Technical Note: Alternating clinical usage of the integral quality monitor transmission detector.

PURPOSE: The purpose of the study was the implementation of a method to use the integral quality monitor (IQM) transmission detector for occasional, alternating usage during patient treatment with intensity modulated radiotherapy. Due to attenuation, the transmission detector must be taken into account during the planning process. The proposed workflow is based on determining a dynamic transmission factor (dTF) required to scale the total number of MU of the original radiotherapy (RT) plan. Thus a very similar radiation therapy plan is obtained that can be used with the IQM detector. METHODS: Ten clinically applied volumetric modulated arc therapy plans were delivered at two beam qualities. A dTF is calculated from each RT plan for which a collapsed RT plan was created for verification using a two-dimensional array with and without the IQM detector. The total number of MU of the original RT plan was scaled by the inverse of the dTF to obtain the modified RT plan for clinical use with the IQM detector. Validation was performed with an electronic three-dimensional phantom and via gamma analysis using strict criteria of 1%/1 mm. RESULTS: Except for one outlier, the gamma pass rate between the original RT plan without IQM and the modified RT plan with IQM was always above 99.5%. The variations of the dTF were smaller than 1% for all tested RT plans. CONCLUSIONS: The results show that the proposed workflow can be used clinically. Thus the IQM transmission detector can also be used occasionally for online verification of RT plans.

Mechanistic Insights into the Directed Assembly of Hydrogel Blocks Mediated by Polyelectrolytes or Microgels.

In this study, we report the directed assembly of hydrogel blocks mediated by electrostatic interactions. We compared two different assembly mechanisms, one mediated by microgel particles and another mediated by direct interaction between oppositely charged blocks. The system consisted of hydrogel blocks made of an interpenetrated network of (hydroxyethyl)methacrylate-poly(ethylene glycol)dimethacrylate (HEMA-PEGDMA) and either positively charged polyethylenimine (PEI) or negatively charged hyaluronic acid (HA). Positively charged hydrogel blocks were pretreated with negatively charged microgel particles (MG) made of N-isopropylacrylamide-methacrylic acid. Both systems (PEI/HA and PEI/MG) demonstrated spontaneous directed assembly, meaning that positive blocks were systematically found in contact with oppositely charged blocks. Directed assembly in water of PEI/HA blocks resulted in large and open aggregates, while PEI/MG blocks exhibited more compact aggregates. Effects of salt and pH were also assessed for both systems. Inhibition of blocks aggregation was found to appear above a critical salt concentration (CSalt*) which was significantly higher for the PEI/HA system (80 mM) compared to the PEI/MG system (5-20 mM). The observed difference was interpreted in terms of the nanostructure of the contact area between blocks. Blocks aggregation was also found to be controlled by the content of negatively charged groups in the microgels as well as the concentration of MG in the suspension (CMG) used to treat the hydrogel block surfaces. Our results shine light on the subtle differences underlying the adhesion mechanisms between hydrogel blocks and suggest new routes toward the design of innovative complex soft materials.

2D, 3D and 4D active compound delivery in tissue engineering and regenerative medicine.

Recent advances in tissue engineering and regenerative medicine have shown that controlling cells microenvironment during growth is a key element to the development of successful therapeutic system. To achieve such control, researchers have first proposed the use of polymeric scaffolds that were able to support cellular growth and, to a certain extent, favor cell organization and tissue structure. With nowadays availability of a large pool of stem cell lines, such approach has appeared to be rather limited since it does not offer the fine control of the cell micro-environment in space and time (4D). Therefore, researchers are currently focusing their efforts on developing strategies that include active compound delivery systems in order to add a fourth dimension to the design of 3D scaffolds. This review will focus on recent concepts and applications of 2D and 3D techniques that have been used to control the load and release of active compounds used to promote cell differentiation and proliferation in or out of a scaffold. We will first present recent advances in the design of 2D polymeric scaffolds and the different techniques that have been used to deposit molecular cues and cells in a controlled fashion. We will continue presenting the recent advances made in the design of 3D scaffolds based on hydrogels as well as polymeric fibers and we will finish by presenting some of the research avenues that are still to be explored.