**8. Conclusions**

Nanocellulose/nanocarbon composites and other hybrid materials containing cellulose nanoparticles (nanofibrils or nanocrystals) and carbon nanoparticles (fullerenes, graphene, carbon nanotubes, nanodiamonds and other carbon nanoparticles) are novel materials that are promising for a wide range of applications in industry, (bio)technology and medicine. This is due to their unique properties, such as high mechanical strength coupled with flexibility and stretchability (composites with graphene, carbon nanotubes and nanodiamond), shape memory (composites with graphene and carbon nanotubes), photodynamic and photothermal activity (composites with fullerenes and graphene), electrical conductivity (composites with graphene and carbon nanotubes), semiconductivity (composites with boron-doped diamond), thermal conductivity (composites with graphene and nanodiamonds), tunable optical transparency (composites with single-walled carbon nanotubes and nanodiamonds), intrinsic fluorescence and luminescence (composites with graphene quantum dots and carbon quantum dots), and high adsorption and filtration capacity (composites with graphene, carbon nanotubes and carbon quantum dots). These properties arise mainly from the advantageous combination of nanocellulose and nanocarbon, which associates and enhances the desirable effects of each of these components. These materials can be prepared relatively easily from a water-based suspension, which is advantageous particularly for biomedical applications. These applications include drug delivery, biosensorics, isolation of various biomolecules, electrical stimulation of damaged tissues, and particularly tissue engineering (bone, neural and vascular) and wound dressing. Our results have proven supportive effects of nanocellulose/carbon nanotube composites on the adhesion and growth of human and porcine adipose tissue-derived stem cells, particularly under dynamic cultivation in a pressure-generating lab-made bioreactor (see Appendix A). However, it should be pointed out that the biomedical applications of nanocellulose/nanocarbon composites are associated with the risk of their potential cytotoxicity and immunogenicity, although this risk appears to be lower than for the single components of these materials.

**Author Contributions:** All authors have read and agree to the published version of the manuscript. Conceptualization, L.B., S.S. and A.S.; methodology, J.P., M.T., R.M., J.S., S.P., A.S., S.S.; software, R.M., J.S., A.B.; validation, L.B., R.M.; formal analysis, L.B., A.B., A.S., S.S.; investigation, J.P., M.T., R.M., J.S., S.P., A.S., S.S.; resources, L.B., P.K.; data curation, J.P., R.M., A.B., A.S.; writing—original draft preparation, L.B., J.P., R.M.; writing—review and editing, A.B., A.S., S.S., P.K.; visualization, J.P., M.T., R.M., A.B.; supervision, L.B., P.K.; project administration, L.B.; funding acquisition, L.B.

**Funding:** This research was funded by the Czech Science Foundation (grant no. 17-00885S). Another support was provided by the BIOCEV – Biotechnology and Biomedicine Centre of the Academy of Sciences and Charles University project (CZ.1.05/1.1.00/02.0109), funded by the European Regional Development Fund.

**Acknowledgments:** Robin Healey (Czech Technical University, Prague) is gratefully acknowledged for his language revision of the manuscript. Panu Lahtinen from VTT (Technical Research Center of Finland, Espoo, Finland) is acknowledged for providing nanocellulose for collaborative work between Tampere University of Technology and Institute of Physiology of the Czech Academy of Sciences.

**Conflicts of Interest:** The authors declare no conflict of interest. The funding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.
