Table 2. Both instrumental methods confirm the effect of the polymer component on the structural properties of HA crystallites. Thus, under the condition of syn- thesis of HA nanoparticles in the presence of poly- mer the size of crystallites decreased compared to pure HA in samples dried at 37 °C. An average size of crystallite increased after annealing and combus- tion of the polymer component in the HA–CS and HA–AG samples. Fig. 5 shows the XRD patterns for the HA–CS and HA–AG samples dried at 37 °C and annealed at 900 °C. According to the XRD analysis, the sample 1 after annealing at 900 °C included two phases: HA (JCDPS 9-432, with 1.67 Ca / P ratio, concentration 97 w %) and CaO (JCDPS 37-1497, concentration 3 w %). The presence of another phase after the tem- perature test indicates the nonstoichiometric output of apatite. The main factor causing a small size of crystallites and high level of microdeformations is an addition of chitosan, which, as has been shown in previous studies [55], reduces crystallinity of apatite and distorts its crystal lattice. In the sample № 2 after annealing at 900 °C only one phase HA (JCPDS 9-432, with 1.67 Ca/P ratio) was found which indicated the stoichiometry of the initial apatite. The nanostructures of the HA–CS and HA-AG composites were examined using TEM, as shown in our previous studies [56]. Table 2. Data of TEM and XRD analysis of structure of HA (pure), HA-CS and HA-AG composites Sample Dried at 37 oC Annealed at 900 ºC TEM with ED XRD XRD a, nm c, nm D, nm L, nm L, nm HA-CS 0.949 0.688 ~80 14.3 55.4 HA-AG 0.945 0.688 ~80 24.6 58.6 HA 0.933 0.684 ~120 33.2 49.41 91 Chitosan-apatite composites: synthesis and properties Antibacterial properties of silver-doped HA-CS composites One of the most important problems in modern im- plantology is bacterial infection. The inflammation in the implant surrounding tissue eventually leads to the loss of the implant. The use of antimicrobial films or coatings is a way for preventing inflammation. Chitosan is one of the natural polysaccharides that can form a film with antibacterial properties. There are several mechanisms of antibacterial activity of chito- san [47]. First, chitosan as a polycation forms electro- static bonds with anionic molecules on the cell sur- face and thereby affects their penetrating ability [57, 58]. Second, chitosan binds to the negatively charged groups of DNA and thus inhibits the RNA synthesis [24, 59]. Finally, the antibacterial activity of chitosan can include both mechanisms, depending on the charge density in interacting components [24, 60]. Due to a large number of OH- and NH2-groups chito- san can easily form chelates with metal ions [21, 61]. A) Fig. 5. A) X-ray diffraction patterns of HA–CS nanocomposites dried at 37 °C and annealed for 1 h at 900 °С. ♦ – as- signed CaO phase; B) X-ray diffraction patterns of HA-AG nanocomposites dried at 37 °C and annealed for 1 h at 900 °С B) 92 L. F. Sukhodub, L. B. Sukhodub, I. V. Chorna Most silver-containing antimicrobial biomaterials consist of either Ag+ ions (silver salts or silver com- plexes) or elemental silver (Ag-nanoparticles) incor- porated into organic (polymers) or inorganic (bio- glasses and HA) matrices [62, 63]. The silver-loaded HA composites are obtained by ion-exchange meth- ods (sol-gel or coprecipitation) that involve the silver substitution for calcium, resulting in a Ca-deficient hydroxyapatite. The antimicrobial response of these materials is good, but there is pH-dependent negative rapid release of silver [64]. Silver nanoparticles have the antibacterial properties, delaying the growth of Gram-positive and Gram-negative bacteria. It is also well known that the antibacterial activity of Ag nanoparticles is caused not only by free Ag+ ions pro- duced from nanoparticle surface but also by the inter- action of small active nanoparticles with the microor- ganisms cells and destruction of their membranes [65–67]. Chitosan-nanosilver-based films exhibit the excellent antibacterial activity against Escherichia coli [61]. Therefore, in the recent research [68], our group has used the termodeposition method [31] for obtaining antimicrobial Ag+-doped hydroxyapatite coatings under physiological conditions with various concentrations of silver ions and therefore different antibacterial activity. Thus, HA-Ag+-coatings were created on both the chitosan- modified and non-mod- ified Ti-6Al-4V substrates. Antibacterial properties were studied by the optical density evaluation of the E.coli ATCC 25922 bacterial suspensions (Institute of Micro bio logy and Immunology, National Academy of Medical Sciences of Ukraine) before and after im- mersing the experimental samples into these suspen- sions. The optical density was measured by spectro- photometry at l=540 nm 2, 24 and 48 h after the sam- ple immersion. The bacterial cell amount was evalu- ated from the optical density measurements of the bacteria suspension with known concentration in CFU mL-1 (Colony Forming Units). It was found that the inclusion of Ag+-ions into the coating significantly reduced the number of bacteria in a sample. Even a stronger effect occurred for the Ag+-ions doped HA coatings, formed at a surface of the substrate with CS layer (Fig. 6). The proposed approach can be taken as a promis- ing method to create antimicrobial coatings for tita- nium implants [68]. Chitosan-biopolymer composites for drug delivery Regenerative medicine plays an important role in the restoring of damaged organs in vivo by the activation of stimulating factors of the organism. One of the advantages of chitosan is the ability of controlling the release of active compounds without the use of toxic organic solutions, because of its good solubili- ty in weakly acid solutions. These circumstances led to the use of CS for the creation of drug delivery systems. For example, CS was once used for dis- solving poorly soluble pharmaceuticals in the syn- thesis of mucoadhesive mixtures [69–71], and for enhancement of the peptides absorption] [72–74]. Nowadays, various types of systems (tablets, cap- sules, microspheres, nanoparticles, films, gels) are created using different methods (coating matrix, a capsule shell, emulsive cross-linking, coacervation/ precipitation, spray drying, ionic gelation, sieving method) [3]. The chosen method must be specific to the determined component in the particular case studied (particle size, thermal and chemical proper- ties of active agents, the stability of the final pro- Fig. 6. Dependence of E.coli growth on the time after immersion of HA–CS (modified substrate), HA–Ag (unmodified substrate) and HA–Ag (modified substrate) coatings in comparison with the HA coating 93 Chitosan-apatite composites: synthesis and properties duct, etc.). The main problem in the drug delivery therapy is to provide the necessary drug concentra- tion at the destination [75]. One of the modern ap- proaches is the use of CaP-biopolymer scaffolds, including polysaccharides of chitosan and alginate in combination with hydroxyapatite, as above dis- cussed. It was shown that chitosan coatings on algi- nate scaffolds enhance osteoblast adhesion and pro- liferation [46]. Additionally, improvements in the composite mechanical properties were achieved in the scaffolds containing both polymers compared to those containing separate polysaccharides [76]. For example, the effectiveness of chitosan and alginate has been shown for more prolonged and controlled release of lidocaine (C14H22N2O), which is a local anesthetic drug, into physiological solution with phosphate buffer (PBS) [75]. According to FTIR spectroscopy, no chemical reactions have been reg- istered between hydroxyapatite, chitosan, alginate and lidocaine. Instead, it has been shown that each polysaccharide affected crystal morphology of the drug: needle-shaped crystals of lidocaine occurred when chitosan was used as a coating, whereas the using alginate as a coating induced the formation of rectangular crystals [75]. Chitosan-metal complexes As noted above, one of the important properties of chitosan is the formation of chelate with metal ions. Some researches prove a higher antimicrobial activ- ity of chitosan-metal complexes compared with pure chitosan [77]. Such complexes were obtained in two stages. First, the nanoparticles of chitosan were pro- duced by ionic gelation between chitosan and sodi- um tripolyphosphate (Na5P3O10), then the obtained nanoparticles were connected (“loaded”) with metal ions (Ag+, Cu2+, Zn2+, Mn2+, Fe2+) [77]. Antibacterial activities of the metal ions doped chitosan nanopar- ticles, pure chitosan nanoparticles, metal ions and 1 w % acetic acid solution ( used as a solvent for chitosan) were evaluated by determination of the minimum inhibitory concentration (MIC) and mini- mum bactericidal concentration (MBC). MIC was determined by the broth dilution method as an equiv- alent to the minimum sample concentration that did not cause the visible bacteria growth in the tube, containing the bacteria suspension and experimental sample. To evaluate MBC, the bacteria suspension aliquot was transferred from each tube without visi- ble growth on a Muller–Hinton (MH) agar plate (MH was used as a growth media) and incubated at 37 oC for 24 h. MBC was determined as the mini- mum sample concentration that did not cause any bacterial growth. Antibacterial properties of the chi- tosan nanoparticles have been significantly improved by the metal ions addition. For example, for the Cu2+ doped CS-nanoparticles, MIC and MBC against E.coli ATCC25922, S.choleraesuis ATCC 50020 and S. aureus 25923 were 21-42 times lower than for pure Cu2+ ions [77]. The report states that Gram- negative bacteria are more sensitive to chitosan-met- al nanoparticles, due to a high negative charge at a surface of the respective cells, on the one hand, and a positive charge of amino groups reinforced by the interaction of macromolecules with metal ions, on the other hand. However, this hypothesis must be confirmed by new experimental and theoretical quantum-chemical researches. Chitosan nanofibers One of the newest applications of chitosan in medi- cine is the development of natural methods for ob- taining chitosan nanofibers [78]. Similar structures are produced by the “Nanospider” technology. The process occurs as follows. 1) In a special chamber between the cathode and anode a voltage of 60 kV is applied. 2) As a result, at a surface of the cathode covered with a thin film of chitosan solution, a spiral flow of polymer molecules is formed (Taylor cone). 3) The velocity of the particles increases with the movement toward the negatively charged electrode; the diameter of individual flow reduces to nanoscale. 4) Solvent molecules are evaporated and the stretched macromolecules are drawn together, i.e. a phase transition from liquid to solid state is observed. 5) The obtained nanofibers are adsorbed to the nega- tively charged base plate material (any substance, a metal substrate, etc.). 94 L. F. Sukhodub, L. B. Sukhodub, I. V. Chorna There are different physical, chemical (the type of solvent, the DD and MW parameters of chitosan, the solution homogenization without formation of macromolecular tangles, the viscosity and electri- cal conductivity of the cathode forming solution) and technological (the humidity in the chamber 30- 50 w %, the distance between electrodes 150- 180 mm) features of this technology to vary for obtaining the chitosan nanofibers with a size of 70- 200 nm. The first attempts of application of the nanostructures, obtained by this technology, in medicine, e.g. as bandage, demonstrate a new per- spective in the effective treatment of burns and similar injuries [78]. Conclusion Chitosan characteristics considered in this review in- dicate a significant potential for its use as a biomate- rial with the required properties (porosity, degree of biodegradation) in the applied medicine, particularly for bone regeneration. However, some extra efforts are necessary to improve the mechanical properties of chitosan-based biomaterials for the applications. Another a very significant feature of chitosan is its ability of interacting with anionic biomolecules such as growth factors, glycosaminoglycans and DNA. The binding to DNA molecules makes it possible to obtain the material suitable for the application in gene therapy. Taking into account a combination of chitosan properties (biocompatibility, antibacterial ability, the complexation with growth factors and DNA) the conclusion can be made that chitosan is a very promising candidate for tissue engineering scaffolds. However, some parameters such as mo- lecular weight, viscosity, should be further examined to exploit the potential of this natural polysaccharide in nanomedicine. Acknowledgements We thank the Ukrainian Fundamental Foundation (project NU/7-2013) for funding our researches, Dr. V.G. 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Отримані хітозан-апатитні композитні матеріали були проаналізовані з використанням методу рентгенівської дифракції для аналізу кристалічної при- роди їх структур. Було виявлено, що додавання хітозану до композитного матеріалу призводить до зниження кристаліч- ності вихідного апатиту. Крім того, акцентовано увагу на анти- бактеріальні властивості хітозану, використанні наночастинок хітозану для отримання нановолокон і створенні системи контрольованої доставки ліків. К л юч ов і с л ов а: хітозан, гідроксиапатит, біокомпозити, рентгенівська дифракція. Хитозан-апатитные композиты: синтез и свойства Л. Ф. Суходуб, Л. Б. Суходуб, И. В. Черная Цель этого краткого обзора – рассмотрение применения уни- кального биополимера хитозана в практической медицине, особенно для инженерии костной ткани. Основное место в стать е отведено синтезу и свойствам инновационных биомате- риалов на основе хитозана, таким как CaP-хитозан (CS-CP)- композиты и хитозан-альгинатные (CS-AG)-скаффолды. В статье освещены физико-химические свойства, спектраль- ные характеристики и химические модификации молекулы хитозана. Полученные хитозан-апатитные композитные мате- риалы были проанализированы с использованием метода рент- геновской дифракции для анализа кристаллической природы их структур. Было обнаружено, что добавление хитозана к композитному материалу приводило к снижению кристаллич- ности исходного апатита. Кроме того, акцентировано внима- ние на антибактериальных свойствах хитозана, использовании наночастиц хитозана для получения нановолокон и создании систем контролируемой доставки лекарств. К л юч е в ы е с л ов а: хитозан, гидроксиапатит, биокомпози- ты, рентгеновская дифракция. Received 21.02.2016