Microfluidic extensional flow device to study mass transfer dynamics in the polymer microparticle formation process.

Polymer microparticles are often used to encapsulate drugs for sustained drug-release treatments. One of the ways they are manufactured is by using a solvent extraction process, in which the polymer solution is emulsified into an aqueous bulk phase using a surfactant as a stabilizing agent, followed by the removal of the solvent. The radius of a polymer drop decreases as a function of time until the polymer reaches the gelling point, after which it is separated and dried. Among the various operating parameters, the rate of solvent extraction is a critical step that affects the morphology and porosity, and consequently, the kinetics of drug release. But a fundamental mechanistic understanding of the solvent extraction dynamics as a function of shear is still unexplored. In this study, we have developed an experimental mass transfer model to predict the extraction by using the microfluidic extensional flow device (MEFD) to probe the shear and extraction dynamics at the level of a single drop in a linear extensional flow field. We used a computer-controlled feedback algorithm to manipulate the flow field and hydrodynamically trap a Hele-Shaw drop and observe the extraction process. For the polymer solution, we used a biocompatible polymer, poly-lactic-co-glycolic acid (PLGA) with ethyl acetate (EtOAc) as the solvent. Our experiments were conducted by varying the extensional rate (G) in the channel from ∼0.1 s-1 to ∼10 s-1, and using an analytical solution of the flow field, we captured the dissolution process and measured the change in drop radius (R) with time (t). Interestingly, we initially observed a short-time asymptote R ∼ t, and later the long-time asymptote of R = constant; both trends were physically explained. The transport model developed in this work can be used to predict extraction rates and polymer microparticle composition for any polymer-solvent system. This work is also an important contribution to the literature on convective mass transfer in partially miscible emulsions.

The Mini-Steamroll: An Abbreviated Variation of the Steamroller Maneuver Following Pneumatic Retinopexy for Rhegmatogenous Retinal Detachment.

PURPOSE: To describe a novel positioning maneuver for patients with rhegmatogenous retinal detachment (RRD) following pneumatic retinopexy(PnR). METHODS: Single-center prospective case series of primary RRDs referred to St. Michael's Hospital, Toronto, Canada, between 2021 and 2023. All patients underwent PnR. Baseline ultra-widefield fundus imaging and repeat imaging 10 minutes after the gas injection was performed. After PnR, patients were instructed to perform the mini-steamroll maneuver which consists of a face-down position for ten minutes followed by positioning to the retinal break. The reduction of subretinal fluid (SRF) volume after the initial face-down position was evaluated with clinical examination and ultra-widefield imaging. RESULTS: Six patients who presented with primary bullous RRD and a sizable superior break were enrolled. The mini-steamroll maneuver resulted in a rapid and significant reduction of SRF in all patients with bullous RRD and large superior breaks, allowing subretinal fluid to be expressed into the vitreous cavity with 10 minutes of face-down positioning. One patient required a sequential PnR. Primary retinal reattachment was achieved in all cases .This approach was well-tolerated by patients. CONCLUSION: This case series demonstrates that the mini-steamroll maneuver may be a suitable alternative for patient positioning following PnR in certain cases. The mini-steamroll is a simpler positioning regimen with the potential benefits of direct-to-break and full steamroller maneuver.

Interfacial Tension of the Water-Diluted Bitumen Interface at High Bitumen Concentrations Measured Using a Microfluidic Technique.

The interfacial tension (IFT) is a critical parameter to inform our understanding of the phenomena of drop breakup and droplet-droplet coalescence in sheared water-in-diluted bitumen (dilbit) emulsions. A microfluidic extensional flow device (MEFD) was used to determine the IFT of the dilbit-water emulsion system for bitumen concentrations of 33%, 50%, and 67% by weight (solvent to bitumen ratio (S/B) = 2, 1, and 0.5, respectively) and two different pH values of water: 8.3 and 9.9. The IFT was observed to increase with the bitumen concentration and decrease significantly upon lowering the water pH. The time scale for achieving the steady state IFT increased with bitumen concentration and was less sensitive to the water pH. But the most important feature of our measurements is that the IFTs recorded were significantly smaller than the values reported in the literature. We recognized two important differences between our studies and prior investigations: measurement of the IFT of water drops in dilbit as opposed to dilbit drops in water in earlier studies, and time scales of measurement of IFT that ranged from hundreds of milliseconds to a few seconds, as compared to a minute or longer in past investigations. These differences were examined carefully, but neither was found to explain the low IFTs measured in our studies. Our work leads to the following hypothesis: the mechanical properties of the interface of a sheared water drop in bitumen are significantly different from a stagnant one.

Mass transfer dynamics in the dissolution of Taylor bubbles.

The knowledge of thermodynamic and mass transfer parameters in gas-liquid systems is critical for the design of macroscale units for separation and reaction processes. The phenomenon of shrinkage of Taylor bubbles upon dissolution has the capability of supplying these design parameters, provided a reliable mathematical model is available for data deconvolution. Unfortunately, the existing models in the literature suffer from at least one of the following three major limitations. First, mass transfer between the bulk liquid segment and the surrounding liquid film has been incorrectly estimated. Second, the liquid segment is assumed to be well mixed, even though there is clear evidence of the contrary in the literature [Yang et al., Chem. Eng. Sci., 2017, 169, 106]. Third, an average mass transfer coefficient is assumed to be valid throughout the dissolution process, despite the fact that bubble velocities can change significantly during dissolution. In this work, we have rectified these limitations and developed a detailed model that takes into account the local concentration gradients and the flow profiles, without resorting to the computationally expensive, full numerical simulations of the fluid flow and concentration distribution equations. To validate the model, experiments were carried out in circular, silica capillaries of different radii by generating segmented flow of CO2 in physical solvents, and the diffusivity and the solubility were subsequently extracted with an error of less than 5%. This work can be extended to the study of gas-liquid-solid reactions in the Taylor flow configuration, and applied to the design of catalyst-coated monolithic reactors.

Near-infrared incoherent broadband cavity enhanced absorption spectroscopy (NIR-IBBCEAS) for detection and quantification of natural gas components.

The principle of near-infrared incoherent broadband cavity enhanced absorption spectroscopy was employed to develop a novel instrument for detecting natural gas leaks as well as for testing the quality of natural gas mixtures. The instrument utilizes the absorption features of methane, butane, ethane, and propane in the wavelength region of 1100 nm to 1250 nm. The absorption cross-section spectrum in this region for methane was adopted from the HITRAN database, and those for the other three gases were measured in the laboratory. A singular-value decomposition (SVD) based analysis scheme was employed for quantifying methane, butane, ethane, and propane by performing a linear least-square fit. The developed instrument achieved a detection limit of 460 ppm, 141 ppm, 175 ppm and 173 ppm for methane, butane, ethane, and propane, respectively, with a measurement time of 1 second and a cavity length of 0.59 m. These detection limits are less than 1% of the Lower Explosive Limit (LEL) for each gas. The sensitivity can be further enhanced by changing the experimental parameters (such as cavity length, lamp power etc.) and using longer averaging intervals. The detection system is a low-cost and portable instrument suitable for performing field monitorings. The results obtained on the gas mixture emphasize the instrument's potential for deployment at industrial facilities dealing with natural gas, where potential leaks pose a threat to public safety.

An exploration of the reflow technique for the fabrication of an in vitro microvascular system to study occlusive clots.

Embolic ischemia and pulmonary embolism are health emergencies that arise when a particle such as a blood clot occludes a smaller blood vessel in the brain or the lungs, and restricts flow of blood downstream of the vessel. In this work, the reflow technique (Wang et al. Biomed. Microdevices 2007, 9, 657) was adapted to produce a microchannel network that mimics the occlusion process. The technique was first revisited and a simple geometrical model was developed to quantitatively explain the shapes of the resulting microchannels for different reflow parameters. A critical modification was introduced to the reflow protocol to fabricate nearly circular microchannels of different diameters from the same master, which is not possible with the traditional reflow technique. To simulate the phenomenon of occlusion by clots, a microchannel network with three generations of branches with different diameters and branching angles was fabricated, into which fibrin clots were introduced. At low constant pressure drop (ΔP), a clot blocked a branch entrance only partially, while at higher ΔP, the branch was completely blocked. Instances of simultaneous blocking of multiple channels by clots, and the consequent changes in the flow rates in the unblocked branches of the network, were also monitored. This work provides the framework for a systematic study of the distribution of clots in a network, and the rate of dissolution of embolic clots upon the introduction of a thrombolytic drug into the network.

The hydrodynamics of segmented two-phase flow in a circular tube with rapidly dissolving drops.

This article discusses boundary integral simulations of dissolving drops flowing through a cylindrical tube for large aspect ratio drops. The dynamics of drop dissolution is determined by three dimensionless parameters: λ, the viscosity of the drop fluid relative to the suspending fluid; Ca, the capillary number defining the ratio of the hydrodynamic force to the interfacial tension force; and k, a dissolution constant based on the velocity of dissolution. For a single dissolving drop, the velocity in the upstream region is greater than the downstream region, and for sufficiently large k, the downstream velocity can be completely reversed, particularly at low Ca. The upstream end of the drop travels faster and experiences greater deformation than the downstream end. The film thickness, δ, between the drop and the tube wall is governed by a delicate balance between dissolution and changes in the outer fluid velocity resulting from a fixed pressure drop across the tube and mass continuity. Therefore, δ, and consequently, the drop average velocity, can increase, decrease or be relatively invariant in time. For two drops flowing in succession, while low Ca drops maintain a nearly constant separation distance during dissolution, at sufficiently large Ca, for all values of k, dissolution increases the separation distance between drops. Under these conditions, the liquid segments between two adjacent drops can no longer be considered as constant volume stirred tanks. These results will guide the choices of geometry and operating parameters that will facilitate the characterization of fast gas-liquid reactions via two-phase segmented flows.

Dispersion of a passive tracer in the pressure-driven flow of a non-colloidal suspension.

This paper numerically quantifies the dispersion of a solute, and in particular, the Taylor dispersion, in the pressure-driven flow of a non-colloidal suspension at moderately high volume fractions (0.2 to 0.5) through conduits of different cross-sectional shapes. An obvious intuition is that the Taylor dispersivity should increase owing to a decrease in the molecular diffusivity of the solute in the presence of particles impermeable to the solute; however, this is true only at low volume fractions. At higher volume fractions, three other physical effects become important, all of which lead to a reduction in Taylor dispersivity relative to a Newtonian fluid. The first is the blunting of the velocity profile resulting from particle migration into the low shear-stress regions, an effect that has been alluded to in the past by Roht et al. [J. Contam. Hydrol., 2013, 14, 10] and is important only at low Péclet numbers (Pe). At higher Pe, the two stronger effects are shear-induced solute self-diffusion, which arises due to shear-induced particle-particle interactions, and secondary convection, which is observed in non-axisymmetric cross-sections as a result of the second normal stress differences exhibited by concentrated suspensions. For a given volume fraction and cross-sectional geometry, a regime map, developed using a scaling analysis, delineates five regimes of dispersion involving one or a combination of the mass transfer mechanisms mentioned above. Our analysis also suggests that the cross-sectional shape can be exploited to enhance or suppress solute dispersion by modifying the secondary current strength and profile.

Changes in alveolar bone density around immediate functionally and nonfunctionally loaded implants.

STATEMENT OF PROBLEM: Few studies compare the radiographic changes in bone density associated with immediate implant loading protocols. PURPOSE: The purpose of this longitudinal study was to quantitatively assess radiographic changes in alveolar bone density around immediate functionally and nonfunctionally loaded implants. MATERIAL AND METHODS: A prospective longitudinal study was conducted in which 20 participants with partially edentulous mandibles received implants that were immediately loaded either functionally (IFL) or nonfunctionally (INFL). Standardized intraoral periapical radiographs were made at baseline, 3, and 6 months. These were digitized and analyzed using the histogram tool of the GNU Image Modulation Program for changes in alveolar bone density at crestal and lateral apical levels around the implant. RESULTS: An increase in the mean lateral apical pixel grayscale values of 4.68 ±0.80 at 3 months and 4.15 ±0.29 at 6 months was observed with IFL, while INFL demonstrated an increase of 5.66 ±0.53 at 3 months and 6.07 ±0.59 at 6 months. A decrease in the mean crestal pixel grayscale values of -24.40 ±7.41 with IFL and -16.86 ±5.14 with INFL was found from baseline to 3 months. CONCLUSIONS: On the basis of this longitudinal study, it was concluded that immediate loading stimulated alveolar bone formation at 6 months after implant placement. The immediate functional loading of implants resulted in a significantly greater degree of bone demineralization at the alveolar crest from implant placement up to 3 months compared with immediate nonfunctional loading.

Adsorption mechanism of myelin basic protein on model substrates and its bridging interaction between the two surfaces.

Myelin basic protein (MBP) is an intrinsically disordered (unstructured) protein known to play an important role in the stability of myelin's multilamellar membrane structure in the central nervous system. The adsorption of MBP and its capacity to interact with and bridge solid substrates has been studied using a surface forces apparatus (SFA) and a quartz crystal microbalance with dissipation (QCM-D). Adsorption experiments show that MBP molecules adsorb to the surfaces in a swollen state before undergoing a conformational change into a more compact structure with a thickness of ∼3 nm. Moreover, this compact structure is able to interact with nearby mica surfaces to form adhesive bridges. The measured adhesion force (energy) between two bridged surfaces is 1.0 ± 0.1 mN/m, (Ead = 0.21 ± 0.02 mJ/m(2)), which is slightly smaller than our previously reported adhesion force of 1.7 mN/m (Ead = 0.36 mJ/m(2)) for MBP adsorbed on two supported lipid bilayers (Lee et al., Proc. Natl. Acad. Sci. U.S.A. 2014, 111, E768-E775). The saturated surface concentration of compact MBP on a single SiO2 surface reaches a stable value of 310 ± 10 ng/cm(2) regardless of the bulk MBP concentration. A kinetic three-step adsorption model was developed that accurately fits the adsorption data. The developed model is a general model, not limited to intrinsically disordered proteins, that can be extended to the adsorption of various chemical compounds that undergo chemical reactions and/or conformational changes upon adsorbing to surfaces. Taken together with our previously published data (Lee et al., Proc. Natl. Acad. Sci. U.S.A. 2014, 111, E768-E775), the present results confirm that conformational changes of MBP upon adsorption are a key for strong adhesion, and that such conformational changes are strongly dependent on the nature of the surfaces.

Origins of microstructural transformations in charged vesicle suspensions: the crowding hypothesis.

It is observed that charged unilamellar vesicles in a suspension can spontaneously deflate and subsequently transition to form bilamellar vesicles, even in the absence of externally applied triggers such as salt or temperature gradients. We provide strong evidence that the driving force for this deflation-induced transition is the repulsive electrostatic pressure between charged vesicles in concentrated suspensions, above a critical effective volume fraction. We use volume fraction measurements and cryogenic transmission electron microscopy imaging to quantitatively follow both the macroscopic and microstructural time-evolution of cationic diC18:1 DEEDMAC vesicle suspensions at different surfactant and salt concentrations. A simple model is developed to estimate the extent of deflation of unilamellar vesicles caused by electrostatic interactions with neighboring vesicles. It is determined that when the effective volume fraction of the suspension exceeds a critical value, charged vesicles in a suspension can experience "crowding" due to overlap of their electrical double layers, which can result in deflation and subsequent microstructural transformations to reduce the effective volume fraction of the suspension. Ordinarily in polydisperse colloidal suspensions, particles interacting via a repulsive potential transform into a glassy state above a critical volume fraction. The behavior of charged vesicle suspensions reported in this paper thus represents a new mechanism for the relaxation of repulsive interactions in crowded situations.

Microfluidic generation of composite biopolymer microgels with tunable compositions and mechanical properties.

To develop an understanding of the nature of complex, spatiotemporal interactions between cells and the extracellular matrix (ECM), artificial ECMs formed from hydrogels with a particular spectrum of properties are being developed at a rapid pace. We report the microfluidic generation of small, monodisperse composite agarose-gelatin hydrogel modules (microgel particles) that can be used for cell encapsulation and can serve as instructive cellular microenvironments. The agarose component of the microgels gelled under reduced temperature, while gelatin modified with phenolic hydroxyl groups underwent peroxidase-catalyzed gelation. Microgel composition, structure, morphology, and rigidity were tuned in a high-throughput manner. The results of this work are important for the generation of libraries of cell-laden polymer microgels for single-cell analysis, tissue engineering, and fundamental studies of the role of local microenvironments in cell fate.

Relating domain size distribution to line tension and molecular dipole density in model cytoplasmic myelin lipid monolayers.

We fit the size distribution of liquid-ordered (L(o)) domains measured from fluorescence images of model cytoplasmic myelin monolayers with an equilibrium thermodynamic expression that includes the competing effects of line tension, λ, dipole density difference, Δm, and the mixing entropy. From these fits, we extract the line tension, λ, and dipole density difference, Δm, between the L(o) and liquid-disordered (L(d)) phases. Both λ and Δm decrease with increasing surface pressure, , although λ/Δm(2) remains roughly constant as the monolayer approaches the miscibility surface pressure. As a result, the mean domain size changed little with surface pressure, although the polydispersity increased significantly. The most probable domain radius was significantly smaller than that predicted by the energy alone, showing that the mixing entropy promotes a greater number of smaller domains. Our results also explain why domain shapes are stable; at equilibrium, only a small fraction of the domains are large enough to undergo theoretically predicted shape fluctuations. Monolayers based on the composition of myelin from animals with experimental allergic encephalomyelitis had slightly lower values of λ and Δm, and a higher area fraction of domains, than control monolayers at all . While it is premature to generalize these results to myelin bilayers, our results show that the domain distribution in myelin may be an equilibrium effect and that subtle changes in surface pressure and composition can alter the distribution of material in the monolayer, which will likely also alter the interactions between monolayers important to the adhesion of the myelin sheath.

Low yield stress measurements with a microfluidic rheometer.

Yield stress, τy, is a key rheological property of complex materials such as gels, dense suspensions, and dense emulsions. While there is a range of established techniques to measure τy in the order of tens to thousands of pascals, the measurement of low τy, specifically below 1 Pa, remains underexplored. In this article, we present the measurement of low apparent τy using a Hele-Shaw microfluidic extensional flow device (MEFD). Using the MEFD, we observe a gradient in shear stress, τ, such that τ is lower near the center or stagnation point, and higher away from the stagnation point. For a yield stress fluid, we observe that, below a certain flow rate, τ exceeds τy only in the outer region, leading to stagnation or unyielding of the fluid in the inner region. We use scaling analysis based on a Hele-Shaw linear extensional flow to deduce τy by measuring the size of the unyielded region, S. We validate this scaling relationship using Carbopol solutions with concentrations ranging between 0.015 to 0.3%, measuring τy as low as ∼10 mPa to ∼1 Pa, and comparing it with τy measured using a standard rheometer. While the experimental lower limit of our technique is 5 mPa, modifying the geometry or improving the image analysis can reduce this limit to the order of 10-4 Pa. The MEFD facilitates rapid measurement of τy, allowing for its real-time assessment. We further report τy of human blood samples between 30 to 80 mPa with their hematocrit ranging between 14 to 63%. Additionally, we determine τy for a mucus simulant (∼0.7 Pa), and lactic drink (∼7 mPa) to demonstrate the versatility of the MEFD technique.

Demonstration of secondary currents in the pressure-driven flow of a concentrated suspension through a square conduit.

The existence of secondary flows in the pressure-driven flow of a concentrated suspension of noncolloidal particles through a conduit of square cross section under creeping flow conditions is confirmed experimentally. This Letter lends support to the idea that secondary currents, rather than shear-induced migration, may actually be the dominant mechanism that determines particle distribution in noncolloidal suspension flows through nonaxisymmetric geometries. This work also establishes that coextrusion of two concentrated suspensions through nonaxisymmetric geometries with a stable suspension-suspension interface is not possible, except in special situations.

Direct measurements of effect of counterion concentration on mechanical properties of cationic vesicles.

Theoretical analyses of charged membranes in aqueous solutions have long predicted that the electric double layer surrounding them contributes significantly to their mechanical properties. Here we report the first, direct experimental measurements of the effect of counterion concentration on the bending and area expansion modulus of cationic surfactant vesicles. Using the classical technique of micropipet aspiration coupled with a modified experimental protocol that is better suited for cationic vesicles, we successfully measure the mechanical properties of a double-tailed cationic surfactant, diethylesterdimethyl ammonium chloride (diC18:1 DEEDMAC) in CaCl2 solutions. It is observed that the area expansion modulus of the charged membrane exhibits no measurable dependence on the counterion concentration, in accordance with existing models of bilayer elasticity. The measured bending modulus, however, is found to vary nonmonotonically and exhibits a minimum in its variation with counterion concentration. The experimental results are interpreted based on theoretical calculations of charged and bare membrane mechanics. It is determined that the initial decrease in bending modulus with increasing counterion concentration may be attributed to a decreasing double layer thickness, while the subsequent increase is likely due to an increasing membrane thickness. These mechanical moduli measurements qualitatively confirm, for the first time, theoretical predictions of a nonmonotonic behavior and the opposing effects of ionic strength on the bending rigidity of charged bilayers.

The yielding behaviour of human mucus.

Mucus is a viscoelastic material with non-linear rheological properties such as a yield stress of the order of a few hundreds of millipascals to a few tens of pascals, due to a complex network of mucins in water along with non-mucin proteins, DNA and cell debris. In this review, we discuss the origin of the yield stress in human mucus, the changes in the rheology of mucus with the occurrence of diseases, and possible clinical applications in disease detection as well as cure. We delve into the domain of mucus rheology, examining both macro- and microrheology. Macrorheology involves investigations conducted at larger length scales (∼ a few hundreds of µm or higher) using traditional rheometers, which probe properties on a bulk scale. It is significant in elucidating various mucosal functions within the human body. This includes rejecting unwanted irritants out of lungs through mucociliary and cough clearance, protecting the stomach wall from the acidic environment as well as biological entities, safeguarding cervical canal from infections and providing a swimming medium for sperms. Additionally, we explore microrheology, which encompasses studies performed at length scales ranging from a few tens of nm to a µm. These microscale studies find various applications, including the context of drug delivery. Finally, we employ scaling analysis to elucidate a few examples in lung, cervical, and gastric mucus, including settling of irritants in lung mucus, yielding of lung mucus in cough clearance and cilial beating, spreading of exogenous surfactants over yielding mucus, swimming of Helicobacter pylori through gastric mucus, and lining of protective mucus in the stomach. The scaling analyses employed on the applications mentioned above provide us with a deeper understanding of the link between the rheology and the physiology of mucus.

IMMEDIATE SUBRETINAL FLUID DISPLACEMENT FROM THE BUOYANT FORCE OF A SMALL GAS BUBBLE IN PNEUMATIC RETINOPEXY: INSIGHTS INTO THE POTENTIAL MECHANISM OF RETINAL DISPLACEMENT AFTER RETINAL DETACHMENT REPAIR.

PURPOSE: To demonstrate how a small gas bubble injected into the vitreous cavity in pneumatic retinopexy for rhegmatogenous retinal detachment causes immediate displacement of subretinal fluid and to gain insights into the potential mechanism of retinal displacement. METHODS: Three patients with rhegmatogenous retinal detachment who underwent pneumatic retinopexy were enrolled and prospectively followed. All patients underwent ultra-widefield fundus photography at baseline and at 1 to 2 minutes after intravitreal gas injection. RESULTS: In all cases, the ultra-widefield fundus photograph demonstrated immediate displacement of subretinal fluid, suggesting that the buoyant force applied to the retina by the bubble was responsible for the displacement of subretinal fluid. The results were extrapolated to determine the buoyant force applied by a small and large gas bubble as in pneumatic retinopexy and pars plana vitrectomy. We determined that the buoyant force applied with a larger bubble in pars plana vitrectomy was substantially greater, and this may lead to retinal displacement. CONCLUSION: Intravitreal gas applies significant buoyant force to the detached retina and subretinal fluid that leads to substantial and rapid displacement of subretinal fluid. Understanding the affect of the buoyant force of the gas bubble on the detached retina can provide insight into possible mechanisms of retinal displacement.

Outer Retinal Corrugations in Rhegmatogenous Retinal Detachment: The Retinal Pigment Epithelium-Photoreceptor Dysregulation Theory.

PURPOSE: Outer retinal folds occur when outer retinal corrugations (ORCs) persist after retinal reattachment with worse functional outcomes. We investigate the pathophysiology of ORCs in vivo. DESIGN: Prospective cohort study. METHODS: Patients with rhegmatogenous retinal detachment (RRD) presenting to St. Michael's Hospital, Toronto, Ontario, Canada, between August 2020 and February 2022 were assessed with swept-source optical coherence tomography (SS-OCT) and ultra-widefield SS-OCT for ORCs. Clinical characteristics of eyes with/without ORCs were compared. Mathematical models were used to deduce mechanical properties leading to ORCs. RESULTS: Sixty-six patients were included. More than half (60.6%, 40/66) were fovea-off and 48.4% (32/66) had ORCs at presentation. All eyes (32/32) with ORCs had retinal pigment epithelium (RPE)-photoreceptor dysregulation for at least 2 days, defined as loss of RPE control with acute, progressive, and extensive RRDs. In all (34/34) eyes without ORCs the RPE was in relative control of the subretinal space with nonprogressive subclinical or small localized or resolving RRDs, or with RPE-photoreceptor dysregulation for fewer than 2 days. Mathematical models indicate that a modulus of elasticity of the outer retina relative to the inner retina of 0.05 to 0.5 leads to ORCs. CONCLUSIONS: ORCs develop with (1) acute exposure of subretinal space to liquified vitreous, (2) for >2 days, that (3) overwhelms RPE capacity, leading to progressive and extensive RRD. Mathematical models suggest that a reduction in the modulus of elasticity of the outer retina occurs such that intrinsic compressive forces, likely related to progressive outer retinal hydration and lateral expansion, lead to ORCs. Understanding the pathophysiology of ORCs has implications for management.

Pathophysiology of outer retinal corrugations: Imaging dataset and mechanical models.

This article presents high-resolution swept-source optical coherence tomography (SS-OCT) imaging data used to elaborate a mechanical model that elucidates the formation of outer retinal corrugations (ORCs) in rhegmatogenous retinal detachments (RRD). The imaging data shared in the repository and presented in this article is related to the research paper entitled "Outer Retinal Corrugations in Rhegmatogenous Retinal Detachment: The Retinal Pigment Epithelium-Photoreceptor Dysregulation Theory" (Muni et al., AJO, 2022). The dataset consists of 69 baseline cross-sectional SS-OCT scans from 66 patients that were assessed for the presence of ORCs and analyzed considering the clinical features of each case. From the 66 cases, we selected SS-OCT images of 4 RRD patients with visible ORCs and no cystoid macular edema (CME) to validate the mechanical model. We modelled the retina as a composite material consisting of the outer retinal layer (photoreceptor layer) and the inner retinal layer (the part of the retina that excludes the photoreceptor layer) with thicknesses T o and T i and elastic modulus E o and E i , respectively. The thickness of the outer and inner retinal layers and the relative increase in the length of the outer retinal layer (γ) were measured from the SS-OCT images. Measurements from the SS-OCT images of patients with RRD demonstrated a 30% increase (γ=0.3) in the length of the outer retinal layer and a 400% increase in the thickness of the outer retinal layer (To). Using the mathematical model, Eo/Ei ranged between 0.05 to 0.5 to result in ORCs with a similar frequency to those observed in the SS-OCT scans.