Propionibacterium acnes susceptibility to low-level 449 nm blue light photobiomodulation.

BACKGROUND AND OBJECTIVE: Recent advances in low-level light devices have opened new treatment options for mild to moderate acne patients. Light therapies have been used to treat a variety of skin conditions over the years but were typically only available as treatments provided by professional clinicians. Clinical application of blue light has proven to be effective for a broader spectral range and at lower fluences than previously utilized. Herein, we tested the hypothesis that sub-milliwatt/cm2 levels of long-wave blue light (449 nm) effectively kills Propionibacterium acnes, a causative agent of acne vulgaris, in vitro. MATERIALS AND METHODS: Two types of LED light boards were designed to facilitate in vitro blue light irradiation to either six-well plates containing fluid culture or a petri plate containing solid medium. P. acnes. Survival was determined by counting colony forming units (CFU) following irradiation. P. acnes was exposed in the presence and absence of oxygen. Coproporphyrin III (CPIII) photoexcitation was spectrophotometrically evaluated at 415 and 440 nm to compare the relative photochemical activities of these wavelengths. RESULTS: 422 and 449 nm blue light killed P. acnes in planktonic culture. Irradiation with 449 nm light also effectively killed P. acnes on a solid agar surface. Variation of time or intensity of light exposure resulted in a fluence-dependent improvement of antimicrobial activity. The presence of oxygen was necessary for killing of P. acnes with 449 nm light. CPIII displayed clear photoexcitation at both 415 and 440 nm, indicating that both wavelengths are capable of initiating CPIII photoexcitation at low incident light intensities (50 uW/cm2 ). CONCLUSION: Herein we demonstrate that sub-milliwatt/cm2 levels of long-wave blue light (449 nm) effectively kill P. acnes. The methods and results presented allow for deeper exploration and design of light therapy treatments. Results from these studies are expanding our understanding of the mode of action and functionality of blue light, allowing for improved options for acne patients. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Chitosan adsorption on hydroxyapatite and its role in preventing acid erosion.

Polymer adsorption onto an artificial saliva (AS) layer is investigated using quartz-crystal microbalance with dissipation (QCM-D) and chitosan as the model polymer. QCM-D is utilized in an innovative manner to monitor in situ adsorption of chitosan (CH) onto a hydroxyapatite (HA) coated crystal and to examine the ability of the adsorbed layer to "protect" the HA upon sequential exposure to acidic solutions. After deposition of a thin AS layer (16 nm), the total thickness on the HA substrate increases to 37 nm upon exposure to CH at pH 5.5 for 10 min. Correspondingly, the surface charge changes from negative (i.e., AS) to positive, consistent with the adsorption the polycationic CH onto or into the AS layer. Upon exposure to an oxidizing agent, the chitosan cross-links and collapses as noted by a decrease in thickness to 10 nm and an increase in the shear modulus by an order of magnitude. Atomic force microscopy (AFM) is used to determine the surface morphology and RMS roughness of the coated and HA surfaces after citric acid challenges. Both physisorbed and cross-linked chitosan are demonstrated to limit and prevent the erosion of HA, respectively.

Dextran functionalized surfaces via reductive amination: morphology, wetting, and adhesion.

Dextran surface grafting density was systematically varied via a two-step process involving SiO(2) amination by aminopropyltriethoxy silane (APTES) followed by oxidized dextran (M(w) = 110 kDa) chemisorption. Dextran oxidation kinetics with sodium metaperiodate (NaIO(4)) were quantified by (1)H NMR and pH measurements. Aldehyde group formation increased with increasing oxidation time. For 0.5 h oxidation time, dried film ellipsometric thickness was constant for solution concentrations ranging from 1 to 4 mg/mL. Dextran layers with the lowest grafting density wetted fastest and displayed the lowest contact angle (theta(APTES) > theta(1 h) > theta(2,4 h) > theta(0.5 h)). Under aqueous conditions, AFM force versus displacement measurements on 0.5 and 4.0 h surfaces exhibited a single displacement jump upon retraction. The 1.0 and 2.0 h surfaces showed two jumps consistent with two populations of chains, namely, loosely and strongly bound dextran. Overall, film morphology and wetting behavior were relatively invariant with grafting density, confirming the method's robustness for preparing biomimetic coatings with consistent properties.