mechanical-mapping-of-spheroids-using-brillouin-spectroscopy

Mechanical Mapping of Spheroids Using Brillouin Spectroscopy

Brillouin spectroscopy, an emerging technique gaining significant interest in biomedical science, allows researchers to gather information related to ...

The extracellular matrix is a highly complex microenvironment, whose various components converge to regulate cell fate. Hydrogels, as water-swollen polymer networks composed by synthetic or natural materials, are ideal candidates to create biologically active substrates that mimic these matrices and target cell behaviour for a desired tissue engineering application. Indeed, the ability to tune their mechanical, structural, and biochemical properties provides a framework to recapitulate native tissues. This review explores how hydrogels have been engineered to harness the chondrogenic response of stem cells for the repair of damaged cartilage tissue. The signalling processes involved in hydrogel-driven chondrogenesis are also discussed, identifying critical pathways that should be taken into account during hydrogel design.

ChondroGELesis: Hydrogels to harness the chondrogenic potential of stem cells.

We show how to control the formation and alignment of gel 'noodles'. Nanostructure alignment can be achieved reproducibly by extensional deformation as the filaments form. Using a spinning technique, very long and highly aligned filaments can be made. The Young's moduli of the gel noodles are similar to that of a bulk gel. By using two syringe pumps in a concentric flow setup, we show that a filament-in-filament morphology can be created.

Controlling the formation and alignment of low molecular weight gel 'noodles'.

Nanotopography presents an effective physical approach for biomaterial cell manipulation mediated through material-extracellular matrix interactions. The extracellular matrix that exists in the cellular microenvironment is crucial for guiding cell behaviours, such as determination of integrin ligation and interaction with growth factors. These interactions with the extracellular matrix regulate downstream mechanotransductive pathways, such as rearrangements in the cytoskeleton and activation of signal cascades. Protein adsorption onto nanotopography strongly influences the conformation and distribution density of extracellular matrix and, therefore, subsequent cell responses. In this review, we first discuss the interactive mechanisms of protein physical adsorption on nanotopography. Secondly, we summarise advances in creating nanotopographical features to instruct desired cell behaviours. Lastly, we focus on the cellular mechanotransductive pathways initiated by nanotopography. This review provides an overview of the current state-of-the-art designs of nanotopography aiming to provide better biomedical materials for the future.

The influence of nanotopography on cell behaviour through interactions with the extracellular matrix - A review.

The design of hydrogels as mimetics of tissues' matrices typically disregards the viscous nature of native tissues and focuses only on their elastic properties. In the case of stem cell chondrogenesis, this has led to contradictory results, likely due to unreported changes in the matrices' viscous modulus. Here, by employing isoelastic matrices with Young's modulus of ≈12 kPa, variations in viscous properties alone (i.e., loss tangent between 0.1 and 0.25) are demonstrated to be sufficient to drive efficient growth factor-free chondrogenesis of human mesenchymal stem cells, both in 2D and 3D cultures. The increase of the viscous component of RGD-functionalized polyacrylamide or polyethylene glycol maleimide hydrogels promotes a phenotype with reduced adhesion, alters mechanosensitive signaling, and boosts cell-cell contacts. In turn, this upregulates the chondrogenic transcription factor SOX9 and supports neocartilage formation, demonstrating that the mechanotransductive response to the viscous nature of the matrix can be harnessed to direct cell fate.

Mind the Viscous Modulus: The Mechanotransductive Response to the Viscous Nature of Isoelastic Matrices Regulates Stem Cell Chondrogenesis.

Collagen-based (COL) hydrogels could be a promising treatment option for injuries to the articular cartilage (AC) becuase of their similarity to AC native extra extracellular matrix. However, the high hydration of COL hydrogels poses challenges for AC's mechanical properties. To address this, we developed a hydrogel platform that incorporating cellulose nanocrystals (CNCs) within COL and followed by plastic compression (PC) procedure to expel the excessive fluid out. This approach significantly improved the mechanical properties of the hydrogels and enhanced the chondrogenic differentiation of mesenchymal stem cells (MSCs). Radially confined PC resulted in higher collagen fibrillar densities together with reducing fibril-fibril distances. Compressed hydrogels containing CNCs exhibited the highest compressive modulus and toughness. MSCs encapsulated in these hydrogels were initially affected by PC, but their viability improved after 7 days. Furthermore, the morphology of the cells and their secretion of glycosaminoglycans (GAGs) were positively influenced by the compressed COL-CNC hydrogel. Our findings shed light on the combined effects of PC and CNCs in improving the physical and mechanical properties of COL and their role in promoting chondrogenesis.

Enhancing chondrogenic differentiation of mesenchymal stem cells through synergistic effects of cellulose nanocrystals and plastic compression in collagen-based hydrogel for cartilage formation.

We report here a method of making polyketones from the coupling of diketones and diols using a manganese pincer complex. The methodology allows us to access various polyketones (polyarylalkylketone) containing aryl, alkyl, and ether functionalities, bridging the gap between the two classes of commercially available polyketones: aliphatic polyketones and polyaryletherketones. Using this methodology, 12 polyketones have been synthesized and characterized using various analytical techniques to understand their chemical, physical, morphological, and mechanical properties. Based on previous reports and our studies, we suggest that the polymerization occurs via a hydrogen-borrowing mechanism that involves the dehydrogenation of diols to dialdehyde followed by aldol condensation of dialdehyde with diketones to form chalcone derivatives and their subsequent hydrogenation to form polyarylalkylketones.

Manganese-Catalyzed Synthesis of Polyketones Using Hydrogen-Borrowing Approach.

Dementia affects a large proportion of the world's population. Approaches that allow for early disease detection and non-invasive monitoring of disease progression are desperately needed. Current approaches are centred on costly imaging technologies such as positron emission tomography and magnetic resonance imaging. We propose an alternative approach to assess neurodegeneration based on diffuse correlation spectroscopy (DCS), a remote and optical sensing technique. We employ this approach to assess neurodegeneration in mouse brains from healthy animals and those with prion disease. We find a statistically significant difference in the optical speckle decorrelation times between prion-diseased and healthy animals. We directly calibrated our DCS technique using hydrogel samples of varying Young's modulus, indicating that we can optically measure changes in the brain tissue stiffness in the order of 60 Pa (corresponding to a 1 s change in speckle decorrelation time). DCS holds promise for contact-free assessment of tissue stiffness alteration due to neurodegeneration, with a similar sensitivity to contact-based (e.g. nanoindentation) approaches.

Optical, contact-free assessment of brain tissue stiffness and neurodegeneration.

The extent to which high-sensitivity cardiac troponin can predict cardiovascular disease (CVD) is uncertain.

Cardiac Troponins and Cardiovascular Disease Risk Prediction: An Individual-Participant-Data Meta-Analysis.

Collagen IV is a major constituent of basement membranes and mutations in the genes COL4A1 and COL4A2 present clinically as a variable, multi-system disorder called COL4A1 (Gould) syndrome. Evidence from case reports supports a cardiac component to this disease, but the phenotypic and functional implications affecting the heart, their progression and underlying mechanisms all remain poorly characterised. Indeed, the role of the basement membrane (BM) in adult cardiac disease remains underexplored. We set out to address these knowledge gaps by combining in-depth phenotypic and molecular analyses of a Col4a1 mutation on cardiac biology in a murine model (Col4a1) of Gould Syndrome. This revealed morphological cardiac defects including cardiomyocyte hypertrophy with myocardial and vascular fibrotic remodelling that impaired cardiac function. The Col4a1 mutation causes systolic and diastolic dysfunction with reduced left ventricular developed pressure. Mechanistically, we show these defects are due to secretion of mutant protein and BM defects rather than collagen misfolding and proteotoxic stress. The BM defects lead to a pro-fibrotic state with increased fibrillar collagen deposition, cardiac stiffness, and ECM compositional defects. These are accompanied by altered regulation of pathways involved in sarcomere formation, sarcolemma stability and cardiomyocyte metabolism, establishing a molecular signature of COL4A1-related cardiac disease. Intriguingly, aspects of this molecular signature including cardiac metabolic pathways, regulation of cardiac muscle contraction and BM component expression, are shared with common cardiomyopathies such as coronary micro-embolism, and dilated, ischemic and hypertrophic obstructive cardiomyopathies. By defining the molecular and phenotypic cardiac components of Gould syndrome these data show that the BM is essential for maintaining systolic and diastolic function and that alterations to the BM leads to a fibrotic response. These data increase insight into the role of the basement membrane and collagen IV in cardiac biology, and highlights mechanisms shared between Gould syndrome and common adult cardiac disease.

Biomechanical and compositional basement membrane defects due to a Col4a1 mutation affect cardiac morphology and function.

Leukaemias, driven by mutations in haematopoietic stem cells (HSCs), rely on interactions with the bone marrow (BM) niche and other cell populations such as mesenchymal stromal cells (MSCs) for growth and survival. While chimeric antigen receptor (CAR) T-cell therapy shows promise for other haematological malignancies, its application to acute myeloid leukaemia (AML) is hindered by tumour heterogeneity and off-target toxicity. Combining CRISPR-Cas9 gene editing with CAR T-cell therapy has potential for selectively targeting AML cells while sparing healthy tissue. However, validating the efficacy of these treatments prior to clinical trial is hampered by the differences between humans and animal models typically used for pre-clinical testing. Furthermore, traditional in vitro models fail to replicate the complexity of the BM niche and often overestimate treatments' efficacy. Here, we present a bioengineered human-cell containing endosteal BM niche model combining a fibronectin-presenting polymeric surface and a synthetic peptide hydrogel (PeptiGel) that mimics native BM tissue's mechanical properties. This platform supports niche phenotypes in MSCs and HSCs and enables the evaluation of combined CRISPR-CAR T-cell therapy, demonstrating potential as a preclinical human model for testing novel therapies.

Synthetic peptide hydrogels as a model of the bone marrow niche demonstrate efficacy of a combined CRISPR-CAR T-cell therapy for acute myeloid leukaemia.

We report here the application of polyetherureas as a new class of aqueous binder for the LiFePO positive electrode material in lithium-ion batteries. Polyetherureas have been synthesized by ruthenium-catalyzed dehydrogenative coupling of polyethylene glycol diamine and methanol avoiding conventionally used toxic diisocyanate feedstock. The best binder performance was obtained when polyetherurea was used in combination with SBR (Styrene-Butadiene Rubber), exhibiting a coulombic efficiency of ∼99.9% and a cell polarization of 30 mV. Remarkably, the combination of polyetherurea/SBR as a binder demonstrates comparable performance as that of CMC (carboxymethyl cellulose), which is a commonly used aqueous binder for lithium-ion batteries. Evidence of the involvement of polyetherureas in binder performance has been provided using IR spectroscopy and scanning electron microscopy. Physical, electrochemical, and mechanical properties of the polyetherurea have been studied using TGA, DSC, powder XRD, cyclic voltammetry, nanoindentation, tensile testing, and 180° peel test that shed light on why this polymer acts as a good binder.

Article	Year
ChondroGELesis: Hydrogels to harness the chondrogenic potential of stem cells. Materials science & engineering. C, Materials for biological applications\| PubMed ID: 33579465	2021
Controlling the formation and alignment of low molecular weight gel 'noodles'. Chemical communications (Cambridge, England)\| PubMed ID: 34378594	2021
The influence of nanotopography on cell behaviour through interactions with the extracellular matrix - A review. Bioactive materials\| PubMed ID: 35386337	2022
Mind the Viscous Modulus: The Mechanotransductive Response to the Viscous Nature of Isoelastic Matrices Regulates Stem Cell Chondrogenesis. Advanced healthcare materials\| PubMed ID: 38014647	2024
Enhancing chondrogenic differentiation of mesenchymal stem cells through synergistic effects of cellulose nanocrystals and plastic compression in collagen-based hydrogel for cartilage format... International journal of biological macromolecules\| PubMed ID: 38830491	2024
Manganese-Catalyzed Synthesis of Polyketones Using Hydrogen-Borrowing Approach. ACS catalysis\| PubMed ID: 39050896	2024
Optical, contact-free assessment of brain tissue stiffness and neurodegeneration. Biomedical optics express\| PubMed ID: 39958854	2025
Cardiac Troponins and Cardiovascular Disease Risk Prediction: An Individual-Participant-Data Meta-Analysis. Journal of the American College of Cardiology\| PubMed ID: 40204376	2025
Biomechanical and compositional basement membrane defects due to a Col4a1 mutation affect cardiac morphology and function. Matrix biology : journal of the International Society for Matrix Biology\| PubMed ID: 40946812	2025
Synthetic peptide hydrogels as a model of the bone marrow niche demonstrate efficacy of a combined CRISPR-CAR T-cell therapy for acute myeloid leukaemia. Biomaterials\| PubMed ID: 41187596	2025
Polyetherureas as aqueous binders for Li ion batteries. Green chemistry : an international journal and green chemistry resource : GC\| PubMed ID: 41306330	2025

Matthew Walker

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