Biocompatible SWCNT Conductive Composites for Biomedical Applications
Abstract
:1. Introduction
2. Materials and Methods
2.1. Molecules and Organics
2.2. Substrates Cleaning
2.3. Streaming Current Measurements
2.4. Fibroblast Cell Culture
2.5. Cell Imaging
2.6. Preparation of Composites
- (i)
- An aqueous dispersion (see Table S1) for the later sonication was produced by adding the appropriate amount of nanotubes to Milli-Q water.
- (ii)
- An ultrasonic homogenizer (Sonicator Qsonica, Newtown, CT, USA, with maximum power of 700 W) was used in order to homogeneously distribute nanotubes in the water. The sonication was performed at 35–40% of the maximum power for 60 min. In order to avoid overheating during the procedure, the glass beaker with water and nanotubes was cooled by ice water.
- (iii)
- Right after the sonication, the obtained dispersion was mixed with albumin, cellulose, or acrylic polymer, respectively. The resulting compound was thoroughly mixed using a magnetic stirrer for 4 h.
- (iv)
- Afterwards, the dispersion was decanted within 24 h, and then mixed again via a magnetic stirrer for 30 min.
- (v)
- Finally, the composite material is sonicated for 30 min right before the drop casting via the laboratory pipette on the cleaned Si/SiO2 substrates.
2.7. Electrical and Thickness Measurements
3. Results and Discussion
3.1. Surface Potential
- -
- In all cases, the initial ζ-potential of the as prepared sample is similar to the value expected for the polymer.
- -
- Due to the exposure to the electrolyte, the ζ-potential changes significantly in time. The rate of the change is different for the different polymers.
- -
- In all cases, the potential shifts towards the ζ-potential of the Si/SiO2 substrate. However, only in the case of acrylate, the potential gets very close to that of the substrate.
- (i)
- Albumin samples change their surface potential during the “day 0” measurement from −(8 ± 0.5) to −(5 ± 0.5) mV within the first hour of the experiment. This value nicely correlates with the ζ-potential of unmodified albumin −(6 ± 0.5) mV [47]. We assume that this is the case due to (i) the low concentration of nanotubes and (ii) nanotubes are mostly immersed inside the film (see Figure 2 day 0). Such strong and intense change of the surface charge is peculiar for each material during the first active stability test caused by the streaming electrolyte, which has quite significant influence on the unstable interface. We assume that this is caused by removal of the excess of silicon particles appeared after the wafer cutting (see Material part) and release of single carbon nanotubes attached to the surface via weak Van der Waals force combined with degradation of the composite itself. After the first hour, the slope changes and ζ-potential begins to decrease linearly at a rate of about 0.12 mV/h. This corresponds to the albumin biodegradation process. The degradation naturally continues during the first passive stability test in the electrolyte. As a result, the second stability test “day 7” starts at around −20 mV, nevertheless, it does not mean that albumin composite is completely dissolved during the first week (Figure 2 day 7 for albumin supports this). The surface potential rapidly restores back to less negative values. The dependence is quite noisy and stabilizes to a smother line only by the end of the experiment. This continues up to −15 mV at a 6 h’ measurement point. Samples are removed from the device and immersed in the electrolyte again. “Day 14” measurement starts at about the same point where the previous measurement was finished −(16 ± 0.5) mV. This time, the line is very smooth and the surface potential values just slightly varies around −15 mV level. It means that the major dissolving process of the composite has already occurred and just some detachment of nanotubes together with ionic exchange between surface and electrolyte take place. Albumin has the least negative surface potential value (≈−24 mV) at pH 7 (see Figure S5), making it surface, among others, the most favorable for certain types of cell (e.g., neurons or fibroblasts), without considering additional surface modification.
- (ii)
- Cellulose samples change their surface potential during the “day 0” measurement from −(41 ± 1) to −(35 ± 1) mV. Similar to albumin samples, this agrees with literature value of unmodified cellulose −(37 ± 1) mV [48]. The first stability test results are very noisy and unstable. This means that a significant change occurs in the composite layer. Most likely, quite large areas of the materials are detached and removed with the electrolyte flow. The second stability test looks much smoother. However, a surface potential is still changing by about 8 mV within 6 h’ measurement. The “day 14” measurement is very stable and linear with a surface potential of −(31 ± 1) mV. This shows that in comparison to albumin, where a major degradation occurred already by the end of the first week, cellulose-based composite gradually dissolves within 2 weeks. Cellulose has the most negative surface potential value (≈−38 mV) at pH 7 (see Figure S5), making its surface, among others, the least favorable for certain types of cells (e.g., neurons or fibroblasts). This is further confirmed during the cell cultivation experiment.
- (iii)
- Similar to cellulose, acrylic polymer composite changes its ζ-potential from more negative to less negative values (towards unmodified Si/SiO2). However, in comparison to cellulose, acrylic polymer changes its surface potential mostly within the first active stability test, i.e., from −(32 ± 0.5) to −(24 ± 0.5) mV. “Day 7” experiment starts with similar values, meaning that during passive stability, no surface changes occurred. The ζ-potential changed to −(20 ± 0.5) mV by the end of the second active stability test. It stabilizes at −(21 ± 0.5) mV and does not change during the second passive stability test and the “Day 14” test. SEM micrographs support this stable behavior showing that acrylic polymer composite does not change its morphology (see Figure 2).
3.2. Scanning Electron Microscopy Imaging
3.3. Electrical Measurements
3.4. Fibroblast Cell Growth on Composites
- -
- Although cell cultures on albumin and acrylic polymer show live cell densities significantly higher than the reference samples, the fibroblast live density on cellulose is only insignificantly lower;
- -
- The investigated SWCNT results in the better proliferation of cells within 48 h in vitro in comparison to reference samples.
4. Conclusions
Supplementary Materials
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Markov, A.; Wördenweber, R.; Ichkitidze, L.; Gerasimenko, A.; Kurilova, U.; Suetina, I.; Mezentseva, M.; Offenhäusser, A.; Telyshev, D. Biocompatible SWCNT Conductive Composites for Biomedical Applications. Nanomaterials 2020, 10, 2492. https://doi.org/10.3390/nano10122492
Markov A, Wördenweber R, Ichkitidze L, Gerasimenko A, Kurilova U, Suetina I, Mezentseva M, Offenhäusser A, Telyshev D. Biocompatible SWCNT Conductive Composites for Biomedical Applications. Nanomaterials. 2020; 10(12):2492. https://doi.org/10.3390/nano10122492
Chicago/Turabian StyleMarkov, Aleksandr, Roger Wördenweber, Levan Ichkitidze, Alexander Gerasimenko, Ulyana Kurilova, Irina Suetina, Marina Mezentseva, Andreas Offenhäusser, and Dmitry Telyshev. 2020. "Biocompatible SWCNT Conductive Composites for Biomedical Applications" Nanomaterials 10, no. 12: 2492. https://doi.org/10.3390/nano10122492