Polymers are composed of repeat of structural units, named monomers and are covalently bonded together as big molecule ( supermolecule ) . It can be made up of indistinguishable monomer units or a mixture of two or more monomers. When merely one species of monomer is used to construct a supermolecule, the merchandise is called a homopolymer. If the concatenation is made up of two types of monomer unit, the stuff is known as copolymer. Copolymers can be subdivided further into four chief classs: statistical copolymers, jumping copolymers, block copolymers and transplant copolymers. ( 1, 2 )
Polymerization is the procedure used to change over monomer molecules into a polymer. There are fundamentally two attacks: chain- growing and step- growing polymerisation. Chain- growing polymers ( besides called add-on polymers ) are made by adding the monomers one at a clip in a insistent mode and the procedure is rapid. ( 2 ) The complete polymerisation procedure takes topographic point in three different phases: foremost, induction, when a individual reactive site which acts as a concatenation bearer is created ; secondly, extension, affecting rapid growing of the concatenation terminal by a kinetic concatenation mechanism and characterized by a long sequence of indistinguishable events, viz. the perennial add-on of more monomer to the turning concatenation ; and thirdly, expiration, whereby the procedure is brought to a arrest when the active centre of the kinetic concatenation is neutralized or transferred. There are three classs of concatenation instigators: free- extremist, cationic and anionic. ( 1 ) The pick of the most appropriate one depends on the interested monomer and the demands of the mark polymer. The most widely used procedure for chain- growing polymer synthesis is free- extremist polymerisation. It is less sensitive to the effects of adventitious drosss compared to ionic chain- growing polymerisations. Another procedure that is normally used is step- growing polymerisation, besides known as condensation polymerisation, produces a polymer by a reaction between two different functional groups which involve riddance of some smaller molecules, such as H2O. Condensation polymers are formed from bi- or polyfunctional monomers and the monomers normally appear in jumping sequence in the polymer concatenation. ( 1-3 )
The physical behaviour of a polymer depends on the microstructure ( besides named constellation ) . The physical agreement of monomer residues along the anchor of the concatenation has strong influence on the other belongingss of a polymer. Polymer architecture can be additive or branched. A additive polymer is the simplest polymer architecture in which the repetition unit is linked merely to two others in a individual anchor. Branched polymers composed of monomers which are non linked entirely in a additive array as the polymerisation procedure produces one or more substituent side ironss from bifunctional monomers. ( 1, 3 )
Polymer- based nanotechnology is much of involvement in pharmaceutical research particularly in the design of drug bringing system. In recent old ages, new sort of polymeric micelles, pluronics, have attracted intensive attending of pharmaceutical chemist. ( 4 ) Pluronic block copolymers is besides known as their non-proprietary name ‘poloxamers ‘ composed of hydrophilic ethene oxide ( EO ) and hydrophobic propene oxide ( PO ) blocks arranged in a basic A-B-A tri-block construction ( Figure 1 ) . ( 5-7 )
Figure 1. Pluronic block copolymer molecule ( A ) and micelle with a solubilized drug ( B ) . ( 7 )
The Numberss of ethylene oxide and propylene oxide units are determined by different hydrophilic-lipophilic balance ( HLB ) . ( 8 ) Pluronics are synthesized utilizing step-wise polymerisation by insistent add-on of EO and PO monomers in aid of Na or K hydrated oxide as accelerator. Due to their amphiphilic nature, pluronic block copolymers display wetting agent belongingss which enable them to interact with both hydrophilic and hydrophobic surfaces and biological membranes. ( 8 ) Wetting agents are organic compounds that allow easier spreading by take downing surface tenseness and besides lower interfacial tenseness between two liquids. It can besides aggregates to organize micelles at certain concentrations which is known as critical micelle concentration ( CMC ) . The characteristics of wetting agents are characterized by pluronic block copolymers as Pluronics have the ability to self-assemble into spherical micelle construction. The block copolymer molecules will stay in its single signifier, termed ‘unimers ‘ , when concentration is below the CMC. In contrast, micelles are formed through a procedure called ‘micellization ‘ when the block copolymer is at concentration above CMC. ( 5 ) Micelles exhibit several morphologist such as rod-like, spherical or lamellar at different concentration of block copolymers, temperature and the length of EO and PO blocks. ( 9 ) These micelles composed of two clearly separated stage which are a hydrophilic outer shell formed by EO ironss and hydrophobic inner nucleus formed by PO ironss due to cohesive interactions in a aqueous media. ( 5, 10, 11 ) The cohesive interactions mentioned refer to hydrophobic interaction, ionic interaction and H bonding. ( 12 )
The architecture of pluronic micelles serve of import factor in drug bringing application. ( 12 ) Its hydrophobic nucleus by itself is termed ‘cargo clasp ‘ and serves as a microenvironment to integrate hydrophobic drugs, for illustration anticancer drugs through hydrophobic interaction. ( 7, 10, 13 ) The procedure named ‘solubilization ‘ is the procedure where the H2O indissoluble compounds are transferred into interior nucleus of miceller solution. ( 5 ) As a consequence, polymeric micelles can function as efficient bearers by heightening solubility and stableness of compounds in physiological environment. ( 14 ) The outer hydrophilic shell on the other manus, furnishes pluronics pharmaceutical behaviour greatly by guaranting the micelles in a spread stage. It is besides responsible in cut downing drug interaction between biomaterials such as cells and proteins through steric-stabilization effects, hence, is expected to considerably command the bringing in life organic structures. ( 7, 12 )
CMC of pluronic block copolymers is important in drug bringing. The figure of micelles elevates as the concentration of block copolymers additions above CMC whereas the concentration of unimers remains changeless where the figure is equal to CMC. The micellization and its construction passages can happen in a broad scope of concentration in the locality of CMC and may every bit good travel beyond the CMC. The acceptable CMC value for pluronic block copolymer varies 3-10 times depending on the method of measuring applied. CMC is of concern as it determines the stableness of micelles in organic structure fluids. ( 5, 15 ) The biological effects of pluronic block copolymers exert on the open cells are defined by the maximum mark concentration of pluronic unimers which is determined by CMC. ( 6 ) The length of the PO and EO blocks has great influence in CMC. CMC decreases when the length of PO additions, hence elevates the net hydrophobicity of the pluronic molecules every bit good as favours the formation of the micelle nucleus. Contrarily, an addition in the length of EO blocks result in addition of CMC. This consequence excites the chance of contact between PO and EO blocks within the nucleus of the micelles. As a consequence, the hydrophobicity of the nucleus and the stableness of the micelles lessening. ( 5, 15 )
The size of the micelles greatly influences drug bringing system. The size of pluronic micelles are normally in the scope of 10 nanometers to 100 nanometers. ( 7, 16 ) These micelles of pluronic block copolymers are clearly within the coveted size scope and the size fluctuation strongly affects the clip taken in blood circulation and the bioavailability of the substances in the organic structure. ( 5 ) The peculiar size enables the micelles to last the filtration of lung and lien. Hence, the needed serum degree of the drug can be maintained as it will undergo less opsonisation and prevent consumption by the macrophages of the reticuloandothelial system ( RES ) and hence, the drug bearers are able to remain in the blood circulation. ( 10 ) The CMC of solution besides depends on temperature. Assorted surveies had shown that PO and EO ironss will desiccate when temperature increases. Consequently, the blocks become indissoluble and aggregative to organize micelles. It is of import to see temperature dependance in micelles formation in drug bringing as decomposition of micelles can happen and let go of solubilized drug at room temperature. Even though the decomposition procedure is reversible, the kinetic factors may do troubles to the drug to re-solubilized. ( 5 )
Since pluronic block copolymers exhibit surfactant belongingss, low molecular mass hydrophobic drugs can be incorporated into interior nucleus of pluronic micelles and heighten drug pharmacokinetics and biodistribution. ( 12 ) Hence, it serves as a good drug bearer for unwritten bringing drugs, to present CNS drugs across blood encephalon barrier and tumor-specific anticancer drugs. Encapsulation of drugs in micelles can heighten the permeableness and keeping consequence ( EPR ) ensuing in a inactive aiming belongings. ( 10, 17 ) Pluronic block copolymers have been widely used in preparations for intervention in drug opposition malignant neoplastic diseases. ( 18 ) Assorted surveies had demonstrated that pluronic block copolymers sensitize immune malignant neoplastic disease cells which induce the cytotoxic activity of the drug b 2 to 3 crease of magnitude. ( 6 ) One of the illustrations that shown this consequence is where the add-on of P85 increases the cytotoxic effects of doxorubicin in immune lines. ( 15 ) Treating drug opposition in malignant neoplastic disease may non be easy as the opposition is exhibited through many mechanisms. Several mechanisms may move together or farther perplex the therapy in certain instances. ( 15 ) For case, multidrug opposition ( MDR ) tumor has been widely identified as one of the most hard types to handle in malignant neoplastic disease chemotherapy. ( 17, 19 ) Development of MDR cells is caused by overexpression of drug outflow transporter, such as P-glycoprotein ( Pgp ) and multidrug resistance-associated proteins ( MRP ) . Pgp belongs to a superfamily of ATP adhering cassette ( ABC ) proteins and a plasma membrane glycoprotein encoded by human MDR1 cistron that pump a broad scope of anticancer drugs out of malignant neoplastic disease cells. ( 5, 17 ) In fact, there are about 40-50 % of malignant neoplastic disease patients exhibit overexpression of Pgp in the malignant tissue. ( 17 ) Pluronic block copolymer appeared to be a powerful inhibitor of Pgp efflux pump. There is grounds to back up this mechanism. It is observed that intervention with pluronic block copolymers can intracellularly accumulate doxorubicin in immune malignant neoplastic disease cells expressed by Pgp outflow transporter. Conversely, drug consumption in non-Pgp-expressing malignant neoplastic disease cells was non observed in the presence of pluronic. Therefore, it can be concluded that pluronic effects specifically on the outflow of Pgp-dependent path in MDR cells. ( 15 )
Some MDR cells display segregation ability in anticancer drugs within cytoplasmatic cysts. These drugs serve as an add-on protective mechanism by diminishing atomic entry of the drugs. The cloistered drug will so deactivate and coerce out of the cell before it can execute its intended action on the cell. ( 7, 20 ) Drug segregation can be achieved by keeping the lift of pH gradients across organelle membranes by activity of H+-ATPase which is an ATP-dependent pump. ( 5 )
Pluronic block copolymers besides play a function in suppressing the glutathione/ glutathione S-transferase ( GSH/GST ) detoxification system by consuming GSH and demobilizing GST in MDR cells. ( 20 ) Inhibition of the GST/GSH detoxification system caused decrease in glutathione junction of selected substrates, for illustration doxorubicin and farther decreases the extent of riddance of these substrates from the cells through the MRP-mediated drug efflux pathway. ( 15 ) MRP exhibit different substrate belongingss and inhibitor specificity from Pgp.When different substrates are used, the complex drug riddance mechanism through MRP and GST/GSH detoxification systems produces different responses to pluronic. First, the organic anion substrates of MRP do non necessitate glutathione junction and they normally respond to pluronic in the same manner as Pgp substrates and accordingly the outflow decreased and substrate accretion in the cells increased. ( 21 ) Second, some compounds, for illustration doxorubicin, that merely go MRP conjugates after glutathione junction are known to depend on GSH degrees besides MRP and GST activities. ( 22 ) Last, compounds that are co-transport with GSH by MRP path short-circuiting glutathione junction can besides demo dependance on GSH and MRP activity without exhibiting it. ( 15 )
There is suggestion that incorporation of pluronic block copolymers are able to alter membrane constructions in chondriosome of MDR cells, followed by release of cytochrome C and addition of ROS degrees in cytol. Such effects promote mitochondria- related proapoptotic cascade in cells and prevent activation of antiapoptotic cellular defense mechanism in MDR cells. ( 7, 15, 20 )
Assorted mechanisms of drug opposition required ingestion of energy to exercise their effects on MDR. The chondriosome are the chief beginning of energy for metamorphosis activity in the cell and might function as a promising site for pluronic block copolymers. Addition of pluronic in chondriosome membranes inhibit cellular respiration which farther deplete ATP degrees and restrain the energy beginning needed in MDR cells. ( 20 ) Angstrom survey had been carried out and it shows that pluronic P85 significantly promotes decrease in ATP degrees selectively in MDR cells whereas no response observed in non-MDR cells. This phenomena explained that P85 response correspond to presence of MDR in cells alternatively of sum of ATP available in the cells. ( 7 ) One of the grounds is that there is difference in the usage of major energy beginning by MDR sensitive cells. It is understood that MDR cells use fatty acids as fuel beginning while drug-sensitive cells utilize glucose metamorphosis. ( 19 ) In add-on, overexpression of Pgp or MRP unusually enhances reactivity to the pluronic sing MDR or non-MDR cells. ( 7, 15 )
Pluronic unimers besides known to deject the microviscosity of cell membranes. The alterations are due to conformational alteration of lipid bilayer in the outflow protein as consequence of immersed of block copolymer concatenation on the membranes. Previous surveies utilizing P85 have shown that alterations in membrane lipid fluidness contribute to suppression of Pgp efflux map. ( 23 ) It has besides concluded that P85 exhibit suppression consequence on Pgp ATPase activity. ( 15 )
Figure 2. Multiple effects of Pluronic block copolymers inMDRcells: 1 ) incorporation of Pluronic
molecules intomembranes and lessening of themembrane microviscosity ; 2 ) initiation ofATP
depletion ; 3 ) suppression of drug outflow transporters ; 4 ) release of cytochrome C from
chondriosomes and increase in ROS degrees in cytol ; 5 ) addition of pro-apoptotic signaling
and lessening of anti-apoptotic defence in MDR cells ; 6 ) suppression of the glutathione/
glutathione S-transferase detoxification system ; and 7 ) abolition of drug segregation
within cytoplasmatic cysts. ( 7 )
In this paper, a survey is carried out to research protein-pluronic interactions in biological responses. Biomaterials are normally used in medical specialty over the old ages and pluronics have attracted great involvement in biomaterials community. Tissue technology is a new field that concern with application of rules of technology and biological science to replace, keep or take damaged tissues. ( 24 ) The high-throughput stuff find can be achieved by synthesis of big library of new stuffs to be screen taking to place new polymers with coveted characteristic. ( 25, 26 ) Polymer microarray had shown to be a promising method to fix polymer libraries. The latest development in this method is the readying of polymer microarrays by consecutive printing of monomers onto the substrate with the assistance of instigators. ( 25 ) Besides, protein surface assimilation to surfaces is unusually of import in tissue technology and biomedical field as it can greatly impact interaction of cells with biomaterials. Protein adhesion belongingss to polymers can be observed by utilizing atomic force microscopy ( AFM ) . The sum of protein to a surface from solution is quantified by fluorescent and radioactive labeling of proteins. ( 27 )
