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Biodegradable polymers

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Biodegradable polymers

  1. 1. BBIIOODDEEGGRRAADDAABBLLEE PPOOLLYYMMEERRSS
  2. 2. Biodegradable Polymer Biodegradable polymers degrade within the body as a result of natural biological processes. They are broken down into biologically acceptable molecules that are metabolized and removed from the body via normal metabolic pathways.
  3. 3. Ideal Characteristics Of Polymers In Biodegradable Delivery System • Inert • Permeability • Biodegradability • Bio-compatilibility
  4. 4. MMeecchhaanniissmm OOff BBiiooddeeggrraaddaabbllee PPoollyymmeerrss BBIIOODDEEGGRRAADDAATTIIOONN ENZYMATIC DEGRADATION HYDROLYSIS BULK EROSION SURFACE EROSION
  5. 5. POLYMER DEGRADATION  The degradation is primarily the process of chain cleavage leading to a reduction in molecular weight. On the other hand, erosion is the sum of all processes leading to the loss of mass from a polymer matrix. Degradation Schemes  The degradation of the polymer can be through either bulk erosion (as in poly(α-hydroxy esters)) or surface erosion (as in polyanhydrides, poly(orthoesters)).  Generally Hydrophobic Polymers degraded by these mechanisms.  Enzymatic degradation  Hydrolysis
  6. 6.  Bulk Erosion : In this process hydrolysis occurs throughout the bulk of the polymer. The matrix can disintegrate before drug depletion, and a large burst in rate of drug delivery can take place.  Surface Erosion: In a surface erosion process hydrolysis of the polymer is confined to the outer surface, and the interior of the matrix remains essentially unchanged.
  7. 7. Type I Erosion  It is evident with water-soluble polymers cross-linked to form a three-dimensional network.  Erosion can occur by cleavage of cross-links (type IA) or cleavage of the water-soluble polymer backbone (type IB)
  8. 8.  Type II Erosion It occurs with polymers that were earlier water-insoluble but converted to water-soluble forms by hydrolysis, ionization or protonation of a pendant group.  Type III Erosion High molecular weight, water-insoluble macromolecules are converted to small, water-soluble molecules by a hydrolytic cleavage of labile bonds in the polymer backbone.
  9. 9. Factors Influence the Degradation Behavior  Chemical Structure and Chemical Composition  Molecular Weight  Presence of Low Mw Compounds (monomer, oligomers, solvents, plasticizers, etc)  Presence of Ionic Groups  Presence of Chain Defects  Configurational Structure  Morphology (crystallinity, presence of microstructure, orientation and residue stress)  Processing methods & Conditions  Method of Sterilization  Storage History  Site of Implantation  Physiochemical Factors (shape, size)  Mechanism of Hydrolysis (enzymes vs water)
  10. 10. SYNTHETIC POLYMERS ♦ Aliphatic Poly (ester)s Poly (glycolic acid) (PGA) Poly (lactic acid) (PLA) Poly (ε-caprolactone) Poly (para-dioxanone) Poly (hydroxybutyrate) Poly (ß-malic acid) ♦ Polyphosphoesters ♦ Polyanhydrides ♦ Poly (ortho esters) ♦ Polyphosphazenes Hydrophilic Hydrophobic Insoluble Surface-active Insoluble biodegradable Imidazolyl derivatives Glyceryl derivatives Glucosyl derivatives ♦ Poly (amino) Acids and Pseudopoly (amino) Acids Poly-L-glutamic acid Poly-L-Lysine (PLL) Hydroxyproline-derived Polyesters Tyrosine-derived poly (iminocarbonates)
  11. 11. Lactide/Glycolide Polymers POLY (GLYCOLIC ACID) ---(--O—C-CH2---)n POLY (LACTIC ACID) --(--O---C—CH---)n POLY (CAPROLACTONE) --(--O—C---(CH2)5---)n  First polymers used in medicine dated back to 1954.  Most commercialized class of Polymers ex : ADRIAMYCIN®  Bio compatible & Bio resorbable  Synthesis & Co polymerisation can be easily done  t ½ ranges from weeks (PLA) to years (PCL). APPLICATIONS : (1) Sutures, ligatures etc. (2) DECAPEPTYL ® , LUPRON DEPOT ®
  12. 12. DEGRADATION IS MAINLY BY (1) ENZYMATIC (2) HYDROLYTIC (3) MICROBIAL ENZYMATIC Esterase, pronase, bromelain HYDROLYSIS R—COO---R1 + H2O R—COOH + R1 –OH MICROBIAL DEGRADATION • Fungi – ‘ FUSARIUM MONILIFORMAE’ • YEAST- ‘CRYPTOCOCCUS’
  13. 13. POLY PHOSPHO ESTERS O --(--P---O---R---O--)-- Poly (Phosphate ) OR1 O --(--P---O---R---O--)-- Poly (Phosphonate) R1  Highly Adjustable properties  Good Biocompatabilty  High Degradability  High Mol.wt gives good strength
  14. 14. Drug Release  Get degraded within 6 months  T1/2 is from 2 to 4 months..  Degradation products – phosphates & alcohol. Applications Paclitaxel, Cisplatin, Plasmid DNA. Sterilisation & stability  Highly susceptible to hydrolysis in open air.  Should be stored in a desiccators.  Sterilization only by gamma irradiation.
  15. 15. POLY ANHYDRIDES HO--[---(C—R1----C)n1-----O-----(C---R2---C-)n2--]n3---OH General structure • Two carboxylic groups at each end • High Degradation rate • Degrade by Surface Erosion • Aromatic P.A’s are slower degrading • Copolymerisation can control degradation rate • Biological tests in Rabbits proved them Non-mutagenic APPLICATIONS : 1) Peptides for osteomylites. 2) Protiens for brain tumour.
  16. 16. Drug Release  Mostly they degrade by Surface Erosion (S.E)  Their t1/2 is less than 30 days.  Due to S.E. proportion of drug released alters with time. Drug Stability  Primary amine containing drugs react at pH 7.2.  The above reaction is not seen below pH 5.0.  They are ideal when action is required for 1 week  They have more application as parentrals.
  17. 17. POLY OLEFINS Properties  A polyolefin is a polymer produced from a simple olefin (also called an alkene with the general formula CnH2n) as a monomer.  Carbon Chain based Polymers.  They contain Double & Triple bonds extensively.  Presence of substituents like cyanoacryl groups enhance degradation rate.  Introduction of vinyl group makes them more stable ex : Teflon Applications 1) Sutures, catheters, implants. 2) Membrane barrier for drugs.
  18. 18. POLY AMIDES PROPERTIES :  A polyamide is a polymer containing monomers of amides joined by peptide bonds.  These are generally called as ‘NYLONS’.  They are generally slow degrading.  By Introduction of copolymers like ‘L-Aspartic Acid', nearly 40% of polymer Is degraded within 1 week.  Mainly degraded In vivo by Non-specific ‘Amidases’  They are more stable when compared to other Polymers. APPLICATIONS : • Haemofiltration Membranes. • Dressings, sutures etc.
  19. 19. ADVANTAGES  Play an essential role in Formulation of CDDS.  Patient compliance is improved.  Bio compatible.  Help in adjusting duration of action of drug.  Most of them are Inert.  Copolymerisation can be done. DISADVANTAGES  Expensive.  Drug release cannot be 100% predicted.
  20. 20. NATURAL POLYMERS These are the polymers obtained from natural resources, and are generally non-toxic. NATURAL POLYMERS PROTEINS Polysaccharides Ex: COLLAGEN ALBUMIN FIBRIN Ex : DEXTRAN CHITOSAN STARCH ADVANTAGES : 1) Readily & Abundantly Available. 2) Comparatively Inexpensive. 3) Non toxic products. 4) Modified to get semi synthetic forms.
  21. 21. PROTEINS ALBUMIN ADVANTAGES • It is a major plasma protein component. • It accounts for more than 55% of total protein in human plasma. • It is used to design particulate drug delivery systems.
  22. 22. Factors Affecting Drug Release From Albumin Microspheres • Physicochemical properties and the concentration of the drug. • Interaction between the drug and the albumin matrix. • Size and density of microspheres. • Nature and degree of cross-linking. • Presence of the enzymes and pH in the environment. USES • Albumin micro-spheres are used to deliver drugs like Insulin, Sulphadiazene, 5-fluorouracil, Prednisolone etc. • It is mainly used in chemotherapy, to achieve high local drug concentration for relatively longer time.
  23. 23. COLLAGEN ADVANTAGES  It is a major structural protein in animals  It is used as sutures ,Dressings, etc.  Readily isolated & purified in large quantities.  Can be processed in variety of forms . DISADVANTAGES  Chance of antigenic response.  Variability in drug release kinetics.  Poor mechanical strength.
  24. 24. SODIUM ALGINATE • Since the use of organic solvents and high temperature is not required even viable bacteria and viruses can be employed. • It protects the antigens and the vaccines against degradation in GIT. • It acts as an adjuvant. USES • Alginates are particularly used as carriers of peptides and other sensitive drug molecules since particulate carriers can be easily prepared in aqueous solution at room temperature. • Alginate micro-spheres are efficiently used for oral delivery of vaccines.
  25. 25. POLYSACCARIDES DEXTRAN • Dextran is a complex branched polysaccharide made of many glucose molecules joined into chains of varying lengths. • It consists of α-D-1,6-glucose-linked glucan with side-chains linked to the backbone of Polymer. • Mol.wt ranges from 1000 to 2,00,000 Daltons • Enzymes from moulds such as ‘PENCILLIUM’ degrade it. APPLICATIONS 1) Replacement of Blood loss. 2) Thrombosis Prophylaxis. 3) Improvement of Rheology.
  26. 26. CHITOSAN • It consists of B-1-4 linked 2 amino-2-deoxy gluco –pyranose moieties. • Commercially manufactured by N-deacetylation of Chitin which is obtained from Mollusc shells. • It is soluble only in acidic pH i.e. when amino group is protonated. • Thereby it readily adheres to bio membranes. • It is degraded mainly by Glycosidases & lysozymes. ADVANTAGES Free availability, Biocompatibility, Biodegradability Bioadhesive, unique properties.
  27. 27. ENVIRONMENTALLY RESPONSIVE POLYMERS  Thermosensitive Polymers e.g. Poly (N-alkyl substututed acrylamides)  Electrically and Chemically Controlled Polymers e.g. PEG & Poly(methacrylic acid) (PMMA), collagen, Poly(pyrrole)  pH Sensitive polymers e.g. Poly(2-ethylacrylic acid) (PEAA)  Azopolymers MISCELLANEOUS POLYMERS  Polymeric Phospholipids  Polyethyleneimine  Polyamidoamine  Polyethylene Glycol

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