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The advantages and limitations of pharmaceutical grade silicone hoses

Time:2017-11-30 Click:

 Pharmaceutical grade silicone hose strengths and limitations

Hoses are well-recognized over the years because of their low cost and ease of use, making them ideal for single-use applications that can reduce costs associated with ensuring cleanliness, in situ cleaning (SIP) or in situ sterilization (SIP) and wastewater treatment . Choosing a suitable hose is not a trivial task: suppliers may not publicly supply the components of their hoses (fluoroelastomers, polyurethanes, polyvinyl chlorides, silicones, polyolefins, etc.) Concept of usefulness.
In fact, the mechanical strength of silicone elastomers is limited and represents only a small fraction of the polymer used in the surroundings, with some of the properties that make them unique in pharmaceutical use. Silicone tube specific parameters of the list, including the arrival or reach of the parameters. Today, silicone tubing has been used extensively in many procedures to aid pharmaceutical production, including fluid transfer, peristaltic pumping and filling operations.
The nature of silicone
Silicone has many interesting properties that make it suitable for use in a variety of hoses, some of which are listed below. Silicone polymer. Silicone is the commercial name for many commercial products, but most are made from polydimethylsiloxane (PDMS). These polymers are characterized by their high covalent bond strength and their resistance to breaking and breaking (silicone has UV stability; it also has thermal and chemical stability and therefore is easy to sterilize). The polarity of the main chain of easy-to-break cracking chain, but the chain of methyl groups can provide maintenance.
Thus, the silicone is hydrophobic and the water has a higher contact angle of polydimethylsiloxane (PDMS) model appearance of 108 °. Because of this hydrophobicity, silicones do not react with aqueous media in the absence of external surfactants, and only react in the presence of strong bases or acids. PDMS exhibits a very low glass transition temperature (Tg of 146K) due to the small interaction between the methyl-methyl molecules between the PDMS chains, a key property of the silicone to become elastomeric. PDMS is "compatible" with hydrocarbons (the polymer dissolves in these non-polar solvents, and the elastomer absorbs and swells in these solvents). PDMS has high permeability to many low molecular weight substances / non-polar substances, such as the above hydrocarbons or gases. This property can be used for oxygenation of cell culture, for example for the Corning E-Cube incubation system.
The composition of silicone polymers is now too much to view. With regard to the comments made here, it is particularly about impurities, notably that the composition of the silicone polymer starts at the end of the distillation without touching the solvent or heavy metals. Impurities are essentially short, linear or cyclic oligomers with a certain degree of volatility. These materials are commonly used as starting oligomers or during the polymerization reaction.
Silicone elastomer. Use cross-linking reaction (curing) simply silicone polymer into three-dimensional mesh or elastomer. With regard to hose manufacture, two cross-linking reactions are preferred: one is peroxide-induced, with peroxides attacking free radicals R ', resulting in bonding between the chains; the other is platinum-catalyzed, organometallic platinum composites The material plays a catalytic role in the SiH groups participating in the vinyl groups. The advantage of this reaction is that there is no secondary product (additive reaction), only a few catalysts (10 ppm platinum) are used and no secondary curing is required.
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Hoses are supplied after extrusion, usually in the form of a 50-foot coil, packed in double sealed polyethylene bags. It is worth mentioning that, because of their thermosetting properties, silicones can not be reprocessed like thermoplastics. Because of the same elements, they can not be heat-sealed; therefore, the silicone tube is attached to the hose barb connector and fastened in opposite directions with two straps securing the hose. Common mold pressure molding is feasible, sometimes used in medical equipment category.
Hose selection needs to think of several important elements. The next sections will address these questions by comparing the nature of the various hose materials and their function in the transfer pump operation.
Hose function
This article gives a brief overview of what is currently used in pharmaceutical production for liquid delivery, peristaltic pumps and irrigation tubing, especially silicone tubing. This article describes the strengths and limitations of this silicone tube and comments on the variables that need thinking.
Appearance and mechanical features
In contrast to some organic thermoplastics, the transparency of silicone is best described as "translucent." This result is due to the fact that the silicone elastomer used to make the hose consists of silicone polymer and amorphous silica. All silicone tubes are translucent because these two materials have different indices of refraction and are not mixed with a specific blend.
Silicone elastomers exhibit a significant mechanical function after curing, which includes medium hardness and high elongation at break, but with lower tensile strength than polyurethane (PU). In contrast to polytetrafluoroethylene (PTFE), they have a tacky appearance and a high coefficient of friction, but with much less rigidity.
They attract dust because they are hydrophobic and are excellent electrical insulators. Their working temperature scale is larger than PVC.
Silicone hoses may contain various disadvantages: Extrusion lines or gels (premature curing in the extruder, perhaps); bubbles (moisture may be absorbed by the two-roll cooling rolls to form water vapor , Or H-Si ≡ and platinum cured products in the adverse reaction of hydroxyl substances constitute hydrogen); particulate pollution.
Limiting the limits of these shortcomings is not a straightforward matter, but they should be specified in the vendor's sales practices. ISO specifications related to silicone elastomers for hose extrusion and even some visual inspection. Other questions relating to mechanical functions touch on floor space and transfer. The question here is to use the smallest footprint to "handle" the hoses in the pipeline and prevent kinking. Demand-minded variables include zigzag radii (the radius of some of the hose twists as measured on some of the innermost and outer surfaces) and tortuosity (the stress required to buckle to a regular radius).
Silicone tubes can sometimes be externally printed with symbols, but because of their low appearance, poor ink adhesion, they can be easily erased using common solvents for cleaning. Silicone can also be mixed. Barium sulfate is commonly used as a white filler for color mixing of substrates, or as coextruded strips for X-ray impermeable medical devices.
Operating temperature
Due to the low glass transition temperature and high thermal stability, the operating temperature of silicone is much broader. Silicone-referenced operating temperatures range from -80 to 215 ° C, the largest of any commercial elastomer.
Chemical resistance
Although they are less likely to be present in pharmaceutical processing such as fermentation or perfusion operations, there are two elements that constrain the chemical resistance of silicones: swelling by certain organic solvents and chemical degradation by strong bases or strong acids.
Silicone swelling in toluene and other hydrocarbon non-polar organic solvents. At the time of swelling, the weight ratio (w / w) is increased by 200%, causing the mechanical properties of the elastomer to weaken, but the bonds do not actually crack, rather the elastomer is "diluted". Swelling is dependent on the time of day and the molecular weight due to its decentralized manipulation. Silicone tubing with low molecular weight silicone swelled rapidly, while high molecular weight silicone was slower (Table 2).
Silicone, on the other hand, can degrade in the presence of strong bases or strong acids, resulting in the hydrolysis of the siloxane bonds and the depolymerization of the siloxane backbone. This constitutes a variety of "measures" (Table 2), and because test conditions and assessments are not always comparable, they sometimes contain conflicting information. In addition, the constitutional component may appear to be more potent than the single component. For example, a mixture of water, alcohol, and a strong base can "wash away" the silicone from laboratory glassware while the individual components have no effect. Therefore, there is no doubt that it is necessary to evaluate the compatibility one by one.
Purity and dissolution
Drug inspectors now categorize the hides and tubes of substances as "effluent" and "eluate." The former refers to substances that are removed under normal conditions of use, while the latter requires excessively high temperatures or strong solvents ("worst case"). The eluate should contain the extract, and the term will be further commented here.
In both cases, hoses made of plasticizers are estimated to have more eosinophilia than an additive-free hose. Silicone itself does not require plasticizers, stabilizers, UV absorbers or antioxidants. Silicone has very little heavy metal content, usually less than 10 ppm, due to its production method. Platinum complexes are used as catalysts for cross-linking reactions but in very small amounts (10 ppm platinum); once hardened, no measurable levels of platinum are detected in the eluate, even with the use of a potent solvent. With regard to silicones, a large part of the eluate consists of the short-chain oligomer 6- (SiMe2O) n-, and thus its acceptable residual amount can be judged by the risk evaluation.
The recommended conditions allow exclusion of the eluate from the product and possible reduction of the swelling, which may affect the interpretation of the data due to the small solvent recovery and the dissolution of the eluate into the swollen elastomeric web.
Of the solvents used, acetone produced the highest concentration of eluate (about 2% by weight), while ethanol, water or other aqueous media produced lower concentrations of the extract. Depending on the purpose of this study, acetone may be the ambivalent solvent for "excessive" research. Silicone tube sample structure is crucial, because the thicker the sample tube thickness, the lower the dissolution rate. As expected, after storage or sterilization, the eluate is reduced.
Clean and sterilize
Hoses are "extruded" method. An article comparing the phytoplankton-related silicones to other hoses mentions the importance of pre-application cleaning: Silicone has no significant effect, while other hoses have reduced phytoplankton growth, Clarifying that in some cases the impact is eliminated after cleaning. Some were cleaned with water for injection (WFI) prior to use, followed by compressed air drying in air-conditioned rooms, but with little detail. Because of its stability, silicones are simply sterilized. The usual sterilization procedures include:
Autoclave (steam) was used for a standard gravity steam sterilization cycle (30 min, 15 psi, 121 ° C) or high speed steam sterilization cycle (15 min, 30 psi, 132 ° C). Note that silicone materials are harder to heat than materials such as thermoplastics and may require more time to heat because of their adiabatic properties.
Gamma radiation, doses up to 2.5 Mrad (25 kGy) do not negatively affect the onset of mechanical function (higher doses may cause some changes).
Ethylene oxide (ETO), given sufficient time to eradicate the residual hexylene oxide gas. Different residual levels of ethylene oxide after hose sterilization have been investigated. Compared with polyvinyl chloride or polyester-polyurethane hoses, silicone absorbs less ethylene oxide and releases more quickly.
Hose function in pump operation
The benefits of peristaltic pumping are obvious (shutdown of the system, no danger of contamination from outside by air or lubricant from the pump). This skill is used not only for pharmaceutical processing but also for extracorporeal blood circulation pumps in cardiopulmonary bypass or hemodialysis. These are the most requested hose applications. They not only request resistance to "chemicals" but also demand resistance to deformation during application (eg, an ever-decreasing flow velocity in hoses), as well as resistance to catastrophic faults / leaks (pump life). The useful life of a pump depends on many factors, such as the pump settings, the product being pumped, and the hose information itself. As a whole, some organic thermoplastics seem to perform as well as silicone, albeit with a lot of contrast data, when only thinking about pump service life.
The resilience or resilience of the elastomer is important and can be measured experimentally, such as compression set (how much "memory" remains in the elastomer after permanent compression) or hysteresis ("low stress-relaxation" cycle How much energy is dissipated between them).
Peeling refers to the amount of particles that perish during the pumping process but degrade and release before the onset of a catastrophic failure or leakage. Peel depends on the composition of the tubing: There have been reports of low peelability of fluoroelastomers and this question has been discussed repeatedly in the context of blood pumping. In addition, the setting of the pump has proven to be crucial. When the closing force is reduced, the silicone tube is also greatly reduced stripping. Significantly, platinum-cured silicone elastomers with lower hysteresis (as described above) again showed very good performance over standard grade platinum tubes (Table 3).
Now that biotech has gone a long way, the capabilities of stainless steel reactors may be lacking. In addition, there is a trend towards a simpler / faster solution, from hoses with fittings to ready-to-use ready-to-assemble devices with hoses, filters, adapters and connections. . This completes the material and gas supply, filtration, sampling or liquid transport. Disposable plastic with hose "assembly equipment" is now replacing some reboilers.
With the correct understanding of the physical and chemical properties of the material, the hose selection also requires grasping: capital, not just the cost, but also includes the use of capital; dangerous handling; for example, the quality of the selected supplier request or control level, such as GMP or , The rules governing the use of end-users (patients), understanding of purity and eluviation characteristics, and the links between these and toxicological discussions; at the end of the day, silicone seems to be well suited to the above request.
Food grade silicone hose

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