Structure formation in soft nanocolloids: liquid-drop model.

Using a model where soft nanocolloids such as spherical polymer brushes and star polymers are viewed as compressible liquid drops, we theoretically explore contact interactions between such particles. By numerically minimizing the phenomenological free energy consisting of bulk and surface terms, we find that at small deformations the drop-drop interaction is pairwise additive and described by a power law. We also propose a theory to describe the small-deformation regime, and the agreement is very good at all drop compressibilities. The large-deformation regime, which is dominated by many-body interactions, is marked by a rich phase diagram which includes the face- and body-centered-cubic, σ, A15, and simple hexagonal lattice as well as isostructural and re-entrant transitions. Most of these features are directly related to the non-convex deformation free energy emerging from many-body effects in the partial-faceting regime. The phase diagram, which depends on just two model parameters, contains many of the condensed phases observed in experiments. We also provide statistical-mechanical arguments that relate the two model parameters to the molecular architecture of the polymeric nanocolloids, chain rigidity, and solvent quality. The model represents a generic framework for the overarching features of the phase behavior of polymeric nanocolloids at high compressions.

Review of applications of fluorescence excitation spectroscopy to dermatology.

Endogenous molecules that exhibit fluorescence hold the potential to serve as reporters of tissue structure, activity and physiology. Fluorescence excitation spectroscopy is one means to measure and express tissue's innate fluorescence. This review focuses on the application of endogenous fluorescence ultraviolet excitation spectroscopy to dermatology.

Fluorescence excitation photography of epidermal cellular proliferation.

BACKGROUND: Fluorescence excitation provides the ability to interrogate innate molecules whose radiation emission correlates with specific functional states of tissue. OBJECTIVES: The present study demonstrates the effectiveness of a novel ultraviolet (UV) fluorescence excitation photography system in its ability to image rapidly proliferating epidermal skin lesions by capturing endogenous fluorescence emissions attributed to tryptophan. METHODS: A clinical prototype UV fluorescence excitation photography system was used to acquire images of endogenous fluorescence ascribed to tryptophan. RESULTS: Twelve human subjects and 11 ex vivo samples with various skin lesions consistently exhibited increased endogenous fluorescence at 340-nm wavelength upon excitation at 295 nm in rapid epidermal proliferations, including psoriasis, actinic keratoses and basal cell carcinoma, compared with surrounding normal skin. In contrast, nonproliferating lesions showed decreased fluorescence. CONCLUSIONS: This simple but robust point-and-shoot imaging system may offer a clinically useful, noncontact, noninvasive device for the diagnosis and detection of skin disease. As opposed to structural imaging modalities, fluorescence excitation imaging at 295/340-nm wavelengths offers high-sensitivity, wide-field functional imaging of cellular proliferation without the need for externally applied dyes or lengthy image processing. Furthermore, the image is instantly available and does not require interpretation or reconstruction.

Enhanced uptake and photoactivation of topical methyl aminolevulinate after fractional CO2 laser pretreatment.

BACKGROUND AND OBJECTIVES: Photodynamic therapy (PDT) of thick skin lesions is limited by topical drug uptake. Ablative fractional resurfacing (AFR) creates vertical channels that may facilitate topical PDT drug penetration and improve PDT-response in deep skin layers. The purpose of this study was to evaluate whether pre-treating the skin with AFR before topically applied methyl aminolevulinate (MAL) could enable a deep PDT-response. MATERIALS AND METHODS: Yorkshire swine were treated under general anesthesia with a fractional CO(2) laser using stacked single pulses of 3 milliseconds, 91.6 mJ per pulse and subsequent topical MAL application for 3 hours (Metvix®). Red light (LED arrays) was then delivered at fluences of 37 and 200 J/cm(2). Fluorescent photography and microscopy was used to quantify MAL-induced porphyrin distribution and PDT-induced photobleaching at the skin surface and five specific depths down to 1,800 µm. RESULTS: Laser-ablated channels were approximately 1,850 µm deep, which significantly increased topical MAL-induced porphyrin fluorescence (hair follicles, dermis, P < 0.0001) and PDT response, both superficially and deep, versus topical MAL application alone. The fraction of porphyrin fluorescence lost by photobleaching was slightly less after 37 J/cm(2) than after 200 J/cm(2) (overall median values 67-90%; 37 vs. 200 J/cm(2), P > 0.05 for all but one comparison). Photobleaching was steady throughout skin layers and did not vary significantly with skin depth at either LED fluence (P > 0.05). CONCLUSIONS: AFR greatly facilitates topical MAL-induced porphyrins and the fraction of photobleached porphyrins is similar for superficial and deep skin. These observations are consistent with AFR-enhanced uptake of MAL, increased porphyrin synthesis, and photodynamic activation of deep porphyrins even at the lower fluence of 37 J/cm(2), widely used in clinical practice. AFR appears to be a clinically practical means for improving PDT deep into the skin. Clinical studies are suggested to evaluate selectivity in targeting dysplastic cell types.

Resistant vasospasm in subarachnoid hemorrhage treated with continuous intraarterial nimodipine infusion.

Cerebral vasospasm complicating aneurysmal subarachnoid hemorrhage is a well-known medical entity. The delayed ischemic neurological deficits (DIND) as a result of vasospasm remain the main cause of morbidity among patients who manage to survive this severe disease pattern. When the traditional treatment options, either medical or interventional, fail to reverse vasospasm, continuous intraarterial infusion of nimodipine through catheters directly into the spastic arteries presents a promising treatment modality. Of 73 patients with aneurysmal subarachnoid hemorrhage between 2008 and 2009, a total of 27 had Hunt and Hess grades of 4 and 5. Fifteen percent of them showed refractory vasospasms and were treated with continuous nimodipine infusion via catheters in both internal carotid arteries. We present the method's indications and possible complications.

Three dimensional rotational angiography in surgical planning of aneurysm clipping.

BACKGROUND: Three-dimensional (3D) angiography is increasingly used in the diagnostics of brain aneurysms. Aim of the present study was to evaluate the accuracy of 3D angiograms with respect to its value for preoperative planning of aneurysm clipping. PATIENTS AND METHODS: The 3D angiograms of 42 patients with subarachnoid bleeding caused by aneurysm rupture of the anterior circle of Willis and the intradural carotid have been compared to intraoperative photographs of the aneurysms. RESULTS: Neighbouring vessels, aneurysm anatomy, arteries originating from the aneurysm wall were accurately shown decreasing the surgical risk of aneurysm clipping. CONCLUSIONS: The 3D images enabled a perfect preoperative planning through the operation by illuminating the aneurysm anatomy, neck localisation and shape and relation of the aneurysm to neighbouring vessels. Operative approach, use of an accurate clip and avoidance of clipping arteries close to the aneurysm have become predictable and safer by the use of 3D angiography.

Vertical ramus osteotomy with Er:YAG laser: a feasibility study.

The general advantages of laser surgery, such as decreased bleeding and dry surgical field, reduced postoperative pain and less oedema, have led to a continuous interest in laser applications for bone cutting. The ability to cut bone with a laser beam would also be of great technical benefit in minimally invasive maxillofacial surgery (endoscopic). The Erbium:yttrium aluminum garnet (Er:YAG) laser has been demonstrated to result in minimal thermal damage of bone, precise cutting, rapid osseous healing and osteoinduction. The purpose of this study was to assess the feasibility of using Er:YAG laser to perform vertical ramus osteotomy, and to determine the most efficient energy per pulse for its completion. Two fresh pig mandibles, one pig cadaver head and one human mandible were used. A different energy per pulse (0.5, 1, 1.5 and 2J/pulse) was used for each osteotomy on the pig mandibles (n=4). Vertical ramus osteotomy was feasible with all energy settings but time decreased considerably from 28 to 5.33 min as the energy per pulse increased. The human and the pig cadaver head mandibles were osteotomized bilaterally with 2000 mJ/pulse that was the most efficient in terms of time. Bone cuts were smooth with no carbonization in all cases.

Resonance Raman study of the dark-adapted form of the purple membrane protein.

The resonance Raman spectrum of the dark-adapted form of the purple membrane protein (bacteriorhodopsin) has been obtained and is compared to the light-adapted pigment and model chromophore spectra. As in the light-adapted form, the chromophore-protein linkage is found to be a protonated Schiff base. Electron delocalization appears to play the dominant role in color regulation. The dark-adapted spectrum indicates a conformation closer to 13-cis than the light-adapted spectrum.

Photomechanical transcutaneous delivery of macromolecules.

Transcutaneous drug delivery has been the subject of intensive research. In certain situations, rapid transcutaneous delivery is very desirable. A mechanical (stress) pulse generated by a single laser pulse was shown to transiently increase the permeability of the stratum corneum in vivo. The barrier function of the stratum corneum recovers within minutes. The increased permeability during these few minutes allows macromolecules to diffuse through the stratum corneum into the viable epidermis and dermis. Macromolecules (40 kDa dextran and 20 nm latex particles) were deposited into the skin using a photomechanical pulse generated by a single 23 ns laser pulse. This treatment can potentially be utilized in therapies that currently require occlusive dressings for hours or day(s).

Custom designed acoustic pulses.

We have used a tunable, infrared, free-electron laser with a Pockels cell controlled pulse duration to generate photoacoustic pulses with separate variable rise times (from 15 to 100 ns), durations (100-400 ns), and amplitudes (0.005-0.1 MPa). The tunability of the free-electron laser across water absorption bands allows the rise time of the thermal-elastically generated acoustical pulsed to be varied, while a Pockels cell controls the duration and cross polarizers control the pressure amplitude. The mechanical effects of pressure transients on biological tissue can have dramatic consequences. In addition to cell necrosis, carefully controlled pressure transients can also be used for therapeutic applications, such as drug delivery and gene therapy. This technique permits systemic probing of how biological tissue is affected by stress transients. © 1999 Society of Photo-Optical Instrumentation Engineers.

Fluorescence excitation spectroscopy for the measurement of epidermal proliferation.

Fluorescence excitation spectroscopy was used to assess cellular turnover in human skin by monitoring changes of endogenous fluorescence. Epidermal proliferation was induced with alpha-hydroxy acids. Commercially available glycolic acid creams (8 and 4% wt/wt concentration) and a vehicle cream (placebo) were applied in a randomized double blinded fashion on subjects' forearms, twice daily for 21 days. Excitation spectra were recorded (excitation 250-360 nm, emission 380 nm) at days 0, 1, 3, 7, 10, 11, 14, 17 and 21. The 295 nm excitation band (assigned to tryptophan moieties) was used in this study as a marker for cellular proliferation. To further reduce the day-to-day variability of the skin fluorescence the intensity of the 295 nm band was normalized to the 334 nm band (assigned to collagen crosslinks). The fluorescence emission intensity from placebo-treated skin remained practically unchanged over the period of the measurements while the fluorescence intensity measured from the glycolic acid-treated skin increased monotonically with treatment. The rate of increase of the excitation intensity with treatment was found to be dose dependent. The epidermal 295 nm band may be used as a quantitative marker to monitor the rate of proliferation of epidermal keratinocytes noninvasively.

Physical characteristics and biological effects of laser-induced stress waves.

Laser-induced stress waves can be generated by one of the following mechanisms: optical breakdown, ablation, or rapid heating of an absorbing medium. These three modes of laser interaction with matter allow the investigation of cellular and tissue responses to stress waves with different characteristics and under different conditions. The effects of stress waves on cells and tissues can be quite disparate. Stress waves can fracture tissue, kill cells, decrease cell viability and increase the permeability of the plasma membrane. They can induce deleterious effects during medical procedures of high power, short pulse lasers or, alternatively, may facilitate new therapeutic modalities, such as drug delivery and gene therapy. This review covers the generation of laser-induced stress waves and their effects on cell cultures and tissue.

Biological effects of laser-induced shock waves: structural and functional cell damage in vitro.

A new experimental design has been used to study the biological effects of laser-induced shock waves which minimizes or eliminates interference from ancillary effects such as bubble formation, ultraviolet (UV) radiation, or formation of radicals. The effects of these shock waves on human lymphocytes and red blood cells have been investigated. Three assays were used to determine cell injury: electron microscopy, ethidium bromide/fluorescein diacetate (EB/FDA) staining and incorporation of tritiated thymidine. The degree of cell damage was related to the pressure and the number of pulses. Cell damage was quantified and correlated using the three assays. Measurements of gross structural alterations as determined by transmission electron microscopy were less sensitive than assays of structural damage (e.g., EB/FDA assay) which were less sensitive than functional assays (e.g., incorporation of tritiated thymidine).

Wide-band acoustic spectroscopy of biological material based on a laser-induced grating technique.

A laser-induced transient grating technique enables fast noncontact acoustic measurements on transparent biological materials in a frequency range from tens of megahertz to 1 GHz. We have applied this method to the characterization of bovine vitreous and found high-frequency acoustic attenuation values to be close to those of water, with a quadratic dependence on frequency, in contrast to low-frequency data. The potential of the technique for studying other biological materials, such as human stratum corneum, is demonstrated.

Physical factors involved in stress-wave-induced cell injury: the effect of stress gradient.

We have studied the biological effects of ablation-induced stress waves in vitro. Mouse breast sarcoma cells (EMT-6) were exposed to stress waves that differed only in rise time. Two assays were used to determine cell injury: incorporation of tritiated thymidine (viability assay), and transmission electron microscopy (morphology assay). We present evidence that the rise time of stress waves can significantly modify cell viability and that cell injury correlates better with the stress gradient than peak stress.

Alteration of cell membrane by stress waves in vitro.

Experiments on the biological effects of laser-induced stress waves indicate that there is a transient increase in the permeability of the cell membrane. A cell viability assay (propidium iodide exclusion) shows that mouse breast sarcoma cells are viable after a stress wave. The kinetics of this transient membrane permeability are measured using time-resolved fluorescence imaging. The efflux of a membrane-impermeable fluorescent probe (calcein) following the application of a 300-bar stress wave implies that there is an increase in the membrane permeability. This efflux ceases within 80 s after a stress wave, suggesting that the membrane is no longer permeable to the fluorescent probe. Fitting the observed kinetics to a simple diffusion model yields an average initial diffusion constant of 2.2 +/- 1.3 x 10(-7) cm2/s for mouse breast sarcoma cells following the application of a laser-induced stress wave.

Stress-wave-induced membrane permeation of red blood cells is facilitated by aquaporins.

Stress waves generated by lasers and extracorporeal lithotripters have been shown to transiently increase the permeability of the plasma membrane, without affecting cell viability. Molecules present in the medium can diffuse into the cytoplasm under the concentration gradient. Molecular uptake under stress waves correlates with the presence of functioning aquaporins in the plasma membrane.

A rapid method to detect dried saliva stains swabbed from human skin using fluorescence spectroscopy.

Saliva on skin is important in forensic trace evidence. If areas where saliva is present can be outlined, this may lead to DNA analysis and identification. This study describes a rapid and non-destructive method to detect dried saliva on the surface of the skin by fluorescence spectroscopy. Eighty-two volunteers deposited samples of their own saliva on the skin of their ventral forearm. A control sample of water was deposited at three different sites on the contralateral arm. Saliva and water control were then allowed to air-dry. Swab samples were taken from dried saliva and control sites and were dissolved in 0.1M KCl solution. Emission spectra were obtained from the solution and were characterized by a principal maximum at 345-355nm with excitation at 282nm. The fluorescence emission intensity was greater than background readings obtained from the control swab site in 80 of 82 volunteers (approximately 97.6%). The fluorescence profile of saliva samples were similar to those obtained from aqueous samples of pure amylase and tryptophan, an endogenous fluorophore in alpha-amylase. The presence of an emission peak at 345-355nm with excitation at 282nm could provide a strong presumptive indication of saliva deposition.

Spectroscopic determination of skin viability. A predictor of postmortem interval.

We have demonstrated that skin viability decreases at a measurable rate following death in an animal model. The decreased skin viability was measured by fluorescein diacetate and ethidium bromide using fluorescence emission spectroscopy. There is significant decrease of the fluorescence intensity of the fluorescein diacetate assay between the 1-4 h, the 6-24 h, and the >40 h time points postmortem. For times between 6-24 h and >40 h postmortem the ethidium bromide assay showed consistent and significant increases in signal. The fluorescence measurements in this study showed that under the experimental conditions the time of death could be determined for <4, 6-24, and >40 hapotmotrem. The application of these assays in the field will require further study of the environmental factors.