Now a days, biomaterials play a vital role and it is the recent advanced technology in biomedical engineering field in various medical applications.
For developing a biomaterials ,it should have some properties when we are implanting,drug delivery and tissue regeneration. It should includes biocompatibility, biodegradable and re absorbable. The quality of these polymers is characterized by narrow molecular weight distribution, low residual monomer content and minimal impurities and it is in well defined chemical structure. The Polyhydroxyester was the first developed biomaterials is used for suture, medical devices to implanting a bone plates when fracture occurs and to regenerate the tissue purpose.RESOMER® polymers are bioresorbable aliphatic polyesters comprised of a range of different ratios of Lactide and glycolide
monomers Poly lactic acid of stereo chemistry. , and end-group of functional. These degradeable homopolymers and copolymers of Lactide and Glycolic afford a variety of properties that range from very stiff, hard semi-crystalline materials with long degradation times, to softer, amorphous materials with faster degradation rates.
DEGRADATION
The presence of water leads to hydrolysis of the RESOMER® polymers. In the first step water wets the surface and diffuses into the polymer. The rate of the diffusion depends on porosity, pore size and surface tension. In the second step, ester linkage hydrolysis cleaves the chain into smaller chain lengths (polymer degradation).As the degradation proceeds, smaller chain segments (<100 g/mole), start to dissolve and polymer erosion takes place .The solubilized monomers/oligomers are then excreted via the kidney or metabolized into carbon dioxide and water.At the end of the process the polymer is completely absorbed and eliminated from the body. The complete disappearance of biodegradable polymers after the duration of their lifecycle (e.g., fixation or drug release) is a highly desired feature. The complete disappearance is an intrinsic characteristic of RESOMER® polymers due to the high water solubility of the monomers. In contrast, hydrophobic monomers of polyanhydrides tend to reside locally long after the polymer has degraded due to their poor solubility.
In addition to the inherent polymer properties, the final performance and residence time of a biodegradable device can be tailored by processing and introduction of copolymers or additives.Strong alkaline or acidic materials can enhance polymer degradation. The microclimate inside the polymers is a crucial factor for release and degradation processes.
An acidic microenvironment could also interfere with the performance of an incorporated drug.
IMPLANT FORMULATION
Several processing technologies can be applied to biodegradable polyesters to formulate coatings, implants, micro- and nanoparticles, or Nano - capsules.
Melt extrusion is one method that is utilized in the production of sutures and preformed implants. Moderate heat can be used to thermally process most RESOMER polymers.
A depot formulation is injected subcutaneously or intramuscularly and contains pharmacological agent which is released in a controlled manner over a long period of time. Recently, smaller sized dexamethasone-loaded PLGA intravitreal implants have reached the market to treat macular edema in the eye.
Microparticles are commonly used for the parenteral delivery of hydrophilic or hydrophobic drugs. The loaded microparticles are commonly prepared via spray drying, coacervation or emulsification with solvent evaporation. The drug is either solubilized or dispersed within the microparticle.RESOMER® polymers can also be formulated as nanoparticles or nano capsules. The primary administration route of the nanoscaled systems is intraveneous injection. The nanoparticles can be used for diagnostic purposes or the treatment of tumors. Other administration routes of nanosized polyesters are oral, dermal, pulmonal or ocular drug delivery. The use of oral administration PLA/ PGA based nanoparticles permits a localized delivery to inflamed tissue, decreases the side effects and increases the efficacy of the treatment.
PEGYLATION
Erosion commences once the molecular weight drops to ~7,000–8,000 g/mole, and occurs at a relatively rapid rate. However, PEGylated PLGA copolymers (PEG-PLGA) show both degradation and erosion without any lag time. Although erosion is faster at the initial stage, as expected for the more hydrophilic PEG-PLGA, PLGA reaches the final mass over a much shorter timeframe.
PEGylated RESOMER® has been used for the encapsulation of Bone Morphogenic Protein II (BMP II).13 The microparticles showed a tunable and controlled release profile and were able to induce bone formation in vivo after subcutaneous injection. PEGylated RESOMER® can be used also for the formulation of emulsifier free nanoparticles and nanocapsules. The particles are known to show long circulation times due to the stealth effect of PEG which reduces the interaction with the system. In conclusion, RESOMER® polymers are biodegradable and diverse materials for a wide range of applications. The development of PEGylated RESOMER® polymers offers new applications in the field of the Biopharmaceutics.
