Biomedical subjects

Stephen A Boppart

Publications and source records attributed to Stephen A Boppart.

At least 19 recordsLinked to original sources

PubMed2026

Microblasting Wound Dressings Mechanically Disrupt Polymicrobial Biofilms to Enhance Healing in Treatment-Resistant Wounds.

Treatment-resistant wounds driven by polymicrobial biofilms are a major clinical challenge, affecting millions globally and leading to chronic inflammation, persistent pain, and poor healing outcomes. These wounds are characterized by mature biofilms reinforced by dense extracellular polymeric substances, which confer strong tolerance to conventional treatments. Despite emerging technologies, such as nanoparticles, bacteriophages, and engineered enzymes, effective clearance of established biofilms remains challenging. Here, we develop a microblasting wound dressing (µBLAST) that delivers spatially confined mechano-chemical disruption at the tissue-biofilm interface to remove viscoelastic biofilm matrices and promote tissue regeneration. The µBLAST is assembled by embedding MnO2-doped diatom biosilica beneath an H2O2-releasing cellulose mesh, enabling localized catalytic microbubble generation within biofilm matrices. Confined expansion and rupture of oxygen bubbles produce localized mechanical stress sufficient to dislodge mature, antibiotic-resistant polymicrobial biofilms, while sustained H2O2 release prolongs particle activity. In a murine wound model infected with mature P. aeruginosa and methicillin-resistant S. aureus biofilms, µBLAST treatment significantly reduces biofilm burden, accelerates re-epithelialization, promotes hair regrowth, and mitigates inflammation. Moreover, µBLAST enhances antibiotic efficacy, suppressing biofilm regrowth even at ten-fold reduced drug doses. These findings highlight confined mechano-chemical biofilm disruption as a therapeutic strategy for treating mature, antibiotic-resistant biofilm infections and promoting tissue regeneration.

Biofilms↗

PubMed2006

High-spectral-resolution coherent anti-Stokes Raman scattering with interferometrically detected broadband chirped pulses.

To achieve high-spectral-resolution multiplex coherent anti-Stokes Raman scattering (CARS), one typically uses a narrowband pump pulse and a broadband Stokes pulse. This is to ensure a correspondence between anti-Stokes and vibrational frequencies. We obtain high-resolution CARS spectra of isopropanol, using a broadband chirped pump pulse and a broadband Stokes pulse, by detecting the anti-Stokes pulse with spectral interferometry. With the temporally resolved anti-Stokes signal, we can remove the chirp of the anti-Stokes pulse and restore high spectral resolution while also rejecting nonresonant scattering.

Equipment Design↗

PubMed2006

Spectroscopic spectral-domain optical coherence microscopy.

The spectroscopic content within optical coherence tomography (OCT) data can provide a wealth of information. Spectroscopic OCT methods are frequently limited by time-frequency trade-offs that limit high spectral and spatial resolution simultaneously. We present spectroscopic spectral-domain optical coherence microscopy performed with a multimodality microscope. Restricting the spatial extent of the signal by using high-numerical-aperture optics makes high-resolution spectroscopic information accessible, facilitated with spectral-domain detection. Simultaneous acquisition of multiphoton microscopy images is used to validate tissue structure and localization of nuclei within individual cells.

Animals↗

PubMed2006

Refractive index of carcinogen-induced rat mammary tumours.

Near-infrared optical techniques for clinical breast cancer screening in humans are rapidly advancing. Based on the computational inversion of the photon diffusion process through the breast, these techniques rely on optical tissue models for accurate image reconstruction. Recent interest has surfaced regarding the effect of refractive index variations on these reconstructions. Although many data exist regarding the scattering and absorption properties of normal and diseased tissue, no measurements of refractive index appear in the literature. In this paper, we present near-infrared refractive index data acquired from N-methyl-N-nitrosourea-induced rat mammary tumours, which are similar in pathology and disease progression to human ductal carcinoma. Eight animals, including one control, were employed in this study, yielding data from 32 tumours as well as adjacent adipose and connective tissues.

Animals↗

PubMed2006

Optical coherence elastography of engineered and developing tissue.

Biomechanical elastic properties are among the many variables used to characterize in vivo and in vitro tissues. Since these properties depend largely on the micro- and macroscopic structural organization tissue, it is crucial to understand the mechanical properties and the alterations that occur tissues respond to external forces or to disease processes. Using a novel technique called coherence elastography (OCE), we mapped the spatially distributed mechanical displacements strains in a representative model of a developing, engineered tissue as cells began to proliferate attach within a three-dimensional collagen matrix. OCE was also performed in the complex tissue of the Xenopus laevis (African frog) tadpole. Displacements were quantified a cross-correlation algorithm on pre- and postcompression images, which were acquired using coherence tomography (OCT). The images of the engineered tissue were acquired over a 10-development period to observe the relative strain differences in various regions. OCE was able differentiate changes in strain over time, which corresponded with cell proliferation and matrix as confirmed with histological observations. By anatomically mapping the regional variation stiffness with micron resolution, it may be possible to provide new insight into the complex by which engineered and natural tissues develop complex structures.

Animals↗

PubMed2006

Inverse scattering for optical coherence tomography.

Inverse scattering theory for optical coherence tomography (OCT) is developed. The results are used to produce algorithms to resolve three-dimensional object structure, taking into account the finite beam width, diffraction, and defocusing effects. The resolution normally achieved only in the focal plane of the OCT system is shown to be available for all illuminated depths in the object without moving the focal plane. Spatially invariant resolution is verified with numerical simulations and indicates an improvement of the high-resolution cross-sectional imaging capabilities of OCT.

Algorithms↗

PubMed2005

Comparative performance analysis of time-frequency distributions for spectroscopic optical coherence tomography.

The analysis of spectroscopic optical coherence tomography (SOCT) signals suffers the trade-off between time resolution and frequency resolution. Various joint time-frequency distributions (TFDs) can optimize this trade-off. Synthesized signals were generated and experimentally acquired data were obtained to compare and validate several different TFDs under different SOCT imaging schemes. Specific criteria were designed to quantify the TFD performance. We found that different SOCT imaging schemes require different optimal TFDs. Cohen's class TFDs generate the most compact time-frequency (TF) analysis, while linear TFDs offer the most reliable TF analysis. In both cases, if some prior information is known, model-based TF analysis can improve the performance.

Algorithms↗

PubMed2005

Imaging magnetically labeled cells with magnetomotive optical coherence tomography.

We introduce a novel contrast mechanism for optical coherence tomography (OCT) whereby the optical scattering of magnetically labeled cells is modified by means of an externally applied magnetic field. This modification is made through the addition of a small electromagnet to the imaging arm of a conventional OCT interferometer. We measure the magnetomotive OCT signal by differencing pairs of axial scans (A-scans) acquired with the magnetic field on and off. Magnetomotive contrast is demonstrated in bulk three-dimensional cell scaffolds containing macrophages labeled with microparticles of iron oxide, demonstrating magnetic-specific contrast over a dynamic range of 30 dB.

Animals↗

PubMed2005

Molecularly sensitive optical coherence tomography.

Molecular contrast in optical coherence tomography (OCT) is demonstrated by use of coherent anti-Stokes Raman scattering (CARS) for molecular sensitivity. Femtosecond laser pulses are focused into a sample by use of a low-numerical-aperture lens to generate CARS photons, and the backreflected CARS signal is interferometrically measured. With the chemical selectivity provided by CARS and the advanced imaging capabilities of OCT, this technique may be useful for molecular contrast imaging in biological tissues. CARS can be generated and interferometrically measured over at least 600 microm of the depth of field of a low-numerical-aperture objective.

Animals↗

PubMed2005

Evaluation of microfluidic biosensor development using microscopic analysis of molecular beacon hybridization kinetics.

Molecular beacons, oligonucleotide probes that fluoresce upon hybridization to a target nucleic acid, can be used in microfluidic devices to detect and quantify nucleic acids in solution as well as inside bacterial cells. Three essential steps towards the development of such devices as integrated microfluidic biosensors using molecular beacons were investigated in the present study. First, experiments using real-time confocal microscopy indicated that diffusion of DNA molecular beacons across a 100-mum diameter microfluidic channel took less than one minute after the flow of reagents was stopped. Second, experiments to evaluate hybridization kinetics of DNA molecular beacons with target nucleic acids in solution showed that DNA molecular beacons can be used to characterize hybridization kinetics in real time in microfluidic channels and that hybridization signals approached their maximum in approximately three minutes. Finally, it was demonstrated that peptide nucleic acid molecular beacons can be used to detect bacterial cells in microfluidic devices. These results suggest that the use of microfluidic devices to detect nucleic acids in solution and in bacterial cells is promising and that further development of an integrated microfluidic biosensor for bacterial detection based on this concept is warranted.

Biosensing Techniques↗

PubMed2005

Deconvolution methods for mitigation of transverse blurring in optical coherence tomography.

Imaging resolution in optical coherence tomography (OCT) is a key determinant for acquiring clinically useful optical biopsies of tissues. In contrast to light or confocal microscopy, the axial and transverse resolutions in OCT are independent and each can be analyzed individually. A method for mitigating transverse blurring and the apparent loss of transverse resolution in OCT by means of Gaussian beam deconvolution is presented. Such a method provides better representation of a specimen by using known physical parameters of a lens. To implement this method, deconvolution algorithms based on a focal-dependent kernel are investigated. First, the direct inverse problem is investigated using two types of regularization, truncated singular value decomposition, and Tikhonov. Second, an iterative expectation maximization algorithm, the Richardson-Lucy algorithm, with a beam-width-dependent iteration scheme is developed. A dynamically iterative Richardson-Lucy algorithm can reduce transverse blurring by providing an improvement in the transverse point-spread-function for sparse scattering samples in regions up to two times larger than the confocal region of the lens. These deblurring improvements inside and outside of the confocal region, which are validated experimentally, are possible without introducing new optical imaging hardware or acquiring multiple images of the same specimen. Implementation of this method in sparse scattering specimens, such as engineered tissues, has the potential to improve cellular detection and categorization.

Algorithms↗

PubMed2005

Optical biopsy of lymph node morphology using optical coherence tomography.

Optical diagnostic imaging techniques are increasingly being used in the clinical environment, allowing for improved screening and diagnosis while minimizing the number of invasive procedures. Diffuse optical tomography, for example, is capable of whole-breast imaging and is being developed as an alternative to traditional X-ray mammography. While this may eventually be a very effective screening method, other optical techniques are better suited for imaging on the cellular and molecular scale. Optical Coherence Tomography (OCT), for instance, is capable of high-resolution cross-sectional imaging of tissue morphology. In a manner analogous to ultrasound imaging except using optics, pulses of near-infrared light are sent into the tissue while coherence-gated reflections are measured interferometrically to form a cross-sectional image of tissue. In this paper we apply OCT techniques for the high-resolution three-dimensional visualization of lymph node morphology. We present the first reported OCT images showing detailed morphological structure and corresponding histological features of lymph nodes from a carcinogen-induced rat mammary tumor model, as well as from a human lymph node containing late stage metastatic disease. The results illustrate the potential for OCT to visualize detailed lymph node structures on the scale of micrometastases and the potential for the detection of metastatic nodal disease intraoperatively.

Animals↗

PubMed2005

Speckle reduction by I-divergence regularization in optical coherence tomography.

For optical coherence tomography (OCT), ultrasound, synthetic-aperture radar, and other coherent ranging methods, speckle can cause spurious detail that detracts from the utility of the image. It is a problem inherent to imaging densely scattering objects with limited bandwidth. Using a method of regularization by minimizing Csiszar's I-divergence measure, we derive a method of speckle minimization that produces an image that both is consistent with the known data and extrapolates additional detail based on constraints on the magnitude of the image. This method is demonstrated on a test image and on an OCT image of a Xenopus laevis tadpole.

Algorithms↗

PubMed2004

Near-infrared dyes as contrast-enhancing agents for spectroscopic optical coherence tomography.

Optical coherence tomography (OCT) images of biological tissues often have low contrast. Spectroscopic optical coherence tomography (SOCT) methods have been developed to enhance contrast but remain limited because most tissues are not spectrally active in the frequency bands of laser sources commonly used in OCT. Near-infrared (NIR) dyes with absorption spectra features within the OCT source spectrum can be used for enhancing contrast in this situation. We introduce and demonstrate the use of NIR dyes as contrast agents for SOCT. Contrast-enhanced images are compared with fluorescence microscopy, demonstrating a link between SOCT and fluorescence imaging.

Apium↗

PubMed2004

Structural and functional imaging of 3D microfluidic mixers using optical coherence tomography.

To achieve high mixing efficiency in microfluidic devices, complex designs are often required. Microfluidic devices have been evaluated with light and confocal microscopy, but fluid-flow characteristics at different depths are difficult to separate from the en face images produced. By using optical coherence tomography (OCT), an imaging modality capable of imaging 3D microstructures at micrometer-scale resolutions over millimeter-size scales, we obtained 3D dynamic functional and structural data for three representative microfluidic mixers: a Y channel mixer, a 3D serpentine mixer, and a vortex mixer. In the serpentine mixer, OCT image analysis revealed that the mixing efficiency was linearly dependent on the Reynolds number, whereas it appeared to have exponential dependence when imaged with light microscopy. The visual overlap of fluid flows in light-microscopy images leads to an overestimation of the mixing efficiency, an effect that was eliminated with OCT imaging. Doppler OCT measurements determined velocity profiles at various points in the serpentine mixer. Mixing patterns in the vortex mixer were compared with light-microscopy and OCT image analysis. These results demonstrate that OCT can significantly improve the characterization of 3D microfluidic device structure and function.

Microfluidics↗

PubMed2004

Nonlinear interferometric vibrational imaging.

Coherent anti-Stokes Raman scattering (CARS) processes are "coherent," but the phase of the anti-Stokes radiation is lost by most incoherent spectroscopic CARS measurements. We propose a Raman microscopy imaging method called nonlinear interferometric vibrational imaging, which measures Raman spectra by obtaining the temporal anti-Stokes signal through nonlinear interferometry. With a more complete knowledge of the anti-Stokes signal, we show through simulations that a high-resolution Raman spectrum can be obtained of a molecule in a single pulse using broad band radiation. This could be useful for identifying the three-dimensional spatial distribution of molecular species in tissue.

DNA↗

PubMed2004

Optical coherence tomography: feasibility for basic research and image-guided surgery of breast cancer.

Diagnostic trends in medicine are being directed toward cellular and molecular processes, where treatment regimens are more amenable for cure. Optical imaging is capable of performing cellular and molecular imaging using the short wavelengths and spectroscopic properties of light. Diffuse optical tomography is an optical imaging technique that has been pursued as an alternative to X-ray mammography. While this technique permits non-invasive optical imaging of the whole breast, to date it is incapable of resolving features at the cellular level. Optical coherence tomography (OCT) is an emerging high-resolution biomedical imaging technology that for larger and undifferentiated cells can perform cellular-level imaging at the expense of imaging depth. OCT performs optical ranging in tissue and is analogous to ultrasound except reflections of near-infrared light are detected rather than sound. In this paper, an overview of the OCT technology is provided, followed by images demonstrating the feasibility of using OCT to image cellular features indicative of breast cancer. OCT images of a well-established carcinogen-induced rat mammary tumor model were acquired. Images from this common experimental model show strong correlation with corresponding histopathology. These results illustrate the potential of OCT for a wide range of basic research studies and for intra-operative image-guidance to identify foci of tumor cells within surgical margins during the surgical treatment of breast cancer.

Animals↗

PubMed2004

Real-time digital signal processing-based optical coherence tomography and Doppler optical coherence tomography.

We present the development and use of a real-time digital signal processing (DSP)-based optical coherence tomography (OCT) and Doppler OCT system. Images of microstructure and transient fluid-flow profiles are acquired using the DSP architecture for real-time processing of computationally intensive calculations. This acquisition system is readily configurable for a wide range of real-time signal processing and image processing applications in OCT.

Algorithms↗