Quantification of continual anthropogenic pollutants released in swimming pools.

Disinfection in swimming pools is often performed by chlorination, However, anthropogenic pollutants from swimmers will react with chlorine and form disinfection by-products (DBPs). DBPs are unwanted from a health point of view, because some are irritating, while others might be carcinogenic. The reduction of anthropogenic pollutants will lead to a reduction in DBPs. This paper investigates the continual release of anthropogenic pollutants by means of controlled sweat experiments in a pool tank during laboratory time-series experiments (LTS experiments) and also during on-site experiments (OS experiments) in a swimming pool. The sweat released during the OS and LTS experiments was very similar. The sweat rate found was 0.1-0.2 L/m(2)/h at water temperatures below 29 °C and increased linearly with increasing water temperatures to 0.8 L/m(2)/h at 35 °C. The continual anthropogenic pollutant release (CAPR) not only consisted of sweat, particles (mainly skin fragments and hair) and micro-organisms, but also sebum (skin lipids) has to be considered. The release of most components can be explained by the composition of sweat. The average release during 30 min of exercise is 250 mg/bather non-purgeable organic carbon (NPOC), 77.3 mg/bather total nitrogen (TN), 37.1 mg/bather urea and 10.1 mg/bather ammonium. The release of NPOC cannot be explained by the composition of sweat and is most probably a result of sebum release. The average release of other components was 1.31 × 10(9) # particles/bather (2-50 µm), 5.2 µg/bather intracellular adenosine triphosphate (cATP) and 9.3 × 10(6) intact cell count/bather (iCC). The pool water temperature was the main parameter to restrain the CAPR. This study showed that a significant amount of the total anthropogenic pollutants release is due to unhygienic behaviour of bathers.

In vivo acid etching effect on bacteria within caries-affected dentin.

Acid etching procedures may disrupt residual bacteria and contribute to the success of incomplete caries removal followed by adhesive restoration. This study evaluated the in vivo effect of acid etching on cariogenic bacterial activity within affected dentin after minimally invasive treatment of caries lesions. Twenty-eight carious permanent teeth received standardized selective caries removal and random acid etch treatment (E) or not (NE) prior to adhesive restoration. Baseline and 3-month dentin biopsies were collected. The number of bacteria and activity of total bacterial cells and Streptococcus mutans were determined by quantitative PCR and RT-PCR. No statistically significant differences were observed in total bacterial number and activity between E and NE treatments (p > 0.3008). For NE, however, the residual S. mutans bacterial cells were reduced (p = 0.0027), while the activity per cell was significantly increased (p = 0.0010) after reentry at 3 months after restoration. This effect was not observed in group E. Although no significant differences were found between groups, this study suggests that acid etching of affected dentin prior to adhesive restoration may directly or indirectly have an inhibitive effect on the activity of residual cariogenic bacteria. Further research is required to investigate this potential effect.

Polymeric system for dual growth factor delivery.

The development of tissues and organs is typically driven by the action of a number of growth factors. However, efforts to regenerate tissues (e.g., bone, blood vessels) typically rely on the delivery of single factors, and this may partially explain the limited clinical utility of many current approaches. One constraint on delivering appropriate combinations of factors is a lack of delivery vehicles that allow for a localized and controlled delivery of more than a single factor. We report a new polymeric system that allows for the tissue-specific delivery of two or more growth factors, with controlled dose and rate of delivery. The utility of this system was investigated in the context of therapeutic angiogenesis. We now demonstrate that dual delivery of vascular endothelial growth factor (VEGF)-165 and platelet-derived growth factor (PDGF)-BB, each with distinct kinetics, from a single, structural polymer scaffold results in the rapid formation of a mature vascular network. This is the first report of a vehicle capable of delivery of multiple angiogenic factors with distinct kinetics, and these results clearly indicate the importance of multiple growth factor action in tissue regeneration and engineering.

Minimally invasive operative care. II. Contemporary techniques and materials: an overview.

SUMMARY: Restorative dentistry has experienced a shift from the mainly reparative dentistry of the 20th century towards a minimal intervention approach. Contemporary operative treatment incorporates the MI philosophy in cavity design. Currently available techniques to pursue minimally invasive restorative treatments are highlighted. Characteristics of adhesive materials that facilitate minimally invasive operative care are discussed. CONCLUSION: When operative intervention is the designated treatment for initial caries, currently available operative techniques and contemporary materials warrant a minimally invasive approach. Minimal intervention applied to the operative field keeps the options open for long-term preservation of the restored tooth.

Minimally invasive operative care. I. Minimal intervention and concepts for minimally invasive cavity preparations.

SUMMARY: From the mainly reparative dentistry of the 20th century, contemporary dentistry shifts towards a minimal intervention (MI) approach encompassing up-to-date caries diagnosis and risk assessment before arriving at a treatment decision. An overview is provided of incorporating MI philosophy into the field of operative dentistry. The ultimate goal of MI is to extend the lifetime of restored teeth with as little intervention as possible. When operative care is indicated, it should be aimed at "prevention of extension." Black's principles for cavity design are considered and put in the perspective of minimally invasive operative care. Guiding principles for contemporary adhesive cavities are reviewed. CONCLUSION: Contemporary operative care should be based on a minimally invasive approach. Minimal intervention is not just a technique, it is a philosophy!

Engineering and characterization of functional human microvessels in immunodeficient mice.

SUMMARY: Current model systems used to investigate angiogenesis in vivo rely on the interpretation of results obtained with nonhuman endothelial cells. Recent advances in tissue engineering and molecular biology suggest the possibility of engineering human microvessels in vivo. Here we show that human dermal microvascular endothelial cells (HDMEC) transplanted into severe combined immunodeficient (SCID) mice on biodegradable polymer matrices differentiate into functional human microvessels that anastomose with the mouse vasculature. HDMEC were stably transduced with Flag epitope or alkaline phosphatase to confirm the human origin of the microvessels. Endothelial cells appeared dispersed throughout the sponge 1 day after transplantation, became organized into empty tubular structures by Day 5, and differentiated into functional microvessels within 7 to 10 days. Human microvessels in SCID mice expressed the physiological markers of angiogenesis: CD31, CD34, vascular cellular adhesion molecule 1 (VCAM-1), and intercellular adhesion molecule 1 (ICAM-1). Human endothelial cells became invested by perivascular smooth muscle alpha-actin-expressing mouse cells 21 days after implantation. This model was used previously to demonstrate that overexpression of the antiapoptotic protein Bcl-2 in HDMEC enhances neovascularization, and that apoptotic disruption of tumor microvessels is associated with apoptosis of surrounding tumor cells. The proposed SCID mouse model of human angiogenesis is ideally suited for the study of the physiology of microvessel development, pathologic neovascular responses such as tumor angiogenesis, and for the development and investigation of strategies designed to enhance the neovascularization of engineered human tissues and organs.

Sustained release of vascular endothelial growth factor from mineralized poly(lactide-co-glycolide) scaffolds for tissue engineering.

Strategies to engineer bone tissue have focused on either: (1) the use of scaffolds for osteogenic cell transplantation or as conductive substrates for guided bone regeneration; or (2) release of inductive bioactive factors from these scaffold materials. This study describes an approach to add an inductive component to an osteoconductive scaffold for bone tissue engineering. We report the release of bioactive vascular endothelial growth factor (VEGF) from a mineralized, porous, degradable polymer scaffold. Three dimensional, porous scaffolds of the copolymer 85 : 15 poly(lactide-co-glycolide) were fabricated by including the growth factor into a gas foaming/particulate leaching process. The scaffold was then mineralized via incubation in a simulated body fluid. Growth of a bone-like mineral film on the inner pore surfaces of the porous scaffold is confirmed by mass increase measurements and quantification of phosphate content within scaffolds. Release of 125I-labeled VEGF was tracked over a 15 day period to determine release kinetics from the mineralized scaffolds. Sustained release from the mineralized scaffolds was achieved, and growth of the mineral film had only a minor effect on the release kinetics from the scaffolds. The VEGF released from the mineralized and non-mineralized scaffolds was over 70% active for up to 12 days following mineralization treatment, and the growth of mineral had little effect on total scaffold porosity.

Bioabsorbable polymer scaffolds for tissue engineering capable of sustained growth factor delivery.

Engineering new tissues utilizing cell transplantation on biodegradable polymer matrices is an attractive approach to treat patients suffering from the loss or dysfunction of a number of tissues and organs. The matrices must maintain structural integrity during the process of tissue formation, and promote the vascularization of the developing tissue. A number of molecules (angiogenic factors) have been identified that promote the formation of new vascular beds from endothelial cells present within tissues, and the localized, controlled delivery of these factors from a matrix may allow an enhanced vascularization of engineered tissues. We have developed a gas foaming polymer processing approach that allows the fabrication of three-dimensional porous matrices from bioabsorbable materials (e.g., copolymers of lactide and glycolide [PLG]) without the use of organic solvents or high temperatures. The effects of several processing parameters (e.g., gas type, polymer composition and molecular weight) on the process were studied. Several gases (CO(2), N(2), He) were utilized in the fabrication process, but only CO(2) resulted in the formation of highly porous, structurally intact matrices. Crystalline polymers (polylactide and polyglycolide) did not form porous matrices, while amorphous copolymers (50:50, 75:25, and 85:15 ratio of lactide:glycolide) foamed to yield matrices with porosity up to 95%. The mechanical properties of matrices were also regulated by the choice of PLG composition and molecular weight. Angiogenic factors (e.g., vascular endothelial growth factor) were subsequently incorporated into matrices during the fabrication process, and released in a controlled manner. Importantly, the released growth factor retains over 90% of its bioactivity. In summary, a promising system for the incorporation and delivery of angiogenic factors from three-dimensional, biodegradable polymer matrices has been developed, and the fabrication process allows incorporation under mild conditions.

Controlled growth factor release from synthetic extracellular matrices.

Polymeric matrices can be used to grow new tissues and organs, and the delivery of growth factors from these matrices is one method to regenerate tissues. A problem with engineering tissues that exist in a mechanically dynamic environment, such as bone, muscle and blood vessels, is that most drug delivery systems have been designed to operate under static conditions. We thought that polymeric matrices, which release growth factors in response to mechanical signals, might provide a new approach to guide tissue formation in mechanically stressed environments. Critical design features for this type of system include the ability to undergo repeated deformation, and a reversible binding of the protein growth factors to polymeric matrices to allow for responses to repeated stimuli. Here we report a model delivery system that can respond to mechanical signalling and upregulate the release of a growth factor to promote blood vessel formation. This approach may find a number of applications, including regeneration and engineering of new tissues and more general drug-delivery applications.

Release from alginate enhances the biological activity of vascular endothelial growth factor.

A primary factor which limits engineering tissues of substantial size is the lack of nutrients readily available to transplanted cells. One potential solution to this nutrient limitation is to encourage the rapid development of a vascular network within three-dimensional tissue engineering matrices. Vascular endothelial growth factor (VEGF) has been identified as a potent stimulator of angiogenesis in vivo. Though effective at stimulating endothelial cells to form blood vessels VEGF degrades rapidly. Spherical alginate beads (3.3+/-0.1 mm diameter) were examined as a means of delivering biologically functional VEGF at a controlled rate over extended times. The alginate beads demonstrated the ability to incorporate VEGF with an efficiency between 30 and 67%, depending on the processing conditions, and release it at a constant rate (5%/day) for up to 14 days in vitro. The released VEGF, when assayed for its ability to stimulate endothelial cells in culture, was found not only to be functional but more potent (three to five times) than the same mass of VEGF added directly to the culture medium. The release kinetics of freeze dried VEGF containing alginate beads were also examined and found to be comparable to non-freeze dried samples.

Development of technologies aiding large-tissue engineering.

There are many clinical situations in which a large tissue mass is required to replace tissue lost to surgical resection (e.g., mastectomy). It is possible that autologous cell transplantation on biodegradable polymer matrices may provide a new therapy to engineer large tissue which can be used to treat these patients. A number of challenges must be met to engineer a large soft tissue mass. These include the design of (1) a structural framework to maintain a space for tissue development, (2) a space-filling matrix which provides for localization of transplanted cells, and (3) a strategy to enhance vascularization of the forming tissue. In this paper we provide an overview of several technologies which are under development to address these issues. Specifically, support matrices to maintain a space for tissue development have been fabricated from polymers of lactide and glycolide. The ability of these structures to resist compressive forces was regulated by the ratio of lactide to glycolide in the polymer. Smooth muscle cell seeding onto polyglycolide fiber-based matrices has been optimized to allow formation of new tissues in vitro and in vivo. Finally, polymer microsphere drug delivery technology is being developed to release vascular endothelial growth factor (VEGF), a potent angiogenic molecule, at the site of tissue formation. This strategy, which combines several different technologies, may ultimately allow for the engineering of large soft tissues.