MICROSPHERES: AS NEW DRUG DELIVERY SYSYTEM

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Vikrant et al. World Journal of Pharmacy and Pharmaceutical Sciences

MICROSPHERES: AS NEW DRUG DELIVERY SYSYTEM

Vikrant Deshmukh*, Shubhangi Warad, Rahul Solunke, Shital Walunj,

Shivaprasad Palve, Ganesh Jagdale

Kasturi shikshan sansthas College of Pharmacy, Shikrapur, Pune, India.

ABSTRACT

Microspheres are characteristically free flowing powders consisting of

proteins or synthetic polymers which are biodegradable in nature and

ideally having a particle size less than 200 µm. A well designed

controlled drug delivery system can overcome some of the problems of

conventional therapy and enhance the therapeutic efficacy of a given

drug. There are various approaches in delivering a therapeutic

substance to the target site in a sustained controlled release fashion.

One such approach is using microspheres as carriers for drugs. It is the

reliable means to deliver the drug to the target site with specificity, if

modified, and to maintain the desired concentration at the site of

interest without untoward effects. Microspheres received much

attention not only for prolonged release, but also for targeting of anticancer drugs to the

tumour. In future by combining various other strategies, microspheres will find the central

place in novel drug delivery, particularly in diseased cell sorting, diagnostics, gene & genetic

materials, safe, targeted and effective in vivo delivery and supplements as miniature versions

of diseased organ and tissues in the body. The purpose of the review is to compile various

types of microspheres, different methods to preparation, its applications and also various

parameters to evaluate their efficiency.

KEY WORDS: Microspheres, Target site, Therapeutic efficacy, Novel drug delivery.

INTRODUCTION

A well designed controlled drug delivery system can overcome some of the problems of

conventional therapy and enhance the therapeutic efficacy of a given drug .To obtain

maximum therapeutic efficacy, it becomes necessary to deliver the agent to the target tissue

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Article Received on 21 August 2013, Revised on 17 Sept 2013, Accepted on 25 October2013

*Correspondence for

Author: * Vikrant Deshmukh

Kasturi shikshan sansthas

college of pharmacy,

Shikrapur, Pune, India.

[email protected]

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in the optimal amount in the right period of time there by causing little toxicity and minimal

side effects1. There are various approaches in delivering a therapeutic substance to the target

site in a sustained controlled release fashion. One such approach is using microspheres as

carriers for drugs. Microspheres are characteristically free flowing powders consisting of

protein or synthetic polymers which are biodegradable in nature and ideally having a particle

size less than 200 µm. In contrast to drug delivery system, the word novel is searching

something out of necessity. The drug has to be delivered for a prolonged period of time and

many medicines have to be taken simultaneously in case of chronic patients. Frequent

administration of drug is necessary when those have shorter half life and all these leads

todecrease in patient’s compliance. In order to overcome the above problems, various types

of controlled release dosage forms are formulated and altered, so that patient compliance

increase through prolonged effect,adverse effect decreases by lowering peak plasma

concentration. The controlled release dosage form maintaining relatively constant drug level

in the plasma by releasing the drug at a predetermined rate for an extended period of time.

One such in Microspheres as carriers of drug become an approach of controlled release

dosage form in novel drug delivery system. Microspheres are defined as “Monolithic sphere

or therapeutic agent distributed throughout the matrix either as a molecular dispersion of

particles” (or) can be defined as structure made up of continuous phase of one or more

miscible polymers in which drug particles are dispersed at the molecular or macroscopic

level. It has a particle size of (1-1000nm).

TYPES OF MICROSPHERES

1. Bio-adhesive microspheres

Adhesion can be defined as sticking of drug to the membrane by using the sticking property

of the water soluble polymers. Adhesion of drug delivery device to the mucosal membrane

such as buccal, ocular, rectal, nasal etc can be termed as bio adhesion. These kinds of

microspheres exhibit a prolonged residence time at the site of application and causes intimate

contact with the absorption site and produces better therapeutic action.The effect of different

polymers on bio adhesive microspheres are given in table I.

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Table I: Effect of polymers on bioadhesive microspheres

DRUG

ROUTEOF ADMINISTRATION

BIOADHESIVE POLYMERS USE

APPLICATION OF POLYMERS

Clonazepam

Nasal Gelatin-Chitosan

Higher concentration of

drug is achieved in brain

PropanalolHcl Nasal

Chitosan- Gelatin

Controlled blood level profile as well

as increased bioavailability of

drug.

Furosemide GI

AD-MMS (PGEFs)

Bioavailability Increases Higher AUC and thereby absorption also

increases.

Amoxicillin GI

Ethylcellulose-Carbopol- 934P

Therapeutic efficacy of drug increases

Gentamicin Nasal

DSM+LPC

Combination of these polymers

improves nasal absorption

Aceclofenac GI

Eudragit (S100,RL100,RS100)

Controlled release of drug is achieved.

2. Magnetic microspheres

This kind of delivery system is very much important which localises the drug to the disease

site. In this larger amount of freely circulating drug can be replaced by smaller amount of

magnetically targeted drug. Magnetic carriers receive magnetic responses to a magnetic field

from incorporated materials that are used for magnetic microspheres are chitosan, dextran etc.

3. Therapeutic magnetic microspheres

Are used to deliver chemotherapeutic agent to liver tumour. Drugs like proteins and peptides

can also be targeted through this system.

4. Diagnostic microspheres

It can be used for imaging liver metastases and also can be used to distinguish bowel loops

from other abdominal structures by forming nano size particles supra magnetic iron oxides.

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5. Floating microspheres

In floating types the bulk density is less than the gastric fluid and so remains buoyant in

stomach without affecting gastric emptying rate. The drug is released slowly at the desired

rate, if the system is floating on gasteric contentand increases gastric residence and increases

fluctuation in plasma concentration. Moreover it also reduces chances ofstriking and dose

dumping. One another way it produces prolonged therapeutic effect and therefore reduces

dosing frequencies. Drug (ketoprofen) given through this form.

6. Radioactive microspheres

Radio emobilisation therapy microspheres sized 10-30 nm are of larger than capillaries and

gets tapped in first capillary bed when they come across. They are injected to the arteries that

lead to tumour of interest. So all these conditions radioactive microspheres deliver high

radiation dose to the targeted areas without damaging thenormal surrounding tissues.9It

differs from drug delivery system, as radio activity is not released from microspheres but acts

from within a radioisotope typical distance and the different kinds of radioactive microsphers

are α emitters, β emitters, γ emitters.

7. Polymeric microspheres

The diffenttypes of polymeric microspheres can be classified as followsand they are

biodegradable polymeric microspheres and Synthetic polymeric microspheres.

8. Biodegradable polymeric microspheres

The natural polymers such as starch are used with the concept that they are biodegradable,

biocompatible, and also bio adhesive in nature. Biodegradable polymers prolongs the

residence time when contact with mucous membrane due toit’s high degree of swelling

property with aqueous medium , results gel formation. The rate and extent of drug release is

controlled by concentration of polymer10 and the release pattern in a sustained manner. The

main drawback is, in clinical use drug loading efficiency of biodegradable microspheres is

complex and is difficult to control the drug release. However they provide wide range of

application in microsphere based treatment.

9. Synthetic polymeric microspheres

The interest of synthetic polymeric microspheres are widely used in clinical application,

moreover that also used as bulking agent, fillers, embolic particles, drug delivery vehicles etc

and proved to be safe and biocompatible.But the main disadvantage of these kind of

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microspheres, are tend to migrate away from injection site and lead to potential risk,

embolismand further organ damage. Differentkinds of polymers used for microsphere.

MATERALS USED

Microspheres used usually are polymers. Theyare classified into two types-

1.Synthetic polymers divided into two types-

a. Non-biodegradable polymers

e.g. Poly methyl methacrylate (PMMA),

Acrolein,

Glycidyl methacrylate,

Epoxy polymers.

b. Biodegradable polymers

e.g. Lactides, Glycolides& their co polymers,

Poly alkyl cyano acrylates,

Poly anhydrides.

2. Natural polymers obtained from different sources

like proteins, carbohydrates and chemically modified

carbohydrates.

Proteins: Albumin, Gelatin, and Collagen.

Carbohydrates: Agarose, Carrageenan, Chitosan,Starch.

Chemically modified carbohydrates: Poly dextran,Poly starch.

METHOD OF PREPERATION

Incorporation of solid, liquid or gases into one or more polymeric coatings can be done by

micro encapsulation technique.The different methods used for various microspheres

preparation depends on particle size, route of administration, duration of drug release and

these above characters related to rpm, method of cross linking, drug of cross linking,

evaporation time, co-precipitation etc. The various methods of preparations are-

1. Emulsion solvent evaporation technique

In this technique the drug is dissolved in polymer which was previously dissolved in

chloroform and the resulting solution is added to aqueous phase containing 0 .2 % sodium of

pvp as emulsifying agent. The above mixture was agitate 500 rpm then the drug and

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polymerwas transformed into fine droplet which solidified into rigid microspheres by solvent

evaporation and then collected by filtration and washed with demineralised water and

desiccated at room temperature for 24 hrs.12 Aceclofenac microspheres were prepared by

this technique.

2. Emulsion cross linking method

In this method drug was dissolved in aqueous gelatine solution which was previously heated

for 1 hr at 40 0C. The solution was added drop wise to liquid paraffin while stirring the

mixture at 1500 rpm for 10 min at 35 0C, results in w/o emulsion then further stirring is done

for 10 min at 15 0C. Thus the produced microspheres were washedrespectively three times

with acetone and isopropyl alcohol which then air dried and dispersed in 5mL of aqueous

glutaraldehyde saturated toluene solution at room temperature for 3 hrs for cross linking and

then was treated with 100mL of 10mm glyciene solution containing 0.1%w/v of tween 80 at

37 0C for 10 min to block unreacted glutaraldehyde.Examples for this technique is Gelatin A

microspheres.

3. Co-acervation method

This process is based on the principle ofdecreasing the solubility of the polymer in organic

phaseto affect the formation of polymer rich phase called thecoacervates. In this method, the

drug particles aredispersed in a solution of the polymer and anincompatible polymer is added

to the system whichmakes first polymer to phase separate and engulf the drugparticles.

Addition of non-solvent results in thesolidification of polymer. Poly lactic acid

(PLA)microspheres have been prepared by this method byusing butadiene as incompatible

polymer. The processvariables are very important since the rate of achievingthecoacervates

determines the distribution of thepolymer film, the particle size and agglomeration of the

formed particles. The agglomeration must be avoided bystirring the suspension using a

suitable speed stirrer sinceas the process of microspheres formation begins theformed

polymerize globules start to stick and form theagglomerates. Therefore the process variables

are criticalas they control the kinetic of the formed particles sincethere is no defined state of

equilibrium attainment.Co-acervation thermal change performed by weighed amount of ethyl

cellulose was dissolved in cyclohexane with vigorous stirring at 80 0C by heating. Then the

drug was finely pulverised and added with vigorous stirring on the above solution and phase

separation was done by reducing temperature and using ice bath. Then above product was

washed twicely with cyclohexaneand air dried then passed through sieve (sieve no. 40) to

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obtain individual microcapsule. Co-acervationon solvent addition Developedby weighed

amount of ethyl cellulose was dissolved in toluene containing propylisobutylene in closed

beaker with magnetic stirring for 6 hr at 500 rpm and the drug is dispersed in it and stirring is

continued for 15 min. Then phase separation is done by petroleum benzoin 5 times with

continuous stirring.After that the microcapsules were washed with n-hexane and air dried for

2 hr and then in oven at 500C for 4 hr.

4. Spray drying technique

These methods are based on the drying of the mist of the polymer and drug in the air.

Depending upon the removal of the solvent or cooling of the solution, the two processes are

named spray drying and spraycongealing respectively. The polymer is first dissolved in

a suitable volatile organic solvent such asdichloromethane, acetone, etc. The drug in the solid

form is then dispersed in the polymer solution under high speed homogenization. This

dispersion is then atomized in a stream of hot air. The atomization leads to theformation of

the small droplets or the fine mist from which the solvent evaporates instantaneously leading

the formation of the microspheres in a size range 1-100 µm. Microparticles are separated

from the hot air by means of the cyclone separator while the traces of solvent are removed by

vacuum drying. One of the major advantages of the process is feasibility of operation under

aseptic conditions. The spray drying process is used to encapsulate various penicillins.

Thiamine mononitrate and sulpha ethylthiadizole are encapsulated in a mixture of mono and

diglycerides of stearic acid and palmitic this was used to prepare polymeric blended

microsphere loaded with ketoprofen drug. It involves dispersing the core material into

liquefied coating material and then spraying the mixture in the environment for solidification

of coating followed by rapid evaporation of solvent. Organic solution of poly (epsilon-

caprolactone) (PCL) and cellulose acetate butyrate (CAB), in different weight ratios and

ketoprofen were prepared and sprayed in different experimental condition achieving drug

loaded microspheres. This is rapid but may loose crystalinity due to fast drying process.

5. Normal polymerization

It is carried out using different techniques as bulk, suspension, precipitation, emulsion and

micellarpolymerization processes. In bulk, a monomer or a mixture of monomers along with

the initiator or catalystis usually heated to initiate polymerization. Polymer so obtained may

be moulded as microspheres. Drug loading may be done during the process of

polymerization. Suspension polymerization also referred as bead or pearl polymerization.

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Here it is carried out by heatingthe monomer or mixture of monomers as dropletsacid using

spray congealing. Very rapid solvent evaporation, however leads to the formation of porous

Micro-particles.

6. Emulsion-solvent diffusion technique

In order to improve the residence time in colon floating microperticles of ketoprofen were

prepared using emulsion solvent diffusion technique. The drug polymer mixture was

dissolved in a mixture of ethanol and dichloromethane (1:1) and then the mixture was added

dropwise to sodium lauryl sulphate (SLS) solution. The solution was stirred with propeller

type agitator at room temperature at 150 rpm for 1 hr. Thus the formed floating microspheres

were washed and dried in a dessicator at room temperature. The following microperticles

were sieved and collected.

7. Multiple emulsion method

Oral controlled release drug delivery of indomethacin was prepared by this technique. In the

beginning powder drug was dispersed in solution (methyl cellulose) followed by

emulsification in ethyl cellulose solution in ethyl acctate. The primary emulsion was then re

emulsified in aqueous medium. Under optimised condition discrete microspheres were

formed during this phase.

8. Ionic gelation

Alginate/chitosan particulate system for diclofenac sodium release was prepared using this

technique. 25 % (w/v) of diclofenac sodium wasadded to 1.2 % (w/v) aqueous solution of

sodium alginate. In order to get the complete solution stirring is continued and after that it

was added dropwise to a solution containing Ca2+ /Al3+ and chitosan solution in acetic acid.

Microspheres which were formed were kept in original solution for 24 hr for internal

gellification followed by filteration for separation. The complete release was obtained at pH

6.4-7.2 but the drug did not release in acidic pH.

9. Hydroxyl appetite microspheres in sphere morphology

This was used to prepare microspheres with peculiar spheres in sphere morphology

microspheres were prepared by o/w emulsion followed by solvent evaporation. At first o/w

emulsion was prepared by dispersing the organic phase (Diclofenac sodium containing 5%

w/w of EVA and appropriate amount of HAP) in aqueous phase of surfactant. The organic

phase was dispersed in the form of tiny droplets which were surrounded by surfactant

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molecules this prevented the droplets from co solvencing and helped them to stay individual

droplets .While stirring the DCM was slowly evaporated and the droplets solidify individual

to become microspheres.

Fig.1.steps in prepration of microspheres

EVALUATION OF MICROSPHERES

1. Particle size analyser

Microsphere (50 mg) was suspended in distilled water (5mL) containing 2%w/v of tween 80,

Toprevent microsphere aggregation, the above suspension is sonicated in water bath and the

particle size was expressed as volume mean diameter in micrometer.

2. Optical microscopy

This method was used to determine particle size by using optical microscope (Meizer

OPTIK) The measurement was done under 450x (10x eye piece and 45x objective) and100

particles were calculated.

3. Angle of contact

The angle of contact is measured to determine the wetting property of a micro particulate

carrier. It determines the nature of microspheres in terms of hydrophilicity or hydrophobicity.

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This thermodynamic property is specific to solid and affected by the presence of the adsorbed

component. The angle of contact ismeasured at the solid/air/water interface. The advancing

and receding angle of contact are measured by placing a droplet in a circular cell mounted

above objective of inverted microscope. Contact angle is measured at 2000C within a minute

of deposition of microspheres.

4. Beaker method

The dosage form in this method is made to adhere at the bottom of the beaker containing the

medium and stirred uniformly using over head stirrer. Volume of the medium used in the

literature for the studies varies from 50-500 ml and the stirrer speed form 60-300 rpm.

5. Modified Keshary-Chien Cell

A specialized apparatus was designed in the laboratory. It comprised of a Keshary-Chien cell

containing distilled water (50ml) at 370 C as dissolution medium. TMDDS (Trans Membrane

Drug Delivery System) was placed in a glass tube fitted with a 10# sieve at the bottom which

reciprocated in the medium at 30strokes per min.

6. Scanning electron microscopy (SEM)

Surface morphology was determined by the method SEM. In this microcapsule were mounted

directly on the SEM sample slub with the help of double sided sticking tape and coated with

gold film under reduced pressure. provides higher resolution in contrast to the LM. SEM

allows investigations of the microspheres surfaces and after particles are cross-sectioned, it

can alsobe used for the investigation of double walled systems.

7. Swelling index

This technique was used for Characterization of sodium alginate microspheres were

performed with swelling index technique Different solution (100mL) were taken such as

(distilled water, buffer solution of pH(1.2, 4.5, 7.4) were taken and alginate microspheres

(100mg) were placed in a wire basket and kept on the above solution and swelling was

allowed at 37 0C and changes in weight variation between initial weight of microspheres and

weight due to swelling was measured by taking weight periodically and soaking with filter

paper.

8. Entrapment efficiency

Microspheres containing of drug (5mg) were crushed and then dissolved in distilled water

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with the help of ultrasonic stirrer for 3 hr, and was filtered then assayed by uv-vis

spectroscopy. Entrapment efficiency is equal to ratio of actual drug content to theoretical

drug content.

9. X-ray diffraction

Change in crystalinity of drug can be determined by this technique. Micro-perticles and its

individual components were analysed by the help of D & discover (Bruker,

Germony).Scanning range angle between 8 0C - 70 0C. Scan speed -4o/min Scintillation

detector Primary silt=1mm Secondary silt=0.6 mm.

10. Thermal analysis

Thermal analysis of microcapsule and its component can be done by using- Differential

scanning calorimetry (DSC).Thermo gravimetric analysis (TGA) Differential thermometric

analysis (DTA) Accurately the sample was weighed and heated on alumina pan at constant

rate of 10oc/min under nitrogen flow of 40 ml/min.

11. UV-FTTR (Fourier transform infra red)

The drug polymer interaction and also degredation of drug while processing for

microencapsulation can be determined by FTIR.

12. Stability studies

By placing the microspheres in screw capped glass container and stored them at following

conditions:

1. Ambient humid condition

2. Room temperature (27+/-2 0C)

3. Oven temperature (40+/-2 0C)

4. Refrigerator (5 0C -80C).

It was carried out of a 60 days and the drug content of the microsphere was analysed.

13. Zeta potential

The polyelectrolyte shell was prepared by incorporating chitosan of different molecular

weight into the W2 phase and the resulting particles were determined by zeta potential

measurement.

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APPLICATION OF MICROSPHERES

Medical application

Release of proteins, hormones and peptides over extended period of time.

Gene therapy with DNA plasmids and also delivery of insulin.

Vaccine delivery for treatment of diseases like hepatitis, diphtheria, birth control.

Targeting tumour vessels, targeting of tumour cells, antigens, by intraarterial application.

Tumour targeting with doxorubicin and also treatments of leishmaniasis.

Magnetic microspheres can be used for stem cell extraction and bone marrow purging.

Used in isolation of antibodies, toxin extraction by affinity chromatography.

Used for various diagnostic tests for infectious diseases like bacterial, viral, and fungal.

Radioactive microsphere’s application

Can be used for radioembolisation of liver and spleen tumours.

Used for radiosynvectomy of arthiritis joint, local radiotherapy, interactivity treatement.

Imaging of liver, spleen, bone marrow, lung etc even imaging of thrombus in deep

veinthrombosis can be done.

Other applications

Fluorescent microspheres can be used for membrane based technologies for flow

cytomettry, cell biology, microbiology, Fluorescent Linked Immuno-Sorbent Assay.

Yttrium 90 can be used for primary treatment of hepatocellular carcinoma and also used

for pretransplant management of HCC with promisingresults.

Microspheres in vaccine delivery the prerequisite of a vaccine is protection against the

microrganism or its toxic product. An ideal vaccine must fulfill the requirement of

efficacy, safety, convenience in application and cost. The aspect of safety and

minimization of adverse reaction is a complex issue. The aspect of safety and the degree

of the production of antibody responses are closely related to mode of application.

Biodegradable delivery systems for vaccines that are given by parenteral route may

overcome the shortcoming of the conventional vaccines.

Targeting using microparticulate carriers concept of targeting, i.e. site specific drug

delivery is a well established dogma, which is gaining full attention. The therapeutic

efficacy of the drug relies on its access and specific interaction with its candidate

receptors. The ability to leave the pool in reproducible, efficient and specific manner is

center to drug action mediated by use of a carrier system. Placement of the particles

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indiscrete anatomical compartment leads to their retention either because of the physical

properties of the environment or biophysical interaction of the particles with the cellular

content of the target tissue.

Monoclonal antibodies mediated microspheres targeting

Chemoembolisation is an endovascular therapy, which involves the selective arterial

embolisation of a tumour together with simultaneous or subsequent local delivery the

chemotherapeutic agent. The theoretical advantage is that such embolisations will not

only provide vascular occlusion but will bring about sustained therapeutic levels of

chemotherapeutics in the areas of the tumour. Chemoembolisation is an extension of

traditional percutaneous embolisation techniques.

Recent Applications of Controlled Release Microspheres

Controlled-release microspheres are in development for a number of interesting and

important applications, especially for delivery of large, fragile drugs like proteins and

nucleicacids. Several recent examples are described below. Controlled-Release Vaccines

Vaccination has been highly successful for controlling or even eradicating many important

types of infectious diseases, and new or improved vaccines are being heavily investigated for

AIDS, hepatitis B, anthrax, and SARS.A frequent problem is the need for repeated

administrations. Single-shot Vaccine delivery systems should provide the antigen(s) and

adjuvant on a prescribed schedule and maintain the bioactivity of the antigen, both during

fabrication of the delivery device and during the often prolonged residence time of the device

in the body. In recent years, much work has focused on developing microsphere-based,

single-administration, vaccine delivery vehicles using a variety of Maintenance of antigen

bioactivity has been problematic due to contact of the proteins with organic solvents and the

hydrophobic polymer, and the use of strong physical forces to produce the microspheres. To

enhance vaccine stability, researchers have been focusing on several approaches, including

the use of adjuvants to protect the protein antigens or by choosing different microsphere

materials. Amajor advantage of microspheres for vaccination is that they can be passively

targeted to antigen-presenting cells (APCs) such as macrophages and dendritic cells. The

ability of APCs to hagocytose particulates is dependent on the particle size. In particular,1- to

10-µm diameter microspheres are optimally taken up by APCs in a number of tissues and

have been shown to enhance antigen-specific T-helper lymphocyte (Th) responsesthus

leading to an enhancement in antigen-specific antibody responses) and elicit acytotoxic T

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lymphocyte (CTL) response (Nixon et al. 1996). T-cell activation in response toantigen-

encapsulating microspheres has been shown to be 100-1000 fold better than antigenalone.

Stabilization of Encapsulated Protein Therapeutics

A major problem with protein encapsulation in polymer particles is loss of protein

bioactivity. Damage to protein scan occur during fabrication of the particles via shear stresses

or other physical forces, through contact with organic solvents, and by loss of water (e.g.,

upon lyophilization) as well as during incubation and release in the warm, moist, in vivo

environment.

Two types of damage occur most often:

(i) Covalent or non-covalent intermolecular aggregation and

(ii) Denaturation. Several studies have investigated the mechanisms of damage. Protein

stability can be enhanced by the addition of excipients to preventaggregation and stabilize the

folded protein structure or through judicious choice of polymeremployed for fabrication of

the devices.

FUTURE CHALLENGES

Future challenges of microspheres look bright particularly in the area of medicinal field

because of its wide spectrum of application in molecular biology, eg: microsphere based

genotyping platform is used to detect six single nucleotide polymorphism, yittrium-90

microspheres is used to prevent tumour after liver transplantation and it’s advanced way in

delivery of vaccines and proteins.

1. Microspheres in cancer therapy

Cancer microsphere technology is the latest trend in cancer therapy. It helps the pharmacist to

formulate the product with maximum therapeutic value and minimum or negligible range side

effects. Cancer is a disease in which the abnormal cells are quite similar to the normal cells,

with just minute genetic or functional change. A major disadvantage of anticancer drugs is

their lack of selectivity for tumor tissue alone, which causes severe side effects and results in

low cure rates. Thus, it is very difficult to target abnormal cells by the conventional method

of the drug delivery system. Microsphere technology is probably the only method that can be

used for site-specific action, without causing significant side effects on normal cells. This

review article describes various microspheres that have been prepared or formulated to

exploit microsphere technology for targeted drug therapy in various cancers.

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CONCLUSION

It has been observed that microspheres are better choice of drug delivery system than many

other types of drug delivery system because it is having the advantage of target specificity

and better patient compliance. Its applications are enormous as they are not only used for

delivering drugs but also for imaging tumours, detecting biomolecular interaction etc. So in

future microspheres will have an important role to play in the advancement of medicinal

field. In future by combining various other strategies, microspheres will find the central place

in novel drug delivery, particularly in diseased cell sorting, diagnostics, gene & genetic

materials, safe, targeted and effective invivo delivery and supplements as miniature versions

of diseased organ and tissues in the body.

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