Hydrogels, due to their unique biocompatibility, flexible methods of synthesis, range of constituents, and desirable physical characteristics, have been the material of choice for many applications in regenerative medicine. They can serve as scaffolds that provide structural integrity to tissue constructs, control drug and protein delivery to tissues and cultures, and serve as adhesives or barriers between tissue and material surfaces. In this work, the properties of hydrogels that are important for tissue engineering applications and the inherent material design constraints and challenges are discussed. Recent research involving several different hydrogels polymerized from a variety of synthetic and natural monomers using typical and novel synthetic methods are highlighted. Finally, special attention is given to the microfabrication techniques that are currently resulting in important advances in the field.

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Under an interagency agreement with the Food and Drug Administration (FDA), a comprehensive literature review was conducted to gather and analyze existing research related to airborne emissions from non-smoldering cigarette butts. Based on the results from the literature review, an experimental plan was developed to measure the airborne emissions from non-smoldering cigarette butts. The literature review found that: 1) Non-smoldering cigarette butts can contain many of the same chemicals found in mainstream and sidestream smoke, and they are a potential source of these chemicals in both indoor and outdoor environments; 2) A number of studies have investigated the chemicals found in cigarette butts and chemicals leached? from cigarette butts into water. However, there are very limited data on the emissions from cigarette butts into air; 3) The emission rates from cigarette butts into air may be minimal for some heavy chemicals (e.g., metals, tobacco-specific nitrosamines), but may be significant for more volatile chemicals (e.g., nicotine, pyridine, benzene); 4) The airborne emissions of cigarette butts may be influenced by the cigarette brand, filter material, butt length, environmental temperature, airflow around the cigarette, number of puffs during smoking, degradation of the butt, and smoking method; 5) Much more data are needed on the airborne emission rates under different conditions. Based on the information from the literature review, the proposed experimental plan aims to fill the data gaps by using a screening tool (e.g. headspace analysis) to examine the airborne emission from non-smoldering cigarette butts under various environmental conditions. Steps in the proposed investigation include development of headspace analysis methods, selection of cigarette brand, determination of butt length, generation of cigarette butts, and determination of the target compounds. The proposed experiments will be conducted under four exposure environments, including small chamber, large chamber (to mimic indoor conditions), Simulation Photo-degradation via High Energy Radiation Emission chamber (SPHERE), with ultra violet radiation to simulate accelerated aging in outdoor environments, and outdoor rooftop (to represent aging in an outdoor environment).

Epidemiological investigations suggest a link between exposure to indoor air chemicals and adverse health effects. Consumer products contain reactive chemicals which can form secondary pollutants which may contribute to these effects. The reaction of limonene and ozone is a well characterized example of this type of indoor air chemistry. The studies described here characterize an in vitro model using an epithelial cell line (A549) or differentiated epithelial tissue (MucilAir™). The model is used to investigate adverse effects following exposure to combinations of limonene and ozone. In A549 cells, exposure to both the parent compounds and reaction products resulted in alterations in inflammatory cytokine production. A one hour exposure to limonene + ozone resulted in decreased proliferation when compared to cells exposed to limonene alone. Repeated dose exposures of limonene or limonene + ozone were conducted on MucilAir™ tissue. No change in proliferation was observed but increases in cytokine production were observed for both the parent compounds and reaction products. Factors such as exposure duration, chemical concentration, and sampling time point were identified to influence result outcome. These findings suggest that exposure to reaction products may produce more severe effects compared to the parent compound.

Reactions between hydrocarbons and ozone or hydroxyl radicals lead to the formation of oxidized species, including reactive oxygen species (ROS), and secondary organic aerosol (SOA) in the troposphere. ROS can be carried deep into the lungs by small aerodynamic particles where they can cause oxidative stress and cell damage. While environmental studies have focused on ROS in the gas phase and rainwater, it is also important to determine concentrations of ROS on respirable particles. Samples of PM 2.5 collected over 3 h at midday on 40 days during November 2011 and September 2012 show that the particulate ROS concentration in Austin, Texas, ranged from a minimum value of 0.02 nmoles H 2 O 2 m −3 air in December to 3.81 nmoles H 2 O 2 m −3 air in September. Results from correlation tests and linear regression analysis on particulate ROS concentrations and environmental conditions (which included ozone and PM 2.5 concentrations, temperature, relative humidity, precipitation and solar radiation) indicate that ambient particulate ROS is significantly influenced by the ambient ozone concentration, temperature and incident solar radiation. Particulate ROS concentrations measured in this study were in the range reported by other studies in the US, Taiwan and Singapore. This study is one of the first to assess seasonal variations in particulate ROS concentrations and helps explain the influence of environmental conditions on particulate ROS concentrations.Published by Copernicus Publications on behalf of the European Geosciences Union.