The applicability of an amidated polysaccharide hydrogel as a cartilage substitute: structural and rheological characterization
Graphical abstract
Introduction
Articular cartilage is a thin layer of deformable, load-bearing material that lines the bony ends of all diarthrodial joints.1 Macroscopic cartilage behavior depends on its complex microscopic structure. Its mechanical properties are determined by the composition of the tissue, mainly collagen and proteoglycans (chondroitin sulfate, hyaluronan, etc.), their assembly at the ultra-molecular level, and their interaction with interstitial fluids. The mixture of fluid and matrix provide the viscous-elastic and mechanical properties necessary for an efficient function of the cartilage tissue.2, 3, 4, 5
Recently, an amidic carboxymethylcellulose (CMCA) based hydrogel was utilized as a cartilage substitute in osteoarthritic rabbit.6 To elucidate hydrogel structure and water–polymer interaction, an analysis was performed by NMR and FT-IR imaging spectroscopy. Particular attention was focused on this aspect because the proteoglycan network, through its interaction with both the collagen fibers and the interstitial water, plays a major role in the static and dynamic mechanical properties of the cartilage. The rheological and the swelling behavior of CMCA hydrogel were then studied.
Section snippets
Materials
The sodium salt of CMC (viscosity 402 mPa s in 2% w/v aqueous solution at 25 °C and carboxymethylation degree of 0.9 ± 0.1 per monosaccharide unit Mw = 200,000) was supplied by Hercules Italia S.p.A (Italy). All the other reagents were purchased from Fluka Chemie AG (Switzerland).
Amidation of polysaccharide
The procedure used to obtain the amidic derivative of CMC was previously reported.7 Briefly, the CMC tetrabutylammonium salt (CMCTBA) was dissolved in N,N′-dimethylformamide (DMF) with mechanical stirring under a nitrogen
Structural characterization of amidic polysaccharide by infrared analysis, potentiometric titration and NMR spectroscopy
The amidation of the CMC polysaccharide was confirmed both qualitatively and quantitatively. The IR spectrum of the modified polysaccharide (CMCA) was compared with that of native polysaccharide (CMC). The CMCA IR spectrum showed a new shoulder centered at 1645 cm−1 which is related to the amidic CO stretching.7 Furthermore, a new small peak centered at 1740 cm−1, related to COOH groups, was present (Fig. 1a). In Figure 1b, the comparison between the IR spectra of CMCA polysaccharide at pH 2 and
Conclusions
An amidic derivative of carboxymethylcellulose-based hydrogel was obtained and characterized in terms of amidation degree. NMR studies and FT-IR imaging spectroscopy demonstrated that the reaction allowed a polymer to be obtained, which was characterized by a regular distribution of amidic groups along the polysaccharide chains. Through this regularity, a homogenous three-dimensional scaffold was obtained which maintained the thixotropic property as well as the linear polysaccharide.16
Acknowledgement
The authors would like to thank the Fondazione Monte dei Paschi di Siena (‘Traslazione clinica attuali conoscenze precliniche nell’ambito dell’ingegneria tessutale muscolo scheletrica per ricostruzioni biologiche da perdite di sostanza traumatiche o patologiche’ project) for financial support.
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