Hsieh Chen

Fractal dimension analysis of periapical reactive bone in response to root canal treatment

OBJECTIVE Mathematical morphology and box counting were used to extract trabecular pattern and to evaluate changes of reactive bone following root canal treatment. STUDY DESIGN Periapical radiographs were digitized and processed with mathematical morphology operations known as skeletonization. The trabecular patterns resulting from this skeletonization process were further analyzed with fractal dimension (FD) analysis using the box-counting method. Two groups of regions of interest (ROI) were selected from 19 subjects for the analysis. RESULTS Seventeen patients in one group and 13 patients in the other showed decreased FD in the reactive bone region after clinically successful root canal treatment (RCT). Significant changes in FD were noted 6 months after RCT (P < .05). Kappa analysis indicated significant reproducibility between the 2 groups of ROIs. CONCLUSIONS Mathematical morphology combined with box counting showed decrease of FD in reactive bone regions after clinically successful endodontic treatment.

Structure and dynamics of blood-clotting-inspired polymer-colloid composites

Dynamic protein and cell aggregates form during the process of blood clotting, particularly in the initial stages where the crosslinks are physical. These aggregates are the scaffold for the final clot. Recently, it has been shown that such aggregates can be formed in the absence of cells, using silica colloids instead [H. Chen, M. A. Fallah, V. Huck, J. I. Angerer, A. J. Reininger, S. W. Schneider, M. F. Schneider and A. Alexander-Katz, Nat. Commun., 2013, 4, 1333]. Here we study the dynamics and structure of such aggregates using computer simulations. Our models are highly coarse-grained, and allow us to probe large length scales over long time scales. Here, we probe the system changing multiple aspects that contribute to the aggregation process, namely density of polymers and colloids, length of polymers, number of binding units per chain, shear rate, etc. In particular we find that the dynamics and structure of the polymers is dominated by the length of the polymers, as well as the number of binders per polymer. Interestingly the density does not have a large effect. Counter-intuitively, long polymers tend to form looser aggregates and sharply transform at higher rates to rather dense aggregates, while at lower rates the structure of the aggregates for the smaller polymers is much more compact. For all the different conditions, we find that they all behave qualitatively the same, yet there are some marked quantitative differences that can be exploited in real experiments. Our results complement recent studies on such aggregates and are important for understanding this newly discovered class of aggregates that could potentially have applications in multiple technologies.

Lattice Boltzmann method for multiscale self-consistent field theory simulations of block copolymers

A new Lattice Boltzmann (LB) approach is introduced to solve for the block copolymer propagator in polymer field theory. This method bridges two desired properties from different numerical techniques, namely: (i) it is robust and stable as the pseudo-spectral method and (ii) it is flexible and allows for grid refinement and arbitrary boundary conditions. While the LB method is not as accurate as the pseudo-spectral method, full self-consistent field theoretic simulations of block copolymers on graphoepitaxial templates yield essentially indistinguishable results from pseudo-spectral calculations. Furthermore, we were able to achieve speedups of ~100× compared to single CPU core implementations by utilizing graphics processing units. We expect this method to be very useful in multi-scale studies where small length scale details have to be resolved, such as in strongly segregating block copolymer blends or nanoparticle-polymer interfaces.

Multidimensional targeting: using physical and chemical forces in unison.

Targeted drug delivery has traditionally relied on finding highly specific biochemical markers at a target location. However, recent developments in this area have shown that purely physical and physicochemical factors are as important and can be used to aid in the targeting process. Here, we review the physicochemical factors affecting the targeting and delivery process and their relation to established biochemical markers. We refer to this combined approach as multidimensional targeting (MDT). More specifically, we examine the role of MDT factors across different length scales of relevance to the drug delivery pathway. Finally, we conclude with our perspective on the future of this burgeoning area.