An optical system for cellular mechanostimulation in 3D hydrogels.

We introduce a method utilizing single laser-generated cavitation bubbles to stimulate cellular mechanotransduction in dermal fibroblasts embedded within 3D hydrogels. We demonstrate that fibroblasts embedded in either amorphous or fibrillar hydrogels engage in Ca signaling following exposure to an impulsive mechanical stimulus provided by a single 250 µm diameter laser-generated cavitation bubble. We find that the spatial extent of the cellular signaling is larger for cells embedded within a fibrous collagen hydrogel as compared to those embedded within an amorphous polyvinyl alcohol polymer (SLO-PVA) hydrogel.

Analysis of relative error in perturbation Monte Carlo simulations of radiative transport.

Significance: Perturbation and differential Monte Carlo (pMC/dMC) methods, used in conjunction with nonlinear optimization methods, have been successfully applied to solve inverse problems in diffuse optics. Application of pMC to systems over a large range of optical properties requires optimal "placement" of baseline conventional Monte Carlo (cMC) simulations to minimize the pMC variance. The inability to predict the growth in pMC solution uncertainty with perturbation size limits the application of pMC, especially for multispectral datasets where the variation of optical properties can be substantial.

Modeling nonlinear optical microscopy in scattering media, part II. Radiation from focal volume to far-field: tutorial.

The development and application of nonlinear optical (NLO) microscopy methods in biomedical research has experienced rapid growth over the past three decades. Despite the compelling power of these methods, optical scattering limits their practical use in biological tissues. This tutorial offers a model-based approach illustrating how analytical methods from classical electromagnetism can be employed to comprehensively model NLO microscopy in scattering media.

Modeling nonlinear optical microscopy in scattering media, part I. Propagation from lens to focal volume: tutorial.

The development and application of nonlinear optical (NLO) microscopy methods in biomedical research have experienced rapid growth over the past three decades. Despite the compelling power of these methods, optical scattering limits their practical use in biological tissues. This tutorial offers a model-based approach illustrating how analytical methods from classical electromagnetism can be employed to comprehensively model NLO microscopy in scattering media.

Radiance backscattered by a strongly scattering medium in the high spatial frequency limit.

We study the radiative transfer of a spatially modulated plane wave incident on a half-space composed of a uniformly scattering and absorbing medium. For spatial frequencies that are large compared to the scattering coefficient, we find that first-order scattering governs the leading behavior of the radiance backscattered by the medium. The first-order scattering approximation reveals a specific curve on the backscattered hemisphere where the radiance is concentrated.

MCCL: an open-source software application for Monte Carlo simulations of radiative transport.

The Monte Carlo Command Line application (MCCL) is an open-source software package that provides Monte Carlo simulations of radiative transport through heterogeneous turbid media. MCCL is available on GitHub through our virtualphotonics.org website, is actively supported, and carries extensive documentation.

Corneal transparency and scleral opacity arises from the nanoarchitecture of the constituent collagen fibrils.

While human scleral and corneal tissues possess similar structural morphology of long parallel cylindrical collagen fibrils, their optical characteristics are markedly different. Using pseudospectral time-domain (PSTD) simulations of Maxwell's equations, we model light propagation through realistic representations of scleral and corneal nanoarchitecture and analyze the transmittance and spatial correlation in the near field. Our simulation results provide differing predictions for scleral opacity and corneal transparency across the vacuum ultraviolet to the mid-infrared spectral region in agreement with experimental data.

Comparative analysis of discrete and continuous absorption weighting estimators used in Monte Carlo simulations of radiative transport in turbid media: erratum.

This erratum corrects the relative error plots and references in our paper [J. Opt. Soc.

Single-shot interferometric measurement of cavitation bubble dynamics.

We demonstrate an interferometric method to provide direct, single-shot measurements of cavitation bubble dynamics with nanoscale spatial and temporal resolution with results that closely match theoretical predictions. Implementation of this method reduces the need for expensive and complex ultra-high speed camera systems for the measurement of single cavitation events. This method can capture dynamics over large time intervals with sub-nanosecond temporal resolution and spatial precision surpassing the optical diffraction limit.

Laser cavitation rheology for measurement of elastic moduli and failure strain within hydrogels.

We introduce laser cavitation rheology (LCR) as a minimally-invasive optical method to characterize mechanical properties within the interior of biological and synthetic aqueous soft materials at high strain-rates. We utilized time-resolved photography to measure cavitation bubble dynamics generated by the delivery of focused 500 ps duration laser radiation at λ = 532 nm within fibrin hydrogels at pulse energies of E = 12, 18 µJ and within polyethylene glycol (600) diacrylate (PEG (600) DA) hydrogels at E = 2, 5, 12 µJ. Elastic moduli and failure strains of fibrin and PEG (600) DA hydrogels were calculated from these measurements by determining parameter values which provide the best fit of the measured data to a theoretical model of cavitation bubble dynamics in a Neo-Hookean viscoelastic medium subject to material failure.

Recovery of layered tissue optical properties from spatial frequency-domain spectroscopy and a deterministic radiative transport solver.

We present a method to recover absorption and reduced scattering spectra for each layer of a two-layer turbid media from spatial frequency-domain spectroscopy data. We focus on systems in which the thickness of the top layer is less than the transport mean free path   (  0.1  -  0.

Optical sampling depth in the spatial frequency domain.

We present a Monte Carlo (MC) method to determine depth-dependent probability distributions of photon visitation and detection for optical reflectance measurements performed in the spatial frequency domain (SFD). These distributions are formed using an MC simulation for radiative transport that utilizes a photon packet weighting procedure consistent with the two-dimensional spatial Fourier transform of the radiative transport equation. This method enables the development of quantitative metrics for SFD optical sampling depth in layered tissue and its dependence on both tissue optical properties and spatial frequency.

Effect of scattering on coherent anti-Stokes Raman scattering (CARS) signals.

We develop a computational framework to examine the factors responsible for scattering-induced distortions of coherent anti-Stokes Raman scattering (CARS) signals in turbid samples. We apply the Huygens-Fresnel wave-based electric field superposition (HF-WEFS) method combined with the radiating dipole approximation to compute the effects of scattering-induced distortions of focal excitation fields on the far-field CARS signal. We analyze the effect of spherical scatterers, placed in the vicinity of the focal volume, on the CARS signal emitted by different objects (2μm diameter solid sphere, 2μm diameter myelin cylinder and 2μm diameter myelin tube).

Development of perturbation Monte Carlo methods for polarized light transport in a discrete particle scattering model.

We present a polarization-sensitive, transport-rigorous perturbation Monte Carlo (pMC) method to model the impact of optical property changes on reflectance measurements within a discrete particle scattering model. The model consists of three log-normally distributed populations of Mie scatterers that approximate biologically relevant cervical tissue properties. Our method provides reflectance estimates for perturbations across wavelength and/or scattering model parameters.

Multi-scale silica structures for improved HIV-1 Capsid (p24) antigen detection.

Silica (SiO2) micro- and nanostructures fabricated with pre-stressed thermoplastic shrink wrap film have been shown to yield far-field fluorescence signal enhancements over their planar or wrinkled counterparts. The SiO2 structures have previously been used for improved detection of fluorescently labelled proteins and DNA. In this work, we probe the mechanism responsible for the dramatic increases in fluorescence signal intensity.

Differential pathlength factor informs evoked stimulus response in a mouse model of Alzheimer's disease.

Baseline optical properties are typically assumed in calculating the differential pathlength factor (DPF) of mouse brains, a value used in the modified Beer-Lambert law to characterize an evoked stimulus response. We used spatial frequency domain imaging to measure in vivo baseline optical properties in 20-month-old control ([Formula: see text]) and triple transgenic APP/PS1/tau (3xTg-AD) ([Formula: see text]) mouse brains. Average [Formula: see text] for control and 3xTg-AD mice was [Formula: see text] and [Formula: see text], respectively, at 460 nm; and [Formula: see text] and [Formula: see text], respectively, at 530 nm.

High-throughput optical screening of cellular mechanotransduction.

We introduce an optical platform for rapid, high-throughput screening of exogenous molecules that affect cellular mechanotransduction. Our method initiates mechanotransduction in adherent cells using single laser-microbeam generated micro-cavitation bubbles (μCBs) without requiring flow chambers or microfluidics. These μCBs expose adherent cells to a microTsunami, a transient microscale burst of hydrodynamic shear stress, which stimulates cells over areas approaching 1mm.

Low-density plasma formation in aqueous biological media using sub-nanosecond laser pulses.

We demonstrate the formation of low- and high-density plasmas in aqueous media using sub-nanosecond laser pulses delivered at low numerical aperture (NA = 0.25). We observe two distinct regimes of plasma formation in deionized water, phosphate buffered saline, Minimum Essential Medium (MEM), and MEM supplemented with phenol red.

Rapid computation of the amplitude and phase of tightly focused optical fields distorted by scattering particles.

We develop an efficient method for accurately calculating the electric field of tightly focused laser beams in the presence of specific configurations of microscopic scatterers. This Huygens-Fresnel wave-based electric field superposition (HF-WEFS) method computes the amplitude and phase of the scattered electric field in excellent agreement with finite difference time-domain (FDTD) solutions of Maxwell's equations. Our HF-WEFS implementation is 2-4 orders of magnitude faster than the FDTD method and enables systematic investigations of the effects of scatterer size and configuration on the focal field.

Coupled forward-adjoint Monte Carlo simulation of spatial-angular light fields to determine optical sensitivity in turbid media.

We present a coupled forward-adjoint Monte Carlo (cFAMC) method to determine the spatially resolved sensitivity distributions produced by optical interrogation of three-dimensional (3-D) tissue volumes. We develop a general computational framework that computes the spatial and angular distributions of the forward-adjoint light fields to provide accurate computations in mesoscopic tissue volumes. We provide full computational details of the cFAMC method and provide results for low- and high-scattering tissues probed using a single pair of optical fibers.

Comparative analysis of discrete and continuous absorption weighting estimators used in Monte Carlo simulations of radiative transport in turbid media.

We examine the relative error of Monte Carlo simulations of radiative transport that employ two commonly used estimators that account for absorption differently, either discretely, at interaction points, or continuously, between interaction points. We provide a rigorous derivation of these discrete and continuous absorption weighting estimators within a stochastic model that we show to be equivalent to an analytic model, based on the radiative transport equation (RTE). We establish that both absorption weighting estimators are unbiased and, therefore, converge to the solution of the RTE.

Hydrodynamic determinants of cell necrosis and molecular delivery produced by pulsed laser microbeam irradiation of adherent cells.

Time-resolved imaging, fluorescence microscopy, and hydrodynamic modeling were used to examine cell lysis and molecular delivery produced by picosecond and nanosecond pulsed laser microbeam irradiation in adherent cell cultures. Pulsed laser microbeam radiation at λ = 532 nm was delivered to confluent monolayers of PtK2 cells via a 40×, 0.8 NA microscope objective.

Radiative transport produced by oblique illumination of turbid media with collimated beams.

We examine the general problem of light transport initiated by oblique illumination of a turbid medium with a collimated beam. This situation has direct relevance to the analysis of cloudy atmospheres, terrestrial surfaces, soft condensed matter, and biological tissues. We introduce a solution approach to the equation of radiative transfer that governs this problem, and develop a comprehensive spherical harmonics expansion method utilizing Fourier decomposition (SHEF(N)).

In vivo multiphoton NADH fluorescence reveals depth-dependent keratinocyte metabolism in human skin.

We employ a clinical multiphoton microscope to monitor in vivo and noninvasively the changes in reduced nicotinamide adenine dinucleotide (NADH) fluorescence of human epidermal cells during arterial occlusion. We correlate these results with measurements of tissue oxy- and deoxyhemoglobin concentration during oxygen deprivation using spatial frequency domain imaging. During arterial occlusion, a decrease in oxyhemoglobin corresponds to an increase in NADH fluorescence in the basal epidermal cells, implying a reduction in basal cell oxidative phosphorylation.

Impact of release dynamics of laser-irradiated polymer micropallets on the viability of selected adherent cells.

We use time-resolved interferometry, fluorescence assays and computational fluid dynamics (CFD) simulations to examine the viability of confluent adherent cell monolayers to selection via laser microbeam release of photoresist polymer micropallets. We demonstrate the importance of laser microbeam pulse energy and focal volume position relative to the glass-pallet interface in governing the threshold energies for pallet release as well as the pallet release dynamics. Measurements using time-resolved interferometry show that increases in laser pulse energy result in increasing pallet release velocities that can approach 10 m s(-1) through aqueous media.