TABLE 2: EXAMPLES
OF SYNTHETIC POLYMERS.
|
CLASS |
EXAMPLES |
|
Polyesters |
Poly(lactic
acid), poly(glycolic acid), poly(hydroxy butyrate), poly( ɛ -
caprolactone), poly(α-malic acid), poly(dioxanones)Polyesters |
|
Polyanhydrides |
Poly(sebacic
acid), poly(adipic acid),poly(terphthalic acid) and various copolymers |
|
Polyamides |
Poly(imino
carbonates), polyamino acids |
|
Phosphorous-based
polymers |
Polyphosphates,
polyphosphonates, polyphosphazenes |
|
Others |
Poly(cyano
acrylates), polyurethanes, polyortho esters, polydihydropyrans, polyacetals |
Why We Prefer Synthetic Materials:
§ Predictable lot-to-lot uniformity
§ Free from concerns of immunogenicity
§ Reliable source of raw materials
Predictable biodegradable profile
Chemistry
of biodegradable polymers Carbonyl bond
to {O, N, S}
Biodegradation
of biodegradable polymers:
[2]
·
Heterogeneous degradation:
It starts at the surface of the microparticle
and proceeds to layers beneath, with the drug being released as polymer
degrades (assuming that biodegradation is the major release rate controlling
process). The degradation rate is constant in this case with the undegraded
carrier retaining its integrity throughout the process.
·
Homogeneous degradation:
It involves a random cleavage
throughout the bulk of the polymer matrix. In this case the molecular weight of
the polymer steadily decreases until a critical value of the molecular weight
is reached. Till this value is reached the carrier system retains its original
shape, whereas beyond this value loss of mass and solubilization of the polymer
commences.
Figure 1: The mechanism of degradation of
biodegradable polymers
Characteristics of biodegradable polymers: [4]
· Inertness
· Permeability
· Non-toxicity
· Bio-compatibility
· Tensile strength
· Mechanical strength
·
Controlled
rate of degradation
Need for biodegradable polymers: [4]
· Polymers have become an essential part of
our daily life.
· Having its numerous advantages, it finds
its use in every field.
· These polymer products account for approx.
150 million tons of non biodegradable waste every year. Such large amounts of
waste leads to various problems, not to mention, a general lack of cleanliness
in the neighborhood.
· It was recognized that the surgical removal
of a drug depleted delivery system was
difficult yet leaving non-biodegradable foreign materials in the body
for an indefinite time period causing toxicity problems.
· While diffusion controlled release is an
excellent means of achieving controlled drug delivery, it is limited by the
polymer permeability.
· There is no need for a second surgery for
removal of Polymers offer tremendous potential as the basis for controlled drug
delivery.
Factors affecting biodegradation: [4]
1)
Chemical structure :
(a) Functional Group
(b) Hydrophobicity
2)
Morphology :
(a) Tensile strength
(b) Branching
3)
Particle size:
Larger the particle size slower the
degradation process.
Mechanism of biodegradable polymers:
Figure 2: Schematic representation of mechanism of
biodegradable polymer
Enzymatic degradation:
Enzymatic degradation takes place with the
help of various enzymes. The type of enzymes used for degradation depends upon
the type of polymer:
· Fungi – ‘ Fusarium Moniliformae’
· Yeast- ‘Cryptococcus
· Enzymes from moulds such as ‘Penicillium’
Polymer degradation:
Degradation ----- chain cleavage
Figure 3: Degradation of biodegradable polymers
Degradation in
two phases
1.
Water penetration (rate determining)
Attacking chemical bonds,
shorter water soluble fragments.
2.
Rapid loss of polymer
Enzymatic attack, solublisation.
Hydrolysis:
Breakdown of organic materials through the
use of water. it is catalyzed by acids, bases, salts or enzymes.
Stages of hydrolysis:
|
|
|
|
|
Functional groups in polymer chains hydrolyze and absorb the water |
|
|
|
Water reacts with the polymer (cleavage of covalent chemical bonds) |
|
|
|
|
|
|
|
Release of degradation products leads to the mass loss which is
characteristic for erosion. |
Erosion:
Erosion ------- loss of mass
1. Bulk erosion
2. Surface erosion
Figure 4: Surface erosion and bulk erosion
Erosion
Type I erosion:
•
Evident
with water soluble polymers cross linked to form
three dimensional networks.
•
Cross
linking still intact.
•
Network
insoluble.
•
Swelling.
•
Solubilisation
by cleavage of water soluble backbone or cross linking
Type II erosion:
•
Polymers
first are water insoluble but converted to water soluble by reaction
with pendant group.
Type III erosion:
•
Polymers
with high molecular weight are broken down and transformed to smaller
water soluble molecules.
Combination:
Figure 5: Degradation of biodegradable polymers
Applications
of biodegradable polymers:
1)
Applications of Biodegradable Polymers
in drug delivery: [8]
In order to
deliver drugs to diseased sites in the body in a more effective and less
invasive way, a new dosage form technology, called drug delivery systems (DDS),
started in the late 1960’s in the USA using polymers. The objectives of DDS
include sustained release of drugs for adesired duration at an optimal dose,
targeting of drugs to diseased sites without affecting healthy sites,
controlled release of drugs by external stimuli, and simple delivery of drugs
mostly through skin and mucous membranes. Polymers are very powerful for this
new pharmaceutical technology. If a drug is administered through a parenteral
route like injection, the polymer used as a drug carrier should be preferably
absorbable, because the polymer is no longer required when the drug delivery
has been accomplished. Therefore, biodegradable polymers are widely used,
especially for the sustained release of drugs through administration by
injection or implantation into the body. For this purpose, absorbable
nanospheres, microspheres, beads, cylinders, and discs are prepared using
biodegradable polymers. The shape of the most widely used drug carriers is a
microsphere, which incorporates drugs and releases them through physical
diffusion, followed by resorption of the microsphere material. Naturally
occurring biodegradable polymers are also used as drug carriers for a sustained
release of drugs. If the drug carrier is soluble in water, the polymer need not
to be biodegradable, because this polymer will be excreted from the body,
associated with urine or feces although excretion will take a long time if the
molecular weight of the polymer is extremely high.
Mechanism
of drug release from biodegradable polymer:[4]
Biodegradable
polymer degrades within the body as a result of natural biological processes,
eliminating the need to remove a drug delivery system after release of the
active agent has been completed. Most biodegradable polymers are designed to
degrade as a result of hydrolysis of the polymer chains into biologically
acceptable and progressively smaller compounds. For some degradable polymers,
most notably the polyanhydrides and polyorthoesters, the degradation occurs
only at the surface of the polymer, resulting in a release rate that is
proportional to the surface area of the drug delivery system. Biodegradable
polymers mainly investigated for drug delivery applications are of either
natural or synthetic origin.
2)
Applications of Biodegradable Polymers in Orthopedics: [5]
Bone is a composite comprise of an organic phase
(base on collagen) by which calcium containing inorganic crystals are embedded
(Fig.2) Specifically, bone is a natural
composite material, which by weight contains about 60% mineral, 30% matrix and
10% water. The matrix bone is primarily consisting of collagen. This organic
component of bone is predominantly responsible for the tensile strength. The
mineral component of bone is of calcium phosphate, and gives rise to the
compressive strength.
Figure 6: Actual
vision inner part of natural bone
In the
body, bone serves as number of functions, such as providing the cells found in
the marrow that differentiates into blood cells, and also acting as a calcium
reservoir. Nevertheless, its primary purpose is to provide mechanical support
for soft tissues and serve as an anchor for the muscles that generate
motion. There are two types of bones,
compact or corical, and cancellous or trabecular (spongy) bone. The anisotropic
structure of bone leads to mechanical properties that exhibit directionally.
This directionality results from the fact that bone has evolved to be both
tough and stiff, two competing properties which are optimized in bone but with
an inherent loss in isotropy. In fact, bone exhibits extraordinary mechanical
properties, displaying both elastic and semi-brittle behavior. Bone plays an
important role in the movement, support and protection of vital organs.
However, it is susceptible to fracture as a result of physiological resorption,
dental losses, trauma injuries, bone pathology, infection, aging, population
and bone disease. The ways of bone repair improve year by year, parallel to the
development of high technologies. Traditional biological methods of bone
defects management includes:
1)
Autogeneous bone graft which harvested from different side of the patient’s
body, it is considered as the ideal bone graft substitute, while the use of auto
graft material is the preferred technique. There are some limitations such as
donor site morbidity, limited donor bone supply, anatomical and structural
problems and elevated levels of resorption during healing.
2)
Allograft bone which is obtained from individuals of the same species as the
receiver Allograft has the disadvantage of eliciting an immunological response
due to the genetic differences and the risk of inducing transmissible disease.
This necessities a thorough sterilization procedure that not only damages the
graft’s biological and mechanical properties, but also expensive.
Reconstruction of bone with fully synthetic artificial bone graft is another
way to provide and create lost bone mineral. It was started past 30 -40 years,
the terms of innovation of ceramic for bone repair and reconstruction become an
interest in the major advance of medical applications .Calcium phosphate is
highly promising as a bone substitute in orthopaedics among the other ceramics
.
This group
of material exhibits high biocompatibility, bioactivity, self setting
characteristic, low setting temperature, adequate stiffness and easy shaping in
complicated geometries. However, several drawbacks do exist causing some problems
that hinder clinical use of calcium phosphate. The problem is that calcium
phosphate is lacks macropores and low porosity making its resorbing rate rather
slow and mechanically brittle, thus restricts its utilization in medical
applications .For the last two decades of the twentieth century, a paradigm
shift occurred from the biostable materials to biodegradable materials
(hydrolytically and enzymatically degradable) for the medical and related
applications . Current trend predicts that in the next couple of years, many of
the permanent prosthetic devices used for temporary therapeutic applications
will be replaced by biodegradable devices that could help the body to repair
and regenerate the damaged bone.
Figure7: Applications of biodegradable polymers in
eroded cartilage
A
biomaterial can be defined as a material intended to interface with biological
system to evaluate, treat, augment or replace any organ or function of the
body. The essential prerequisite to qualify a material as a biomaterial is its
biocompatibility, which is the ability of the material to perform with an
appropriate host response in a specific application. The host response to an
implant depends on factors ranging from the chemical, physical and biological
of the materials to the shape and structure of the implant. Biodegradable
polymers are materials that fulfill the above requirement. The chemical,
physical, mechanical polymers will vary with the time and degradation products
produced have different level of bone compatibility. Notwithstanding,
biodegradable polymers sometimes fall short of achieving satisfactory results
in bone fixation. These results should not necessarily be taken as a negative
factor, since they are available to be reinforced with other materials like ceramics,
metals, or clay in order to improve their mechanical properties and meet the
promising requirements in bone substitute. Often, from the medical point of
view, biodegradable polymer with sufficient mechanical strength and optimized
lifetime in the body, which could finally be replaced by bone, is most
desirable. Biodegradable polymers lack in mechanical properties. It is
desirable to reinforce it with other biocompatible substance to enhance its
properties. The best partner in reinforcing with ceramic is calcium phosphate,
especially hydroxyapatite (HA) since their condition mimic natural bone
composition. Facing a complex biological and sensitive system as the human
body, the requirement for bone repair using biodegradable polymers are manifold
and challenging. Biodegradable polymers offer a number of advantages for
developing bone at defect sites. The key advantages include the ability to
tailor mechanical properties and degradation kinetic. Biodegradable polymers
can differ in their molecular weight (MW), polydispersity, crystallinity,
structure and thermal transition, allowing different absorption rates. By means
of porosity, biodegradable polymers can be used to impart macro porosity to the
cement as polymers degrade and expose macrospores to bony in growth. The
strengthening of the graft from the bone growth and the deposition of the new
bone should offset the weakening of the graft due to polymer degradation. In
bone application, biodegradable polymer or its composite can be prepared in two
forms, scaffold and dense. Usually, scaffold is used to associate with cell
seeded in purpose of cell growth to form bone. Scaffolds are able to promote
cellular interactions and process uniformly interconnected pores with adequate
structural integrity. The interaction between cell and substrate is related to
the osteogenic cells attachment, adhesion and spreading and its quality will
influence cell proliferation and differentiation. Cell can be obtained from
calvarine , trabecular bone , human embryonic stem (HES) cells and bovine
osteoblasts (BOB) . Dense form of biodegradable polymer can be obtained from
forging, hot or cold pressing. Formation of bone in this particular form is
usually by immersing the sample in simulated body fluid (SBF). SBF is the most
favored model solution simulating the inorganic part of the blood plasma. The
ions concentrations of simulated body fluid are nearly equal to those of blood
plasma by maintaining the ph at 7.25 for the apatite nucleation. Though various
studies have been done throughout the scientific community on biodegradable
polymers, there is yet a systematic report on the application of biodegradable
polymers on bone engineering.
3)
Applications of biodegradable polymers
in ocular drug delivery: [11]
Ophthalmic drug delivery is challenging due
to unique anatomy and physiology of the eye. The natural protective mechanisms
of the eye render this organ inaccessible to foreign substances and drug
molecules. A successful therapeutic treatment requires maintaining the
therapeutic drug concentration at the target site by circumventing the
anatomical and physiological barriers. The major ocular drug delivery routes
include topical, systemic and local administration. Topical mode of
administration is the most preferred route to treat anterior segment diseases
because of ease of application. However, the ocular bioavailability of
topically applied drugs is less than 5% and it is difficult to achieve
therapeutic drug concentration at the target site. Poor bioavailability mainly
results from the precorneal factors such as blinking, transient residence time
in cul-de-sac, and nasolacrimal drainage. In addition, the lipoidal nature of
the corneal epithelium restricts the entry of hydrophilic drug molecules and
the water- laden stroma acts as limiting membrane for lipophilic molecules.
Moreover, physicochemical properties of a drug entity itself determine the
diffusion resistance and relative impermeability offered by various ocular
tissues. To overcome these barriers and to increase contact time of the drug on
the eye surface, absorption enhancers and/or viscosity enhancers are generally
used in the ocular formulations. So far, these approaches have limited success
to address the problem of poor bioavailability from topical route to treat anterior
segment diseases. On the other hand, for the treatment of posterior segment
diseases either systemic or local route is preferred because of the poor
corneal drug permeation. Systemic administration requires higher dosage and
frequent administration that results in severe adverse effects. Local
injections, particularly intravitreal and subconjunctival injections are
alternate strategies to achieve therapeutic concentration in the vitreo-retinal
disorders. However, to maintain the effective concentration repeated injections
are required, which causes clinical complications or patient discomfort.
Further, the presence of different efflux pumps such as P-glycoprotein,
multidrug resistance associated proteins, and breast cancer resistant protein
on various ocular tissues restrict the entry of the drug molecules into the
eye. Many approaches have been evaluated to improve ophthalmic drug delivery.
Application of controlled drug delivery systems was anticipated as an effective
approach to circumvent all these limitations. Controlled drug delivery systems
release the drug in a sustained and controlled manner by which the therapeutic
concentration is maintained for the prolonged period of time. These systems
provide many practical advantages: they avoid frequent administration, which is
a major non-compliance with many chronic eye disorders.
1) Natural
biodegradable polymers used for ocular drug delivery:
· Gelatin,
·
Collagen,
·
Chitosan
2) Synthetic biodegradable polymers used for ocular
drug delivery :
· Poly N-vinylpyrrolidone
(PVP)
· Poly (lacticide)
(PLA), poly (glycolide), and their copolymers polylactide-co- glycolide (PLGA)
· Poly- ε-caprolactone (PCL)
· Poly (alkyl
cynoacrylates) (PACA)
· Polyanhydrides
· Poly (orthoester)
(peos)
4) Applications
of Biodegradable Polymers as Effective/specific delivery carriers for
proteins and peptides: [10]
Biodegradable
polymers are having many advantages as effective/specific delivery carriers For
proteins and peptides. Some of the advantages and limitations are enlisted in
Fig. No.(8).
Figure8: Advantages and limitations of protein and peptides.
5) Applications of Biodegradable Polymers in Surgical use: [6]
Figure 9: Applications of biodegradable polymers in surgical use
Application
of biodegradable polymers to medicine did not start recently and has already a
long history. As is seen, most of the applications are for surgery. The largest
and longest use of biodegradable polymers is for suturing. Collagen fibers
obtained from animal intestines have been long used as absorbable suture after
chromium treatment. The use of synthetic biodegradable polymers for suture
started in USA in the 1970. Commercial polymers used for this purpose include
polyglycolide, which is still the largest in volume production, together with a
glycolide- L-lactide (90:10) copolymer. The sutures made from these glycolide
polymers are of braid type processed from multi-filaments, but synthetic
absorbable sutures of mono-filament type also at present are commercially
available. The biodegradable polymers of the next largest consumption in
surgery are for hemostasis, sealing, and adhesion to tissues. Liquid-type
products are mostly used for these purposes. Immediately after application of a
liquid to a defective tissue where hemostasis, sealing, or adhesion is needed,
the liquid sets to a gel and covers the defect to stop bleeding, seal a hole,
or adhere two separated tissues. As the gelled material is no longer necessary
after healing of the treated tissue, it should be biodegradable and finally absorbed
into the body. The biomaterials used to prepare such liquid products include
fibrinogen (a serum protein), 2-cyanoacrylates, and a gelatin/
resorcinol/formaldehyde mixture. 2-Cyanoacrylates solidify upon contact with
tissues as a result of polymerization to polymers that are hydrolysable at room
temperature and neutral ph, but yield formaldehyde as a hydrolysis by-product.
Regenerated collagen is also used as a hemostatic agent in forms of fiber,
powder, and assemblies. Another possible application of biodegradable polymers
is the fixation of fractured bones. Currently, metals are widely used for this
purpose in orthopaedic and oral surgeries in the form of plates, pins, screws,
and wires, but they need removal after re-union of fractured bones by further
surgery. It would be very beneficial to patients if these fixation devices can
be fabricated using biodegradable polymers because there would be no need for a
re-operation. Attempts to replace the metals with biodegradable devices have
already started, as will be described later.’
6) Applications of Biodegradable Polymers in tissue engineering: [6, 7]
Figure 10: Applications of biodegradable polymers in
tissue
engineering
Tissue
engineering is an emerging technology to create biological tissues for replacements
of defective or lost tissues using cells and cell growth factors. Also,
scaffolds are required for tissue construction if of the lost part of the
tissue is so large that it cannot be cured by conventional drug administration.
At present, such largely diseased tissues and organs are replaced either with
artificial organs or transplanted organs, but both of the therapeutic methods
involve some problems. As mentioned earlier, the biocompatibility of clinically
used artificial organs is mostly not safisticatory enough to prevent severe
foreign-body reactions And to fully perform the objective of the artificial
organs aimed for patients. The bio functionality of current artificial organs
is still poor. On the contrary, the bio functionality of transplanted organs is
as excellent as healthy human organs, but the patients with transplanted organs
are suffering from side-effects induced by immuno-suppresive drugs
administered. Another major problem of organ transplantation is shortage of
organ donors. The final objective of tissue engineering is to solve these
problems by providing biological tissues and organs that are more excellent in
both biofunctionality and biocompatibility than the conventional artificial
organs. Biodegradable polymers are required to fabricate scaffolds For cell
proliferation and differentiation which result in tissue regeneration or
construction. Biodegradable polymers are necessary also for a sustained release
of growth factors at the location of tissue regeneration. Generally, scaffolds
used in tissue engineering are porous and Three-dimensional to encourage
infiltration of a large number of cells into the scaffolds. Currently, the
polymers used for scaffolding include collagen, glycolide-lactide copolymers,
other copolymers of lactide, and cross linked polysaccharides.
7) Applications
of Biodegradable Polymers in Waste management: [9]
There is a
world-wide research effort to develop biodegradable polymers as a waste
management option for polymers in the environment. Biodegradation is expected to be the major
mechanism of loss for most chemicals released into the environment. This
process refers to the degradation and assimilation of polymers by living
microorganisms to produce degradation products. The most important organisms in
biodegradation are fungi, bacteria and algae. Natural polymers are degraded in
biological systems by oxidation and hydrolysis. Biodegradable materials degrade
into biomass, carbon dioxide and methane. In the case of synthetic polymers,
microbial utilization of its carbon backbone as a carbon source is required.
Bacteria important in the biodegradation process include, inter alia, Bacillus,
Pseudomonas, Klebsiella, Actinomycetes, Nocardia, Streptomyces,
Thermoactinomycetes, Micromonospora, Mycobacterium, Rhodococcus,
Flavobacterium, Comamonas, Escherichia, Azotobacter
and Alcaligenes (some of them can accumulate polymer up to 90% of their
dry mass). Fungi active in the biodegradation process are Sporotrichum,
Talaromyces, Phanerochaete, Ganoderma, Thermoascus, Thielavia,
Paecilomyces, Thermomyces, Geotrichum, Cladosporium, Phlebia, Trametes,
Candida, Penicillium, Chaetomium, and Aerobasidium. The
biodegradation process can be divided into
(1) Aerobic biodegradation:
If oxygen
is present, aerobic biodegradation occurs and Carbon dioxide is produced.
Polymer + O2 CO2 + H2O +
biomass + residue(s)
(2)Anaerobic biodegradation:
If there is
no oxygen, an anaerobic degradation occurs and methane is produced.
Polymer CO2
+ CH4 + H2O + biomass+ residue(s)
Figure 11:
Schematic representation of polymer degradation under aerobic and anaerobic
conditions.
When
conversion of biodegradable materials or biomass to gases (like carbon dioxide,
methane, and nitrogen compounds), water, salts, minerals and residual biomass
occurs, this process is called mineralization. Mineralization is complete when
all the biodegradable materials or biomass are consumed and all the carbon is
converted to carbon dioxide. Biodegradable materials have the proven capability
to decompose in the most common environment where the material is disposed,
within one year, through natural biological processes into non-toxic
carbonaceous soil, water or carbon dioxide
8) Applications of Biodegradable Polymers in Packing Materials: [12]
Figure12: Packing materials
A wide
range of materials are used for packaging applications including metal, glass,
wood, paper or pulp-based materials, plastics or combination of more than one
materials as composites. They are applied in three broad categories of
packaging: primary packaging (in contact with the goods and taken home by
consumers), secondary packaging (covers the larger packaging, i.e., boxes, used
to carry quantities of primary packaged goods), tertiary packaging (used to
assist transport of large quantities of goods, i.e., wooden pallets and plastic
wrapping). Secondary and tertiary packaging materials have less material
variation and they are relatively easier to collect and sort for recycling
purposes. Primary packaging materials are dispersed into households and also
they are largely mixed, contaminated and often damaged and thus pose problems
in recycling or reuse of the materials. Over 67 million tonnes of packaging
waste is generated annually in the EU, comprising about one-third of all
municipal solid waste. In the UK, 3.2 million tons of household waste produced
annually is packaging, which equates to over 12% of the total household waste
produced. In developed countries, food packaging represents 60% of all packaging.
This is due primarily to strict food packaging regulations and also the drive
to enhance appearance and so increase sales. In the UK, the proportion of food
that is unfit for consumption before it reaches the consumer is 2%, whereas in
developing countries, where packaging is not as widespread, this loss can be in
excess of 40%. Starch is the most commonly used natural polymer in
biodegradable packing production as it is abundant, inexpensive, readily
available and biodegradable in many environments.
9) Applications of Biodegradable Polymers in Agriculture:
For this
application, the most important property of biodegradable polymers is in fact
their biodegradability. Starch-based polymers are the most used biopolymers in
this area. They meet the biodegradability criteria and have a sufficient life
time to act. Plastic films were first introduced for greenhouse coverings
fumigation and mulching in the 1930s. Young plants are susceptible to frost and
must be covered. The main actions of biodegradable cover films are to conserve
the moisture, to increase soil temperature and to reduce weeds in order to
improve the rate of growth in plants. At the end of the season, the film can be
left into the soil, where it is biodegraded. Another application bases on the
production of bands of sowing. These are bands which contain seeds regularly
distributed as well as nutriments. In the field of geotextiles, we can mention
the use of textiles based on biopolymers for filtration and drainage and the
use of the geogrilles. Biodegradable polymers can be used for the controlled
release of agricultural chemicals. The active agent can be dissolved, dispersed
or encapsulated by the polymer matrix or coating, or is a part of the
macromolecular backbone or pendent side chain. The agricultural chemicals
concerned are pesticides and nutrients, fertilizer, pheromones to repel
insects. The natural polymers used in controlled release systems are typically
starch, cellulose, chitin, aliginic acid and lignin. In horticulture threads, clips,
staples, bags of fertilizer, envelopes of ensilage and trays with seeds are
applications mentioned for biopolymers. Containers such as biodegradable plant
pots and disposable composting containers and bags are other agricultural
applications. The pots are seeded directly in the soil, and break down as the
plant begins to grow. When starch is placed in contact with soil
microorganisms, it degrades into non toxic products. This is the reason why
starch films are used as agricultural mulch films. In marine agriculture,
biopolymers are used to make ropes and fishing nets
10) Applications of Biodegradable Polymers in Others fields:
Biopolymers
are also used in shape specific applications such as in the automotive,
electronics or construction sectors.
Automotive:
The
automotive sector aims to prepare lighter cars by use of bioplastics and Biocomposites.
Natural fibers can replace glass fibers as reinforcement materials in plastic
car parts. We await the development of the bio-composite materials. For example
the PLA is mixed with fibers of kenaf for replace the panels of car doors and
dashboards (Toyota Internet site). Starch-based polymers are used as additive
in the manufacturing of tires. It reduces the resistance to the movement and
the consumption of fuel and in fine greenhouse gas emissions (Novamont Internet
site).
Electronics:
PLA and
kenaf are used as composite in electronics applications. Compact disks based on
PLA are also launched on the market by the Pioneer and Sanyo groups. Fujitsu
Company has launched a computer case made of PLA.
Construction:
PLA fiber
is used for the padding and the paving stones of carpet. Its inflammability,
lower than that of the synthetic fibers, offers more security. Its
antibacterial and antifungal properties avoid allergy problems. The fiber is
also resistant to UV radiation.
Sports and
leisure:
Some
fishing hooks and biodegradable golf tees (Vegeplast, France) are based on
starch. PLA fiber is used for sports clothes. It combines the comfort of the
natural fibers and the resistance of synthetic fibers.
Applications
with short-term life character and disposability:
Aliphatic
polyesters like PLA, PBS, PCL and their copolymers are used as biodegradable
plastics for disposable consumer products, like disposable food service items
(disposable cutlery and plates, for example). Other products are diapers,
cotton stalk and sanitary products.
Unusual
applications:
There are a
lot of other applications which do not fit into any of the previous categories.
Thus combs, pens and mouse pads made of biodegradable polymers have also been
invented, mostly for use as marketing tools. Biodegradable polymers can be used
to modify food textures. Due to its non toxicity, alginate has been used as a
food additive and a thickener in salad dressings and ice creams. Chitin and
chitosan are used as food and feed additives. PLA is used for compostable food.
CONCLUSION:
There are a
seemingly limitless number of areas where biodegradable polymer materials may
find use. The sectors of agriculture, automotives, medicine, and packaging all
require environmentally friendly polymers. Wide range of biodegradable polymers
is currently available. Although many people consider biodegradable polymers
very attractive and necessary for the co-existence of the human society with
the nature, global production of biodegradable polymers is not as large as
expected. The major reason for this seems to be not their poor properties as
materials but their high production costs. Consumers do not want to pay much for
conventional daily products even if they are urgently required to keep our
environments both inside and outside the human body safe and clean. The largest
challenge to polymer scientists is to manufacture at a reasonably low cost
biodegradable polymers having well-balanced biodegradability and mechanical
properties. The most appropriate biodegradable polymer for the targeted end use
will be selected taking into account the ratio polymer cost/performance.
FUTURE
PROSPECTIVE:
Just as
nature has used biological polymers as the material of choice, mankind will
chose biodegradable polymeric materials as the choice material.
· Humans have progressed from the Stone Age,
through the Bronze, Iron, and Steel Ages into its current age, the Age of
Polymers. An age in which synthetic polymers are will be the material of
choice.
· Biodegradable Polymeric materials have a
vast potential for exciting new applications in the foreseeable future.
· Indeed, biodegradable polymers will play an
increasingly important role in all aspects of your life. The large number of
current and future applications of biodegradable polymeric materials has
created a great national need for persons specifically trained to carry out
research and development in polymer science and engineering.
· A person choosing a career in this field
can expect to achieve both financial reward and personal fulfillment.
REFERENCE:
1. Patrick J. Sinko
“Martin’s physical pharmacy and pharmaceutical sciences” sixth edition pg.no.492-515
2.
N. K. Jain; Advances in Controlled and Novel Drug
Delivery; First Edition, Reprint 2003; CBS Publishers and Distributors; pg. No.1
– 17
3. Kumar A. Ashwin,
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