Polymer Science for Pharmaceuticals
BPH 2201
Pharmaceutics II
Md. Imran Nur Manik
Lecturer
Department of Pharmacy
Primeasia University
Lecturer
Department of Pharmacy
Primeasia University
Polymer Science for Pharmaceuticals
Introduction
Polymer Science or Macromolecular Science is a subfield of Materials Science. It is relatively a new branch of science; concerned with polymers, primarily synthetic polymers such as plastics and elastomers.
Polymer Science has been the backbone for the development of new formulations for past few years and its advances have led to development of several applications in pharmaceutical science.
Definition: Polymers
The term "polymer" derives from the ancient Greek word polus, meaning "many, much" and meros, meaning "parts", and refers to a molecule whose structure is composed of multiple repeating units.
Polymers are high molecular weight compounds or macromolecules composed of many repeating subunits called “MONOMERS”, connected by covalent bonds or chemical bonds. The reaction involving combination of two or more monomer units to form a long chain polymer is termed as polymerization.
The key difference between early polymers and pharmaceutical polymers is biocompatibility.
These are widely used as Pharmaceutical aids like suspending agents, Emulsifying agents, Adhesives, Coating agents, Adjuvants etc. Packaging material and medical devices both in conventional and controlled drug delivery systems.
Other Definitions
A Polymer is like a thread that is joined by many coins punched through the center, in the end we get a string of coins, the coins would be the monomers and the chain with the coins would be the polymer.
E.g. Polyethylene = Ethylene-ethylene-ethylene-ethylene-…
Polymers are long chain giant organic molecules assembled from many smaller molecules called monomers. A polymer is analogous to a necklace made from many small beads.
Herman Staudinger, who received the Nobel Prize in Chemistry in 1953, coined the term “macromolecule” in 1922 and used it in reference to polymers. The difference between the polymers and macromolecules is that polymers are made of repeating units, whereas the term macromolecule refers to any large molecule, not necessarily just those made of repeating units. So, polymers are considered to be a subset of macromolecules.
A monomer is a small molecule that combines with other molecules of the same or different types to form a polymer. If two, three, four, or five monomers are attached to each other, the product is known as a dimer, trimer, tetramer, or pentamer, respectively. An oligomer contains from 30 to 100 monomeric units. Products containing more than 200 monomers are simply called a polymer (Fig. 20–1). From a thermodynamic perspective, polymers cannot exist in the gaseous state because of their high molecular weight. They exist only as liquids or high solid materials.
Classification of Polymers
- Based on Backbone
1. Polymers with carbon chain backbone:
Polyethylene, Polypropylene, Polystyrene, Poly (vinyl chloride), Polyacrylonitrile, Polyacrylamide, Poly (vinyl alcohol), Poly (methyl methacrylate), Poly vinylpyrrolidone
2. Polymers with heterochain backbone:
Poly (ethylene oxide), Poly (propylene oxide), cellulose (Poly-glucopse,β→1.4), Amyloose (Poly-glucoside,α→1,4) {Component of starch), Pectinic acid (Polygalacvtouronoside), Polyehylene glycolterepthalate, Polydimethylsiloxane etc.
B. Based on Occurrence
- Natural polymers: Natural polymers are derived from natural sources and can be polysaccharides and proteins in chemical nature.
Protein-based polymers: Collagen, albumin, gelatin
Polysaccharides: Agarose, alginate, carrageenan, hyaluronic acid, dextran, chitosan, cyclodextrins
- Synthetic polymers: Synthetic polymers are of artificial origin which consists of fibers like Teflon and Dacron, Synthetic Rubbers, Plastics and PVC.
It has the following subtypes
I. Biodegradable Polymers: Biodegradable polymers are defined as polymers comprised of monomers linked to one another through functional groups and have unstable links in the backbone.
They are broken down into biologically acceptable molecules that are metabolized and removed from the body via normal metabolic pathways.
It includes the followings
a. Natural bio-degradable polymers: These polymers are very common in nature. The use of these polymers is limited because of their high costs and questionable purity.
Examples-Albumin, Collagen, Gelatin, Starch etc.
b. Synthetic Bio-degradable polymers:
These types of polymers are preferred rather than natural bio-degradable polymers due to their inertness and easy and cheap formulation.
Synthetic bio-degradable polymers have following advantages over natural ones:
- Localized delivery of drug.
- Sustain delivery of drug.
- Stabilization of drug.
- Reduced side effects etc.
Examples- Poly lactide homopolymer, Polyester etc.
c. Semi-Synthetic Polymers:
These types of polymers are derived from naturally occurring polymers by means of chemical modifications.
E.g. Vulcanized rubber, Gun cotton, Cellulose diacetate, HPMC etc.
d.Polyesters: Poly (lactic acid), poly(glycolic acid), poly(hydroxy butyrate),
poly(∈- caprolactone), poly(β-malic acid), poly(dioxanones)
poly(∈- caprolactone), poly(β-malic acid), poly(dioxanones)
e.Polyanhydrides: Poly (sebacic acid), poly(adipic acid),poly(terphthalic acid) and various copolymers
f.Polyamides: Poly (imino carbonates), polyamino acids
g.Phosphorous-based polymers: Polyphosphates, polyphosphonates, polyphosphazenes
h.Others: Poly (cyano acrylates), polyurethanes, polyortho esters, polydihydropyrans, polyacetals
II. Non-biodegradable: It includes the followings
a.Cellulose derivatives: Carboxymethyl cellulose, ethyl cellulose, cellulose acetate, cellulose acetate propionate, hydroxypropyl methyl cellulose
b.Silicones: Polydimethylsiloxane, colloidal silica
c. Acrylic polymers: Polymethacrylates, poly(methyl methacrylate),polyhydro(ethylmethacrylate)
d.Others: Polyvinyl pyrrolidone, ethyl vinyl acetate, poloxamers, poloxamines
C. Based Upon Molecular Forces
I. Thermoplastic Polymer: Some polymer are soften on heating and can be converted into any shape that they can retain on cooling. Such polymer that soften on heating and stiffen on cooling are termed as `thermoplastic’ polymers. Ex. Polyethylene, PVC, nylon, sealing wax.
II. Thermosetting Polymer : Polymer that become an infusible and insoluble mass on heating are called ‘thermosetting’ polymers. Thermosetting polymers are cross-linked polymers, which are formed upon combined application of a cross-linker and heat or combined application of heat and reaction of internal functional groups.
Plastics made of these polymers cannot be stretched, are rigid and have a high melting point.
III. Elastomers: When plastics are vulcanised into rubbery products exhibiting good strength and elongation, polymers are known as ‘elastomers’. E.g. silicone rubber, natural rubber, synthetic rubber, etc.
IV. Fibres: The polymers which are filament like materials, having their length at least 100 times to their diameter, are said to be ‘fibres’. E.g. Nylon, terylene.
D. Based on Composition:
1. Homopolymer:
Homopolymers- consist of chains with identical bonding linkages to each monomer unit. This usually implies that the polymer is made from all identical monomer molecules.
These may be represented as : -[A-A-A-A-A-A]-
e.g. Polyethylene, polystyrene
2. Copolymer:
A polymer of two or more different monomers. The synthetic rubber used to make tire treads and shoe soles, for example, is a copolymer made of the monomers butadiene and styrene
These may be represented as : -[A-B-A-B-A-B]-
e.g. Silicone, Ethyl cellulose
E. Based on polymerization mechanisms:
1. Addition polymers:
Addition polymers are formed when monomer units are separately added to form long chains without elimination of any by-product molecules.This polymers are formed by reactions between monomer molecules possessing multiple bonds.
E.g. Polyethylene, Polypropylene, Styrene- butadiene rubber etc.
2. Condensation polymer
Condensation polymers are formed when the monomers containing active functional groups react together with the elimination of a small molecule like water, ammonia, alcohol etc.
E.g. Nylon-66, Polyester, Bakelite etc.
F. Based upon linkage
Based upon linkage it can be classified as:
I. Linear polymer: Molecules has definite backbone and does not have long chain branches. e.g. Polyformaldehyde,Polyesters, Polycarbonates etc.
II. Branched polymers: It has long chain branches that cannot be defined. It may also have short chain branches.E.g. Polyethylene, HPLD Polyethylene etc.
Fig: Branched polymers Fig: Cross-linking polymers
II. Cross-linking polymers:
In this type all molecules are chemically bonded together, forming a three dimensional network. The bonding is usually covalent but other types such as ionic bond are also possible. Cross-linked polymers are produced from linear and branched polymers or directly from chemical precursor. E.g. Natural rubber, polyacrylamide gels,epoxies, Alkyd resins etc.
Physical, chemical and mechanical properties of Polymer
Polymer properties are broadly divided into several classes based on the scale at which the property is defined as well as upon its physical basis. These are as follows:
The first and most important attribute of the repeat units (monomer residues, also known as "mers") comprising a polymer is its identity. Polymers that contain only a single type of repeat unit are known as homopolymers, while polymers containing a mixture of repeat units are known as copolymers.
For example, polynucleotides such as DNA are composed of a variety of nucleotide subunits.A polymer molecule containing ionizable subunits is known as a polyelectrolyte or ionomer.
The microstructure of a polymer (sometimes called configuration) relates to the physical arrangement of monomer residues along the backbone of the chain. These are the elements of polymer structure that require the breaking of a covalent bond in order to change.
An important microstructural feature of a polymer is its architecture and shape, which relates to the way in which the branch points lead to a deviation from a simple linear chain. A polymer's architecture affects many of its physical properties including, solution viscosity, solubility in various solvents, glass transition temperature and the size of individual polymer coils in solution.
The physical properties of a polymer are strongly dependent on the size or length of the polymer chain. For example, as chain length is increased, melting and boiling temperatures increase quickly. Increasing chain length furthermore tends to decrease chain mobility, increase strength and toughness, and increase the glass transition temperature (Tg).
Monomers within a copolymer may be organized along the backbone in a variety of ways.
- Alternating copolymers
- Periodic copolymers
- Statistical copolymers
- Block
Tacticity describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule.
There are three types: isotactic (all substituents on the same side), atactic (random placement of substituents), and syndiotactic (alternating placement of substituents).
Polymer morphology generally describes the arrangement and microscale ordering of polymer chains in space.
Synthetic polymers may consist of both crystalline and amorphous regions; the degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material.
The space occupied by a polymer molecule is generally expressed in terms of radius of gyration, which is an average distance from the center of mass of the chain to the chain itself.
These are the properties that dictate how the polymer actually behaves on a macroscopic scale.
The tensile strength is very important in applications that rely upon a polymer's physical strength or durability.
It is defined, for small strains, as the ratio of rate of change of stress to strain. Like tensile strength, this is highly relevant in polymer applications involving the physical properties of polymers, such as rubber bands.
Transport properties are very important in many applications of polymers for films and membranes.
The term melting point, when applied to polymers, suggests not a solid–liquid phase transition but a transition from a crystalline or semi-crystalline phase to a solid amorphous phase.
A parameter of particular interest in synthetic polymer manufacturing is the glass transition temperature (Tg), at which amorphous polymers undergo a transition from a rubbery, viscous liquid, to a brittle, glassy amorphous solid on cooling. The glass transition temperature may be engineered by altering the degree of branching or crosslinking in the polymer or by the addition of plasticizer.
In general, polymeric mixtures are far less miscible than mixtures of small molecule materials. In dilute solution, the properties of the polymer are characterized by the interaction between the solvent and the polymer.
Inclusion of plasticizers tends to lower Tg and increase polymer flexibility.
The attractive forces between polymer chains play a large part in determining polymer's properties.
Polymers such as Poly(methyl methacrylate) ;PMMA and HEMA: MMA are used as matrices in the gain medium of solid-state dye lasers that are also known as polymer lasers.
Characteristics of an ideal polymer
An ideal polymer should have the following properties
- It should be versatile and possess a wide range of mechanical, physical, chemical properties.
- It should be non‐toxic.
- It should have good mechanical strength.
- It should be easily administered.
- It should be inexpensive and easy to fabricate the dosage form.
- It should be inert to host tissue.
- It should be compatible with environment.
- It should be easily administrable.
- It should have good mechanical strength.
Selection Parameters for Biomedical Polymers
The design and selection of biomaterials depend on different properties –
Host Response: The response of the host organism (local and systemic) to the implanted polymeric material or device.
Biocompatibility: The ability of a material to perform with an appropriate host response, in a specific application.
Toxicology: Should not be toxic
Appropriate Design and Manufacturability: Biomaterials should be machinable, moldable, extrudable.
Mechanical Properties of Biomedical polymers: Tensile strength, yield strength, elastic modulus, surface finish, creep, and hardness.
Application of Biomedical Polymers
- Artificial Heart.
- Bones, Joints, and Teeth.
- Contact Lenses and Intraocular Lenses.
- Artificial Kidney and Hemodialysis Materials.
- Oxygen-Transport Membranes.
- Surgical Sutures.
POLYMERS IN PHARMACEUTICAL AND BIOMEDICAL APPLICATIONS
Water-Soluble Synthetic Polymers
Poly (acrylic acid): Immobilization of cationic drugs, base for Carbopol polymers
Poly (ethylene oxide): Coagulant, flocculent, swelling agent
Poly (ethylene glycol): plasticizer, base for suppositories
Poly (vinyl pyrrolidone): Used to make betadine (iodine complex of PVP) with less toxicity than iodine, plasma replacement, and tablet granulation
Poly (vinyl alcohol): Water-soluble packaging, tablet binder, tablet coating
Polyacrylamide: Gel electrophoresis to separate proteins based on their molecular weights, coagulant,absorbent
Poly (isopropyl acrylamide) and poly (cyclopropyl methacrylamide): Thermogelling acrylamide derivatives, its balance of hydrogen bonding, and hydrophobic association changes with temperature
Cellulose-Based Polymers
Ethyl cellulose: Insoluble but dispersible in water, aqueous coating system for sustained release applications
Carboxymethyl cellulose: Superdisintegrant, emulsion stabilizer
Hydroxyethyl and hydroxypropyl celluloses: Soluble in water and in alcohol, tablet coating
Hydroxypropyl methyl cellulose: Binder for tablet matrix and tablet coating, gelatin alternative as capsule material
Cellulose acetate phthalate: Enteric coating
Hydrocolloids
Alginic acid: Oral and topical pharmaceutical products; thickening and suspending agent in a variety of pastes, creams, and gels, as well as a stabilizing agent for oil-in-water emulsions; binder and disintegrant
Carrageenan: Modified release, viscosifier
Chitosan: Cosmetics and controlled drug delivery applications, mucoadhesive dosage forms, rapid release dosage forms
Hyaluronic acid: Reduction of scar tissue, cosmetics
Pectinic acid: Drug delivery
Water-Insoluble Biodegradable Polymers
(Lactide-co-glycolide) polymers: Microparticle–nanoparticle for protein delivery
Starch-Based Polymers
Starch: Glidant, a diluent in tablets and capsules, a disintegrant in tablets and capsules, a tablet binder
Sodium starch glycolate: Superdisintegrant for tablets and capsules in oral delivery
Plastics and Rubbers
Polyurethane: Transdermal patch backing (soft, comfortable, moderate moisture transmission), blood pump, artificial heart, and vascular grafts, foam in biomedical and industrial products
Silicones: Pacifier, therapeutic devices, implants, medical grade adhesive for transdermal delivery
Polycarbonate: Case for biomedical and pharmaceutical products
Polychloroprene: Septum for injection, plungers for syringes, and valve components
Polyisobutylene: Pressure sensitive adhesives for transdermal delivery
Polycyanoacrylate: Biodegradable tissue adhesives in surgery, a drug carrier in nano- and microparticles
Poly (vinyl acetate): Binder for chewing gum
Polystyrene: Petri dishes and containers for cell culture
Polypropylene: Tight packaging, heat shrinkable films, containers
Poly (vinyl chloride): Blood bag, hoses, and tubing
Polyethylene: Transdermal patch backing for drug in adhesive design, wrap, packaging, containers
Poly (methyl methacrylate): Hard contact lenses
Poly (hydroxyethyl methacrylate): Soft contact lenses
Ethylene vinyl acetate and polyethylene terephthalate:Transdermal patch backing (occlusive, heat sealable, translucent)
Ethylene vinyl acetate and polyethylene: Transdermal patch backing (heat sealable, occlusive, translucent)
Polyethylene and polyethylene terephthalate: Transdermal patch backing (when ethylene vinyl acetate copolymer is incompatible with the drug)
PLASTICIZER
A plasticizer or softener is a substance incorporated in a material (usually a plastic) to increase the flexibility, elongation, workability, dispensability.
A Plasticizer is a distinct polymer additive, that increase the plasticity or viscosity of a material.
Ideal properties of plasticizers:
- It should be flexible resilient (স্থিতিস্থাপক elastic) and easier to handle.
- It should be non-volatile with high boiling point.
- It should not come out from materials to which it is added.
- Plasticizers used for internal purpose should be non-toxic.
- Lower the tensile strength and softening temperature, of the polymeric materials to which it is added.
- It should reduce the brittleness, improve flow, flexibility, and increase toughness, shear strength, and impart resistance to the polymeric film coating.
- It should lower the glass transition temperature of the polymeric film coating. It should reduce the viscosity of materials to which it is added.
- It should impart permanent properties such as liability, shock resistance, hand drop.
- The main role of the plasticizer is to improve mechanical properties of the polymers by increasing flexibility, decreasing tensile strength and lowering the second order transition temperature.
Why do we need plasticizers?
Almost all the film forming agents or polymers are brittle in nature do to their complex structure. Most commonly used polymers are the cellulose derivatives or cellulose related compounds like HPMC, MC, EC, Nitrocellulose, HPMCP etc. These polymers are widely used as film forming materials as they:-
- Produce transparent films
- Produce intact films
- They have lower values for water vapor permeability rate.
- They have lower values for oxygen transmission rates.
They can be structurally modified to achieve sustained release, like HPMC can be converted to HPMCP for enteric coating.
But due to presence of multiple polymeric strands within a single molecule of polymer makes them brittle. When such a material is applied as a film coat on to tablet a smooth film is not be obtained. This condition necessitates the addition of plasticizers to the coating/Film forming dispersions. The addition of plasticizers to polymeric material causes them to diffuse within the polymers and cause polymer deformation and coalescence into homogeneous films.
The effectiveness of plasticizers on polymeric dispersion depends upon polymer compatibility and the permanence of plasticizer during the course of shelf life, or when it comes in contact with physiological fluids.
Effect of Plasticizers
- Easy melt
- Improve flexibility
- Increase Softness and Flexibility.
- Improve Process ability.
- Alters Softening point, Tensile Strength, Elongation at break & Impact.
Mechanism of action
- The mechanism of action of plasticizers is defined as to interpose between every individual strand of polymer and thereby causing breakdown of polymer -polymer interactions.
- The tertiary structure of the polymer is modified into more porous, flexible and with less cohesive structure.
- Plasticizers soften and swell the polymer (latex spheres) which aids in overcoming their resistance to deformation.
- As a result the plasticized polymer would deform at a lower tensile force as compared to without plasticizer. This enhances the polymer -plasticizer interaction.
- This effect in turn enhances the film elongation effect.
- This interaction to a greater extend depends upon the glass transition temperature of polymers. Glass transition temperature, Tg is the temperature at which hard glassy polymer is converted into a rubbery material.
- All polymers have higher glass transition temperatures and addition of plasticizers reduces the glass transition temperature.
- As plasticizers usually possess relatively long alkyl chains, they have the effect of screening the polymer chains from each other, thereby preventing them from re-forming the chain-chain interactions which give the unplasticized polymer its rigidity.
Plasticization
Plasticization, in general, refers to a change in the thermal and mechanical properties of a given polymer which involves:
(a) Lowering of rigidity at room temperature;
(b) Lowering of temperature, at which substantial deformations can be effected with not too large forces;
(c) Increase of the elongation to break at room temperature;
(d) Increase of the toughness (impact strength) down to the lowest temperature of serviceability.
These effects can be achieved:
(1) By compounding the given polymer with a low molecular weight compound or with another polymer and
(2) By introducing into the original polymer a comonomer(one of the constituents of a copolymer) which reduces crystallizability and increases chain flexiblity
Plasticization theories
There are mainly 03 theories regarding plasticization. Therese are as follows.
Lubricity theory:
- According to Lubricity Theory the Plasticizer acts as a lubricant, reducing intermolecular friction between polymer molecules responsible for rigidity of the polymer.
- This theory a.ssumes the rigidity of the resin (pure polymer) arises from “intermolecular friction.”
- A “dry” polymer, a resin without plasticizer, is rigid because friction exists between its chains, binding them into a network.
- When the polymer is heated in order to be plasticized, the binding is weakened and the smaller plasticizer molecules are able to slip in between the chains.
- When the polymer cools, the plasticizer molecules act as a lubricant between the chains, allowing them to “slip.”
Gel theory:
- According to Gel Theory the Polymers are formed by an internal three-dimensional network.
- The plasticizer molecules break up the polymer-polymer interaction by getting in between the chains and “obscuring” these interaction sites from the polymer molecules.
- Resin-resin interactions occur at “centers of attachment.”
- Plasticizer molecules break these interactions and masks the centers from each other, preventing re-formation.
- This theory is not sufficient to describe interaction– should be combined with Lubricity Theory.
The free volume theory:
- According to the Free Volume Theory the Plasticizer lowers the glass transition temperature (Tg) of the polymer.
- The free volume of a polymer can be described as the “empty internal space” available for the movement of the polymer chains. The free volume of a polymer greatly increases when it reaches the glass transition temperature.
- At the glass transition temperature, the molecular motion begins to occur, which corresponds to an increase in the free volume of the polymer.
- Plasticizer is meant to decrease the glass transition temperature, imparting increased flexibility to polymer at room temperature.
- These plasticizer molecules are having low glass transition temperature than the polymer, so that Tg of the resulting mixture will be lower.
Mechanistic Theory: Plasticizer molecules are not bound permanently to the polymer molecules form.
PLASTICIZERS IN FILM COATING
There are more than 300 different types of plasticizers available. The most commonly used plasticizers are ester like phthalates, adipates and trimellitates.
The commonly used plasticizers can be categorized into three groups:
1. Polyols:
(a) Glycerol (glycerin);
(b) Propylene glycol;
s(c) Polyethylene glycols PEG (generally the 200–6000 grades).
2. Organic esters:
(a) Phthalate esters (diethyl, dibutyl);
(b) Dibutyl sebacete;
(c) Citrate esters (triethyl, acetyl triethyl, acetyl tributyl);
(d) Triacetin.
3. Oils/ glycerides:
(a) Castor oil;
(b) Acetylated monoglycerides;
(c) Fractionated coconut oil
4. Newer Plasticizers – DBS (Dibutyl Sebacate).
Plasticized Polymers
A plasticizer is added to a polymer formulation to enhance its flexibility and to help its processing. It facilitates relative movement of polymer chains against each other. The addition of a plasticizer to a polymer results in a reduction in the glass transition temperature of the mixture. Since plasticizers increase molecular motion, drug molecules can diffuse through the plasticized polymer matrix at a higher rate depending on the plasticizer concentration.
Example: Plasticized Polymers
- Fluoxetine (ProzacWeekly) (fluoxetine hydrochloride) capsules contain hydroxypropyl methylcellulose and hydroxypropyl cellulose acetate succinate plasticized with sodium lauryl sulfate and triethyl citrate.
- Omeprazole magnesium (Prilosec), a delayed release oral suspension, contains hydroxypropyl cellulose, hydroxypropyl methylcellulose, and methacrylic acid copolymer plasticized with glyceryl monostearate, triethyl citrate, and polysorbate.
- Triacetin can be found in ranitidine HCl (Zantac) 150-tablet formulations, which contains hydroxypropyl methylcellulose as its polymer matrix.
- Dibutyl sebacate is found in methylphenidate HCl (Metadate) CDwhich contains polymers such as povidone, hydroxypropyl methylcellulose, and ethyl cellulose.
Elastomers
An elastomer is a polymer with viscoelasticity (having both viscosity and elasticity) .The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred when referring to vulcanisates.
Elastomeric materials are those materials that are made of polymers that are joined by chemical bonds, acquiring a final slightly cross-linked structure. The main characteristic of elastomer materials is the high elongation and flexibility or elasticity of these materials, against its breaking or cracking.
Depending on the distribution and degree of the chemical bonds of the polymers, elastomeric materials can have properties or characteristics similar to thermosets or thermoplastics, so elastomeric materials can be classified into:
- Thermoset Elastomers - are those elastomer materials which do not melt when heated.
- Thermoplastic Elastomers - are those elastomers which melt when heated.
Properties of elastomer materials:
- Do not melt (before melting they pass into a gaseous state.).
- Swell in the presence of certain solvents.
- Generally insoluble.
- Flexible and elastic.
- Lower creep resistance than the thermoplastic materials.
Examples and applications of elastomer plastic materials:
- Natural rubber – It is used in the pharmaceutical vial closures.
- Polyurethanes – Generally they are used in these medical applications:
- Diaphragms
- Membranes
- Surgical apparatus
- Mechanical supports
- Neoprene – It is used primarily in the manufacture of Medical gloves.
- Silicone – Silicones are used in a wide range of materials and areas due their excellent thermal and chemical resistance. Silicones are used today in many life-saving medical devices like pacemakers or hydrocephalic shunts. They are also used as excipients in topical formulations or adhesives to affix transdermal drug delivery systems. They also have found use as active pharmaceutical ingredients in products such as antacid and antiflatulent formulations.
- Medical Thermoplastic elastomers (TPE) products include drip chambers, seals, medical hoses, artificial skin to many of the artificial human body parts, drug encapsulation purposes etc.
Water soluble polymers
Water soluble polymers have a wide range of industrial applications like food, pharmaceuticals, paint, textiles, paper, constructions, adhesives, coatings, water treatment, etc.
Generally the water soluble polymers have been divided into two categories
(1) Synthetic and
(2) Natural.
1. Synthetic Water Soluble Polymers
Synthetic water-soluble polymers are substances that dissolve, disperse or swell in water and, thus, modify the physical properties of aqueous systems in the form of gellation, thickening or emulsification/stabilization. These polymers usually have repeating units or blocks of units; the polymer chains contain hydrophilic groups that are substituents or are incorporated into the backbone.
The hydrophilic groups may be nonionic, anionic, cationic or amphoteric.
Poly (ethylene glycol) (PEG): PEG-Intron-Chronic hepatitis C
Polyvinyl pyrrolidone: It is mainly used as a binder in tablet formulations
Polyacrylic acid (PAA): Polyacrylic acid is a biodegradable water soluble polymer with various industrial applications, including as a super adsorbent (e.g., in disposable nappies), in water treatment, etc.
2. Natural Water Soluble Polymers
Xanthan Gum: Xanthan gum is widely used in cosmetics and in toothpastes. Xanthan gum is used as a thickener and stabilizer in personal care products like creams, eye gels.
Pectin: Pectin has been used in the pharmaceutical industry for a wide range of applications Pure and standardized pectin has been used as a binding agent in tablets. High Methoxy (HM) pectin is used as monolithic bioerodible system, preparation of directly compressible tablets along with HPMC.
Chitosan Derivatives: It has been used as a mucoadhesive, oral absorption enhancer and in protein and gene delivery.
Dextran: Dextran as macromolecular carriers, e.g., hydrogels,
Carrageenan: Carrageenan is considered to be a good substitute for gelatin (animal-based product) in hard and soft gel capsules.
Guar Gum: Guar gum is used as a binder, disintegrant in tablet formulations. It also acts as a stabilizers, emulsifier, thickening, and suspending agent in liquid formulations.
Cellulose Ethers:
Hydroxypropylmethyl cellulose (HPMC)
Hydroxypropyl cellulose (HPC)
Hydroxyethyl cellulose (HEC)
Sodium carboxy methyl cellulose (Na-CMC)
They are mainly used as binders, coating agents, emulsifying, stabilizing, agents, and tablet disintegrants.
Sodium CMC: It is used as an emulsifying agent in pharmaceuticals, and in cosmetics. It is a preferred polymer because it has wide range of functional properties like binding, thickening, stabilizing agent.
BIODEGRADABLE POLYMERS
- Biodegradable polymers are defined as polymers comprised of monomers linked to one another through functional groups and have unstable links in the backbone.
- They are broken down into biologically acceptable molecules that are metabolized and removed from the body via normal metabolic pathways.
- Based on biodegradability polymers are classified as:
1. Biodegradable polymers
eg: collagen, poly glycolic acid etc.,
FACTORS AFFECTING BIODEGRADATION OF POLYMERS
- Morphological factors
- Shape & size
- Variation of diffusion coefficient and mechanical stresses
- Chemical factors
- Chemical structure & composition
- Presence of ionic group and configuration structure
- Molecular weight and presence of low molecular weight compounds
- Physical factors
- Processing condition
- Sterilization process
Others
- » Chemical structure.
- » Chemical composition.
- » Distribution of repeat units inmultimers.
- » Presents of ionic groups.
- » Presence of unexpected units or chain defects.
- » Configuration structure.
- » Molecular weight.
- » Molecular-weight distribution.
- » Annealing.
- » Morphology (amorphous/semi-crystalline, microstructures, residual stresses).
- » Presence of low-molecular-weight compounds.
- » Processing conditions.
- » Sterilization process.
- » Storage history.
- » Shape.
- » Site of implantation.
- » Adsorbed and absorbed compounds (water, lipids, ions, etc.).
- » Physicochemical factors (ionexchange, ionic strength, and pH).
- » Physical factors (shape and size changes, variations of diffusion coefficients, mechanical stresses, stress- and solvent-induced
- cracking, etc.).
- » Mechanism of hydrolysis (enzymes versus water).
ADVANTAGES OF BIODEGRADABLE POLYMERS
- Localized delivery of drug
- Sustained delivery of drug
- Stabilization of drug
- Decrease in dosing frequency
- Reduce side effects
- Improved patient compliance
- Controllable degradation rate
APPLICATIONS OF BIODEGRADABLE POLYMERS
- Polymer system for gene therapy.
- Biodegradable polymer for ocular, tissue engineering, vascular, orthopedic, skin adhesive & surgical glues.
- Bio degradable drug system for therapeutic agents such as anti tumor, antipsychotic agent, anti-inflammatory agent.
- Polymeric materials are used in and on soil to improve aeration, and promote plant growth and health.
- Many biomaterials, especially heart valve replacements and blood vessels, are made of polymers like Dacron, Teflon and polyurethane.
No comments:
Post a Comment