I když historie objevů a využití chemických
prvků v souvislosti s jejich technickým významem i dějinnými událostmi je z
hlediska metodologického zajímavá, je jí věnován velmi malý prostor ve výuce
přírodních věd na všech stupních vzdělávací soustavy. Fascinující myšlenka,
že rozmanitost přírody, která nás obklopuje, je tvořena jen z relativně
malého počtu „stavebních kamenů“, se vynořila ve vývoji lidského myšlení
poměrně brzy a nahradila tak ještě starší domněnku, že svět vznikl z jediné
prahmoty. S touto představou se můžeme setkat již v indických vědách
pocházejících zhruba z 12. století před naším letopočtem a v nejstarších
písemných pramenech řecké kultury.
Jako látka byl uhlík znám již v pravěku (dřevěné uhlí, saze), ale skutečnost
, že se jedná o prvek, byla prokázána až v druhé polovině osmnáctého století.
Mezinárodní název uhlíku “carbon” je odvozen od latinského carbo, čímž
Římané označovali dřevěné uhlí. Uhlík se široce vyskytuje v přírodě,
elementární uhlík byl dokázán ve vesmíru: na Slunci, hvězdách, kometách a v
atmosféře planet.
V porovnání s ostatními prvky má uhlík řadu unikátních vlastností jak
fyzikálních (mechanických), tak i chemických, např.:
nejpevnější a
nejtvrdší materiál – diamant
nejlepší mazadlo (lubrikant) – grafit
nejpevnější vlákna
nejlepší adsorbent plynů – aktivní uhlí
nejlepší héliová bariéra – skelný uhlík
nejvíce sloučenin jak anorganických, tak zejména organických
nejrozmanitější struktury objevené v posledních desetiletích jako je
molekula fullerenu, nanotrubice, magnetické nanopěny
Z výše uvedeného výčtu je zřejmé, že uhlík má mezi prvky zcela výjimečné
postavení a můžeme jej korunovat na „krále prvků“. Historie jeho poznávání a
využívání je velmi dlouhá a bohatá. Protože však komplexní souhrn informací
by byl nepřehledný, dovolili jsme si jej rozdělit podle forem uhlíku, zvlášť
tedy základní informace o dřevěném uhlí, aktivním uhlí a sazích, informace o
diamantu, grafitu (a uhlíkových vláknech a nanovláknech) a moderních formách
uhlíku:
Informace o dřevěném uhlí, aktivním uhlí a sazích
velký třesk
vznik prvků vodíkovým, heliovým a uhlíkovým hořením – vznik
uhlíku ve Vesmíru a jeho přeměna na další prvky
–20 000 let
lidstvo poznalo oheň a dřevěné uhlí
3750 BC
Egypťané a Sumerové používají dřevěné uhlí k redukci Cu, Sn a Zn z
jejich rud
2000 BC
Dřevěné uhlí se používá jako domácí bezdýmé palivo
1500 BC
Egypťané použili dřevěné uhlí v medicíně (trávicí potíže)
450 BC
Féničané uskladňují pitnou vodu v sudech pokrytých
zevnitř dřevěným uhlím, na Hindu byly použity filtry z písku a
dřevěného uhlí pro úpravu pitné vody
400 BC
Hippokrates popisuje širší využití dřevěného uhlí v
medicíně
100 BC
"inkoust indiánů" vyráběný ze sazí
50 BC
Číňané a Egypťané používají saze jako černý pigment
50 AD
Plinius starší ve svém díle Naturalis historia
popsal diamant a lékařské použití dřevěného uhlí
157 AD
Klaudius Galen uvádí 500 lékařských předpisů na
lékařské využití dřevěného uhlí
1478
Leonardo da Vinci kreslí své náčrty dřevěným uhlem
1773
C.W. Scheele používá práškové dřevěné uhlí k
adsorpci plynů
1777
kondenzační teorie adsorpce na dřevěném uhlí
1785
J.T. Lowitz – adsorpce organických par na dřevěném
uhlí, odbarvování vodných roztoků
1789
A.L. Lavoisier navrhl název „carbon“
1794
dřevěné uhlí použito v Anglii k odbarvení cukerných
sirupů, ale postup utajen
1805
Gruillon (Francie) – první průmyslové využití
dřevěného uhlí v cukrovarnictví
1805
H. Davy ukázal, že zdrojem svítivosti plamene jsou
saze
1805-1808
B. Delessert rozšiřuje čištění cukerné šťávy do
všech cukrovarů
1811-1817
první „kostní“ uhlí
1812
první cukr z řepy (čištěný dřevěným uhlím)
1822
A.A. Bussy popsal, že odbarvovací schopnost uhlí
závisí na technologii jeho výroby (teplota, čas, chemismus)
1854
použití filtrů s dřevěným uhlím na ventilaci kanálů
v Londýně
1862
Lipscombe připravil uhlí pro úpravu pitné vody
1865
Hunter připravil uhlí ze skořápek kokosových ořechů
1881
H.G.J. Kayser použil termín „adsorpce“
1901
Von Ostrejko – aktivní uhlí za použití chloridů před
karbonizací a opatrnou oxidací pomocí vodní páry nebo CO2
1911
první průmyslové aktivní uhlí značka Eponit (Fantovy
závody, Rakousko)
1913
Wünsch reaktivuje Eponit pomocí chloridu zinečnatého
1922
saze rozkladem zemního plynu (hlavní produkt vodík
pro vzducholodě)
1935
Česká republika zahájila jako první na světě
tabletování aktivního uhlí
Historická data související s diamantem
vznik Země
200 km pod povrchem Země vzniká za vysokých teplot a
tlaků diamant
800 BC
V Indii nalezeny diamant v náplavách řek
500-600 BC
diamanty z Indie dováženy do Evropy
322-185 BC
diamant v Evropě součástí šperků
1074
Maďarská královnina koruna má snad první opracovaný
diamant
H.W. Kroto, R.F. Curl a R.E. Smalley získali Nobelovu cenu za objev
fullerenu
2001
monokrystaly z uhlíkových nanotrubic
2002
připravena uhlíková nanopěna
2003
použití fullerenů v medicíně
2003
tranzistor z uhlíkových nanotrubic
2004
vlákno v žárovce z uhlíkových nanotrubic
2004
zjištěny paramagnetické vlastnosti uhlíkových nanopěn
Obr. 1 Modely nanotrubic
V historii měla každé období mezi prvky svého
„favorita“. V pravěku a raném středověku to byly kovy – zlato, stříbro, měď
a železo, v pozdním středověku patřily k těmto prvkům antimon a fosfor. V
období počátků moderní chemie se na toto místo dostal kyslík. Současné
období je charakterizováno „uměle“ připravenými prvky. Které prvky se
dostanou do popředí zájmu v dalším období můžeme pouze spekulovat, ale
uhlík, který v posledních letech nabízí neuvěřitelně široké možnosti
aplikací a forem, bude určitě především v souvislosti s nástupem
nanotechnologií jedním z prvních v řadě.
Jak je z výše uvedeného přehledu patrné, historie objevů a využití uhlíku a
jeho sloučenin je velmi dlouhá a teprve další rozvoj vědy a techniky ukáže
meze jeho využití v časech budoucích. Považujeme–li zlato za „krále kovů“,
pak uhlík je zcela určitě „králem prvků“.
Poznámka: na adrese jan.gregr@vslib.cz
je možné objednat tento text doplněný obrázky ve formě plakátu o rozměru cca
84 x 63 cm.
ODDĚLENÍ KOMPOZITNÍCH A UHLÍKOVÝCH MATERIÁLŮ
SOUČASNÝ VÝZKUM
Výzkumná činnost je zaměřena na studium moderních vláknových kompozitů (biokompatibilních
kompozitů uhlík – uhlík a sklo-siloxan a tepelně odolných kompozitů s
keramickou matricí) připravovaných pyrolýzou kompozitů (prekurzorů) s
polymerní matricí. Věnuje se optimalizaci procesů přípravy, vztahům mezi
strukturou a vlastnostmi studovaných materiálů, a hledání možných aplikací.
Jako vláknová výztuž kompozitů jsou používána uhlíková vlákna nebo tkaniny,
keramická vlákna (SiC nebo Al2O3) nebo vlákna a tkaniny z E-skla, R-skla či
taveného čediče. Pravidelné vrstevnaté uspořádání vláken smočených polymerní
matricí vytváří strukturu budoucího kompozitu a určuje anizotropii jeho
vlastností. Druh použitého polymeru předurčuje typ matrice vzniklé pyrolýzou
(tj. tepelným rozkladem v inertní atmosféře): při použití fenolické
pryskyřice vzniká kompozit s matricí uhlíkovou, zatímco z polysiloxanové
pryskyřice vzniká tepelně odolná keramická matrice obsahující skupiny SiOC.
Procesy přípravy zahrnují také opakovanou impregnaci kompozitů pryskyřicí s
cílem zvýšit jejich hustotu a snížit výskyt dutin, vysokoteplotní zpracování
(až 2500°C pro kompozit uhlík-uhlík) pro zlepšení mechanických vlastností a
infiltraci pyrolytickým uhlíkem či křemíkem z plynné fáze pro zlepšení
povrchových vlastností.
Mikrostruktura připravených kompozitů je sledována optickou mikroskopií a
kvantitativně hodnocena metodou obrazové analýzy. Mechanické vlastnosti
(modul pružnosti a mez pevnosti) jsou studovány pomocí univerzálního
testovacího stroje do teploty 1400°C. Dynamické moduly v tahu a ve smyku
jsou měřeny metodou rezonančních frekvencí při laboratorní teplotě. Poznatky
slouží nejen k posouzení sladění mechanických vlastností kompozitů s
vlastnostmi kostí v případě biomateriálů, ale též k hodnocení odolnosti (či
degradace) kompozitů v nepříznivých podmínkách a k optimalizaci volby
výchozích složek a procesů tepelné přípravy.
Biokompatibilita připravených kompozitů, tj. zejména testy „ in vitro“a „in
vivo“ a jejich možné využití v chirurgických implantátech jsou zkoumány ve
spolupráci s externími pracovišti.
Otiskujeme poslední publikovaný článek z 12. mezinárodní konference
biomedicínského inženýrství (The 12th International Conference on Biomedical
Engineering
7 - 10 December 2005, Suntec Singapore International Convention and
Exhibition Centre, SINGAPORE).
BIOMECHANICAL PROPERTIES OF POROUS
COMPOSITES BASED ON GLASS AND POLYSILOXANE
K. Balik*, M. Sochor**, T. Suchy*,**, M.
Cerny*, R. Sedlacek**, H. Hulejova*** and V. Pesakova***
* Institute of Rock Structure and
Mechanics, Academy of Sciences of the Czech Republic, Prague, Czech Republic
** Faculty of Mechanical Engineering, Department of Mechanics, Czech
Technical University, Prague, Czech Republic
*** Institute of Rheumatism, Prague, Czech Republic
Abstract
Fiber composites, based on glass fibers and polysiloxanes, were prepared. On
their surface, pores, having sizes ranging 200-400, 400-600 and larger than
600 m, were made, and, into the matrices of
selected composites, powdered hydroxyapatite was added. The materials were
then tested mechanically: their flexural strength, Young’s modulus of
elasticity in tension and modulus of elasticity in shear and strength in
compression were measured. Also the wettability of the composites was
measured, and in-vitro and in-vivo tests were carried out. The composites
displayed good mechanical properties, comparable with those of the human
bone, and a satisfactory bio-tolerance.
INTRODUCTION
Efforts to produce artificial replacements of
parts of the human body have a very long history. In ancient civilizations,
whether ancient Indians, Egyptians or Chinese, this concerned primarily
replacements of facial parts: ears, noses, teeth, etc. With regard to the
bone surgery, natural replacements, which can be obtained by operating on
the patient, are now frequently used, which, however, entail some
disadvantages: an additional operation, possible infection and loss of blood.
To prevent them, artificial replacements are used instead. The best known
ones are metal implants. Their problem consists in their higher rigidity
being unnatural for the bone, which can lead to the spongialization of the
bone [1]. On the other hand, disadvantages of synthetic polymers lie in
their low mechanical strength. Ceramic and glass materials are also
frequently used. Some of them show a very good bioactivity, which enables a
good osseo-integration. However, their frequent disadvantages are either a
low mechanical strength, or, when having a higher strength, a considerable
brittleness. Composite materials, to be used in the bone surgery, have been
studied as well. Carbon-polymer composites have outstanding mechanical
properties, but when exposed for a longer period of time in the body, the
polymer tends to degrade to a monomer, which is no longer biotolerant.
Carbon-carbon composites also show satisfactory mechanical properties, they
are bio-inert, but their preparation is very demanding and expensive, and,
when exposed to the live organism, they often release carbon particles [2,
3, 4, 5, 6].
The purpose of this study was to suggest a simple method of preparing
composite materials, which would display close mechanical properties to the
human bones, with optimum size of open pores, which would enable the down-growth
of osteoblasts, and containing additional bioactive components in the matrix.
Materials and Methods
The composites were prepared from a plain-woven V240 cloth (E-glass,
VETROTEX, Litomysl, Czech Republic) and from 21055 satin-woven fabric (R-glass,
VETROTEX, Saint Gobain, France) and polysiloxanes LUKOSIL 901 (L901) and
LUKOSIL M130 (M130) (Lucebni zavody Kolin, Czech Republic) as the matrix
precursor. The precursor used enables curing at temperatures of 200-350°C in
a nitrogen atmosphere. The composite formed of R-glass + L901 was excluded
from further tests, because it displayed excessive delamination. The
percentages by fiber volume (Vf) in the composites with woven material from
E-glass were 52%, and in the sample with R-glass 65%.
For further treatment, aiming at enhancing the material ability to stimulate
the down-growth of bone tissue, we chose the R-glass+M130 composite type,
which displayed the most suitable mechanical properties (see Results) as
compared with the properties of the human cortical bone and, at the same
time, satisfied the high demands imposed on the biotolerance of implants.
With regard to the treatment of the surface structure, a method of pressing
separated fractions of special salt into the surface of the uncured
composite and their subsequent elution after curing was applied (see Figures
1 and 2). In this way, three types of surfaces were obtained with different
open pore sizes: 200-400, 400-600 and over 600 m. The porous samples,
inclusive of the samples with untreated surface, were then subjected to in
vivo and in vitro tests. Another group of samples consisted of materials
with the same surface treatment, but simultaneously modified by adding
matrix with an admixture of powder hydroxyapatite (HAp), particle size 5
m.
Figure 1: Treated surface of the glass
composite
(R-glass+M130, pore sizes 400-600 m)
To guarantee the correctness of results obtained, the composite mechanical
properties were tested using several methods. Young’s modulus (Eres.) and
the shear modulus in elasticity (Gres.) were measured by the ERUDITE
electrodynamic resonant frequency tester. Young’s modulus (E4p.b.) and the
bending strength (Rm) were determined by a four-point and a three-point
bending arrangements on the INSPEKT material tester. Young’s modulus (Estr.)
and the compressive strength (Rstr). were measured on samples with
dimensions enabling the application of strain gauges while loading the
samples parallel to the composite laminae in the MTS material tester.
Figure 2: Detail of the pore (R-glass+M130, pore sizes ranging from 400 to
600 m)
To assess the effect of the various sizes of open pores on the wettability
of the composites by a body fluid solution, the samples were tested using
the Wilhelmy plate method in a simulated body fluid (SBF).
Biotolerance tests are an indispensable part of developing bio-materials.
Biological properties were observed using in-vitro tests: adherence,
proliferation and metabolic activity of cells growing on the tested
materials, and levels of inflammatory cytokines exprimed during the
cultivation into the cell medium. The medium of this cultivation experiment
was performed for cytokines TNF-, IL-1 detection using the immuno-chemiluminescence
method of the Immulite analyser (DCP, Los Angeles, USA).
In-vivo tests were carried out in the form of testing the mechanical
strength of the bone-implant interface (Pull-off tests, Nakamura’s method,
[7, 8, 9, 10]): the implants had been implanted for 7 weeks in the rabbit
femur and, after extracted, they were subjected to tensile tests in which
the samples were loaded perpendicular to the adhesion surface (see Fig. 3).
These pull-off tests were carried out on R-glass+M130 samples with untreated
surface and on three types of samples differing in pores size ranging
200-400, 400-600 and over 600 m. First results
obtained by this method were used to determine the optimum size of the pores,
and next samples to be tested were further modified by HAp.
Figure 3: The segment of a rabbit bone with the composite sample
Results
The purpose of the mechanical tests was to test the behavior of the
composites. A material was sought to have properties similar to those of the
human bone. The mechanical testing performed (see Figures 4 - 6) indicated
that the glass composites can be applied, with regard to their lower
rigidity and a sufficient flexural strength, for example as internal bone
plates for osteosynthesis of long bones. The bone plates made of this
material can guarantee sufficient transfer of load and, moreover, enable a
partial loading of the bone, which beneficially effects the proliferation of
the bone tissue and its remodeling.
Figure 4: The Mechanical properties of the glass composites
Figure 5: Young’s modulus of the glass composites and the human bone [11,
12]
Figure 6: Flexural strength of the glass composites and the human bone [11,
12]
Figure 7: Advancing contact angles, based on the pore sizes, characterize
the wettability of the composites
The results of the in-vitro tests indicate that the glass composites are not
toxic and do not cause any reaction in the human organism, which would
hinder their easy acceptance. This fundamental assumption was also confirmed
by the in-vivo tests, carried out in rabbits. Apart from the comparison of
materials with different surface structures, the pull-off tests also
provided further facts about the composites developed. None of the rabbits
displayed inflammation processes, or other side reactions to the implanted
materials.
The pull-off tests carried out provided further data useful in assessing the
effect of the size of open pores on the growth of bone tissue. The results
indicate that the optimum pore size, stimulating bone tissue growth without
an excessive formation of fibrous tissue, which depreciates the strength of
the connection, ranges from 400 to 600 m. A stronger adhesion can be
achieved by adding hydroxyapatite to the composite matrix. Materials with
HAp displayed the strongest adhesion with the bones of the tested animals (see
Figure 8).
Figure 8: First results of the pull-off tests of the R-glass+M130 samples.
Relation: applied force- pore size
Discussion
Composite materials, which combine glass woven fabrics and polysiloxane
resins, display good mechanical properties, comparable with the human bone,
and also suitable bio-tolerance. Moreover, further treatment, namely a
change in the surface structure and changes of chemical composition by
adding HAp to the matrix, are able to stimulate osteoblasts at the implant-bone
interface to grow into open pores of optimum size.
Conclusions
Depending on the final treatments, it is possible to use these materials in
two ways: as an inert material, which does not adhere to the bone, e.g., for
use in the form of internal bone plates, or as a material supporting the
down-growth of osteoblasts, hence in the form of materials of filling-in and
connecting elements. Their optical properties, skin color, moreover, enable
them to be used in the dental and facial surgery.
Acknowledgements
This study was supported by the Grant Agency of the Czech Republic, GACR,
under the project No. 106/03/1167 and by the Ministry of Education project:
Transdisciplinary research in Biomedical Engineering II., No. MSM
6840770012.
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Czech – Polish Workshop on Advanced Composites
11. listopadu proběhl na našem ústavu česko – polský seminář zaměřený na
pokročilé kompozitní materiály. Každoroční workshop se letos soustředil
především na povrchové vlastnosti kompozitů určených pro tkáňové
inženýrství, hovořilo se o chování lidských tkání ve vztahu k implantovaným
kompozitním náhradám a o jejich biokompabilitě. Seminář se zaměřil na nové
směry ve vývoji kompozitů, například na nanotechnologie nebo na použití
nových materiálů jako kompozitních složek. Byly předneseny následující
příspěvky.
NEW PTFE – BASED COMPOSITE MEMBRANE FOR GUIDED BONE REGENERATION
E. Stodolak*, M. Blazewicz*, B. Czajkowska**
* Department of Biomaterials, Faculty of Materials Science and Ceramics, AGH
University Science and Technology, Krakow, Poland
** Department of Immunology, Collegium Medicum, Jagiellonian University,
Krakow, Poland
GBR technique allows to rebuild the osseous structure in predictably way. It
can be made by separating and isolating competing tissues from a healing
defect by the means of specific type of material barrier. For such technique
an implant material in the form of membrane is frequently used. Besides
obvious biocompatibility, such material ought to be capable of inhibiting
the connective tissue migration into the diseased site. It has to provide a
specific stiffness and sufficient strength and make a suitable space over
the healing site. An alternative for pure polymers membrane are composites
consisting of biostable polymers reinforced with biocompatible fibrous
components.
The goal of this work was to manufacture new composite membrane for guided
bone regeneration. The composite was made of three components, namely PTFE
matrix modified with carbon fibers as reinforcement possessing proven
biocompatibility. As a third alginate compounds biopolymer was used. The
composite samples in the form of thin membranes were prepared. stodolak@agh.edu.pl
MANUFACTURING OF CARBON NANOFIBER WEBS FROM ELECTROSPUN NANOFIBER PRECURSORS
E. Košťáková*, J. Grégr**,
J. Müllerová**
*Department of Nonwovens, Faculty of Textile
Engineering, Technical University of Liberec, Hálkova 6, 46117 Liberec,
Czech Republic
**Department of Chemistry, Faculty of Education, Technical University of
Liberec, Hálkova 6, 46117 Liberec, Czech Republic
Introduction
Nanofibers are generally fibers of diameter smaller than 1 m. This article
is focused on nanofibers produced during electrospinning process (Forhams,
1934). Modification of the method with higher efficiency of nanofiber
production has been developed recently at TUL and patented (Jirsák et al.,
2003 b).
First experiments of carbonization of electrospun nanofibers have been
realized in last years. Electrospun nanofiber materials made from non-aqueous
solutions are used as a precursor for carbonization in majority of articles:
e.g. polyacrylonitril (Wang et al., 2003 a, Wang et al., 2003 b),
polybenzimidazol (Kim and Kim, 2004, Kim et al., 2004). Only one article
being engaged in carbonization water-soluble polymer – polyvinyl alcohol
nanofibers was published on web (Fong, 2004).
Polyvinyl alcohol unfix physically fixed water in the course at heating, a
decomposition reactions occur at the temperature over 200 °C (Smolinski,
2003). Primarily polyens arise, thus water peels by degradation of hydroxyl
(OH) groups and hydrogen from carbon chain of macromolecule. This reaction
manifests itself by gradual yellowing, browning and then blackening of
fibers. If there is faster heating, it leads to decomposition to
acetaldehyde and crotonaldehyde and whole original structure of chains can
be damaged (destroyed). Polyen chains can their self each other join by
means of Diels-Alder addition at careful heating and eventual catalysis, or
their take place to intramolecular cycling. Created unsaturated cyclic
compounds are already considerably more stable against additional increasing
of temperature. An aromatization of these cycles comes into being at
temperature above 450 °C, thus a basic graphite structure arises. Remains of
water in the structure accelerate decomposition of structure to volatile
aldehydes, accordingly usage of flame retardant catalysts is convenient for
acquirement of the biggest possible carbonization gain.
Fig.1. Van der Waals surface of two chains of polyvinyl alcohol (a), Van der
Waals surface of two polyvinyl alcohol chains cross-linked (dehydration) by
phosphoric acid (b).
Experimental part
During our experiments, we have elected following operation: (i) a producing
of electrospun nanofiber web, (ii) an impregnation of web by means of
combustion retarder, (iii) stabilization - dehydration at temperature and (iv)
carbonization.
The nanofiber materials used in these experiments were produced at TUL and
had these parameters: PVA (polyvinylalcohol) with addition of glyoxal and
phosphoric acid for later cross-linking at 140°C for 10 minutes.; random
orientation of fibers; surface density 5 gm-2; average diameter
of fibers 236 ± 79 nm. We have tested more then twenty different samples,
which were created with different temperature cycles (regimes) up to 215 °C
in laboratory drier with different concentrations of combustion retarders –
phosphoric acid (H3PO4) in water solution and also we
used no aqueous solutions: H3PO4 in ethyl alcohol,
butyl alcohol and isopropyl alcohol, and (NH4)H2PO4
in ethyl alcohol.
Carbonization of samples was accomplished in a special oven (HIP) at these
conditions: inert nitrogen atmosphere, maximal temperature 1100 °C, pressure
inside 5 bars, rate of temperature’s growth 5 °C/minute.
We have studied result dehydrated nanofiber materials by means of infrared
spectroscopy and DSC, we have prepared images by means of scanning electron
microscope (SEM) and we have tested a result samples in the course of
combustion. After carbonization, we have used the same methods for studying
a result samples.
Results and conclusions
Impregnation by means of water solution: Results showed us the best samples
were stabilized by regime a up to 200 °C, water solution of 1,25 % and 2,5 %
by volume of H3PO4. These samples were after
stabilization completely black, they did not burn with flame and damaging,
DSC outputs did not show any changes, infrared spectrum showed a decline of
OH and CH groups and creating of conjugated double C=C bonds. However the
sticking of nanofibers after dehydration is visible from SEM pictures (see
Fig.2). Impregnation by means of alcohol solutions (the best was usage of
butyl alcohol) brought better results respecting the structure of resulting
carbonized samples. Of course we want to produce the carbon nanofibers with
large surface area, because we supposed that our carbonized electrospun
polyvinylalcohol nanofiber materials could be used as adsorbent or catalysts
because of the high surface density of the resulting carbon nanofiber
materials. We are determined to continue the research in the branch, use
other special method for detection of surface and material composition of
the nanofibers after the method of carbonization.
Fig.2. SEM images: (a) Polyvinyl alcohol nanofibers; (b) carbonized
nanofiber webs after impregnation of 1,25 % of H3PO4 in water solution; (c
and d) PVA nanofibers dipped to alcohols and drying at normal temperature -
(c) Butyl alcohol; (d) Isopropyl alcohol. The scale is 5 m at the pictures
(a), (b) and (c), 10 m at the picture (d).
References
Forhams A. (a): US Patent, 1,975,504 (1934)
Jirsák O. et al. (b): CZ patent 2003-2414 (2003)
Wang Y., Furlan R., Ramos I., Santiago-Aviles J. (a): IEEE
Transactions on Nanotechnology, 2, 39 (2003)
CERAMIC MATRIX COMPOSITES OBTAINED FROM POLYSILOXANE PRECURSORS
T. Gumula, S. Blazewicz
AGH University of Science and Technology,Faculty
of Materials Science and Ceramics, Department of Biomaterials, Krakow,
Poland
The aim of this work was to obtain new ceramic matrix composites reinforced
with carbon fibres by pyrolytic conversion of organosilicon polymer. Four
types of polysiloxane resins differing in carbon to silicon molar ratio and
oxygen concentration were used. The conversion mechanism from pure
polysiloxane resins to carbide phase and conversion mechanism of these
resins to ceramic phase in the presence of carbon fibres were investigated.
The experiments were led in three temperature ranges, corresponding to
composite manufacturing stages, namely moulding and curing, heat treatment
up to 1000oC and final heat treatment in the temperature ranges
from 1000 to 1700oC.
The study on composites revealed that thermal decomposition mechanism of
pure resins in the presence of carbon fibres up to 1000oC is similar as
without fibres. Above 1000oC thermal decomposition of the
matrices in the presence of fibres is more intense - the process occurs both
in solid and in gas phases. The presence of carbon fibres results in
developing of matrix surface area and produces higher mass losses and higher
porosity of composite. As it results from the XRD analysis, at the
temperature of 1700oC composite matrices contain nanosized silicon carbide.
SEM and EDS analysis show that silicon carbide protective layer onto the
fibre-matrix interface is created. Moreover, nanosized silicon carbide
fibres crystallize in composite pores. Owing to the presence of the
protective silicon carbide layer created from gas phase in the fibre-matrix
interface, highly porous C/SiC composites represent significantly high
oxidation resistance.
The process of repeated densification of porous
matrix with polysiloxane polymer and additional heat treatment lead to
further improvement of mechanical properties and oxidation resistance of
composites. tgumula@agh.edu.pl
MECHANICAL PROPERTIES OF CONTINUOUS BASALT FIBRES AT ELEVATED TEMPERATURES
M. Černý*, P. Glogar*, J.
Grégr**, P. Jakeš**, V. Kovacic***, J. Militký***, Z. Sucharda*
*Institute of Rock Structure and Mechanics, V
Holesovickach 41, CZ-18209 Prague 8, Czech Republic
**MDI Technologies, Ohradní 61, Prague 4, Czech Republic,
***Technical University of Liberec, Czech Republic
Continuous basalt fibers (CBF) - a novel class of man made mineral fibers -
possess good thermal and electric insulating properties. CBF can also be
used – in form of filaments or fabrics – as reinforcement in composites with
concrete or thermosetting resin matrix. Good thermal stability of CBF allows
even utilising their reinforcing function in fibrous composites manufactured
with help of an additional heat treatment. It is therefore desirable to
investigate thermomechanical properties of CBF at elevated temperature
because they can play a significant role in forming the microstructure and
the resulting mechanical properties of the composites. In the present study,
two commercially available basalt fiber types are examined and their
properties are compared to those of conventional glass fibers. A trial
basalt fiber prepared in the MDI Technologies laboratory using microwave
melting and drawing the fiber through ceramic bushings was also included in
the study. m.cerny@irsm.cas.cz
TRIBOLOGICAL PROPERTIES OF CARBON-CARBON COMPOSITE AND OF A SURFACE LAYER OF
PYROLYTIC CARBON
Z. Tolde, V. Starý
Dept. of Materials Engineering, Fac. of Mech. Engn.,
CTU in Prague, Karlovo nám. 13, CZ-121 35 Prague 2, Czech Republic
We measured the coefficient of friction and wear resistance of 2D carbon-carbon
composite and of a surface layer of pyrolytic carbon (graphite). To explain
these measurements we also measured the surface roughness and microhardness
of both the composite and the layer. Due to its exclusive properties, this
material system is often used in biomedical applications (bone and joint
implants), machinery (friction-bearing parts) and in the aircraft industry (parts
of the braking system). We studied the samples both with native (as prepared)
surfaces and also with surfaces prepared by grinding and
polishing, to obtain samples with various roughnesses. The measurements
demonstrate the excellent tribological properties of the surfaces,
especially the very low friction coefficient and the very good wear
resistance of the surface of a pyrolytic carbon layer on the polished 2D C-C
composite. tolde@seznam.cz
COMMON PRINCIPLES OF THE ADHESION OF CELLS TO ARTIFICIAL MATERIALS DESIGNED
FOR TISSUE ENGINEERING
L. Bačáková
Dept. of Growth and Differentiation of Cell
Populations, Institute of Physiology, Academy of Sciences of the Czech
Republic, Vídeňská 1083, CZ-142 20 Praha 4, Czech Republic
Artificial and nature-derived materials, such as synthetic polymers, carbon
materials, ceramics, metals and various composites of all these materials
are of increasing importance in medicine and various biotechnologies. A new
interdisciplinary scientific field called Tissue Engineering aims at
construction of so-called bioartificial replacements of damaged tissues or
organs, i.e. structures containing artificial material mimicking the natural
extracellular matrix (ECM) and differentiated well functioning cells. For
this purpose, the artificial materials should actively control the cell
behavior, such as extent and strength of cell adhesion, migration and growth
activity of cells, starting differentiation program in cells, secretion of
various molecules by cells etc. The design of bioactive materials is based
on the knowledge of the molecular mechanisms of cell-material interaction.
On conventionally used artificial materials (i.e. materials not endowed with
ligands for cell adhesion receptors), the cells adhere through ECM molecules
(mainly fibronectin, vitronectin, collagen, laminin) adsorbed to the
material surface from body fluids or the serum of the culture media. Cells
bind specific sites on the adsorbed ECM molecules, e.g. certain amino acid
sequences of the adsorbed proteins, by their adhesion receptors (integrins
or non-integrin adhesion molecules, e.g. proteoglycans). Adhesion and
further behavior of cells is strongly dependent on the species of the
adsorbed molecules (e.g., cell adhesion-mediating fibronectin or vitronectin
versus cell non-adhesive albumin), absolute amount of these molecules, and
particularly on their spatial conformation, flexibility and accessibility of
specific amino acid sequences or other cell-binding domains by cell adhesion
receptors. This character of protein adsorption can be, at least partly,
controlled by physicochemical properties of the material surface, such as
presence of certain chemical functional groups (-OH, =O, -COOH, -NH2),
polarity, wettability, electrical charge, surface compliance (i.e.,
stiffness vs. elasticity), and surface topography, i.e. the size, shape and
distribution of the surface irregularities. Nanostructured surfaces of
advanced biomaterials promote cell adhesion by adsorption of ECM molecules
in conformation very close to that in the natural ECM. On the other hand,
the adsorption of entire protein molecules is less controllable and
associated with the risk of immune reaction and pathogen transfer. Thus
there is an effort to functionalize the materials only with cell-binding
domains of the ECM molecules, such as amino acid sequences containing RGD,
REDV, KQAGDV, YIGSR, IKVAV, KRSR and other motifs. These oligopeptides are
attached against bioinert background, not allowing aberrant protein
adsorption and cell adhesion, in defined concentration and spatial
distribution which can contribute to a more precise control of cell behavior.
Some of these oligopeptides bind preferentially a certain cell type (e.g.
REDV endothelial cells, KQAGDV vascular smooth muscle cells, YIGSR and IKVAV
neurons, KRSR osteoblasts) which could be utilized for regionally-selective
cell adhesion (e.g. endothelial cells on the luminal surface of
bioartificial vessels, osteoblast on bone implants instead competitive cell
types, mainly fibroblasts etc.). After binding adhesion ligands, adhesion
receptors are recruited into specific nano- or microdomains on the cell
membrane, i.e. focal adhesion plaques, where they communicate with many
structural and signaling molecules (e.g. talin, vinculin, focal adhesion
kinase etc.), and through actin cytoskeleton also with various enzymes,
cellular organelles and nucleus. By this way, the signal from extracelular
environments, represented by an artificial material, is delivered to the
cellular genome, and can influence its expression and proteosynthesis.
The results presented in this review were supported by the Grant Agency of
the Acad. Sci. CR (grants No. A5011301, A4050202 and 1P05QC012) and the
Ministry of Education, Youth and Sports of CR (COST, Action 527.130, grant
No. 1P05OC012). lucy@biomed.cas.cz
RELATION OF SURFACE ROUGHNESS TO THE BIOCOMPATIBILITY OF PYROLYTIC GRAPHITE
M. Douděrová, L.
Bačáková, V. Starý
Dept. of Materials Engineering, Fac. of Mech. Engn.,
CTU in Prague, Institute of Physiology, Academy of Sciences of the Czech
Republic
The material which should come into the contact with cells has to be
biocompatible. It means, that the material must not have a negative
influence on to cells and simultaneously cells must not degrade the material.
For the material are during in vitro examinations important especially
chemical and morphological properties of the surface. An important
morphological property of the surface is e.g. its roughness. Dependence of
surface roughness parameters on cell areas was evaluated in this study. margita.douderova@centrum.cz
POLY(L-LACTIDE-CO-GLYCOLIDE) SCAFFOLDS FOR BONE TISSUE ENGINEERING
E. Filová*, L. Bačáková*,
E. Pamula**
*Institute of Physiology, Academy of Sciences of
the Czech Republic, Vídeňská 1083, 142 40 Prague 4 - Krč, Czech Republic
**AGH University of Science and Technology, Faculty of Materials Science and
Ceramics, Department of Biomaterials, 30 Mickiewicza Ave., 30-059 Kraków,
Poland
Degradable copolymer of L-lactide and glycolide (PLG) was synthesized by
ring opening polymerization using zirconium acetylacetonate [Zr(acac)4] as a
biocompatible initiator. The structure of the copolymer was studied by
nuclear magnetic resonance spectroscopy (NMR) and gel permeation
chromatography (GPC). The porous scaffolds of defined microstructure were
prepared by solvent casting / salt particulate leaching which resulted in
creation of three types of scaffolds with the same porosity (87% ± 1%) but
different diameters of pores (600 m, 200
m and 40 m).
The potential of the scaffolds for cell colonization was tested in a
conventional static cell culture system using human osteoblast-like MG 63
cells. The morphology of cells, their number and presence inside the pores
were evaluated on days 5 and 7 after seeding. For this evaluation,
conventional fluorescence microscopy of cells stained with propidium iodide,
laser confocal microscopy as well as counting of trypsinized cells in a
Bürker hemocytometer were used. The highest number of cells was found on the
scaffolds of the largest pore size (more than 120,000 cells/sample on day
7), whereas on the scaffolds with the medium and smallest pore diameter, the
cell number was almost three times lower and similar for both pore sizes.
The cells on the scaffolds of large or medium pore size infiltrated the
inside part of the material, whereas on the scaffolds of small pore size,
the cells were able to bridge the pore entrances and form a monolayer only
on the material surface. These results suggest that the PLG scaffolds with
the largest pore diameter (600 m) are the most
suitable for colonization with osteogenic cells.
Supported by the Ministry of Education, Youth and Sports of the Czech
Republic (project COST, Action 527.130, grant No. 1P05OC012).
*AGH University of Science and Technology, Faculty of
Materials Science and Ceramics, Department of Biomaterials
**Institte of Physiology, Academy of Science of the Czech Republic, Praha
***Department of Cytobiology and Histochemistry, Collegium Medicum,
Jagiellonian University, Krakow, Poland
The work presents selected examples of application of carbon nanotubes and
nanofibers in cell culture and tissue engineering. Some aspects of
biocompatibility in vivo and in vitro are considered. The response of living
cells to carbon nanoparticles and bulk surface functionalized with nanosized
carbon particles is performed. Histological and histochemical analyses of
possible mechanism of migration of carbon nanoparticles in the form of
single and multi wall nanotubes in living organism is shown. mblazew@uci.agh.edu.pl
HUMAN OSTEOBLAST-LIKE MG 63 CELLS IN CULTURES ON BIOGLASS FIBERS
Ľ. Grausová, L. Bačáková
Institute of Physiology, Academy of Sciences of the Czech
Republic, Vídeňská 1083, 142 40 Prague 4 - Krč, Czech Republic
The adhesion and proliferation of human osteoblast-like MG63 cells on
bioglass fibers was studied. Four types of fibers were studied, different in
their thickness and amount of SiO2: (1) fibers containing 20% of
SiO2 and produced at the speed of 800 m/min; (2) fibers
containing 20% of SiO2 and produced at the speed of 1600 m/min;
(3) fibers containing 30% of SiO2 produced at the speed of 800
m/min; (4) fibers containing 30% of SiO2 produced at the speed of
1600 m/min. The diameter of the fibers produced at lower speed was 26
m, whereas in the fibers manufactured at the
higher speed, it was twice a lower. The fibers were sterilized by H2O2–plasma
method (Sterrad), placed in 24-well polystyrene multidishes (TPP,
Switzerland; diameter of 1.5 cm) and seeded with MG 63 cells. Each well
contained 500 fibers of the length of 1 cm, 30 000 cells and 1.5 ml of the
Dulbecco-modified Eagle minimum essential medium supplemented with 10 % of
fetal bovine serum. As control samples, the polystyrene culture dishes as
well as microscopic glass coverslips were used. On day 1, 3 and 7 after
seeding, the cells on some samples were visualized by staining with
propidium iodide and their morphology was evaluated in fluorescence
microscope. From the other samples, the cells were detached by
trypsinization and counted in Bϋrker haemocytometer. On day 1 after seeding
the number of cell initially adhering on bioglass fibers ranged in average
from 950 to 2,090 cells/cm2, which was significantly less than on
the polystyrene dishes (18560 cells/cm2) or glass coverslips
(15000 cells/cm2). Similar trend also persisted in both 3- and 7-day-old
cultures. On day 7 after seeding, the final cell population densities on the
polystyrene and glass coverslips reached in average 98500 and 82100 cells/cm2,
respectively, whereas on the bioglass fibers, the density ranged only from
20150 to 23970 cells/cm2 (no significant differences among the
different groups of fibers were found). Nevertheless, the cells on the glass
fibers were viable, capable of proliferation and relatively well spread (i.e.,
spindle-shaped with the long axis oriented in parallel with fibers), which
suggests that their lower number was due to the relatively small diameter
and surface curvature of the fibers, less appropriate for a higher degree of
cell spreading, rather that to a possible cytotoxicity of the material. The
bioglass fibers could be used e.g. for reinforcement of polymeric materials
for bone tissue engineering.
Supported by the Ministry of Education, Youth and Sports of the Czech
Republic (project COST, Action 527.130, grant No. 1P05OC012). grausica@orangemail.sk
JUST KNUCKLE DOWN AND FINISH IT
GLASS FIBERS AND POLYSILOXANE BASED COMPOSITES FOR BIOMEDICAL APPLICATIONS
T. Suchý*, **, K. Balík**, M.
Sochor*, M. Černý**, V. Pešáková***, H. Hulejová***
*Faculty of Mechanical Engineering/Department of Mechanics,
Czech Technical University in Prague, Prague, Czech Republic
**Institute of Rock Structure and Mechanics/Department of Carbon and
Composites, Czech Academy of Sciences, Prague, Czech Republic
***Institute of Rheumatism, Prague, Czech Republic
The study presented deals with development of advanced composite materials
to be used in the bone tissue engineering, based on the polysiloxane matrix
and glass fibres, and endowed with 3D porous architecture. An extended
experimental investigation was necessary for obtaining physical and chemical
properties of the composite materials, namely their mechanical properties,
porosity, void fraction, surface roughness. All these parameters had to be
modified and studied, using both in vitro and in vivo testing, for achieving
an optimum bone tissue ingrowth and maturation. suchyt@irsm.cas.cz
Informace o konferencích
26-30 March 2006
The American Chemical Society, Fuel Division Symposium on
Chemistry of Carbon Materials and Nanomaterials to be held in Atlanta. The
symposium features research on the synthesis, properties, and applications
of carbon materials and their novel nanoforms. Emphasis is on the common
chemistry that underlies carbon science for both new and traditional
materials. Topics include, but are not limited to:
Molecular Engineering in Carbon Material Synthesis
Carbon-Based Catalysts and Sorbents
Novel Carbon Forms and Their Application Fields
Carbon Nanoparticles and Their Derivatives
Premium Carbon Products from Coal
Carbon Composites and Nanocomposites
Activated Carbon for Environment Applications
Surface Chemistry and Functionalization
33rd International Conference on Metallurgical Coatings and
Thin Films will be held at the Town and Country Hotel in San Diego, Ca.
Sponsored by the Applied Surface Science Division of the AVS, the meeting
draws more than 600 attendees to participate over 50 technical sessions,
including a symposium dedicated to carbon and nitride materials.
Other symposia include:
Coatings for Use at High Temperature
Hard Coatings and Vapor Deposition Technology
Optical Thin Films
Tribology and Mechanical Behavior of Coatings and Thin Films
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Specific carbon-related sessions include:
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Diamond and Diamond-like Carbon Materials
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Carbon and Nitride Materials
http://www2.avs.org/conferences/icmctf/call/default.asp www.icmctf.org icmctf@mindspring.com
16-21 July 2006
The Carbon conference series comprises leading international
meetings dedicated to the science and technology of carbon materials. Carbon
2006 will be hosted by the British Carbon Group and will be held at The
Robert Gordon University in the historic Scottish city of Aberdeen. In
addition, this year the conference will be preceded by an optional 'Nanoporous
Carbons' summer school, and the main conference will be incorporating
NanoteC06. C2006 conference sessions include, but are not limited to:
Adsorption
Fundamentals
Applications
Activated carbon
Biological applications
Carbon Fibres
Carbonization, Mesophase, Pyrolysis and Thermal processes
C-C composite materials
Diamond
Environmental Applications
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Fundamentals
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Special forms of carbon www.carbon2006.org confer@globalnet.co.uk
20-23 February 2007
Second International Conference on
Recent Advances in Composite Materials will be held in New Delhi, India. The
meeting will attempt to discuss all the critical aspects of metal-matrix
composites, fibre composites, and ceramic composites.
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be obtaining on request.
Bank connection:
Czech National Bank, Prague 1, Na Příkopě street 28, 115 03, account no.
635-081/0710 Variable Symbol 468888
Subscription office:
J. Netrestová
IRSM AS CR
V Holešovičkách 41
182 09 Prague 8, Czech Republic
E-mail: irsm@irsm.cas.cz
Tel. +420 266 009 318
INSTRUCTIONS FOR AUTHORS
Submissions:
Acta Montana accepts original papers in English concerning all aspects of
mentioned disciplines. Authors should submit three hard copies of their
contribution and identical text file in MS Word (any version) and in case of
need other files (figures, tables etc.) by e-mail, on 3.5" floppy disc, ZIP or
CD-ROM. The Editorial Board on the basis of reviews of at least two referees
makes the decision upon their publication. Author first named will receive one
volume of Acta Montana and twenty reprints free of charge.
The manuscript must contain:
Title, full names of all authors, their affiliations and addresses including
phone number, fax number and e-mail address, abstract, keywords and main body of
paper (all in English).
It can be included:
Tables at max. size 24x16 cm and min. font size 9 pt, in text or on separate
pages. Tables must be written really as tables (in columns), not as text (in
rows). Captions of all tables must be on separate page. Figures: Black and white
photographs, drawing or maps in good quality (min. 600 dpi) are acceptable.
Charts and diagrams must be in black and white, description of axes must be at
sufficient size in due to possibility of reducing. Figures may be placed in text
or as separate files. Only permitted formats of these files are (*.doc, *.xls,
*.ptt, *.bmp, *.pcx, *.tif, *.jpg, *.gif). Figures are to be referred as Fig.
Arabic numeral and should be numbered consecutively, according to their sequence
in the text. Caption must no be in placed in the figure area. List of captions
of all figures must be on the separate page. Required size of the pictures in
the text must be denoted at the list of captions. Color illustrations are
tolerable (min. 1200 dpi), but at author's expense 75 EUR per 1 page A4). These
pages, (pressed on one side) will be placed on end of the paper as appendix.
Variables, constants and other symbols in mathematical functions and also in the
text are accepted written exclusively at MS Equation Editor or MS MathType. All
used symbols must be explained in text or in the List of symbols.
References quoted in the text must be in form (author, year), e.g., (Balik,
2001), (Rudajev et al., 2002). All references should be listed together at the
end of the paper in alphabetic order as:
First name, signatures of surnames, (names of other authors except last) and
(First name, signatures of surnames of last author): year, title, journal,
number, pages
e.g. Mierzejewski, M., Korzak, F. and Kaczalek, M.: 2002, Geodynamic research of
recent movements in the Karkonosze Mts, Acta Montana ser.A., 15(126), 56-78
Paper must be supplied as final version. At press-proof it is possible to
correct only typing errors, other changes of text are not acceptable.