Nanomechanical mapping helps explain differences in outcomes of eye microsurgery: A comparative study of macular pathologies

RETINAL TECTONICS AFTER MACULAR PUCKER SURGERY: Thickness Changes and En Face Displacement Recovery

PURPOSE

To study visual function, retinal layer thickness changes, and tangential displacement after pars plana vitrectomy for epiretinal membrane.

METHODS

Retrospective series of patients undergoing pars plana vitrectomy for epiretinal membrane, with 6-month follow-up including best-corrected visual acuity, optical coherence tomography, M-charts, epiretinal membrane grading, and infrared fundus photograph at time 0 (T0, preop) at months 1 (T1), 3 (T3), and 6 (T6) postop (±1 week). Retinal layer thickness and tangential ( en face ) retinal displacement between successive times for the entire retinal surface and the central horizontal and vertical meridian were also measured. En face displacement was calculated as optical flow of consecutive images.

RESULTS

Average best-corrected visual acuity improved from 0.28 ± 0.08 logarithm of Minimum Angle of Resolution at T0 to 0.16 ± 0.25 at T6 ( P = 0.05), best-corrected visual acuity improvement correlated with best corrected visual acuity (BCVA) at T0 ( P < 0.001). Vertical metamorphopsia decreased from 1.33° ± 0.70° at T0 to 0.82° ± 0.69° at T6 ( P < 0.05). Foveal thickness reduced from 453 ± 53 µ m at T0 to 359 ± 31 µ m at T6 ( P < 0.05) and reduction correlated with best-corrected visual acuity improvement ( P < 0.05). Foveal layers decreased ( P < 0.05) in all cases. The mean en face deformation was 155.82 ± 50.17 µ m and mostly occurred in the first month: T0-T1 displacement was 83.59 ± 30.28 µ m, T1-T3 was 36.28 ± 14.45 µ m, while T3-T6 was 39.11 ± 22.79 µ m ( P < 0.001) on average. Perifoveal and parafoveal deformation correlated with optical coherence tomography foveal thickness reduction at all time intervals (1, 3, and 6 months: P < 0.01).

CONCLUSION

Epiretinal membrane peeling affects all retinal layer thickness and results in new force balance across the entire retina and tangential displacement. Both en face and in-depth changes correlate with visual function.

Atomic force microscopy-mediated mechanobiological profiling of complex human tissues

Tissue mechanobiology is an emerging field with the overarching goal of understanding the interplay between biophysical and biochemical responses affecting development, physiology, and disease. Changes in mechanical properties including stiffness and viscosity have been shown to describe how cells and tissues respond to mechanical cues and modify critical biological functions. To quantitatively characterize the mechanical properties of tissues at physiologically relevant conditions, atomic force microscopy (AFM) has emerged as a highly versatile biomechanical technology. In this review, we describe the fundamental principles of AFM, typical AFM modalities used for tissue mechanics, and commonly used elastic and viscoelastic contact mechanics models to characterize complex human tissues. Furthermore, we discuss the application of AFM-based mechanobiology to characterize the mechanical responses within complex human tissues to track their developmental, physiological/functional, and diseased states, including oral, hearing, and cancer-related tissues. Finally, we discuss the current outlook and challenges to further advance the field of tissue mechanobiology. Altogether, AFM-based tissue mechanobiology provides a mechanistic understanding of biological processes governing the unique functions of tissues.

Sensing red blood cell nano-mechanics: Toward a novel blood biomarker for Alzheimer's disease

Red blood cells (RBCs) are characterized by a remarkable elasticity, which allows them to undergo very large deformation when passing through small vessels and capillaries. This extreme deformability is altered in various clinical conditions, suggesting that the analysis of red blood cell (RBC) mechanics has potential applications in the search for non-invasive and cost-effective blood biomarkers. Here, we provide a comparative study of the mechanical response of RBCs in patients with Alzheimer's disease (AD) and healthy subjects. For this purpose, RBC viscoelastic response was investigated using atomic force microscopy (AFM) in the force spectroscopy mode. Two types of analyses were performed: (i) a conventional analysis of AFM force-distance (FD) curves, which allowed us to retrieve the apparent Young's modulus, E; and (ii) a more in-depth analysis of time-dependent relaxation curves in the framework of the standard linear solid (SLS) model, which allowed us to estimate cell viscosity and elasticity, independently. Our data demonstrate that, while conventional analysis of AFM FD curves fails in distinguishing the two groups, the mechanical parameters obtained with the SLS model show a very good classification ability. The diagnostic performance of mechanical parameters was assessed using receiving operator characteristic (ROC) curves, showing very large areas under the curves (AUC) for selected biomarkers (AUC > 0.9). Taken all together, the data presented here demonstrate that RBC mechanics are significantly altered in AD, also highlighting the key role played by viscous forces. These RBC abnormalities in AD, which include both a modified elasticity and viscosity, could be considered a potential source of plasmatic biomarkers in the field of liquid biopsy to be used in combination with more established indicators of the pathology.

Recent Advances in the Label-Free Characterization of Exosomes for Cancer Liquid Biopsy: From Scattering and Spectroscopy to Nanoindentation and Nanodevices

Exosomes (EXOs) are nano-sized vesicles secreted by most cell types. They are abundant in bio-fluids and harbor specific molecular constituents from their parental cells. Due to these characteristics, EXOs have a great potential in cancer diagnostics for liquid biopsy and personalized medicine. Despite this unique potential, EXOs are not yet widely applied in clinical settings, with two main factors hindering their translational process in diagnostics. Firstly, conventional extraction methods are time-consuming, require large sample volumes and expensive equipment, and often do not provide high-purity samples. Secondly, characterization methods have some limitations, because they are often qualitative, need extensive labeling or complex sampling procedures that can induce artifacts. In this context, novel label-free approaches are rapidly emerging, and are holding potential to revolutionize EXO diagnostics. These methods include the use of nanodevices for EXO purification, and vibrational spectroscopies, scattering, and nanoindentation for characterization. In this progress report, we summarize recent key advances in label-free techniques for EXO purification and characterization. We point out that these methods contribute to reducing costs and processing times, provide complementary information compared to the conventional characterization techniques, and enhance flexibility, thus favoring the discovery of novel and unexplored EXO-based biomarkers. In this process, the impact of nanotechnology is systematically highlighted, showing how the effectiveness of these techniques can be enhanced using nanomaterials, such as plasmonic nanoparticles and nanostructured surfaces, which enable the exploitation of advanced physical phenomena occurring at the nanoscale level.

Biomechanical properties of retina and choroid: a comprehensive review of techniques and translational relevance

Studying the biomechanical properties of biological tissue is crucial to improve our understanding of disease pathogenesis. The biomechanical characteristics of the cornea, sclera and the optic nerve head have been well addressed with an extensive literature and an in-depth understanding of their significance whilst, in comparison, knowledge of the retina and choroid is relatively limited. Knowledge of these tissues is important not only to clarify the underlying pathogenesis of a wide variety of retinal and vitreoretinal diseases, including age-related macular degeneration, hereditary retinal dystrophies and vitreoretinal interface diseases but also to optimise the surgical handling of retinal tissues and, potentially, the design and properties of implantable retinal prostheses and subretinal therapies. Our aim with this article is to comprehensively review existing knowledge of the biomechanical properties of retina, internal limiting membrane (ILM) and the Bruch’s membrane–choroidal complex (BMCC), highlighting the potential implications for clinical and surgical practice. Prior to this we review the testing methodologies that have been used both in vitro, and those starting to be used in vivo to aid understanding of their results and significance.

Fourier Transform Infrared Spectroscopy as a useful tool for the automated classification of cancer cell-derived exosomes obtained under different culture conditions

Exosomes possess great potential as cancer biomarkers in personalized medicine due to their easy accessibility and capability of representing their parental cells. To boost the translational process of exosomes in diagnostics, the development of novel and effective strategies for their label-free and automated characterization is highly desirable. In this context, Fourier Transform Infrared Spectroscopy (FTIR) has great potential as it provides direct access to specific biomolecular bands that give compositional information on exosomes in terms of their protein, lipid and genetic content. Here, we used FTIR spectroscopy in the mid-Infrared (mid-IR) range to study exosomes released from human colorectal adenocarcinoma HT-29 cancer cells cultured in different media. To this purpose, cells were studied in well-fed condition of growth, with 10% of exosome-depleted FBS (EVd-FBS), and under serum starvation with 0.5% EVd-FBS. Our data show the presence of statistically significant differences in the shape of the Amide I and II bands in the two conditions. Based on these differences, we showed the possibility to automatically classify cancer cell-derived exosomes using Principal Component Analysis combined with Linear Discriminant Analysis (PCA-LDA); we tested the effectiveness of the classifier with a cross-validation approach, obtaining very high accuracy, precision, and recall. Aside from classification purposes, our FTIR data provide hints on the underlying cellular mechanisms responsible for the compositional differences in exosomes, suggesting a possible role of starvation-induced autophagy.

Searching for the Mechanical Fingerprint of Pre-diabetes in T1DM: A Case Report Study

We report the case of a 38 year-old Caucasian man enrolled in a study aimed at investigating the physical properties of red blood cells (RBCs) using advanced microscopy techniques, including Atomic Force Microscopy (AFM). At the time of his first enrolment in the study, he had normal Fasting Plasma Glucose (FPG) values, a BMI of 24.1, and no other symptoms of diabetes, including fatigue, high triglycerides, low HDL cholesterol, and altered inflammatory and corpuscular RBC indices. The subject reported no family history of diabetes, obesity, and cardiovascular diseases. Despite his apparently healthy conditions, the biomechanics of his RBCs was altered, showing increased values of stiffness and viscosity. More than 1 year after the mechanical measurements, the subject was admitted to the Operational Unit of Diabetology of the Policlinico Gemelli Hospital with high blood glucose and glycosylated hemoglobin (HbA1c) levels and diagnosed with type 1 diabetes (T1DM). Here, we show these data, and we discuss the hypothesis that RBC mechanical properties could be sensitive to changes occurring during the pre-diabetic phase of T1DM.

Erythrocyte viscoelastic recovery after liver transplantation in a cirrhotic patient affected by spur cell anaemia

In physiological conditions, red blood cells (RBCs) are capable of dramatic deformations when passing through the microvasculature. This extreme deformability is closely related to the RBC biconcave shape, to the fluidic nature of the haemoglobin and the cell membrane structure, primarily consisting of a phospholipid bilayer with an underlying two-dimensional spectrin network. In many pathological and inflammatory conditions, the shape and the extreme deformability of erythrocytes appear to be significantly altered. These findings have stimulated intense research towards the search and validation of novel erythrocyte-based mechanical biomarkers, useful for disease diagnosis and therapy monitoring. In this study, we investigated with Atomic Force Microscopy (AFM) the mechanical properties of erythrocytes obtained from a 68 years old cirrhotic man diagnosed with spur cell anaemia and cold agglutinated disease, before and after liver transplantation. Mechanical changes are compared with ultrastructural alterations as studied by scanning electron microscopy and discussed according to confocal fluorescence microscopy results, showing possible alterations induced by the cirrhotic environment at the level of the RBCs cytoskeletal organisation and lipidic composition. Taken together, the results here presented show that liver transplantation not only contributes to restoring the proper RBC morphology, but it also induces recovery of the physiological viscous behaviour of cells, further stressing the relevance of viscous and dissipative forces in determining the RBC biomechanical response.

Study of wetting of the animal retinas by Water and organic liquids and its Implications for ophthalmology

Interfacial properties of the animal retinas are reported. Wetting of the retina-retinal pigment epithelium-choroid-sclera tissues of cow, sheep, and pig eyes by water, silicone and castor oil was explored experimentally. Both water and silicone oils demonstrated complete wetting of the retina, regardless of the viscosity of the silicone oil, whereas the castor oil demonstrated a partial wetting regime. Similar wetting regimes were observed for sheep, cow and pig retinas. The intact surface of animal retina was found to be both hydrophilic and oleophilic. Wetting experiments with double sandwich oil/water layers were performed. Water demonstrated stronger affinity to the retina than silicone and castor oils, and eventually replaced the oils at the liquid/retina interface. We conclude that aqueous solutions continuously secreted in the living eye may displace silicone oil from the retinal surface and contribute to retinal re-detachment. Study of dynamics of wetting of the animal retina by water and organic oils is reported. The exponent describing the dynamics of spreading of the castor oil is lower than that predicted by the Tanner law. Castor oil may provide more effective tamponade than silicone oil.

Elastic hysteresis loop acts as cell deformability in erythrocyte aging

The decrease in cellular deformability shows strong correlation with erythrocyte aging. Cell deformation can be divided into passive deformation and active deformation; however, the active deformation has been ignored in previous studies. In this work, Young's moduli of age-related erythrocytes were tested by atomic force microscopy. Furthermore, the deformation and passive and active deformation values were calculated by respective areas. Our results showed that erythrocytes in the densest fraction had the highest values of the Young's modulus, deformation, and active deformation, but the lowest values of passive deformation. Moreover, values of the deformation and active deformation both increased gradually with erythrocyte aging. The present data indicate that the elastic hysteresis loop between the approach and the retract curve could be regarded as erythrocyte deformability, and cellular deformability could be characterized by energy states. In addition, active deformation might be a crucial mechanical factor for clearing aged erythrocytes. This could provide an important information on erythrocyte biomechanics in the removal of aged cell.

VEGF Upregulates EGFR Expression to Stimulate Chemotactic Behaviors in the rMC-1 Model of Müller Glia

Progressive vision loss in adults has become increasingly prevalent worldwide due to retinopathies associated with aging, genetics, and epigenetic factors that damage the retinal microvasculature. Insufficient supply of oxygen and/or nutrients upregulates factors such as vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF), which can induce abnormal angiogenesis and damage the structural arrangement of the retinal blood barrier (BRB). Müller glia (MG) regulate the diffusion of essential compounds across the BRB and respond to retinal insults via reactive gliosis, which includes cell hypertrophy, migration, and/or proliferation near areas of elevated VEGF concentration. Increasing concentrations of exogenous VEGF, upregulated by retinal pigmented epithelium cells, and endogenous epidermal growth factor receptor (EGF-R) stimulation in MG, implicated in MG proliferative and migratory behavior, often lead to progressive and permanent vision loss. Our project examined the chemotactic responses of the rMC-1 cell line, a mammalian MG model, toward VEGF and EGF signaling fields in transwell assays, and within respective concentration gradient fields produced in the glia line (gLL) microfluidic system previously described by our group. rMC-1 receptor expression in defined ligand fields was also evaluated using quantitative polymerase chain reaction (qPCR) and immunocytochemical staining. Results illustrate dramatic increases in rMC-1 chemotactic responses towards EGF gradient fields after pre-treatment with VEGF. In addition, qPCR illustrated significant upregulation of EGF-R upon VEGF pre-treatment, which was higher than that induced by its cognate ligand, EGF. These results suggest interplay of molecular pathways between VEGF and EGF-R that have remained understudied in MG but are significant to the development of effective anti-VEGF treatments needed for a variety of retinopathies.

A time-dependent study of nano-mechanical and ultrastructural properties of internal limiting membrane under ocriplasmin treatment

Vitreomacular traction (VMT) syndrome has only been surgically treated for a long time. Recently, enzymatic vitreolysis with ocriplasmin has emerged as a possible option to release VMT and, in some cases, close full thickness macular holes (FTMHs). Despite its clinical relevance, gathering information about the ocriplasmin-induced alterations of the Inner Limiting Membrane (ILM) of the retina in a clinical study is a complex task, mainly because of the inter-individual variability among patients. To obtain more insights into the mechanism underlying the drug action, we studied in-vitro the mechanical and morphological changes of the ILM using Atomic Force Microscopy (AFM). To this aim, we measured the ILM average Young's modulus (YM), hysteresis (H) and adhesion work (A) over time under ocriplasmin treatment. Our data unveil a time-dependent increase in the membrane YM of 19% of its initial value, along with changes in its adhesive and dissipative behavior. Such modifications well correlate with the morphological alterations detected in the AFM imaging mode. Taken all together, the results here presented provide more insights into the mechanism underlying the ocriplasmin action in-vivo, suggesting that it is only able to alter the top-most layer of the vitreal side of the membrane, not compromising the inner ILM structure.