bluuebunny/crossref_metadata_2025 huggingface dataset:
Grain Boundary States in Float-Zone-Si-Bicrystals
Authors: Petermann G. , Haasen P.
Published: March 2011

A near Σ25 grain boundary has been studied electrically in FZ-silicon at various degrees of n-doping. The boundary is electrically active without previous heat treatment. A unique density-of-states can be derived from dc and ac measurements at all dopings and temperatures investigated. The model of the charged g.b. includes potential fluctuations in the g.b. plane. Admittance spectroscopy allows to differentiate between g.b. states and deep centers its the compensating space charge zone.
Nitrogen Contamination in Simox Wafer
Authors: Davis G. E. , Jones K. S. , Prussin S.
Published: March 2011

Nitrogen was found in as-implanted SIMOX wafers. The redistribution of the nitrogen within the SIMOX structure was studied after the formation anneal for different temperatures (up to 1250 °C), times, ambients (nitrogen plus 1% oxygen and argon), and anneal with and without a capping layer. The nitrogen was found to be concentrated in the buried SiO2 layer and the adjacent damaged silicon regions in the as-implanted oxygen wafers. During the formation anneal, the nitrogen was found to collect(build-up) at the Si/SiO2 buried layer interface. It is postulated that an oxynitride is preferentially formed at the interface where the dangling silicon bonds can capture the soluble nitrogen.
Melting and Solidification Dynamics in Zone Melting of Si Films.
Authors: Dutartre D.
Published: March 2011

We discuss the physics involved in the melting and solidification of Silicon On Insulator thin films (SOI) using lamp or graphite strip heaters. The melting front, called “explosive melting”, controls to a large part the final morphological quality of the SOI film. It exhibits instabilities which can (i) nucleate the dewetting of the film, (ii) cause voids, and (iii) produce a poor surface morphology. The morphologies of the solidification fronts are analyzed. We show that, depending on the experimental conditions, different physical mechanisms are responsible for the front breakdown. Thus we propose that the variety of front morphologies results from the variety of the mechanisms involved, and of their combinations with the “faceting effects”.
Zone-Melting Recrystallization of Silicon on Alumina
Authors: Letavic T. J. , Maby E. W. , Gutmann R. J.
Published: March 2011

Polysilicon-on-alumina films have been zone-melt recrystallized with a graphite strip heater. High levels of in-plane stress and stress concentrations due to alumina grain pull-outs cause tensile failure at high temperature. This can be avoided by phosphorus incorporation into an SiOo layer between the polysilicon film and the alumina substrate. The glass layer provides high-temperature viscoelastic strain relief and planarizes the alumina substrate. Double-crystal diffractometry and anisotropic etch techniques indicate that the recrystallized silicon-on-alumina film texture is (100).
TEM and SEM Studies of Multiple Silicon on Insulator Films for Three Dimensional Circuits.
Authors: Williams D.A. , McMahon R.A. , Ahmed H. , Barfoot K.M. , Godfrey D.J. , Dunne B. , Mathewson A.
Published: March 2011

Multiple layers of silicon on insulator have been recrystallized using a dual electron beam technique. The aim of the investigations was to produce structures suitable for three dimensional circuit applications, and so a number of strategies have been used, providing a range of opportunities for such applications. In particular, two layers of silicon on insulator have been recrystallized simultaneously, and also a second layer has been recrystallized, seeded from a previously regrown film.
Hot Electron Transistors Using Si/CoSi2
Authors: Levi A. F. J. , Tung R. T. , Batstone J. L. , Anzlowar M.
Published: March 2011

We have explored the possibility of fabricating a metal base transistor in the Si/CoSi2 material system. Utilizing recent advances in the growth of thin, pinhole free, CoSi2 layers on Si(111) we have measured the transistor characteristics of a Si/CoSi2/Si structure. The observed low common emitter current gain is attributed to an absence of current carrying states in the CoSi2 transistor base.
Buried Layer Tungsten Deposits In Porous Silicon: Metal Penetration Depth and Film Purity Determinants
Authors: Blewer Robert S. , Tsao Sylvia S. , Gutierrez Gina M.
Published: March 2011

Infiltration of anodically prepared porous silicon with tungsten hexafluoride gas has been investigated as a function of silicon porosity, source gas pressure and carrier gas type and flow rate. The depth of tungsten metallization in the silicon has been shown to depend most sensitively on the WF, partial pressure, and less on the flow rate and carrier gas type. Penetration depths of 30 pirn have been attained. Structural integrity of the tungsten layer is dependent on the porosity of the starting material and the degree of internal oxidation of the porous silicon surface area.
Materials and Processes For Silicon TFT's On Aluminosilicate Glass: An Alternative Soi Technology
Authors: Troxell John R. , Harrington Marie I. , Erskine James C. , Dumbaugh William H. , Fehlner Francis P. , Miller Roger A.
Published: March 2011

As-deposited polycrystalline silicon and argon ion laser recrystallized silicon thin film transistors (TFT's) have been fabricated on Corning Code 1729 glass substrates. This novel aluminosilicate glass has an expansion coefficient matched to that of silicon and a chemical durability comparable to that of fused silica. N-channel enhancement mode transistors were made using conventional IC device fabrication procedures (including thermal oxidation to form the gate insulator) modified to have a maximum processing temperature of 800 C. The- polycrystalline silicon TFT's exhibit leakage currents of less than 2x10-11 A/ μm; of channel width and good stability and reproducibility. Transistors made in the recrystallized silicon show field effect electron mobilities as high as 270 cm2/V s, approximately 15 times the mobility of comparable devices made in as-deposited polycrystalline silicon. The recrystallized silicon devices also exhibit lower threshold voltages and lower leakage currents than do the comparable polycrystalline silicon devices. Major advantages of this TFT technology include the use of a novel, potentially low cost glass substrate and the simultaneous processing of both polycrystalline and recrystallized silicon devices on the same substrate material. This approach represents a new avenue for the incorporation of active devices into a variety of applications including integrated active matrix displays.
Thin (100 nm) SOS for Application to Beyond VLSI Microelectronics
Authors: Reedy Ronald E. , Garcia Graham A.
Published: March 2011

Of the numerous requirements for advanced VLSI silicon microelectronics, power dissipation per unit area, speed, packing density and radiation hardness are especially important. Power dissipation and speed have forced an evolutionary path from PMOS to NMOS to NMOS E/D and to the currently used CMOS. As evidenced by the large number of publications, CMOS on an insulating substrate is receiving increased attention due to its potential as the next generation in MOS evolution. We review results of our previous and current research in silicon on sapphire (SOS) which has led to high quality ultrathin SOS (<100 nm thick) appropriate for high density CMOS circuitry. Basic materials developments, device performance, and CMOS design considerations in 100 nm thick improved SOS will be discussed.
Formation of Double Layered SOI With Controlled Crystal Orientation
Authors: Miyajima Toshiaki , Tsuji Hideyuki , Maekawa Masashi , Koba Masayoshi
Published: March 2011

For the crystal orientation control of multi-layered SOI (Silicon on Insulator) by the laser recrystallization technology, the shape and size of seeds were investigated. By utilizing dot seeds less than 3μm square instead of a line seed, the crystal orientation control of a SOI layer was successfully realized without causing evaporation of silicon. Moreover, the dot seed method enabled us to control the crystal orientation of multi-layered SOI by virtue of small heat flow through seed regions.

In the mean time, it was proved that the SOI crystal orientation gradually rotated as the crystal propagated away from the seeds and that the degree of rotation in the second SOI layer was smaller than that in the first one.
Elimination of Defects in Laser-Recrystallized SOI by Stress Relief
Authors: Martinez Andre , Pandya Ranjana , Arnold Emil
Published: March 2011

We report the application of a stress-relief technique aimed at reducing the density of dislocations and subgrain boundaries in laser-recrystallized Silicon-On-Insulator (SOI) material. By providing alternate mechanisms for relieving the stresses responsible for defect generation in the Si film, it is possible to exercise a large degree of control over the subgrain boundary density. Large areas of SOI material completely free of dislocations and subgrain boundaries have been obtained by inserting a low-viscosity layer under the silicon film and using an appropriately shaped cw laser beam as the heat source. During the process of zone-melt recrystallization this layer softens and provides an alternative stress relief mechanism, thus reducing the mechanical constraint on the growing crystal. Several examples of subgrain boundary control are described, which have resulted in crystalline regions in excess of 300 μm by several millimeters completely free of low-angle grain boundaries and dislocations.
Laser Recrystallized SOM for Strain Gauge Applications
Authors: Kunshan Xing , Xuemin Xu , Chenglu Lin , Songsheng Tan , Shihchang Tsou
Published: March 2011

A novel material SOM (Silicon on Metal) was obtained by laser recrystallization. 0.5miti amorphous-Si film was deposited by glow discharge on a metal substrate covered with lym CVD Si02 Boron ions were implanted in a-Si at an energy of 60KeV and a dose of 5xl015cm-2. A CW argon laser was used to recrystal-lize a-Si film. After CW argon laser irradiation, a-Si was recrystallized and the grain size was increased to 10x40ym, the concentration profile of impurities became uniform and the electrical properties of SOM were improved significantly, sheet resistance lower than 60Ω/⃞n was obtained. The gauge factor of recrystallized SOM materials measured by a cantilever transducer was higher than 30. The devices made of this material have pressure sensitivity of 6mV/V for pressure range 1 bar.
Formation of Buried Nitride Layers in (110) Silicon
Authors: Datye Abhaya K. , Kaushik Vidya S. , Kendall Don L. , Martinez-Tovar Bernardo , Myers David R.
Published: March 2011

High fluence ion implantation of N (1x1018/cm2 at 150 keV) has been used to form buried nitride layers in (110) silicon. After annealing at 1200 C for 5 hrs. a continuous, polycrystalline alpha-Si,N- layer (200 nm thick) is observed beneath a surface silicon film 306 nm thick. The upper Si/Si3N4 interface appears to be more abrupt than that observed in (100) silicon with minimal dendritic intergrowth and no evidence for microtwinning in the silicon. Furthermore, a band of nitride precipitates can be detected 500 nm below the continuous nitride layer. These nitride precipitates grow semi-coherently within the silicon with no observable strain or misfit dislocations within the silicon. The nitride precipitates are internally faulted to accomodate the 10% lattice mismatch in the (0001) nitride direction. Short term anneals reveal that the precipitates have fully crystallized within 10 min. at 1200 C while the continuous nitride layer is still amorphous.
Total Dielectric Isolation (TDI) of Device Islands Using SIMOX/SOI Technology
Authors: Hemment P L F , Robinson A K , Reeson K J , Davis J R , Kilner J R , Chater R J , Stoemenos J
Published: March 2011

A method of achieving total dielectric isolation (TDI) of device islands (or larger areas) using ion beam synthesis to form a continuous but non planar layer of SiO2is described. The technique involves implantation through a patterned masking layer in which windows have been opened to define the dimensions and location of the islands. TDI structures have been successfully formed in annealed (1300°C, 5 hours) wafers implanted with a dose of 2.2 x 1018O+cm2at 200 keV, using a thermal oxide mask of thickness 4750 Å.
Pyridine N-Oxides As Polymeric Nonlinear Optical Materials
Authors: Griffin Anselm C. , Bhatti Amjad M. , Howell Greg A.
Published: March 2011

Three polymers containing pyridine N-oxide imine pendant moieties were prepared and examined. Although the appropriate low molar mass model compound is liquid crystalline, the polymers are not mesogenic. Two of them form fibers and clear, transparent glasses. Side reactions involving the N-oxide group during polymerization are postulated as leading to the lack of mesomorphism in these materials although the π-chromophore remains essentially intact for the bulk of the material as judged by UV-Vis and other spectral data. They may have NLO application as poled polymeric glasses.
Nonlinear Optical Response of Excitons Confined to one Dimension
Authors: Greene B. I. , Orenstein J. , Thakur M. , Rapkine D. H.
Published: March 2011

We present femtosecond time-resolved transient absorption data taken on polydiacetylene-pTS single crystals over the entire wavelength region of exciton resonance. Observed optical changes are accounted for by a model which predicts quantitatively the large resonant and nonresonant optical nonlinearities.
Quasiparticle Excitations in Polyenes and Polyacetylene
Authors: Tavan Paul , Schulten Klaus
Published: March 2011

We apply the Pariser-Parr-Pople Hamiltonian to study many-electron excitations in polyenes and polyacetylene. The excited singlet states of polyenes, calculated by a multireference double excitation expansion, are classified as quasi-particle excitations, namely as triplet-triplet magnons and particle-hole excitons. From finite polyene spectra we derive approximate dispersion relations for these quasi-particles in the infinite polyene, i.e. polyacetylene.
Quadratic and Cubic Nonlinearities in Solution of Intramolecular Charge Transfer Aromatic Molecules A Quantum Two-Level Approach
Authors: Barzoukas M. , Fremaux P. , Josse D. , Kajzar F. , Zyss J.
Published: March 2011

A two-level expression of the second-order hyperpolarizability (y) is proposed, and shown to contain a negative charge transfer (CT) contribution. Frequency dispersed measurements of the quadratic and cubic susceptibility of N-(4-nitropheny1)-L-prolinol (NPP), N-(4-nitrophenyl)-N-methylaminoacetonitrile (NPAN) and 2-(N-prolinol)-5-nitropyridine (PNP) are reported. The electric field induced second-harmonic generation (EFISH) and third-harmonic generation (THG) techniques in solution are used. A two-level model dispersion of y as from THG measurements is shown to lead to a neglegible electronic contribution to the overall EFISH nonlinearity, as compared to the orientational contribution. The theoretical β-components of these molecules, obtained consistently by finite-field and perturbational approaches, clearly confirm that the β-tensor is one-dimensional along the donor-acceptor CT axis. The off resonance quadratic polarizabilities (β) of these molecules are sequenced as follows : β(NPP)> β(PNP)> β(NPAN). However this increased efficiency is obtained at the expense of the transparency range.
Semiconductor-Doped Polymers. Linear and Nonlinear Optical Properties.
Authors: Wang Y. , Suna A. , Mahler W.
Published: March 2011

Semiconductor clusters with sizes of a few to hundreds of Å, covering the entire range from molecular to bulk, have been prepared within polymer films. For PbS, the band-gap shifts to higher energy as the cluster size decreases and eventually converges to the transition energy of the first excited state of PbS molecule. The observed dependence of band-gap on cluster size can be explained by a tightbinding model that takes into account the effects of band nonparabolicity. These semiconductor-doped polymers represent a new class of nonlinear optical materials. Here we present the nonlinear optical properties of polymer films doped with 50 A CdS and discuss the possible mechanisms.
Third Order Nonlinear Optical Susceptibility of Trans-(CH)x: A Degenerate Ground State Conjugated Polymer
Authors: Sinclair M. , Moses D. , Akagi K. , Heeger A. J.
Published: March 2011

The promise of conducting polymers as fast response nonlinear optical materials has been recently emphasized [1,3]. Polymers such as polyacetylene, polythiophene and the soluble (and processible) poly(3-alkylthienylenes) contain a high density of x-electrons, and they are known to exhibit photoinduced absorption and photoinduced bleaching, indicating major shifts of oscillator strength upon photoexcitation [2,4]. For polyacetylene, these nonlinear effects have been studied in detail in the picosecond [5a,b] and sub-picosecond [5c] time regime and correlated with the photoproduction of charge carriers through fast photoconductivity measurements [6]. The data have demonstrated ultra-fast response with nonlinear shifts in oscillator strength occurring at times of the order of 10-13 seconds. These resonant nonlinear optical properties are intrinsic; they originate from the nonlinearity of the self-localized photoexcitations [7] which characterize this class of polymers: solitons, polarons and bipolarons [4].
Rational Construction of Polymeric Nonlinear Optical Materials. Properties of Chromophore-Functionalized Polystyrenes
Authors: Ye C. , Minami N. , Marks T. J. , Yang J. , Wong G. K.
Published: March 2011

Processable polymeric nonlinear optical materials can be synthesized by functionalizing a glassy macromolecule with chromophores having large quadratic hyperpolarizabilities, followed by poling in an electric field. In the present case, the functionalization of polystyrene with 4- (4-nitrophenylaza)(N-ethyl)(2-hydroxyethyl))aniline, 4-(4-N,N-dimethylaminostyryl) pyridine, and N-(4-nitrophenyl)-L-prolinol is described. Particularly noteworthy is the high level of chromophore units that can be incorporated into transparent films of these materials, the high second harmonic coefficients that can be achieved (as high as d33 – 11 × 10-9 esu at 1064 nm), and the long-term temporal stability of the second harmonic generation capacity.
A New Intramolecular Charge Transfer Material for Nonlinear Optics: Piperonal Derivatives
Authors: Mori Y. , Okamoto M. , Wada T. , Sasabe H.
Published: March 2011

This paper describes a new organic nonlinear material, piperoniridene ethyl cyano acetate which shows short cut-off wavelength, good nonlinearity (better than POM in powder) and good crystallinity. These features of this compound encourage its application in second harmonic generation (SHG) coupled with semiconductor laser.
An Optically Detected Magnetic Resonance Study of Recombination Mechanisms in Polythiophene
Authors: Hess B. C. , Shinar J. , Vardeny Z. , Ehrenfreund E. , Wudl F.
Published: March 2011

From detailed optically detected magnetic resonance measurements in polythiophene, we show that the g=2.003 signal is luminescence enhancing, and that the signal comes from a broad photoluminescence band peaking near 1.65 eV. This band is tentatively assigned to Phe radiative recombination of polarons, with lifetimes between 10-8 and 5×10-5sec.
An Efficient Second-Harmonic Generating Crystal: 4-(Aminobenzophenone)
Authors: Guha S. , Frazier C. C. , Chauchard E. , Chen W. P. , Cockerham M. P.
Published: March 2011

Efficient, phase-matched second-harmonic generation of 1.064 µm radiation has been observed with single crystals of 4-aminobenzophenone (ABP). These crystals are tr nsparent from 420–2000 nm and have damage thresholds exceeding 30 GW/cm2 (for a 30-picosecond laser pulse).
Implementation of Neural Networks: Optical Architectures and Devices
Authors: Malloy Kevin J. , Giles C. Lee
Published: March 2011

We introduce neural networks as a new basis for computation. The role optics can play In implementing neural networks is discussed in terms of the requirements for optical systems and devices. A conclusion is drawn that the rapidly evolving knowledge of neural network models argues for a flexible and adaptable device technology. Such a technology is described using the self electro-optic effect device as an example.
In vitro Study of the Rheological Effect of Mixtures of Perfluorotributylamine (FC-43) and Stroma Free Hemoglobin (SFH) On Sickled Erythrocytes
Authors: Reindorf Carl A. , Thompson Novelette E.
Published: March 2011

Stroma Free Hemoglobin (SFH) and Perfluorotributylamine (FC-43) have been extensively studied as oxygen carriers. Therefore, capitalizing on the role of oxygen reversing sickling, and thus decreasing resistance, this study was undertaken to investigate possible differences in the rheological effects of mixtures of FC-43 and SFH at different ratios. We used the positive pressure cell filtration system (PPCFS) of Lessin and Kurantsin- Mills. FC-43 was purchased from Alpha Therapeutics Corporation, and SFH was prepared by the method of Rabiner et al. The FC-43/SFH mixtures were made on a volume basis in ratios of 1:1 and 1:2. Fresh sickle cell anemia (HbSS) blood was used to prepare 0.2% cell suspensions which were deoxygenated, by bubbling with moist N2 for one hour. Studies of the rheological effects of FC-43/SFH mixtures on sickled erythrocytes were determined by obtaining filtration measurements on the following:- 1. sickle cells in ambient air; 2. deoxygenated sickle cells; 3. deoxygenated sickle cells + oxygenated FC-43/SFH (1:1 v/v); 4. deoxygenated sickle cells + oxygenated FC - 43/SFH (1:2 v/v). The results showed that treatment of deoxygenated sickle erythrocytes with oxygenated SFH/FC-43 mixtures decreased the flow resistance of the deoxygenated cells. Secondly, the SFH/FC-43 (1:2 v/v) mixture caused greater decrease in flow resistance than the 1:1 mixture.

Therefore it is reasonable to conclude that the mixtures of SFH/FC-43 (1:2 v/v) ratio appear to have a additive effect in reducing the flow resistance i.e. increasing the filterability of sickled erythrocytes.
Standardization and Control of Biomedical Devices
Authors: Singleton D. Gregory
Published: March 2011

The passage of the Medical Device Amendements to the Food Drug and Cosmetic Act on May 28, 1976 placed a huge number of products under the regulatory authority of the Food and Drug Administration (FDA). This increased responsibility took many forms related to device evaluation which will be discussed in this paper. In order to institute control of all devices it was necessary to “take inventory” of what was on the market. This was accomplished by establishing device panels for the various medical specialties composed of experts familiar with the devices areas who compiled a generic device list for their specialty areas. Each device was classified according to its hazard potential and existing data related to safety and effectiveness.
Host Response to Intraosseous Implants Placed in Ha Grafted Mandibles
Authors: Boyne Philip J.
Published: March 2011

In the past, the effectiveness of intraosseous fixation devices in Hydroxyapatite (HA) implanted and bone grafted areas has not been well defined. Previous definitions of the histologic meaning of osteointegration have implied that only through contact with viable calcified osseous matrix or all implant surfaces is an intraosseous fixture fully integrated or attached (1). Such a definition would preclude the use of these implants in previously bone grafted, HA implanted, or otherwise compromised sites. The purpose of this work was to study the surface interface of metallic intraosseous fixtures in HA implanted and xenogeneic bone-implanted mandibular extraction sockets of mature Macaca fascicularis monkeys and Papio anubis baboons.
Quantitative Histology and Mechanical Testing of a Biodegradable Bone Cement
Authors: Gerhart Tobin N. , Renshaw A. A. , Hayes W. C.
Published: March 2011

We have developed a particulate composite bone cement consisting of a particulate phase of tricalcium phosphate (TCP) particles bound together by a polymeric matric phase (PPF). This matrix hardens through a free radical polymerization reaction in vivo within several minutes after mixing. The initial mechanical strength of our particulate composite bone cement results from the matrix, but over time this degrades and the strength is augmented by bone ingrowth and incorporation of the tricalcium phosphate particles. Possible orthopaedic applications include fixation of fractures, augmenting fixation of implants in osteoporetic bone, and temporary stabilization of bone ingrowth prostheses.
Comparison of Dense Versus Porous Hydroxylapatite (HA) Particles for Rat Mandibular Defect Repair
Authors: Fredette Stephen A. , Hanker Jacob S. , Terry Bill C. , Giammara Beverly L.
Published: March 2011

Repair was compared in 4.4mm experimental rat mandibular ramus defects implanted with dense or porous HA particles with or without a plaster binder. Animals were sacrificed 6 months postimplantation. Specimens underwent gross, radiographic, histochemical and X-ray microanalytical examination. Gross and radiographic examinations showed good particle containment or retention only in defects filled with implants containing plaster. Only porous HA/plaster filled defects showed bone formation throughout the implant when examined histochemically by the PATS reaction and by X-ray microanalysis. They also showed greater radiographic opacity compared to dense HA/plaster implants. Only porous HA/plaster implants showed macroscopic bone formation. Examination of defects filled with porous HA/plaster or porous HA alone by the PATS reaction showed new cancellous bone around, and through the pores of, retained particles. The dense HA/plaster implants showed some new bone around the rims of the defects with only occasional bony incorporation of an HA particle. Dense particles in other areas showed only soft tissue encapsulation. Defects implanted with dense HA without plaster showed no new bone formation but retained particles were incorporated by fibrovascular tissue.
Osteogenesis in Cat Cranioplasty with Composite Hydroxylapatite/Plaster
Authors: Hanker Jacob S. , Yates Peggy E. , Giammara Beverly L. , Rawlings Charles E. , Ovelmen-Levitt Janice , Georgiade Nicholas G. , Wilkins Robert F.
Published: March 2011

Composite hydroxylapatite (HA)/plaster alloplasts were studied for frontal and parietal cranioplasty. The experimental defects were created in 61 anesthetized cats. They were filled with a moist 2:1 mixture of durapatite/plaster or Interpore/plaster containing 0.85% potassium sulfate. After setting, the implant site was sutured. The filled defects were very firm by physical examination and showed little particle scatter by radiography. At the time this report was prepared only 43 of the cat skulls were available for examination. After sacrifice, postmortem visual examination (VE) of the skulls suggested that new bone had formed over some implants. In most implants, however, VE could not determine whether new bone had formed between the HA particles. Probing examination (PE) of the parietal implants with a periodontal explorer gave a better indication; the presence of new bone rather than soft tissue between the HA particles was confirmed by x-ray microanalysis. The ventral surfaces (VS) of the parietal implants showed greater degrees of bone formation by PE; only 12 of 43 parietal implants showed a high degree of bone formation on the dorsal surfaces (DS) by PE whereas 34 of 43 showed this on the VS. The highly significant difference (^3X) in the amount of bone formation on the VS compared with the DS suggests that this osteogenesis, like that observed in cranial trauma, may be stimulated by the dura which acts as a periosteum by supplying blood vessels to the implant.
Effects of Compression During Formation on the Mechanical Strengths and Physical Properties of Composite Hydroxylapatite/Plaster Implants for Bone Reconstruction
Authors: Cowden K. , Giammara B. , Georgiade N. , Noecker R. , Hanker J.
Published: March 2011

Composite hydroxylapatite/plaster of Paris implants, preformed or formed during the surgical implantation procedure, are undergoing study for the surgical reconstruction of craniofacial bones. It is frequently necessary to accelerate setting times of the hydroxylapatite/plaster (HA/PP) mixtures by the addition of potassium sulfate; in many of these cases rapid delivery of the moistened implant mixture to the surgical site may be achieved by employing a non-tapered syringe with a plunger. This device can facilitate implantation of quick-setting moistened mixtures through soft tissue tunnels or small incisions, and can result in a less invasive surgical procedure. During experimental surgery it was found beneficial to effect maximum compression of the moistened HA/PP mixture against a sterile glass plate prior to its extrusion from the cylinder. This resulted in elimination of excess water from the mixture. Discs formed from compressed mixtures showed greater mechanical or breaking strengths after setting than discs formed without prior compression when evaluated with a Stokes Hardness-Tester. Examination by light and scanning electron microscopy confirmed the greater compactness of the compressed mixtures.
Critical Evaluation of an in Vitro Model for Evaluation of Platelet Reactivity of Biomaterials
Authors: Connolly Raymond , Shoenfeld Norman , Ramberg Karen , Callow Allan D.
Published: March 2011

An in vitro model for measuring platelet reactivity to a variety of biomaterial candidates for vascular grafts is described. A model consisting of a standard area of test material exposed to freshly labeled In platelets in plasma was evaluated. The platelets were isolated from ACD anticoagulated blood and resuspended in ACD plasma. It has been previously demonstrated that platelets so treated circulate in the body and will deposit on biomaterials exposed to the blood in vivo. The in vitro test consisted of an incubation of the platelets and materials at 37°C for one hour. At the end of the incubation, the platelet rich plasma was removed and the materials washed and removed for gamma counting. Platelet reactivity was normalized as a percentage of the counts on the material to counts in an aliquot of the platelet-plasma incubation media. The maximum uptake of platelets occurred within one hour. Platelets from three species, human, baboon, and dog were tested. Platelet uptake by Dacron and PTFE were in the range of 30–40% and 1–5% respectively. This is in accord with the known reactivity of these two vascular graft materials in vivo.

A second series of studies were conducted with physically and pharmacologically inactivated platelets and inert particles. Those studies suggest that the initial results do not represent a biologic event but may reflect the porosity of the materials. This emphasizes the necessity of adequately defining an in vitro model against known in vivo activity.
Various Forms of Crosslinked Dextran Gel as Surface Wound Covering Materials
Authors: Wang Paul Y.
Published: March 2011

Dextran and its crosslinked beads have many biomedical applications. If stirring to maintain the epichlorohydrin emulsion is stopped in about 7 minutes, crosslinked dextran gel sheets can be prepared. The elastic sheet obtained after washing in water, followed by treatment with propylene glycol containing 15% isopropanol is suitable as a covering on rodent skin wound. Antibacterial agents can be dispersed into the sheet or admixed in the paste form of the gel.

In standard tests, a 4 cm × 4 cm surface wound on the back of a 400-g Wistar rat was covered with the dextran gel material. The evaporation loss was found to reduce immediately from 94 mg H20/cm2/hr to 1/2 of this value which became 12.5 mg H20/cm2hr in 18 hours. Such a covered wound healed in 10–17 days with 10–15% distortion, while the controls were delayed to 25 ± 7 days with >65% wound contraction.

Another modification of the gel material involves the surface attachment of the positively charged 2-diethylaminoethyl function (DEAE). Although up to 2.41 mM DEAE groups/g gel can be introduced, only <10% is on the gel surface. Tests with mouse 3T3 fibroblists showed 5 that it was possible to increase the cell binding from 9 × 103 to 2 × 105 cells/cm2. Therefore, the gel material may have potential as a substrate for dermal cells as well for later transfer.
Hydrotheral Synthesis of Hydroxyapatite Powders with Zirconia Dispersion
Authors: Ioku Koji , Yoshimura Masahiro , Sōmiya Shigeyuki
Published: March 2011

Hydroxyapatite (HAp) fine powders dispersed with zirconia were prepared by hydrothermal techniques at 200°C, under 2 MPa for 10 h. The transmission electron microscopy (TEM) showed the homogeneous mixtures of HAp and zirconia.The HAp powders were stoichiometric fine single crystals of about 90 nm × 25 nm in size and the zirconia powders were also fine single crystals of about 10 nm in size. The reactivity between HAp and zirconia was examined. According to the X-ray diffractometry (XRD), decomposition of HAp to B-tricalcium phosphate (β-TCP) was observed above 800°C then β-TCP was transformed into α-TCP at about 1200°C.
The Role of Extracellular Fluid on the Electrical and Electromechanical Properties of Bone: A Review
Authors: Chakkalakal Dennis A.
Published: March 2011

The cells in living bone – osteocytes, osteoblasts and osteoclasts – are embedded in a porous material consisting of an organic-inorganic composite solid containing a distribution of fixed charges, permeated by ionic fluids flowing through a complex network of channels. In the weight-bearing long bones of the body, the largest of these channels are up to a few hundred microns in diameter and contain blood vessels which are connected to the blood supply in the central canal of the long bones. These channels establish fluid connectivity with the cells (osteocytes) responsible for maintenance of the bone tissue through small canals (canaliculi) with diameters ranging down to a tenth of a micron. Outside the blood vessels, perivascular fluid permeates these channels. The solid matrix is itself porous with a high degree of composite material organization beginning at the macromolecular level. The internal connectivity of the pore fraction of the solid, which is not as extensive as the network of channels, and the connectivity of this pore fraction with the fluid channels may affect physiological functions, through its influence on mechanical, electrical and electromechanical properties of the extracellular matrix. It seems apparent that the structure and physical properties of the extracellular material of bone will largely determine the physicochemical environment of the cells. Thus, a materials characterization of the extracellular matrix of living bone has become an essential part of the efforts to advance our knowledge of bone physiology and pathology. This paper is a review of the present state of knowledge of the electrical and electromechanical properties of this material with emphasis on studies that appear to have the most physiological significance.
Comparison of Osteoconduction in Porous Implants of Co-Cr-Mo, Vitreous Carbon, Silicone Rubber and Hydroxyapatite in Rabbit Bone Defects
Authors: Shors Edwin C. , White Gene W. , Kopchok George
Published: March 2011

There is a need for new materials which attach to bone. Attachment can occur through bioactive surfaces or porosity. The Replamineform process can be used to produce polymers, metals and ceramics with these properties. In this study, porous implants were manufactured in cobalt-chromemolybdenum (Co-Cr-Mo) vitreous carbon and silicone rubber. The pores were 200 pm in diameter and fully interconnected. The biocompatibility and osteoconduction of these materials was compared to porous hydroxyapatite (Interpore 200 HA). In 10 rabbits, blocks (2mm×3mm×5mm) of each material were implanted subperiosteally onto the femur, or rods (5mm D×10 L) were press-fit into unicortical defects of the proximal tibia. Explants were harvested at 1–6 months, sectioned midsagitally and embedded in plastic for histomorphometry using SEM or bright field microscopy. Bone grew up to and into all implants by two months. However, implants of porous Co-Cr-Mo, vitreous carbon and silicone rubber had less bone than implants of hydroxyapatite. Also, bone formed in direct apposition to hydroxyapatite, but secondly incorporated the other materials. Moreover, implants containing hydroxyapatite in the pores of the Co-Cr-Mo induced more complete and intimate bone ingrowth. This study demonstrates the potential for bone ingrowth and bonding into a range of biocompatible materials with interconnected porosity and the superior osteconduction of porous hydroxyapatite.
Mini Short-Rod Fracture Toughness Testing of Bone Cements Exhibitng Elastic-Plastic Behaviour
Authors: Wang C. T. , Pilliar R. M.
Published: March 2011

Fracture of bone cement is considered to be a major factor contributing to total joint replacement failures because of implant loosening. While plane-strain fracture toughness (Klc) provides a parameter for assessing fracture resistance, the standard methods for testing (ASTM E399) require (1) the use of specimens greater than a certain minimum size (for bone cement this minimum size is greater than that found in clinical applications) and (2) fatigue precracking of specimens prior to testing. The short-rod fracture toughness test proposed by Barker offers a method of testing not requiring fatigue precracking and furthermore, it appears that a valid fracture toughness value can be determined using a modified miniature test specimen that we have proposed. Our mini short-rod specimen size approaches the actual dimensions of bone cement as used clinically. In this study mini short-rod fracture toughness test specimens were used to assess fracture toughness for two commercial brands of bone cement (Simplex-P and Zimmer LVC). An elastic-plastic fracture mechanics (EPFM) analysis was used to obtain experimental results with a plasticity correction factor being introduced. The cements were assessed as a function of method of preparation (hand mixed versus centrifuged) and aging conditions (3 days in air versus 7 days in distilled water at 37° C). The results indicated that (1) true fracture toughness values could be obtained only using an EPFM analysis for these specimens, (2) centrifugation did not significantly affect fracture toughness and (3) a significant difference in the plasticity correction factor due to water aging at 37° C was indicated for only the hand-mixed Zimmer LVC cement. There was, however, no significant change in fracture toughness due to water aging.
Complex Dielectric Properties of Tooth Constituents
Authors: Masi James V. , Masi Louis C.
Published: March 2011

Due to the recently indicated causal relationship between the piezoelectric properties of teeth and the formation of root caries, a study was undertaken to further classify the dielectric properties of the actual tooth constituents. The properties considered are the real and imaginary components of the complex dielectric constant, including the electrical conductivity, for human teeth in vitro, both dry and saline solution saturated. The frequency range covered is from 1 Hz to 1.35 GHz. An attempt has been made to present the data for the two most prominent constituents, namely, enamel and dentin. Ways in which the dielectric properties can aid physiological studies and an understanding of the caries process are also described. Some possible explanations for the biological and physiological processes in the dielectric properties of tooth constituents are given. Pathological variations among teeth are noted. Some hypotheses for causal relationships between caries and electrical properties of natural dental constituents are proposed.
Adhesion and Electrical Insulation of Thin Polymeric Coatings Under Saline Exposure
Authors: Leyden R. N. , Basiulis D. I.
Published: March 2011

A study was made of the adhesion of insulating polymer coatings under long term exposure to electrical bias. Since a common mode of failure in implanted devices is the penetration of water into poorly adhering insulation/conductor interfaces followed by electrolytic degradation, development of processes, primers, and insulators with good adhesion that resist the effects of water were sought. Polyimide coatings were tested for their ion barrier properties by immersion of insulated comb patterns in saline with 9 V D.C. bias between the comb fingers. Leakage currents, measured over three years exposure, increased from several picoamps initially to several nanoamps in surviving specimens. Subsequent studies showed that dramatic improvements in the moisture durability of the adhesion could be obtained using Hitachi's aluminum chelate type primer. Whereas the peel strength of polyimide on unprimed platinum fell more than 90% after several hours of boiling saline exposure, the peel strength of polyimide coatings on primed surfaces remained at over 80% of their initial values. ESCA analysis of the peel interfaces showed that both aluminum oxide and polyimide remain on the substrate after peeling back the polyimide. This suggests a combination of cohesive and adhesive failure at the primer/polyimide interface. The effects of exposure of the polymer/substrate interfaces (edges) to saline and electrochemical stress were examined by patterning circular openings in the polyimide. A 10 V anodic potential was found to damage adhesion to titanium as far as 75 microns away from the edge. Pulsing at 500 Hz, 1 V peak to peak was found to have no measurable effect in the short term.
Softenable, Shape-Memory Thermoplastic for Use in Biomedical Devices
Authors: White Kathleen A. , Ward Robert S.
Published: March 2011

Many implantable biomedical devices could benefit from a material with a strongly temperature-dependent modulus. Catheters made from such a material could be inserted as a stiff plastic, and upon reaching body temperature, would soften dramatically to minimize erosion of adjacent tissue. Sutures could be stiff during placement in an incision, heated slightly to form a shape to hold the suture in place, and then cooled. A new family of materials known as softenable, shape-memory thermoplastics have a distinct and adjustable thermal transition that produces a dramatic change in modulus at a predetermined temperature (range)
The Role of Fibrinogen in Platelet Interaction with Methacrylate Polymers
Authors: Lindon Jack N. , Shiba Eiichi , Kushner Leslie , Salzman Edwin W.
Published: March 2011

When blood comes in contact with a foreign surface, protein adsorption occurs within seconds and precedes the arrival of blood cells. Since a layer of plasma proteins is laid down on any surface in contact with blood before the platelets arrive, differences in platelet reactivity with different surfaces must result from variations in the nature of the protein-surface interactions. These interactions may vary in terms of which proteins bind to the surfaces, the amounts bound, and the various changes in protein conformation induced by surface contact.
Effects of Ion Implantation on Protein Adsorption onto Silicone Rubber
Authors: Suzuki Yoshiaki , Kusakabe Masahiro , Iwaki Masaya , Kusakabe Kiyoko , Akiba Hiromichi , Suzuki Masaaki
Published: March 2011

A study has been made on the surface wettability, atomic ratio, chemical structure, chemical bonding states and plasma protein adsorption of ion implanted silicone rubbers. C+-, N2+-, 02+-, Ar+- and Na+-ion implantations were performed at an energy of 150 keV at room temperature. The doses ranged from 1x1012 to 1x1017 ions/cm2. Ion implantation caused the surface roughness to increase by 1–5 times. Surface wettability was estimated by means of a sessile drop method using water. With increasing ion dose, the contact angle of water decreased from 98.9° to 48.5°. However, if the sample was in the air, the contact angle of water returned to its initial valve in time elapsed. The results of XPS measurements showed that implanted elements were incorporated in a gaussian like distribution and host elements were redistributed in the polymer matrix. No change of binding energies of 01s, CIS, Si2p and Si2p can be observed upon ion implantation. Results of FT-IR-ATR showed that C+-, N2+-, 02+-, and Ar+-ion implantation decomposed the original chemical bonds to form the new radicals. The amounts of new radicals are related to doses of implanted ions. In contrast, Na+-ion implantation hardly formed new radicals. The amount of albumin adsorbed onto 02+-, Ar+-, N2+-, and C+- ion implanted silicone is less than that on unimplanted specimens, but more fibrinogen is adsorbed. Na+-ion implantation produced an increase in the amount of adsorbed albumin as the dose increased. In summary, Na+ion implantation produces effects that are attributable to the additional implanted constituent in the surface of the silicone, and 02+-, N2+-, C+-, and Ar+-ion implantations primarily cause radiation effects on silicone rubber.
Ion Implanted Glassy Carbon - Comparison Wear Testing with Pyrolytic Carbon
Authors: Pollock John T. A. , Wielunski Leszek S.
Published: March 2011

Comparative wear data for unimplanted and implanted (50 keV, 5 × 1015 N+ cm−2) glassy carbon (GC) and pyrolytic carbon (PC) are reported. The implanted GC is about 120 times more resistant to diamond abrasion than unimplanted GC and at least 10 times more resistant than PC. In sliding tests, using a ruby ball as the abrader, the implanted GC is almost unaffected for the conditions employed (50 g load, 30,000 revs) compared with the unimplanted GC and unimplanted PC each of which endured measurable wear. The reasons for the enhancement of wear resistance and the ease with which 1–2 μm thick layers may be produced are discussed.
Biocorrosion Studies of Gold and Rhodium Ion Implanted Titanium and Ti-6Al-4V Alloy
Authors: Lee In-Seop , Buchanan R. A. , Williams J. M.
Published: March 2011

Concern continues over the possible long-term biological effects of corrosion products released by degradation of metallic surgical implant materials in the human body. One approach to improve long-term biological performance involves surface modifications to significantly reduce degradation rates. Fundamentally, the elements with lowest driving forces (lowest ΔG functions) for corrosion in aqueous solutions over a wide pH range are the noble metals. With regard to surface-modifications, one of the most effective methods is through ion implantation.

In the present on-going study, static in vitro corrosion properties of noble-metal ion-implanted surgical Ti-6Al-4V and commercially-pure(CP) Ti are being investigated in nonpassivating acid and passivating saline solutions. It was postulated that during the early stages of corrosion (or during a corrosion pretreatment) the implanted noble metal would enrich at the surface and significantly reduce subsequent corrosion rates. Thus far, the effects of ion-implanted Au and Rh have been studied, with mixed results. The Au implanted material yielded early benefits, but the enhanced corrosion resistance deteriorated with time, probably because the Au, during the enrichment stage, was not adequately adherent to the substrate. On the other hand, the observed behavior for the Rh implanted material appeared to follow the postulated mechanism, with both initial and time-dependent improvements in corrosion resistance.