Plant virus incorporated hydrogels as scaffolds for tissue engineering possess low immunogenicity in vivo

A Combination of Flexible Modified Plant Virus Nanoparticles Enables Additive Effects Resulting in Improved Osteogenesis

Plant virus nanoparticles (VNPs) genetically engineered to present osteogenic cues provide a promising method for biofunctionalizing hydrogels in bone tissue engineering. Flexible Potato virus X (PVX) nanoparticles substantially enhance the attachment and differentiation of human mesenchymal stem cells (hMSCs) by presenting the RGD motif, hydroxyapatite-binding peptide (HABP), or consecutive polyglutamates (E8) in a concentration-dependent manner. Therefore, it is hypothesized that Tobacco mosaic virus nanoparticles, which present 1.6 times more functional peptides than PVX, will meliorate such an impact. This study hypothesizes that cultivating hMSCs on a surface coated with a combination of two VNPs presenting peptides for either cell attachment or mineralization can achieve additionally enhancing effects on osteogenesis. Calcium minerals deposited by differentiating hMSCs increases two to threefold for this combination, while the Alkaline Phosphatase activity of hMSCs grown on the PVX-RGD/PVX-HABP-coated surface significantly surpasses any other VNP combination. Superior additive effects are observed for the first time by employing a combination of VNPs with varying functionalities. It is found that the flexible VNP geometry plays a more critical role than the concentration of functional peptides. In conclusion, various peptide-presenting plant VNPs exhibit an additive enhancing effect offering significant potential for effectively functionalizing cell-containing hydrogels in bone tissue engineering.

Bacteriophages: Status quo and emerging trends toward one health approach

The alarming rise in antimicrobial resistance (AMR) among the drug-resistant pathogens has been attributed to the ESKAPEE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa, Enterobacter sp., and Escherichia coli). Recently, these AMR microbes have become difficult to treat, as they have rendered the existing therapeutics ineffective. Thus, there is an urgent need for effective alternatives to lessen or eliminate the current infections and limit the spread of emerging diseases under the "One Health" framework. Bacteriophages (phages) are naturally occurring biological resources with extraordinary potential for biomedical, agriculture/food safety, environmental protection, and energy production. Specific unique properties of phages, such as their bactericidal activity, host specificity, potency, and biocompatibility, make them desirable candidates in therapeutics. The recent biotechnological advancement has broadened the repertoire of phage applications in nanoscience, material science, physical chemistry, and soft-matter research. Herein, we present a comprehensive review, coupling the substantial aspects of phages with their applicability status and emerging opportunities in several interdependent areas under one health concept. Consolidating the recent state-of-the-art studies that integrate human, animal, plant, and environment health, the following points have been highlighted: (i) The biomedical and pharmacological advantages of phages and their antimicrobial derivatives with particular emphasis on in-vivo and clinical studies. (ii) The remarkable potential of phages to be altered, improved, and applied for drug delivery, biosensors, biomedical imaging, tissue engineering, energy, and catalysis. (iii) Resurgence of phages in biocontrol of plant, food, and animal-borne pathogens. (iv) Commercialization of phage-based products, current challenges, and perspectives.

Antisense RNA (asRNA) technology: the concept and applications in crop improvement and sustainable agriculture

Antisense RNA (asRNA) technology is a method used to silence genes and inhibit their expression. Gene function relies on expression, which follows the central dogma of molecular biology. The use of asRNA can regulate gene expression by targeting specific mRNAs, which can result in changes in phenotype, disease resistance, and other traits associated with protein expression profiles. This technology uses short, single-stranded oligonucleotide strands that are complementary to the targeted mRNA. Manipulating and regulating protein expression during its translation can either knock out or knock down the expression of a gene of interest. Therefore, functional genomics can benefit from this technology since it allows for the regulation of protein expression. In this review, we discuss the concept, and applications of asRNA technology which include delaying ripening, prolonging shelf life, biofortification, and increasing biotic and abiotic resistance among others in crop improvement and sustainable agriculture.

Hydrogels as Scaffolds in Bone-Related Tissue Engineering and Regeneration

Several years have passed since the medical and scientific communities leaned toward tissue engineering as the most promising field to aid bone diseases and defects resulting from degenerative conditions or trauma. Owing to their histocompatibility and non-immunogenicity, bone grafts, precisely autografts, have long been the gold standard in bone tissue therapies. However, due to issues associated with grafting, especially the surgical risks and soaring prices of the procedures, alternatives are being extensively sought and researched. Fibrous and non-fibrous materials, synthetic substitutes, or cell-based products are just a few examples of research directions explored as potential solutions. A very promising subgroup of these replacements involves hydrogels. Biomaterials resembling the bone extracellular matrix and therefore acting as 3D scaffolds, providing the appropriate mechanical support and basis for cell growth and tissue regeneration. Additional possibility of using various stimuli in the form of growth factors, cells, etc., within the hydrogel structure, extends their use as bioactive agent delivery platforms and acts in favor of their further directed development. The aim of this review is to bring the reader closer to the fascinating subject of hydrogel scaffolds and present the potential of these materials, applied in bone and cartilage tissue engineering and regeneration.

Gelatin-methacryloyl hydrogels containing turnip mosaic virus for fabrication of nanostructured materials for tissue engineering

Current tissue engineering techniques frequently rely on hydrogels to support cell growth, as these materials strongly mimic the extracellular matrix. However, hydrogels often need ad hoc customization to generate specific tissue constructs. One popular strategy for hydrogel functionalization is to add nanoparticles to them. Here, we present a plant viral nanoparticle the turnip mosaic virus (TuMV), as a promising additive for gelatin methacryloyl (GelMA) hydrogels for the engineering of mammalian tissues. TuMV is a flexuous, elongated, tubular protein nanoparticle (700–750 nm long and 12–15 nm wide) and is incapable of infecting mammalian cells. These flexuous nanoparticles spontaneously form entangled nanomeshes in aqueous environments, and we hypothesized that this nanomesh structure could serve as a nanoscaffold for cells. Human fibroblasts loaded into GelMA-TuMV hydrogels exhibited similar metabolic activity to that of cells loaded in pristine GelMA hydrogels. However, cells cultured in GelMA-TuMV formed clusters and assumed an elongated morphology in contrast to the homogeneous and confluent cultures seen on GelMA surfaces, suggesting that the nanoscaffold material per se did not favor cell adhesion. We also covalently conjugated TuMV particles with epidermal growth factor (EGF) using a straightforward reaction scheme based on a Staudinger reaction. BJ cells cultured on the functionalized scaffolds increased their confluency by approximately 30% compared to growth with unconjugated EGF. We also provide examples of the use of GelMA-TuMV hydrogels in different biofabrication scenarios, include casting, flow-based-manufacture of filaments, and bioprinting. We envision TuMV as a versatile nanobiomaterial that can be useful for tissue engineering.

Biocompatibility study of tobacco mosaic virus nanoparticles on human alveolar bone cells

One of the most important factors in a dental implant's success is an adequate quantity of supporting bone. However, there are still some limitations for the bone substitution material. Previous studies found that tobacco mosaic virus (TMV) had the potential for bone formation induction. The aim of this study was to evaluate the biocompatibility of TMV with primary human alveolar bone cells. Primary human alveolar bone cells were cultured on TMV coated substrates. Cell viability, alkaline phosphatase activity, calcium matrix mineralization forming ability, immunofluorescence staining for osteocalcin synthesis and cell morphology were assessed. The results showed that primary human alveolar bone cells cultured on the TMV coated substrates had a higher metabolic rate than the non-TMV coated control group at days 1, 3, 7 and 14. Moreover, the calcium deposition was positive and the alkaline phosphatase activity assay was found significantly greater than the control group at day 14 (p < 0.05). The osteocalcin protein synthesis was found in both the TMV coated substrates and the control group. The immunofluorescence study revealed that in the TMV coated substrates group, the cell morphology changed into a polygonal shape and aggregated more quickly than the control group. The present findings conclude that TMV is biocompatible with primary human alveolar bone cells and also shows osteoinduction potential.

Protein Cages: From Fundamentals to Advanced Applications

Proteins that self-assemble into polyhedral shell-like structures are useful molecular containers both in nature and in the laboratory. Here we review efforts to repurpose diverse protein cages, including viral capsids, ferritins, bacterial microcompartments, and designed capsules, as vaccines, drug delivery vehicles, targeted imaging agents, nanoreactors, templates for controlled materials synthesis, building blocks for higher-order architectures, and more. A deep understanding of the principles underlying the construction, function, and evolution of natural systems has been key to tailoring selective cargo encapsulation and interactions with both biological systems and synthetic materials through protein engineering and directed evolution. The ability to adapt and design increasingly sophisticated capsid structures and functions stands to benefit the fields of catalysis, materials science, and medicine.

Biofabrication of muscle fibers enhanced with plant viral nanoparticles using surface chaotic flows

Multiple human tissues exhibit fibrous nature. Therefore, the fabrication of hydrogel filaments for tissue engineering is a trending topic. Current tissue models are made of materials that often require further enhancement for appropriate cell attachment, proliferation and differentiation. Here we present a simple strategy, based on the use of surface chaotic flows amenable to mathematical modeling, to fabricate continuous, long and thin filaments of gelatin methacryloyl (GelMA). The fabrication of these filaments is achieved by chaotic advection in a finely controlled and miniaturized version of the journal bearing system. A drop of GelMA pregel is injected on a higher-density viscous fluid (glycerin) and a chaotic flow is applied through an iterative process. The millimeter-scale hydrogel drop is exponentially deformed and elongated to generate a meter-scale fiber, which was then polymerized under UV-light exposure. Computational fluid dynamic (CFD) simulations are conducted to determine the characteristics of the flow and design the experimental conditions for fabrication of the fibers. GelMA fibers were effectively used as scaffolds for C2C12 myoblast cells. Experimental results demonstrate an accurate accordance with CFD simulations for the predicted length of the fibers. Plant-based viral nanoparticles (i.e.Turnip mosaic virus; TuMV) were then integrated to the hydrogel fibers as a secondary nano-scaffold for cells for enhanced muscle tissue engineering. The addition of TuMV significantly increased the metabolic activity of the cell-seeded fibers (p* < 0.05), strengthened cell attachment throughout the first 28 d, improved cell alignment, and promoted the generation of structures that resemble natural mammal muscle tissues. Chaotic two-dimensional-printing is proven to be a viable method for the fabrication of hydrogel fibers. The combined use of thin and long GelMA hydrogel fibers enhanced with flexuous virions offers a promising alternative for scaffolding of muscle cells and show potential to be used as cost-effective models for muscle tissue engineering purposes.

The pharmacology of plant virus nanoparticles

The application of nanoparticles for medical purposes has made enormous strides in providing new solutions to health problems. The observation that plant virus-based nanoparticles (VNPs) can be repurposed and engineered as smart bio-vehicles for targeted drug delivery and imaging has launched extensive research for improving the therapeutic and diagnostic management of various diseases. There is evidence that VNPs are promising high value nanocarriers with potential for translational development. This is mainly due to their unique features, encompassing structural uniformity, ease of manufacture and functionalization by means of expression, chemical biology and self-assembly. While the development pipeline is moving rapidly, with many reports focusing on engineering and manufacturing aspects to tailor the properties and efficacy of VNPs, fewer studies have focused on gaining insights into the nanotoxicity of this novel platform nanotechnology. Herein, we discuss the pharmacology of VNPs as a function of formulation and route of administration. VNPs are reviewed in the context of their application as therapeutic adjuvants or nanocarrier excipients to initiate, enhance, attenuate or impede the formulation's toxicity. The summary of the data however also underlines the need for meticulous VNP structure-nanotoxicity studies to improve our understanding of their in vivo fates and pharmacological profiles to pave the way for translation of VNP-based formulations into the clinical setting.

Biocompatibility study of modified injectable hyaluronic acid hydrogel with mannitol/BSA to alveolar bone cells

The quality and quantity of bone are crucial to the success of dental implant treatment. Recently, bone grafting materials have reached some limitations. This study aimed to evaluate the biocompatibility of novel drug delivery material, injectable methacrylated hyaluronic acid hydrogel incorporated with different ratios of mannitol and BSA (Man/BSA MeHA), to human alveolar bone cells. The three-dimensionally encapsulated cell culture was evaluated with the resazurin cell viability test, alkaline phosphatase activity assay, immunohistochemistry test for collagen type-I synthesis, and cell morphology. The results showed that the encapsulated cells were viable in all four ratios of Man/BSA MeHA hydrogel and the average metabolic rate was not less than the control group. The morphology test showed round shape cells at the upper portion of the hydrogel and fibroblast-like or polygonal shape at the lower portion of hydrogel next to the culture plate. All four groups could express enzyme alkaline phosphatase and collagen type-I. In conclusion, four ratios of Man/BSA MeHA hydrogel were biocompatible with primary human alveolar bone cells.

Attachment of Ultralow Amount of Engineered Plant Viral Nanoparticles to Mesenchymal Stem Cells Enhances Osteogenesis and Mineralization

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 viral nanoparticles for packaging and in vivo delivery of bioactive cargos

Nanoparticles have unique capabilities and considerable promise for many different biological uses. One capability is delivering bioactive cargos to specific cells, tissues, or organisms. Depending on the task, there are multiple variables to consider including nanoparticle selection, targeting strategies, and incorporating cargo so it can be delivered in a biologically active form. One nanoparticle option, genetically controlled plant viral nanoparticles (PVNPs), is highly uniform within a given virus but quite variable between viruses with a broad range of useful properties. PVNPs are flexible and versatile tools for incorporating and delivering a wide range of small or large molecule cargos. Furthermore, PVNPs can be modified to create nanostructures that can solve problems in medical, environmental, and basic research. This review discusses the currently available techniques for delivering bioactive cargos with PVNPs and potential cargos that can be delivered with these strategies. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

From infection to healing: The use of plant viruses in bioactive hydrogels

Plant viruses show great diversity in shape and size, but each species forms unique nucleoprotein particles that are symmetrical and monodisperse. The genetically programed structure of plant viruses allows them to be modified by genetic engineering, bioconjugation, or encapsulation to form virus nanoparticles (VNPs) that are suitable for a broad range of applications. Plant VNPs can be used to present foreign proteins or epitopes, to construct inorganic hybrid materials, or to carry molecular cargos, allowing their utilization as imaging reagents, immunomodulators, therapeutics, nanoreactors, and biosensors. The medical applications of plant viruses benefit from their inability to infect and replicate in human cells. The structural properties of plant viruses also make them useful as components of hydrogels for tissue engineering. Hydrogels are three-dimensional networks composed of hydrophilic polymers that can absorb large amounts of water. They are used as supports for tissue regeneration, as reservoirs for controlled drug release, and are found in contact lenses, many wound healing materials, and hygiene products. They are also useful in ecological applications such as wastewater treatment. Hydrogel-based matrices are structurally similar to the native extracellular matrix (ECM) and provide a scaffold for the attachment of cells. To fully replicate the functions of the ECM it is necessary to augment hydrogels with biological cues that regulate cellular interactions. This can be achieved by incorporating functionalized VNPs displaying ligands that influence the mechanical characteristics of hydrogels and their biological properties, promoting the survival, proliferation, migration, and differentiation of embedded cells. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement.

Peroxidase activities of gold nanowires synthesized by TMV as template and their application in detection of cancer cells

A sensing methodology that combines Au, tobacco mosaic virus (TMV), and folic acid for selective, sensitive, and colorimetric detection of tumor cells based on the peroxidase-like activity was reported in this study. Gold nanowires with a high aspect ratio were synthesized using TMV as a template. Au@TMV nanowire (AT) complex was obtained with diameter of 4 nm and length between 200 and 300 nm. In addition, since TMV was biocompatible and had many amino and carboxyl groups on its surface, AT was conjugated by folate to form a folic acid (FA)-conjugated AT composite (ATF) and tested by FTIR measurements. Furthermore, the peroxidase-like properties were studied and the optimal conditions for mimic enzyme activity were optimized. Finally, HeLa and other tumor cells expressed excessive receptors of folate on the surface, which can specifically bind to folic acid. As the specific binding of ATF with HeLa cells, the peroxidase properties of ATF were used for detection of cancer cells (Scheme 1). The cancer cells were detected not only qualitatively but also quantitatively. In this study, as low as 2000 cancer cells/mL could be detected using the current method.

Plant virus-based materials for biomedical applications: Trends and prospects

Nanomaterials composed of plant viral components are finding their way into medical technology and health care, as they offer singular properties. Precisely shaped, tailored virus nanoparticles (VNPs) with multivalent protein surfaces are efficiently loaded with functional compounds such as contrast agents and drugs, and serve as carrier templates and targeting vehicles displaying e.g. peptides and synthetic molecules. Multiple modifications enable uses including vaccination, biosensing, tissue engineering, intravital delivery and theranostics. Novel concepts exploit self-organization capacities of viral building blocks into hierarchical 2D and 3D structures, and their conversion into biocompatible, biodegradable units. High yields of VNPs and proteins can be harvested from plants after a few days so that various products have reached or are close to commercialization. The article delineates potentials and limitations of biomedical plant VNP uses, integrating perspectives of chemistry, biomaterials sciences, molecular plant virology and process engineering.

Development of improved dual-diazonium reagents for faster crosslinking of tobacco mosaic virus to form hydrogels

New bench-stable reagents with two diazonium sites were designed and synthesized for protein crosslinking. Because of the faster diazonium-tyrosine coupling reaction, hydrogels from the crosslinking of tobacco mosaic virus and the reagent DDA-3 could be prepared within 1 min at room temperature. Furthermore, hydrogels with the introduction of disulfide bonds viaDDA-4 could be chemically degraded by dithiothreitol. Our results provided a facile approach for the direct construction of virus-based hydrogels.

Improved dual-diazonium reagents were developed for more efficient crosslinking of tobacco mosaic virus to form hydrogels.

Antisense RNA: the new favorite in genetic research

Antisense RNA molecule represents a unique type of DNA transcript that comprises 19-23 nucleotides and is complementary to mRNA. Antisense RNAs play the crucial role in regulating gene expression at multiple levels, such as at replication, transcription, and translation. In addition, artificial antisense RNAs can effectively regulate the expression of related genes in host cells. With the development of antisense RNA, investigating the functions of antisense RNAs has emerged as a hot research field. This review summarizes our current understanding of antisense RNAs, particularly of the formation of antisense RNAs and their mechanism of regulating the expression of their target genes. In addition, we detail the effects and applications of antisense RNAs in antivirus and anticancer treatments and in regulating the expression of related genes in plants and microorganisms. This review is intended to highlight the key role of antisense RNA in genetic research and guide new investigators to the study of antisense RNAs.

Emerging Strategies for Stem Cell Lineage Commitment in Tissue Engineering and Regenerative Medicine

Stem cells have transformed the fields of tissue engineering and regenerative medicine, and their potential to further advance these fields cannot be overstated. The stem cell niche is a dynamic microenvironment that determines cell fate during development and tissue repair following an injury. Classically, stem cells were studied in isolation of their microenvironment; however, contemporary research has produced a myriad of evidence that shows the importance of multiple aspects of the stem cell niche in regulating their processes. In the context of tissue engineering and regenerative medicine studies, the niche is an artificial environment provided by culture conditions. In vitro culture conditions may involve coculturing with other cell types, developing specific biomaterials, and applying relevant forces to promote the desired lineage commitment. Considerable advance has been made over the past few years toward directed stem cell differentiation; however, the unspecific differentiation of stem cells yielding a mixed population of cells has been a challenge. In this review, we provide a systematic review of the emerging strategies used for lineage commitment within the context of tissue engineering and regenerative medicine. These strategies include scaffold pore-size and pore-shape gradients, stress relaxation, sonic and electromagnetic effects, and magnetic forces. Finally, we provide insights and perspectives into future directions focusing on signaling pathways activated during lineage commitment using external stimuli.

Compartmentalized supramolecular hydrogels based on viral nanocages towards sophisticated cargo administration

Introduction of compartments with defined spaces inside a hydrogel network brings unique features, such as cargo quantification, stabilization and diminishment of burst release, which are all desired for biomedical applications. As a proof of concept, guest-modified cowpea chlorotic mottle virus (CCMV) particles and complementary guest-modified hydroxylpropyl cellulose (HPC) were non-covalently cross-linked through the formation of ternary host-guest complexes with cucurbit[8]uril (CB[8]). Furthermore, CCMV based virus-like particles (VLPs) loaded with tetrasulfonated zinc phthalocyanine (ZnPc) were prepared, with a loading efficiency up to 99%, which are subsequently successfully integrated inside the supramolecular hydrogel network. It was shown that compartments provided by protein cages not only help to quantify the loaded ZnPc cargo, but also improve the water solubility of ZnPc to avoid undesired aggregation. Moreover, the VLPs together with ZnPc cargo can be released in a controlled way without an initial burst release. The photodynamic effect of ZnPc molecules was retained after encapsulation of capsid protein and release from the hydrogel. This line of research suggests a new approach for sophisticated drug administration in supramolecular hydrogels.

Virus-like particles as crosslinkers in fibrous biomimetic hydrogels: approaches towards capsid rupture and gel repair

Biological hydrogels can become many times stiffer under deformation. This unique ability has only recently been realised in fully synthetic gels. Typically, these networks are composed of semi-flexible polymers and bundles and show such large mechanical responses at very small strains, which makes them particularly suitable for application as strain-responsive materials. In this work, we introduced strain-responsiveness by crosslinking the architecture with a multi-functional virus-like particle. At high stresses, we find that the virus particles disintegrate, which creates an (irreversible) mechanical energy dissipation pathway, analogous to the high stress response of fibrin networks. A cooling-heating cycle allows for re-crosslinking at the damaged site, which gives rise to much stronger hydrogels. Virus particles and capsids are promising drug delivery vehicles and our approach offers an effective strategy to trigger the release mechanically without compromising the mechanical integrity of the host material.

Covalent incorporation of tobacco mosaic virus increases the stiffness of poly(ethylene glycol) diacrylate hydrogels

Hydrogels are versatile materials, finding applications as adsorbers, supports for biosensors and biocatalysts or as scaffolds for tissue engineering. A frequently used building block for chemically cross-linked hydrogels is poly(ethylene glycol) diacrylate (PEG-DA). However, after curing, PEG-DA hydrogels cannot be functionalized easily. In this contribution, the stiff, rod-like tobacco mosaic virus (TMV) is investigated as a functional additive to PEG-DA hydrogels. TMV consists of more than 2000 identical coat proteins and can therefore present more than 2000 functional sites per TMV available for coupling, and thus has been used as a template or building block for nano-scaled hybrid materials for many years. Here, PEG-DA (M n = 700 g mol-1) hydrogels are combined with a thiol-group presenting TMV mutant (TMVCys). By covalent coupling of TMVCys into the hydrogel matrix via the thiol-Michael reaction, the storage modulus of the hydrogels is increased compared to pure PEG-DA hydrogels and to hydrogels containing wildtype TMV (wt-TMV) which is not coupled covalently into the hydrogel matrix. In contrast, the swelling behaviour of the hydrogels is not altered by TMVCys or wt-TMV. Transmission electron microscopy reveals that the TMV particles are well dispersed in the hydrogels without any large aggregates. These findings give rise to the conclusion that well-defined hydrogels were obtained which offer the possibility to use the incorporated TMV as multivalent carrier templates e.g. for enzymes in future studies.

Upregulation of osteogenesis of mesenchymal stem cells with virus-based thin films

A major aim of tissue engineering is to develop biomimetic scaffolding materials that can guide the proliferation, self-renewal and differentiation of multipotent stem cells into specific lineages. Cellular functions can be controlled by the interactions between cells and biomaterials. Therefore, the surface chemistry and topography of support materials play a pivotal role in modulating cell behaviors at many stages of cell growth and development. Due to their highly ordered structure and programmable surface chemistries, which provide unique topography as biomaterials, viral nanoparticles have been utilized as building blocks for targeted cell growth and differentiation. This review article discusses the fabrication of two-dimensional virus-based thin film on substrates and highlights the study of the effect of chemical and physical cues introduced by plant virus nanoparticle thin films on the promotion of osteogenic differentiation of BMSCs.

In Vitro Assembly of Virus-Derived Designer Shells Around Inorganic Nanoparticles

Nanoparticle-templated assembly of virus shells provides a promising approach to the production of hybrid nanomaterials and a potential avenue toward new mechanistic insights in virus phenomena originating in many-body effects, which cannot be understood from examining the properties of molecular subunits alone. This approach complements the successful molecular biology perspective traditionally used in virology, and promises a deeper understanding of viruses and virus-like particles through an expanded methodological toolbox. Here we present protocols for forming a virus coat protein shell around functionalized inorganic nanoparticles.

Engineered Potato virus X nanoparticles support hydroxyapatite nucleation for improved bone tissue replacement

Bionanoparticles based on filamentous phages or flexuous viruses are interesting candidates for meeting the challenges of tailoring biomineralization in hydrogel-based bone tissue substitutes. We hypothesized that hydroxyapatite crystal nucleation and matrix mineralization can be significantly increased by mineralization-inducing (MIP) and integrin binding motif (RGD) peptides presented on biomimetic nanoparticles. In this study, Potato virus X (PVX), a flexible rod-shaped plant virus was genetically engineered to present these functional peptides on its particle surface. Recombinant PVX-MIP/RGD particles were isolated from infected Nicotiana benthamiana plants and characterized by western blot, SEM, TEM, and TPLSM in MSC cultures. The presence of RGD was proven by cell attachment, spreading, and vinculin cluster analysis, and MIP by in vitro mineralization and osteogenic differentiation assays. Thus the tailored surface of genetically engineered PVX forms fibril-like nanostructures which enables enhanced focal adhesion-dependent cell adhesion, and matrix mineralization verified by Alizarin. Hydroxyapatite crystal nucleation is supported on recombinant PVX particles leading to a biomimetic network and bundle-like structures similar to mineralized collagen fibrils. In conclusion, the recombinant flexuous PVX nanoparticles exhibit properties with great potential for bone tissue substitutes.

STATEMENT OF SIGNIFICANCE

A suitable biomaterial for tissue engineering should be able to mimic the endogenous extracellular matrix by presenting biochemical and biophysical cues. Novel hydrogel-based materials seek to meet the criteria of cytocompatibility, biodegradability, printability, and crosslinkability under mild conditions. However, a majority of existing hydrogels lack cell-interactive motifs, which are crucial to modulate cellular responses. The incorporation of the plant virus PVX to the hydrogel could improve functions like integrin-binding and mineralization due to peptide-presentation on the particle surface. The tailored surface of genetically engineered PVX forms fibril-like nanostructures which enables enhanced focal adhesion-dependent cell adhesion and matrix mineralization and offers great potential for the development of new hydrogel compositions for bone tissue substitutes.

Design of virus-based nanomaterials for medicine, biotechnology, and energy

This review provides an overview of recent developments in "chemical virology." Viruses, as materials, provide unique nanoscale scaffolds that have relevance in chemical biology and nanotechnology, with diverse areas of applications. Some fundamental advantages of viruses, compared to synthetically programmed materials, include the highly precise spatial arrangement of their subunits into a diverse array of shapes and sizes and many available avenues for easy and reproducible modification. Here, we will first survey the broad distribution of viruses and various methods for producing virus-based nanoparticles, as well as engineering principles used to impart new functionalities. We will then examine the broad range of applications and implications of virus-based materials, focusing on the medical, biotechnology, and energy sectors. We anticipate that this field will continue to evolve and grow, with exciting new possibilities stemming from advancements in the rational design of virus-based nanomaterials.

Novel roles for well-known players: from tobacco mosaic virus pests to enzymatically active assemblies

The rod-shaped nanoparticles of the widespread plant pathogen tobacco mosaic virus (TMV) have been a matter of intense debates and cutting-edge research for more than a hundred years. During the late 19th century, their behavior in filtration tests applied to the agent causing the 'plant mosaic disease' eventually led to the discrimination of viruses from bacteria. Thereafter, they promoted the development of biophysical cornerstone techniques such as electron microscopy and ultracentrifugation. Since the 1950s, the robust, helically arranged nucleoprotein complexes consisting of a single RNA and more than 2100 identical coat protein subunits have enabled molecular studies which have pioneered the understanding of viral replication and self-assembly, and elucidated major aspects of virus-host interplay, which can lead to agronomically relevant diseases. However, during the last decades, TMV has acquired a new reputation as a well-defined high-yield nanotemplate with multivalent protein surfaces, allowing for an ordered high-density presentation of multiple active molecules or synthetic compounds. Amino acid side chains exposed on the viral coat may be tailored genetically or biochemically to meet the demands for selective conjugation reactions, or to directly engineer novel functionality on TMV-derived nanosticks. The natural TMV size (length: 300 nm) in combination with functional ligands such as peptides, enzymes, dyes, drugs or inorganic materials is advantageous for applications ranging from biomedical imaging and therapy approaches over surface enlargement of battery electrodes to the immobilization of enzymes. TMV building blocks are also amenable to external control of in vitro assembly and re-organization into technically expedient new shapes or arrays, which bears a unique potential for the development of 'smart' functional 3D structures. Among those, materials designed for enzyme-based biodetection layouts, which are routinely applied, e.g., for monitoring blood sugar concentrations, might profit particularly from the presence of TMV rods: Their surfaces were recently shown to stabilize enzymatic activities upon repeated consecutive uses and over several weeks. This review gives the reader a ride through strikingly diverse achievements obtained with TMV-based particles, compares them to the progress with related viruses, and focuses on latest results revealing special advantages for enzyme-based biosensing formats, which might be of high interest for diagnostics employing 'systems-on-a-chip'.

Modified TMV Particles as Beneficial Scaffolds to Present Sensor Enzymes

Tobacco mosaic virus (TMV) is a robust nanotubular nucleoprotein scaffold increasingly employed for the high density presentation of functional molecules such as peptides, fluorescent dyes, and antibodies. We report on its use as advantageous carrier for sensor enzymes. A TMV mutant with a cysteine residue exposed on every coat protein (CP) subunit (TMVCys) enabled the coupling of bifunctional maleimide-polyethylene glycol (PEG)-biotin linkers (TMVCys/Bio). Its surface was equipped with two streptavidin [SA]-conjugated enzymes: glucose oxidase ([SA]-GOx) and horseradish peroxidase ([SA]-HRP). At least 50% of the CPs were decorated with a linker molecule, and all thereof with active enzymes. Upon use as adapter scaffolds in conventional "high-binding" microtiter plates, TMV sticks allowed the immobilization of up to 45-fold higher catalytic activities than control samples with the same input of enzymes. Moreover, they increased storage stability and reusability in relation to enzymes applied directly to microtiter plate wells. The functionalized TMV adsorbed to solid supports showed a homogeneous distribution of the conjugated enzymes and structural integrity of the nanorods upon transmission electron and atomic force microscopy. The high surface-increase and steric accessibility of the viral scaffolds in combination with the biochemical environment provided by the plant viral coat may explain the beneficial effects. TMV can, thus, serve as a favorable multivalent nanoscale platform for the ordered presentation of bioactive proteins.

Advances in Functional Assemblies for Regenerative Medicine

The ability to synthesise bioresponsive systems and selectively active biochemistries using polymer-based materials with supramolecular features has led to a surge in research interest directed towards their development as next generation biomaterials for drug delivery, medical device design and tissue engineering.

Virus-based nanomaterials as positron emission tomography and magnetic resonance contrast agents: from technology development to translational medicine

Viruses have recently emerged as ideal protein scaffolds for a new class of contrast agents that can be used in medical imaging procedures such as positron emission tomography (PET) and magnetic resonance imaging (MRI). Whereas synthetic nanoparticles are difficult to produce as homogeneous formulations due to the inherently stochastic nature of the synthesis process, virus-based nanoparticles are genetically encoded and are therefore produced as homogeneous and monodisperse preparations with a high degree of quality control. Because the virus capsids have a defined chemical structure that has evolved to carry cargoes of nucleic acids, they can be modified to carry precisely defined cargoes of contrast agents and can be decorated with spatially defined contrast reagents on the internal or external surfaces. Viral nanoparticles can also be genetically programed or conjugated with targeting ligands to deliver contrast agents to specific cells, and the natural biocompatibility of viruses means that they are cleared rapidly from the body. Nanoparticles based on bacteriophages and plant viruses are safe for use in humans and can be produced inexpensively in large quantities as self-assembling recombinant proteins. Based on these considerations, a new generation of contrast agents has been developed using bacteriophages and plant viruses as scaffolds to carry positron-emitting radioisotopes such as [(18) F] fluorodeoxyglucose for PET imaging and iron oxide or Gd(3+) for MRI. Although challenges such as immunogenicity, loading efficiency, and regulatory compliance remain to be address, virus-based nanoparticles represent a promising new enabling technology for a new generation of highly biocompatible and biodegradable targeted imaging reagents.

Peptide-equipped tobacco mosaic virus templates for selective and controllable biomineral deposition

The coating of regular-shaped, readily available nanorod biotemplates with inorganic compounds has attracted increasing interest during recent years. The goal is an effective, bioinspired fabrication of fiber-reinforced composites and robust, miniaturized technical devices. Major challenges in the synthesis of applicable mineralized nanorods lie in selectivity and adjustability of the inorganic material deposited on the biological, rod-shaped backbones, with respect to thickness and surface profile of the resulting coating, as well as the avoidance of aggregation into extended superstructures. Nanotubular tobacco mosaic virus (TMV) templates have proved particularly suitable towards this goal: Their multivalent protein coating can be modified by high-surface-density conjugation of peptides, inducing and governing silica deposition from precursor solutions in vitro. In this study, TMV has been equipped with mineralization-directing peptides designed to yield silica coatings in a reliable and predictable manner via precipitation from tetraethoxysilane (TEOS) precursors. Three peptide groups were compared regarding their influence on silica polymerization: (i) two peptide variants with alternating basic and acidic residues, i.e. lysine-aspartic acid (KD) x motifs expected to act as charge-relay systems promoting TEOS hydrolysis and silica polymerization; (ii) a tetrahistidine-exposing polypeptide (CA4H4) known to induce silicification due to the positive charge of its clustered imidazole side chains; and (iii) two peptides with high ZnO binding affinity. Differential effects on the mineralization of the TMV surface were demonstrated, where a (KD) x charge-relay peptide (designed in this study) led to the most reproducible and selective silica deposition. A homogenous coating of the biotemplate and tight control of shell thickness were achieved.

The Impact of Aspect Ratio on the Biodistribution and Tumor Homing of Rigid Soft-Matter Nanorods

The size and shape of nanocarriers can affect their fate in vivo, but little is known about the effect of nanocarrier aspect ratio on biodistribution in the setting of cancer imaging and drug delivery. The production of nanoscale anisotropic materials is a technical challenge. A unique biotemplating approach based on of rod-shaped nucleoprotein nanoparticles with predetermined aspect ratios (AR 3.5, 7, and 16.5) is used. These rigid, soft-matter nanoassemblies are derived from tobacco mosaic virus (TMV) components. The role of nanoparticle aspect ratio is investigated, while keeping the surface chemistries constant, using either PEGylated stealth nanoparticles or receptor-targeted RGD-displaying formulations. Aspect ratio has a profound impact on the behavior of the nanoparticles in vivo and in vitro. PEGylated nanorods with the lowest aspect ratio (AR 3.5) achieve the most efficient passive tumor-homing behavior because they can diffuse most easily, whereas RGD-labeled particles with a medium aspect ratio (AR 7) are more efficient at tumor targeting because this requires a balance between infusibility and ligand-receptor interactions. The in vivo behavior of nanoparticles can therefore be tailored to control biodistribution, longevity, and tumor penetration by modulating a single parameter: the aspect ratio of the nanocarrier.

Charge-transfer interactions for the fabrication of multifunctional viral nanoparticles

In this paper, a facile strategy to fabricate multifunctional viral nanoparticles was described by introducing charge-transfer interactions between a pyrenyl motif with dinitrophenyl and pyridinium-contained guest molecules.