Production, surface modification, physicochemical properties, biocompatibility, and bioimaging applications of nanodiamonds

Nanodiamonds (ND) are chemically inert and stable owing to their sp3 covalent bonding structure, but their surface sp2 graphitic carbons can be easily homogenized with diverse functional groups via oxidation, reduction, hydrogenation, amination, and halogenation. Further surface conjugation of NDs with hydrophilic ligands can boost their colloidal stability and functionality. In addition, NDs are non-toxic as they are made of carbons. They exhibit stable fluorescence without photobleaching. They also possess paramagnetic and ferromagnetic properties, making them suitable for use as a new type of fluorescence imaging (FI) and magnetic resonance imaging (MRI) probe. In this review, we focused on recently developed ND production methods, surface homogenization and functionalization methods, biocompatibilities, and biomedical imaging applications as FI and MRI probes. Finally, we discussed future perspectives.

Nanodiamond enhanced mechanical and biological properties of extrudable gelatin hydrogel cross-linked with tannic acid and ferrous sulphate

Background

The requirements for cell-encapsulated injectable and bioprintable hydrogels are extrusion ability, cell supportive micro-environment and reasonable post-printing stability for the acclimatization of the cells in the target site. Detonation nanodiamond (ND) has shown its potential to improve the mechanical and biological properties of such hydrogels. Enhancing the performance properties of natural biopolymer gelatin-based hydrogels can widen their biomedical application possibilities to various areas including drug delivery, tissue engineering and 3D bioprinting.

Method

In this study, natural cross-linker tannic acid (TA) is used along with ferrous sulphate (FS) to optimize the swelling and disintegration of extrudable and 3D printable gelatin hydrogels. The amounts of TA and FS are restricted to improve the extrusion ability of the gels in 3D printing. Further, ND particles (detonation type) are dispersed using twin screw extrusion technology to study their effect on mechanical and biological properties of the 3D printing hydrogel.

Results

The improved dispersion of ND particles helps to improve compressive strength almost ten times and dynamic modulus three times using 40 mg ND (2% w/w of gelatin). The surface-functional groups of detonation ND also contributed for such improvement in mechanical properties due to higher interaction with the hydrogel matrix. The stability of the hydrogels in water was also improved to 7 days. Four times improvement of the cell growth and proliferation was observed in ND based hydrogel.

Conclusion

The cell-supportive nature of these moderately stable and extrudable ND dispersed gelatin hydrogels makes them a good candidate for short term regenerative applications of cell-encapsulated injectable hydrogels with better mechanical properties.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40824-022-00285-3.

The3He nuclear magnetic relaxation in nematically ordered Al2O3aerogels: effects of4He and nitrogen pre-plating

The results of³He gas pulsed NMR spin-lattice relaxation study in high-porosity (84.9%-97.9%) nematically ordered Al₂O₃aerogels at 1.5 and 4.2 K are presented. The linear dependence ofT₁on gas pressure is observed in aerogels that are pre-plated by helium-4. Nitrogen pre-plating prior to helium-4 pre-plating weakly decreases the³He gas spin-lattice relaxation rate. A few possible mechanisms plausibly involved in³He nuclear magnetic relaxation in aerogels are considered. The suggested nuclear spin-lattice relaxation model due to some magnetically 'dirty' aerogel fibers allows to estimate the effective mean free path of³He atoms in aerogel.

Reply to 'Comment on "Angstrom-scale probing of paramagnetic centers location in nanodiamonds by 3He NMR at low temperatures"' by A. Shames, V. Osipov and A. Panich, Phys. Chem. Chem. Phys. 2018, 20, DOI

Shames et al. made a comment on our article (DOI: 10.1039/C7CP05898E) stating that their experience in EPR studies of detonation nanodiamonds suggests the existence of two main types of paramagnetic center in detonation nanodiamonds which questions our results. In this reply we provide insights into why there is only one main type of paramagnetic centers detected in nanodiamonds used in this work, which validates the correctness of the proposed original method to determine the distances between paramagnetic centers and nanoparticle surfaces by 3He NMR.

Comment on "Angstrom-scale probing of paramagnetic center location in nanodiamonds by 3He NMR at low temperatures" by V. Kuzmin, K. Safiullin, G. Dolgorukov, A. Stanislavovas, E. Alakshin, T. Safin, B. Yavkin, S. Orlinskii, A. Kiiamov, M. Presnyakov, A. Klochkov and M. Tagirov, Phys. Chem. Chem. Phys., 2018, 20, 1476

Kuzmin et al. reported on the application of the 3He NMR relaxometry technique to localization of intrinsic paramagnetic defects in detonation nanodiamond (DND) particles. We found some inconsistencies in the DND characterization, the model of paramagnetic defects' allocation used in that work as well as the estimation of distances between 3He NMR probes and paramagnetic defects, which question the results obtained.