Genetically engineered materials: Proteins and beyond

Information-rich molecules provide opportunities for evolution. Genetically engineered materials are superior in that their properties are coded within genetic sequences and could be fine-tuned. In this review, we elaborate the concept of genetically engineered materials (GEMs) using examples ranging from engineered protein materials to engineered living materials. Protein-based materials are the materials of choice by nature. Recent progress in protein engineering has led to opportunities to tune their sequences for optimal material performance. Proteins also play a central role in living materials where they act in concert with other biological components as well as nonbiological cofactors, giving rise to living features. While the existing GEMs are often limited to those constructed by building blocks of biological origin, being genetically engineerable does not preclude nonbiologic or synthetic materials, the latter of which have yet to be fully explored.

Perfluoropentane-filled chitosan poly-acrylic acid nanobubbles with high stability for long-term ultrasound imaging in vivo

Reducing the size of ultrasound contrast agents (UCAs) will decrease the intensity of the ultrasound echogenic signals and reduce the stability of the bubbles. Therefore, it is a challenge to design nanobubbles that are less than 200 nm in size and that have both good imaging abilities and high stability for long-term imaging in vivo. In this work, we successfully prepared perfluoropentane-filled chitosan poly-acrylic acid (PFP-CS-PAA) nanobubbles with a size of about 100 nm via a direct simple core-template-free strategy. In vitro tests demonstrated that the nanobubbles showed satisfactory imaging capabilities in non-linear harmonic imaging mode and had significantly better stability than commercial Sonovue® lipid microbubbles. It was valuable to discover that the prepared PFP-CS-PAA nanobubbles could exhibit good imaging quality in rat livers for 10 min after intravenous injection. Also, the PFP-CS-PAA nanobubbles could maintain imaging capabilities in nude mouse tumors for 7 days after intratumoral injection, which indicated that these nanobubbles could keep their stability for a long time in vivo. To the best of our knowledge, the ultrasound imaging persistence time in vivo was the longest of currently reported polymer nanobubbles that are smaller than 200 nm. This new nanosized UCA with high stability has great potential for long-term ultrasound imaging in vivo. Tumor cellular uptake and histological analysis revealed that PFP-CS-PAA nanobubbles could be taken up into tumor cells, but no intracellular uptake was observed in the case of Sonovue®. Animal fluorescence imaging in vivo demonstrated that PFP-CS-PAA nanobubbles could be effectively cleared after intravenous injection within 168 h. MTT assays indicated that PFP-CS-PAA nanobubbles had appropriate biocompatibility. Abnormal levels of blood urea nitrogen were detected after the intravenous administration of PFP-CS-PAA nanobubbles to rats, and body-weight gain was inhibited for up to 6 d, but, after that, body weights recovered their tendency to increase.

Self-assembled Viral Nanoparticles as Targeted Anticancer Vehicles

Viral nanoparticles (VNPs) comprise a variety of mammalian viruses, plant viruses, and bacteriophages, that have been adopted as building blocks and supra-molecular templates in nanotechnology. VNPs demonstrate the dynamic, monodisperse, polyvalent, and symmetrical architectures which represent examples of such biological templates. These programmable scaffolds have been exploited for genetic and chemical manipulation for displaying of targeted moieties together with encapsulation of various payloads for diagnosis or therapeutic intervention. The drug delivery system based on VNPs offer diverse advantages over synthetic nanoparticles, including biocompatibility, biodegradability, water solubility, and high uptake capability. Here we summarize the recent progress of VNPs especially as targeted anticancer vehicles from the encapsulation and surface modification mechanisms, involved viruses and VNPs, to their application potentials.

Adsorption and self-assembly of M13 phage into directionally organized structures on C and SiO2 films

A versatile method for the directional assembly of M13 phage using amorphous carbon and SiO2 thin films was demonstrated. A high affinity of the M13 phage macromolecules for incorporation into aligned structures on an amorphous carbon surface was observed at the concentration range, in which the viral nanofibers tend to disorder. In contrast, the viral particles showed less freedom to adopt an aligned orientation on SiO2 films when deposited in close vicinity. Here an interpretation of the role of the carbon surface in significant enhancement of adsorption and generation of viral arrays with a high orientational order was proposed in terms of surface chemistry and competitive electrostatic interactions. This study suggests the use of amorphous carbon substrates as a template for directional organization of a closely-packed and two-dimensional M13 viral film, which can be a promising route to mineralize a variety of smooth and homogeneous inorganic nanostructure layers.

X-ray spatial frequency heterodyne imaging of protein-based nanobubble contrast agents

Spatial Frequency Heterodyne Imaging (SFHI) is a novel x-ray scatter imaging technique that utilizes nanoparticle contrast agents. The enhanced sensitivity of this new technique relative to traditional absorption-based x-ray radiography makes it promising for applications in biomedical and materials imaging. Although previous studies on SFHI have utilized only metal nanoparticle contrast agents, we show that nanomaterials with a much lower electron density are also suitable. We prepared protein-based "nanobubble" contrast agents that are comprised of protein cage architectures filled with gas. Results show that these nanobubbles provide contrast in SFHI comparable to that of gold nanoparticles of similar size.

Formation mechanism of chalcogenide nanocrystals confined inside genetically engineered virus-like particles

Engineered virus-like particles (VLP) are attractive for fabricating nanostructured materials for applications in diverse areas such as catalysis, drug delivery, biomedicine, composites, etc. Basic understanding of the interaction between the inorganic guest and biomolecular host is thus important for the controlled synthesis of inorganic nanoparticles inside VLP and rational assembly of ordered VLP-based hierarchical nanostructures. We have investigated in detail the formation mechanism and growth kinetics of semiconducting nanocrystals confined inside genetically engineered bacteriophage P22 VLP using semiconducting CdS as a prototypical example. The selective nucleation and growth of CdS at the engineered sites is found to be uniform during the early stage, followed by a more stochastic growth process. Furthermore, kinetic studies reveal that the presence of an engineered biotemplate helps in significantly retarding the reaction rate. These findings provide guidance for the controlled synthesis of a wide range of other inorganic materials confined inside VLP, and are of practical importance for the rational design of VLP-based hierarchical nanostuctures.

Biomimetic antigenic nanoparticles elicit controlled protective immune response to influenza

Here we present a biomimetic strategy toward nanoparticle design for controlled immune response through encapsulation of conserved internal influenza proteins on the interior of virus-like particles (VLPs) to direct CD8+ cytotoxic T cell protection. Programmed encapsulation and sequestration of the conserved nucleoprotein (NP) from influenza on the interior of a VLP, derived from the bacteriophage P22, results in a vaccine that provides multistrain protection against 100 times lethal doses of influenza in an NP specific CD8+ T cell-dependent manner. VLP assembly and encapsulation of the immunogenic NP cargo protein is the result of a genetically programmed self-assembly making this strategy amendable to the quick production of vaccines to rapidly emerging pathogens. Addition of adjuvants or targeting molecules were not required for eliciting the protective response.