R. Rox Anderson

Selective Cell Targeting with Light-Absorbing Microparticles and Nanoparticles

We describe a new method for selective cell targeting based on the use of light-absorbing microparticles and nanoparticles that are heated by short laser pulses to create highly localized cell damage. The method is closely related to chromophore-assisted laser inactivation and photodynamic therapy, but is driven solely by light absorption, without the need for photochemical intermediates (particularly singlet oxygen). The mechanism of light-particle interaction was investigated by nanosecond time-resolved microscopy and by thermal modeling. The extent of light-induced damage was investigated by cell lethality, by cell membrane permeability, and by protein inactivation. Strong particle size dependence was found for these interactions. A technique based on light to target endogenous particles is already being exploited to treat pigmented cells in dermatology and ophthalmology. With exogenous particles, phamacokinetics and biodistribution studies are needed before the method can be evaluated against photodynamic therapy for cancer treatment. However, particles are unique, unlike photosensitizers, in that they can remain stable and inert in cells for extended periods. Thus they may be particularly useful for prelabeling cells in engineered tissue before implantation. Subsequent irradiation with laser pulses will allow control of the implanted cells (inactivation or modulation) in a noninvasive manner.

ERYTHEMA AND MELANOGENESIS ACTION SPECTRA OF NORMAL HUMAN SKIN

Abstract The action spectra for delayed erythema and melanogenesis in Caucasian human skin are determined for wavelengths between 250 and 435 nm. The untanned skin of very fair volunteers was observed after single exposures to a range of fluences of monochromatic radiation. At wavelengths longer than 300 nm the two action spectra are indistinguishable, and at wavelengths shorter than 300 nm, they are of similar shape despite a distinct separation. This suggests a common or similar chromophore for initiation of the vascular and pigmentary responses to UV. A broad minimum in the action spectra occurs near 280 nm, a maximum near 296 nm, and for wavelengths longer than 300 nm, increasingly larger fluences of radiation are required to induce delayed erythema and melanogenesis. Between 304 and 334 nm both action spectra exhibit a rapid decrease of almost three orders of magnitude. In contrast, between 334 and 405 nm the spectra decrease by only one order of magnitude, and there is a suggestion of a small maximum at or near 365 nm. Different chromophores, sites of damage, or response mechanisms may be responsible for induction of delayed erythema at these longer wavelengths. After spectral corrections for the optical effects of the stratum corneum, the shape and magnitude of the action spectra are grossly consistent with a mechanism in which DNA is the primary chromophore initiating the response pathways for wavelengths less than 313 nm. Whatever the actual basis for these action spectra may be, they are of practical significance in predicting skin response to sources of ultraviolet radiation.

Damage to hair follicles by normal-mode ruby laser pulses

BACKGROUND Although many temporary treatments exist for hirsutism and hypertrichosis, a practical and permanent hair removal treatment is needed. OBJECTIVE Our purpose was to study the use of normal-mode ruby laser pulses (694 nm, 270 microseconds, 6 mm beam diameter) for hair follicle destruction by selective photothermolysis. METHODS Histologically assessed damage in ex vivo black-haired dog skin after the use of different laser fluences was used to design a human study; 13 volunteers with brown or black hair were exposed to normal-mode ruby laser pulses at fluences of 30 to 60 J/cm2, delivered to both shaved and wax-epilated skin sites. An optical delivery device designed to maximize light delivery to the reticular dermis was used. Hair regrowth was assessed at 1, 3, and 6 months after exposure by counting terminal hairs. RESULTS Fluence-dependent selective thermal injury to follicles was observed histologically. There was a significant delay in hair growth in all subjects at all laser-treated sites compared with the unexposed shaven and epilated control sites. At 6 months, there was significant hair loss only in the areas shaved before treatment at the highest fluence. At 6 months, four subjects had less than 50% regrowth, two of whom showed no change between 3 and 6 months. Transient pigmentary changes were observed; there was no scarring. CONCLUSION Selective photothermolysis of hair follicles with the normal-mode ruby laser produces a growth delay consistent with induction of prolonged telogen with apparently permanent hair removal in some cases.

Video-rate confocal scanning laser microscope for imaging human tissues in vivo

We have built a video-rate confocal scanning laser microscope for reflectance imaging of human skin and oral mucosa in vivo. Design and imaging parameters were determined for optimum resolution and contrast. Mechanical skin-holding fixtures and oral tissue clamps were made for stable objective lens-to-tissue contact such that gross tissue motion relative to the microscope was minimized. Confocal imaging was possible to maximum depths of 350 microm in human skin and 450 microm in oral mucosa, with measured lateral resolution of 0.5-1 microm and axial resolution (section thickness) of 3-5 microm at the 1064-nm wavelength. This resolution is comparable with that of conventional microscopy of excised biopsies (histology). Normal and abnormal tissue morphology and dynamic processes were observed.

Transmittance of nonionizing radiation in human tissues.

Abstract— Spectral transmittance of 400–865 nm radiation through various human structures, including the skull with scalp, the chest wall, abdominal wall and scrotum, is presented. There is essentially no visible light of wavelengths shorter than 500 nm transmitted through the chest or the abdominal wall. In contrast, 10−5–10−4 of blue light can reach the brain and testes. Transmittance of all tissues increases progressively with wavelength from 600 to 814nm. The maximal transmittances are 10−2–10−1 for skulls and scrota, and 10−3–10−2 for chest and abdominal walls. Tissue thickness, optical absorption and scattering are major influencing factors.

The Thermal Properties of Bovine Joint Capsule The Basic Science of Laser- and Radiofrequency-Induced Capsular Shrinkage

Orthopaedic surgeons have recently adapted the hol mium:yttrium-aluminum-garnet (YAG) laser for the shrinkage of capsular tissues for treatment of glenohu meral instability. The molecular mechanism of capsular shrinkage has not been documented to date. This study examined the effects of heating on bovine calf knee capsule and subsequent shrinkage of the cap sule. Capsule specimens were placed in a saline bath at temperatures ranging from 55° to 75°C for 1, 3, 5, and 10 minutes. Shrinkage was quantified by digital imaging, and the tissue was examined by light and polarized light microscopy. Tissue contraction was not measurable at or below 57.5°C. At 60°C, tissue shrink age occurred with corresponding basophilic staining and loss of birefringence in collagen fibers. For speci mens heated at 60°C and 62°C, shrinkage directly correlated with duration of thermal exposure. Maximal shrinkage of approximately 50% in length occurred at and above 65°C with thermal exposures of 1 minute or greater. This study demonstrates that thermal shrink age of bovine knee capsule correlates with denatur ation of collagen fibers and depends on both time and temperature. Capsular shrinkage treatments may be performed with any energy source that is capable of well-controlled heating of capsular tissue and does not depend on the special properties of laser light.

Topical Aminolevulinic Acid-Photodynamic Therapy for the Treatment of Acne Vulgaris

Background: Photodynamic therapy (PDT) is useful for the treatment of epidermal neoplasia but may also have use in the treatment of inflammatory dermatoses. The purpose of this study was to evaluate the safety and efficacy of PDT in the treatment of acne on the face.

Analytical modeling for the optical properties of the skin with in vitro and in vivo applications.

Abstract— Analytical modeling that interrelates the optical properties of multilayered structures is applied to the skin. The mathematical approach is based on relations of diffuse reflectance and transmittance of a multilayered system and the diffuse reflectance and transmittance of each component layer. The formula can also be derived from the Kubelka–Munk theory of radiation transfer. Using both collimated and diffuse incident irradiance, the applicability of the model to human epidermis over the UV and visible region has been verified. The model has been applied to calculate the absorption and scattering coefficients of human epidermis in vitro, and to estimate the epidermal transmittance under simulated in vivo condition.

Fractional CO2 laser‐assisted drug delivery

Ablative fractional resurfacing (AFR) creates vertical channels that might assist the delivery of topically applied drugs into skin. The purpose of this study was to evaluate drug delivery by CO2 laser AFR using methyl 5‐aminolevulinate (MAL), a porphyrin precursor, as a test drug.

Selective cryolysis: a novel method of non-invasive fat removal.

Excess fat poses a host of local and systemic problems. Various energy sources, for example, laser, ultrasound, and radiofrequency electric current have been studied as potential non‐invasive treatments aimed at local destruction of subcutaneous fat. Cryosurgery at very low temperatures is routinely used for non‐specific tissue destruction, however the potential for tissue‐specific cold injury has not been investigated. This study describes non‐invasive cold‐induced selective destruction of subcutaneous fat.