Flax fibre reinforced alginate poloxamer hydrogel: assessment of mechanical and 4D printing potential

The mechanical and printing performance of a new biomaterial, flax fibre-reinforced alginate-poloxamer based hydrogel, for load-bearing and 4D printing biomedical applications is described in this study. The-self suspendable ability of the material was evaluated by optimising the printing parameters and conducting a collapse test. 1% of the flax fibre weight fraction was sufficient to obtain an optimum hydrogel composite from a mechanical perspective. The collapse test showed that the addition of flax fibres allowed a consistent print without support over longer distances (8 and 10 mm) than the unreinforced hydrogel. The addition of 1% of flax fibres increased the viscosity by 39% and 129% at strain rates of 1 rad s-1 and 5 rad s-1, respectively, compared to the unreinforced hydrogel. The distributions of fibre size and orientation inside the material were also evaluated to identify the internal morphology of the material. The difference of coefficients of moisture expansion between the printing direction (1.29 × 10-1) and the transverse direction (6.03 × 10-1) showed potential for hygromorphic actuation in 4D printing. The actuation authority was demonstrated by printing a [0°; 90°] stacking sequence and rosette-like structures, which were then actuated using humidity gradients. Adding fibres to the hydrogel improved the repeatability of the actuation, while lowering the actuation authority from 0.11 mm-1 to 0.08 mm-1. Overall, this study highlighted the structural and actuation-related benefits of adding flax fibres to hydrogels.

Protocol to decellularize porcine right ventricular outflow tracts using a 3D printed flow chamber

Surgical treatment of pediatric congenital heart disease with tissue grafts is a lifesaving intervention. Decellularization to reduce immunogenicity of tissue grafts is an increasingly popular alternative to glutaraldehyde fixation. Here, we present a protocol to decellularize porcine right ventricular outflow tracts using a 3D printed flow chamber. We describe steps for 3D printing the flow rig, preparing porcine tissue, and using the flow rig to utilize shear forces for decellularization. We then detail procedures for characterizing the acellular scaffold. For complete details on the use and execution of this protocol, please refer to Vafaee et al.1.

Technological advances in the use of viral and non-viral vectors for delivering genetic and non-genetic cargos for cancer therapy

The burden of cancer is increasing globally. Several challenges facing its mainstream treatment approaches have formed the basis for the development of targeted delivery systems to carry and distribute anti-cancer payloads to their defined targets. This site-specific delivery of drug molecules and gene payloads to selectively target druggable biomarkers aimed at inducing cell death while sparing normal cells is the principal goal for cancer therapy. An important advantage of a delivery vector either viral or non-viral is the cumulative ability to penetrate the haphazardly arranged and immunosuppressive tumour microenvironment of solid tumours and or withstand antibody-mediated immune response. Biotechnological approaches incorporating rational protein engineering for the development of targeted delivery systems which may serve as vehicles for packaging and distribution of anti-cancer agents to selectively target and kill cancer cells are highly desired. Over the years, these chemically and genetically modified delivery systems have aimed at distribution and selective accumulation of drug molecules at receptor sites resulting in constant maintenance of high drug bioavailability for effective anti-tumour activity. In this review, we highlighted the state-of-the art viral and non-viral drug and gene delivery systems and those under developments focusing on cancer therapy.

Modular Bioorthogonal Lipid Nanoparticle Modification Platforms for Cardiac Homing

Lipid nanoparticles (LNPs) are becoming widely adopted as vectors for the delivery of therapeutic payloads but generally lack intrinsic tissue-homing properties. These extracellular vesicle (EV) mimetics can be targeted toward the liver, lung, or spleen via charge modification of their lipid headgroups. Homing to other tissues has only been achieved via covalent surface modification strategies using small-molecule ligands, peptides, or monoclonal antibodies─methods that are challenging to couple with large-scale manufacturing. Herein, we design a novel modular artificial membrane-binding protein (AMBP) platform for the modification of LNPs postformation. The system is composed of two protein modules that can be readily coupled using bioorthogonal chemistry to yield the AMBP. The first is a membrane anchor module comprising a supercharged green fluorescent protein (scGFP) electrostatically conjugated to a dynamic polymer surfactant corona. The second is a functional module containing a cardiac tissue fibronectin homing sequence from the bacterial adhesin CshA. We demonstrate that LNPs modified using the AMBP exhibit a 20-fold increase in uptake by fibronectin-rich C2C12 cells under static conditions and a 10-fold increase under physiologically relevant shear stresses, with no loss of cell viability. Moreover, we show targeted localization of the AMBP-modified LNPs in zebrafish hearts, highlighting their therapeutic potential as a vector for the treatment of cardiac disease and, more generally, as a smart vector.

A rapid high throughput bioprinted colorectal cancer spheroid platform forin vitrodrug- and radiation-response

We describe the development of a high-throughput bioprinted colorectal cancer (CRC) spheroid platform with high levels of automation, information content, and low cell number requirement. This is achieved via the formulation of a hydrogel bioink with a compressive Young's modulus that is commensurate with that of colonic tissue (1-3 kPa), which supports exponential growth of spheroids from a wide range of CRC cell lines. The resulting spheroids display tight cell-cell junctions, bioink matrix-cell interactions and necrotic hypoxic cores. By combining high content light microscopy imaging and processing with rapid multiwell plate bioprinting, dose-response profiles are generated from CRC spheroids challenged with oxaliplatin (OX) and fluorouracil (5FU), as well as radiotherapy. Bioprinted CRC spheroids are shown to exhibit high levels of chemoresistance relative to cell monolayers, and OX was found to be significantly less effective against tumour spheroids than in monolayer culture, when compared to 5FU.

A Rationally Designed Supercharged Protein-Enzyme Chimera Self-Assembles In Situ to Yield Bifunctional Composite Textiles

Catalytically active materials for the enhancement of personalized protective equipment (PPE) could be advantageous to help alleviate threats posed by neurotoxic organophosphorus compounds (OPs). Accordingly, a chimeric protein comprised of a supercharged green fluorescent protein (scGFP) and phosphotriesterase from Agrobacterium radiobacter (arPTE) was designed to drive the polymer surfactant (S^-)-mediated self-assembly of microclusters to produce robust, enzymatically active materials. The chimera scGFP-arPTE was structurally characterized via circular dichroism spectroscopy and synchrotron radiation small-angle X-ray scattering, and its biophysical properties were determined. Significantly, the chimera exhibited greater thermal stability than the native constituent proteins, as well as a higher catalytic turnover number (k_cat). Furthermore, scGFP-arPTE was electrostatically complexed with monomeric S^-, driving self-assembly into [scGFP-arPTE][S^-] nanoclusters, which could be dehydrated and cross-linked to yield enzymatically active [scGFP-arPTE][S^-] porous films with a high-order structure. Moreover, these clusters could self-assemble within cotton fibers to generate active composite textiles without the need for the pretreatment of the fabrics. Significantly, the resulting materials maintained the biophysical activities of both constituent proteins and displayed recyclable and persistent activity against the nerve agent simulant paraoxon.

Three-Dimensional Printable Enzymatically Active Plastics

Here, we describe a facile route to the synthesis of enzymatically active highly fabricable plastics, where the enzyme is an intrinsic component of the material. This is facilitated by the formation of an electrostatically stabilized enzyme-polymer surfactant nanoconstruct, which, after lyophilization and melting, affords stable macromolecular dispersions in a wide range of organic solvents. A selection of plastics can then be co-dissolved in the dispersions, which provides a route to bespoke 3D enzyme plastic nanocomposite structures using a wide range of fabrication techniques, including melt electrowriting, casting, and piston-driven 3D printing. The resulting constructs comprising active phosphotriesterase (arPTE) readily detoxify organophosphates with persistent activity over repeated cycles and for long time periods. Moreover, we show that the protein guest molecules, such as arPTE or sfGFP, increase the compressive Young's modulus of the plastics and that the identity of the biomolecule influences the nanomorphology and mechanical properties of the resulting materials. Overall, we demonstrate that these biologically active nanocomposite plastics are compatible with state-of-the-art 3D fabrication techniques and that the methodology could be readily applied to produce robust and on-demand smart nanomaterial structures.

Measuring Nanoparticle Penetration Through Bio-Mimetic Gels

Background

In cancer nanomedicine, drugs are transported by nanocarriers through a biological system to produce a therapeutic effect. The efficacy of the treatment is affected by the ability of the nanocarriers to overcome biological transport barriers to reach their target. In this work, we focus on the process of nanocarrier penetration through tumour tissue after extravasation. Visualising the dynamics of nanocarriers in tissue is difficult in vivo, and in vitro assays often do not capture the spatial and physical constraints relevant to model tissue penetration.

Methods

We propose a new simple, low-cost method to observe the transport dynamics of nanoparticles through a tissue-mimetic microfluidic chip. After loading a chip with triplicate conditions of gel type and loading with microparticles, microscopic analysis allows for tracking of fluorescent nanoparticles as they move through hydrogels (Matrigel and Collagen I) with and without cell-sized microparticles. A bespoke image-processing codebase written in MATLAB allows for statistical analysis of this tracking, and time-dependent dynamics can be determined.

Results

To demonstrate the method, we show size-dependence of transport mechanics can be observed, with diffusion of fluorescein dye throughout the channel in 8 h, while 20 nm carboxylate FluoSphere diffusion was hindered through both Collagen I and Matrigel™. Statistical measurements of the results are generated through the software package and show the significance of both size and presence of microparticles on penetration depth.

Conclusion

This provides an easy-to-understand output for the end user to measure nanoparticle tissue penetration, enabling the first steps towards future automated experimentation of transport dynamics for rational nanocarrier design.

Controlling Protein Nanocage Assembly with Hydrostatic Pressure

Controlling the assembly and disassembly of nanoscale protein cages for the capture and internalization of protein or non-proteinaceous components is fundamentally important to a diverse range of bionanotechnological applications. Here, we study the reversible, pressure-induced dissociation of a natural protein nanocage, E. coli bacterioferritin (Bfr), using synchrotron radiation small-angle X-ray scattering (SAXS) and circular dichroism (CD). We demonstrate that hydrostatic pressures of 450 MPa are sufficient to completely dissociate the Bfr 24-mer into protein dimers, and the reversibility and kinetics of the reassembly process can be controlled by selecting appropriate buffer conditions. We also demonstrate that the heme B prosthetic group present at the subunit dimer interface influences the stability and pressure lability of the cage, despite its location being discrete from the interdimer interface that is key to cage assembly. This indicates a major cage-stabilizing role for heme within this family of ferritins.

Fabrication of New Hybrid Scaffolds for in vivo Perivascular Application to Treat Limb Ischemia

Cell therapies are emerging as a new therapeutic frontier for the treatment of ischemic disease. However, femoral occlusions can be challenging environments for effective therapeutic cell delivery. In this study, cell-engineered hybrid scaffolds are implanted around the occluded femoral artery and the therapeutic benefit through the formation of new collateral arteries is investigated. First, it is reported the fabrication of different hybrid “hard-soft” 3D channel-shaped scaffolds comprising either poly(ε-caprolactone) (PCL) or polylactic-co-glycolic acid (PLGA) and electro-spun of gelatin (GL) nanofibers. Both PCL-GL and PLGA-GL scaffolds show anisotropic characteristics in mechanical tests and PLGA displays a greater rigidity and faster degradability in wet conditions. The resulting constructs are engineered using human adventitial pericytes (APCs) and both exhibit excellent biocompatibility. The 3D environment also induces expressional changes in APCs, conferring a more pronounced proangiogenic secretory profile. Bioprinting of alginate-pluronic gel (AG/PL), containing APCs and endothelial cells, completes the hybrid scaffold providing accurate spatial organization of the delivered cells. The scaffolds implantation around the mice occluded femoral artery shows that bioengineered PLGA hybrid scaffold outperforms the PCL counterpart accelerating limb blood flow recovery through the formation arterioles with diameters >50 μm, demonstrating the therapeutic potential in stimulating reparative angiogenesis.

Biopolymeric Coacervate Microvectors for the Delivery of Functional Proteins to Cells

The extent to which biologic payloads can be effectively delivered to cells is a limiting factor in the development of new therapies. Limitations arise from the lack of pharmacokinetic stability of biologics in vivo. Encapsulating biologics in a protective delivery vector has the potential to improve delivery profile and enhance performance. Coacervate microdroplets are developed as cell-mimetic materials with established potential for the stabilization of biological molecules, such as proteins and nucleic acids. Here, the development of biodegradable coacervate microvectors (comprising synthetically modified amylose polymers) is presented, for the delivery of biologic payloads to cells. Amylose-based coacervate microdroplets are stable under physiological conditions (e.g., temperature and ionic strength), are noncytotoxic owing to their biopolymeric structure, spontaneously interacted with the cell membrane, and are able to deliver and release proteinaceous payloads beyond the plasma membrane. In particular, myoglobin, an oxygen storage and antioxidant protein, is successfully delivered into human mesenchymal stem cells (hMSCs) within 24 h. Furthermore, coacervate microvectors are implemented for the delivery of human bone morphogenetic protein 2 growth factor, inducing differentiation of hMSCs into osteoprogenitor cells. This study demonstrates the potential of coacervate microdroplets as delivery microvectors for biomedical research and the development of new therapies.

3D Bioprinting: The Emergence of Programmable Biodesign

Until recently, bioprinting was largely limited to highly interdisciplinary research teams, as the process requires significant input from specialists in the fields of materials science, engineering, and cell biology. With the advent of commercially available high-performance bioprinters, the field has become accessible to a wider range of research groups, who can now buy the hardware off the shelf instead of having to build it from scratch. As a result, bioprinting has rapidly expanded to address a wide array of research foci, which include organotypic in vitro models, complex engineered tissues, and even bioprinted microbial systems. Moreover, in the early days, the range of suitable bioinks was limited. Now, there is a plethora of viable options to suit many cell phenotypes. This rapidly evolving dynamic environment creates endless opportunities for scientists to design and construct highly complex biological systems. However, this scientific diversity presents its own set of challenges, such as defining standardized protocols for characterizing bioprinted structures, which is essential for eventual organ replacement. In this progress report, the current state-of-the-art in the field of bioprinting is discussed, with a special emphasis on recent hardware developments, bioprinting for regenerative medicine, and late-breaking nontraditional topics.

Chondroinduction of Mesenchymal Stem Cells on Cellulose-Silk Composite Nanofibrous Substrates: The Role of Substrate Elasticity

Smart biomaterials with an inherent capacity to elicit specific behaviors in lieu of biological prompts would be advantageous for regenerative medicine applications. In this work, we employ an electrospinning technique to model the in vivo nanofibrous extracellular matrix (ECM) of cartilage using a chondroinductive cellulose and silk polymer blend (75:25 ratio). This natural polymer composite is directly electrospun for the first time, into nanofibers without post-spun treatment, using a trifluoroacetic acid and acetic acid cosolvent system. Biocompatibility of the composite nanofibres with human mesenchymal stem cells (hMSCs) is demonstrated and its inherent capacity to direct chondrogenic stem cell differentiation, in the absence of stimulating growth factors, is confirmed. This chondrogenic stimulation could be countered biochemically using fibroblast growth factor-2, a growth factor used to enhance the proliferation of hMSCs. Furthermore, the potential mechanisms driving this chondroinduction at the cell-biomaterial interface is investigated. Composite substrates are fabricated as two-dimensional film surfaces and cultured with hMSCs in the presence of chemicals that interfere with their biochemical and mechanical signaling pathways. Preventing substrate surface elasticity transmission resulted in a significant downregulation of chondrogenic gene expression. Interference with the classical chondrogenic Smad2/3 phosphorylation pathway did not impact chondrogenesis. The results highlight the importance of substrate mechanical elasticity on hMSCs chondroinduction and its independence to known chondrogenic biochemical pathways. The newly fabricated scaffolds provide the foundation for designing a robust, self-inductive, and cost-effective biomimetic biomaterial for cartilage tissue engineering.

Sequential Electrostatic Assembly of a Polymer Surfactant Corona Increases Activity of the Phosphotriesterase arPTE

We present a new methodology for the generation of discrete molecularly dispersed enzyme-polymer-surfactant bioconjugates. Significantly, we demonstrate that >3-fold increase in the catalytic efficiency of the diffusion-limited phosphotriesterase arPTE can be achieved through sequential electrostatic addition of cationic and anionic polymer surfactants, respectively. Here, the polymer surfactants assemble on the surface of the enzyme via ion exchange to yield a compact corona. The observed rate enhancement is consistent with a mechanism whereby the polymer-surfactant corona gives rise to a decrease in the dielectric constant in the vicinity of the active site of the enzyme, accelerating the rate-determining product diffusion step. The facile methodology has significant potential for increasing the efficiency of enzymes and could therefore have a substantially positive impact for industrial enzymology.

Designer artificial membrane binding proteins to direct stem cells to the myocardium

We present a new cell membrane modification methodology where the inherent heart tissue homing properties of the infectious bacteria Streptococcus gordonii are transferred to human stem cells. This is achieved via the rational design of a chimeric protein-polymer surfactant cell membrane binding construct, comprising the cardiac fibronectin (Fn) binding domain of the bacterial adhesin protein CshA fused to a supercharged protein. Significantly, the protein-polymer surfactant hybrid spontaneously inserts into the plasma membrane of stem cells without cytotoxicity, instilling the cells with a high affinity for immobilized fibronectin. Moreover, we show that this cell membrane reengineering approach significantly improves retention and homing of stem cells delivered either intracardially or intravenously to the myocardium in a mouse model.

Artificial cell membrane binding thrombin constructs drive in situ fibrin hydrogel formation

Cell membrane re-engineering is emerging as a powerful tool for the development of next generation cell therapies, as it allows the user to augment therapeutic cells to provide additional functionalities, such as homing, adhesion or hypoxia resistance. To date, however, there are few examples where the plasma membrane is re-engineered to display active enzymes that promote extracellular matrix protein assembly. Here, we report on a self-contained matrix-forming system where the membrane of human mesenchymal stem cells is modified to display a novel thrombin construct, giving rise to spontaneous fibrin hydrogel nucleation and growth at near human plasma concentrations of fibrinogen. The cell membrane modification process is realised through the synthesis of a membrane-binding supercationic thrombin-polymer surfactant complex. Significantly, the resulting robust cellular fibrin hydrogel constructs can be differentiated down osteogenic and adipogenic lineages, giving rise to self-supporting monoliths that exhibit Young's moduli that reflect their respective extracellular matrix compositions.

Engineering Anisotropic Muscle Tissue using Acoustic Cell Patterning

Tissue engineering has offered unique opportunities for disease modeling and regenerative medicine; however, the success of these strategies is dependent on faithful reproduction of native cellular organization. Here, it is reported that ultrasound standing waves can be used to organize myoblast populations in material systems for the engineering of aligned muscle tissue constructs. Patterned muscle engineered using type I collagen hydrogels exhibits significant anisotropy in tensile strength, and under mechanical constraint, produced microscale alignment on a cell and fiber level. Moreover, acoustic patterning of myoblasts in gelatin methacryloyl hydrogels significantly enhances myofibrillogenesis and promotes the formation of muscle fibers containing aligned bundles of myotubes, with a width of 120-150 µm and a spacing of 180-220 µm. The ability to remotely pattern fibers of aligned myotubes without any material cues or complex fabrication procedures represents a significant advance in the field of muscle tissue engineering. In general, these results are the first instance of engineered cell fibers formed from the differentiation of acoustically patterned cells. It is anticipated that this versatile methodology can be applied to many complex tissue morphologies, with broader relevance for spatially organized cell cultures, organoid development, and bioelectronics.

Biodegradable, Drug-Loaded Nanovectors via Direct Hydration as a New Platform for Cancer Therapeutics

The stabilization and transport of low-solubility drugs, by encapsulation in nanoscopic delivery vectors (nanovectors), is a key paradigm in nanomedicine. However, the problems of carrier toxicity, specificity, and producibility create a bottleneck in the development of new nanomedical technologies. Copolymeric nanoparticles are an excellent platform for nanovector engineering due to their structural versatility; however, conventional fabrication processes rely upon harmful chemicals that necessitate purification. In engineering a more robust (copolymeric) nanovector platform, it is necessary to reconsider the entire process from copolymer synthesis through self-assembly and functionalization. To this end, a process is developed whereby biodegradable copolymers of poly(ethylene glycol)-block-poly(trimethylene carbonate), synthesized via organocatalyzed ring-opening polymerization, undergo assembly into highly uniform, drug-loaded micelles without the use of harmful solvents or the need for purification. The direct hydration methodology, employing oligo(ethylene glycol) as a nontoxic dispersant, facilitates rapid preparation of pristine, drug-loaded nanovectors that require no further processing. This method is robust, fast, and scalable. Utilizing parthenolide, an exciting candidate for treatment of acute lymphoblastic leukemia (ALL), discrete nanovectors are generated that show strikingly low carrier toxicity and high levels of specific therapeutic efficacy against primary ALL cells (as compared to normal hematopoietic cells).

Gene-Mediated Chemical Communication in Synthetic Protocell Communities

A gene-directed chemical communication pathway between synthetic protocell signaling transmitters (lipid vesicles) and receivers (proteinosomes) was designed, built and tested using a bottom-up modular approach comprising small molecule transcriptional control, cell-free gene expression, porin-directed efflux, substrate signaling, and enzyme cascade-mediated processing.

Engineered basement membranes: from in vivo considerations to cell-based assays

Engineered basement membranes are required to mimic in vivo properties within cell-based assays.

The effect of surface charge on the thermal stability and ice recrystallization inhibition activity of antifreeze protein III (AFP III)

The aim of this study was to examine the effect of chemical cationization on the structure and function of antifreeze protein III (AFP III) over an extreme temperature range (-40°C to +90°C) using far-UV synchrotron radiation circular dichroism (SRCD) and ice recrystallization inhibition (IRI) assays. Chemical cationization was able to produce a modified AFP III with a net cationic charge at physiological pH that had enhanced resistance to denaturation at elevated temperatures, with no immediate negative impact on protein structure at subzero temperatures. Furthermore, cationized AFP III retained an IRI activity similar to that of native AFP III. Consequently, chemical cationization may provide a pathway to the development of more robust antifreeze proteins as supplementary cryoprotectants in the cryopreservation of clinically relevant cells.

High-Resolution Patterned Cellular Constructs by Droplet-Based 3D Printing

Bioprinting is an emerging technique for the fabrication of living tissues that allows cells to be arranged in predetermined three-dimensional (3D) architectures. However, to date, there are limited examples of bioprinted constructs containing multiple cell types patterned at high-resolution. Here we present a low-cost process that employs 3D printing of aqueous droplets containing mammalian cells to produce robust, patterned constructs in oil, which were reproducibly transferred to culture medium. Human embryonic kidney (HEK) cells and ovine mesenchymal stem cells (oMSCs) were printed at tissue-relevant densities (107 cells mL-1) and a high droplet resolution of 1 nL. High-resolution 3D geometries were printed with features of ≤200 μm; these included an arborised cell junction, a diagonal-plane junction and an osteochondral interface. The printed cells showed high viability (90% on average) and HEK cells within the printed structures were shown to proliferate under culture conditions. Significantly, a five-week tissue engineering study demonstrated that printed oMSCs could be differentiated down the chondrogenic lineage to generate cartilage-like structures containing type II collagen.

Bioprinting: uncovering the utility layer-by-layer

Bioprinting is becoming a must have capability in tissue engineering research. Key to the growth of the field is the inherent flexibility, which can be used to answer basic scientific questions that can only be addressed under 3D culture conditions, or organ-on-chip systems that could quickly replace underperforming animal models. Almost certainly the most challenging application of bioprinting will be for bottom-up tissue construction, which faces many of the same challenges as scaffold-based tissue engineering. In this review, the current state-of-the-art approaches to 3D bioprinting are discussed in terms of performance and suitability. This is complemented by an overview of hydrogel-based bioinks, with a special emphasis on composite biomaterial systems.

Strategies for cell membrane functionalization

The ability to rationally manipulate and augment the cytoplasmic membrane can be used to overcome many of the challenges faced by conventional cellular therapies and provide innovative opportunities when combined with new biotechnologies. The focus of this review is on emerging strategies used in cell functionalization, highlighting both pioneering approaches and recent developments. These will be discussed within the context of future directions in this rapidly evolving field.

Regulation of Scaffold Cell Adhesion Using Artificial Membrane Binding Proteins

The rapid pace of development in biotechnology has placed great importance on controlling cell-material interactions. In practice, this involves attempting to decouple the contributions from adhesion molecules, cell membrane receptors, and scaffold surface chemistry and morphology, which is extremely challenging. Accordingly, a strategy is presented in which different chemical, biochemical, and morphological properties of 3D biomaterials are systematically varied to produce novel scaffolds with tuneable cell affinities. Specifically, cationized and surfactant-conjugated proteins, recently shown to have non-native membrane affinity, are covalently attached to 3D scaffolds of collagen or carboxymethyl-dextran, yielding surface-functionalized 3D architectures with predictable cell immobilization profiles. The artificial membrane-binding proteins enhance cellular adhesion of human mesenchymal stem cells (hMSCs) via electrostatic and hydrophobic binding mechanisms. Furthermore, functionalizing the 3D scaffolds with cationized or surfactant-conjugated myoglobin prevents a slowdown in proliferation of seeded hMSCs cultured for seven days under hypoxic conditions.

Multi-enzyme cascade reactions using protein–polymer surfactant self-standing films

Self-supporting bio-catalytically active multi-enzyme films fabricated via hierarchical assembly of enzyme–polymer surfactant nanoconjugates are capable of sustaining cascade reactions.

Synthesis of Cationized Magnetoferritin for Ultra-fast Magnetization of Cells

Many important biomedical applications, such as cell imaging and remote manipulation, can be achieved by labeling cells with superparamagnetic iron oxide nanoparticles (SPIONs). Achieving sufficient cellular uptake of SPIONs is a challenge that has traditionally been met by exposing cells to elevated concentrations of SPIONs or by prolonging exposure times (up to 72 hr). However, these strategies are likely to mediate toxicity. Here, we present the synthesis of the protein-based SPION magnetoferritin as well as a facile surface functionalization protocol that enables rapid cell magnetization using low exposure concentrations. The SPION core of magnetoferritin consists of cobalt-doped iron oxide with an average particle diameter of 8.2 nm mineralized inside the cavity of horse spleen apo-ferritin. Chemical cationization of magnetoferritin produced a novel, highly membrane-active SPION that magnetized human mesenchymal stem cells (hMSCs) using incubation times as short as one minute and iron concentrations as lows as 0.2 mM.

Effect of Bioconjugation on the Reduction Potential of Heme Proteins

The modification of protein surfaces employing cationic and anionic species enables the assembly of these biomaterials into highly sophisticated hierarchical structures. Such modifications can allow bioconjugates to retain or amplify their functionalities under conditions in which their native structure would be severely compromised. In this work, we assess the effect of this type of bioconjugation on the redox properties of two model heme proteins, that is, cytochrome c (CytC) and myoglobin (Mb). In particular, the work focuses on the sequential modification by 3-dimethylamino propylamine (DMAPA) and 4-nonylphenyl 3-sulfopropyl ether (S1) anionic surfactant. Bioconjugation with DMAPA and S1 are the initial steps in the generation of pure liquid proteins, which remain active in the absence of water and up to temperatures above 150 °C. Thin-layer spectroelectrochemistry reveals that DMAPA cationization leads to a distribution of bioconjugate structures featuring reduction potentials shifted up to 380 mV more negative than the native proteins. Analysis based on circular dichroism, MALDI-TOF mass spectrometry, and zeta potential measurements suggest that the shift in the reduction potentials are not linked to protein denaturation, but to changes in the spin state of the heme. These alterations of the spin states originate from subtle structural changes induced by DMAPA attachment. Interestingly, electrostatic coupling of anionic surfactant S1 shifts the reduction potential closer to that of the native protein, demonstrating that the modifications of the heme electronic configuration are linked to surface charges.

3D Bioprinting Using a Templated Porous Bioink

3D tissue printing with adult stem cells is reported. A novel cell-containing multicomponent bioink is used in a two-step 3D printing process to engineer bone and cartilage architectures.

Ultra-fast stem cell labelling using cationised magnetoferritin

Magnetic cell labelling with superparamagnetic iron oxide nanoparticles (SPIONs) facilitates many important biotechnological applications, such as cell imaging and remote manipulation. However, to achieve adequate cellular loading of SPIONs, long incubation times (24 hours and more) or laborious surface functionalisation are often employed, which can adversely affect cell function. Here, we demonstrate that chemical cationisation of magnetoferritin produces a highly membrane-active nanoparticle that can magnetise human mesenchymal stem cells (hMSCs) using incubation times as short as one minute. Magnetisation persisted for several weeks in culture and provided significant T2* contrast enhancement during magnetic resonance imaging. Exposure to cationised magnetoferritin did not adversely affect the membrane integrity, proliferation and multi-lineage differentiation capacity of hMSCs, which provides the first detailed evidence for the biocompatibility of magnetoferritin. The combination of synthetic ease and flexibility, the rapidity of labelling and absence of cytotoxicity make this novel nanoparticle system an easily accessible and versatile platform for a range of cell-based therapies in regenerative medicine.

Dynamic Behavior in Enzyme-Polymer Surfactant Hydrogel Films

Dynamic protein-polymer surfactant films are highly hydrophilic and show a soft solid to hydrogel transition upon hydration to produce a swollen hydrogel. An unusual reversible autospreading/self-folding response is observed when the water-saturated films are transferred from water into air.

Photocatalytic multiphase micro-droplet reactors based on complex coacervation

We describe the synthesis and characterisation of novel photocatalytic multiphase micro-droplet reactors comprising TiO2 nanosheets dispersed in poly(diallyldimethylammonium) chloride and adenosine 5'-triphosphate or poly(ethylene glycol) 4-nonylphenyl 3-sulfopropyl complex coacervates. We demonstrate significant variations in the degree of equilibrium partitioning of small molecule dyes into the coacervate droplet systems and exploit this behaviour to successfully conduct selective photocatalytic dye degradation.

Cell paintballing using optically targeted coacervate microdroplets

We present a new approach for the directed delivery of biomolecular payloads to individual cells with high spatial precision. This was accomplished via active sequestration of proteins, oligonucleotides or molecular dyes into coacervate microdroplets, which were then delivered to specific regions of stem cell membranes using a dynamic holographic assembler, resulting in spontaneous coacervate microdroplet-membrane fusion. The facile preparation, high sequestration efficiency and inherent membrane affinity of the microdroplets make this novel "cell paintballing" technology a highly advantageous option for spatially-directed cell functionalization, with potential applications in single cell stimulation, transfection and differentiation.

Artificial membrane-binding proteins stimulate oxygenation of stem cells during engineering of large cartilage tissue

Restricted oxygen diffusion can result in central cell necrosis in engineered tissue, a problem that is exacerbated when engineering large tissue constructs for clinical application. Here we show that pre-treating human mesenchymal stem cells (hMSCs) with synthetic membrane-active myoglobin-polymer–surfactant complexes can provide a reservoir of oxygen capable of alleviating necrosis at the centre of hyaline cartilage. This is achieved through the development of a new cell functionalization methodology based on polymer–surfactant conjugation, which allows the delivery of functional proteins to the hMSC membrane. This new approach circumvents the need for cell surface engineering using protein chimerization or genetic transfection, and we demonstrate that the surface-modified hMSCs retain their ability to proliferate and to undergo multilineage differentiation. The functionalization technology is facile, versatile and non-disruptive, and in addition to tissue oxygenation, it should have far-reaching application in a host of tissue engineering and cell-based therapies.

Avoiding central cell necrosis at the centre of large engineered tissue constructs is an important issue for in vitro tissue engineering. Here, the authors demonstrate that this problem may be overcome by oxygenating human mesenchymal stem cells with artificial membrane-binding proteins.

Structure and function of the silicifying peptide R5

The first detailed description of the structure and function of the silicifying peptide R5.

Fatty acid membrane assembly on coacervate microdroplets as a step towards a hybrid protocell model

Mechanisms of prebiotic compartmentalization are central to providing insights into how protocellular systems emerged on the early Earth. Protocell models are based predominantly on the membrane self-assembly of fatty-acid vesicles, although membrane-free scenarios that involve liquid-liquid microphase separation (coacervation) have also been considered. Here we integrate these alternative models of prebiotic compartmentalization and develop a hybrid protocell model based on the spontaneous self-assembly of a continuous fatty-acid membrane at the surface of preformed coacervate microdroplets prepared from cationic peptides/polyelectrolytes and adenosine triphosphate or oligo/polyribonucleotides. We show that the coacervate-supported membrane is multilamellar, and mediates the selective uptake or exclusion of small and large molecules. The coacervate interior can be disassembled without loss of membrane integrity, and fusion and growth of the hybrid protocells can be induced under conditions of high ionic strength. Our results highlight how notions of membrane-mediated compartmentalization, chemical enrichment and internalized structuration can be integrated in protocell models via simple chemical and physical processes.

Enhanced catalytic activity in organic solvents using molecularly dispersed haemoglobin-polymer surfactant constructs

The surface of haemoglobin (Hb) is chemically modified to produce molecular dispersions of discrete core-shell Hb-polymer surfactant bionanoconjugates in water and organic solvents. The hybrid nanoconstructs exhibit peroxidase-like catalytic activity with enhanced turnover rates compared with native Hb in water.

Isolation of a highly reactive β-sheet-rich intermediate of lysozyme in a solvent-free liquid phase

The thermal denaturation of solvent-free liquid lysozyme at temperatures in excess of 200 °C was studied by synchrotron radiation circular dichroism spectroscopy. Temperature-dependent changes in the secondary structure were used to map the equilibrium denaturation pathway and characterize a reactive β-sheet-rich unfolding intermediate that was stable in the solvent-free liquid phase under anhydrous conditions but which underwent irreversible aggregation in the presence of water. The unfolding intermediate had a transition temperature of 78 °C and was extremely stable to temperature, eventually reaching the fully denatured state at 178 °C. We propose that the three-stage denaturation pathway arises from the decreased stability of the native state due to the absence of any appreciable hydrophobic effect, along with an entropically derived stabilization of the reactive intermediate associated with molecular crowding in the solvent-free liquid.

Enzymatically active self-standing protein-polymer surfactant films prepared by hierarchical self-assembly

Cross-linked protein-polymer surfactant films consisting of enzymatically active hybrid nanoclusters are prepared using a novel approach based on electrostatically mediated hierarchical self-assembly. The free-standing films are structurally robust, highly hydrophilic, and exhibit sustained fluorescence or recyclable enzymatic phosphatase or oxido-reductase behavior.

Magnetizing DNA and proteins using responsive surfactants

DNA chains and their movement in solvent may now be controlled simply by surfactant binding and the switching "on" and "off" of a magnetic field adding a new paradigm to the study and control, condensation and manipulation of DNA (and other biomolecules). Such control is essential for biotechnological applications such as transfection and the regulation of gene suppression, as well as in materials science concerning soft molecular self-assemblies.

Liquid viruses by nanoscale engineering of capsid surfaces

Surface engineering of plant virus capsids via cationization (1) and stoichiometric coupling of a polymer surfactant coronal layer (2) produces a highly concentrated, solvent-free liquid virus at 28 °C. These ionic bionanoconstructs are viscoelastic, retain plant infectivity and can be dispersed in a range of organic solvents for aerosol delivery.

Nematic director-induced switching of assemblies of hexagonally packed gold nanorods

Self-assembled disc-shaped clusters of hexagonally packed, thiol-functionalized gold nanorods are prepared and dispersed in thermotropic nematic liquid crystals. The resultant hybrid complex fluids exhibit colloidal anisotropy with very high orientational order and are characterized by SAXS as shown in the figure. Precise, reconfigurable control of the cluster orientation at very low electric field strengths (0.18 V μm(-1) ) is achieved.