Concept Of Biodegradable Polymer Biology Essay

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bio-degradation is a combination of two words bio and degradation where bio means livinig things and degradation means broken into part-part so, biodegradation is a process in which any polymer are degraded into micro-organisms. Biodegradable polymer are polymer that can be broken down bybacteria, fungi or other simple organisms .

Biodegradation is the process in which a product is capable of being broken down into innocuous sub-products, like CO2 and water, by the action of living things (as microorganisms). A banana peel will biodegrade into biomass, CO2 and water. Products that are susceptible of biodegradation are also referred as "bioactive". Biodegradable polymers indicate that solid polymeric materials or devices which break down to macromolecule degradation with dispersion in an animal body. If degraded and res orbedddd in vivo, they can be called the bio-resorbable polymers. (i.e. which are eliminated through natural pathways either by simple filtration of degradation by -products or after their metabolization.)

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A wide variety of natural and synthetic biodegradable polymers have been investigated for medical and pharmaceutical applications. Natural biodegradable polymers like Collagen, Albumin, Gelatin, Hemoglobin, Chitin, Chitosan, Hyaluronic acid (HA), and Alginic acid have been studied for medical applications. The use of these natural polymers is limited due to their higher costs and questionable purity. For the last three decades, synthetic biodegradable polymers have been increasingly used as medical, pharmaceutical and tissue-engineering products, because they are free from most of the problems associated with the natural polymers. Amongst the different classes of synthetic biodegradable polymers, the thermoplastic aliphatic poly (esters) like PLA (Polylactide), PGA (polyglycolide) and their copolymers (PLGA) have generated tremendous interest due to their favorable properties such as good biocompatibility, biodegradability, bioresorbability and mechanical strength.

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Nowadays, biocomposites research is focused in cost reduction of biodegradable plastics. On this regard, the blending of low-cost fillers into the biodegradable polymer has become an alternative solution and, over the past two decades, terrestrial plants fibers, mainly starch, have been receiving considerable attention. However, because plant fibers are derived from ligno-cellulose, which contains polarized hydroxyl groups, major limitations of using them include poor interfacial adhesion and difficulties in mixing due to poor wetting of the fiber with the matrix, reducing greatly their potential to be used as fillers. In addition, the high energy prices concerns about petroleum supplies and the greater recognition of the environmental consequences of fossil fuels have driven interest in the bioenergy , Under the expectative of high consume of sources of terrestrial biomass for this target, it should look forward to other sources of biodegradable fillers that could replace or compete with plant fibers. An attractive alternative are biopolymers from marine environment, such as agar, that are extracted from marine plants (seaweeds)

Among the industrially attractive biopolymers from marine environment, agar is known to widely use in different industrial fields (i.e., food and pharmaceutical). Agar polymers synthesized by species of red seaweeds belonging to the genus Gracilaria, Gelidium, and Ptero-cladia constitute a complex mixture of molecules, containing several extremes in their structure. Sulphate hemiesters, methyl ethers, and pyruvic ketals can alter in a number of ways the structural regularity of agar based on strictly 1,3-linked [beta]-D-galactopyranose and 1,4-linked 3,6 anhydro-[alpha]-L-galactopyranose residues. It belongs to the class of gel-forming polymer, and its microstructural, mechanical, and rheological properties of agar gels can be described by a "crosslinked network" model [2],[3] In this model, a homogeneous aqueous sol is gradually changing to an elastic and turbid gel network during cooling. This transformation is reversible and this cycle could be repeated several times without compromising gel mechanical properties . These colloids have been explored as biodegradable films casting archeological pieces, dental, and sculpture moulds as well as composites . A thorough literature study revealed that no much work has been done on the agar incorporated into polymeric matrices. Hence, the present research concentrated on the development of agar particle reinforced PBAT biocomposites. The composites were developed using extrusion and injection molding technique. The PBAT-agar biocomposites were characterized for physico-mechanical, thermal, and morphological analysis. The influence of the agar particles on the filler-matrix compatibility was investigated. The experiments have focused to demonstrate the feasibility to prepare biocomposites using agar as filler.[2][3]

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2. Some definition:

2.1 Degradation:

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Degradation is process in which a product is capable of being chemically degraded, changing its mechanical and chemical properties. A product is degradable when it can change its properties in time scale due to action of heat, light or mechanical stress.

2.2 Biodegradability:

The degree by which biodegradation leads to mineralization (the conversion of organic materials to naturally occurring gasses and inorganic constituents) and biomass.[2]

3. Types of degradable polymer:

There are different type of degradable polymer

3.1. Biodegradable polymer: biodegradable polymer are those that are capable of undergoing decomposition into corbon dioxide methane water inorganic compound or biomass in which the predominate machanism is the enzymatic action of micro-organisms that can be measured by standardize tests in a specific time(090 to 180 days) , reflecting available disposal condition.

3.2. Compostable polymer: these are those that are degradable under composting condition. To meet this definition they must break down under the action of micro-organisms(bacteria, fungi,algae) achieve total mineraization (conversing into carbon dioxide methane water inorganic compounds or biomass under the aerobic condition ) and minerlization rate must be high and compatible with composting process.

Oho polymer: Oho degradable polymer are those that undergoingcontrolled degradation through the incorporation of 'pro-degradant' additrive(additive that can trigger and accelerate the degradation process). These polymer undergo accelarate oxidative degradation initiated by natural daylight ,heat and/or machenical stress, and embrittle in enviourment and erode under the influence of weathering.

Photodegradable polymer: Photodegradable polymer are those that break down through the action of ultravoilet light, which degradabes the chemical bond or link in the polymer . This process can be assisted by the presence of UV-sensitive additives in the polymer.

Water-soluble polymer: Water-soluble polymers are those that dissolve in the water whithin a designated temprature range and then biodegrable in contact with micro oranisms.

4. Classification of biodegradable of polymer.:

Biodegradable polymer are classified in three following groups depending on their origin:

Microbial

Naturally occurring polymer

Synthetic biodegradable polymer

4.1 Microbial origin:

These are wide range of material such as polyesters, polysaccharides. Considerable interest arose when large scale controlled processes were developed.These are used in pharma , textile ,paper, food, cosmetics and plastics industry.

4.2 Naturally occurring polymer:

These polymer are originated from nature such as given below

Animal origin

Marine origin

Agriculture feedstock

Animal origin: commonly these are polypeptides. Mostly neither soluble nor fusable without degradation especially in their natural form .as wool, gelatine , collagen These are used in pharma, biomedical, textile, food industry.

4.2.2.1 Marine origin chitin and chitosan:Chitin is a polysaccharides found in shell of crabs and lobsters (and insects). These are insoluble in negative form chitosan ,which is partially deacetylated chitin is water soluble.Biocompatible, have antimicrobial properties and have ability to absorb heavy metal ions. Application of it in the pharma, biomedical, food.cosmetics and plastic industry.

4.2.2.2 Marine origin: alginateAlginate is polysaccharides originating from different seaweeds. In presence of polyvalent cations these are in form of insoluble gel. These are used in pharma and food industry.

4.2.3 [i]Agriculture feedstocks: starch: Produced in form granules and is combination of two polymers amylose and amylopectin . amylase is a linear polymer whereas amylopectin is branched.these are very abundant polymers.These are used in food, cosmetics, plastics, paper industry.

[ii]Agriculture feedstocks : cellulose: These are differ from other polysaccharides in some respects since its molecular chain being very long and consisting of one repeating unit. These are occur in crystalline states naturally. It is modified for further application and use as ether esters and acetal. These are used in textile, paper and plastics industry.

4.3 Synthetic biodegradable polymers:

5. HOW TO BIODEGRADED THE POLYMER:

Most polymeric implants are biodegraded by one of two common chemical degradation mechanisms: (i) hydrolysis and (ii) oxidation. The chemical structure is among the most important factors which affect the biodegradation of polymeric implants. Hydrolytic biodegradations are often accompanied by substantial decrease of pH, whilst oxidative biodegradation processes are usually very slow due to consumption of stoichiometric amounts of oxidising agents. A dramatic acceleration of the biodegradation can be expected, if the biodegradation can be initiated by catalytic amounts of oxidation agents. Poly(ethylene carbonate) (PEC) and poly(trimethylene carbonate) (PTMC) are presumably biodegraded by such catalytic oxidation processes. Their biodegradation shows all the characteristics of surface erosion. Poly(ethylene carbonate) is utilised as a surface eroding

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biocompatible polymer for controlled delivery of peptide and protein drugs

6. General Mechanism of Biodegradation:

The term biodegradable plastics normally refers to an attack by micro-organisms on non-water soluble polymer based materials (plastics). This implies that the biodegradation of plastics is usually a heterogeneous process. Because of a lack of water-solubility and the size of the polymer molecules,micro-organisms are unable to transport the polymeric material directly into the cells where most biochemical processes take place; rather,they must first excrete extra-cellular enzymes which depolymerize the polymers outside the cells (Figure1).As a consequence,if the molar mass of the polymers can be sufficiently reduced to generate water-soluble intermediates, these can be transported into the micro-organisms and fed into the appropriate metabolic pathway.As a result, the end- products of the seme tabolic processes include water carbon-dioxide and methane(in the case of an aerobic degradation), together with a new biomass.The extra cellular enzymes are too large to penetrate deeply into the polymer material, and so act only on the polymer surface; consequently, the biodegradation of plastics is usually a surface erosion process.Although the enzyme catalyzed chain length reduction of polymers is in many cases the primary process of biodegradation, non-biotic chemical and physical processes can also act on the polymer, either in parallel or as a first stage solely on the polymer. These non-biotic effects include chemical hydrolysis,thermal polymer degradation, and oxidation or scission of the polymer chains by irradiation (photo degradation). For some materials, these effects are used directly to induce the biodegradation process[as.poly(lactic-acid); pro-oxidant modified polyethylene], but they must also to be taken into account when biodegradation is caused pre-dominantly by extra cellular enzymes. Because of the co-existence of biotic and non-biotic processes, the entire mechanism of polymer degradation could in many cases also be referred to as environmental degradation.

Environmental factors not only influence the polymer to be degraded, they also have a crucial influence on the microbial population and on the activity of the different micro-organisms themselves.Parameters such as humidity, temperature, pH, salinity, the presence or absence of oxygen and the supply of different nutrients have important effects on the microbial degradation of polymers, and so these conditions must be considered when the biodegradability of plastics is tested.

Another complicating factor in plastics biodegradation is the complexity of the plastic materials with regard to their possible structures and compositions . In many cases plastics do not consist simply of only one chemical homogeneous component, but

contain different polymers (blends) or low molecular weight additives (e.g.,plasticiz-ers). Moreover, within one polymer itself different structural elements can be present(copolymers), and these may either be distributed statistically along the polymer chains(random copolymers) or distributed alternately ( alternating copolyesters); they may also be used to build longer blocks of each structure (block-copolymers). Another structural characteristic of a polymer is the possible branching of chains or the formation of networks(cross-linked polymers). These different structures of a polymer, despite having the same overall

composition can directly influence accessibility of the material to the enzyme-catalyzed polymer chain cleavage, and also have a crucial impact on higher- ordered structures of the polymers (crystals, crystallinity, glass transition) which have been shown pre-dominantly to control the degradation behavior of many polymers (Marten,2000).Additionally, the crystallinity and crystal morphology is dependent upon the processing conditions, and can change with time. All of the above described factors must be considered when measuring thebiodegradation of plastics and interpreting the results, and this makes the testing of plastics biodegradability a highly inter disciplinary process.

7. Advantages:

The advantages of these biodegradable polymers (PLA, PGA and their copolymers) are that they offer favorable properties such as good biocompatibility, biodegradability, bioresorbability and mechanical strength. They possess processing facility, great variety, adaptability and reliability. The major benefits are listed below.

They possess low or negligible toxicity of degradation products, in terms of both

local tissue response and systemic response. Histological response is generally

predictable.

Adequate Mechanical properties address short-term function and do not interfere

with long-term function. They can be tailored to a wider range of properties. They

have the capability to form the polymer into the final product design and make it

easier to control lot-to-lot uniformity and mechanical properties.

Drug delivery compatibility in applications that release or attachment of active

compounds.

These polymers have been consistently approved numerous use in humans for

medical and pharmaceutical applications by FDA.

For bone repair and regeneration, stress concentration at rigid implant (i.e.

stainless steel implant) was associated with either bone fractures or implant as a

result of resorption leading to weakening of the bone and need to remove the implant

when bone fractures have been repaired. Biodegradable implants can be engineered

to degrade at a rate that will transfer load to the fracture bone by degrees and

obviates the need for a second operation to remove the implant. Furthermore, use of

biodegradable implants eliminates the risks associated with the presence of foreign

materials (non-biodegradable) permanently in the body, such as tumorogenic

potential. For example, products from corrosion of metals can accumulate within the

fibrous tissue capsule at the capsule-implant interface.

Some of the most exciting opportunities have been applied to drug delivery and

tissue engineering for these polymers. Various polymeric devices like microcapsules,

microspheres, tablet, films, and other implants have been fabricated by using these

polymers for release of a variety of drugs. These materials can provide a suitable

substrate for cell to grow new tissues and organs and can be utilized as scaffolding

materials for tissue engineering. In addition, a three-dimensional scaffold enhances

the use of growth factors and other active agents released from the matrices. The

three-dimensional scaffold made of biodegradable polymers as well as growth factors

and other active agents can also enhance cell and tissue growth into/around the

degrading polymer.

Degradation begins with random hydrolysis in an aqueous environment through

cleavage of its backbone ester linkages. Most of the literature indicates that these poly

(ester) polymers do not involve any enzymatic activity and is purely through a

hydrolytic mechanism. In vivo, however, enzymes are considered to enhance the

initial degradation. The PLA, PGA and their copolymers biodegrades into lactic and

glycolic acids. Lactic acid enters the tricarboxylic acid (TCA) cycle and is metabolized

and excreted from the body as energy, carbon dioxide and water. Glycolic acid is

either eliminated unchanged in the kidney or enter the TCA cycle and is excreted as

energy, carbon dioxide and water. So they are biodegradable and bioresorbable

polymers.

In general, crystalline L-PLA is more resistant to hydrolytic degradation than the

amorphous DL form. Time required for L-PLA implants to be absorbed is relatively

long and depends on polymer quality, processing conditions, implant site, and

physical dimensions of the implant. The biodegradation rate of copolymers is

dependent on the molar ratio of lactide/glycolide, molecular weight of the polymers,

the degree of crystallinity and the Tg of the polymers. Altering the chemical

composition by increasing the glycolide mole ratio in the copolymer increases the rate

of biodegradation. For example, a copolymer of 50% DL-lactide and 50% glycolide

degrades faster than other copolymers. Factors affecting the hydrolytic degradation

behavior of PLA, PGA and their copolymers are listed in the following table.

Factors affecting the hydrolytic degradation behavior of polyester polymers

Chemical composition.

Molecular weight and Molecular weight distribution.

Physical-chemical factor. (pH, ionic strength, temp,) Additives. (solvent, monomers, catalyst)

Morphology. (crystalline, amorphous)

Glass transition temperature. (rubbery, glassy)

Device dimensions. (shape, size, porosity, surface to volume ratio)

Mechanism of hydrolysis. (autocatalytic, noncatalytic, enzymatic)

Processing history. (injection, molding, extrusion, sterilization)

Site of implantation.

8. oxo biodegradation of plastic:

Oxo-Biodegradable plastics (OBP's) are plastics materials, generally traditional polyolifins, that undergo a two step degradation, initially by an oxidative process that is promoted by inclusion of catalytic additives & subsequently by bio-degradation.Products made from these materials degrade under conditions of sunlight (UV) heat &/or mechanical stress to complete the cycle of resource utilization & return otherwise intractable plastics to their natural origins.

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advantage of oxo-biodegradable polymers:

Does not leave fragments of petro-polymers in the soil.

Passes all the standard eco-toxicity tests.

Is safe for long-term contact with food.

Does not contain organo-chlorine, PCBs or "heavy metals."

Does not emit methane or nitrous oxide, even deep in a landfill. Can be made from recyclate.

Can be safely recycled.

9. Conclusion:-

Hence overall discussion we can see that a biodegradable polymer plays very important role in modern time . It is very effective to reduce the pollution . In our daily life we use very big part of polymers these polymers are harmful for the enviourment such as plastic which is not destroy and cause of many types of pollution . But by degradation of these we destroy the polythene and it is not harmful for our enviourment . And by biodegeradation of polymer these polymer are reduce in microorganisms which are the fovorable of enviourment and soil.