Surface modification of polyethylene terephthalate using PEO-polybutadiene-PEO triblock copolymers

The initial step of thrombus formation on blood-contacting biomaterials is known to be adsorption of blood proteins followed by platelet adhesion. It is generally accepted that surface modification of the biomaterials with poly(ethylene oxide) (PEO) substantially reduces protein adsorption and cell adhesion. Dacron® (polyethylene terephthalate) fabric, which is one of the biomaterials commonly used in blood-contacting devices, was grafted with PEO. A simple two-step procedure for covalent grafting of PEO onto the surface of Dacron® fabric was used. The surface was first treated with PEO-polybutadiene-PEO (PEO-PB-PEO) triblock copolymer, to introduce a layer of double bonds onto the surface. The Dacron® surface was then exposed to a solution of Pluronic® F108 (PF108), a commercially available PEO-poly(propylene oxide)-PEO (PEO-PPO-PEO) triblock copolymer. The surface with two adsorbed layers of PEO-PB-PEO and PF108 was γ-irradiated in the presence of PF108 in the bulk solution for a total radiation dose of 0.8 Mrad. The bulk concentrations of PEO-PB-PEO and PF108 were varied to maximize the efficiency of PEO grafting. Fibrinogen adsorption on PEO-grafted surfaces was reduced more than 90%, compared with that on control surfaces, irrespective of the bulk concentrations of polymers used for grafting. Platelet adhesion was also reduced substantially by PEO grafting. Only a few round platelets were able to adhere to the PEO-grafted surface, while the control surface was fully covered with aggregates of activated platelets. PEO grafting on polyethylene terephthalate using PEO-PB-PEO and PEO-PPO-PEO block copolymers is a simple approach that can be used for various other biomaterials.     

Loading Rate Effects for Flaws Undergoing Mixed-Mode I/III Fracture

Experimental Mechanics - The effect of loading rate on the fracture properties of materials had been the subject of interest for more than four decades. However, the effect of loading rates on...     

Chemo‐ and Stereoselective Iron‐Catalyzed Hydrosilylation of Ketones

The reduction of ketones with polymethylhydrosiloxane (PMHS) gives the corresponding alcohols in good to excellent yield applying iron‐based catalyst systems. In the case of prochiral ketones, the use of Fe(OAc)₂/(S,S)‐Me‐DuPhos leads to high enantioselectivity up to 99 % ee. The reaction proceeds in the presence of several functional groups such as esters, halides as well as conjugated double bonds, with high chemoselectivity. The advantage of this protocol is that the reaction requires no activating agents or additives.     

Ryle and Intentionality

After some opening comments on how I think one should approach the philosophy of mind, I look at what relatively little Gilbert Ryle had to say explicitly about intentionality, that occurring almost exclusively in his several papers on phenomenology. Then, I discuss the notion of intentionality with respect to the doctrines of The Concept of Mind, although neither the word nor the idea, strictly speaking, appears anywhere in the book. Following more exposition of my own views, including an argument I have made for a certain specific theory of intentionality, I close with some reflections on Ryle as a modern-day Aristotelian.     

Docking of Atomic Clusters Through Nonlinear Optimization

The problem of molecular docking is defined as that of finding a minimum energy configuration of a pair of molecular structures (usually consisting of proteins, DNA or RNA fragments). It is often assumed that the two interacting structures can be considered as rigid bodies and that it is of interest to researchers to develop methods which enable to discover the potential binding sites. Many different models have been proposed in the literature for the definition of the potential energy between two molecular structures, most of which contain at least a term (known as Van Der Waals interaction) which accounts for pairwise attraction between atoms, a repulsion term and a term which takes into account electrostatic forces (Coulomb interaction). Some well known models, and in particular those used in rigid docking, are based on the assumption that the only terms which are relevant in the process of docking are pairwise interactions between atoms belonging to the two different parts of the structure. In this paper the problem of finding the lowest energy configuration of a pair of biomolecular structures, considered as rigid bodies, is defined and formulated as a global optimization problem. In terms of dimension of the search space this formulation is not 'high-dimensional', as there are only six degrees of freedom: 3 translation and 3 rotation parameters. However the energy surface of the docking problem is characterized by a huge number of local minima; moreover each function evaluation is quite expensive (interesting structures usually possess a few thousand atoms each). So there is a strong need both of local and of global optimization procedures. In this paper a local optimization technique, based upon standard non linear programming software and a penalized objective function, is introduced and its potential usefulness in the context of global optimization is outlined.