GREEN MATERIALS FOR METAL NANOPARTICLES SYNTHESIS

INTRODUCTION:

Nanoparticles are fine particles having diameter in the range of 1 nanometer to 100 nanometer . Metal nanoparticles are very special  because of their surface porperties ,they are simply very large molecules .The synthesis and stabilization of large structurally -well-defined metal clusters requires the presence of surface bound moieties that are now referred as”LIGANDS” as opposed to “ADSORBATES”.We can consider metal nanoparticle as ATOMIC CLUSTER . Nanoparticles have fascinating optical and electronic properties so they have wide applications in fields like nanoelectronics and heterogeneous catalysis .Metal nanoparticles synthesis has problem of instability of particles due to themodynamic  , electronic repulsion and many other factors causing FORMATION OF AGGLOMERATES OF METAL IONS.  Metal nanoparticles are widely used in catalysis and electrocatalysis. Metal nanoparticles can lower time of reaction ,decrease cost of catalyst and improve effectiveness and efficiency of catalytic process. There are two main challenges in this area of catalysis ,the first is developement methods for stabilizing nanoclusters by eliminating aggregation without blocking most of active sites on cluster surfaces or otherwise reducing catalytic efficiency , the second key challenge involves controlling cluster size ,size distribution and perhaps even particle shape. Metal nanoparticles synthesis is carried on support called as” TEMPLETE” on which metal clusters get adsorbed . Today scientist are engaged in  finding out new eco friendly  green materials which may be served as templetes to get rid of  costly synthetic templetes such as  “DENDRIMERS “.Dendrimers are 3 DIAMENSIONAL STRUCTURES . nanoparticles synthesis using dendrimers  involves mixing of metal ion and dendrimer and subsequent reduction of metal ion (shown in figure below , borohydride ion is used as reducing agent)

nano

GREEN TEMPLETES FOR NANOPARTICLES SYNTHESIS :

Green materials i.e biomaterials which are biodegradable prove beneficial source for application in nanoparticles synthesis at industrial level . From the stone age to the scientific era of today man is emulating the nature for finding solutions to many problems . “TEMPLETE ” for synthesis should possess porous structure and active sites for binding metal ions cluster . The structure and properties of metal nanoparticles are found to be particularly useful when these materials have regular or patterned structure.Living organisms show an amazing hierarchical arrangement of their organic and inorganic components .Unique pattern from nanoscale to macroscopic scales can be seen in wood , cork , bone , ivory , sea shells ,etc .

CELLULOSE AND BOVINE BONE AS TEMPLETE FOR NANOPARTICLES SYNTHESIS :

CELLULOSE IS NATURAL CARBOHYDRATE RICH IN OXYGEN CONTAINING ANHYDROGLUCOSE UNITS LINKED BY HYDROGEN BOND.NATURAL CELLULOSE FIBERS HAVE A POROUS STRUCTURE ,COMPOSED OF 10-30 nm MICROFIBERS WIDELY CONNECTED IN ALL 3-D .THIS FIBROUS MORPHOLGY CAN PROVIDE A UNIQUE SCENARIO FOR PARTICLE SYNTHESIS , ALLOWING IMPROVED ACCESS OF MOLECULES INCORPORATED TO NANOPOROUS FILMS .THIS UNIQUE ARCHITECTURE ALLOWS FOR SIZE AND SPACE DISTRIBUTION CONTROL OF NANOPARTICLES BY ADJUSTING PARAMETERS SUCH AS CONCENTRATION OF METAL IONS AND REDUCTION TIME.THESE NANPOROUS STRUCTURES ALONG WITH HIGH DENSITY OF OXYGEN IN THE CELLULOSE FIBERS COMBINE TO CREATE HIGHLY EFFECTIVE NANO REACTORS.  NANOPORES ARE ESSENTIAL FOR CONTROLLED DIFFUSION OF METAL IONS AND REDUCING AGENTS AND OXYGEN AND HYDROXYL GROUPS DO HELP IN STABILIZATION OF RESULTING METAL NANOPARTICLES. 

BONE IS A BIOMATERIAL COMPOSED MAINLY OF CALCIUM PHOSPHATE ALONG WITH DIFFERENT ANIONS SUCH AS FLUORIDE,CHLORIDE,HYDROXYL,ETC.  HYDROXYAPATITE CAN BE FOUND MAINLY IN BONES AND TEETH WHICH HAS REGULAR HEXAGONAL CRYSTAL STRUCTURE AND PREDICTABLE SPACING GROUPS. BIOLOGICAL APATITES POSSESS STRUCTURAL IMPERFECTIONS DUE TO INCORPORATION OF SODIUM,POTASSIUM,MAGNESIUM,CHLORIDE AND FLUORIDE IONS. 

BOVINE BONES ARE COMPOSED MAINLY OF HYDROXYAPATITE ALONG WITH COLLAGEN AND PROTEIN IN LESS EXTENT. POROUS STRUCTURE OF BOVINE BONE CAN BE USED AS NANO REACTOR FOR CONTROLLED SYNTHESIS OF PARTICLES WITH DEFINED STRUCTURES. HIGH DENSITY OF ELECTRO NEGATIVE LINKAGES DUE TO HYDROXYL IONS INSIDE CREVICES OF BONES MAY CONTROL DIFFUSIONAL GROWTH AND FORCE NEWLY FORMED NANOPARTICLES TO AGGREGATE ALONG THE EDGES OF HEXAGONAL SURFACE OF THE BONE. THE RENOWNED APPLICATION OF BOVINE BONE FOR SYNTHESIS OF PLATINUM(Pt) AND SILVER (Ag) NANOPARTICLES IS APPRECIABLE. FOR PLATINUM PARTICLES REDUCTION OF SALT PLATIUM (IV)CHLORIDE WITH SODIUM BOROHYDRIDE AND IN CASE OF SILVER PARTICLES REDUCTION OF SILVER NITRATE WITH SODIUM BOROHYDRIDE IS DONE ON BONE SURFACE . THE USE OF NATURAL RENEWABLE, ABUNDANT AND LOW COST MATERIAL SUCH AS BONE FOR CONTROLLED SYNTHESIS OF METAL NANOPARTICLES AT ROOM TEMPERATURE AND USE OF WATER AS SOLVENT OPEN AN INTERESTING AREA FOR CHEMICAL SYNTHESIS WITH GREEN AND SUSTAINABLE APPROACH.

 

 

 

IN THE WORLD OF POLYMER COMPOSITES

Over the years , polymer composites have been proposed for various application in biomedical engineering .Composites are those materials that contain two or more distinct continuous phases ,on larger scale than atomic.Normally ,the constituent components retain their identities in composites.Most of living tissues such as bone ,dentin,collagen,cartilage and skin are essentially composites.In composites ,properties such as elasticity modulus and other mechanical properties can be significantly different from those of the constituents alone but are considerably altered by constituent structures and contents , from structural point of view, mechanical properties of composites are different in different directions ,i.e composites are anisotropic in nature .Synthetic composites are essentially combination of two constituent phases i.e ,reinforcing phase such as fiber or particle and continuous phase called matrix.

The primary motive in development of bio- composites is that by varying type and distribution of reinforcing phases in composites it is possible to access wide range of mechanical and biological properties ,and hence to optimize the structure and performance of biomedical devices and their interaction with surrounding tissues .

Classification of biocomposites based on their reinforcement form:

snip_20170919230504

Another classification for biocomposites is based on their biodegradibility i.e fully resorbable,partially resorbable and non resorbable.

Resorbable biocomposites are made from those fibers and matrices both of which are fully absorbable in body and they are extensively used for internal fracture fixation applications.POLYLACTIC ACID POLYMERS are widely  used  resorbable biocomposites as-1)their degradation rate in the body can be controlled by varying molecular weight,changing proportions of D and L enantiomers,copolymerising it with polyglycolic acid ,2)if crystallization of polylactic acid polymer is prevented ,their degradation products are non -toxic , biocompatible and easily metabolised . problem associated with polylactic acid polymer is degradation behavior of both phases ,especially of interphase between them .

Partially resorbable composites are conjucted by non absorbable reinforcing materials and absorbable matrix materials.They are used as bone replacements ,bone cements and also internal fracture fixators . combinations for making partially resorbable composites – PMMA(polymethylmethacrylate) and PBT(POLYBUTYLENE TEREPHTHALATE) as non resorbible matrix with polylactic acid polymer or polyalkanoates and alumina or calcium carbonate as non resorbable filter phases.commercial application – composite of POLYETHYLENE AND HYDROXYAPATITE (HA) being in some bone graft and replacement applications .

Biomedical applications of polymer composites:

  1. HARD TISSUE APPLICATIONS
  2. SOFT TISSUE APPLICATIONS
  3. DENTAL APPLICATIONS

HARD TISSUE APPLICATIONS-

1 ) BONE FRACTURE REPAIR

2 ) BONE PLATES

3 ) INTRAMEDULLARY NAILS

4 ) SPINE INSTRUMENTATION

5 ) JOINT REPLACEMENTS

SOFT TISSUE APPLICATIONS –

1 ) BULK SPACE FILLERS ( ARTIFICIAL CARTILAGE )

2 ) ENCAPSULANTS AND CARRIERS ( URETER PROSTHESIS , CATHETERS,TENDONS,LIGAMENTS )

DENTAL APPLICATIONS –

1 ) DENTAL COMPOSITE RESIN

2 ) DENTAL IMPLANT AND BRIDGE

3 ) ORTHODONTIC ARCH WIRES AND BRACKETS

BONE PLATE

(a)  a typical composite bone plate made using braided carbon fiber fabric and epoxy matrix (b)  composite bone plate made of carbon / polyetheretherketone (PEEK) material system