Research - Biodegradable Polymers - Report Writing - Assessment Answer

Research Assignment

Assignment Task

Introduction

The concern of human on the environment, the knowledge about the direct consequences of destroying the environment on human’s race and the decrease in the available dump lands made the research advance and look for environmental friendly products to replace the currently present ones. Furthermore, other than protecting the environment biodegradable polymers have wide range of application in biomedicine. Biodegradable polymers are polymers derived from agricultural feedstock and have many uses since they are light in weight, low in cost and easy to process. Mainly most of the natural polymers are biodegradable polymers and they have big importance in the polymer market that is currently controlled by petrol based polymers (Schimmel, Lou, Warren, & Shahbazi, 2005).

Composition and structure of biodegradable polymers

There are many kinds of biodegradable polymers that are made of different substances such as:

• Starch based polymers: these are taken from the starch extracted out of wheat, corn, potatoes and other starch products. Out of these all corn is the least expensive source of starch.
• According to the Australian Academy of science since starch is soluble in water it can be easily changed into biodegradable plastic and the process of changing starch from lactic acid monomer to biodegradable polymer is called polylacticide “ PLA” (Salt, 2002).
• Bacteria based biodegradable plastics are formed from bacteria colonies that produce polyhydroxyalkanoate (PHA) and the plastic forms degrade aerobically and anaerobically and under alkaline conditions ("Commercial production of biodegradable materials scheduled to begin next year.," 2003).
• Soy based plastics: the high percentage of fats in soy beans is used to produce plastics (Berkesch, 2005).

How are biodegradable polymers made?

• Starch made polymer by transforming the starch into altered polymer so that it would stop deforming. Then biodegradable starch can be formed by using one of plastic technologies for example, injection molding, blow molding, film blowing foaming, thermoforming and extrusion. Starch polymers mainly can be used to manufacture plastic bags that can be used for groceries and home use then after we want to recycle it we can feed it to animals since starch is part of their diet (Berkesch, 2005).
• Bacteria based plastics are formed using the protein that a bacterium produces, this type of polymer is important since its mechanical properties can be changed according to the needs of the product. Researches are developing these type of biodegradable polymers also for medical use and for products that are used only once (Berkesch, 2005).
• Soy bean biodegradable polymers are widely used and they are being used in automotive industry by ford. They can be synthesized using compression or injection molding process (Berkesch, 2005).

The most special feature about biodegradable polymers is their ability to degrade in the environment thus making it environmental friendly. Plastics and polymers that are made from petroleum take long time to degrade, and thus polluting the environment.

Some of properties of biodegradable polymers:

The important properties possessed by biodegradable biomaterials are as following:

(1) It should not induce inflammation when inserted inside the body,

(2) Its degradation time should be adjustable according to the need,

(3) It should possess appropriate mechanical strength for support,

(4) It degradation should produce non-toxic products that can be easily resorbed or excreted out of the body,

(5) It should have appropriate permeability to support the designed application.

These properties of biopolymers are mainly attributed to their material chemistry, molecular weight, hydrophobicity, surface charge, water adsorption, degradation and erosion mechanism. Depending upon the applicability, the choice and thus the properties of the polymeric biomaterial vary greatly (Ulery, Nair, & Laurencin, 2011).

Some of the biodegradable polymers for medical usage

• Polyhydroxyalkanoates (PHA)

PHA are thermoplastic biopolymers. They show a varied material properties ranging from rigid and brittle, flexible plastics to strong and tough elastic materials. These properties depend on the chemistry of the structure. These polymers have great potential for different medical applications owing to their biocompatibility. These are generally used in wound care, for making surgical sutures, bone plates and bandages. These are also used to regulate the drug release inside the body. They are also used for manufacturing products related to personal hygiene. An example of polymer belonging to this category is polyhydroxybutyrate (PHB). It has high crystalinity and very brittle (Williams & Martin, 2005).

• Polylactic acid (PLA)

The monomeric subunits used to form the lactide basedpolymers are producedfromglycolic acid, DL-lactic acid and L/D-lactic acid. PLA-PGA materials are most commonly used for therapeutic purposes. Devices made using this material have been used for controlling the discharge of various drugs like antibiotics, anticancer,antimalarial agents, proteins, hormones, etc inside the body fluids. The copolymers can also be molded into microsphere, small capsules, implants, and hollow fibersfor various biomedical applications. Sutures made up of polylactide as the incision heals, and hence are commonly used in surgical operations. PLA-PGA copolymersare extensively used in orthopedic treatments and surgery (Agrawal, Athanasiou, & Heckman, 1997). It is used to make screws and plates for the fracture treatment and as filling in bone defects. The copolymer is also used as a scaffold to assist cartilage formation in the body. Copolymers of PLA and PGA are very useful as their rate of degradation can be adjusted according to the needs. Hence prostheses made of PLA-PGA are biocompatible and nontoxic.

• Polyamino Acids

Polyamino acids form an important category under synthetic polymers. These are synthesized by chemical polymerization of the naturally occurring amino-acids. One example of polymer falling in this group includes polyaspartate polymer produced from asparticacid. It has properties similar topolyacrylates. The polyaspartate polymers resemble natural aspartate-rich proteins obtained from oyster shells, whichplay a key role in maintaining the level of minerals. Derivation of polyaspartate compounds from natural precursors makes them biodegradable and hence can be used to replace polymers derived frompetroleum like polyacrylate and polyacrylamide. There special mineralization andionic properties make them very useful for various medical applications. Some of these include superabsorbents diapers, tartar control agents (toothpaste) in dental treatment, heart valves, for preventing pathological levels of calcification, microencapsulation of drugs for in vivodelivery (Onar, 2004).

• Collagen/Gelatin

Collagen is a naturally occurring protein used in the food industry and manufacturing of cosmetics. Collagenis a very usefulbiomaterial. Collagen forms a transparent hydrogel which have high degree of oxygen permeabilitywhencross-linked in 5-10% aqueoussolution.This hydrogelisprocessed to formsoft contact lens.Collagenbiomaterialis also usedfor creating drug delivery systemsforslowreleaseof drugs. Aslow releasedrug delivery systemwas jointly developed byas the drug carrier (Koseki & Sano, 1999). Regenerated collagen is further used as a hemostatic agent in forms of fiber, powder, and assemblies (Onar, 2004).

• Silk

A silk thread naturally produced by a silkworm. The core of the silk fibre is composed of fibroid which is covered with sericine from outside. Removal of sericine when removed by the process of degumming leads to a fine silk thread. Silk is alsofound to be a biologically active material. Silk has been shown to depict similarbiocompatibility in vitroand in vivowhen compared with other biomaterials like PLA and collagen. A wire rope matrix was developed by a group of scientists for the synthesis of autologous tissue engineeredanterior cruciate ligaments (ACL) using silk and stem cells from the patient’s own body (Altman et al., 2003). Also,it was found that the polymers modified using sericin and its derivatives are useful as degradable biomaterials for biomedical applications. It is also useful for making functionalmembranes, fibers and fabrics (Zhang, 2002).

• Chitin

Chitin and chitosan are well known naturally occurring biodegradable polymers. These areavailable from various animals and plants sources. These two biomaterials have a number of useful physiochemical properties like high strength, biodegradability, and nontoxicity. Thesepolymers are widelybeing used in medicine. Chitosan is commonly used in the process of wound healing by incorporating it into bandages andsutures. It isalso used to speed up the process of repairing tissues.Aqueous solution of chitosan can also be used to treat burns. Chitosan is also used as a material for contact and intra-ocular lensesbecause of its high oxygenpermeability. Chitosanhas also been found to accelerateblood clotting. Sincechitin compounds arebiological degradable they can also beusedin drug delivery systems.Chitosan carriers can slowly release the drugs and hence arecrucialincancer chemotherapy.Since chemotherapeuticagents are often highly toxic and require long administration periods, chitin carriers are a good option. Nonwoven chitin fabric is used as anartificial skin because of its property of good adhesion to the human body surface. It further helps in stimulating the formation of new skin. It further speeds up healing process and reduces pain (Singh & Ray, 2000).

• Hyaluronic Acid

Hyaluronic acid (HA) is a natural product found considerably in many vertebrate tissues. It is also found in many bacteria as an extracellular polysaccharide. HA has been shown to aid intissue formation. It regulates our lymphatic system and provides a matrix for repairing and protecting the reproductive cells. It also lubricates thejoints. HA is used in many biomedicalapplications because of its role in various developmental andregulatory processes. Its property of degrading into simple sugars makes it an attractive biomaterial for the researchers. It is mainly used in eye surgery,arthritis treatment and wound-healing preparations now a days (Kogan, Šoltés, Stern, & Gemeiner, 2007).

Main categories of biomedical applications where these biopolymers are used

• Cardiovascular Applications

Cardiovascular diseases are one of the leading causes of mortality in the world. Suitable vein autografts are not always available for all the patients and hence arises the need of synthetic grafts. Although synthetic grafts made up of polyethylene terephthalate (PET) are used for replacing large blood vessels, they have reduced potential compared to autografts because of thrombosis, restenosis, and calcium deposition. Also these are inert and non-degradable. These are often rigid and incompatible with the native arteries, which increases thrombosis and neointimal hyperplasia. Citrate-based biodegradable elastomers are important biomaterial being used for the same these days (Kumbar, Laurencin, & Deng, 2014).

• Orthopedic Applications

Bone is a dynamic skeletal tissue which has the capacity of regenerate itself but still over 2.2 million bone-grafting procedures are performed annually worldwide to treat orthopedic pathological conditions. These include fractures, tumor resections, and osteoporosis. But this grafting process has certain limitations due to less availability, complications from donor site morbidity, and possible risk of pathogen transmission. Synthetic counterparts of bones are not able to provide mechanical strength and mimic the native composition of bone tissue. The incorporation of ceramic particles further improve the mechanical properties but is limited by the amount of total ceramic that can be incorporated into the composite. Thus inflammation, long degradation times, and poor bone integration are significant limitations for the use of these materials. Therefore, the search for a suitable alternative material for bone tissue-engineered is required which can the innate composition of bone. It should be able to provide adequate mechanical properties, minimize inflammatory responses, quickly induce bone regeneration, and fully integrate with the surrounding tissue within a year of implantation remains a significant challenge (Kumbar et al., 2014).

Bio-imaging and Drug Delivery

Dr. Yang’s Lab developed aliphatic BPLPs using biocompatible monomers, including citric acid and amino acids. The unique characteristics of BPLPs have made it possible to use these for bio-imaging and drug delivery. It has also eliminated the long-term concern of fluorescent dyes and inorganic QDs, as well as their conjugation difficulties (Kumbar et al., 2014).

Other Applications

The other major use of biopolymers is in the area of tissue bio-adhesive, cell and drug delivery, endoscopic mucosal resection, nerve tissue engineering and gene delivery (Kumbar et al., 2014).

Summary

The importance of biodegradable polymers made the research in this field advance since they are one of the most valuable things that can protect the nature and the environment. Lately, biodegradable polymers are being widely used in many industries due to their cheap price and distinct properties. These types of polymers are taking the place of plastics and other fuel based polymers that are harmful to the environment. Finally, the biomedical applications of biodegradable polymers are numerous and biodegradable polymers constitute a big part of revolutionizing medicine in general and drug delivery methods in particular.