Influence of Charge and Heat on the Mechanical Properties of Scaffolds from Ionic Complexation of Chitosan and Carboxymethyl Cellulose

Abstract

As one of the most abundant, multifunctional biological polymers, polysaccharides are considered promising materials to prepare tissue engineering scaffolds. When properly designed, wetted porous scaffolds can have biomechanics similar to living tissue and provide suitable fluid transport, both of which are key features for in vitro and in vivo tissue growth. They can further mimic the components and function of glycosaminoglycans found in the extracellular matrix of tissues. In this study, we investigate scaffolds formed by charge complexation between anionic carboxymethyl cellulose and cationic protonated chitosan under well-controlled conditions. Freeze-drying and dehydrothermal heat treatment were then used to obtain porous materials with exceptional, unprecendent mechanical properties and dimensional long-term stability in cell growth media. We investigated how complexation conditions, charge ratio, and heat treatment significantly influence the resulting fluid uptake and biomechanics. Surprisingly, materials with high compressive strength, high elastic modulus, and significant shape recovery are obtained under certain conditions. We address this mostly to a balanced charge ratio and the formation of covalent amide bonds between the polymers without the use of additional cross-linkers. The scaffolds promoted clustered cell adhesion and showed no cytotoxic effects as assessed by cell viability assay and live/dead staining with human adipose tissue-derived mesenchymal stem cells. We suggest that similar scaffolds or biomaterials comprising other polysaccharides have a large potential for cartilage tissue engineering and that elucidating the reason for the observed peculiar biomechanics can stimulate further research.

Organic acid cross-linked 3D printed cellulose nanocomposite bioscaffolds with controlled porosity, mechanical strength, and biocompatibility

“…This may be because of dehydration of CA and subsequent formation of unsaturated acids in the scaffold (see Figure 2 ) ( Cai et al., 2019 ; Kučerová et al., 2016 ). The coloration of the scaffold can also be because of the degradation of NFC and CMC to a certain extent at higher temperature as reported in our previous work ( Dobaj Štiglic et al., 2021 ). Our aim was to obtain acid-free scaffolds; otherwise, excess or residual acid could lead to undesirable cytotoxic effects.…”

“…The Ink 0 /120°C ( Figure S7 B) showed the characteristic peaks because of the carbon atoms of NFC or CMC appeared at δ C 61 (C6), 70–80 (C2, C3, C5, and C7), 81 (C4), and 105 ppm (C1; the respective carbons are numbered in Figure 6 ). Besides this, the carboxyl carbon (C8) of the CMC carboxylate group is observed at δ C 178 ppm ( Dobaj Štiglic et al., 2021 ; Gürer et al., 2021 ; Mohan et al., 2020 ) (see Figure S7 ). All these characteristic peaks are also observed for CA cross-linked sample (Ink 2.5 /120°C/N, Figure 6 A), in addition to the methylene carbon atoms of CA at δ C 45 ppm (C2∗-C4∗) ( Sun et al., 2019 ).…”

“…Furthermore, other factors such as the type of polymers, viscosity, solid content, and cross-linking type can also be vital in determining the pore size of resulting scaffolds ( Li et al., 2017 ; Mirtaghavi et al., 2020 ). For example, the increased addition of large molecules, such as chitosan ( Dobaj Štiglic et al., 2021 ; Lin and Yeh, 2012 ), polyvinyl alcohol ( Kanimozhi et al., 2018 ), collagen ( Pawelec et al., 2014 ; Pottathara et al., 2021 ), alginate ( Bahrami et al., 2019 ), or smaller molecules e.g., citric acid ( Wu et al., 2019a ) and ferulic acid ( Mathew and Abraham, 2008 ), have been shown to reduce the scaffold porosity/pore size. A similar behavior is also observed for our scaffolds and the increasing amount of CA.…”

“…In the second step of degradation (between 250°C and 350°C) the DTG curves in Figure 7 B (see insert) indicate a maximum weight loss rate of 35% for NFC/CMC composite scaffolds compared to the neat polymer (NFC: 64% and CMC: 25%). This is because of CMC or CA decarboxylation reactions and the onset decomposition of NFC among other factors ( Dobaj Štiglic et al., 2021 ; Mohan et al., 2020 ). Surprisingly, cross-linking with CA at all concentrations does not considerably influence the thermal stability of the scaffolds compared to non-cross-linked ones (Ink 0 /120°C) despite the large differences in the mechanical properties of the scaffolds as a function of CA concentration (see below).…”

“…3D Scaffolds for TE applications not only need to be mechanically stable to support cell adhesion and proliferation without collapsing, but they also need to be gradually replaced by native ECM and therefore (slowly) biodegradable ( Dobaj Štiglic et al., 2021 ; Milojević et al., 2019 ; Mohan et al., 2018 ; Reddy et al., 2021 ). Therefore, we investigated the in vitro degradation of scaffolds in biofluids at 37°C and pH 7.4, mimicking the native tissue environment, and the results are shown in Figures 8 C and 8D.…”