The Half Decent Pharmaceutical Chemistry Blog

These days there are many innovative drug delivery systems but none of them are as customisable as liposomes.

In the sixties, it was observed that when phospholipids are introduced in water, microparticles (smaller than 10 µm) tend to form. These particles are actually vesicles, a bilayer membrane containing a liquid solution: an ideal environment for many drugs.

Obviously the phospholipids can be chosen among an incredibly wide spectrum: the base bound to the hydrophilic head as well as the length and number of double bonds of the lipophilic part can all vary, in order to optimise the characteristics of the vehicle.
The great thing about liposomes is that they are 100% biocompatible and, thanks to their size, can be injected.

Very practical. A liposome can not only carry hydrophilic substances, but lipophilic molecules too: these drugs will interact with the lipophilic chains of the phospholipids. Amphiphilic substances, unsurprisingly, can be easily loaded in a liposome as well.

So many options lead to four different kinds of release: a drug can diffuse away from the vesicle, pass in the aqueous medium and finally enter the target cell following its gradient. The liposome can undergo endocitosis. Whenever the drug tightly binds to the phospholipids, this can be introduced in a cell through lipids exchange between liposome and cell. Finally, a liposome can release its content in the cell as a result of a membrane fusion.

Like the membrane of our cells, cholesterol can be introduced in order to achieve the optimal fluidity of the vesicle. But, in this case, what cholesterol does is actually to reduce the fluidity and increase the stability of the vehicle.
This requires a lot of care: you see, for each liposome made from a unique type of phospholipid there is a temperature (called main transition temperature) which has to be accurately known before we add cholesterol.
In fact, if we work below that temperature, the lipids will behave like a tough gel and the insertion will go terribly wrong: cholesterol will interact with the hydrophilic heads solely and disturb the order of the membrane, making the vesicle too fluid and permeable.
On the contrary, when the temperature is raised above the main transition temperature, we end up with liquid crystals. Cholesterol can therefore move freely and find its normal position in the bilayer membrane.
Generally up to 50% of cholesterol can be added.

In a nutshell, all you need to synthesize liposomes are water, the right quantity of cholesterol and the correct ionic strength. And make sure you’re working above the main transition temperature of your phospholipids(s)!

There are four types of liposomes, according to their size: SUV (small unilamellar vesicle), LUV (large unilamellar vesicle), MLV (multilamellar vesicle) and MVV (multivesicular vesicle). 

LUVs are my favourite ones (fortunately I had the opportunity to talk about them during my last exam): they are simply perfect delivery systems. Larger than SUVs, they can be loaded with higher doses, but, because they are still unilamellar systems, they are synthesized using a rather simple technique called solution casting (which yields MLVs), followed by high pressure extrusion (according to the diameter of the pores SUVs or LUVs can be produced). 

Solution casting begins with lipids destroyed by solvents such as dichloromethane or chloroform. This operation is carried out in a round-bottom flask: the solvent is then rapidly evaporated, leaving a film of phospholipids on the inner surface. An aqueous solution of the drug is added and, to increase the chances of yielding vesicles, glass microspheres are also employed: vesicles should form spontaneously, as the system tries to minimize its energy, but to increase the yield, you have to work this way. 

My favourite thing about LUVs, however, is one of their applications: the so-called stealth liposomes. Thing is, liposomes work wonderfully when it comes to endogenous physical targeting: pH-dependent, temperature-dependent and immunoliposomes are all valid vehicles, but stealth systems really rock.

PEGs cover the vesicles: as a result, the half-life is dramatically increased, because the immune system is unable to detect it. Stealth liposomes have been successfully used to parentally administer doxorubicin hydrochloride.Last but not least, liposomes are probably the best choice as carrier in non-viral gene therapy.

Not everything about molecular biology is enjoyable. In particular, it’s full of silly acronyms and abbreviations that highlight an awful lack of imagination of those who firstly named the protein or sequence. The TATA-box, just to considered something well-known by everyone who had to do with molecular biology at some point, was named after the mere sequence of nucleotides (T-A-T-A-A-A-A). How banal is that?!

Molecular biology, however, isn’t the only place where ugly abbreviations are frequently found. These days it looks like a general trend.  No doubt, they are easy to remember and, sometimes, not too complicated to interpret.

In the past, on the other hand, scientists generally had a much broader general knowledge, knew decently about literature and, in my opinion, were wittier and more handsome. So, they were capable of finding much catchier acronyms, abbreviations and names for what they discovered.
Yeah, that was pioneer science, but I’d still like to see some lunacy in the articles I read.

Nowadays, nobody would look to the Bible for a name. That is exactly what Marcus Reiner did when wanted to name a number he proposed to express the fluidity of a material: this was the Deborah Number.

Don’t think, anyway, that this value is something that has to do with rheology only. Swelling-controlled drug delivery systems utilize the Deborah number to check the kinetics that regulates how the drug is released.
In this case, the Deborah number fulfils the vital role of linking the rate at which water enters in the polymeric shell with the relaxation of the polymer. In this context, we define the Deborah number as the ratio of the relaxation (t_c) and diffusion time (t_p). For example, When De is higher than 1, the system will have a Fick-type kinetics, as diffusion is the limiting agent (the polymer has rubbery state, but hasn’t swollen).

The interesting thing about swelling-controlled systems is that they can release the active substance with zero order kinetics and are rather easy to yield.
First, the polymer has to be an hydrogel: these materials can absorb great quantity of water without dissolving, as they aren’t linear chains but show an intricate, cross-linked structures. pHEMA, PVA and chitosan can all be employed to make the outer shell.
The polymer is put in a beaker with water, the content of the core (i.e. a drug), and a radical initiator.
EGDMA is finally added in a such a quantity that, considering the HEMA/EGDMA ratio, we yield the porous structure we need.
As the final product is immerged in water, the structure begins to swell and widen because water lowers the T_g (glass transition temperature) below 37°C. Large pores appear and what is in the core starts to come out of the system.

It’s time, once again, to crack food but, on this occasion, I’m going to give you a really useful, practical tip for preparing a lovely appetizer, which looks perfect for a summer, sunny dinner. You see, if there’s something an industrial pharmacist knows well, it’s how to mix stuff.

Imagine you spent an entire day on the beach and forgot to switch on your mobile. At the end of the afternoon, on the way to your house you check your messages and realise your friends are coming and they want to try your famous Habanero Prawn Cocktail. Although you have all the ingredients, you’ll still have no time to prepare the Cherry Tomato Emulsion that goes with it.
“Oh no!” you think “They are coming! What a shame: I’ll disgrace myself!”

But don’t worry, lad, because I’m here with the perfect solution for you: the ultimate, most powerful mixer you could possibly choose to prepare an emulsion (or suspension). Besides the fact that it’s a savagely potent machine, the great thing is that we’re not talking about a huge reactor or something like that. Actually, it’s rather handy.
What you need in such a desperate situation is simply a sonotrode.

Basically, this machine consists of an ultrasounds generator, a linker arm (often made of titanium) and the sonotrode itself, immersed in what is going to be our final suspension/emulsion. This element is a piezoelectric ceramic flat washer.

The engine works at very high frequency (20-30 KHz) and generates up to 500 V. Generally, the machine is set to work at 20 KHz, which is the frequency of elastic vibration of ceramic.
The washer vibrates, inducing a high frequency of strong impacts (expansion and compression) in the liquid.

These days, the sonotrode is often placed in a slightly bigger mould, yielding a few micrometers wide space where the material undergoes this dramatic series of impacts between the vibrating sonotrode and a probe.
The energy of the system is therefore rapidly increased and that is exactly what you need to yield a stable emulsion.

Last but not least, sonotrodes are used in pharmaceutical factories more and more because of a phenomenon that often occurs in a suspension where a sonotrode is operating: cavitation.
Briefly, an air bubble trapped in the dense, viscous material suddenly reaches 5000°C and a mind blowing pressure of 5000 atm (for a very short amount of time, of course) due to the energy delivered through the vibration of the piezoelectric washer: as a result the bubble implodes.
This not only reduces the chances of finding nasty air bubbles in the final product (that might ruin everything) but, amazingly, it works nicely for bacteria too, helping sterilize the emulsion.
So, there you are: if you go on holidays, always remember to bring a sonotrode with you!

Live Earth, the absolutely useless, pointless, eco-friendly, non-sense mega event, is finally over so today, I guess, we can go on polluting and heating the plant as usual, right? Before I kick things off properly let me explain why I dare criticize yesterday’s massive parade. Obviously I am not saying global warming doesn’t exist or doesn’t represent a concrete threat to mankind. What I can’t stand, though, is hypocrisy: watching all those celebrities (most of the performers where rubbish, although I enjoyed some good ones, but, you know, I watched it for nothing more than 30 minutes…) brainwashing me, endlessly saying how much of a polluter I’ve been so far and how I’ll have to behave from now on, showing off, on the other side, their commitment to the cause…sorry but that made me sick. Literally, I couldn’t bear it so I don’t know what kind of breakthrough plan Madonna might have unveiled, once she, as well as most of the people there, had promoted her new single/video/album/whatever or simply herself.

I’m sorry but I have better things to do that listening to someone who, having bought a hybrid car or thrown a can in a recycle bin, believes to have seen the light and saved the planet.

I just have a couple of questions: how many of the people involved in the shows actually DO NOT own a SUV? How much carbon dioxide was produced by the means of transport the audience chose to reach the arenas where the concerts took place?

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It’s time to show some more nice pictures (not animated, unluckily) that display how a pharmaceutical plant looks like. For no particular reason I’ve decided to talk about boilers…

Steam still plays a key role in modern factories. There are actually two types of vapour utilized to transport thermal energy: grey and white steam.
The former is generally used for heating the plant itself, for supplying energy to a variety of different kinds of machines (technical steam) and for the producing the white one. It contains traces of oil, electrolytes and many more. Condensing it yields a water which is too dirty to be utilized in the manufacturing of any pharmaceutical product.

There are two main types of boilers that  yield grey vapour: smoke- and water-tube boilers.

Horizontal tubes pass in a huge cylinder filled with “dirty” water in a smoke-tube boiler. The smoke produced by the combustion heats the water.
This system, unfortunately, due to physical properties of smoke, needs two-, three-, four-ways tube, so that most of heat we gained is utilized (at least 90% of the heat of combustion). Moreover, these structures have a rather limited pressure tolerance.

Certainly water-tube boilers are much more reliable and efficient but complicated.

The main tubes run vertically through a huge chamber where combustion takes place: this directly raises the temperature of water as smoke embraces the tubes. To avoid an waste of energy, an intricate web of small water tubes is built right in front of the inner surface of the combustion chamber.
Such a complex machine, predictably, is more expensive than a smoke-tube boiler, which is therefore a better option for small factories.

White vapour comes from sterile water, which is that employed when vials and other injectable drugs are manufactured.

Either sterile water and white vapour require high standards of purity. In a nutshell, the less these substances are manipulated and transported, the easiest the result will satisfy the purity criteria in the end.

To yield white steam a special boiler is needed. The magnificent picture shows how it works: plainly, sterile water, placed in a cylinder of stainless steel, boils as hot tubes of grey steam constantly heat it.

 

 

Apparently ψ*ψ is the only reader of this blog in this period, so, given that she liked special effects, here is the complete series of animations.

I suggest you listen to electronic music while looking at them.

Enjoy yourself!