Physicochemical and biological characteristics of chitosan/κ-carrageenan thin layer-by-layer films for surface modification of nitinol

Highlights

• Biopolymer layer-by-layer nanocoatings change the surface properties of nitinol plates.

• Using κ-carrageenan as the top layer reduces hydrophobicity and surface roughness.

• The use of chitosan as the lower layer of the film allows increasing the stability polymer coatings on the nitinol.

• Chitosan/carrageenan films that were applied to nitinol plates reduce cytotoxicity in relation to the MG-63 cells line.

Abstract

Thin films based on the natural polysaccharides κ-carrageenan (Carr) and chitosan (Chit) were formed by layer-by-layer deposition technique. Surface topography and mechanical characteristics (Young's modulus, adhesion strength) of the polymer films with different number of layers were determined using various modes of atomic force microscopy (AFM). Polymer films were used to deposit on the surface of nitinol (NiTi) plates. The creation of polysaccharide coatings on nitinol led to a change in surface properties, such as hydrophilicity and root mean square roughness. in vitro cytotoxicity assay for nitinol plates with and without polymer coating by the MG-63 osteoblast-like cell line was conducted and was shown that all the studied samples are not toxic. A decrease in cytotoxicity for samples with a polymer film consisting of 4 layers of chitosan and carrageenan was shown as compared to an uncoated nitinol plates.

Introduction

Nitinol (titanium nickelide, NiTi) is an alloy of nickel and titanium, which has superelasticity and shape memory effect. This is the ability of the material after preliminary deformation to return to its original form when the temperature changes (Huang, 2002). Nitinol is a bioinert material (Siu and Man, 2013), and its unique mechanical characteristics open up perspectives for its application in tissue engineering for the construction of medical implants (Bhardwaj et al., 2019).

Despite obvious advantages, biomedical use of nitinol-based materials is limited. The disadvantage of this material is the release of toxic nickel ions into the surrounding tissues during the presence in the organisms (Arndt et al., 2005). Nickel ions can cause allergic reactions, and is also a carcinogen (Chakraborty et al., 2019). Protective oxide TiO₂, which is obtained on the surface of nitinol using various physicochemical methods, can reduce the release of nickel ions (Milošev and Kapun, 2012). In this case, formation of an additional barrier on the surface, for example, using a polymer film, to a greater extent allows to reduce the release of Ni ions from the material (Nagaraja et al., 2018). In (Bakhshi et al., 2011), the non-biodegradable synthetic polymer POSS – PSU (Kannan et al., 2006) crosslinked with 3-aminopropyltriethoxysilane for electrodynamic deposition onto a pre-modified nitinol surface of stents was used. This process made it possible to increase the corrosion resistance of nitinol by reducing the rate and decreasing the amount of nickel ions released. The main disadvantage of this approach is the processing complexity and the need for special equipment. In addition, in some practical applications, the biodegradability of the materials and the release of non-toxic products will be the advantage. Therefore, studies in the area of natural degradable biopolymers are important. This approach includes the use of bioactive coatings. Various auxiliary elements, such as polymer coatings (Flamini et al., 2018), can be used to create the desired microenvironment on nitinol to simulate a natural extracellular matrix. It was reported that the extracellular microenvironment formed by oppositely charged polymers demonstrates good biocompatibility (Samuel et al., 2011). Currently, the method layer-by-layer assembly of charged layers is widely used due to its simplicity and ability to vary the thickness and composition of the coating (Hua et al., 2003).

In their work (Liu et al., 2011), researchers created multilayer films based on the natural polymers - heparin and alginate. Biocompatibility and interaction with blood components were studied. However, a synthetic polycation diazoresin was additionally added as a positively charged component, since heparin and alginate both have negatively charged functional groups. Chitosan is the only natural cationic biopolymer, therefore coatings based on chitosan and anionic polysaccharides do not require the use of intermediate components for thin films formation (Drozd et al., 2019).

The natural polysaccharide chitosan incorporated free amino groups that have a positive charge under acidic conditions. Therefore, it can be used as one of the components in the LbL films formation process (Ariga et al., 2007). Chitosan is widely used to obtain various biomaterials, due to such properties as biocompatibility, biodegradability, mucoadhesion, low toxicity (Kim et al., 2008) and bioactivity. Its properties such as hemostatic, antibacterial, antioxidant activity, as well as the ability to wound healing are important when creating chitosan-based biomedical materials (Mittal et al., 2018; Anraku et al., 2018; Muxika et al., 2017).

The carrageenan molecule is a partially sulfated galactose and 3,6-anhydrogalactose chains connected by alternating β-(1-4) and α-(1-3) glycosides bonds. The main source of carrageenan is the red algae Rhodóphyta. Due to its water-retaining properties, it is widely used in the food industry, and it is also applied in biomedicine (Liu et al., 2014), in the field of controlled release (Nanaki et al., 2010; Ghanam and Kleinebudde, 2011; Pavli et al., 2010) and drug delivery (Kianfar et al., 2013). The presence of anionic functional groups in the structure of a molecule allows being used carrageenan to create biomaterials by the LbL method with positively charged components due to electrostatic interactions (Temoçin, 2019; Martins et al., 2020).

The aims of the work were to form thin films based on chitosan and κ-carrageenan, to study their some physico-chemical properties and cytocompatibility, to determine the possibilities of their biomedical use in bone engineering.