Imperial College London

Professor Molly Stevens

Faculty of EngineeringDepartment of Materials

Professor of Biomedical Materials and Regenerative Medicine
 
 
 
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Contact

 

+44 (0)20 7594 6804m.stevens

 
 
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Location

 

208Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

374 results found

Blakney AK, Zhu Y, McKay PF, Bouton CR, Yeow J, Tang J, Hu K, Samnuan K, Grigsby CL, Shattock RJ, Stevens MMet al., 2020, Big is beautiful: enhanced saRNA delivery and immunogenicity by a higher molecular weight, bioreducible, cationic polymer, ACS Nano, Vol: 14, Pages: 5711-5727, ISSN: 1936-0851

Self-amplifying RNA (saRNA) vaccines are highly advantageous, as they result in enhanced protein expression compared to mRNA (mRNA), thus minimizing the required dose. However, previous delivery strategies were optimized for siRNA or mRNA and do not necessarily deliver saRNA efficiently due to structural differences of these RNAs, thus motivating the development of saRNA delivery platforms. Here, we engineer a bioreducible, linear, cationic polymer called “pABOL” for saRNA delivery and show that increasing its molecular weight enhances delivery both in vitro and in vivo. We demonstrate that pABOL enhances protein expression and cellular uptake via both intramuscular and intradermal injection compared to commercially available polymers in vivo and that intramuscular injection confers complete protection against influenza challenge. Due to the scalability of polymer synthesis and ease of formulation preparation, we anticipate that this polymer is highly clinically translatable as a delivery vehicle for saRNA for both vaccines and therapeutics.

Journal article

Seong H, Higgins SG, Penders J, Armstrong JPK, Crowder SW, Moore AC, Sero JE, Becce M, Stevens MMet al., 2020, Size-tunable nanoneedle arrays for influencing stem cell morphology, gene expression and nuclear membrane curvature, ACS Nano, ISSN: 1936-0851

High-aspect-ratio nanostructures have emerged as versatile platforms for intracellular sensing and biomolecule delivery. Here, we present a microfabrication approach in which a combination of reactive ion etching protocols was used to produce high-aspect-ratio, nondegradable silicon nanoneedle arrays with tip diameters that can be finely tuned between 20 and 700 nm. We used these arrays to guide the long-term culture of human mesenchymal stem cells (hMSCs). Notably, we used the nanoneedle tip diameter to control the morphology, nuclear size and F-actin alignment of interfaced hMSCs, and to regulate the expression of nuclear lamina genes, Yes-associated protein (YAP) target genes and focal adhesion genes. These topography-driven changes were attributed to signaling by Rho-family GTPase pathways, differences in the effective stiffness of the nanoneedle arrays and the degree of nuclear membrane impingement, with the latter clearly visualized using focused-ion beam scanning electron microscopy (FIB-SEM). Our approach to design high-aspect-ratio nanostructures will be broadly applicable to design biomaterials and biomedical devices used for long-term cell stimulation and monitoring.

Journal article

Kauscher U, Pender J, Nagelkerke A, Holme M, Nele V, Massi L, Gopal S, Whittaker T, Stevens Met al., 2020, Gold nanocluster extracellular vesicle supraparticles: Self-assembled nanostructures for 3D uptake visualization, Langmuir: the ACS journal of surfaces and colloids, Vol: 36, Pages: 3912-3923, ISSN: 0743-7463

Extracellular vesicles (EVs) are secreted by the vast majority of cells and are being intensively studied due to their emerging involvement in a variety of cellular communication processes. However, the study of their cellular uptake and fate has been hampered by difficulty in imaging EVs against the cellular background. Here, we show that EVs combined with hydrophobic gold nanoclusters (AuNCs) can self-assemble into supraparticles, offering an excellent labeling strategy for high-resolution electron microscopic imaging in vitro. We have tracked and visualized the reuptake of breast cancer cell-derived EV AuNC supraparticles into their parent cells, from early endocytosis to lysosomal degradation, using focused ion beam-scanning electron microscopy (FIB-SEM). The presence of gold within the EVs and lysosomes was confirmed via DF-STEM EDX analysis of lift-out sections. The demonstrated formation of AuNC EV supraparticles will facilitate future applications in EV imaging as well as the EV-assisted cellular delivery of AuNCs.

Journal article

Moroz-Omori EV, Satyapertiwi D, Ramel MC, Hogset H, Sunyovszki I, Liu Z, Wojciechowski J, Zhang Y, Grigsby CL, Casimiro Brito L, Bugeon L, Dallman M, Stevens Met al., 2020, Photoswitchable gRNAs for spatiotemporally controlled CRISPR-Cas-based genomic regulation, ACS Central Science, ISSN: 2374-7943

The recently discovered CRISPR-Cas gene editing system and its derivatives have found numerous applications in fundamental biology research and pharmaceutical sciences. The need for precise external control over the gene editing and regulatory events has driven the development of inducible CRISPR-Cas systems. While most of the light-controllable CRISPR-Cas systems are based on protein engineering, we developed an alternative synthetic approach based on modification of crRNA/tracrRNA duplex (guide RNA or gRNA) with photocaging groups, preventing the gRNA from recognizing its genome target sequence until its deprotection is induced within seconds of illumination. This approach relies on a straightforward solid-phase synthesis of the photocaged gRNAs, with simpler purification and characterization processes in comparison to engineering a light-responsive protein. We have demonstrated the feasibility of photocaging of gRNAs and light-mediated DNA cleavage upon brief exposure to light in vitro. We have achieved light-mediated spatiotemporally resolved gene editing as well as gene activation in cells, whereas photocaged gRNAs showed virtually no detectable gene editing or activation in the absence of light irradiation. Finally, we have applied this system to spatiotemporally control gene editing in zebrafish embryos in vivo, enabling the use of this strategy for developmental biology and tissue engineering applications.

Journal article

Liu H, Du Y, St-Pierre J-P, Bergholt MS, Autefage H, Wang J, Cai M, Yang G, Stevens M, Shengmin Zet al., 2020, Bioenergetic-active materials enhance tissue regeneration by modulating cellular metabolic state, Science Advances, Vol: 6, Pages: 1-15, ISSN: 2375-2548

Cellular bioenergetics (CBE) plays a critical role in tissue regeneration. Physiologically, an enhanced metabolic state facilitates anabolic biosynthesis and mitosis to accelerate regeneration. However, the development of approaches to reprogram CBE, towards the treatment of substantial tissue injuries, hasbeen limited thus far. Here, we show that induced repair in a rabbit model of weight-bearing bone defects is greatly enhanced using a bioenergetic-active material (BAM) scaffold, compared to commercialized poly (lactic acid) and calcium phosphate ceramic scaffolds. This material was composed of energy-active units that can be released in a sustained degradation-mediated fashion once implanted. By establishing an intramitochondrial metabolic bypass, the internalized energy-active units significantly elevatemitochondria membrane potential (ΔΨm) to supply increased bioenergetic levels and accelerate bone formation. The ready-to-use material developed here represents a highly efficient and easy-to-implement therapeutic approach toward tissue regeneration, withpromise for bench-to-bedside translation.

Journal article

Wang ST, Gray MA, Xuan S, Lin Y, Byrnes J, Nguyen AI, Todorova N, Stevens M, Bertozzi CR, Zuckermann RN, Gang Oet al., 2020, DNA origami protection and molecular interfacing through engineered sequence-defined peptoids, Proceedings of the National Academy of Sciences of USA, Vol: 117, Pages: 6339-6348, ISSN: 0027-8424

DNA nanotechnology has established approaches for designing programmable and precisely controlled nanoscale architectures through specific Watson−Crick base-pairing, molecular plasticity, and intermolecular connectivity. In particular, superior control over DNA origami structures could be beneficial for biomedical applications, including biosensing, in vivo imaging, and drug and gene delivery. However, protecting DNA origami structures in complex biological fluids while preserving their structural characteristics remains a major challenge for enabling these applications. Here, we developed a class of structurally well-defined peptoids to protect DNA origamis in ionic and bioactive conditions and systematically explored the effects of peptoid architecture and sequence dependency on DNA origami stability. The applicability of this approach for drug delivery, bioimaging, and cell targeting was also demonstrated. A series of peptoids (PE1–9) with two types of architectures, termed as “brush” and “block,” were built from positively charged monomers and neutral oligo-ethyleneoxy monomers, where certain designs were found to greatly enhance the stability of DNA origami. Through experimental and molecular dynamics studies, we demonstrated the role of sequence-dependent electrostatic interactions of peptoids with the DNA backbone. We showed that octahedral DNA origamis coated with peptoid (PE2) can be used as carriers for anticancer drug and protein, where the peptoid modulated the rate of drug release and prolonged protein stability against proteolytic hydrolysis. Finally, we synthesized two alkyne-modified peptoids (PE8 and PE9), conjugated with fluorophore and antibody, to make stable DNA origamis with imaging and cell-targeting capabilities. Our results demonstrate an approach toward functional and physiologically stable DNA origami for biomedical applications.

Journal article

Higgins S, Becce M, Belessiotis Richards A, Seong H, Sero J, Stevens Met al., 2020, High-aspect-ratio nanostructured surfaces as biological metamaterials, Advanced Materials, Vol: 32, Pages: 1-44, ISSN: 0935-9648

Materials patterned with high-aspect-ratio nanostructures have features on similar lengthscales to cellular components. These surfaces are an extreme topography on the cellular leveland have become useful tools for perturbing and sensing the cellular environment. Motivationcomes from the ability of high-aspect-ratio nanostructures to deliver cargoes into cells andtissues, access the intracellular environment, and control cell behavior. These structuresdirectly perturb cells’ ability to sense and respond to external forces, influencing cell fate andenabling new mechanistic studies. Through careful design of their nanoscale structure, thesesystems act as biological metamaterials, eliciting unusual biological responses. Whilepredominantly used to interface eukaryotic cells, there is growing interest in non-animal andprokaryotic cell interfacing. Both experimental and theoretical studies have attempted todevelop a mechanistic understanding for the observed behaviors, predominantly focusing onthe cell – nanostructure interface. Here, we consider how high-aspect-ratio nanostructuredsurfaces are used to both stimulate and sense biological systems and discuss remainingresearch questions.

Journal article

Armstrong JPK, Keane TJ, Roques AC, Stephen Patrick P, Mooney CM, Kuan W-L, Pisupati V, Oreffo ROC, Stuckey D, Watt FM, Forbes SJ, Barker RA, Stevens Met al., A blueprint for translational regenerative medicine, Science Translational Medicine, ISSN: 1946-6234

The last few decades have produced a large number of proof-of-concept studies in regenerative medicine.However, the route to clinical adoption is fraught with technical and translational obstacles that frequentlyconsign promising academic solutions to the so-called “valley of death.” This review is intended to serve as ablueprint for translational regenerative medicine: we suggest principles to help guide cell and materialselection, present key in vivo imaging modalities and argue that the host immune response should beconsidered throughout therapeutic development. Finally, we suggest a pathway to navigate the oftencomplex regulatory and manufacturing landscape of translational regenerative medicine.

Journal article

Roberts DA, Pilgrim BS, Dell TN, Stevens MMet al., Dynamic pH responsivity of triazole-based self-immolative linkers, Chemical Science, Vol: 11, Pages: 3713-3718, ISSN: 2041-6520

Gating the release of chemical payloads in response to transient signals is an important feature of ‘smart’ delivery systems. Herein, we report a triazole-based self-immolative linker that can be reversibly paused or slowed and restarted throughout its elimination cascade in response to pH changes in both organic and organic-aqueous solvents. The linker is conveniently prepared using the alkyne–azide cycloaddition reaction, which introduces a 1,4-triazole ring that expresses a pH-sensitive intermediate during its elimination sequence. Using a series of model compounds, we demonstrate that this intermediate can be switched between active and dormant states depending on the presence of acid or base, cleanly gating the release of payload in response to a fluctuating external stimulus.

Journal article

Armstrong J, Stevens M, 2020, Using remote fields for complex tissue engineering, Trends in Biotechnology, Vol: 38, Pages: 254-263, ISSN: 0167-7799

Great strides have been taken towards the in vitro engineering of clinically-relevant tissue constructsusing the classic triad of cells, materials and biochemical factors. In this perspective, we highlight ways in which these elements can be manipulated or stimulated using a fourth component: the application of remote fields.This arena has gained great momentum over the last few years, with a recent surge of interest in using magnetic, optical and acoustic fields to guide the organization of cells, materials and growth factors. We summarize recent developments and trends in this arena and then lay out a series of challenges that we believe, if met, could enable the widespread adoption of remote fields in mainstream tissue engineering.

Journal article

Spicer CD, Pujari-Palmer M, Autefage H, Insley G, Procter P, Engqvist H, Stevens M, Stevens Met al., 2020, Synthesis of phospho-amino acid analogues as tissue adhesive cement additives, ACS Central Science, Vol: 6, Pages: 226-231, ISSN: 2374-7943

In this paper we report the synthesis of a library of phospho-amino acid analogues, via a novel single-step allyl-phosphoester protection/Pd-mediated deprotection strategy. These phosphoserine and phosphotyrosine analogues were then applied as additives to create adhesive calcium phosphate cements, allowing us to probe the chemical origins of the increased surface binding strength. We demonstrate the importance of multiple calcium binding motifs in mediating adhesion, as well as highlighting the crucial role played by substrate hydrophobicity and orientation in controlling binding strength.

Journal article

Li S, Tallia F, Mohammed AA, Stevens MM, Jones JRet al., 2020, Scaffold channel size influences stem cell differentiation pathway in 3-D printed silica hybrid scaffolds for cartilage regeneration, Biomaterials Science, ISSN: 2047-4830

We report that 3-D printed scaffold channel size can direct bone marrow derived stem cell differentiation. Treatment of articular cartilage trauma injuries, such as microfracture surgery, have limited success because durability is limited as fibrocartilage forms. A scaffold-assisted approach, combining microfracture with biomaterials has potential if the scaffold can promote articular cartilage production and share load with cartilage. Here, we investigated human bone marrow derived stromal cell (hBMSC) differentiation in vitro in 3-D printed silica/poly(tetrahydrofuran)/poly(ε-caprolactone) hybrid scaffolds with specific channel sizes. Channel widths of ∼230 μm (210 ± 22 μm mean strut size, 42.4 ± 3.9% porosity) provoked hBMSC differentiation down a chondrogenic path, with collagen Type II matrix prevalent, indicative of hyaline cartilage. When pores were larger (∼500 μm, 229 ± 29 μm mean strut size, 63.8 ± 1.6% porosity) collagen Type I was dominant, indicating fibrocartilage. There was less matrix and voids in smaller channels (∼100 μm, 218 ± 28 μm mean strut size, 31.2 ± 2.9% porosity). Our findings suggest that a 200–250 μm pore channel width, in combination with the surface chemistry and stiffness of the scaffold, is optimal for cell–cell interactions to promote chondrogenic differentiation and enable the chondrocytes to maintain their phenotype.

Journal article

Zwi Dantsis L, Wang B, Marijon C, Zonetti S, Ferrini A, Massi L, Stuckey DJ, Terracciano C, Stevens Met al., 2020, Remote magnetic nanoparticle manipulation enables the dynamic patterning of cardiac tissues, Advanced Materials, Vol: 32, Pages: 1-6, ISSN: 0935-9648

The ability to manipulate cellular organization within soft materials has important potential in biomedicine and regenerative medicine; however, it often requires complex fabrication procedures. Here, we develop a simple, cost-effective, and one-step approach that enables the control of cell orientation within 3-dimensional (3D) collagen hydrogels to dynamically create various tailored microstructures of cardiac tissues. This isachieved by incorporating iron-oxide nanoparticles into human cardiomyocytes (CMs) and applying a short-term external magnetic field to orient the cells along the applied field to impart different shapes without any mechanical supports. The patterned constructs areviable and functional, canbe detected by T2*-weighted MRI and induceno alteration to normal cardiac function after grafting onto rat hearts. This strategy paves the way to creating customized, macroscale, 3D tissue constructs with various cell-types for therapeutic and bioengineering applications, as well as providing powerful models for investigating tissue behavior.

Journal article

Taylor-Weiner H, Grigsby CL, Ferreira DMS, Dias JM, Stevens MM, Ruas JL, Teixeira AIet al., 2020, Modeling the transport of nuclear proteins along single skeletal muscle cells., Proceedings of the National Academy of Sciences of USA, Vol: 117, Pages: 2978-2986, ISSN: 0027-8424

Skeletal muscle cells contain hundreds of myonuclei within a shared cytoplasm, presenting unique challenges for regulating gene expression. Certain transcriptional programs (e.g., postsynaptic machinery) are segregated to specialized domains, while others (e.g., contractile proteins) do not show spatial confinement. Furthermore, local stimuli, such as denervation, can induce transcriptional responses that are propagated along the muscle cells. Regulated transport of nuclear proteins (e.g., transcription factors) between myonuclei represents a potential mechanism for coordinating gene expression. However, the principles underlying the transport of nuclear proteins within multinucleated cells remain poorly defined. Here we used a mosaic transfection model to create myotubes that contained exactly one myonucleus expressing a fluorescent nuclear reporter and monitored its distribution among all myonuclei. We found that the transport properties of these model nuclear proteins in myotubes depended on molecular weight and nuclear import rate, as well as on myotube width. Interestingly, muscle hypertrophy increased the transport of high molecular weight nuclear proteins, while atrophy restricted the transport of smaller nuclear proteins. We have developed a mathematical model of nuclear protein transport within a myotube that recapitulates the results of our in vitro experiments. To test the relevance to nuclear proteins expressed in skeletal muscle, we studied the transport of two transcription factors-aryl hydrocarbon receptor nuclear translocator and sine oculis homeobox 1-and found that their distributions were similar to the reporter proteins with corresponding molecular weights. Together, these results define a set of variables that can be used to predict the spatial distributions of nuclear proteins within a myotube.

Journal article

Ouyang L, Armstrong J, Salmeron-Sanchez M, Stevens Met al., 2020, Assembly of living building blocks to engineer complex tissues, Advanced Functional Materials, ISSN: 1616-301X

The great demand for tissue and organ grafts, compounded by an aging demographic and a shortage of available donors, has driven the development of bioengineering approaches that can generate biomimetic tissues in vitro. Despite the considerable progress in conventional scaffold‐based tissue engineering, the recreation of physiological complexity has remained a challenge. Bottom‐up tissue engineering strategies have opened up a new avenue for the modular assembly of living building blocks into customized tissue architectures. This Progress Report overviews the recent progress and trends in the fabrication and assembly of living building blocks, with a key highlight on emerging bioprinting technologies that can be used for modular assembly and complexity in tissue engineering. By summarizing the work to date, providing new classifications of different living building blocks, highlighting state‐of‐the‐art research and trends, and offering personal perspectives on future opportunities, this Progress Report aims to aid and inspire other researchers working in the field of modular tissue engineering.

Journal article

Blache U, Stevens M, Gentleman E, 2020, Harnessing the secreted extracellular matrix to engineer tissues, Nature Biomedical Engineering, Vol: 4, Pages: 357-363, ISSN: 2157-846X

Journal article

Kim N, Thomas MR, Bergholt MS, Pence IJ, Seong H, Charchar P, Todorova N, Nagelkerke A, Belessiotis-Richard A, Payne D, Gelmi A, Yarovsky I, Stevens Met al., 2020, Surface enhanced raman scattering artificial nose for high dimensionality fingerprinting, Nature Communications, Vol: 11, Pages: 1-12, ISSN: 2041-1723

Label-free surface-enhanced Raman spectroscopy (SERS) can interrogate systems by directly fingerprinting its components’ unique physicochemical properties. In complex biological systemshowever, this can yield highly overlapping spectra that hinder sample identification. Here, we present an artificial-nose inspired SERS fingerprinting approach where spectral data is obtained as a function of sensor surface chemical functionality. Supported by molecular dynamics modelling, we show that mildly selective self-assembled monolayers can influence the strength and configuration in which analytes interact with plasmonic surfaces, diversifying the resulting SERS fingerprints. Since each sensor generates a modulated signature, the implicit value of increasing the dimensionality of datasets is shown using cell lysates for all possible combinations of up to 9 fingerprints. Reliable improvements in mean discriminatory accuracy towards 100% is achieved with each additional surface functionality. This arrayed label-free platform illustrates the wide-ranging potential of high dimensionality artificial-nose based sensing systems for more reliable assessment of complex biological matrices.

Journal article

Nele V, Schutt CE, Wojciechowski J, Kit-Anan W, Doutch JJ, Armstrong J, Stevens Met al., Ultrasound-triggered enzymatic gelation, Advanced Materials, ISSN: 0935-9648

Hydrogels are formed using various triggers, including light irradiation, pH adjustment, heating,cooling or chemical addition. In this report, a new method for forming hydrogels is introduced:ultrasound-triggered enzymatic gelation. Specifically, ultrasound is used as a stimulus to liberateliposomal calcium ions, which then trigger the enzymatic activity of transglutaminase. Theactivated enzyme catalyzes the formation of fibrinogen hydrogels through covalent intermolecularcrosslinking. The catalysis and gelation processes are monitored in real time and both the enzymekinetics and final hydrogel properties are controlled by varying the initial ultrasound exposure time.This technology is extended to microbubble-liposome conjugates, which exhibit a stronger responseto the applied acoustic field and are also used for ultrasound-triggered enzymatic hydrogelation. Tothe best of our knowledge, these results are the first instance in which ultrasound has been used as atrigger for either enzyme catalysis or enzymatic hydrogelation. This approach is highly versatile and Peer reviewed version of the manuscript published in final form at Advanced Materials (2020)2could be readily applied to different ion-dependent enzymes or gelation systems. Moreover, thiswork paves the way for the use of ultrasound as a remote trigger for in vivo hydrogelation.

Journal article

Ouyang L, Armstrong J, Chen Q, Lin Y, Stevens Met al., 2020, Void-free 3D bioprinting for in-situ endothelialization and microfluidic perfusion, Advanced Functional Materials, Vol: 30, ISSN: 1616-301X

Two major challenges of 3D bioprinting are the retention of structural fidelity and efficient endothelialization for tissue vascularization. We address both of these issues by introducinga versatile3D bioprinting strategy, in which a templating bioink is deposited layer-by-layer alongside a matrix bioink to establish void-free multimaterial structures. After crosslinking the matrix phase, the templating phase issacrificedto create a well-defined 3D network of interconnected tubular channels. This void-free 3D printing (VF-3DP) approachcircumvents the traditional concerns of structural collapse, deformation and oxygen inhibition, moreover, it can be readily used to printmaterials that are widely considered “unprintable”. By pre-loading endothelial cells into the templating bioink, the inner surface of the channels can be efficiently cellularized with a confluent endothelial layer. This in-situ endothelializationmethod can be used to produce endothelium with a far greater uniformity than can be achieved using the conventional post-seeding approach. This VF-3DP approach canalsobe extended beyond tissue fabrication and towards customized hydrogel-based microfluidics and self-supported perfusable hydrogel constructs.

Journal article

Hansel C, Holme M, Gopal S, Stevens Met al., 2020, Advances in high-resolution microscopy for the study of intracellular interactions with biomaterials, Biomaterials, Vol: 226, ISSN: 0142-9612

The study of sophisticated biomaterials and their cellular targets requires visualization methods with exquisite spatial and temporal resolution to discern cell organelles and molecular events. Monitoring cell-material interactions at high resolution is key for the continued development and optimization of biomaterials, for monitoring cell uptake of cargo, and for understanding the cell response to extracellular cues. This review evaluates the advantages and disadvantages of different forms of electron microscopy and super-resolution microscopy in elucidating how biomaterial surface chemistry and topography can affect intracellular events at the nanoscale.

Journal article

Horgan C, Nagelkerke A, Whittaker TE, Nele V, Massi L, Kauscher U, Bergholt M, Hood SR, Stevens Met al., Molecular imaging of extracellular vesicles in vitro via Raman metabolic labelling, Journal of Materials Chemistry B, ISSN: 2050-750X

Journal article

Li Z, Kosuri S, Foster H, Cohen J, Jumeaux C, Stevens MM, Chapman R, Gormley AJet al., 2019, A dual wavelength polymerization and bioconjugation strategy for high throughput synthesis of multivalent ligands, Journal of the American Chemical Society, Vol: 141, Pages: 19823-19830, ISSN: 0002-7863

Structure–function relationships for multivalent polymer scaffolds are highly complex due to the wide diversity of architectures offered by such macromolecules. Evaluation of this landscape has traditionally been accomplished case-by-case due to the experimental difficulty associated with making these complex conjugates. Here, we introduce a simple dual-wavelength, two-step polymerize and click approach for making combinatorial conjugate libraries. It proceeds by incorporation of a polymerization friendly cyclopropenone-masked dibenzocyclooctyne into the side chain of linear polymers or the α-chain end of star polymers. Polymerizations are performed under visible light using an oxygen tolerant porphyrin-catalyzed photoinduced electron/energy transfer-reversible addition–fragmentation chain-transfer (PET-RAFT) process, after which the deprotection and click reaction is triggered by UV light. Using this approach, we are able to precisely control the valency and position of ligands on a polymer scaffold in a manner conducive to high throughput synthesis.

Journal article

Bjornmalm A, Wong LM, Wojciechowski J, Penders J, Horgan C, Booth MA, Martin NG, Sattler S, Stevens Met al., 2019, In vivo biocompatibility and immunogenicity of metal-phenolic gelation, Chemical Science, Vol: 10, Pages: 10179-10194, ISSN: 2041-6520

In vivo forming hydrogels are of interest for diverse biomedical applications due totheir ease-of-use and minimal invasiveness and therefore high translational potential. Supramolecular hydrogels that can be assembled usingmetal–phenolic coordination of naturally occurring polyphenols and group IV metal ions (e.g. TiIVor ZrIV) provide a versatile and robust platform for engineering such materials. However, the in situformation and in vivoresponse tothis new class of materials has not yet been reported. Here, we demonstrate that metal–phenolic supramolecular gelation occurs successfully in vivo and we investigate the host response to the material over 14 weeks. TheTiIV–tannic acid materials form stable gels that are well-tolerated following subcutaneous injection. Histology reveals a mild foreign body reaction, and titanium biodistribution studies show low accumulation in distal tissues. Compared to poloxamer-based hydrogels (commonly used for in vivogelation), TiIV–tannic acid materials show a substantially improved in vitrodrug release profile for the corticosteroid dexamethasone (from <1 dayto >10 days). These results provide essential in vivo characterization for this new class of metal–phenolic hydrogels, and highlight their potential suitability for biomedical applications in areas such as drug deliveryand regenerative medicine

Journal article

Hachim D, Whittaker TE, Kim H, Stevens Met al., 2019, Glycosaminoglycan-based biomaterials for growth factor and cytokine delivery: making the right choices, Journal of Controlled Release, Vol: 313, Pages: 131-147, ISSN: 0168-3659

Controlled, localized drug delivery is a long-standing goal of medical research, realization of which could reduce the harmful side-effects of drugs and allow more effective treatment of wounds, cancers, organ damage and other diseases. This is particularly the case for protein “drugs” and other therapeutic biological cargoes, which can be challenging to deliver effectively by conventional systemic administration. However, developing biocompatible materials that can sequester large quantities of protein and release them in a sustained and controlled manner has proven challenging. Glycosaminoglycans (GAGs) represent a promising class of bio-derived materials that possess these key properties and can additionally potentially enhance the biological effects of the delivered protein. They are a diverse group of linear polysaccharides with varied functionalities and suitabilities for different cargoes. However, most investigations so far have focused on a relatively small subset of GAGs – particularly heparin, a readily available, promiscuously-binding GAG. There is emerging evidence that for many applications other GAGs are in fact more suitable for regulated and sustained delivery. In this review, we aim to illuminate the beneficial properties of various GAGs with reference to specific protein cargoes, and to provide guidelines for informed choice of GAGs for therapeutic applications.

Journal article

Loynachan C, Soleimany AP, Dudani JS, Lin Y, Najer A, Bekdemir A, Chen Q, Bhatia SN, Stevens Met al., 2019, Renal clearable catalytic gold nanoclusters for in vivo disease monitoring, Nature Nanotechnology, Vol: 14, Pages: 883-890, ISSN: 1748-3387

Ultra-small gold nanoclusters (AuNCs) have emerged as agile probes for in vivo imaging, asthey exhibit exceptional tumour accumulation and efficient renal clearance properties.However, their intrinsic catalytic activity, which can enable increased detection sensitivity, hasyet to be explored for in vivo sensing. By exploiting the peroxidase-mimicking activity of AuNCsand the precise nanometer size filtration of the kidney, we designed multifunctional proteasenanosensors that respond to disease microenvironments to produce a direct colorimetricurinary readout of disease state in less than 1 h. We monitored the catalytic activity of AuNCsin collected urine of a mouse model of colorectal cancer where tumour-bearing mice showeda 13-fold increase in colorimetric signal compared to healthy mice. Nanosensors wereeliminated completely through hepatic and renal excretion within 4 weeks after injection withno evidence of toxicity. We envision that this modular approach will enable rapid detection ofa diverse range of diseases by exploiting their specific enzymatic signatures.

Journal article

Wang S-T, Lin Y, NIelsen MH, Song CY, Thomas MT, Spicer C, Kroger R, Ercius P, Aloni S, Stevens Met al., 2019, Shape-controlled synthesis and in situ characterisation of anisotropic AU nanomaterials using liquid cell transmission electron microscopy, Nanoscale, Vol: 36, Pages: 16801-16809, ISSN: 2040-3364

Understanding the mechanisms behind crystal nucleation and growth is afundamental requirement for the design and production of bespoke nanomaterials withcontrolled sizes and morphologies. Herein, we select gold (Au) nanoparticles as themodel system for our study due to their representative applications in biology,electronics and optoelectronics. We investigate the radiation-induced in situ growth ofgold (Au) particles using liquid cell transmission electron microscopy (LCTEM) andstudy the growth kinetics of non-spherical Au structures. Under controlled electronfluence, liquid flow rate and Au3+ ion supply, we show the favoured diffusion-limitedgrowth of multi-twinned nascent Au seed particles into branched structures when usingthin liquid cells (100 nm and 250 nm) in LCTEM, whereas faceted structures (e.g.,spheres, rods, and prisms) formed when using a 1 µm thick liquid cell. In addition, weobserved that anisotropic Au growth could be modulated by Au-binding amyloid fibrils,which we ascribe to their capability of regulating Au3+ ion diffusion and mass transfer in solution. We anticipate that this study will provide new perspectives on the shapecontrolled synthesis of anisotropic metallic nanomaterials using LCTEM.

Journal article

Gopal S, Chiappini C, Armstrong J, Chen Q, Serio A, Hsu C, Meinert C, Klein TJ, Hutmacher DW, Stevens Met al., 2019, Immunogold FIB-SEM: combining volumetric ultrastructure visualization with 3D biomolecular analysis to dissect cell-environment interactions, Advanced Materials, Vol: 31, Pages: 1-8, ISSN: 0935-9648

Volumetric imaging techniques capable of correlating structural and functional information with nanoscale resolution are necessary to broaden the insight into cellular processes within complex biological systems. The recent emergence of focused ion beam scanning electron microscopy (FIB‐SEM) has provided unparalleled insight through the volumetric investigation of ultrastructure; however, it does not provide biomolecular information at equivalent resolution. Here, immunogold FIB‐SEM, which combines antigen labeling with in situ FIB‐SEM imaging, is developed in order to spatially map ultrastructural and biomolecular information simultaneously. This method is applied to investigate two different cell–material systems: the localization of histone epigenetic modifications in neural stem cells cultured on microstructured substrates and the distribution of nuclear pore complexes in myoblasts differentiated on a soft hydrogel surface. Immunogold FIB‐SEM offers the potential for broad applicability to correlate structure and function with nanoscale resolution when addressing questions across cell biology, biomaterials, and regenerative medicine.

Journal article

Belessiotis-Richards A, Higgins SG, Butterworth B, Stevens MM, Alexander-Katz Aet al., 2019, Single-nanometer changes in nanopore geometry influence curvature, local properties, and protein localization in membrane simulations, Nano Letters, Vol: 19, Pages: 4770-4778, ISSN: 1530-6984

Nanoporous surfaces are used in many applications in intracellular sensing and drug delivery. However, the effects of such nanostructures on cell membrane properties are still far from understood. Here, we use coarse-grained molecular dynamics simulations to show that nanoporous substrates can stimulate membrane-curvature effects and that this curvature-sensing effect is much more sensitive than previously thought. We define a series of design parameters for inducing a nanoscale membrane curvature and show that nanopore taper plays a key role in membrane deformation, elucidating a previously unexplored fabrication parameter applicable to many nanostructured biomaterials. We report significant changes in the membrane area per lipid and thickness at regions of curvature. Finally, we demonstrate that regions of the nanopore-induced membrane curvature act as local hotspots for an increased bioactivity. We show spontaneous binding and localization of the epsin N-terminal homology (ENTH) domain to the regions of curvature. Understanding this interplay between the membrane curvature and nanoporosity at the biointerface helps both explain recent biological results and suggests a pathway for developing the next generation of cell-active substrates.

Journal article

Wang Y, Kim E, Lin Y, Kim N, Kit-Anan W, Gopal S, Agarwal S, Howes P, Stevens Met al., 2019, Rolling circle transcription-amplified hierarchically structured organic-inorganic hybrid RNA flowers for enzyme immobilization, ACS Applied Materials and Interfaces, Vol: 11, Pages: 22932-22940, ISSN: 1944-8244

Programmable nucleic acids have emerged as powerful building blocks for the bottom-up fabrication of two- or three-dimensional nano- and microsized constructs. Here we describe the construction of organic–inorganic hybrid RNA flowers (hRNFs) via rolling circle transcription (RCT), an enzyme-catalyzed nucleic acid amplification reaction. These hRNFs are highly adaptive structures with controlled sizes, specific nucleic acid sequences, and a highly porous nature. We demonstrated that hRNFs are applicable as potential biological platforms, where the hRNF scaffold can be engineered for versatile surface functionalization and the inorganic component (magnesium ions) can serve as an enzyme cofactor. For surface functionalization, we proposed robust and straightforward approaches including in situ synthesis of functional hRNFs and postfunctionalization of hRNFs that enable facile conjugation with various biomolecules and nanomaterials (i.e., proteins, enzymes, organic dyes, inorganic nanoparticles) using selective chemistries (i.e., avidin–biotin interaction, copper-free click reaction). In particular, we showed that hRNFs can serve as soft scaffolds for β-galactosidase immobilization and greatly enhance enzymatic activity and stability. Therefore, the proposed concepts and methodologies are not only fundamentally interesting when designing RNA scaffolds or RNA bionanomaterials assembled with enzymes but also have significant implications on their future utilization in biomedical applications ranging from enzyme cascades to biosensing and drug delivery.

Journal article

Autefage H, Allen F, Tang HM, Kallepitis C, Gentleman E, Reznikov N, Nitiputri K, Nommeots-Nomm A, Young G, Lee PD, Pierce BF, Wagermaier W, Fratzl P, Goodship A, Jones JR, Blunn G, Stevens Met al., 2019, Multiscale analyses reveal native-like lamellar bone repair and near perfect bone-contact with porous strontium-loaded bioactive glass, Biomaterials, Vol: 209, Pages: 152-162, ISSN: 0142-9612

The efficient healing of critical-sized bone defects using synthetic biomaterial-based strategies is promising but remains challenging as it requires the development of biomaterials that combine a 3D porous architecture and a robust biological activity. Bioactive glasses (BGs) are attractive candidates as they stimulate a biological response that favors osteogenesis and vascularization, but amorphous 3D porous BGs are difficult to produce because conventional compositions crystallize during processing. Here, we rationally designed a porous, strontium-releasing, bioactive glass-based scaffold (pSrBG) whose composition was tailored to deliver strontium and whose properties were optimized to retain an amorphous phase, induce tissue infiltration and encourage bone formation. The hypothesis was that it would allow the repair of a critical-sized defect in an ovine model with newly-formed bone exhibiting physiological matrix composition and structural architecture. Histological and histomorphometric analyses combined with indentation testing showed pSrBG encouraged near perfect bone-to-material contact and the formation of well-organized lamellar bone. Analysis of bone quality by a combination of Raman spectral imaging, small-angle X-ray scattering, X-ray fluorescence and focused ion beam-scanning electron microscopy demonstrated that the repaired tissue was akin to that of normal, healthy bone, and incorporated small amounts of strontium in the newly formed bone mineral. These data show the potential of pSrBG to induce an efficient repair of critical-sized bone defects and establish the importance of thorough multi-scale characterization in assessing biomaterial outcomes in large animal models.

Journal article

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