Collagen type I is a material widely used for 3D cell culture and tissue engineering. Different architectures, such as gels, sponges, membranes, and nanofibers, can be fabricated with it. In collagen hydrogels, the formation of fibrils and fibers depends on various parameters, such as the source of collagen, pH, temperature, concentration, age, etc. In this work, we study the fibrillogenesis process in collagen type I hydrogels with different types of microbeads embedded, using optical techniques such as turbidity assay and confocal reflectance microscopy. We observe that microbeads embedded in the collagen matrix hydrogels modify the fibrillogenesis. Our results show that carboxylated fluorescent microbeads accelerate 3.6 times the gelation, while silica microbeads slow down the formation of collagen fibrils by a factor of 1.9, both compared to pure collagen hydrogels. Our observations suggest that carboxylate microbeads act as nucleation sites and the early collagen fibrils bind to the microbeads.
Collagen Type I , Hydrogels , Microspheres , Hydrogels/chemistry , Collagen Type I/chemistry , Animals , Collagen/chemistry , Tissue Engineering/methods , Hydrogen-Ion Concentration , Biocompatible Materials/chemistry , Silicon Dioxide/chemistry , Microscopy, Confocal , Temperature , Carboxylic Acids/chemistry , Materials Testing
Focus precision and stability is crucial in confocal microscopy not only for image sharpness but also to avoid radiometric fluctuations that can wrongly be interpreted as variations of the fluorescence intensity in the sample. Here we report a focus variation provoked by a continuous wave laser of 810-nm wavelength introduced along the optical path of an inverted confocal microscope with an oil immersion ×60 objective. When the laser is turned on or off, the focus position drifts toward lower or high values of the vertical coordinate z, respectively. The maximum drift observed was 2.25 ðm for a laser power of 40 mW at the sample and over a 600-s exposure time. The temporal evolution of the focus position is well fitted by exponential curves that mimic temperature variations due to a heat source. Our analysis strongly suggests that the focus drift is due to heating of the immersion oil.
Lasers , Light , Hot Temperature , Microscopy, Confocal/methods , Temperature
We demonstrate a novel structure based on smart carbon nanocomposites intended for fabricating laser-triggered drug delivery devices (DDDs). The performance of the devices relies on nanocomposites' photothermal effects that are based on polydimethylsiloxane (PDMS) with carbon nanoparticles (CNPs). Upon evaluating the main features of the nanocomposites through physicochemical and photomechanical characterizations, we identified the main photomechanical features to be considered for selecting a nanocomposite for the DDDs. The capabilities of the PDMS/CNPs prototypes for drug delivery were tested using rhodamine-B (Rh-B) as a marker solution, allowing for visualizing and quantifying the release of the marker contained within the device. Our results showed that the DDDs readily expel the Rh-B from the reservoir upon laser irradiation and the amount of released Rh-B depends on the exposure time. Additionally, we identified two main Rh-B release mechanisms, the first one is based on the device elastic deformation and the second one is based on bubble generation and its expansion into the device. Both mechanisms were further elucidated through numerical simulations and compared with the experimental results. These promising results demonstrate that an inexpensive nanocomposite such as PDMS/CNPs can serve as a foundation for novel DDDs with spatial and temporal release control through laser irradiation.
Drug Carriers/chemistry , Nanocomposites/chemistry , Smart Materials/chemistry , Carbon/chemistry , Dimethylpolysiloxanes/chemistry , Drug Carriers/radiation effects , Elasticity , Lasers , Light , Mechanical Phenomena , Nanocomposites/radiation effects , Rhodamines/chemistry , Smart Materials/radiation effects
We demonstrate a fiber optic probe incorporating functional polymer composites for controlled generation of photothermal effects. The probe combines carbon-based and rare-earth composites on the tip of standard multimode fibers, thus yielding a compact fiber optic photothermal probe (FOPP) whose temperature can be measured simultaneously through fluorescent thermometry. We evaluate the thermal features of the probe through experiments and numerical calculations showing that large thermal gradients are obtained within the vicinity of the heating zone. The temperatures achieved with the FOPP are within the ranges of interest for hyperthermia and can be attained using low optical powers (< 280 mW).
Photothermal therapy has shown to be a promising technique for local treatment of tumors. However, the main challenge for this technique is the availability of localized heat sources to minimize thermal damage in the surrounding healthy tissue. In this work, we demonstrate the use of optical fiber microheaters for inducing thermal lesions in soft tissue. The proposed devices incorporate carbon nanotubes or gold nanolayers on the tips of optical fibers for enhanced photothermal effects and heating of ex vivo biological tissues. We report preliminary results of small size photothermal lesions induced on mice liver tissues. The morphology of the resulting lesions shows that optical fiber microheaters may render useful for delivering highly localized heat for photothermal therapy.
The advent of nanotechnology has triggered novel developments and applications for polymer-based membranes with embedded or coated nanoparticles. As an example, interaction of laser radiation with metallic and carbon nanoparticles has shown to provide optically triggered responses in otherwise transparent media. Incorporation of these materials inside polymers has led to generation of plasmonic and photothermal effects through the enhanced optical absorption of these polymer composites. In this work, we focus on the photothermal effects produced in polydimethylsiloxane (PDMS) membranes with embedded carbon nanoparticles via light absorption. Relevant physical parameters of these composites, such as nanoparticle concentration, density, geometry and dimensions, are used to analyze the photothermal features of the membranes. In particular, we analyze the heat generation and conduction in the membranes, showing that different effects can be achieved and controlled depending on the physical and thermal properties of the composite material. Several novel applications of these light responsive membranes are also demonstrated, including low-power laser-assisted micro-patterning and optomechanical deformation. Furthermore, we show that these polymer-nanoparticle composites can also be used as coatings in photonic and microfluidic applications, thereby offering an attractive platform for developing light-activated photonic and optofluidic devices.
We show that fiber optic tips can be used as microbubble generators in liquid media. Using standard single-mode silica fibers incorporating nanoparticles (carbon nanoparticles and metallic powders), bubbles can be generated with low optical powers owing to the enhanced photothermal effects of the coating materials. We provide details about the hydrodynamic effects generated in the vicinity of the fiber tip during the coating process, bubble generation and growth. Flow visualization techniques show that thermal effects lead to bubble formation on the tip of the fibers, and coating optimization is crucial for optimal performance of the probes.
