Chemistry and chemical
technologies / 5.
C.т.s. Rodionov I.V.
The basic physical-chemical and mechanical
characteristics of biocompatible coverings medical
bone implants
Biotolerant materials
are characterized by formation of superficial active particles and the weakened
adhesion of proteins because what fibrinous fibres of the curtailed blood settle down along a surface
implant. Thus bone cells does not reach a surface implant, on a bone surface
the coarse-fibred structure is formed, and between
implant and a bone there is a layer collagenic fibres. It represents a capsule around implant from low
strong to a fibrous fabric thickness up to 0,2 mm that can cause infringement
of stability of position implant at action of functional loadings,
lead to his shaking and danger of an inflammation biofabrics.
Biotolerant qualities stainless steels, cobaltchromic alloys, polythene, polythenetereftalate possess, they are used at
manufacturing implants with small terms of functioning and small loadings.
Bioinert
materials do not create on a surface of active particles that allows to be
generated on it to a film of strongly adsorbed proteins of blood and a mesh
layer of fibrinous fibres.
On these fibres there is a growth bone cells to a
surface implant and formation of amorphous structures bone matrics
on a surface implant. Due to it there is a biophysical communication between a
bone fabric and a surface implant at presence in this zone of a thin layer of a
fibrous fabric thickness about 0,02 mm. It limits density of formed bone
structures on a surface implants and durability of his position in contact to a
bone. Zirconium, tantalum concern to bioinert
materials, metaloxidics, bioglass,
bioglasscrystal substances, carbon materials, polymethylmetacrilate, polytetrafluorinethene
the titan, they are successfully applied for implants long and constant
functioning, maintaining the raised loadings.
Bioactive
materials possess similarity of a chemical compound to a mineral component bone
matrics and ability to decomposition at interaction
with a biofabric. On a surface of such materials the
layer amorphous albuminous structures providing
physical and chemical communication of a bone fabric with implant is formed. In
these conditions there is an ionization of atoms and diffusion ions through an albuminous layer in bone matrics
to course of bioelectrochemical reactions. Due to it
develops decomposition a material, and in formed structural emptiness
germination of bone cells with formation reparative osteogenese
and biointegration implant begins. In result the
strong biotechnical system «a bone-implant» with high
stability of functioning is created. Bioactivity
differ calcium-phosphatic connections – hydroxiapatite and threecalciumphosphate,
on a chemical compound corresponding to a mineral component bone matrics. Besides qualities of bioactivity
can get such bioinert materials, as metaloxyds, bioglass, bioglasscrystal substances, carbon materials, at creation
of morphological heterogeneity and porosity of their surface. Application of bioactive materials for manufacturing implants provides
their most effective functioning due to course of processes osteointegration.
Participation
implant in performance of mechanical functions a bone shows to it requirements
of mechanical compatibility at which his mechanical interaction with a bone
does not create in a material implant and in a bone fabric the pressure
causing inadmissible deformations, destructions or an
inflammation of a biofabric.
The level of mechanical compatibility implant depends on a necessary
combination mechanical properties of his material, rigidity and rationality of
a design, the circuit of an arrangement implants in system. The given factors
get out according to mechanical characteristics a bone and functional loadings on implant. Thus it is taken into account, that
the major biomechanical characteristic bone implant
is his rigidity at a stretching or a bend. Rigidity, for example, bone segments
of the basic-impellent device, in particular, the bottom finiteness,
considerably exceeds rigidity metal implants so at functional loadings the bone practically is not deformed, and implant
can receive deformation of a bend, twisting, a stretching [2].
Implant a bone segment of the basic-impellent device can test average loadings
a bend 500 N, stretching efforts – 50 N, the braiding moment – 5 Nm, bending moment – 20 Nm. Stomatologic implants receive
action of chewing vertical forces 150 N, lateral forces – 20 N, frequency of
their appendix makes 1,0-1,3 Hz. The greatest internal pressure in implant and thus
should not exceed a bone 500 МPа, keeping
elastic character for a material implant or coming nearer to pressure of a
limit fluidity and creating small deformations.
On the resulted bases for bone implants and
systems biocompatible materials with the raised
module of elasticity are used at high values bending rigidity implant and
factor rigidity of his design. Besides the material should possess the
increased limit of fluidity, the minimal allowable plasticity and the optimum
durability, necessary endurance, hardness and wear resistance. To to the greatest degree specified requirements satisfy metal
bioinert alloys Ti, Zr, Co-Cr, corrosion-proof chromnickel steel. Polymeric organic and inorganic
materials do not possess a necessary complex of mechanical properties that at
action on implant functional loadings to provide
occurrence only small elastic deformations. Therefore they are not used for
manufacturing a bearing basis implants, except for the carbon composite used
for some kinds implants at an osteosynthesis.
Giving of bioactivity
to mechanically compatible materials is reached due to creation of special biocoverings on metal implants, providing their effective osteointegration and a high level of adaptation in an organism.
Formation biocoverings
with qualities of biomechanical compatibility can be
carried out by various ways with use of many technologies, such as
electrochemical anodi oxidation, thermal oxidation in
various gas environments, plasma powder sprayd and
other technological processes.
The basic physical and chemical and mechanical
characteristics of received coverings implants are phase and element structures,
thickness, a roughness and morphological heterogeneity of a surface, corrosion
stability in bioenvironments, and also microhardness and adhesive durability. The specified
characteristics of coverings cause a level of biological and mechanical
compatibility implants, provide their reliable functioning in biostructures.
The phase condition of biocoverings
bone implants causes character of their physical-chemical and mechanical
properties. Single-phase the structure provides uniformity of structure and
properties a covering in all his volume, multiphase – creates heterogeneity of
structural components a covering, and also distinction properties of his
material, shown in various values of those or other parameters the separate
phases included in a covering.
The important characteristic of biocoverings bone implants is the thickness determining, at
necessary open porosity of 30-60 %, depth of germination cells of biofabrics in time a surface, than physicomechanical
interaction implant and bone structures with formation of strong system « a
covering – a bone » is reached. As a rule, on biocompatible
metals create coverings thickness up to 150 microns providing reliable biointegration implant and possessing high characteristics
of durability. The raised values thickness cause occurrence in a covering of
the significant internal pressure resulting in essential decrease of his
mechanical durability and adhesive properties.
Roughnesses a
relief of a surface bone implants define character of their physicomechanical
interaction with surrounding biofabric and create
necessary conditions for germination cells of biostructures
in microhollows of the various form and depth with
formation of strong interrelation implant with a fabric. Therefore, to
formation a high degree a roughness of a surface implants pays the big
attention. Besides the initial roughness implants considerably raises adhesion
and superficial porosity a rendered biocovering
because of strong mechanical coupling his particles with a basis and relative
recurrence of microrelief metal by layers a covering.
Between a covering implant and there is a bioelectrochemical interaction to formation and adhesion on
a surface of albuminous structures, their growth and
penetration into deepenings, and also time relief of
a surface in conditions certain destruction its material bioenvironment.
As a result of such interaction bone implant the strong biotechnical
system « implant – a surrounding fabric» with high efficiency of functioning is
created. Thus on formation of qualities bioactivity
the big influence is rendered with morphological heterogeneity of a surface
implant, determined by a complex parameters of its roughness, and also
parameters of ledges and deepenings, switching time.
Therefore research microgeometry a surface of biocoverings is the major stage in development and creation
bone implants with a high level of biocompatibility.
The best functioning implants is
provided in conditions of their integration with bioenvironment due to bioelectrochemical interaction when at
presence microroughnesses a surfaces of material in
them sprout cells of biostructures. The given
processes characterize the bioactivity shown by many bioceramic materials, used as coverings.
Many technologies allow to generate
a covering on medical bone implants with a necessary complex structural
qualities of bioactivity and required biotechnical parameters. Functioning such implants
proceeds in conditions of action on their surface of a fabric liquid, blood, a
lymph and other liquid components present in structures of an organism. The
given liquids have a water basis and possess properties of electrolits,
rendering on a covering corrosive attack. Anodi processes
thus are characterized by ionization of atoms a material of a covering and
metal impurity, diffusion of ions in surrounding bioenvironment
with its formation with saturation of fabrics by harmful ions. Because it vary
structure and properties of a surface implant, and also there is an infringement
normal cellular processes in biostructures, there is
a danger of the inflammatory phenomena and tearing away implant, that is
substantially connected to a phase-structural condition and corrosion behaviour of biocovering.
Therefore by development of metal bone systems to research corrosion properties
of biocoverings pays the big attention [3, 4].
Bone implants test
not only biological, but also mechanical influence of the surrounding bioenvironment during long time. Therefore for formation of
strong functional biotechnical system «implant – a
bone» to a covering give a necessary combination of adhesion, porosity,
morphological heterogeneity of a superficial structure. Definition of the given
parameters demands application of special complex methods research, and at the
same time their values are in interrelation with microhardness
of a covering. Thereof it is possible to carry out quality assurance a received
complex of key parameters of bioactivity a covering
by use concerning a simple method of definition microhardness.
Adhesive
durability of biocoverings bone implants is the
important operational characteristic as implant with a covering tests influence
not only liquid environments of an organism, but also significant mechanical loadings [5]. The size of adhesion should exclude danger
detachment coverings at functioning implant, therefore she is taken into
account in relation to size of the greatest durability a bone fabric and the
requirement of the certain safety factor. For bone implants adhesion of a
covering should make approximately 28-30 МРа, that allows to provide high physicomechanical
interrelation in system «implant – a covering» and to create conditions for
long functioning implant in surrounding biofabrics.
Thus,
the most important physical-chemical and mechanical characteristics of materials
and the coverings used in modern orthopedic medicine are considered, features
parameters biological and mechanical compatibility bone implants with coverings
are underlined.
The
literature:
1. Rodionov I.V., Butovsky K.G. Biological and mechanical compatibility materials bone
implants / Материали за III-а Международна научна практична конференция «Умение и нововъведения», 2007. Т.13. София, България.
С. 12-14.
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4. Родионов И.В., Серянов Ю.В., Бутовский К.Г. Коррозионное поведение плазменно-порошковых титан-гидроксиапатитовых биопокрытий в модельном физиологическом растворе // Инженерная физика, №3, 2006. С. 20-23.
5. Бутовский К.Г., Лясникова А.В., Лепилин А.В., Лясников В.Н. Биоактивные материалы и покрытия в дентальной имплантологии. Уч. пособие. Саратов: Сарат. гос. техн. ун-т, 2004. – 94 с.