Blog 6: Chitosan-based Micro- and Nanoparticle Systems

Mehdi’s Blogs

In this unit, we learned about two types of new materials: composite and natural. Of particular interest are natural materials that we can modify to fit our needs. These include proteins, polysaccharides, and polynucleotides. Natural materials have several benefits, among which the lower chances of immunorejection and the cheaper costs are key. In keeping with my theme,  I will discuss recent advances on chitosan-based micro- and nanoparticles for drug delivery.

Chitosan is a polysaccharide commonly associated and similar in structure to cellulose. An important difference between the two is the primary amine group on chitosan gives it special properties that are very useful in pharmaceutical applications. Similarly, unlike many other natural polymers, chitosan has a positive charge and is mucoadhesive. an important adhesive property that allows for prolonged duration of drug release. Chitosan is derived from chitin, which is naturally abundant and biocompatible but inert. When treated in a concentrated alkali solution, chitin becomes chitosan, a long-chain polymer that is reactive and can be produced in forms such as powdder, paste, film, fiber, etc. Chitosan is highly biocompatible with living tissues. It breaks down slowly to harmless amino sugars that are completely absorbed into the body. It is also nontoxic and can be easily removed without causing side-effects. In addition, chitosan is anti-microbial and known to absorb toxic metals. And finally, as mentioned, it has high adhesion and coagulation due to its muchoadhesive qualities.

With respect to nano- or micro-particles, Chitosan also has several advantages. (1) such particles provide controlled release, (2) don’t need toxic organic solvents since it can readily dissolve in aqueous acidic solution, (3) has a linear polamine that can be easily cross-linked, (4) its cationic nature promotes additional ionic cross-linking, (5) it is mucoadhesive, so it can readily adhere to the site of absorption. Added to these are chitosan’s numerous biocompatibilities and antimicrobial advantages

. Above are a list of chitosan-based drug delivery systems and the methods used to formulate them, as well as the drugs they were used to deliver. In this blog, I will discuss a couple formulation methods that I found interesting or valuable.

Emulsion cross-linking:

Similar to traditional nanoparticle formulation methods, water-in-oil emulision is prepared by emulsifying the CS aqueous solution at an interface with oil. A surfactant is used to decrease surface energy and stabilize aqueous droplets. This emulsion is then cross-linked with an agent to  harden the droplets. Based on the emulsification intensity, the size of the particles can be controlled; but size also depends on the extent of cross-linking agent used. Some drawbacks to this method are its tedious process and the use of the harsh agents that can chemically react to disrupt the particle morphology, if nothing worse. That said, the method is cheaper and a proven technique. It is shown below in a diagram:

Spray-drying

This is a common technique to produce powders, granules, or agglomerates from a solution mixture of drug and excipient. First, chitosan is dissolved in acid, dispersed in solution, and cross-linked. A stream of hot air is then used to atomize the solution. This leads to small droplet formation; the solvent evaporates instantaneously, revealing free flowing particles. Basic parameters, such as the size of the nozzle, spray flow rate, atomization pressure, air temperature, and again, the extent of cross-linking all can be controlled to precisely determine size. 

Reverse Micellar Method

The micelle method is also one that we briefly covered in class. Reverse micelles are highly favorable because they are thermodynamically stable mixtures of water, oil, and surfactant arranged  in an amphiphilic way. Unlike normal micelles, reverse micelles have an aqueous core; they are  “homogenous structures at a microscopic scale in aqueous and oil micro-domains” separated by surfactant-rich films. This aqueous core can be used as a nanoreactor. Because the particles are highly monodispersed, reverse micelles will produce fine nanoparticles. While vortexing in this mircroemulsion phase, chitosan and drugg are added, and a cross-linking agent follows.

In addition to particle formulation, drug loading in these systems can be done during preparation or after. The drug is either embedded in the matrix or adsorbed on the surface. Both have advantages and disadvantages: maximum drug loading is achieved when added during formation, but adding on the sruface protexts the durg from being affected by formation parameters.

Finally, drug release from chitosan systems either (a) releases from the surface of the particles, in a burst effect; (b) by diffusion through the rubbery matrix, caused by water penetrating the system, transforming it into a rubbery matrix, and allowing the drug to diffuse through in an initially slow but later, rapid release profile; (c) due to erosion of the system, followed by rapid release.

Overall, chitosan has been proven to be a safe, biocompatible, and advantageous material to use in pharmaceutical applications. The study of chitsan-based nano- and micro-particle systems shows a lot of potential for being new solutions to the table in the future!

Source:

Agnihotri, Sunil A, Nadagouda Mallikarjuna, Tejraj Aminabhavi. “Recent advances on chitosan-based micro- and nanoparticles in drug delivery.” Jounral of Controlled Release, 2004.

Mehdi’s Blog

Post 4:

Intro:

Made up of oxides, carbides, phosphates, metal carbonates, and metalloids such as calcium, titanium, silicon, etc., ceramic nanoparticles provide an alternative source material from traditional organic polymers. Thomas et. al. say that ceramic nanoparticles are among some of the best carriers of drugs, genes, proteins, and other common uses for nanoparticles. This is because of developed techniques that have been able to control to an extent the size range, surface properties, porosity, surface area to volume ratio, and other characteristics that make ceramic nanoparticles suitable for use as drug delivery systems.

Some background:

Ceramic nanoparticles are those materials whose properties lie between metals and non-metals. As a results, they have low electrical and thermal conductivity (like non-metals), high elastic modulus (like metals), and resistance to corrosive environments. Like all the materials we’ve covered, these properties are a result of the strong ionic bonds between the molecules that make up a ceramic. Right away, ceramic nanoparticles have an advantage in that they can easily be prepared in the right size, shape, and porosity. Ceramics also have high stability, high loading capacity, easy incorporation of hydrophobic and hydrophilic systems, and do not undergo swelling or changes in porosity with change in pH.

SEM image of Silica raspberry particles

Because this article reviews several inorganic materials, I will focus on one ceramic that we briefly mentioned in class: calcium phosphates, such as hydroxyapatite. In class, we learned that calcium phosphates are natural and found in calcified vertebrate tissues. In particular, hydroxyapatite has a similar chemical structure to bone mineral, and as a result has high biocompatibility. We classified it as an osteoconductive and osteointegrative material, which means that it is very bioactive and has an affinity for proteins and bone cells that allows it to integrate and adhere to bone material. According to Thomas et. al., calcium phosphates have advantages in that they can deliver drugs in minimally invasive ways (such as orally or through inhalation), are easy to formulate, take longer to biodegrade (calcify and conduct bone tissues), are stable under temperature and pH variations, can have enhanced bioavailability and compatibility during formulation, and most importantly, possess the same chemistry, crystalline structure, and size as their most commonly targeted tissue: bone. Though other materials such as tricalcium phosphates are used, their properties are distinct: based on different ratios of calcium to phosphate, the physical and mechanical properties of these ceramics shifts from amorphous to crystalline, stable to unstable at room temperature, and rapid to slow hydrolysis. Thus, hydroxyapatite is considered the best choice for sustained drug delivery.

Methods of Synthesis:

Hydroxyapatite nanoparticle structures: SEM and TEM

Because they are crystalline ceramics, Hydroxyapatites are most commonly synthesized through wet chemical precipitation from solution. As we learned in class, precipitation is the simple chemical reaction that produces crystal growth. The reaction of calcium hydroxide with hydrogen phosphates yields nanocrystals of hydroxyapatite. But as we learned in class, crystallization is highly vulnerable to changes in reaction conditions. These can be used to our advantage: through careful control of pH, reaction temperature, reactant addition rate, and other factors, produces specific desired nanoparticles of sizes typically under 100nm.

Another method of synthesis is shared by lipid nanoparticles: surfactant based emulsion. Through this, two immiscible liquids such as water and oil are agitated under the presence of an amphiphilic surface-active agent to disperse the water phase into an oil phase. This causes the formation of reverse micelle microdroplets that provide geometrically restricted regions for the synthesis of nano-phase materials. The microemulsion of of aqueous cyclohexane and phosphoric acid with the organic phase of calcium nitrate and surfactant produced hydroxyapatite particles between 30 to 50nm with needle and spherical morphologies. While it produces excellent morphology with little agglomeration, microemulsion results in low yields.

A final method I will discuss is the sol-gel process, a soft chemistry path that converts metal alkoxides into amorphous gels through hydrolysis and condensation reactions. These are then turned into ceramics by heating at low temperatures. Benefits of the sol-gel method compared to conventional techniques is a higher chemical and structural homogeneity, because there is molecular-level mixing of the calcium and and phosphorous precursors. The main disadvantage is the side hydrolysis of phosphates.

Applications of Calcium Phosphate in Drug Delivery:

As we discussed in class, hydroxyapatite finds its best uses in the treatment of bone diseases such as osteoporosis. This is due to its uniquely crystalline structure and its natural associations with bone tissue, as I mentioned earlier. Slowly, hydroxyapatite formulations are being explored for the treatment of cancer and other diseases as well. Delivery systems of hydroxyapatite particles are able to extend drug release do it the material’s low degradation rate and high biocompatibility. Furthermore, hydroxyapatite is easily linked with other materials that can reinforce its therapeutic effects and drug release. Previous work has shown that Amoxicillin loaded iron doped particles or superparamagnetic iron hydroxyapatite  nanoparticles possess excellent biocompatibility. Furthermore, they cause greater osteoblastic cell proliferation when exposed to a static magnetic field. As we discussed in class, hydroxyapatite makes for ideal scaffolding material because of its high integrative ability. As a result, super-paramagnetic responsive nanofibrous scaffolds have been shown to produce accelerated bone formation in rabbits. Hydroxyapatite can be combined with magnetite or silica to create pH responsive, “smart” drug delivery systems. Similarly, nanoparticles can be grafted with poly(N-isopropylacrylamide) to produce thermal-responsive, smart delivery systems with enhanced bioactivity.

Biomimetic Hydroxyapatite-containing composite Nano-fibrous scaffolds for bone tissue engineering

These examples are just a few related to one class of inorganic nanoparticles of a large group of materials that holds exciting potential for the field of drug delivery. Thomas et al. says it best: “Ceramic nanoparticles hold the promise of better, safer, and cost- effective drug delivery agents in future of biomedical science.”

Thomas, Shindu C. et. al. “Ceramic Nanoparticles: Fabrication Methods and Applications in Drug Delivery.” Current Pharmaceutical Design, vol 21, 2015.

Hi everyone, welcome to my blog #3.

Given that our two lectures this week concerned a) nanoparticles and b) patenting, I thought I’d look into a curious situation in the current scientific community over a development in nanoparticle synthesis: the use of the PRINT technique.

PRINT, or Particle Replication in Non-wetting Templates, was a clever idea implemented by the DeSimone research group at UNC Chapel Hill. In order to better determine the shape of their synthesized nanoparticles, they used a 3D printed elastomeric mold comprised of a low surface energy perfluoropolyether network. This allowed scientists to, for the first time, produce with control monodisperse and shape- and stereo- specific nanoparticles.

To recap: traditional polymeric nanoparticles are made from the sonication of mixed solvents. This is an inexpensive technique, but what scientists save in money they lack in control.  Sonication results most often in basic spherical nanoparticles. Sometimes, and often randomly, other basic shapes can be achieved through combinations of different materials, temperatures, pH, and solvents. But an increasing body of literature points to the advantages of formulating specific or complex shapes for certain targets: rod-shaped nanoparticles extravasate into tumors better than spherical nanoparticles. But there is little literature about a reliable way to formulate specific polymeric nanoparticle shapes. Even what literature exists concerns specific molecules, and is not easily generalized. Certain nanocarriers currently achievable are liposomes, dendrimers, micelles, and polymeric particles.

Instead the PRINT technique uses a template to produce exact sizes, shapes, compositions, and surface functionality. This was revolutionary, because it allowed precise loading of delicate cargos in formations, shapes, and functionalities that would maximize their extravasation into tumors. Scientists in the DeSimone group used elastomeric solids that enabled high-resolution imprint lithography, applying a technique commonly used in microelectronics. PRINT is analogous to the mass production technologies used to create nanoscale devises, transistors, and microprocessors. Thus, it is a truly engineered drug delivery approach, providing scientists simultaneous control over every parameter that influences succesful drug delivery. Further, the lithography of PRINT allows for replications of the master template in order to create homogenous and monodisperse particles. The master template also allows complete control over particle shape. Geometries such as spheres, cylinders, discs, and toroids can now be reliable formulated with precise ratios.

The matrix formulation is also successful with a variety of organic materials, including albumin, hydrogels, PLLA, PLGA, and more. This formulation can be carefully altered in order to control such specific characteristics as porosity, texture, and modulus of the particle. Further, because it is highly compatible, PRINT is open to straightforward incorporation of cargo: hydrophilic or hydrophoboic, biologicals, peptides, proteins, oligonucleotides, siRNA, contrast agents, radiotracers, and fluorophores. Even more, the exact concentrations of such cargos can be chosenfor specific needs, since PRINT doesn’t rely on the trapping of particles during fabrications, as in the case with liposomes and micelles. Finally, surface functionalization can be modified through the matrix composition or postfunctionalization with moieties: surfaces accommodate targeting peptides, antibodies, aptamers, avidin/biotin complexes, cationic/anionic charges, and “stealth” PEG chains for steric stabilization.

The DeSimone group claims that theirs is the only current technology that can independently design and control each of these attributes to create truly engineered nanocarriers for drug therapies. For the first time, nanoparticles can deliver drugs with precises paramters of bioavailability, biodistribution, and targeting. There is enormous potential. So what did the DeSimone group do? Put a lock on any use of PRINT outside of their lab. For the duration of the patent, from 2007 until this year (they are trying to currently extend), only the DeSimone group has access to PRINT technology.

Their exact claims are rather interesting: as we now know, inventors take liberties in the “claims” section of the patent. Here, they can stretch the “uses and implications” of their invention as much as they which—given that others may contest exact nuances later. Some of the claims made by the DeSimone group are that their patent explored the idea of a method that forms a nanoparticle from “a patterned template and a substrate,” “disposing a volume of liquid material in…the patterned template” or a “plurality of recessed areas,” and “forming one or more particles by…contacting [a] patterned template surface with the substrate.”

Labs around the world that might want access to such technology to explore the implications of drug delivery are still left trying to approximate the current techniques for formulating specific nanoparticles, which have experienced little progress aside from DeSimone’s PRINT technology. The patent has also prevented other labs from testing the limits of this technology; we do not know yet if it is sustainable, although some suspect that in practice, such a technique would end up far more expensive than current sonicating techniques. Overall, there continues to remain a small gap in the literature concerning the issue of nanoparticle shape. While most labs have gotten around the problem by working with materials that already have defined and useful shapes, or else settling for spherical nanoparticles that have a lower rate of extravasation. There is much work to be done in determining a cost efficient and easy way to manipulate the shapes of nanoparticles and take advantage of the full potential of nanoparticle drug therapeutics.

Gratton, Stephanie E.A.. “Nanofabricated Particles for engineered drug therapies: A preliminary biodistribution study of PRINT nanoparticles.” Journal of Controlled Release, 2007.

Mehdi’s Biomaterials Blog: Post 2

9/29/18

This week, we learned about nanoparticle drug delivery systems, as well as certain drawbacks and limitations scientists are facing in translating implement the vast research in clinical trials. A quick recap: nanoparticles are exciting because of their relatively huge surface area compared with microparticles or other bulk materials. Thus, while nanoparticles intrinsically don’t have any currently known novel properties, their formulations with other compounds and polymers hold great potential for drug delivery. Nanoparticle systems are created solely for the purpose of clinical use: the important factors that need to be considered are how a system reduces drug dosage, improves efficacy and safety, drug solubility, etc.

Within the field of drug delivery, targeted drug delivery to tumors holds the most intriguing place among the scientific community. The majority of drug delivery articles have been posted about this. This is because nanoparticles are intrinsically able to permeate and be retained inside the tumor microenvironment; likewise, their accumulation inside the tumor is vastly increased simply by increasing blood circulation time. However, recently there has been a general disappointment among the scientific community over the prospect of actively targeted drug delivery. This is because of the poor statistical efficiency of such drug delivery systems: less than 10% of the dose actually reaches the tumor, such systems are too dependent on passive permeation into tumor environments, and each system takes an unsustainably long and individualized time to create.

Thus, scientists have began to focus specifically on those biologically dynamic factors that every intravenously delivered nanoparticle system inherently depends on: the physical (temperature, light, magnetism, electricity), chemical (pH and ions), and biological (enzymes, antibodies, small molecules) components that nanoparticles drugs would encounter in the tumor microenvironment.

Enter: Smart Nanoparticles

Smart nanoparticles have been engineered to respond to factors such as ultrasound, light, and temperature. After delivery, UV or radiofrequency waves are used with high spatial and temporal resolution to enhance extravasation of drugs to the interstitial space. This has allowed various liposome and micelle formations to form  chains and multivalently stick to tumors; alternatively, the nanosphere shell has been split open to fully release the drug to the entire volume of a tumor site. Further, using ultrasound for about 20min induces tumor vessels for maximum extravasation to nanoparticles; further heating results in very fast release of the drug from the nanoparticles.

However, these developments also come with limitations: a chain of specific events needs to happen for this highly efficient drug delivery, including precise temperature changes for example that are simply unrealistic in a large system such as the human body.

The article concludes by admitting that scientists have been complacent in their design of nanoparticle formulations. The current design is based on the passive EPR effect, even though most publications assert that the drug delivery through EPR is marginal at best. As a result, very few nanoparticle formulations have been translated to clinical trials, despite their potential. Mouse studies are simply too disconnected from clinical practice. This makes me recall Professor Gonzalez’s stress on human centered design. Perhaps the scientific community is approaching the study of nanoparticle delivery to tumors inefficiently by focusing on mouse models. For over two decades, the EPR effect has been considered the primary focus of drug delivery. Perhaps now it is time to examine the advantages of nanoparticle drug delivery systems with respect to the human body first.

HI, WELCOME to my blog on biomaterials and their applications!

I chose to take this class (and major in Biomedical Engineering) for the vast applications of biomaterials I saw in translational medicine at local and global scales: global health, particularly in conflict-ridden zones such as Yemen, Syria, or parts of Pakistan, is certainly a passionate concern of mine.

Further, I joined the Zhou Lab here at Yale, where I was able to work firsthand on creating nanoparticles from different polymers in order to target the blood-brain barrier to treat glioblastomas.

THUS,

I have formed a tentative theme for my blog throughout this course. Broadly, it is the intersection of biomaterials, nano-medicine, and global health. I will aim to highlight specific advancements in drug delivery and nano-scale technologies that have held large-scale implications around the world. Alternatively, I will also examine biomaterials technologies other than nanoparticles that have already benefited crisis and conflict-ridden areas, and the challenges in budget, scale, design, and effectiveness they faced in successfully reaching victim populations. Together, by the end of this course, I hope to have a collection of resources and blog posts about the global health implications of biomaterials technologies, especially within nano-medicine.

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