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1.
Opt Express ; 21(19): 22645-56, 2013 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-24104152

RESUMO

Since one hundred years it is known that some scarab beetles reflect elliptically and near-circular polarized light as demonstrated by Michelson for the beetle Chrysina resplendens. The handedness of the polarization is in a majority of cases left-handed but also right-handed polarization has been found. In addition, brilliant colors with metallic shine are observed. The polarization and color effects are generated in the beetle exoskeleton, the so-called cuticle. The objective of this work is to demonstrate that structural parameters and materials optical functions of these photonic structures can be extracted by advanced modeling of spectral multi-angle Mueller-matrix data recorded from beetle cuticles. A dual-rotating compensator ellipsometer is used to record normalized Mueller-matrix data in the spectral range 400 - 800 nm at angles of incidence in the range 25-75°. Analysis of data measured on the scarab beetle Cetonia aurata are presented in detail. The model used in the analysis mimics a chiral nanostructure and is based on a twisted layered structure. Given the complexity of the nanostructure, an excellent fit between experimental and model data is achieved. The obtained model parameters are the spectral variation of the refractive indices of the cuticle layers and structural parameters of the chiral structure.


Assuntos
Algoritmos , Besouros/fisiologia , Besouros/ultraestrutura , Tegumento Comum/fisiologia , Modelos Biológicos , Refratometria/métodos , Animais , Simulação por Computador , Modelos Estatísticos , Análise de Regressão , Propriedades de Superfície
2.
Biomatter ; 2(2): 94-102, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-23507807

RESUMO

Many of the failures of total joint replacements are related to tribology, i.e., wear of the cup, head and liner. Accumulation of wear particles at the implants can be linked to osteolysis which leads to bone loss and in the end aseptic implant loosening. Therefore it is highly desirable to reduce the generation of wear particles from the implant surfaces. Silicon nitride (Si(3)N(4)) has shown to be biocompatible and have a low wear rate when sliding against itself and is therefore a good candidate as a hip joint material. Furthermore, wear particles of Si(3)N(4) are predicted to slowly dissolve in polar liquids and they therefore have the potential to be resorbed in vivo, potentially reducing the risk for aseptic loosening. In this study, it was shown that α-Si(3)N(4)-powder dissolves in PBS. Adsorption of blood plasma indicated a good acceptance of Si(3)N(4) in the body with relatively low immune response. Si(3)N(4) sliding against Si(3)N(4) showed low wear rates both in bovine serum and PBS compared with the other tested wear couples. Tribofilms were built up on the Si(3)N(4) surfaces both in PBS and in bovine serum, controlling the friction and wear characteristics.


Assuntos
Artroplastia de Quadril/instrumentação , Articulação do Quadril/patologia , Falha de Prótese , Compostos de Silício/química , Adsorção , Animais , Artroplastia de Quadril/métodos , Materiais Biocompatíveis/química , Bovinos , Humanos , Sistema Imunitário , Teste de Materiais , Microscopia Eletrônica de Varredura , Osteólise , Plasma/efeitos dos fármacos , Risco , Solubilidade , Estresse Mecânico , Propriedades de Superfície
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