Angelo Gaitas

Hollow atomic force microscopy (AFM) cantilevers add pressure-driven fluid handling to force sensing at the probe tip. Most are made of silicon, silicon nitride or SU-8 epoxy, which fail by brittle fracture when overloaded. We fabricated a microfluidic AFM cantilever from PI-2611 polyimide, chosen for its high tensile strength and large elongation at break. The hollow cantilever, nominally 250 µm long, 44 µm wide and 10 µm thick, was built by multilayer polyimide surface micromachining over a sacrificial aluminum channel, released by backside deep reactive ion etching and coated with titanium/gold for optical detection. Its internal channel ends in a 4 µm distal aperture. The cantilever was bent against a sharp needle in 30 sequential runs at stage-travel settings increasing from 150 to 250 µm while the force was recorded. It withstood the complete sequence and carried load in every run, reaching forces of up to 0.40 mN. The eight runs at the final 250 µm setting gave an apparent stiffness of 4.90 ± 0.29 N/m (mean ± standard deviation), consistent with AFM resonance-derived estimates of 4.88 N/m from the thermal-noise spectrum and 4.86 N/m from an active frequency sweep. In liquid, air emerged from the distal aperture and suction held a microsphere at the tip. These results show that a polyimide microfluidic AFM cantilever can survive repeated large-deflection bending.

Neuronal activity is energetically demanding and generates heat as a metabolic byproduct. Here we investigated localized temperature changes in mouse hippocampal brain slices during intense synaptic activation. Using fast-response thermocouple microprobes placed in the tissue, we measured real-time temperature fluctuations during high-frequency (100 Hz) electrical stimulation of Schaffer collateral inputs. Stimulation induced a local temperature increase (peak ΔT = 0.54 ± 0.07 °C; n = 4). In contrast, when action potentials were blocked with tetrodotoxin (TTX), the same stimulation produced no measurable temperature rise. These results demonstrate that high-frequency neural firing and synaptic transmission can transiently elevate local brain tissue temperature, presumably due to increased metabolic activity and adenosine triphosphate (ATP) consumption. The hippocampus tolerated these small temperature shifts, but even modest heating could influence neuronal function. Our findings provide direct experimental evidence linking synaptic activity to localized brain heat production, and underscore the importance of considering thermogenesis under stimulation conditions that give rise to forms of synaptic plasticity.

Embryonic development is intricately regulated by mechanical properties such as stiffness, which influence developmental viability and implantation success – factors critical in assisted reproductive technologies (ART). Traditional embryo evaluation relies predominantly on morphology, lacking quantitative mechanical parameters that could enhance selection accuracy. Recent studies indicate that the stiffness (elasticity) of the zona pellucida (ZP) – the glycoprotein-rich extracellular matrix surrounding mammalian oocytes and embryos – correlates with embryo quality and developmental potential. However, current biomechanical characterization techniques – including micropipette aspiration, atomic force microscopy (AFM), microtactile sensors, and microelectromechanical systems (MEMS) based sensors – either pose risks of mechanical damage or involve complex, time-consuming procedures unsuitable for clinical settings. Here, we introduce a novel approach leveraging fluidic force microscopy cantilevers to non-invasively evaluate embryo biomechanics. Our proof-of-concept study demonstrates rapid, precise stiffness profiling of intact mouse embryos (specifically ZP elasticity). Using gentle microsuction attachment with no chemical adhesives or rigid immobilization, the method preserves embryo integrity while providing reproducible elasticity measurements. This method combines the precision of AFM with minimal invasiveness, offering a promising new quantitative biomechanical indicator to augment clinical embryo assessment and paving the way for broader applications in reproductive biology.

Embryonic development is intricately regulated by mechanical properties such as stiffness, which influence developmental viability and implantation success – factors critical in assisted reproductive technologies (ART). Traditional embryo evaluation relies predominantly on morphology, lacking quantitative mechanical parameters that could enhance selection accuracy. Recent studies indicate that the stiffness (elasticity) of the zona pellucida (ZP) – the glycoprotein-rich extracellular matrix surrounding mammalian oocytes and embryos – correlates with embryo quality and developmental potential. However, current biomechanical characterization techniques – including micropipette aspiration, atomic force microscopy (AFM), microtactile sensors, and MEMS-based systems – either pose risks of mechanical damage or involve complex, time-consuming procedures unsuitable for clinical settings. Here, we introduce a novel approach leveraging fluidic force microscopy cantilevers to non-invasively evaluate embryo biomechanics. Our proof-of-concept study demonstrates rapid, precise stiffness profiling of intact mouse embryos (specifically ZP elasticity) in under one minute per embryo. Using gentle microsuction attachment with no chemical adhesives or rigid immobilization, the method preserves embryo integrity while providing reproducible elasticity measurements. This method combines the precision of AFM with minimal invasiveness, offering a promising new quantitative biomechanical indicator to augment clinical embryo assessment and paving the way for broader applications in reproductive biology.

Our study reveals that the nano-mechanical measures of elasticity and cell mass change significantly through induced pluripotent stem cell (iPSC) differentiation to cardiomyocytes, providing a reliable method to evaluate such processes.

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) hold enormous potential in cardiac disease modeling, drug screening, and regenerative medicine. Furthermore, patient-specific iPSC-CMS can be tested for personalized medicine. To provide a deeper understanding of the contractile force dynamics of iPSC-CMs, we employed Atomic Force Microscopy (AFM) as an advanced detection tool to distinguish the characteristics of force dynamics at a single cell level. We measured normal (vertical) and lateral (axial) force at different pacing frequencies. We found a significant correlation between normal and lateral force. We also observed a significant force–frequency relationship for both types of forces. This work represents the first demonstration of the correlation of normal and lateral force from individual iPSC-CMs. The identification of this correlation is relevant because it validates the comparison across systems and models that can only account for either normal or lateral force. These findings enhance our understanding of iPSC-CM properties, thereby paving the way for the development of therapeutic strategies in cardiovascular medicine.

Graphene has been a material of interest due to its versatile properties and wide variety of applications. However, production has been one of the most challenging aspects of graphene and multilayer graphene (MLG). Most synthesis techniques require elevated temperatures and additional steps to transfer graphene or MLG to a substrate, which compromises the integrity of the film. In this paper, metal-induced crystallization is explored to locally synthesize MLG directly on metal films, creating an MLG-metal composite and directly on insulating substrates with a moving resistive nanoheater probe at much lower temperature conditions (~ 250 °C). Raman spectroscopy shows that the resultant carbon structure has properties of MLG. The presented tip-based approach offers a much simpler MLG fabrication solution by eliminating the photolithographic and transfer steps of MLG.

In this article, a review of a series of applications of atomic force microscopy (AFM) and fluidic Atomic Force Microscopy (fluidic AFM, hereafter fluidFM) in single‐cell studies is presented. AFM applications involving single‐cell and extracellular vesicle (EV) studies, colloidal force spectroscopy, and single‐cell adhesion measurements are discussed. FluidFM is an offshoot of AFM that combines a microfluidic cantilever with AFM and has enabled the research community to conduct biological, pathological, and pharmacological studies on cells at the single‐cell level in a liquid environment. In this review, capacities of fluidFM are discussed to illustrate (1) the speed with which sequential measurements of adhesion using coated colloid beads can be done, (2) the ability to assess lateral binding forces of endothelial or epithelial cells in a confluent cell monolayer in an appropriate physiological environment, and (3) the ease of measurement of vertical binding forces of intercellular adhesion between heterogeneous cells. Furthermore, key applications of fluidFM are reviewed regarding to EV absorption, manipulation of a single living cell by intracellular injection, sampling of cellular fluid from a single living cell, patch clamping, and mass measurements of a single living cell.

Reliably measuring small mass changes at the single-cell level is challenging. In this manuscript, we report the use of microfluidic cantilevers in liquid with sub-nanogram scale weight sensing capability for the measurement of cellular mass changes of living single cells. With this instrumentation, we were able to perform fast mass measurements within 3 min. We show results of mass measurements of polystyrene and metal beads of various sizes (smallest weight measured at 280 ± 95 pg) and live single-cell mass measurements in a physiologically relevant environment. We also performed finite element analysis to simulate and optimize the structural design and materials of cantilevers. Our simulation results indicate that using polymer materials, such as SU8 and polyimide, could improve the minimal detectable mass by three-fold compared to conventional silicon cantilevers. The simulations also suggest that smaller dimensions of length, width, and thickness would improve the mass detection capability of microfluidic cantilevers.