NATURAL POLYMERS

CONTENTS:

Introduction Definition Classification of natural polymers Properties and disadvantages Biodegradation mechanisms Factors affecting on biodegradation of

natural polymers Uses and applications Examples

INTRODUCTION A polymer is a large molecule (macromolecules)

composed of many repeated subunits, known as monomers.

Natural polymers and their derivatives are commonly used in medicine and pharmacy.

Particular attention has recently been paid to natural polymers, because they are biocompatiable and biodegradable, so they can be hydrolyzed into removable and non-toxic products.

monomer

monomer

Dimer polymerRepeat

attachment of monomers

DEFINITION

The natural polymer is produced by living organisms and result from only raw materials that are found in nature.

CLASSIFICATION

Classification of Natural polymersBased on source

Plant Animal Microbes

Polysaccharidese.g. Cellulose, Starch, Alginate.

Proteinse.g. Gluten (Gelatin), Albumin.

Polysaccharidese.g. Chitin (Chitosan), Hyaluronate.

Polyesterse.g. Poly(3-hydroxylalkonate) dervitives.

Polysaccharidese.g. Hyaluronate.

The natural polymers are classified based on source or structure.

CLASSIFICATIONClassification of natural polymers based on

structure.polysacchridesCellulose, alginate,dextran, chitosan 

and  Pollulan.Polypeptides

&Proteinsgelatin, albumin,lecitin, and legumin.

polynucleotidesDNA RNA

PolyestersPoly (3-hdroxyalkonate)

NATURAL RUBBER Natural rubber is another example

of a natural polymer. It is made from only Carbon and

Hydrogen. It is a product of Isoprene

polymerization.

Isoprene

Monomer Polymer

Isoprenen

Polyisoprene:Natural rubber

Natural rubber

PROPERTIES & ADVANTAGES Most of natural polymers are naturally built by condensation

polymerization Natural polymers tend to be readily biodegradable - they show no

adverse effects on the environment or human beings. Non-toxic/ non-inflammatory - all of these materials are

carbohydrates or proteins in nature and composed of repeating monosaccharide or amino acid units respectively. Hence they are non-toxic.

Biocompatible - their rate of degradation is generally inversely proportional to the extent of chemical modification

Highly porous For molecular weight the average molecular weight that can be only

defined Easy and cheap to preparation and production in comparison with

synthetic polymers Capable of attachment with other molecules – most of these materials

have variety of functional groups leading to readily modify Easy availability and renewable resources

DISADVANTAGES

Microbial contamination during production due to their natural sources.

Batch to batch variation – as result to difference of resources and resource regions.

Slow Process – as the production rate is depends upon the environment and many other factors, it can’t be changed. So natural polymers have a slow rate of production.

potential impurities – may also result in unwanted immune reactions.

Heavy metal contamination – that often associated with herbal polymeric excipeints.

BIODEGRADATION MECHANISMS The term 'biodegradation' is limited to the chemical processes that

alter either the molecular weight or solubility of the polymer Natural polymers are biodegradable since they have unstable links in

their backbone and structure They are broken down into biologically acceptable molecules that are

metabolized and removed from the body via normal metabolic pathways

BIODEGRADATION

ENZYMATIC DEGRADATION COMBINATIONHYDROLYSIS

BULK EROSION SURFACE EROSION

FACTORS AFFECTING BIODEGRADATION OF POLYMERS

Morphological factors Shape & size

Chemical factors Chemical structure & composition Presence of ionic group and configuration

structure Molecular weight

Physical factors Variation of diffusion coefficient

USES & APPLICATIONS IN PHARMACY

The wide range of properties and applications vary depending on studied natural polymer

They are either additives or active materials. Gene and drug delivery systems. Release-controlled drug delivery systems. Protecting of susceptible drugs or plasmids

from degradation. Offer different and more easily routes for

drug administration

CHITOSAN: Introduction:

Chitin is a macromolecule found in the shells of crabs, lobsters, shrimps and insects

Chitosan is obtained by partial deacetylation of chitin. Chitin is insoluble in its native form but chitosan, the

partly deacetylated form, is water soluble. Chemistry:

linear co-polymer of β(1-4) linked glucosamine and N-acetyl-D-glucosamine.

PHYSIOCHEMICAL PROPERTIES Odorless, white or creamy-white powder Chelates many transitional metal ions Highly basic polysacharides in acidic pH, it gets solubilized due to protonation

of free amino groups and the resultant soluble polysaccharide is positively charged.

hydrophilic in nature thereby it has the ability to form gels at acidic pH.

Degraded by lysozyme to it’s by products glucosamine and n-acetyl glucosamine

APPLICATION Ocular delivery:

making contact lens- optical clarity, sufficient optical correction, gas permeability, particularly towards oxygen, wettability and immunological compatibility.

antimicrobial and wound healing properties of chitosan along with an excellent film capability make chitosan suitable for development of ocular bandage lenses.

Colon drug delivery: Degraded by microflora present in human colon which

supports colon drug delivery Coating material:

Good film forming property and mucoadhesive property

Mucosal delivery: Chitosan gets protonated in acidic solution, so it

binds strongly to negatively charged cell surface making it useful to formulate bioadhesive dosage forms.

Transdermal drug delivery: Studies on propranolol hydrochloride (prop-HCl)

delivery systems using various chitosan membranes with different crosslink densities as drug release controlling membranes and chitosan gel as the drug reservoir have been performed.

Gene Delivery: Chitosan, typically isolated from the shell of

shrimp, has the ability to react with DNA and compact it to produce a nanoparticle. Such nanoparticles are more readily taken up by cells.

HYALURONIC ACID: Introduction

Carbohydrate polyanionic mucopolysacharide, occurring naturally in all living organisms.

Can be several thousands of sugar long One of most hydrophilic molecules, also known as natural

moisturizer Generally found in sodium salt form i.e. as sodium hyaluronate

Chemistry The alternating disaccharide units are linked by (1→4) inter

glycosidic linkage. Chains consist upto 30,000 repeating units so it has high

molecular weight range (1000 to 10,000,000 Da).

PROPERTIES

Biodegradable, biocompatible, non-toxic, non- immunogenic, non-inflammatory, linear chain polysaccharide

very hydrophilic; it adsorbs water making it hygroscopic readily soluble in water, and produces a gel Its viscous solutions have unusual rheological properties

(pseudoplasticity) and are exceedingly lubricious To improve the mechanical properties and control the

degradation rate, HA can be chemically modified or crosslinked to form a hydrogel

The gel is dependent upon a number of factors including the length of the chain, cross-linking, pH

APPLICATION

They are used in the preparation of gels for delivery of drugs to eye and installation into other cavities.

Microparticulate HA carrier: Sustained-release formulations (e.g. protein drugs) have

been developed using spray-dried HA microparticles which act as a protein reservoir

Also protects the drugs from denaturation and increases their bioactivity

Ocular drug delivery: Its viscosity and pseudoplastic behavior which provide

mucoadhesive property can increase the ocular residence time

Cell targetting: The expression of CD-44 (cluster determinant 44) and

RHAMM (receptor for hyaluronate-mediated motility) receptors by various tumour cells, which are endogenous ligands for HA, makes this a good candidate for drug targeting to cancer cells

Nasal delivery: A nanocarrier composed of hyaluronic acid(HA) and

chitosan(CH) was reported to encapsulate bovine serum albumin (BSA) and cyclosporine A for the nasal delivery of macromolecules

Topical drug delivery: Surface hydration and film formation enhance the

permeability of the skin to topical drugs also promotes drug retention and localization in the epidermis

HA has been used in tissue engineering for the cartilage replacement in the joints

Used in cosmetics, skin care system, as anti ageing therapy (antioxidant nature)

GELATIN:

INTRODUCTION Gelatin is a natural water soluble functional polymer (protein)

that is derived by partial hydrolysis of collagen (chief protein component in skin, bones and white connective tissues of the animal body).

It is commonly used for pharmaceutical and medical applications because of its biodegradability and biocompatibility in physiological environments.

GELATIN TYPES Gelatin derived from an acid-treated precursor is known as

Type-A and gelatin derived from an alkali-treated process is known as Type-B.

Results in a difference in isoelectric points (IP), being 7 – 9 for gelatin type A and 4 – 5 for gelatin type B.

MFG OF GELATIN

PHYSICOCHEMICAL PROPERTIES Formation of thermo-reversible gels in water: When gelatin granules are

soaked in cold water they hydrate into discrete, swollen particles. On being warmed, these swollen particles dissolve to form a solution.

Soluble in aqueous solutions of polyhydric alcohols such as glycerol and propylene glycol.

Insoluble in less polar organic solvents such as benzene, acetone, primary alcohols and dimethylformamide.

Gelatin stored in air-tight containers at room temperature remains unchanged for long periods of time. When dry gelatin is heated above 45° C in air at relatively high humidity (above 60% RH) it gradually loses its ability to swell and dissolve.

Sterile solutions of gelatin when stored cold are stable indefinitely; but at elevated temperatures the solutions are susceptible to hydrolysis.

Gelatin is composed of 50.5% carbon, 6.8% hydrogen, 17% nitrogen and 25.2% oxygen. It gives typical protein reactions and is hydrolyzed by most proteolytic enzymes to yield its peptide or amino acid components.

APPLICATION

Two-Piece Hard Capsules Soft Elastic Gelatin Capsules As a binder in Tablet Tablet Coating Suppositories Gelatin Emulsions Microencapsulation Source of essential amino acids Absorbable Gelatin Sponge Gelatin as Nanoparticle and microparticles.

ALBUMIN Introduction:

It is a major plasma protein component. It accounts for more than 55% of total protein in human

plasma. There are two specific types includes:

human serum albumin bovine serum albumin (BSA): often used in medical and molecular

biology labs.

Applications: 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.