Functionalized copolymers and their composites with polylactide and hydroxyapatite

Synthetic copolymers poly(-caprolactone-co-vinylphosphonic acid) (P(MDOVPA) and poly(-caprolactone-co-dimethylvinylphosphoester) (P(MDOVPE)) were used to prepare composites with polylactide (PLac) and hydroxyapatite (HAp). The P(MDOVPA) is used as filler in PLac films, as it has pendant functional groups P(O)(OH)₂, providing nucleation sites for the deposition of HAp in simulated body fluid. HAp growth on P(MDOVPA) powder and PLac-P(MDOVPA) film was observed by Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD). P(MDOVPE) and PLac blend are miscible, and the incorporation of hydrophilic P(MDOVPA) into PLac increased the hydrophilicity of the blend. Synthetic HAp was used to make multilayered, alternating organic–inorganic composites with porous PLac-P(MDOVPE) blends. ©©1999©Kluwer Academic Publishers     

Non cell adhesive photopolymerized cross-linked layers (I): synthesis and characterization

The aim of this study is to design an effective hydrogel, which has good potential for application in the field of tissue regeneration. Ultimately, the polymeric biomaterial will be used as a bottom, non-cell adhering layer of a polymeric scaffold, which will inhibit the adhesion and proliferation of fibroblast cells. A series of terpolymer hydrogels were prepared from MMA/HPOEM/MePOEM monomers based on varying formulations. The gels were polymerized via free radical polymerization under UV and characterized by TGA, DSC and FTIR studies. Furthermore, the double bond conversion, gel content and swelling properties of the polymer were analyzed and correlated to its crosslinking density, which revealed details about the hydrogels character. Finally, cell culture experiments were used to compare the UV-cured polymer to its thermally derived non-functionalized polymer of the same formulation. Inverted optical microscopy was used to demonstrate cell-resistance of both materials with respect to a control Tissue Culture PolyStyrene plate. ©2003 Kluwer Acadamic Publishers     

Development of potentially degradable materials for marine applications. III. Polyethylene-polyethylene oxide blends

The effect of a simulated marine environment on unstabilized polyethylene-polyethylene oxide blends, having varying polyethylene oxide content (up to 40% by weight), with or without a metal catalyst (e.g., cobalt (III) acetylacetonate) and a metal containing plasticizer (e.g., aluminum stearate), has been studied for 10 weeks exposure time. In the absence of metal catalyst and plasticizer, phase separation of polyethylene oxide was quite evident visually after melt mixing and subsequent regular compression molding of polyethylene-polyethylene oxide blends. However, these blends rendered better and uniform mixing in the presence of metal catalyst and plasticizer. Since polyethylene oxide is a water soluble component of the system, % weight loss increased significantly with increase in its content after exposure to brine. These blends have been further characterized by tensile properties, optical and scanning electron microscopy, and thermal analysis in order to monitor mechanical as well as morphological changes.     

Synthesis of Aluminum Nitride/Boron Nitride Composite Materials

Aluminum nitride/boron nitride composite was synthesized by using boric acid, urea, and aluminum chloride (or aluminum lactate) as the starting compounds. The starting materials were dissolved in water and mixed homogeneously. Ammonolysis of this aqueous solution resulted in the formation of a precomposite gel, which converted into the aluminum nitride/boron nitride composite on further heat treatment. Characterization of both the precomposite and the composite powders included powder X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Analysis of the composite revealed that the aluminum nitride phase had a hexagonal structure, and the boron nitride phase a turbostratic structures.     

The effects of rigidity of internal fixation plates on long bone remodeling. A biomechanical and quantitative histological study

The effect of rigidity of internal fixation plates on long bone remodeling was studied using two types of plates with considerable differences in stiffness. The plated bones were subjected to bioengineering quantitative histological, and cortical thickness studies after 9 and 12 months. The biomechanical results, together with the quantitative histological measurements of the macroscopic architecture, showed that tissue characteristics of the plated bones were similar. However, because of the larger cortical area, the less regidly plated femora can sustain significantly higher loads and energy before failure. Cortical thickness measurements also showed that rigid plate immobilization results in thinning of the cortex of the underlying bone. The experimental results suggest that cortical bone remodels according to functional stress demands, and the osteoporosis secondary to rigid plate protection is consequent to thinking of its cortex.     

Self‐Healing of a Confined Phase Change Memory Device with a Metallic Surfactant Layer

Understanding and possibly recovering from the failure mechanisms of phase change memories (PCMs) are critical to improving their cycle life. Extensive electrical testing and postfailure electron microscopy analysis have shown that stuck–set failure can be recovered. Here, self‐healing of novel confined PCM devices is directly shown by controlling the electromigration of the phase change material at the nanoscale. In contrast to the current mushroom PCM, the confined PCM has a metallic surfactant layer, which enables effective Joule heating to control the phase change material even in the presence of a large void. In situ transmission electron microscope movies show that the voltage polarity controls the direction of electromigration of the phase change material, which can be used to fill nanoscale voids that form during programing. Surprisingly, a single voltage pulse can induce dramatic migration of antimony (Sb) due to high current density in the PCM device. Based on the finding, self‐healing of a large void inside a confined PCM device with a metallic liner is demonstrated for the first time.     

A joint feature selection framework for multivariate resource usage prediction in cloud servers using stability and prediction performance

Resource provisioning in cloud servers depends on future resource utilization of different jobs. As resource utilization trends vary dynamically, effective resource provisioning requires prediction of future resource utilization. The problem becomes more complicated as performance metrics related to one resource may depend on utilization of other resources also. In this paper, different multivariate frameworks are proposed for improving the future resource metric prediction in cloud. Different techniques for identifying the set of resource metrics relevant for the prediction of desired resource metric are analyzed. The proposed multivariate feature selection and prediction frameworks are validated for CPU utilization prediction in Google cluster trace. Joint analysis based on the prediction performance of the multivariate framework as well as its stability is used for selecting the most suitable feature selection framework. The results of the joint analysis indicate that features selected using the Granger causality technique perform best for multivariate resource usage prediction.     

Surgical and endovascular intervention for infrainguinal vein graft stenosis

PURPOSE: The purpose of this study was to evaluate the stenosis-free patency of open repair (vein-patch angioplasty, interposition, jump grafting) and percutaneous transluminal balloon angioplasty (PTA) of 144 vein graft stenoses that were detected during duplex scan surveillance after infrainguinal vein bypass grafting. METHODS: Patients who underwent revision of an infrainguinal vein bypass graft were analyzed for type of vein conduit, vascular laboratory findings leading to revision, repair techniques, assisted graft patency rate, procedure mortality rate, and restenosis of the repair site. RESULTS: The time of postoperative revision ranged from 1 day to 133 months (mean, 13 months). One hundred eighteen primary and 26 recurrent stenoses (peak systolic velocity, >300 cm/s) in 52 tibial and 35 popliteal vein bypass grafts were identified by means of duplex scanning. The repairs consisted of 77 open procedures (vein-patch angioplasty, 28; vein interposition, 33; jump graft, 9; primary repair, 3) and 67 PTAs. No patient died as a result of intervention. Cumulative assisted graft patency rate (life-table analysis) was 91% at 1 year and 80% at 3 years. At 2 years, cumulative assisted graft patency rate was comparable for saphenous vein grafts (reversed, 94%; in situ, 88%; nonreversed, 63%) and alternative vein grafts (89%). Stenosis-free patency rate at 2 years was identical (P =.55) for surgical intervention (63%) and endovascular intervention (63%) but varied with type of surgical revision (P =.04) and time of intervention (<4 months, 45%; >4 months, 71%; P =.006). The use of duplex scan-monitored PTA to treat focal stenoses (<2 cm) and late-appearing stenoses (>3 months) was associated with a stenosis-free patency rate that was 89% at 1 year. After intervention, the alternative vein bypass grafts necessitated twice the reinterventions per month of graft survival (P =.01). Bypass graft to the popliteal versus infrageniculate arteries, site of graft stenosis (vein conduit, anastomotic region), and repair of a primary versus a recurrent stenosis did not influence the outcome after intervention. CONCLUSION: The revision of duplex scan-detected vein graft stenosis with surgical or endovascular techniques was associated with an excellent patency rate, including when intervention on alternative vein conduits or treatment of restenosis was necessary. When PTA was selected on the basis of clinical and duplex scan selection criteria, the endovascular treatment of focal vein graft stenosis was effective, durable, and comparable with the surgical revision of more extensive lesions.