The potential and benefits of nanoparticles in nanobiotechnology have been enthusiastically discussed in recent literature; however, little is known about the potential risks of contamination by accidental contact during production or use. Although theories of transdermal drug delivery suggest that skin structure and composition do not allow the penetration of materials larger than 600 Da, some articles on particle penetration into the skin have been recently published. Consequently, we wanted to evaluate whether metallic nanoparticles smaller than 10 nm could penetrate and eventually permeate the skin. Two different stabilized nanoparticle dispersions were applied to excised human skin samples using vertical diffusion cells. At established time points, solutions in receiving chambers were quantified for nanoparticle concentration, and skin was processed for light transmission and electron microscope examination. The results of this study showed that nanoparticles were able to penetrate the hair follicle and stratum corneum (SC), occasionally reaching the viable epidermis. Yet, nanoparticles were unable to permeate the skin. These results represent a breakthrough in skin penetration because it is early evidence where rigid nanoparticles have been shown to passively reach the viable epidermis through the SC lipidic matrix.

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Photopolymerization is a widely explored technology that has recently been recognized to have also great potentialities in the biomedical field. This paper aims to provide a general overview of this technology by briefly describing materials and methods used to produce linear or crosslinked polymer networks for drug delivery, tissue engineering and cell encapsulation. In addition, potentialities and areas of investigation that are not fully explored but that could provide solutions for better control over the technology when applied to the biomedical field will be indicated as well.  2006 Society of Chemical Industry Keywords: photopolymerization; drug delivery; tissue engineering; cell encapsulation OVERVIEW OF PHOTOPOLYMERS AND THEIR USEFULNESS IN BIOMATERIAL APPLICATIONPhotopolymerization is a technique that uses light to initiate and propagate a polymerization reaction to form a linear or crosslinked polymer structure. This technology has been widely explored in optoelectronics (e.g. videodisc coatings, photolithographic resists, aspherical lens production), non-linear optics (e.g. optical fiber communication, photonic integrated circuits, holographic data storage), the coating industry, the paint and printing ink industries, in adhesives, in composite materials, in the production of high resolution images (e.g. printing plates, optical discs, microcircuits), in three-dimensional stereolithography, in holographic recordings and in the food industry.1 Recently, the use of photopolymerization has been also proposed for the production of biomaterial-based polymer networks that could be differently fabricated for specific biomedical applications. The interest beyond these applications is due to a combination of properties held by photopolymerizable precursors and/or photopolymerized polymer networks. Some of the most important attributes are: ease in production and implantation; possibility of carrying out photopolymerization in vivo or ex vivo, which respectively allow for production-and-implantation via minimal invasive surgery, and for fabrication of complex shaped polymeric matrices; in several cases, spatial and temporal control of the polymerization process; versatility of formulation and application; possibility of entrapping a wide range of substances and cells; formulation ingredients can be stored in the most appropriate conditions until use, when they have to be mixed together before production of polymer networks.Consequently, scientists have suggested the utilization of photopolymerized polymer networks in drug delivery, 2 -13 tissue engineering, 14 -34 cell encapsulation, 35 -55 and as tissue barriers, 56 -60 fillers, 61,62 biomimetic coatings and materials, 1,63 -65 adsorption membranes, 1,66 contact lenses, 1 and dental restorative materials (e.g. dental composites, pit and fissure sealants, dentine bonding agents and cements, dental adhesives, denture and elastomeric impression materials), 1,67 -69 and for the production of microfluidic devices, nanodevices and nano-patterne...

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