**5. Conclusions and Future Outlook**

Recently, various high-throughput nanomaterial fabrication methods have been demonstrated for hybrid bioelectronics. But, there remain substantial challenges to be overcome. Recent attempts to optimize printing parameters for gravure, flexography, screen, inkjet, and slot die printing have opened new possibilities for highly scalable soft electronics and critically needed hybrid biosensors. In addition, novel approaches to high throughput printing, such as flexography aided by CNT stamps, set the leading edge in print resolution, homogeneity, and quality [60]. Significant progress within the last decade on ink rheology optimization and material-interface studies allows for the high-resolution patterning of many functional nanomaterials. And these materials are being extensively studied for a diverse set of bioelectronics applications. This field, however, remains in its infancy, and there are several critical challenges to be overcome. First, electronic circuits require more than interconnects, and the further study of printed vias and material adhesion in multiple layer prints is of high importance. Second, printing resolutions remain low for many methods; thus, new approaches to increasing resolution must be investigated. Third, inkjet printing offers substantial advantages in prototyping and manufacturing costs. Still, recent works have not implemented commercially tested roll-to-roll inkjet printing to the degree necessary to make inkjet printing a desirable method for high throughput nanomaterial fabrication. Finally, such as gravure roll geometries and materials, printing parameters should be reimagined for nanomaterial applications instead of simply relying on processes optimized for inks without large-volume loadings or dispersion challenges. Overall, recent progress in the field of nanomaterial printing offers great hope that a new class of hybrid flexible bioelectronics can provide the affordable, long-term usable devices necessary to help the millions of people suffering from undiagnosed diseases. However, new investigations into novel printing approaches and further optimization of current methods are greatly needed before this vision is made a reality.

**Author Contributions:** N.Z. and W.-H.Y. conceived and designed the materials in this paper. All authors conducted reviews of materials and printing technologies, designed figures, and reviewed all sections. All authors wrote the paper together. All authors have read and agreed to the published version of the manuscript.

**Funding:** We acknowledge the support from the IEN Center for Human-Centric Interfaces and Engineering at Georgia Tech.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** No new data were created or analyzed in this study.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

