270 research outputs found
Reconstruction of irradiated bone segmental defects with a biomaterial associating MBCP+®, microstructured collagen membrane and total bone marrow grafting: An experimental study in rabbits
The bone tissue engineering models used today are still a long way from any oncologic application as immediate postimplantation irradiation would decrease their osteoinductive potential. The aim of this study was to reconstruct a segmental critical size defect in a weight-bearing bone irradiated after implantation. Six white New Zealand rabbits were immediately implanted with a biomaterial associating resorbable collagen membrane EZ® filled and micro-macroporous biphasic calcium phosphate granules (MBCP+®). After a daily schedule of radiation delivery, and within 4 weeks, a total autologous bone marrow (BM) graft was injected percutaneously into the center of the implant. All the animals were sacrificed at 16 weeks. Successful osseous colonization was found to have bridged the entire length of the defects. Identical distribution of bone ingrowth and residual ceramics at the different levels of the implant suggests that the BM graft plays an osteoinductive role in the center of the defect. Periosteum-like formation was observed at the periphery, with the collagen membrane most likely playing a role. This model succeeded in bridging a large segmental defect in weight-bearing bone with immediate postimplantation fractionated radiation delivery. This has significant implications for the bone tissue engineering approach to patients with cancer-related bone defects
Modulated Rashba interaction in a quantum wire: Spin and charge dynamics
It was recently shown that a spatially modulated Rashba spin-orbit coupling
in a quantum wire drives a transition from a metallic to an insulating state
when the wave number of the modulation becomes commensurate with the Fermi wave
length of the electrons in the wire. It was suggested that the effect may be
put to practical use in a future spin transistor design. In the present article
we revisit the problem and present a detailed analysis of the underlying
physics. First, we explore how the build-up of charge density wave correlations
in the quantum wire due to the periodic gate configuration that produces the
Rashba modulation influences the transition to the insulating state. The
interplay between the modulations of the charge density and that of the
spin-orbit coupling turns out to be quite subtle: Depending on the relative
phase between the two modulations, the joint action of the Rashba interaction
and charge density wave correlations may either enhance or reduce the Rashba
current blockade effect. Secondly, we inquire about the role of the Dresselhaus
spin-orbit coupling that is generically present in a quantum wire embedded in
semiconductor heterostructure. While the Dresselhaus coupling is found to work
against the current blockade of the insulating state, the effect is small in
most materials. Using an effective field theory approach, we also carry out an
analysis of effects from electron- electron interactions, and show how the
single-particle gap in the insulating state can be extracted from the more
easily accessible collective charge and spin excitation thresholds. The
smallness of the single-particle gap together with the anti-phase relation
between the Rashba and chemical potential modulations pose serious difficulties
for realizing a Rashba-controlled current switch in an InAs-based device. Some
alternative designs are discussed.Comment: 20 pages, 6 figure
EVALUATION OF THE NEWLY FORMED BONE IN IRRADIATED AREAS BY ADDITION OF MESENCHYMAL STEM CELLS TO THE ASSOCIATION OF BIPHASIC CALCIUM PHOSPHATE AND TOTAL BONE MARROW
Oral Communication presented at the ";Forum des Jeunes Chercheurs";, Brest (France) 2011
Radiation effects on bone healing and reconstruction: interpretation of the literature
Objective
Reconstructing irradiated mandibles with biomaterials is still a challenge but little investigated. We collected data that could help us understand studies in the field of regeneration with biomaterials and irradiated bone.
Study design
Systematic review of the literature.
Results
Delay and duration of radiation delivery and total equivalent dose are the most variable parameters in the various studies, resulting in confusion when interpreting the literature. Most reproducible experiments show that radiation reduces osteogenic cell numbers, alters cytokine capacity, and delays and damages bone remodeling. Interindividual variations and how such changes become irreversible lesions are still uncertain. In the case of regeneration using biomaterials, most studies have addressed the question of reconstruction in previously irradiated bone. The results show that osseointegration is often possible, although the failure rate is higher. The sooner the implantation takes place after the end of the radiation, the higher the likelihood of failure. Few studies have focused on primary reconstruction followed by early irradiation, and most of the currently available engineering models would be altered by radiation. Good outcomes have been obtained with bone morphogenetic protein and with total bone marrow transplanation.
Conclusion
This review points out the difficulties in achieving reproducible experiments and interpreting literature in this underinvestigated field
Mandibular Segmental Defect Regenerated With Macroporous Biphasic Calcium Phosphate, Collagen Membrane, and Bone Marrow Graft in Dogs
OBJECTIVE:
To reconstruct segmental mandibulectomy using calcium phosphate ceramics and collagen membrane with a delayed bone marrow grafting in experimental animals.
DESIGN:
Defects of segmental mandibulectomy were filled with calcium phosphate granules and wrapped with a collagen membrane in 4 dogs and left empty as a control in 2 dogs. Two months later, a bone marrow graft was injected into the center of the implants. Animals were humanely killed after a 16-week delay.
SUBJECTS:
Six adult beagles were included in this study.
INTERVENTION:
Segmental mandibulectomy.
MAIN OUTCOME MEASURE:
Bone ingrowth and material resorption in the reconstructed segment.
RESULTS:
Successful osseous colonization bridged the whole length of the defects. The good new bone formation at the center and the periosteum-like formation at the periphery suggest the osteoinductive role of the bone marrow graft and the healing scaffold role of the membrane.
CONCLUSIONS:
This model succeeded in regenerating a large segmental defect in the mandible. An investigation with a postimplantation radiation delivery schedule is required with the use of this model, which should be considered as a preclinical study for a bone tissue engineering approach in patients with cancer-related bone defects
Guidelines of the French Society of Otorhinolaryngology (SFORL), short version. Extension assessment and principles of resection in cutaneous head and neck tumors
AbstractCutaneous head and neck tumors mainly comprise malignant melanoma, squamous cell carcinoma, trichoblastic carcinoma, Merkel cell carcinoma, adnexal carcinoma, dermatofibrosarcoma protuberans, sclerodermiform basalioma and angiosarcoma. Adapted management requires an experienced team with good knowledge of the various parameters relating to health status, histology, location and extension: risk factors for aggression, extension assessment, resection margin requirements, indications for specific procedures, such as lateral temporal bone resection, orbital exenteration, resection of the calvarium and meningeal envelopes, neck dissection and muscle resection
The electronic properties of bilayer graphene
We review the electronic properties of bilayer graphene, beginning with a
description of the tight-binding model of bilayer graphene and the derivation
of the effective Hamiltonian describing massive chiral quasiparticles in two
parabolic bands at low energy. We take into account five tight-binding
parameters of the Slonczewski-Weiss-McClure model of bulk graphite plus intra-
and interlayer asymmetry between atomic sites which induce band gaps in the
low-energy spectrum. The Hartree model of screening and band-gap opening due to
interlayer asymmetry in the presence of external gates is presented. The
tight-binding model is used to describe optical and transport properties
including the integer quantum Hall effect, and we also discuss orbital
magnetism, phonons and the influence of strain on electronic properties. We
conclude with an overview of electronic interaction effects.Comment: review, 31 pages, 15 figure
Negative Thermal Expansion Coefficient of Graphene Measured by Raman Spectroscopy
The thermal expansion coefficient (TEC) of single-layer graphene is estimated
with temperature-dependent Raman spectroscopy in the temperature range between
200 and 400 K. It is found to be strongly dependent on temperature but remains
negative in the whole temperature range, with a room temperature value of
-8.0x10^{-6} K^{-1}. The strain caused by the TEC mismatch between graphene and
the substrate plays a crucial role in determining the physical properties of
graphene, and hence its effect must be accounted for in the interpretation of
experimental data taken at cryogenic or elevated temperatures.Comment: 17 pagese, 3 figures, and supporting information (4 pages, 3
figures); Nano Letters, 201
A Scaling Approach for Interacting Quantum Wires -a Possible Explanation for the 0.7 Anomalous Conductance
We consider a weakly interacting finite wire with short and long range
interactions. The long range interactions enhance the scattering and
renormalize the wire to a strongly interacting limit. For large screening
lengths, the renormalized charge stiffness Luttinger parameter
decreases to , giving rise to a Wigner crystal at T=0 with an
anomalous conductance at finite temperatures.
For short screening lengths, the renormalized Luttinger parameter
is restricted to . As a result, at temperatures
larger than the magnetic exchange energy we find an interacting metal which for
is equivalent to the Hubbard model, with
the anomalous conductance .Comment: 26 pages and 6 figure
Properties of Graphene: A Theoretical Perspective
In this review, we provide an in-depth description of the physics of
monolayer and bilayer graphene from a theorist's perspective. We discuss the
physical properties of graphene in an external magnetic field, reflecting the
chiral nature of the quasiparticles near the Dirac point with a Landau level at
zero energy. We address the unique integer quantum Hall effects, the role of
electron correlations, and the recent observation of the fractional quantum
Hall effect in the monolayer graphene. The quantum Hall effect in bilayer
graphene is fundamentally different from that of a monolayer, reflecting the
unique band structure of this system. The theory of transport in the absence of
an external magnetic field is discussed in detail, along with the role of
disorder studied in various theoretical models. We highlight the differences
and similarities between monolayer and bilayer graphene, and focus on
thermodynamic properties such as the compressibility, the plasmon spectra, the
weak localization correction, quantum Hall effect, and optical properties.
Confinement of electrons in graphene is nontrivial due to Klein tunneling. We
review various theoretical and experimental studies of quantum confined
structures made from graphene. The band structure of graphene nanoribbons and
the role of the sublattice symmetry, edge geometry and the size of the
nanoribbon on the electronic and magnetic properties are very active areas of
research, and a detailed review of these topics is presented. Also, the effects
of substrate interactions, adsorbed atoms, lattice defects and doping on the
band structure of finite-sized graphene systems are discussed. We also include
a brief description of graphane -- gapped material obtained from graphene by
attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic
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