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

495 results found

Shamsabadi A, Haghighi T, Carvalho S, Frenette LC, Stevens Met al., 2024, The nanozyme revolution: enhancing the performance of medical biosensing platforms, Advanced Materials, Vol: 36, Pages: 1-15, ISSN: 0935-9648

Nanozymes represent a class of nanosized materials that exhibit innate catalytic properties similar to biological enzymes. The unique features of these materials have positioned them as promising candidates for applications in clinical sensing devices, specifically those employed at the point-of-care. They notably have found use as a means to amplify signals in nanosensor-based platforms and thereby improve sensor detection limits. Recent developments in the understanding of the fundamental chemistries underpinning these materials have enabled the development of highly effective nanozymes capable of sensing clinically relevant biomarkers at detection limits that compete with “gold-standard” techniques. However, there remain considerable hurdles that need to be overcome before these nanozyme-based sensors can be utilized in a platform ready for clinical use. An overview of the current understandings of nanozymes for disease diagnostics and biosensing applications and the unmet challenges that must be considered prior to their translation in clinical diagnostic tests is provided.

Journal article

Xie R, Cao Y, Sun R, Wang R, Morgan A, Kim J, Callens SJP, Xie K, Zuo J, Lin J, Zhuo K, Lu X, Stevens Met al., 2024, Magnetically driven formation of 3D freestanding soft bioscaffolds, Science Advances, Vol: 10, ISSN: 2375-2548

3D soft bioscaffolds have great promise in tissue engineering, biohybrid robotics, and organ-on-a-chip engineering applications. Though emerging three-dimensional (3D) printing techniques offer versatility for assembling soft biomaterials, challenges persist in overcoming the deformation or collapse of delicate 3D structures during fabrication, especially for overhanging or thin features. This study introduces a magnet-assisted fabrication strategy that uses a magnetic field to trigger shape morphing and provide remote temporary support, enabling the straightforward creation of soft bioscaffolds with overhangs and thin-walled structures in 3D. We demonstrate the versatility and effectiveness of our strategy through the fabrication of bioscaffolds that replicate the complex 3D topology of branching vascular systems. Furthermore, we engineered hydrogel-based bioscaffolds to support biohybrid soft actuators capable of walking motion triggered by cardiomyocytes. This approach opens new possibilities for shaping hydrogel materials into complex 3D morphologies, which will further empower a broad range of biomedical applications.

Journal article

Najer A, Kim J, Saunders C, Che J, Baum J, Stevens Met al., 2024, Enhanced Antimalarial and Anti-Sequestration Activity of Methoxybenzenesulfonate-Modified Biopolymers and Nanoparticles for Tackling Severe Malaria, ACS Infectious Diseases, ISSN: 2373-8227

Journal article

Rochet LNC, Bahou C, Wojciechowski JP, Koutsopetras I, Britton P, Spears RJ, Thanasi IA, Shao B, Zhong L, Bučar D-K, Aliev AE, Porter MJ, Stevens MM, Baker JR, Chudasama Vet al., 2023, Use of pyridazinediones for tuneable and reversible covalent cysteine modification applied to peptides, proteins and hydrogels, Chemical Science, Vol: 14, Pages: 13743-13754, ISSN: 2041-6520

Reversible cysteine modification has been found to be a useful tool for a plethora of applications such as selective enzymatic inhibition, activity-based protein profiling and/or cargo release from a protein or a material. However, only a limited number of reagents display reliable dynamic/reversible thiol modification and, in most cases, many of these reagents suffer from issues of stability, a lack of modularity and/or poor rate tunability. In this work, we demonstrate the potential of pyridazinediones as novel reversible and tuneable covalent cysteine modifiers. We show that the electrophilicity of pyridazinediones correlates to the rates of the Michael addition and retro-Michael deconjugation reactions, demonstrating that pyridazinediones provide an enticing platform for readily tuneable and reversible thiol addition/release. We explore the regioselectivity of the novel reaction and unveil the reason for the fundamental increased reactivity of aryl bearing pyridazinediones by using DFT calculations and corroborating findings with SCXRD. We also applied this fundamental discovery to making more rapid disulfide rebridging agents in related work. We finally provide the groundwork for potential applications in various areas with exemplification using readily functionalised "clickable" pyridazinediones on clinically relevant cysteine and disulfide conjugated proteins, as well as on a hydrogel material.

Journal article

Reumann D, Krauditsch C, Novatchkova M, Sozzi E, Wong SN, Zabolocki M, Priouret M, Doleschall B, Ritzau-Reid KI, Piber M, Morassut I, Fieseler C, Fiorenzano A, Stevens MM, Zimmer M, Bardy C, Parmar M, Knoblich JAet al., 2023, In vitro modeling of the human dopaminergic system using spatially arranged ventral midbrain-striatum-cortex assembloids, Nature Methods, Vol: 20, Pages: 2034-2047, ISSN: 1548-7091

Ventral midbrain dopaminergic neurons project to the striatum as well as the cortex and are involved in movement control and reward-related cognition. In Parkinson's disease, nigrostriatal midbrain dopaminergic neurons degenerate and cause typical Parkinson's disease motor-related impairments, while the dysfunction of mesocorticolimbic midbrain dopaminergic neurons is implicated in addiction and neuropsychiatric disorders. Study of the development and selective neurodegeneration of the human dopaminergic system, however, has been limited due to the lack of an appropriate model and access to human material. Here, we have developed a human in vitro model that recapitulates key aspects of dopaminergic innervation of the striatum and cortex. These spatially arranged ventral midbrain-striatum-cortical organoids (MISCOs) can be used to study dopaminergic neuron maturation, innervation and function with implications for cell therapy and addiction research. We detail protocols for growing ventral midbrain, striatal and cortical organoids and describe how they fuse in a linear manner when placed in custom embedding molds. We report the formation of functional long-range dopaminergic connections to striatal and cortical tissues in MISCOs, and show that injected, ventral midbrain-patterned progenitors can mature and innervate the tissue. Using these assembloids, we examine dopaminergic circuit perturbations and show that chronic cocaine treatment causes long-lasting morphological, functional and transcriptional changes that persist upon drug withdrawal. Thus, our method opens new avenues to investigate human dopaminergic cell transplantation and circuitry reconstruction as well as the effect of drugs on the human dopaminergic system.

Journal article

Zhang J, Zhu Y, Njel C, Liu Y, Dallabernardina P, Stevens MM, Seeberger PH, Savateev O, Loeffler FFet al., 2023, Metal-free photoanodes for C-H functionalization, Nature Communications, Vol: 14, ISSN: 2041-1723

Organic semiconductors, such as carbon nitride, when employed as powders, show attractive photocatalytic properties, but their photoelectrochemical performance suffers from low charge transport capability, charge carrier recombination, and self-oxidation. High film-substrate affinity and well-designed heterojunction structures may address these issues, achieved through advanced film generation techniques. Here, we introduce a spin coating pretreatment of a conductive substrate with a multipurpose polymer and a supramolecular precursor, followed by chemical vapor deposition for the synthesis of dual-layer carbon nitride photoelectrodes. These photoelectrodes are composed of a porous microtubular top layer and an interlayer between the porous film and the conductive substrate. The polymer improves the polymerization degree of carbon nitride and introduces C-C bonds to increase its electrical conductivity. These carbon nitride photoelectrodes exhibit state-of-the-art photoelectrochemical performance and achieve high yield in C-H functionalization. This carbon nitride photoelectrode synthesis strategy may be readily adapted to other reported processes to optimize their performance.

Journal article

Geng H, Lupton EJ, Ma Y, Sun R, Grigsby CL, Brachi G, Li X, Zhou K, Stuckey D, Stevens Met al., 2023, Hybrid polypyrrole and polydopamine nanosheets for precise Raman/photoacoustic imaging and photothermal therapy, Advanced Healthcare Materials, Vol: 12, Pages: 1-21, ISSN: 2192-2640

The development of near-infrared light (NIR)-responsive conductive polymers provides a useful theranostic platform for malignant tumours by maximizing spatial resolution with deep tissue penetration for diagnosis and photothermal therapy. Herein, we demonstrated the self-assembly of ultrathin two-dimensional (2D) polypyrrole nanosheets utilizing dopamine as a capping agent and a monolayer of octadecylamine as a template. The 2D polypyrrole-polydopamine nanostructure (DPPy) had tunable size distribution which showed strong absorption in the first and second near-infrared windows, enabling photoacoustic imaging and photothermal therapy. The hybrid double-layer was demonstrated to increase Raman intensity for 3D Raman imaging (up to two orders of magnitude enhancement and spatial resolution up to 1 μm). The acidic environment drove reversible doping of polypyrrole, which could be detected by Raman spectroscopy. The combined properties of the nanosheets could substantially enhance performance in dual-mode Raman and photoacoustic guided photothermal therapy, as shown by the 69% light to heat conversion efficiency and higher cytotoxicity against cancer spheroids. These pH-responsive features highlight the potential of 2D conductive polymers for applications in accurate, highly efficient theranostics.

Journal article

Ritzau-Reid K, Callens S, Xie R, Cihova M, Reumann D, Grigbsy CL, Prados Martin L, Wang R, Moore AC, Armstrong J, Knoblich J, Stevens Met al., 2023, Microfibrous scaffolds guide stem cell lumenogenesis and brain organoid engineering, Advanced Materials, Vol: 35, ISSN: 0935-9648

3D organoids are widely used as tractable in vitro models capable of elucidating aspects of human development and disease. However, the manual and low-throughput culture methods, coupled with a low reproducibility and geometric heterogeneity, restrict the scope and application of organoid research. Combining expertise from stem cell biology and bioengineering offers a promising approach to address some of these limitations. Here, melt electrospinning writing is used to generate tuneable grid scaffolds that can guide the self-organization of pluripotent stem cells into patterned arrays of embryoid bodies. Grid geometry is shown to be a key determinant of stem cell self-organization, guiding the position and size of emerging lumens via curvature-controlled tissue growth. Two distinct methods for culturing scaffold-grown embryoid bodies into either interconnected or spatially discrete cerebral organoids are reported. These scaffolds provide a high-throughput method to generate, culture, and analyze large numbers of organoids, substantially reducing the time investment and manual labor involved in conventional methods of organoid culture. It is anticipated that this methodological development will open up new opportunities for guiding pluripotent stem cell culture, studying lumenogenesis, and generating large numbers of uniform organoids for high-throughput screening.

Journal article

Rahman T, Tavana S, Nicoleta B, Raftery K, Morgan G, Schaer T, Smith NG, Moore A, Bull J, Molly S, Newell Net al., 2023, Quantifying internal intervertebral disc strains to assess nucleus replacement device designs: a digital volume correlation and ultrahigh-resolution MRI study, Frontiers in Bioengineering and Biotechnology, Vol: 11, ISSN: 2296-4185

Introduction: Nucleus replacement has been proposed as a treatment to restore biomechanics and relieve pain in degenerate intervertebral discs (IVDs). Multiple nucleus replacement devices (NRDs) have been developed, however, none are currently used routinely in clinic. A better understanding of the interactions between NRDs and surrounding tissues may provide insight into the causes of implant failure and provide target properties for future NRD designs. The aim of this study was to non-invasively quantify 3D strains within the IVD through three stages of nucleus replacement surgery: intact, post-nuclectomy, and post-treatment.Methods: Digital volume correlation (DVC) combined with 9.4T MRI was used to measure strains in seven human cadaveric specimens (42 ± 18 years) when axially compressed to 1 kN. Nucleus material was removed from each specimen creating a cavity that was filled with a hydrogel-based NRD.Results: Nucleus removal led to loss of disc height (12.6 ± 4.4%, p = 0.004) which was restored post-treatment (within 5.3 ± 3.1% of the intact state, p > 0.05). Nuclectomy led to increased circumferential strains in the lateral annulus region compared to the intact state (−4.0 ± 3.4% vs. 1.7 ± 6.0%, p = 0.013), and increased maximum shear strains in the posterior annulus region (14.6 ± 1.7% vs. 19.4 ± 2.6%, p = 0.021). In both cases, the NRD was able to restore these strain values to their intact levels (p ≥ 0.192).Discussion: The ability of the NRD to restore IVD biomechanics and some strain types to intact state levels supports nucleus replacement surgery as a viable treatment option. The DVC-MRI method used in the present study could serve as a useful tool to assess future NRD designs to help improve performance in future clinical trials.

Journal article

Saunders C, de Villiers CA, Stevens MM, 2023, Single particle chemical characterisation of nanoformulations for cargo delivery, American Association of Pharmaceutical Scientists (AAPS) Journal, Vol: 25, ISSN: 1550-7416

Nanoparticles can encapsulate a range of therapeutics, from small molecule drugs to sensitive biologics, to significantly improve their biodistribution and biostability. Whilst the regulatory approval of several of these nanoformulations has proven their translatability, there remain several hurdles to the translation of future nanoformulations, leading to a high rate of candidate nanoformulations failing during the drug development process. One barrier is that the difficulty in tightly controlling nanoscale particle synthesis leads to particle-to-particle heterogeneity, which hinders manufacturing and quality control, and regulatory quality checks. To understand and mitigate this heterogeneity requires advancements in nanoformulation characterisation beyond traditional bulk methods to more precise, single particle techniques. In this review, we compare commercially available single particle techniques, with a particular focus on single particle Raman spectroscopy, to provide a guide to adoption of these methods into development workflows, to ultimately reduce barriers to the translation of future nanoformulations.

Journal article

Moore AC, Hennessy MG, Nogueira LP, Franks SJ, Taffetani M, Seong H, Kang YK, Tan WS, Miklosic G, El Laham R, Zhou K, Zharova L, King JR, Wagner B, Haugen HJ, Münch A, Stevens MMet al., 2023, Fiber reinforced hydrated networks recapitulate the poroelastic mechanics of articular cartilage, Acta Biomaterialia, Vol: 167, Pages: 69-82, ISSN: 1742-7061

The role of poroelasticity on the functional performance of articular cartilage has been established in the scientific literature since the 1960s. Despite the extensive knowledge on this topic there remain few attempts to design for poroelasticity and to our knowledge no demonstration of an engineered poroelastic material that approaches the physiological performance. In this paper, we report on the development of an engineered material that begins to approach physiological poroelasticity. We quantify poroelasticity using the fluid load fraction, apply mixture theory to model the material system, and determine cytocompatibility using primary human mesenchymal stem cells. The design approach is based on a fiber reinforced hydrated network and uses routine fabrication methods (electrohydrodynamic deposition) and materials (poly[ɛ-caprolactone] and gelatin) to develop the engineered poroelastic material. This composite material achieved a mean peak fluid load fraction of 68%, displayed consistency with mixture theory, and demonstrated cytocompatibility. This work creates a foundation for designing poroelastic cartilage implants and developing scaffold systems to study chondrocyte mechanobiology and tissue engineering. STATEMENT OF SIGNIFICANCE: Poroelasticity drives the functional mechanics of articular cartilage (load bearing and lubrication). In this work we develop the design rationale and approach to produce a poroelastic material, known as a fiber reinforced hydrated network (FiHy™), that begins to approach the native performance of articular cartilage. This is the first engineered material system capable of exceeding isotropic linear poroelastic theory. The framework developed here enables fundamental studies of poroelasticity and the development of translational materials for cartilage repair.

Journal article

Hagey DW, Ojansivu M, Bostancioglu BR, Saher O, Bost JP, Gustafsson MO, Gramignoli R, Svahn M, Gupta D, Stevens MM, Goergens A, EL Andaloussi Set al., 2023, The cellular response to extracellular vesicles is dependent on their cell source and dose, Science Advances, Vol: 9, ISSN: 2375-2548

Extracellular vesicles (EVs) have been established to play important roles in cell-cell communication and shown promise as therapeutic agents. However, we still lack a basic understanding of how cells respond upon exposure to EVs from different cell sources at various doses. Thus, we treated fibroblasts with EVs from 12 different cell sources at doses between 20 and 200,000 per cell, analyzed their transcriptional effects, and functionally confirmed the findings in various cell types in vitro, and in vivo using single-cell RNA sequencing. Unbiased global analysis revealed EV dose to have a more significant effect than cell source, such that high doses down-regulated exocytosis and up-regulated lysosomal activity. However, EV cell source–specific responses were observed at low doses, and these reflected the activities of the EV’s source cells. Last, we assessed EV-derived transcript abundance and found that immune cell-derived EVs were most associated with recipient cells. Together, this study provides important insights into the cellular response to EVs.

Journal article

Najer A, Rifaie Graham O, Yeow J, Christopher A, Chami M, Stevens Met al., 2023, Differences in human plasma protein interactions between various polymersomes and stealth liposomes as observed by fluorescence correlation spectroscopy, Macromolecular Bioscience, Vol: 23, ISSN: 1616-5187

A significant factor hindering the clinical translation of polymersomes as vesicular nanocarriers is the limited availability of comparative studies detailing their interaction with blood plasma proteins compared to liposomes. Here, polymersomes are self-assembled via film rehydration, solvent exchange, and polymerization-induced self-assembly using five different block copolymers. The hydrophilic blocks are composed of anti-fouling polymers, poly(ethylene glycol) (PEG) or poly(2-methyl-2-oxazoline) (PMOXA), and all the data is benchmarked to PEGylated “stealth” liposomes. High colloidal stability in human plasma (HP) is confirmed for all but two tested nanovesicles. In situ fluorescence correlation spectroscopy measurements are then performed after incubating unlabeled nanovesicles with fluorescently labeled HP or the specific labeled plasma proteins, human serum albumin, and clusterin (apolipoprotein J). The binding of HP to PMOXA-polymersomes could explain their relatively short circulation times found previously. In contrast, PEGylated liposomes also interact with HP but accumulate high levels of clusterin, providing them with their known prolonged circulation time. The absence of significant protein binding for most PEG-polymersomes indicates mechanistic differences in protein interactions and associated downstream effects, such as cell uptake and circulation time, compared to PEGylated liposomes. These are key observations for bringing polymersomes closer to clinical translation and highlighting the importance of such comparative studies.

Journal article

Saunders C, Foote J, Wojciechowski J, Cammack A, Pedersen S, Doutch JJ, Barriga HMG, Holme MN, Penders J, Chami M, Najer A, Stevens Met al., 2023, Revealing population heterogeneity in vesicle-based nanomedicines using automated, single particle Raman analysis, ACS Nano, Vol: 17, Pages: 11713-11728, ISSN: 1936-0851

The intrinsic heterogeneity of many nanoformulations is currently challenging to characterise on boththe single particle and population level. Therefore there is great opportunity to develop newtechniques to describe and understand nanomedicine heterogeneity, which will aid translation to theclinic by informing manufacturing quality control, characterisation for regulatory bodies, andconnecting nanoformulation properties to clinical outcomes to enable rational design. Here, wepresent an analytical technique to provide such information, whilst measuring the nanocarrier andcargo simultaneously with label-free, non-destructive single particle automated Raman trappinganalysis (SPARTA). We first synthesised a library of model compounds covering a range ofhydrophilicities and providing distinct Raman signals. These compounds were then loaded into modelnanovesicles (polymersomes) that can load both hydrophobic and hydrophilic cargo into themembrane or core regions respectively. Using our analytical framework, we characterised theheterogeneity of the population by correlating the per particle membrane and cargo signals. We foundthat core and membrane loading can be distinguished, and we detected sub-populations of highlyloaded particlesin certain cases. We then confirmed suitability of our technique in liposomes, anotherPeer reviewed version of the manuscript published in final form in ACS Nano (2023)2nanovesicle class, including the commercial formulation Doxil. Our label-free analytical techniqueprecisely determines cargo location alongside loading and release heterogeneity in nanomedicines,which could be instrumental for future quality control, regulatory body protocols and development ofstructure-function relationships, to bring more nanomedicines to the clinic

Journal article

Sych T, Schlegel J, Barriga HMG, Ojansivu M, Hanke L, Weber F, Bostancioglu RB, Ezzat K, Stangl H, Plochberger B, Laurencikiene J, El Andaloussi S, Fuerth D, Stevens MM, Sezgin Eet al., 2023, High-throughput measurement of the content and properties of nano-sized bioparticles with single-particle profiler, Nature Biotechnology, ISSN: 1087-0156

We introduce a method, single-particle profiler, that provides single-particle information on the content and biophysical properties of thousands of particles in the size range 5–200 nm. We use our single-particle profiler to measure the messenger RNA encapsulation efficiency of lipid nanoparticles, the viral binding efficiencies of different nanobodies, and the biophysical heterogeneity of liposomes, lipoproteins, exosomes and viruses.

Journal article

Øvrebø Ø, Ojansivu M, Kartasalo K, Barriga HMG, Ranefall P, Holme MN, Stevens Met al., 2023, RegiSTORM: channel registration for multi-color stochastic optical reconstruction microscopy, BMC Bioinformatics, Vol: 24, Pages: 1-18, ISSN: 1471-2105

Background: Stochastic optical reconstruction microscopy (STORM), a super-resolution microscopy technique based on single-molecule localizations, has become popular to characterize sub-diffraction limit targets. However, due to lengthy image acquisition, STORM recordings are prone to sample drift. Existing cross-correlation or fiducial marker-based algorithms allow correcting the drift within each channel, but misalignment between channels remains due to interchannel drift accumulating during sequential channel acquisition. This is a major drawback in multi-color STORM, a technique of utmost importance for the characterization of various biological interactions. Results: We developed RegiSTORM, a software for reducing channel misalignment by accurately registering STORM channels utilizing fiducial markers in the sample. RegiSTORM identifies fiducials from the STORM localization data based on their non-blinking nature and uses them as landmarks for channel registration. We first demonstrated accurate registration on recordings of fiducials only, as evidenced by significantly reduced target registration error (TRE) with all the tested channel combinations. Next, we validated the performance in a more practically relevant setup on cells multi-stained for tubulin. Finally, we showed that RegiSTORM successfully registers two-color STORM recordings of cargo-loaded lipid nanoparticles without fiducials, demonstrating the broader applicability of this software. Conclusions: The developed RegiSTORM software was demonstrated to be able to accurately register multiple STORM channels and is freely available as open-source (MIT license) at https://github.com/oystein676/RegiSTORM.git and DOI:10.5281/zenodo.5509861 (archived), and runs as a standalone executable (Windows) or via Python (Mac OS, Linux).

Journal article

Lalone V, Aizenshtadt A, Goertz J, Skottvoll FS, Barbero Mota M, You J, Zhao X, Berg HE, Stokowiec J, Yu M, Schwendeman A, Scholz H, Wilson SR, Krauss S, Stevens Met al., 2023, Quantitative chemometric phenotyping of three-dimensional liver organoids by Raman spectral imaging, Cell Reports: Methods, Vol: 3, Pages: 1-21, ISSN: 2667-2375

Confocal Raman spectral imaging (RSI) enables high-content, label-free visualization of a wide range of molecules in biological specimens without sample preparation. However, reliable quantification of the deconvoluted spectra is needed. Here we develop an integrated bioanalytical methodology, qRamanomics, to qualify RSI as a tissue phantom calibrated tool for quantitative spatial chemotyping of major classes of biomolecules. Next, we apply qRamanomics to fixed 3D liver organoids generated from stem-cell-derived or primary hepatocytes to assess specimen variation and maturity. We then demonstrate the utility of qRamanomics for identifying biomolecular response signatures from a panel of liver-altering drugs, probing drug-induced compositional changes in 3D organoids followed by in situ monitoring of drug metabolism and accumulation. Quantitative chemometric phenotyping constitutes an important step in developing quantitative label-free interrogation of 3D biological specimens.

Journal article

Fernandez-Galiana A, Bibikova O, Pedersen S, Stevens Met al., 2023, Fundamentals and applications of Raman-based techniques for the design and development of active biomedical materials, Advanced Materials, ISSN: 0935-9648

Raman spectroscopy is an analytical method based on light–matter interactions that can interrogate the vibrational modes of matter and provide representative molecular fingerprints. Mediated by its label-free, non-invasive nature, and high molecular specificity, Raman-based techniques have become ubiquitous tools for in situ characterization of materials. This review comprehensively describes the theoretical and practical background of Raman spectroscopy and its advanced variants. The numerous facets of material characterization that Raman scattering can reveal, including biomolecular identification, solid-to-solid phase transitions, and spatial mapping of biomolecular species in bioactive materials, are highlighted. The review illustrates the potential of these techniques in the context of active biomedical material design and development by highlighting representative studies from the literature. These studies cover the use of Raman spectroscopy for the characterization of both natural and synthetic biomaterials, including engineered tissue constructs, biopolymer systems, ceramics, and nanoparticle formulations, among others. To increase the accessibility and adoption of these techniques, the present review also provides the reader with practical recommendations on the integration of Raman techniques into the experimental laboratory toolbox. Finally, perspectives on how recent developments in plasmon- and coherently-enhanced Raman spectroscopy can propel Raman from underutilized to critical for biomaterial development are provided.

Journal article

Creamer A, Lo Fiego A, Agliano A, Prados Martin L, Hogset H, Najer A, Richards D, Wojciechowski J, Foote J, Kim N, Monahan A, Tang J, Shamsabadi A, Rochet LNC, Thanasi IA, de la Ballina LR, Rapley CL, Turnock S, Love EA, Bugeon L, Dallman MJ, Heeney M, Kramer-Marek G, Chudasama V, Fenaroli F, Stevens Met al., 2023, Modular synthesis of semiconducting graft co-polymers to achieve ‘clickable’ fluorescent nanoparticles with long circulation and specific cancer targeting, Advanced Materials, Pages: 1-14, ISSN: 0935-9648

Semiconducting polymer nanoparticles (SPNs) are explored for applications in cancer theranostics because of their high absorption coefficients, photostability, and biocompatibility. However, SPNs are susceptible to aggregation and protein fouling in physiological conditions, which can be detrimental for in vivo applications. Here, a method for achieving colloidally stable and low-fouling SPNs is described by grafting poly(ethylene glycol) (PEG) onto the backbone of the fluorescent semiconducting polymer, poly(9,9′-dioctylfluorene-5-fluoro-2,1,3-benzothiadiazole), in a simple one-step substitution reaction, postpolymerization. Further, by utilizing azide-functionalized PEG, anti-human epidermal growth factor receptor 2 (HER2) antibodies, antibody fragments, or affibodies are site-specifically “clicked” onto the SPN surface, which allows the functionalized SPNs to specifically target HER2-positive cancer cells. In vivo, the PEGylated SPNs are found to have excellent circulation efficiencies in zebrafish embryos for up to seven days postinjection. SPNs functionalized with affibodies are then shown to be able to target HER2 expressing cancer cells in a zebrafish xenograft model. The covalent PEGylated SPN system described herein shows great potential for cancer theranostics.

Journal article

Solanki A, Autefage H, Rodriguez A, Agarwal S, Penide J, Mahat M, Whittaker T, Nommeots-Nomm A, Littmann E, Payne D, Metcalfe A, Quintero F, Pou J, Stevens M, Jones Jet al., 2023, Cobalt containing glass fibres and their synergistic effect on the HIF-1 pathway for wound healing applications, Frontiers in Bioengineering and Biotechnology, Vol: 11, Pages: 1-15, ISSN: 2296-4185

Introduction and Methods: Chronic wounds are a major healthcare problem, but their healing may be improved by developing biomaterials which can stimulate angiogenesis, e.g. by activating the Hypoxia Inducible Factor (HIF) pathway. Here, novel glass fibres were produced by laser spinning. The hypothesis was that silicate glass fibres that deliver cobalt ions will activate the HIF pathway and promote the expression of angiogenic genes. The glass composition was designed to biodegrade and release ions, but not form a hydroxyapatite layer in body fluid.Results and Discussion: Dissolution studies demonstrated that hydroxyapatite did not form. When keratinocyte cells were exposed to conditioned media from the cobalt-containing glass fibres, significantly higher amounts of HIF-1α and Vascular Endothelial Growth Factor (VEGF) were measured compared to when the cells were exposed to media with equivalent amounts of cobalt chloride. This was attributed to a synergistic effect of the combination of cobalt and other therapeutic ions released from the glass. The effect was also much greater than the sum of HIF-1α and VEGF expression when the cells were cultured with cobalt ions and with dissolution products from the Co-free glass, and was proven to not be due to a rise in pH. The ability of the glass fibres to activate the HIF-1 pathway and promote VEGF expression shows the potential for their use in chronic wound dressings.

Journal article

Callens SJP, Fan D, van Hengel IAJ, Minneboo M, Díaz-Payno PJ, Stevens MM, Fratila-Apachitei LE, Zadpoor AAet al., 2023, Emergent collective organization of bone cells in complex curvature fields, Nature Communications, Vol: 14, Pages: 1-19, ISSN: 2041-1723

Individual cells and multicellular systems respond to cell-scale curvatures in their environments, guiding migration, orientation, and tissue formation. However, it remains largely unclear how cells collectively explore and pattern complex landscapes with curvature gradients across the Euclidean and non-Euclidean spectra. Here, we show that mathematically designed substrates with controlled curvature variations induce multicellular spatiotemporal organization of preosteoblasts. We quantify curvature-induced patterning and find that cells generally prefer regions with at least one negative principal curvature. However, we also show that the developing tissue can eventually cover unfavorably curved territories, can bridge large portions of the substrates, and is often characterized by collectively aligned stress fibers. We demonstrate that this is partly regulated by cellular contractility and extracellular matrix development, underscoring the mechanical nature of curvature guidance. Our findings offer a geometric perspective on cell-environment interactions that could be harnessed in tissue engineering and regenerative medicine applications.

Journal article

Lee J, Mulay P, Tamasi MJ, Yeow J, Stevens MM, Gormley AJet al., 2023, A fully automated platform for photoinitiated RAFT polymerization, Digital Discovery, Vol: 2, Pages: 219-233, ISSN: 2635-098X

Oxygen tolerant polymerizations including Photoinduced Electron/Energy Transfer-Reversible Addition–Fragmentation Chain-Transfer (PET-RAFT) polymerization allow for high-throughput synthesis of diverse polymer architectures on the benchtop in parallel. Recent developments have further increased throughput using liquid handling robotics to automate reagent handling and dispensing into well plates thus enabling the combinatorial synthesis of large polymer libraries. Although liquid handling robotics can enable automated polymer reagent dispensing in well plates, photoinitiation and reaction monitoring require automation to provide a platform that enables the reliable and robust synthesis of various polymer compositions in high-throughput where polymers with desired molecular weights and low dispersity are obtained. Here, we describe the development of a robotic platform to fully automate PET-RAFT polymerizations and provide individual control of reactions performed in well plates. On our platform, reagents are automatically dispensed in well plates, photoinitiated in individual wells with a custom-designed lightbox until the polymerizations are complete, and monitored online in real-time by tracking fluorescence intensities on a fluorescence plate reader, with well plate transfers between instruments occurring via a robotic arm. We found that this platform enabled robust parallel polymer synthesis of both acrylate and acrylamide homopolymers and copolymers, with high monomer conversions and low dispersity. The successful polymerizations obtained on this platform make it an efficient tool for combinatorial polymer chemistry. In addition, with the inclusion of machine learning protocols to help navigate the polymer space towards specific properties of interest, this robotic platform can ultimately become a self-driving lab that can dispense, synthesize, and monitor large polymer libraries.

Journal article

Tan WS, Moore AC, Stevens M, 2023, Minimum design requirements for a poroelastic mimic of articular cartilage, Journal of The Mechanical Behavior of Biomedical Materials, Vol: 137, ISSN: 1751-6161

The exceptional functional performance of articular cartilage (load-bearing and lubrication) is attributed to its poroelastic structure and resulting interstitial fluid pressure. Despite this, there remains no engineered cartilage repair material capable of achieving physiologically relevant poroelasticity. In this work we develop in silico models to guide the design approach for poroelastic mimics of articular cartilage. We implement the constitutive models in FEBio, a PDE solver for multiphasic mechanics problems in biological and soft materials. We investigate the influence of strain rate, boundary conditions at the contact interface, and fiber modulus on the reaction force and load sharing between the solid and fluid phases. The results agree with the existing literature that when fibers are incorporated the fraction of load supported by fluid pressure is greatly amplified and increases with the fiber modulus. This result demonstrates that a stiff fibrous phase is a primary design requirement for poroelastic mimics of articular cartilage. The poroelastic model is fit to experimental stress-relaxation data from bovine and porcine cartilage to determine if sufficient design constraints have been identified. In addition, we fit experimental data from FiHy™, an engineered material which is claimed to be poroelastic. The fiber-reinforced poroelastic model was able to capture the primary physics of these materials and demonstrates that FiHy™ is beginning to approach a cartilage-like poroelastic response. We also develop a fiber-reinforced poroelastic model with a bonded interface (rigid contact) to fit stress relaxation data from an osteochondral explant and FiHy™ + bone substitute. The model fit quality is similar for both the chondral and osteochondral configurations and clearly captures the first order physics. Based on this, we propose that physiological poroelastic mimics of articular cartilage should be developed under a fiber-reinforced poroel

Journal article

Armstrong JP, Pchelintseva E, Treumuth S, Campanella C, Meinert C, Klein TJ, Hutmacher DW, Drinkwater BW, Stevens MMet al., 2022, Tissue engineering cartilage with deep zone cytoarchitecture by high-resolution acoustic cell patterning, Advanced Healthcare Materials, Vol: 11, ISSN: 2192-2640

The ultimate objective of tissue engineering is to fabricate artificial living constructs with a structural organization and function that faithfully resembles their native tissue counterparts. For example, the deep zone of articular cartilage possesses a distinctive anisotropic architecture with chondrocytes organized in aligned arrays ≈1–2 cells wide, features that are oriented parallel to surrounding extracellular matrix fibers and orthogonal to the underlying subchondral bone. Although there are major advances in fabricating custom tissue architectures, it remains a significant technical challenge to precisely recreate such fine cellular features in vitro. Here, it is shown that ultrasound standing waves can be used to remotely organize living chondrocytes into high-resolution anisotropic arrays, distributed throughout the full volume of agarose hydrogels. It is demonstrated that this cytoarchitecture is maintained throughout a five-week course of in vitro tissue engineering, producing hyaline cartilage with cellular and extracellular matrix organization analogous to the deep zone of native articular cartilage. It is anticipated that this acoustic cell patterning method will provide unprecedented opportunities to interrogate in vitro the contribution of chondrocyte organization to the development of aligned extracellular matrix fibers, and ultimately, the design of new mechanically anisotropic tissue grafts for articular cartilage regeneration.

Journal article

Sun R, Song X, Zhou K, Zuo Y, Wang R, Rifaie Graham O, Leng Y, Peeler D, Xie R, Geng H, Brachi G, Ma Y, Liu Y, Barron L, Stevens Met al., 2022, Assembly of fillable microrobotic systems by microfluidic loading with dip sealing, Advanced Materials, Vol: 35, Pages: 1-14, ISSN: 0935-9648

Microrobots can provide spatiotemporally well-controlled cargo delivery that can improve therapeutic efficiency compared to conventional drug delivery strategies. Robust microfabrication methods to expand the variety of materials or cargoes that can be incorporated into microrobots can greatly broaden the scope of their functions. However, current surface coating or direct blending techniques used for cargo loading result in inefficient loading and poor cargo protection during transportation, which leads to cargo waste, degradation and non-specific release. Herein, a versatile platform to fabricate fillable microrobots using microfluidic loading and dip sealing (MLDS) is presented. MLDS enables the encapsulation of different types of cargoes within hollow microrobots and protection of cargo integrity. The technique is supported by high-resolution 3D printing with an integrated microfluidic loading system, which realizes a highly precise loading process and improves cargo loading capacity. A corresponding dip sealing strategy is developed to encase and protect the loaded cargo whilst maintaining the geometric and structural integrity of the loaded microrobots. This dip sealing technique is suitable for different materials, including thermal and light-responsive materials. The MLDS platform provides new opportunities for microrobotic systems in targeted drug delivery, environmental sensing, and chemically powered micromotor applications.

Journal article

Hu T, Brinker CJ, Chan WCW, Chen C, Chen X, Ho D, Kataoka K, Kotov NA, Liz-Marzan LM, Nel AE, Parak WJ, Stevens Met al., 2022, Publishing Translational Research of Nanomedicine in <i>ACS Nano</i>, Publisher: AMER CHEMICAL SOC

Other

Budd J, Miller BS, Weckman NE, Cherkaoui D, Huang D, Fongwen N, Han G-R, Broto M, Estcourt CS, Gibbs J, Pillay D, Sonnenberg P, Meurant R, Thomas M, Keegan N, Stevens M, Nastouli E, Topol EJ, Johnson AM, Shahmanesh M, Ozcan A, Collins JJ, Fernandez Suarez M, Rodriguez B, Peeling RW, McKendry RAet al., 2022, Lateral flow test engineering and lessons learned from COVID-19, Nature Reviews Bioengineering, ISSN: 2731-6092

The acceptability and feasibility of large-scale testing with lateral flow tests (LFTs) for clinical and public health purposes has been demonstrated in the COVID-19 pandemic. LFTs can detect analytes in a variety of samples, providing a rapid read-out, which allows self-testing and decentralised diagnosis. In this Review, we examine the changing LFT landscape with a focus on lessons learned from COVID- 9. We discuss implications of LFTs for decentralised testing of infectious diseases, including diseases of epidemic potential, the ‘silent pandemic’ of antimicrobial resistance, and other acute and chronic infections. Bioengineering approaches will play a key role in increasing the sensitivity and specificity of LFTs, improving sample preparation, incorporating nucleic acid amplification and detection, andenabling multiplexing, digital connection and green manufacturing, with the aim to create the next generation of highly-accurate, easy-to-use, affordable and digitally-connected LFTs. We conclude with recommendations, including the building of a global network of LFT research and development hubs tofacilitate and strengthen future diagnostic resilience.

Journal article

Rifaie Graham O, Yeow J, Najer A, Wang R, Sun R, Zhou K, Dell T, Adrianus C, Thanapongpibul C, Chami M, Mann S, Read de Alaniz J, Stevens Met al., 2022, Photoswitchable gating of non-equilibrium enzymatic feedback in chemically communicating polymersome nanoreactors, Nature Chemistry, Vol: 15, Pages: 110-118, ISSN: 1755-4330

The circadian rhythm generates out-of-equilibrium metabolite oscillations controlled by feedbackloops under light/dark cycles. Here we describe a non-equilibrium nanosystem comprising a binarypopulation of enzyme-containing polymersomes capable of light-gated chemical communication,controllable feedback and coupling to macroscopic oscillations. The populations consist of esterase-containing polymersomes functionalised with photo-responsive Donor-Acceptor Stenhouse Adducts(DASA) and light-insensitive semi-permeable urease-loaded polymersomes. The DASA-polymersomemembrane becomes permeable under green light, switching on esterase activity and decreasing thepH, which in turn initiates production of alkali in the urease-containing population. A pH-sensitivepigment that absorbs green light when protonated provides a negative feedback loop for deactivatingthe DASA-polymersomes. Simultaneously, increased alkali production deprotonates the pigment, re-activating esterase activity by opening the membrane gate. We utilise light-mediated fluctuations ofpH to perform non-equilibrium communication between the nanoreactors and use the feedback loopsto induce work as chemomechanical swelling/deswelling oscillations in a crosslinked hydrogel. Weenvision possible applications in artificial organelles, protocells, and soft robotics.

Journal article

Speidel AT, Chivers PRA, Wood CS, Roberts DA, Correia IP, Caravaca AS, Chan YKV, Hansel CS, Heimgärtner J, Müller E, Ziesmer J, Sotiriou GA, Olofsson PS, Stevens Met al., 2022, Tailored biocompatible polyurethane-poly(ethylene glycol) hydrogels as a versatile nonfouling biomaterial, Advanced Healthcare Materials, Vol: 11, Pages: 1-13, ISSN: 2192-2640

Polyurethane-based hydrogels are relatively inexpensive and mechanically robust biomaterials with ideal properties for various applications, including drug delivery, prosthetics, implant coatings, soft robotics, and tissue engineering. In this report, a simple method is presented for synthesizing and casting biocompatible polyurethane-poly(ethylene glycol) (PU-PEG) hydrogels with tunable mechanical properties, nonfouling characteristics, and sustained tolerability as an implantable material or coating. The hydrogels are synthesized via a simple one-pot method using commercially available precursors and low toxicity solvents and reagents, yielding a consistent and biocompatible gel platform primed for long-term biomaterial applications. The mechanical and physical properties of the gels are easily controlled by varying the curing concentration, producing networks with complex shear moduli of 0.82–190 kPa, similar to a range of human soft tissues. When evaluated against a mechanically matched poly(dimethylsiloxane) (PDMS) formulation, the PU-PEG hydrogels demonstrated favorable nonfouling characteristics, including comparable adsorption of plasma proteins (albumin and fibrinogen) and significantly reduced cellular adhesion. Moreover, preliminary murine implant studies reveal a mild foreign body response after 41 days. Due to the tunable mechanical properties, excellent biocompatibility, and sustained in vivo tolerability of these hydrogels, it is proposed that this method offers a simplified platform for fabricating soft PU-based biomaterials for a variety of applications.

Journal article

Song X, Sun R, Wang R, Zhuo K, Xie R, Lin J, Georgiev D, Paraschiv A-A, Zhao R, Stevens Met al., 2022, Puffball-inspired microrobotic systems with robust payload, strong protection, and targeted locomotion for on-demand drug delivery, Advanced Materials, Vol: 34, Pages: 1-14, ISSN: 0935-9648

Microrobots have been recognized as transformative solutions for drug delivery systems (DDSs) because they can navigate through the body to specific locations and enable targeted drug release. However, their realization is substantially limited by insufficient payload capacity, unavoidable drug leakage/deactivation, and strict modification/stability criteria for drugs. Natural puffballs possess fascinating features that are highly desirable for DDSs, including a large fruitbody for storing spores, a flexible protective cap, and environmentally-triggered release mechanisms. This report presents a puffball-inspired microrobotic system which incorporates: an internal chamber for loading large drug quantities and spatial drug separation; and a near-infrared-responsive top-sealing layer offering strong drug protection and on-demand release. These puffball-inspired microrobots (PIMs) display tunable loading capacities up to high concentrations and enhanced drug protection with minimal drug leakage.Upon near-infrared laser irradiation, on-demand drug delivery with rapid release efficiency is achieved. The PIMs also demonstrate translational motion velocities, switchable motion modes, and precise locomotion under a rotating magnetic field. This work provides strong proof-of-concept for a DDS that combines the superior locomotion capability of microrobots with theunique characteristics of puffballs, thereby illustrating a versatile avenue for development of a new generation of microrobots for targeted drug delivery.

Journal article

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