Hydrogel-based materials are widely used to mimic the extracellular matrix in bone tissue engineering, although they often lack biofunctional cues. In the authors' previous work, Potato virus X (PVX), a flexible rod-shaped biocompatible plant virus nanoparticle (VNP) with 1270 coat protein subunits, is genetically modified to present functional peptides for generating a bone substitute. Here, PVX is engineered to present mineralization-and osteogenesis-associated peptides and laden in hydrogels at a concentration lower by two orders of magnitude. Its competence in mineralization is demonstrated both on 2D surfaces and in hydrogels and the superiority of enriched peptides on VNPs is verified and compared with free peptides and VNPs presenting fewer functional peptides. Alkaline phosphatase activity and Alizarin red staining of human mesenchymal stem cells increase 1.2-1.7 times when stimulate by VNPs. Engineered PVX adheres to cells, exhibiting a stimulation of biomimetic peptides in close proximity to the cells. The retention of VNPs in hydrogels is monitored and more than 80% of VNPs remain inside after several washing steps. The mechanical properties of VNP-laden hydrogels are investigated, including viscosity, gelling temperature, and compressive tangent modulus. This study demonstrates that recombinant PVX nanoparticles are excellent candidates for hydrogel nanocomposites in bone tissue engineering.

Plant virus nanoparticles are promising candidates for the development of novel materials, including nanocomposites and scaffolds/carriers for functional molecules such as enzymes. Their advantages for enzyme immobilization include a modular organization, a robust and programmable structure, and a simple, cost-effective production. However, the activity of many enzymes relies on posttranslational modification and most plant viruses replicate in the cytoplasm, so functional enzymes cannot be displayed on the virus surface by direct coat protein fusions. An alternative display system to present the Trichoderma reesei endoglucanase Cel12A on potato virus X (PVX) using SpyTag/SpyCatcher (ST/SC) technology was recently developed by the authors, which allows the carrier and enzyme to be produced separately before isopeptide conjugation. Although kinetic analysis clearly indicated efficient biocatalyst activity, the PVX carrier interfered with substrate binding. To overcome this, the suitability of tobacco mosaic virus (TMV) was tested, which can also accommodate a larger number of ST peptides. We produced TMV particles displaying ST as a new platform for the immobilization of enzymes such as Cel12A, and compared its performance to the established PVX-ST platform in terms of catalytic efficiency. Although more enzyme molecules were immobilized on the TMV-ST particles, we found that the rigid scaffold and helical spacing significantly affected enzyme activity.

The use of nanoparticles for agrochemical delivery is an important step toward achieving global food security. Specifically, the ability to target the delivery of pesticides and other useful chemicals into the soil will greatly improve the efficiency and efficacy of these molecules, mitigating crop losses associated with pests and parasitic organisms. While synthetic nanoparticles can be a good delivery vehicle and demonstrate high mobility in the soil, their fate and persistence have some implications for human and environmental health. Therefore, using proteinaceous materials such as plant virus nanoparticles, which have already been adapted for the soil, provides a fruitful avenue of exploration. Previously, tobacco mild green mosaic virus (TMGMV) and red clover necrotic mosaic virus (RCNMV) have shown high soil mobility and nematicide delivery for the treatment of plant parasitic nematodes. To further the use of these plant virus nanoparticles in soil delivery applications, understanding the properties of the soil and the nanoparticles is essential. In this work, we assessed the mobility of TMGMV, potato virus X, and tobacco mosaic virus with a genetically encoded lysine on its surface (TMV-Lys) and virus-like particles of physalis mottle virus (PhMV) in four types of soil. The particles were loaded in a cylindrical column of soil, eluted, and analyzed for the protein signal. A mathematical model was used to compare their relative mobility. Data indicate that TMGMV has higher soil mobility compared to the other plant virus-based nanoparticles analyzed, and this appeared to be independent of the soil environment. Data indicate that the presence of a highdensity lysine corona may not be favorable for soil applications. While this work provides insights into nanoparticle design rules for soil applications, data also highlight that more systemic studies are needed to delineate the design rules for soil delivery of nanocarriers.

Plant virus nanoparticles (VNPs) have advantages for applications in biomedicine and materials science due to their safety, biocompatibility and versatility. They are used to display functional amino acids or small peptides via coat protein fusions, but assembly of VNPs is strongly influenced by certain modifications. These limitations can be circumvented by plug-and-display systems. Combination with optogenetic proteins allows the design of VNP shuttles for spatially directed distribution of proteins.

In article number 2001245 by Ulrich Commandeur, Horst Fischer, and co‐workers, plant virus nanoparticles, engineered with functional peptides, are laden in mesenchymal stem cellembedded hydrogels at an ultralow concentration for generating a bone substitute. Their competence in stimulation of mineralization and osteogenesis, and the superiority of enriched functional peptides on its surface are verified, demonstrating an excellent candidate for hydrogel composites in bone tissue engineering.