bluuebunny/crossref_metadata_2025 huggingface dataset:
E‐model based comparison of multiple description coding and layered coding in packet networks
Authors: Zhou Yugang , Chan Wai‐Yip
Published: February 2007

We examine the performance of multiple description coding (MDC) with and without the use of automatic repeat request (ARQ) protocols for packet network communication, in comparison with layered coding (LC). The rate‐distortion lower bound of MDC and LC are incorporated into an E‐model based performance measure, which accounts for the additional costs of excess rates and delay incurred from using ARQ. The results show that the relative merits of the schemes depend on the values of the packet loss rates and round‐trip‐time (RTT). LC is superior for small RTT and unaided MDC is superior for large RTT. For moderate RTT, LC is preferred for small packet loss rates and MDC aided by ARQ is preferred for large packet loss rates. Copyright © 2007 John Wiley & Sons, Ltd.
Radio‐optic demonstrator for distributed antenna system indoor wireless applications using low‐cost VCSELs
Authors: Dayoub Iyad , Zaouche Abdelouahib , Rouvaen Jean Michel , Lethien Christophe , Vilcot Jean‐Pierre , Decoster Didier
Published: February 2007

Integration of wireless and optical networks would offer a potential solution for high bandwidth, mobility and cost reduction in the access networks. Radio over optical fibre (RoF) combines the capacity of optical networks with the flexibility and mobility of wireless access networks. In this paper, an economic demonstrator for RoF indoor applications is proposed using in‐building pre‐installed multimode fibre (MMF), low cost 850 nm VCSELs and 50 µm MMF pigtailed photodiodes. The system is dedicated to Distributed Antenna System (DAS) indoor wireless applications. To evaluate our system, error vector magnitude (EVM) measurements and eye‐diagrams have been demonstrated. Copyright © 2007 John Wiley & Sons, Ltd.
Proxy caching algorithms and implementation for time‐shifted TV services
Authors: Wauters Tim , Van De Meerssche Wim , Backx Peter , De Turck Filip , Dhoedt Bart , Demeester Piet , Van Caenegem Tom , Six Erwin
Published: February 2007

The increasing popularity of multimedia streaming applications introduces new challenges in content distribution networks (CDNs). Streaming services such as Video on Demand (VoD) or digital television over the Internet (IPTV) are very bandwidth‐intensive and cannot tolerate the high start‐up delays and poor loss properties of today's Internet. To solve these problems, caching (the initial segment of) popular streams at proxies could be envisaged. This paper presents a novel caching algorithm and architecture for time‐shifted television (tsTV) and its implementation, using the IETF's Real‐Time Streaming Protocol (RTSP). The algorithm uses sliding caching windows with sizes depending on content popularity and/or distance metrics. The caches can work in stand‐alone mode as well as in co‐operative mode. This paper shows that the network load can already be reduced considerably using small diskless caches, especially when using co‐operative caching. A prototype implementation is detailed and evaluated through performance measurements. Copyright © 2007 John Wiley & Sons, Ltd.
The presence of active Cdk5 associated with p35 in astrocytes and its important role in process elongation of scratched astrocyte
Authors: He Yi , Li Hui‐Li , Xie Wei‐Yan , Yang Chun‐Zhang , Yu Albert Cheung Hoi , Wang Yun
Published: February 2007

Cyclin‐dependent kinase 5 (Cdk5) is a unique member of the Cdk family; its kinase activity requires association with its activator, p35 or p39. p35 is the strongest and best characterized activator. Previous studies showed that p35 is a neuron‐specific protein that restricts Cdk5 activity in neurons. However, a high expression level of Cdk5 is found in astrocytes, which raises the possibility that astrocytic Cdk5 is functional. Here we show the presence of functional Cdk5 associated with p35 in astrocytes and demonstrate its important role in process elongation of scratched astrocytes. We found that p35 and glial fibrillary acidic protein (GFAP) were co‐localized in primary cultured and acute isolated brain cells. Cdk5 could form an immunocomplex with p35 and its activity was shown in pure primary cultured astrocytes. p35 was upregulated in astrocytes injured by scratching, concomitantly with upregulation of Cdk5 kinase activity. Pretreatment of the scratched astrocytes with a Cdk5 inhibitor, roscovitine, could delay wound healing by inhibiting the reorganization of tubulin, GFAP, and the extension of hypertrophic processes. Moreover, overexpression of dominant negative Cdk5 could shorten the length of extending protrusion of reactive astrocytes. Thus, our findings demonstrated that functional Cdk5, associated with p35, was expressed in astrocytes and its activity could be upregulated in reactive astrocytes, a new role of Cdk5 that has never been reported in the nervous system. The present study may provide new insight for understanding the multifunctional protein complex Cdk5/p35 in the nervous system. © 2007 Wiley‐Liss, Inc.
Single‐trial analysis of oddball event‐related potentials in simultaneous EEG‐fMRI
Authors: Bénar Christian‐G. , Schön Daniele , Grimault Stephan , Nazarian Bruno , Burle Boris , Roth Muriel , Badier Jean‐Michel , Marquis Patrick , Liegeois‐Chauvel Catherine , Anton Jean‐Luc
Published: February 2007

There has recently been a growing interest in the use of simultaneous electroencephalography (EEG) and functional MRI (fMRI) for evoked activity in cognitive paradigms, thereby obtaining functional datasets with both high spatial and temporal resolution. The simultaneous recording permits obtaining event‐related potentials (ERPs) and MR images in the same environment, conditions of stimulation, and subject state; it also enables tracing the joint fluctuations of EEG and fMRI signals. The goal of this study was to investigate the possibility of tracking the trial‐to‐trial changes in event‐related EEG activity, and of using this information as a parameter in fMRI analysis. We used an auditory oddball paradigm and obtained single‐trial amplitude and latency features from the EEG acquired during fMRI scanning. The single‐trial P300 latency presented significant correlation with parameters external to the EEG (target‐to‐target interval and reaction time). Moreover, we obtained significant fMRI activations for the modulation by P300 amplitude and latency, both at the single‐subject and at the group level. Our results indicate that, in line with other studies, the EEG can bring a new dimension to the field of fMRI analysis by providing fine temporal information on the fluctuations in brain activity. Hum Brain Mapp, 2007. © 2007 Wiley‐Liss, Inc.
Psychiatric disorders and labor market outcomes: evidence from the National Latino and Asian American Study
Authors: Chatterji Pinka , Alegría Margarita , Lu Mingshan , Takeuchi David
Published: February 2007

This paper investigates to what extent psychiatric disorders and mental distress affect labor market outcomes in two rapidly growing populations that have not been studied to date–ethnic minorities of Latino and Asian descent, most of whom are immigrants. Using data from the National Latino and Asian American Study (NLAAS), we examine the labor market effects of meeting diagnostic criteria for any psychiatric disorder in the past 12 months as well as the effects of psychiatric distress in the past year. The labor market outcomes analyzed are current employment status, the number of weeks worked in the past year among those who are employed, and having at least one work absence in the past month among those who are employed. Among Latinos, psychiatric disorders and mental distress are associated with detrimental effects on employment and absenteeism, similar to effects found in previous analyses of mostly white, American born populations. Among Asians, we find more mixed evidence that psychiatric disorders and mental distress detract from labor market outcomes. Our findings suggest that reducing disparities and expanding access to effective treatment may have significant labor market benefits–not just for majority populations, as has been demonstrated, but also for Asians and Latinos. Copyright © 2007 John Wiley & Sons, Ltd.
Improving the measurement of health system output growth
Authors: Castelli Adriana , Dawson Diane , Gravelle Hugh , Street Andrew
Published: February 2007

National income accounting practice is to weight health service activities by their cost so that they can be aggregated into an output index. Quality changes are ignored. We propose an ‘ideal’ value weighted output index in which the value attached to each output reflects its contribution to health outcomes and other characteristics valued by patients. Calculation of the index for the health system as a whole is currently infeasible because of a lack of data, especially on health outcomes. We demonstrate alternative ways of combining health outcome data with existing information on post‐treatment survival, life expectancy and waiting times to construct quality adjusted cost weighted and health outcome weighted indices for a small set of hospital activities for which there are health outcome data. Copyright © 2007 John Wiley & Sons, Ltd.
Demand assessment and price‐elasticity estimation of quality‐improved primary health care in palestine: a contribution from the contingent valuation method
Authors: Mataria Awad , Luchini Stéphane , Daoud Yousef , Moatti Jean‐Paul
Published: February 2007

This paper proposes a new methodology to assess demand and price‐elasticity for health care, based on patients' stated willingness to pay (WTP) values for certain aspects of health care quality improvements. A conceptual analysis of how respondents consider contingent valuation (CV) questions allowed us to specify a probability density function of stated WTP values, and consequently, to model a demand function for quality‐improved health care, using a parametric survival approach. The model was empirically estimated using a CV study intended to assess patients' values for improving the quality of primary health care (PHC) services in Palestine. A random sample of 499 individuals was interviewed following medical consultation in four PHC centers. Quality was assessed using a multi‐attribute approach; and respondents valued seven specific quality improvements using a decomposed valuation scenario and a payment card elicitation technique. Our results suggest an inelastic demand at low user fees levels, and when the price‐increase is accompanied with substantial quality‐improvements. Nevertheless, demand becomes more and more elastic if user fees continue to rise. On the other hand, patients' reactions to price‐increase turn out to depend on their level of income. Our results can be used to design successful health care financing strategies that include a consideration of patients' preferences and financial capacities. Copyright © 2007 John Wiley & Sons, Ltd.
Biomembrane mimetic polymer poly (2‐methacryloyloxyethyl phosphorylcholine‐co‐n‐butyl methacrylate) at the interface of polyurethane surfaces
Authors: Lee I. , Kobayashi K. , Sun H.Y. , Takatani S. , Zhong L.G.
Published: February 2007

Polyurethane (PU) is widely used to make artificial heart and blood vessel wells; however, its thrombogenicity in vivo is still in question. The biomembrane‐mimetic and water‐soluble polymers, poly (2‐methacryloyloxyethyl phosphorylcholine‐co‐n‐butyl methacrylate) (PMB), were used to modify polyurethane (PU) surfaces for improving their hemocompatibility. The morphologies of the PMB modified PU surfaces were examined by using atomic force microscopy and the parameters of the PMB absorption kinetics were extracted from dynamic water contact angle measurements. Two‐phase domains, the hard and soft segment phases, were observed on the PU surfaces under the aqueous conditions. The absorbed PMB molecules formed the isolated layers first on the hydrophobic hard segments, and subsequently networked as the PMB concentration increased. The increments of PMB concentration led to the decrement of the effective molar activation (wetting) free energy ΔG. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Fabrication and characterization of porous hyaluronic acid–collagen composite scaffolds
Authors: Tang Shunqing , Vickers Scott M. , Hsu Hu‐Ping , Spector Myron
Published: February 2007

Hyaluronic acid (HA) plays a vital role in many tissues, influencing water content and mechanical function, and has been shown to have positive biological effects on cell behavior in vitro. To begin to determine whether these benefits can be accessed if HA is incorporated into collagen‐based scaffolds for tissue engineering, HA‐collagen composite matrices were prepared and selected properties evaluated. HA‐collagen scaffolds were cross‐linked with carbodiimide and loss rates of HA in culture medium assessed. Scaffold pore structures were evaluated by light and electron microscopy. Adult canine chondrocytes were grown in selected HA‐collagen scaffolds to assess the effects of HA on cell behavior. Homogenous HA‐collagen slurries were achieved when polyionic complexes were suppressed. HA was uniformly distributed through the scaffolds, which demonstrated honeycomb‐like pores with interconnectivity among pores increasing as HA content increased. Virtually all of the HA added to the collagen slurry was incorporated into the composite scaffolds that underwent a 7‐day cross‐linking protocol. After 5 days in culture medium, the HA content in the scaffolds was 5–7% regardless of initial HA loading. After only 2 weeks in culture cartilaginous tissue was found in the chondrocyte‐seeded HA‐collagen scaffolds. This study contributes to the understanding of the effects of HA content, pH, and cross‐link treatment on pore characteristics and degradation behavior essential for the design of HA‐collagen scaffolds. The demonstration that these scaffolds can be populated by chondrocytes and support in vitro formation of cartilaginous tissue warrants further investigation of this material system for tissue engineering. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Development of superporous hydroxyapatites and their examination with a culture of primary rat osteoblasts
Authors: Sakamoto Michiko , Nakasu Masanori , Matsumoto Toshio , Okihana Hiroyuki
Published: February 2007

When the usage of hydroxyapatite (HAp) was first approved at clinics by the Kouseishou (Japanese FDA) as a bone substitute (APACERAM), the upper limit of pore content was set at 60%. Cells play an important role in bone repair, especially in regeneration therapy, but on using these HAps, the cells cannot penetrate deeply into them because their inside pores rarely connect. To promote cell penetration into the inside of the HAps, we have developed superporous HAps (HAp‐Ss). First, phosphoric acid was added to a calcium hydroxide solution, and the mixture was dried by the spray‐dry method to produce fine primary particles. Then, two kinds of surfactants were used to form a large amount of pores. These two HAp‐Ss have 85% porosity and interconnected pores in the inside. They were tested with a culture of primary rat osteoblasts, which showed good penetration therein. The penetrated osteoblasts maintained high alkaline phosphatase activity during the culture period. This indicates that the developed HAp‐Ss are very good bone substitutes and also useful scaffolds in bone regeneration therapy. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Cationized pullulan 3D matrices as new materials for gene transfer
Authors: San Juan Aurélie , Hlawaty Hanna , Chaubet Frédéric , Letourneur Didier , Feldman Laurent J.
Published: February 2007

This study deals with the development of a novel biocompatible cationized pullulan three‐dimensional matrix for gene delivery. A water‐soluble cationic polysaccharide, diethylaminoethyl‐pullulan (DEAE‐pullulan), was first synthesized and characterized. Fluorescence quenching and gel retardation assays evidenced the complexation in solution of DNA with DEAE‐pullulan, but not with neutral pullulan. On cultured smooth muscle cells (SMCs) incubated with DEAE‐pullulan and a plasmid vector expressing a secreted form of alkaline phosphatase (pSEAP), SEAP activity was 150‐fold higher than with pSEAP alone or pSEAP with neutral pullulan. DEAE‐pullulan was then chemically crosslinked using phosphorus oxychloride. The resulting matrices were obtained in less than a minute and molded as discs of 12 mm diameter and 2 mm thickness. Such DEAE‐pullulan 3D matrices were loaded with up to 50 μg of plasmid DNA, with a homogeneous plasmid loading observed with YOYO‐1 fluorescence staining. Moreover, the DEAE‐pullulan matrix was shown to protect pSEAP from DNase I degradation. Incubation of cultured SMCs with pSEAP‐loaded DEAE‐pullulan matrices resulted in significant gene transfer without cell toxicity. This study suggests that these cationized pullulan 3D matrices could be useful biomaterials for local gene transfer. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
The role of the surface chemistry of CoCr alloy particles in the phagocytosis and DNA damage of fibroblast cells
Authors: Lewis A. C. , Ladon D. , Heard P. J. , Peto L. , Learmonth I.
Published: February 2007

Surface chemistry of CoCr particles is demonstrated to be fundamental to the process of phagocytosis by fibroblast cells in vitro. Particles preincubated in serum for 5 days and washed in water before addition to cell cultures were phagocytosed less readily than were particles preincubated in minimal essential medium (MEM) for 1 h and washed in water. This was explained by the coating of calcium phosphate and protein on the serum‐immersed particles investigated by time‐of‐flight secondary ion mass spectroscopy. The cells incubated with the serum‐immersed particles had a reduced mitotic index when compared with the MEM‐immersed particles, indicating that the phagocytosed particles were causing cell cycle arrest. The release of soluble ions measured by electrothermal atomic absorption spectroscopy within the first hour of particle immersion in MEM was identified as the most likely cause for the DNA damage measured by single cell gel electrophoresis (“Comet” assay). Cryofocused ion beam SEM with a spatial resolution of 8 nm was used to cross section cells, to investigate the location of the phagocytosed particles, some of which were found within the nuclear membrane. This paper demonstrated that consideration of the surface chemistry is essential to understand the processes of the effects of orthopedic wear debris. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Coating nanothickness degradable films on nanocrystalline hydroxyapatite particles to improve the bonding strength between nanohydroxyapatite and degradable polymer matrix
Authors: Nichols Heather L. , Zhang Ning , Zhang Jing , Shi Donglu , Bhaduri Sarit , Wen Xuejun
Published: February 2007

Hydroxyapatite (HA) nanoparticles are similar to bone apatite in size, phase composition, and crystal structure. When compared with micron‐size HA particles, nano‐HA possesses improved mechanical properties and superior bioactivity for promoting bone growth and regeneration. However, scaffolds fabricated from nano‐HA alone cannot meet the mechanical requirements for direct‐loading applications. A number of studies suggest that nanostructured composites may offer surface and/or chemical properties of native bone, and therefore represent ideal substrates to support bone regeneration. However, a common problem with nanohydroxyapatite (nano‐HA)–polymer composites is the weak binding strength between the nano‐HA filler and the polymer matrix since they are two different categories of materials and cannot form covalent bonds between them during the mixing process. Often, the mechanical strength of the composite is compromised due to the phase separation of the HA filler from the polymer matrix during the tissue repair process. To overcome this problem, an ultrathin degradable polymer film was grafted onto the surface of nano‐HA using a radio‐frequency plasma polymerization technology from acrylic acid monomers. The treated nano‐HA powders are expected to bind to the polymer matrix via covalent bonds, thus enhancing the mechanical properties of the resultant composites. High‐resolution transmission electron microscopy (HRTEM) experiments showed that an extremely thin polymer film (2 nm) was uniformly deposited on the surfaces of the nanoparticles. The HRTEM results were confirmed by X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectroscopy (TOFSIMS). Tensile tests performed on the specimens revealed that the degradable coating had improved elastic and strength properties when compared with the nondegradable and uncoated controls. XPS and TOSIMS data revealed that more functional carboxyl groups were formed on degradable coatings than cross‐linked nondegradable coatings. Cytocompatibility assay demonstrated that both the degradable and nondegradable coatings are cytocompatible. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Peptide surface modification of methacrylamide chitosan for neural tissue engineering applications
Authors: Yu Laura M. Y. , Kazazian Karineh , Shoichet Molly S.
Published: February 2007

Nerve fibres are guided to their targets by the combined actions of chemotactic and haptotactic stimuli; however, translating these stimuli to a scaffold that will promote nerve regeneration is nontrivial. In pursuit of this goal, we synthesized and characterized cell‐adhesive, biodegradable chitosan scaffolds. Chitosan amine groups were reacted with methacrylic anhydride resulting in a water soluble methacrylamide chitosan (MC) that was then crosslinked by radical polymerization resulting in a scaffold. Biodegradability by lysozyme and penetrability of the scaffold by rat superior cervical ganglion (SCG) neurons were studied. Maleimide‐terminated cell adhesive peptides, mi‐GDPGYIGSR and mi‐GQASSIKVAV, were coupled to a thiolated form of MC to promote cell adhesion. The MC scaffold was found to be porous, biodegradable, and to allow neurite penetration. Interestingly, all of these properties were found to depend upon the amount of initiator used in crosslinking. Covalent modification of the MC scaffold with cell adhesive peptides significantly improved neuronal adhesion and neurite outgrowth. The MC can be crosslinked to form a novel scaffold, where our results demonstrate its suitability in neural tissue engineering and its potential for other engineered tissues, such as cartilage repair, where chitosan has already demonstrated some utility. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Characterization of biomimetic calcium phosphate on phosphorylated chitosan films
Authors: Chesnutt B. M. , Yuan Y. , Brahmandam N. , Yang Y. , Ong J. L. , Haggard W. O. , Bumgardner J. D.
Published: February 2007

This study examined the effect of chitosan degree of deacetylation (DDA), concentration of simulated body fluid (SBF), and mineralization time on the composition, structure, and crystallinity of calcium phosphate (CaP) biomimetically deposited on chitosan and on osteoblast cell growth. Phosphorylated chitosan films of 92.3%, 87.4%, and 80.6% DDA were soaked in SBF (1.0× or 1.5×) for 7, 14, or 21 days. Scanning electron microscopy revealed that CaP precipitated from 1.5× SBF had a porous, granular morphology; while the coatings precipitated in 1.0× SBF were smoother and more uniform. X‐ray diffraction showed that films mineralized in 1.0× SBF were amorphous, while films mineralized in 1.5× SBF for 21 days exhibited crystalline peaks similar to hydroxyapatite, with the most crystalline peaks seen on 92.3% DDA chitosan. When mineralized films were placed in cell media for 14 days, more calcium phosphate precipitated onto all films, and the most calcium phosphate was found on 92.3% DDA films mineralized in 1.5× SBF. After seven days of osteoblast culture, there were approximately three times as many cells (based on DNA measurements, p < 0.05) on 92.3% DDA films soaked in 1.0× SBF for seven or 21 days than on 80.6% DDA films soaked in 1.0× SBF for any length of time or any films soaked in 1.5× SBF. The DDA of chitosan, concentration of SBF and mineralization time affect the structure of and biological response to chitosan/biomimetic CaP films, and these factors must be considered when designing new materials to be used in orthopaedic and dental/craniofacial implant applications. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Robotic deposition of model hydroxyapatite scaffolds with multiple architectures and multiscale porosity for bone tissue engineering
Authors: Dellinger Jennifer G. , Cesarano Joseph , Jamison Russell D.
Published: February 2007

Model hydroxyapatite (HA) scaffolds with porosities spanning multiple length scales were fabricated by robocasting, a solid freeform fabrication technique based on the robotic deposition of colloidal pastes. Scaffolds of various architectures including periodic, radial, and superlattice structures were constructed. Macropores (100–600 μm) were designed by controlling the arrangement and spacing between rods of HA. Micropores (1–30 μm) and submicron pores (less than 1 μm) were produced within the rods by including polymer microsphere porogens in the HA pastes and by controlling the sintering of the scaffolds. These model scaffolds may be used to systematically study the effects of scaffold porosity on bone ingrowth processes both in vitro and in vivo. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
In vitro growth and differentiated activities of human periodontal ligament fibroblasts cultured on salmon collagen gel
Authors: Nagai Nobuhiro , Mori Kazuo , Satoh Yasuharu , Takahashi Noritaka , Yunoki Shunji , Tajima Kenji , Munekata Masanobu
Published: February 2007

Marine‐derived collagen is expected to be a much safer alternative to calf collagen, which in medical applications carries the risk of bovine spongiform encephalopathy. In this study, acid‐soluble collagen was extracted from salmon skin and crosslinked with 1‐ethyl‐3‐(3‐dimethylaminopropyl)‐carbodiimide during fibril formation to produce a crosslinked salmon collagen (SC) gel. The growth rates and the differentiated functions of human periodontal ligament fibroblasts (HPdLFs) cultured on the SC gel were investigated. Growth was faster on the SC gel than on porcine collagen (PC) gel. In addition, the HPdLFs cultured on the SC gel exhibited higher alkaline phosphatase (ALP) activity than those cultured on the PC gel. Quantitative RT‐PCR revealed higher mRNA expression of type I collagen, ALP, and osteocalcin in the HPdLFs cultured on the SC gel. HPdLFs had a flat shape on the SC gel and a spindle shape on the PC gel, as revealed by observation with scanning electron microscopy and immunostaining with cytoskeletal protein and vinculin. The results showed that HPdLFs could grow and show highly differentiated activity on the SC gel as well as on the PC gel. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Novel tubular composite matrix for bone repair
Authors: Kofron M.D. , Cooper J.A. , Kumbar S.G. , Laurencin C.T.
Published: February 2007

Tissue engineering develops organ replacements to overcome the limitations associated with autografts and allografts. The work presented here details the development of biodegradable, porous, three‐dimensional polymer–ceramic‐sintered microsphere matrices to support bone regeneration. Poly(lactide‐co‐glycolide)/hydroxyapatite microspheres were formed using solvent evaporation technique. Individual microspheres were placed in a cylindrical mold and sintered at various temperatures. Scaffolds were characterized using scanning electron microscopy, mercury porosimetry, and mechanical testing in compression. After varying the temperature of sintering, a single temperature was selected and the time of sintering was varied. Mechanical testing indicated that as the sintering temperature or time was increased, the elastic modulus, compressive strength, maximum compressive load, and energy at failure significantly increased. Furthermore, increasing the sintering temperature or time resulted in a decreased porosity and the spherical morphology of the microspheres was lost as the microspheres blended together. To more closely mimic the bone marrow cavity observed in native bone tissue, tubular composite‐sintered microsphere matrices were formed. These scaffolds demonstrated no statistically significant difference in compressive mechanical properties when compared with cylindrical composite‐sintered microsphere matrices of the same dimension. One potential application for these scaffolds is bone regeneration. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Surface mechanical properties, corrosion resistance, and cytocompatibility of nitrogen plasma‐implanted nickel–titanium alloys: A comparative study with commonly used medical grade materials
Authors: Yeung K.W.K. , Poon R.W.Y. , Chu P.K. , Chung C.Y. , Liu X.Y. , Lu W.W. , Chan D. , Chan S.C.W. , Luk K.D.K. , Cheung K.M.C.
Published: February 2007

Stainless steel and titanium alloys are the most common metallic orthopedic materials. Recently, nickel–titanium (NiTi) shape memory alloys have attracted much attention due to their shape memory effect and super‐elasticity. However, this alloy consists of equal amounts of nickel and titanium, and nickel is a well known sensitizer to cause allergy or other deleterious effects in living tissues. Nickel ion leaching is correspondingly worse if the surface corrosion resistance deteriorates. We have therefore modified the NiTi surface by nitrogen plasma immersion ion implantation (PIII). The surface chemistry and corrosion resistance of the implanted samples were studied and compared with those of the untreated NiTi alloys, stainless steel, and Ti‐6Al‐4V alloy serving as controls. Immersion tests were carried out to investigate the extent of nickel leaching under simulated human body conditions and cytocompatibility tests were conducted using enhanced green fluorescent protein mice osteoblasts. The X‐ray photoelectron spectroscopy results reveal that a thin titanium nitride (TiN) layer with higher hardness is formed on the surface after nitrogen PIII. The corrosion resistance of the implanted sample is also superior to that of the untreated NiTi and stainless steel and comparable to that of titanium alloy. The release of nickel ions is significantly reduced compared with the untreated NiTi. The sample with surface TiN exhibits the highest amount of cell proliferation whereas stainless steel fares the worst. Compared with coatings, the plasma‐implanted structure does not delaminate as easily and nitrogen PIII is a viable way to improve the properties of NiTi orthopedic implants. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Macroporous condensed poly(tetra fluoro‐ethylene). II. In vivo effect on adhesion formation and tissue integration
Authors: Voskerician Gabriela , Rodriguez Analiz , Gingras Peter H.
Published: February 2007

This study investigated the in vivo correlation between construct parameters (surface area, pore size) and polymer chemistry in modulating mesh‐intestinal adhesions and mesh‐abdominal wall integration of condensed poly(tetra fluoro‐ethylene) (cPTFE) in hernia repair. A defect created by excising a 2 cm circular section of the abdominal wall from a rat was repaired with cPTFE or either one of the following synthetic meshes: expanded PTFE (ePTFE), ePTFE + polypropylene (PP), PP or PP + oxidized regenerated cellulose (ORC). The intestinal adhesion and abdominal wall integration were studied quantitatively by measuring the pull‐out force required to separate each mesh from the respective tissue at 1 and 3 months postimplantation. The hydrophobic, large pore meshes, such as cPTFE and ePTFE + PP led to reduced adhesions. Further, the presence of ORC contributed to reduction in adhesions of the more hydrophilic PP + ORC mesh. The large pore size, thinner meshes such as cPTFE and PP + ORC led to better tissue integration compared to the other meshes tested. Through hydrophobic chemistry, low profile, and increased pore size, cPTFE balances the rapid resolution of the inflammatory and wound healing response that resists adhesion formation, with efficient integration within the surrounding abdominal tissue. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Surface characteristics, biocompatibility, and mechanical properties of nickel‐titanium plasma‐implanted with nitrogen at different implantation voltages
Authors: Liu X.M. , Wu S.L. , Chan Y.L. , Chu Paul K. , Chung C.Y. , Chu C.L. , Yeung K.W.K. , Lu W.W. , Cheung K.M.C. , Luk K.D.K.
Published: February 2007

NiTi shape memory alloy is one of the promising orthopedic materials due to the unique shape memory effect and superelasticity. However, the large amount of Ni in the alloy may cause allergic reactions and toxic effects thereby limiting its applications. In this work, the surface of NiTi alloy was modified by nitrogen plasma immersion ion implantation (N‐PIII) at various voltages. The materials were characterized by X‐ray photoelectron spectroscopy (XPS). The topography and roughness before and after N‐PIII were measured by atomic force microscope. The effects of the modified surfaces on nickel release and cytotoxicity were assessed by immersion tests and cell cultures. The XPS results reveal that near‐surface Ni concentration is significantly reduced by PIII and the surface TiN layer suppresses nickel release and favors osteoblast proliferation, especially for samples implanted at higher voltages. The surfaces produced at higher voltages of 30 and 40 kV show better adhesion ability to osteoblasts compared to the unimplanted and 20 kV PIII samples. The effects of heating during PIII on the phase transformation behavior and cyclic deformation response of the materials were investigated by differential scanning calorimetry and three‐point bending tests. Our results show that N‐PIII conducted using the proper conditions improves the biocompatibility and mechanical properties of the NiTi alloy significantly. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Effects of cefuroxime on human osteoblasts in vitro
Authors: Salzmann G.M. , Naal F.D. , von Knoch F. , Tuebel J. , Gradinger R. , Imhoff A.B. , Schauwecker J.
Published: February 2007

The local application of antibiotics in bone cement achieves high local effective antibiotic concentrations. Cefuroxime is widely used for antibiotic prophylaxis in orthopedic surgery, and several reports highlighted a beneficial outcome if cefuroxime‐impregnated bone cement was used, but there is a lack of information of direct cefuroxime effects on human bone cells. We, therefore, cultured osteoblasts, previously derived from human trabecular bone specimens and used as a cell‐pool further on, with different concentrations of cefuroxime (0–1000 μg/mL) for 24, 48, or 72 h. For reversibility testing, osteoblasts were cultivated for 24 h with cefuroxime followed by 48 h without antibiotics. Cell proliferation (MTT), cytotoxicity (lactate dehydrogenase (LDH)‐activity), cell metabolism (alkaline phosphatase (ALP)‐activity), and extracellular matrix calcification (Alizarin staining) were assessed after antibiotic treatment. Cefuroxime concentrations of 25–100 μg/mL had little or no effect on cellular proliferation. Proliferation was significantly stimulated at 250 and 1000 μg/mL at each time. LDH‐activity significantly increased at the highest concentration of 1000 μg/mL at 72 h. ALP‐activity first increased at lower concentrations and then significantly decreased at 1000 μg/mL at 48 and 72 h. Similar to ALP‐activity, calcification increased at lower concentrations and was not detectable at 1000 μg/mL. All revealed effects at 24 h were at least partially reversible. In the present study, we demonstrated that cefuroxime at lower concentrations had no inhibiting effects on human osteoblasts. In contrast, higher concentrations significantly altered osteoblastic function. When administered locally in total joint arthroplasty, for example, in antibiotic‐impregnated bone cement, cefuroxime might critically impair osteoblastic function and periprosthetic bone metabolism. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Biomedical modification of poly(L‐lactide) by blending with lecithin
Authors: Zhu N. , Cui F.Z. , Hu K. , Zhu L.
Published: February 2007

Lecithin was, for the first time, blended with PLLA to prepare scaffold material for tissue engineering applications in the present study. Solution blending was used to incorporate Lecithin (containing 0–10 wt %) with PLLA to enhance the blend films biocompatibility, hydrophilicity and toughness while maintaining mechanical strength of PLLA. The results of FTIR‐ATR analysis indicated that the amino groups of lecitin existed in the films. DSC analysis indicated that Tg decreased with the increase of lecithin content in the blend films. The percentage elongation markedly increased with increase of lecithin content. The proliferation and viability of the vascular smooth muscle cell cultures on PLLA/Lecithin (containing 3–7 wt %) films were significantly enhanced compared to pure PLLA on tissue culture plates. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Electrophoretic deposition of zirconia‐Bioglass® composite coatings for biomedical implants
Authors: Radice S. , Kern P. , Bürki G. , Michler J. , Textor M.
Published: February 2007

Composite bilayer coatings on Ti6Al4V substrates were prepared by electrophoretic deposition, a simple and fast low temperature coating technique. Biocompatible yttrium‐stabilized zirconia (YSZ) in the form of nanoparticles and bioactive Bioglass® (45S5) in the form of microparticles were chosen as coating materials. The first layer consisted of 5 μm of YSZ, deposited with the intention to avoid any metal tissue contact. The second layer consisted of 15‐μm thick 45S5‐YSZ composite, supposed to react with the surrounding bone tissue and to enhance implant fixation. The adsorption of YSZ nanoparticles on 45S5 microparticles in organic suspension was found to invert the surface charge of the 45S5 particles from negative to positive. This enabled cathodic electrophoretic deposition of 45S5, avoiding uncontrolled anodization (oxidation) of the substrate. The coatings were sintered at 900°C for 2 h under argon flow. The characterization was performed using SEM, EDX, and nanoindentation (cross section). Potential applications in the orthopedics field are discussed. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Poly‐L‐lactic acid/hydroxyapatite hybrid membrane for bone tissue regeneration
Authors: Sui Gang , Yang Xiaoping , Mei Fang , Hu Xiaoyang , Chen Guoqiang , Deng Xuliang , Ryu Seungkon
Published: February 2007

Poly‐L‐lactic acid (PLLA)/hydroxyapatite (HA) hybrid membranes were fabricated via electrospinning of the PLLA/HA dispersion for use in bone tissue regeneration. The structural properties and morphologies of PLLA and PLLA/HA hybrid membrane were investigated by measuring the Brunauer‐Emmett‐Teller specific surface area, observations of SEM, and TEM. The dispersion and integrating of HA nanoparticles in the hybrid membrane were studied by energy dispersion X‐ray analysis and FTIR. The mechanical properties of PLLA/HA membrane were also measured by tensile tests. For exploring biological behaviors of the hybrid membrane, in vitro degradation tests were carried out. The osteoblast cell (MG‐63) was cultured in PLLA/HA hybrid membrane extract containing medium; the cell adhesion and growth capability were investigated by SEM observation and MTT assay. HA nanoparticles were not only dispersed in the PLLA but also reacted with the functional group of PLLA, resulting in strong surface bonding and high tensile strength of hybrid membrane. The cell adhesion and growth on the PLLA/HA hybrid membrane were far better than those on the pure PLLA membrane, which proves that the PLLA/HA hybrid membrane can be one of the promising biomaterials for bone tissue regeneration. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Elevation of transforming growth factor beta (TGFβ) and its downstream mediators in subcutaneous foreign body capsule tissue
Authors: Li Allen G. , Quinn Matthew J. , Siddiqui Yasmin , Wood Michael D. , Federiuk Isaac F. , Duman Heather M. , Ward W. Kenneth
Published: February 2007

Foreign body encapsulation represents a chronic fibrotic response and has been a major obstacle that reduces the useful life of implanted biomedical devices. The precise mechanism underlying such an encapsulation is still unknown. We hypothesized that, considering its central role in many other fibrotic conditions, transforming growth factor β (TGFβ) may play an important role during the formation of foreign body capsule (FBC). In the present study, we implanted mock sensors in rats subcutaneously and excised FBC samples at day 7, 21, and 48–55 postimplantation. The most abundant TGFβ isoform in all tissues was TGFβ1, which was expressed minimally in control tissue. The expression of both TGFβ1 RNA and protein was significantly increased in FBC tissues at all time points, with the highest level in day 7 FBC. The number of cells stained for phosphorylated Smad2, an indication of activated TGFβ signaling, paralleled the expression of TGFβ. A similar dynamic change was also observed in the numbers of FBC myofibroblasts, which in response to TGFβ, differentiate from quiescent fibroblasts and synthesize collagen. Type I collagen, the most prominent downstream target of TGFβ in fibrosis, was found in abundance in the FBC, especially during the latter time periods. We suggest that TGFβ plays an important role in the FBC formation. Inhibition of TGFβ signaling could be a promising strategy in the prevention of FBC formation, thereby extending the useful life of subcutaneous implants. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
The effect of yield damage on the viscoelastic properties of cortical bone tissue as measured by dynamic mechanical analysis
Authors: Yeni Yener N. , Shaffer Richard R. , Baker Kevin C. , Dong X. Neil , Grimm Michele J. , Les Clifford M. , Fyhrie David P.
Published: February 2007

We have previously shown, using Dynamic Mechanical Analysis (DMA), that the presence of a defect in cortical bone tissue affects the apparent viscoelastic properties of that bone. However, mechanically induced damage is more complex than a machined defect making it difficult to predict its effect on bone viscoelasticity. We performed DMA measurements before and after introduction of yield damage into cortical bone beams from sheep radii. The specimens were placed in a DMA machine and baseline measurements of storage modulus (E1) and loss factor (tanδ) were performed using a 3‐point bending configuration for a frequency range of 1–10 Hz. Measurements were done in all four bending directions (cranial, caudal, medial, and lateral) in random order. After subjecting the specimens to monotonic yield damage in a servohydraulic testing machine with the load applied to the cranial surface, oscillatory tests were repeated. To supplement results from the current experiment, additional analyses were performed on data from experiments where bone was either cut or fatigue‐loaded between viscoelasticity measurements. Introduction of mechanical damage increased tan δ and frequency sensitivity of E1, consistent with the assertion that increased energy dissipation in damaged bone might contribute to its increased resistance to fatigue and fracture. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Bacteria–surface interaction in the presence of proteins and surface attached poly(ethylene glycol) methacrylate chains
Authors: Tedjo Chrysanty , Neoh K.G. , Kang E.T. , Fang Ning , Chan Vincent
Published: February 2007

This study analyzes the adhesion behavior of the gram positive bacteria, Staphylococcus aureus (S. aureus), and the gram negative bacteria, Escherichia coli (E. coli), on polypyrrole (PPY) surfaces in the presence of poly(ethylene glycol) methacrylate (PEGMA) chains and plasma proteins (bovine serum albumin and bovine plasma fibrinogen) either preadsorbed on the film surface or in the bacterial suspension. Bacterial adhesion experiments performed in a suspension of bacterial cells and protein may give important insights on the behavior of bacterial adhesion in an in vivo environment. Protein adsorption and bacterial adhesion on PEGMA‐grafted PPY films were reduced by about a factor of 2–4 compared with those on the pristine PPY films. In addition, the number of bacterial cells adhering on the substrate is dependent not only on the type of protein present, but also the sequence of exposure to the protein relative to the bacteria. Furthermore, bacteria–surface adhesion force was measured using the atomic force microscopy with increasing lateral force to detach the individual cell. The adhesion force of S. aureus is influenced by PEGMA and plasma protein modification and is significantly higher than that of E. coli for all substrates tested. The number of adherent cells on the substrate is shown to be directly correlated to the bacterial adhesion force. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Roles of MMP/TIMP in regulating matrix swelling and cell migration during chick corneal development
Authors: Huh Man‐Il , Lee Young‐Mi , Seo Seong‐Kyung , Kang Bong‐Seok , Chang Yongmin , Lee Young‐Sup , Fini M. Elizabeth , Kang Shin‐Sung , Jung Jae‐Chang
Published: February 2007

Tissue remodeling is central to embryonic development. Here, we used immunohistochemistry, Western blotting, and RT‐PCR analysis to investigate the roles of matrix metalloproteinases (MMPs) and the related “a disintegrin and metalloproteinase“ (ADAM) family proteinases in chick corneal development. While MMP‐13 was expressed in developing chick corneas from embryonic day (ED) 5 to ED 10, its inhibitor, tissue inhibitors of metalloproteinase‐1 (TIMP‐1), was expressed from ED 18 to 2 days post‐hatching (P2). Early MMP‐13 activity may be associated with degradation of type IX collagen from the primary stroma, which loosens the collagen fibrils and facilitates neural crest (NC) cell migration. The membrane‐bound and secreted forms of ADAM10 were both detected throughout corneal development, and active ADAM10 formed a cleavage complex with CD44v6, a CD44 splice variant that is a major cell surface adhesion molecule for hyaluronic acid (HA) and has been implicated in cell migration. Both CD44v6 and its ectodomain cleavage products were detected from ED 5 to ED 14, and a broad‐spectrum MMP inhibitor blocked ectodomain cleavage in cultured stromal cells. These findings suggest that ADAM10 mediates CD44v6 cleavage in the developing cornea, facilitating NC cell‐derived mesenchymal cell migration. Finally, we identified high levels of active membrane‐type 3‐MMP (MT3‐MMP) in developing corneas at ED 7, ED 14, and ED 18. MT3‐MMP takes part in MMP‐2 activation and possibly also CD44v6 shedding, suggesting that this pathway may be involved in cell migration. These findings collectively show for the first time that multiple MMPs, ADAMs, and TIMPs appear to functionally interact during corneal development. J. Cell. Biochem. 101:1222–1237, 2007. © 2007 Wiley‐Liss, Inc.