Summary Of Frequently Asked Questions about Freeze Dryers And Freeze-Dried Samples

1 After Lyophilization And Layering, The Lower Layer Shrank

Phenomenon: After freeze-drying and layering, the lower layer shrinks. Or the entire product shrinks. Some of the product freezes well, some shrink into very few almost empty bottles

Possible cause analysis and solution: Not pre-frozen, sublimation is too fast, it may be that the local temperature is too high or the pressure is too high, resulting in local melting.

1. If your drug solute is relatively small, such problems are more likely to occur.

2. Whether the rubber plug of the shrunken product is well sealed. On the contrary, if the product is easy to absorb moisture, this phenomenon will also occur.

The main reason is that the material below is not completely dry, and after leaving the warehouse, the ice cubes in the supported material fuse and collapse. It is very likely that: the material is heated too fast and too early after entering the warehouse, the eutectic point of the material is not reached, and the bottom layer of the material boils.

It should be that the temperature has risen faster, and the water has not been removed, causing the lower part to melt;

It may be that the glass transition temperature of the drug is low, and it is recommended to find the reason on the prescription.

Why is the lower layer looser than the upper layer? You can see obvious pores because the sublimation of water starts from the upper layer. When the temperature rises above the eutectic point, the water in the lower layer is partially self-dissolved due to the failure to sublimate in time after absorbing heat.

This is normal, because the freezing technology we use takes a certain amount of time. During this freezing time, some slightly soluble substances will crystallize and precipitate in the lower layer of the material. The sublimation temperature requirement is different from that of the lower layer, which is caused by sublimation. Solution: Lower the sublimation temperature once and prolong the sublimation time.

The temperature rises faster, and the moisture is not completely removed, causing the lower part to melt.

Caused by rapid heating! After all the water in the material is sublimated or unloaded, the material layer with a lot of water at the bottom will partially melt!

Appropriately extending the drying time can effectively avoid such phenomena!

2 Freeze-Dried Surface With A Layer Of Skin

Phenomenon: When vacuuming, a lot of small bubbles formed on the surface, and a layer of the surface was detached after freeze-drying. It’s ugly and sometimes floats all over the box.

I do freeze-dried biologics. Recently, the sample has been stratified, and the one I used is a 2ml vial. The filling volume is 1ml, and the layering of the product mainly appears in the middle of the sample, separated from top to bottom. What is the reason?

Possible cause analysis and solution: before the vacuum degree reaches the requirement, the surface of the material has been partially thawed and the pre-freezing is not good, the water is not completely frozen, and the water overflows to form air bubbles when vacuuming.

This phenomenon is most likely due to the migration of salts from the lyophilized samples to the surface. Pre-freezing solutions can be enhanced.

Simply keep the material warm to see if it is caused by too fast sublimation, and there are other reasons.

The change of the front box pressure during the primary drying, because the vacuum degree affects the sublimation speed, you can first check the freeze-drying record data to see if there are any abnormal fluctuations in the front box pressure and product temperature.

In addition, you can confirm where the delaminated bottles are located, the bottles around the plate will sublimate faster than the bottles in the middle.

Comparing the before and after two times, is there any difference in the change of the vacuum? Some people think that your sublimation section does not have enough heat preservation time.

Could it be that the early drying is too fast, which caused this. The main reason is that there is no such product now, so repeated experiments cannot be done for a period of time.

In the early stage of drying, the vacuum degree is relatively low at about 50 at -40 and -35, and the temperature above the eutectic point is about 100. Only when the temperature is kept at 30 in the later stage, the vacuum degree will drop to a few ubar.

Obviously, your delamination is caused by excess heat. Your vacuum at the eutectic point is too high. You can consider extending the heat preservation near the eutectic point (below) to make the product basically dry, and then rise to the eutectic point In fact, the vacuum of the second temperature rise should not be able to rise significantly, and will not exceed the vacuum at the eutectic point. If there is any disagreement, discuss it again!

The control of the vacuum is mainly dominated by your heat supply, as well as factors such as the performance of your vacuum pump, the cleanliness of the oil, and the temperature of the water trap.

One is the freeze-drying time, excipients, one-time sublimation time, and vacuum, whether you control it manually or fully automatic.

The shrinkage of the lower layer is that the water has not been sublimated. The more the same carriage is loaded, the slower it runs.

Also look at your packaging time, if the time is too long, there will be stratification, and there is control of the freeze-drying time.

It is normal for the different positions of the samples to differ by a few degrees. For example, there is a temperature difference of 4-7 degrees between the center of the slab and the edge of the product (a large amount of freeze-drying), and the time for one freeze-drying is longer during freeze-drying.

3 Freeze-Dried Air Bubbles And Wall-Hanging Problem Solving

Phenomenon: 2ml vials of freeze-dried biological products always have problems of air bubbles and hanging on the wall. It is very serious, mainly because of the filling. The machine is a ceramic pump from Nanjing Bojian Company. There are similar problems in the same industry. How to solve it and give help?

Possible cause analysis and solution: You can try to reduce the filling speed, and it should be effective.

Wall hanging: the filling speed has a certain relationship, and the box should also be paid attention to. Bubbles: Concentration and heating rate control.

Bubbles take into account the filling speed, and you can consider slowing down the filling speed. In addition, after filling, place it for a period of time before deep freezing. Too many bubbles are easy to hang on the wall.

For air bubbles, we open a hole near the highest point of the dispensing tube, and add a section of silicone tube as an emptying tube, so that most of the air bubbles in the tube can be eliminated. Pay attention to observe the liquid level change of the emptying tube during operation. In addition, I don’t know if your filling liquid is circulated. Some liquids are prone to foam and bubbles when they are circulated.

Hanging on the wall, I think the main reason is the problem of personnel operation. In addition, it is also related to the diameter of the filling needle. If it is too thin, the impact of the liquid medicine will increase and it will splash back on the bottle wall.

4 About The Foaming Phenomenon Of Freeze-Drying

Phenomenon: Many freeze-dried medicines will have blisters. The reasons are mainly summarized as follows:

Possible cause analysis and solution:

1. The freezing is not firm;

2. Failure to grasp the properties of materials;

3. The vacuum is not well controlled;

4. There is a problem with the heating procedure;

5. The surface structure of the freeze-dried object is dense, which is caused by the discharge of internal gas during drying. The main phenomenon is that the pre-freezing is not well-frozen. In the case of pre-freezing, the vacuum control is not good and no foaming will occur, and heating too fast will cause dry damage;

6. If the vacuum control is not good, there will be a phenomenon of starting;

7. The equipment should be well maintained;

8. To freeze, the product must be frozen thoroughly first, and the thickness of the material should be controlled below 15mm as much as possible. The use of excipients, slow freezing can help form large ice crystals, thus helping to improve the sublimation drying rate, reaching 10 degrees below the eutectic point Keep for 1-2 hours afterward;

9. Sublimation drying, the condenser (water catcher) is pre-cooled to -45 degrees and then vacuumized, the vacuum is controlled at 50-100pa (some books say that the vacuum degree is 10-30pa, depending on the actual situation of different materials Select the appropriate vacuum degree, if the vacuum is too low or the product is not frozen through, the surface of the product will boil, and bubbles will run from the product to the outside, affecting the appearance and sublimation rate of the product) At the same time, the product starts to be heated slowly, and the temperature control should be controlled The temperature of the product does not exceed its eutectic temperature, because simply put, the heating temperature cannot melt the product (there are other methods to determine);

10. Foaming occurs as soon as the vacuum is pumped, which means that there is no freezing and the material is not completely crystallized;

11. Foaming occurs as soon as the vacuum is pumped, which means that there is no freezing and the material is not completely crystallized;

12. If it is heated for a period of time and then foams, it is heating too fast, and the temperature of the material exceeds the temperature of the eutectic point, so that the material melts and foams;

13. The first drying stage (sublimation stage) enters the analysis before the end, so that the temperature of the ice-containing material that has not been sublimated will rise and melt and foam;

14. If the concentration is too high without treatment, a layer of crystalline salt is formed on the surface of the material during pre-freezing. This layer of crystalline salt seriously affects the passage of water vapor when the material is sublimated, so that it will bulge in a short time (about 1 hour) after heating, and it will cause severe foaming.

5 Effect Of Freeze-Drying Curve On Product Clarity

Phenomenon: The clarity is not very good after freeze-drying.

Possible cause analysis and solution:

You can do an experiment to see if the impact of the first drying on the product is to take the product out of the box after the first drying to check the clarity, and then compare it with the clarity after the second drying. Of course, keep 2 tubes of the original solution. The three are compared. Generally, the secondary drying has an impact on the clarity of some, and I have encountered it.

One of the breeds I make is determined by the curve. The cooling rate remains the same, if the time is short, it will lead to unqualified temperature.

I also encountered your problem today. After analysis, the rate of prefreezing has a direct impact on this. Generally speaking, the finer the ice crystals, the better the solubility and clarity. So on today’s sample, I adopted quick-freezing to see how the effect is, and discuss it after the results come out.

If the product is not completely freeze-dried or the vacuum and plate temperature settings are not good after the product is freeze-dried. The first reason is that there is no freeze-dried product that causes the moisture in the material to evaporate, and the latter reason is that the material is severely dehydrated and deteriorated after the freeze-drying is completed (for example: burnt).

Generally, it is affected by the speed of pre-freezing, and there is also the problem of the heating temperature during your second sublimation.

I think it is mainly due to the temperature and time of secondary drying. The product temperature should not be too high, and the time should not be too long. I can’t explain the theory. I can only assume that it is the intermolecular force inside the solid at a higher temperature for a longer time Changes occur and form a tighter intermolecular structure, which leads to a decrease in solubility in water, thereby affecting clarity (poor clarity should be caused by incomplete dissolution of solids). To make a far-fetched analogy-clay can dissolve in water However, it can be sintered into a solid ceramic at high temperature. It can be seen that the temperature has a great influence on the product. It is just a hypothesis…

It is related to the long time after the material is mixed and the machine is put into the box and turned on. This statement seems to be a bit problematic. GMP seems to have a time limit for the sterilization and filtration of liquid medicine to the end of filling. Although the time limit of each enterprise is different, this should not affect the clarity of the product. We have a product that so far, although the clarity of the product appears normal after dissolution (it takes longer than normal to fully dissolve, about a minute or so, and requires constant shaking), the insoluble particulates The detection is that there is no way to meet the requirements of the Pharmacopoeia.

After several months of small tests, my problem is that I have made relatively large changes in the quick-freezing temperature and secondary drying time. The temperature of the second drying should not be too high. Try to lower the temperature if the drying can meet the standard. The analytical drying temperature of my product is only 15 degrees, and the time can be extended. This is my result. I hope it will be useful to everyone.

I think the above problem is related to your process PH and filter, see you step by step to check.

If it is related to “process PH and filter”, then I will test some of the samples after filling under the same conditions for insoluble particles, which is in compliance with the regulations, but there is a problem with the freeze-dried samples, so follow up Whether “the process PH is related to the filter” is related.

6 The Problem Of Slow Dissolution Of Freeze-Dried Vaccines

Phenomenon: The freeze-dried vaccine is slow to dissolve, and the frozen shape is good.

Possible cause analysis and solution: The dried product shrinks and the dissolution rate decreases.

Try quick freezing to see that the size of the ice crystals has a certain relationship with the dissolution.

7 Products Cracked

Phenomenon: Some time ago, a batch of medicines were frozen and everything was qualified, but the finished product was split from the middle. It was the cross-section of the medicine, not from the middle of the bottle. How to solve it?

Possible cause analysis and solution: The cross-section of the middle part of the drug is cracked, mainly due to the rapid temperature rise, which is caused by the rapid temperature rise between the early stage and the late stage. Later, the temperature rises slightly slowly, which can be solved.

My products are always partly layered, so I suspect that it is better to adjust on the freeze-drying curve, and the other is to consider the temperature transfer system of the equipment! Experiments are ongoing.

This phenomenon is generally caused by incomplete sublimation drying and too fast analysis drying. After the sample water line is dried, there is a period of constant temperature time (the length of time is determined by the properties of the product), the temperature of the condenser is very low, and the vacuum degree is also very low before entering the analytical drying, so generally this kind of splitting will not occur The phenomenon.

8 Finding Out The Root Cause Of The Abnormal Phenomenon Of Freeze-Dried Powder Injection

In the production process of freeze-dried powder injection, some abnormal situations often occur, which affect the product quality. The production personnel must effectively control the product prescription design, production process parameters, production environment control, and operator hygiene conditions, and effectively verify the production equipment, clean area environment, freeze-drying curve, etc., in order to effectively Avoid abnormal phenomena of freeze-dried products and improve product quality.

Phenomenon 1: The Water Content Exceeds The Standard

The water content specified in the quality standard of freeze-dried powder injection is relatively low. The main reasons causing its water content to exceed the standard are: too much liquid medicine loaded into the container, and the liquid medicine layer is too thick; insufficient heat supply during the drying process reduces the evaporation; insufficient vacuum, water vapor cannot be discharged smoothly; condensation The temperature of the chamber is too high to effectively capture the water vapor; the freeze-drying time is short; the air humidity in the vacuum drying oven is high;

Measures: Production personnel must take corresponding solutions for different reasons. For example, adjust the size of the vial according to the volume of the liquid medicine and reduce the thickness of the liquid, which should generally be controlled at 10-15 mm; strengthen the heat supply to promote water evaporation; check the reason for the low degree of vacuum to rule out leakage points or abnormalities in the vacuum system; The temperature of the condenser is below -60°C; retry the freeze-drying curve to ensure that the moisture content of the freeze-dried product is qualified; the gas in the box should be sterilized and dehydrated, especially for products that are easy to absorb moisture; The temperature when the product is out of the box is slightly higher than the production environment temperature.

Phenomenon 2: Spray Bottle

The spray bottle is because the temperature of the pre-freezing does not reach below the eutectic point of the product, and the product is not frozen; or the temperature rises too fast during the sublimation drying, and the local overheating causes some products to melt into liquid. Under high vacuum conditions, a small amount of liquid changes from the dried solid The surface is formed by blowing through the pores.

Measures: In order to prevent spraying the bottle, the pre-freezing temperature should be strictly controlled at 10°C~20°C below the eutectic point, and kept for more than 2 hours, so that the medicine is frozen and then heated up. At the same time, the heat supply during sublimation drying should be well controlled, the heating rate should be slowed down appropriately, and the temperature should not exceed the eutectic point. This overcomes the squirt bottle phenomenon.

Phenomenon 3: Unqualified Appearance

The normal appearance of freeze-dried powder injection should be uniform in color, dense in pores, keeping the volume and shape basically unchanged before freeze-drying, and forming a lumpy or spongy mass structure. However, if the weight concentration of the solution is greater than 30%, the product is likely to shrink, collapse, and not full. In addition, when drying, the frozen surface is the first to dehydrate to form a dense dry shell, and the sublimated water vapor below escapes from the interstices between the molecules of the dried surface. At this time, if the concentration of the solution is too high, the gap between the molecules is small, the air permeability is poor, the resistance of water vapor to pass through is large, and a large number of water molecules have no time to escape, and the stagnation time in the dry layer is long, so that part of the dried medicine will gradually deliquesce, which will cause The volume of the product shrinks, and the shape is not full or collapsed. If the weight concentration of the liquid medicine is lower than 4%, the medicine will scatter along with the water vapor when vacuuming; or it will become a fluffy loose structure after drying, and the substance of this structure will dissipate after the vacuum is released, making the product into a hollow shape. Another situation is that the concentration of the liquid medicine is too low, which makes the product loose and easy to attract moisture. At the same time, because the specific surface area is too large, the product is easy to shrink, and the mechanical strength of the dried product is too low. Once it is vibrated, it will disperse into powder and adhere to the bottle wall.

In terms of freeze-drying process, if the thickness of the liquid medicine is greater than 20 mm, the drying time will be prolonged, which will also cause the appearance of the product to be unqualified. In addition, at the beginning of freezing, the cooling speed is fast, so that the product forms fine crystals, the density is high, the resistance to sublimation is relatively large, the water is not easy to evaporate, and the product will gradually deliquesce, resulting in volume shrinkage and resulting in an unfulfilled shape or a lump. If the freezing speed is too slow and the ice crystals grow for a long time, it is easy to concentrate, resulting in the separation of the drug and the solvent, and the uneven structure of the finished product.

Measures: rationally design the formula of freeze-dried solution. Generally, the appropriate weight concentration is between 4% and 25%, and the optimum concentration is between 10% and 15%. If the concentration is lower than 4%, excipients (such as mannitol, dextran, lactose, etc.) can be added appropriately. If the concentration is high, it is necessary to control the thickness of the freeze-dried product, or reduce the concentration, and use a large container to fill the liquid medicine. During the freeze-drying process, the cooling rate should be controlled at 5°C to 6°C per hour. In the first sublimation drying stage, the temperature of the product should be lower than the eutectic point, and the temperature rise should not be fast, and should be controlled at about 5°C per hour. If the heating is too fast, when the product has a lot of water, the temperature exceeds its eutectic point, which will cause the product to melt and appear defects in appearance. In the second sublimation stage, although the water content in the product is low at this time, the heating rate can be moderate? But the temperature must be controlled below the safe temperature, otherwise there will be agglomeration. In addition, the airtightness of the product packaging is not good, and the appearance is unqualified or even the internal quality is unqualified within the validity period.

Phenomenon 4: The Product Is Cold And Pops Off The Bottom

The main reason is that the product is not frozen solid in the pre-freezing stage. If the product is not completely frozen, the system will start to vacuum the box, so that when the pressure reaches a certain value, the part that has not been frozen will start to evaporate and boil, resulting in exothermic phenomenon, while its own temperature Drop sharply, and when reaching the eutectic point temperature, the product freezes, and then the phenomenon of bottle bursting and bottoming begins to appear. As the pressure continues to drop, the temperature also drops accordingly. Generally, the vacuum pump of the freeze dryer can reach below 0.1 mbar, which means that the temperature of the medicine in the box reaches about -40°C. Since the vial bottom and the lower plate do not have the above-mentioned evaporative freezing characteristics, the vial cannot withstand such a large temperature difference in a short period of time, causing the vial to explode and fall off the bottom.

Measures: To solve the problem of cold explosion and bottoming off, production personnel must strictly implement the pre-freezing parameters, and confirm that the product is frozen firmly before vacuuming.

Freeze vacuum drying technology is widely used in the production of more than 700 varieties of antibiotic products, traditional Chinese medicine, and health care products. Freeze-dried powder is obtained by freezing the drug solution that needs to be dried into a solid in advance through freeze-drying technology, and then sublimating the drug directly from the frozen solid state without going through the liquid state under low temperature and high vacuum conditions. Freeze-dried powder products must meet the quality requirements of general injections, such as sterility, no pyrogens, and no foreign matter, and should also be a complete freeze-dried block or sponge with sufficient strength and not broken into powder , full shape, no shrinkage, uniform color, low water content, good porosity, and can be quickly redissolved after adding water.

9 Quality Analysis Of Freeze-Dried Products

Different products have different quality indicators, such as product moisture content, storage stability. Reduction, the survival rate of live bacteria or the potency of drugs. Nutritional ingredients in food, preservation rate of aromatic ingredients, etc. Many of these indicators need to use special instruments and equipment to test according to the methods stipulated in relevant standards. At the freeze-drying site, the analysis and judgment are mainly based on the shape of the product. Now, based on my work experience and referring to the works of many scholars, I will discuss and summarize the reasons for the shape of the product. I hope that all my colleagues will participate in the discussion to improve together.

The normal appearance of freeze-dried products is uniform in color, dense in pores, and maintains the volume before freeze-drying. The shape is basically unchanged, forming a spongy mass structure. If there are hard shells, shrinkage, collapse, voids, dust, and broken phenomena, they are all abnormal shapes and unqualified products. We will analyze them in several situations below.

1. The quality of the product looks good before it leaves the box, but it shrinks shortly after it leaves the box, or there are hollow pieces. The reason is that the product is not completely dried and there are residual ice crystals. After leaving the box, the temperature and pressure of the product are above the eutectic point, the ice melts into water, and the water is absorbed by the dried material around it, resulting in voids and shrinkage.

Incomplete drying of the product may be caused by some of the following reasons:

A. The drying time is too short or the temperature is too low, or both. If the thermometer and vacuum gauge are normal and the drying is not complete for several consecutive batches, the drying time should be extended and the sublimation temperature should be increased if possible. If the product quality was normal before, it may be caused by packaging errors, freezing rate errors, and vacuum degree errors. The drying time should also be extended appropriately. It may also be that the thermometer is not accurate, and the actual sublimation temperature is lower than the set sublimation temperature.

B. The freezing rate is too fast. The grains are too fine, which slows down the rate of sublimation. Due to the reduction of the filling capacity, or the cooling time of the empty box is too long, and the temperature is too low, the freezing rate will be accelerated and the grains will be finer, which will hinder the escape of water vapor. Therefore, it is necessary to prolong the drying time or reduce the freezing rate.

C. The freezing is not complete, so that a gap or air resistance is formed between the frozen product and the container wall, reducing the heat transfer effect. Due to incomplete freezing, evaporative freezing occurs during vacuum sublimation, which reduces the volume of the product and forms a gap between the product and the container wall, and heat cannot be transferred to the product. As the sublimation proceeds, the ice around the frozen block sublimes first, forming a layer of adiabatic drying layer surrounding the frozen block, making it more difficult for heat to be transferred to the frozen object, so the required drying time is prolonged.

D. Some products are not completely dried. It may be caused by too much temperature difference between the shelves, too much warping of the tray or shelf, uneven or uneven bottom of the bottle containing the product, or uneven distribution of the product. For low-quality freeze dryers, the only way to extend the freeze-drying time is to make the moisture content of most products meet the requirements.

2. When the product is out of the box, the product is a skeleton structure with a large gap, even a fluffy substance, and the fluffy substance dissipates quickly after it is out of the box. The main reason is that there are too few solid substances in the product formula. When freezing, the volume occupied by free water forming pure ice increases, and the pores formed after sublimation are also large, which may cause useful components to scatter together with water vapor during sublimation. The fluff-like substance formed is originally a solid component of the product, and when it meets air, it will absorb water vapor and melt and disappear. The solution is to add fillers to the formulation.

3. When the product is out of the box, there are defects such as bubble pits, drying shrinkage, collapse, and voids. The main reason is that the freezing temperature is too high, or the time is too short, and the product has not been completely frozen; or the temperature is too high and the pressure is too high during the first stage of drying, so that part of the product melts. Evacuate sublimation when it is not frozen, and the external pressure drops rapidly to cause bubbling; the melted product evaporates and concentrates, and it will take on a shrunken shape; part of the undried product is melted due to excessive heating, which will also make the dried part solid Substance dissolves in it, causing the dried part to melt into a void or collapse. Therefore, during operation, the product must be frozen firmly, and the eutectic temperature of the product cannot be exceeded during sublimation, and the sublimation temperature cannot exceed the melting temperature of the product.

4. The product is uneven in color and porosity in the depth direction. It may be that the undissolved components in the solution precipitated due to the long standing time after aliquoting.

10 Aspects About The Impact Of Ambient Temperature And Humidity On The Freeze-Drying Process

The influence of ambient temperature and humidity is only before entering the freeze-drying box and when it is out of the box, and it has no effect during the freeze-drying process.

However, the temperature and humidity of the environment have an impact on the freeze-drying process, the time required for freeze-drying, and even the final freeze-dried product. The most prominent is the effect of relative humidity on freeze-drying time!

The ambient temperature has no direct impact on the freeze-dried product, but has a certain impact on other equipment of the freeze dryer, such as the refrigerator. If the ambient temperature is too high (not the central air-conditioning as the condensation) will have some influence. Generally speaking, the current machine will not have any impact. If it is an old-fashioned freeze dryer, it will have a great impact.

11 Judgment Of Freeze-Dried Products And Unqualified:

Delamination, shrinkage, spray bottle, sticky bottom, discoloration, cavitation, moisture, clarity, insoluble particles, poor solubility, bubbling, shrinkage, cracking, bottle appearance, etc.