Porous Silica | A Novel Drug Delivery System
Porous Silica | A Novel Drug Delivery System
Drugs have a optimum concentration range which they are most effective, in concentrations above or below this range the drug might be toxic or of no benefit at all.
In the graph above, the line in blue shows conventional drug concentrations, and the line in black shows the optimum concentration level. The trend in the industry is to move towards the black line, this will offer a potential solution to patient noncompliance and can be achieved through controlled drug release.
In many cases drugs lose their activity even before reaching their target. Ineffective targeting leads to drug loss and degradation. More than 40% of anticancer drugs being developed show aqueous solubility problems, this leads to poor absorption and low bio availability of the drugs.
To reduce harmful side effects, increase drug bio availability and the drug concentration in the required areas it is essential to develop novel drug delivery systems capable of targeting the right areas and giving the right release profiles.
Mesoporous Silica
Mesoporous materials represent one of the three types of porous materials classified by IUPAC as materials with a pore width between 2 and 50nm.
Mesoporous silica with a pore size of 2.0 50.0 nm is of great relevance for life science applications as most of the biological molecules and pharmaceuticals are within the order of a few nanometers. Recent advances in technology have made it possible to tailor the porosity and other properties of mesoporous silica, which make it particularly interesting as a drug delivery system.
These materials have very large surface areas (around 1000 m2/g) and pore volume, a particle size of 1 to 5m and can possess a variety of internal pore structures. In addition it is possible to functionalize their internal and the external surfaces with groups such as amines, thiol, etc.
As drug delivery vehicles, mesoporous silica offers significant benefits. Some of these are:
Controlled and sustained release
Targeted delivery
Increased drug solubility
Additionally, mesoporous silica is biodegradable and an approved food.
Loading and Release of Active | Use of functionalised surface
Drugs can be loaded into the Porous silica materials by selecting the right characteristics of a porous material in terms of their pore size, morphology and particle size. For encapsulation, the drug is dissolved and a mesoporous matrix is placed in the solution, followed by refluxing. Finally the loaded silica particles are separated by centrifugation or filtration.
Another method for loading a drug is by conjugating the drug with the internal wall of the pore. This is achieved by functionalizing the internal surface of the pore and leads to a covalent or electrostatic interaction with the drug molecule.
There are several factors that need to considered before loading a drug in porous materials such as pH, drug solubility, solvent, polarity, temperature and chemical nature of the drug under selected testing conditions to determine the most suitable loading protocol.
The release process is then carried out placing the drug-loaded mesoporous matrices into a solution and monitoring the drug concentration along the test time. UV spectroscopy and HPLC are the common characterization techniques used to follow the release profiles of the drugs from the porous structures.
Controlled Release | Mesoporous Silica
With control over the pore structure, it is possible to achieve different release profiles. Recent work shows that, more complex 3-Dimensional porous structures show very fast release of a drug compared to 2-dimensional cylindrical structures.
By combining particles with different release profiles, it is possible to tailor release profiles, offering a potential solution to patient non-compliance.
Targeted Delivery
With mesoporous silica, it is possible to conjugate the external surface of the particles with targeting agents, such as foliate. In the case of foliate conjugation, these particles can be targeted to the foliate receptors on tumor cells for anti cancer drugs.
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