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Table of contents
- Drug Designing & Intellectual Properties International Journal
- Role of Polymer Synthesis in Drug Delivery, Medical Device Manufacturing
Zhang et al. BMPs are biologically active molecules that have the ability of initiating new bone formation, and they used for clinical applications in combination with biomaterials, such as bone-graft replacements to stimulate bone repair.
On the contrary, the bone that is forming by degradation of PLA was in very small quantity. Chang et al. Li et al. PLA stents are degradable type that later can be removed from human body Consequently, PLA stents displayed a promising future in the treatment of ureteral injuries.
Qin et al. Brekke mentioned the use of PLA for improving the ability of dental wound healing, and they mentioned that a surgical dressing made from PLA could reduce the incidence of mandibular third molar extraction wound failure PLA are using in drug delivery system because it is completely biodegradable, it has better encapsulation capacity, biocompatible and less toxic. Polymeric drug release occurs in three ways: erosion, diffusion and swelling. The degradation occurs when water enters the biodegradable polymer containing monomers connected by ester bonds with each other.
The ester bonds breaks randomly by hydrolytic ester cleavage, leading to subsequent erosion of the device. PLA and their copolymers in the form of nano-particles were in the encapsulation process of many drugs, such as psychotic, restenosis, hormones, oridonin, dermatotherapy, and protein BSA Methods to obtain these nano-particles are solvent evaporation, solvent displacement, salting out, and emulsion solvent diffusion. Ling and Huang 30 used the poly lactic-co-glycolic acid nano-particles for loading the drug, paclitaxel.
Rancan et al. In this method, PLA first dissolved in acetone, the solution was then mixes with an aqueous solution with continuous stirring, and the solvent was then allowing evaporating under lowered pressure at room temperature to obtain the PLA - NPs. To obtain fluorescent particles, where fluorescent dye along with PLA dissolved in acetone and then same method followed. PLA-NPs examined on human skin were ideal contenders for designing of drug delivery systems, which could target active compounds into hair follicles. PLA polymers are required to prepare biodegradable suture anchors, screws and fixation pins These absorbable screws and pins have been widely used in clinical applications, more commonly where high mechanical strength was not required.
In some cases, high mechanical strength of the PLA was required, so that techniques used to improve the mechanical properties of PLA, specifically impact tensile strength and modulus of fracture in bone fixation, where both metal and biodegradable plate, pins and rods has limited their applications in fracture fixation Bostman et al. PLGA has attracted significant interest as a principle material for medical applications because of its biocompatibility and biodegradation rate depending upon the molecular weight of polymer and ratio of its copolymer.
According to FDA, PLGA is safe to use in human body, provided better interaction with biological materials by modifying its surface properties. PLGA is a hydrophilic, crystalline polymer with comparatively fast deterioration rate as compared to other biodegradable polymers. Typically, the PLGA co-polymers are preferable compared to its constituent homo-polymers for the mixture of bone replacement constructs, as PLGA recommend high- grade control as compared to its degradation properties by differing the ratio of its monomers. PLGA is usually used in conjunction with other materials including ceramics, biologically active glass, in order to provide PLGA more bionics and able to intensify bone reformation Hence, PLGA - based bone replacements have classified according to their types and application: such as scaffolds, fibers, hydrogels or microspheres These are classified on ratio basis of monomers used.
Different processing techniques are use for synthesizing PLGA and the physico-chemical properties of the final product strongly affected by the process parameters. The enzymatic ring-opening polymerization takes place in presence of enzyme lipases, under favourable reaction conditions including temperature, pH and pressure, but this reaction is time consuming, as a result low molecular weight PLGA gets produced Properties of PLGA: Physical properties of PLGA depends on various parameters, such as molecular weight of the monomers, the ratio of lactic acid and glycolic acid, the response time to water and the temperature at which it can be stored PLGA found in two forms such as D and L-isomers, due to presence of two enantiomeric isomers of lactide e.
Drug Designing & Intellectual Properties International Journal
D and L isomers, based on the position of pendant methyl group present on the alpha carbon of PLA. While Glycolic acid does not have the methyl side group as compared to Lactic acid , that makes it highly crystalline, copolymers of PLGA are amorphous in nature. PLGA degrades by breakdown of its ester linkages, via bulk or heterogeneous erosion, in aqueous environments.
Thoroughly its degradation is carried out in three steps: i Hydration: where water gets perforated through the amorphous region and obstruct hydrogen bonds and the Vander Waals forces, as a result glass transition temperature Tg decreases. In initial degradation, covalent bonds cleaved by decreasing molecular weight. PLGA dissolved by using different solvents such as chlorinated solvents, tetrahydrofuran, acetone or ethyl acetate 45 and it can be drawn into different shape and size, which can encapsulate bio-molecules of different size range. Besides degradation, Lactic acid and Glycolic acid obtained as by-products.
The degradation rate of PLGA is long lasting and affected by wide range of parameters. Increased molecular weight of conventional PLGAs i. Functionalization of end-groups: the end-capped polymers having ester end opposed by free carboxylic group indicates longer degradation half-lives 46, However, the degradation behaviour of PLGA is highly influenced by the shape of the device based on the penetrability of water.
Moreover, the surrounding media that is acidic in nature escalates the degradation rate of the PLGA owing to autocatalysis. Moreover, the glass transition temperature Tg of PLGA will decrease, if the lactic acid contents in the copolymer decreases, as well with decrease in molecular weight of the copolymer B Fibrous Scaffolds: These scaffolds are supposed to have exceptional potential for bone tissue reformation.
Several processes to obtain micro and Nano-fibrous composite scaffolds have used Morgan used the wet-spinning method for obtaining hollow fibers, as scaffolds applied in combination with human bone marrow stromal cell that helps in initiating natural bone fixation and reconstruction In comparison, the nano-fibrous composites possess similar structure to natural bone extracellular matrix ECM and they can take secondary stimuli to the cultured cells. The electro-spinning is the process, that represent simple and versatile technique used for fabricating extremely thin non-interweaved fibers whose diameter is in nanometers to microns range Furthermore, in bone regeneration electro spun fibers are assumed to play a role in sustaining mechanical properties, still as allowing bio-degradability, and acting as a real osteoconductive scaffold after addition or being coated by ceramic particles 54, C Hydrogels: Hydrogels are another class of scaffolds that commonly used for tissue engineering applications.
Hydrogels, such as fibrin, hyaluronic acid and Pluronic F, have shown promising result for effective growth factor delivery As reported by Dhillon et al. This scaffold system has recently demonstrated to assist bone repair in vivo in a murine calvarial defect model However, there are drawbacks to use hydrogels for bone regeneration as they have low mechanical strength, which can hinder their individual use as bone replacements D Injectable Microspheres: Amorphous PLGA copolymers are suitable for biomedical applications, as provides a more homogeneous dispersion of the active species in the polymer matrix Recently, negatively charged inorganic HA nanoparticles were assembling together with positively charged PLGA microspheres dispersed in deionized water to create a cohesive colloidal gel This material was held together by electrostatic forces that may be disrupted by facilitate extrusion, moulding, or injection.
These used in a multitude of ways, from developing screws for bone fixation 61 - 63 treating periodontal pathogens 64 and producing buccal mucosa 65 or indirect pulp-capping procedures 66, PLGA can be used in periodontal treatment, for better local administration of antibiotics and to decrease the systemic side effects of general antibiotic delivery 68 in the form of PLGA implants, disks 69 , and dental films In addition, gel composite fabrics of PLGA used in bone regeneration 71 , as high degradable PLGA and SiO 2 - CaO gel nonwoven fabrics that exposed to simulated body fluid for 1 week led to a deposition of a layer of apatite crystals on their surface Granular composite of gatifloxacin-loaded PLGA and b-tricalcium phosphate is local delivery means in the treatment of osteomyelitis, as the composite managed to deliver gatifloxacin slowly and showed sufficient bacterial activity in vitro against Streptococcus milleri and Bacteroides n fragilis , microorganisms responsible for osteomyelitis.
Also, after only 4-week implantation GFLX-loaded PLGA and TCP managed to significantly reduce the inflammation and support the osteoconduction and vascularization of the treated sites in rabbit mandible Moreover, sterilized PLGA scaffold is a promising material for producing tissue engineered buccal mucosa Additionally, PLGA composites with bio-ceramics can be used in direct pulp capping 74, either by incorporating growth factors into PLGA micro particles or by direct pulp capping with PLGA composites of mechanically exposed teeth.
However, no hard tissue in direct pulp capping with PLGA and pulp necrosis was evident due to the low adhesion of PLGA to the pulp despite the biocompatibility shown in cellular test. Therefore, PLGA composites with bio-ceramics remain a better option than PLGA alone in pulp capping, with better tissue response as compared to calcium hydroxide The promising results of the PLGA materials suggest the need for further studies mainly in the domain of delivery of substances to the dental tissues or concerning the pulp capping abilities exhibited by the PLGA composites.
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PCL became commercially available and various efforts required in order identifying synthetic polymers that can degrade with the help of microorganisms PCL is hydrophobic water fearing and semi-crystalline in nature; its crystallinity decreases with increase in molecular weight. Therefore, during the resorbable-polymer-boom, in s and s, the PCL and their copolymers were extensively used in variety of drug-delivery devices. Several advantages of PCL such as: its degradation kinetics and mechanical properties can be tailored, ease of shaping and manufacturing allows suitable pore sizes that are favourable to growing tissue and permits the controlled delivery of drug encapsulated within their matrix.
For enabling favourable cell response functional groups added, that provides the polymer more hydrophilicity, adhesiveness, or biocompatibility. The medical device industries were eager to replace metal devices such as plates, screws, nails, etc. Additionally, both the medical device and drug-delivery community accounted that faster resorbable polymer also had fewer percieved disadvantages corresponding to the long-term degradation the degradation time for PCL is around 3 - 4 years and intracellular resorption pathways.
A comeback of PCL has propelled back into the domain of biomaterials with the rise of a new field, specifically tissue engineering. In fact, PCL can be used in wide variety of scaffold manufacturing technologies and its comparatively economical manufacturing routes, as compared to other aliphatic polyesters, is highly advantageous.
It has been use in conjunction with other polymers such as cellulose propionate CP , cellulose acetate butyrate CAB , polylactic acid PLA and polylactic-co-glycolic acid PLGA for influencing the release rate of drug from microcapsules The compatibility of PCL with different polymers relies on the ratios involved and is mostly use to have better command over the penetrability of the delivery systems. PCL copolymers can be made using several monomers, e.
Biodegradation: PCLs can be biodegraded with the help of bacteria and fungi that are outdoor living organisms, but they cannot biodegrade in the bodies of animal and human because they have the lack of suitable enzymes It is broadly accepted that hydrolytic degradation of poly -hydroxy esters begin through either surface or bulk degradation pathways. Surface degradation or erosion implies the hydrolytic scission only at the surface of the polymer backbone This situation appears when the rates of hydrolytic cleavage of chain and the making of oligomers and monomers, which disperse into the surroundings, is rapid than the rate of water intrusion into the polymer bulk.
This generally results in thinning of the polymer with respect to time without influencing the molecular weight of the inner bulk of the polymer, which would usually remain unchanged over the period of degradation When the water enters the entire polymer bulk degradation occurs, that because the hydrolysis all over the entire polymer matrix due to random hydrolytic chain scission, an overall reduction in molecular weight takes place. When the water molecule diffuses into the polymer bulk, hydrolysis of the chains enables the monomers or oligomers to diffuse out of the polymer bulk, slowly erosion will occur and equilibrium for the diffusion - reaction would attained.
The internal autocatalysis was provoked by the degradation mechanism through the carboxyl and hydroxyl end group by-products when the equilibrium of diffusion reaction was disturbed. Because the surface oligomers and carboxyl groups may freely diffuse into the surroundings during the surface erosion condition , while in the case of bulk degradation an acidic gradient can be produced in the form of the newly generated carboxyl end group formed during the cleavage of ester bonds by the internal concentration of autocatalysis products.
This, in turn, increases the internal degradation as compared to the surface, resulting in as an outer layer of higher molecular weight skin along with a lower molecular weight, degraded, interior. When the internal oligomers become small enough that quickly diffuses via the outer layer, followed by the beginning of weight loss, and decreased rate of chain scission producing a hollow structure having the higher molecular weight.
The quick release of acid by - products and these oligomers can result in inflammatory reactions in vivo , as described in the literature of bioresorbable device In addition to poor vascularization or low metabolic activity, local and temporary disturbances may arise to the surrounding tissue unable to buffer the pH change this has been observed from an example of fiber-reinforced PGA pins used in the orthopedic surgery due to which osmotic pressure is increased by the local fluid accumulation at the time of rapid degradation The homopolymer PCL takes total degradation time of 2 — 4 years depending upon the initial molecular weight of the device Various other studies on degradation using PCL in different in vitro saline and in vivo rabbit conditions describes that both the rates of hydrolytic degradation were similar, and thus concluded that involvement of enzymes was not a significant factor in the first degradation phase that is 0 — 12 months in the process of degradation Ali and coworkers 90 studied the mechanism of in vitro degradation of PCL with the help of gel permeation chromatography, differential scanning calorimetry and scanning electron microscopy.
Persenaire and coworkers 91 suggested mechanism of two-stage thermal degradation of PCL and it was observed in the first stage that there was a statistical breakage of the polyester chains through pyrolysis reaction of ester. Sivalingam and coworkers studied the thermal degradation in two ways in bulk and solution 92 and observed that the polymer degraded by random cleaving of the chain and specific cleavage of chain at the end in solution and bulk, respectively. Pitt and coworkers displayed that, the in vivo degradation mechanism of PCL, PLA and other copolymers was qualitatively.
The rate of degradation of random copolymers was higher as compared to those of the homo polymers under same conditions The degradation kinetics of PCL extremely depends upon the molecular weight of the polymer. The structures having high molecular weight take more time to degrade, as moderated through the length of the polymer chain.
Recently Sun and co-workers outlined a long-term study in which degradation of PCL in vivo observed in rats for 3 years In rats, for the detection of the rates of distribution, absorption and excretion of PCL, radioactive labelling was use. The molecular weight of PCL reduced linearly with respect to time. The first radioactive tracers detected after 15 days of implantation in plasma. Simultaneously, radioactive excreta recovered from feces and urine. Pulkkinen 98 and his coworkers manifested that PCL linked with 2,2-bis 2-oxazoline also known as PCL-O was degraded enzymatically in vitro through surface erosion, which allows the novel use of PCL-O for drug delivery system and various other medical applications.
The in vivo evaluation of the rate of degradation, erosion causes weight loss and toxicity of PCL-O poly ester-amides was done. After 12 weeks of an implantation, weight loss of polymer discs was observed up to NMR, differential scanning calorimetry DSC and gel permeation chromatography GPC techniques also scanning electron microscopy SEM micrographs pre and post implantation were carried out and in vitro hydrolysis studies inclusively indicates the in vivo surface erosion of PCL-O polymers based on the enzyme.
The in vivo evaluation shows that the PCL-O polymer is highly compatible, safe and sensitive towards enzymes. The in vivo evaluation was base on the conclusion of the studies such as hematology, clinical chemistry and histology of the area and organs of the implantation such as heart, liver, kidney, brain etc. In the last a few decades more than papers being published the literature of the biomaterials and tissue-tissue-engineering, which used scaffolds, based on PCL, only a few researchers have mentioned the methods of the degradation and the kinetics of resorption of the scaffolds made of PCL PCL in Drug-Delivery Systems: PCL is suitable for controlled delivery of drug due to various advantages: high permeability for several drugs, excellent biocompatibility and it can completely excrete from the body once get bio-resorbed.
PCL is suitable for long-term drug delivery system expanding up to more than 1 year because the rate of its biodegradation is slower than that of other polymers.
PCL also has the capability of making compatible blends by using other polymers, which can influence the degradation kinetics; it can also ease the altering to fulfill desirable drug release profiles The rate of drug release from PCL based on factors such as the type of formation, techniques of preparation, the content of PCL, percentage, and size of the drug loaded within the microcapsules. Because PCL has higher permeability so it has mixed with other polymers for improving stress, resistance against cracks and for controlling the release rate of the drug.
In last few years, PCL have become a major area of research in order to develop controlled drug delivery systems mainly used for proteins and peptides PCL Applied in Tissue Engineering: An interdisciplinary field of science that use the principles of life sciences and engineering in order to obtain biological replacements that helps in replacing, retaining, or improving the functions of whole organs or tissues including bone, cartilage, and blood vessels is known as tissue engineering Certain structural and mechanical properties required by the tissues involved in the repairing process of tissues for appropriate functioning.
The term tissue engineering is also being involved in performing specific biochemical functions employing cells inside a support system that artificially created including an artificial liver, or pancreas. In tissue engineering, some powerful developments made that helps in yielding a unique set of implementation strategies and tissue replacement. Due to the low melting point, superior rheological and mechanical property, PCL has gain a lot of attention as biomaterial in cardiovascular and bone tissue engineering.
PCL is a biomaterial, which offers itself extremely well for the fabrication of scaffold. PCL is an extremely adaptable bioresorbable polymer and because of its accomplished rheological properties it can be utilized approximately by any of the polymer processing technology for producing wide range of scaffolds 6. The scaffolds are of supporting the attachment of cells, cell proliferation and in vitro differentiation and it can transplant in vivo.
There is a broad range of techniques used for manufacturing scaffolds for tissue engineering, but one should pay attention to the specifications of the scaffolds and for understanding the exchange of factors influencing the composition and design criteria of the material. The most advantageous characteristic of any polymeric scaffold implantable material will be co-ordination of degraded polymer by the substitution of the natural tissue produced by the cells. The kinetics of resorption and degradation of the scaffold are created to permit the implanted cells to increase rapidly and secrete their individual extracellular matrix in the dynamic and static cell-implantation stage that is from 1 - 12 weeks as associated with the scaffold slowly resorbs leaving enough places for cell multiplication and the growth of new tissues.
The 3D scaffolds were used to maintain the physical support till the time engineered tissues have adequate mechanical integrity to support it.
Chen et al. The following features are advantageous for scaffold candidates The growth of cells and transport of metabolic waste and nutrients requires 3-D and extremely permeable structures with having an interconnected pore network. The appropriate surface chemistry of biomaterials is required for the attachment, proliferation and differentiation of the cells. The mechanical property of biomaterial should match the properties of tissues at the implantation site. PLA and PLGA could have various biomedical applications such as in tissue engineering, drug delivery and biomedical devices due the good biocompatibility and bioresorbable property.
In addition, however the biopolymers have several biomedical applications a few chemical and physical modifications is required to improve the mechanical property to completely get absorbed into the implanted site. The development of modified and blended biomaterials to make it biocompatible and less crystallized is cost effective.
A few academic attentions are required for the development method to prepare bio-compatible bioplastics and application in other biomedical field for the next generation implantation. Int J Pharm Sci Res ; 9 2 : Article Information Sr No: 1. Download: Cited By: 0.
Role of Polymer Synthesis in Drug Delivery, Medical Device Manufacturing
Authors: K. Bano, R. DOI: Published: 01 February, Aliphatic Biodegradable Polyesters and Copolymers: 1. Biomaterials ; — Canadian Journal of Chemistry ; — Progress in Biomaterials ; 2: 8. Li S: Scaffolding in Tissue Engineering. Edition P. Not everyone knows what Polymer Synthesis is, but many have heard of new innovations in how drugs are delivered and absorbed into the body.
Thanks to polymer synthesis, implantable devices are administering consistent medications into patients who sorely need them; those with pacemakers are being spared from dangerous infections; and orthopedic pins, vascular grafts and sutures are possible. Polymerizations occur in many forms and are created through the repetitive chemical bonding of individual monomers. Assorted combinations of heat, pressure and catalysis alter the chemical bonds that hold monomers together, causing them to bond with one another. Most often, they do so in a linear fashion, creating chains of repetitive molecules.
Polymer synthesis has grown substantially over the past few years thanks to advances in drug delivery and the controlled release of therapeutic agents in constant doses over long periods. What is driving the market is the growth in chronic diseases, as well as advances in technology, combined with a better understanding of drug metabolism in patients.
Drugs to deliver insulin, anti-cancer or anti-infection drugs are being administered directly into the body through drug delivery devices. These devices help in expanding the effectiveness of the drug being delivered by controlling time, measurement, and place of arrival of the drugs in the body. Plastics created by polymer synthesis are enabling this form of drug delivery.
The devices can be conventional or implantable, such as infusion pumps. Infusion catheters such as valves, IV sets, needles, and cannulas are also used for drug delivery. It is used to make a variety of different products, which once implanted into patients, allows the active ingredients to be diffused over time throughout the body. They are used to deliver a number of medications to treat numerous conditions.