Evaluating Clinical Safety and Analytical Impact of Subvisible Silicone Oil Particles in Biopharmaceutical Products

Silicone oil is a commonly used lubricant in pre-filled syringes (PFSs) and can migrate over time into solution in the form of silicone oil particles (SiOPs). The presence of these SiOPs can result in elevated subvisible particle counts in PFS drug products compared to other drug presentations such as vials or cartridges. Their presence in products presents analytical challenges as they complicate quantitation and characterization of other types of subvisible particles in solution. Previous studies have suggested that they can potentially act as adjuvant resulting in potential safety risks for patients. In this paper we present several analytical case studies describing the impact of the presence of SiOPs in biotherapeutics on the analysis of the drug as well as clinical case studies examining the effect of SiOPs on patient safety. The analytical case studies demonstrate that orthogonal techniques, especially flow imaging, can help differentiate SiOPs from other types of particulate matter. The clinical case studies showed no difference in the observed patient safety profile across multiple drugs, patient populations, and routes of administration, indicating that the presence of SiOPs does not impact patient safety.

Sub-Visible Particle Classification and Label Consistency Analysis for Flow-Imaging Microscopy Via Machine Learning Methods

Sub-visible particles can be a quality concern in pharmaceutical products, especially parenteral preparations. To quantify and characterize these particles, liquid samples may be passed through a flow-imaging microscopy instrument that also generates images of each detected particle. Machine learning techniques have increasingly been applied to this kind of data to detect changes in experimental conditions or classify specific types of particles, primarily focusing on silicone oil. That technique generally requires manual labeling of particle images by subject matter experts, a time-consuming and complex task. In this study, we created artificial datasets of silicone oil, protein particles, and glass particles that mimicked complex datasets of particles found in biopharmaceutical products. We used unsupervised learning techniques to effectively describe particle composition by sample. We then trained independent one-class classifiers to detect specific particle populations: silicone oil and glass particles. We also studied the consistency of the particle labels used to evaluate these models. Our results show that one-class classifiers are a reasonable choice for handling heterogeneous flow-imaging microscopy data and that unsupervised learning can aid in the labeling process. However, we found agreement among experts to be rather low, especially for smaller particles (< 8 µm for our Micro-Flow Imaging data). Given the fact that particle label confidence is not usually reported in the literature, we recommend more careful assessment of this topic in the future.

An ex vivo headspace gas chromatography-mass spectrometry method for the determination of short-chain siloxanes in silicon oil tamponades used in ophthalmic surgery

Being able to facilitate retinal reattachment by preventing water migration into the subretinal space, silicone oils are widely used as long-term intraocular tamponade to treat cases of retinal detachment. Various commercial tamponades constituted by linear polydimethylsiloxane polymers with different molecular weights and cyclic impurities are available. In this study, for the first time, an untargeted headspace-gas-chromatography-mass spectrometry (HS-GC-MS) method was developed to identify low-molecular weight contaminants in three different types of silicone oil tamponades, namely Siluron 2000, RS-OIL ECS5000 and Densiron Xtra. Both commercial and post-operative tamponades were analysed to screen for the different classes of compounds present in the samples. The most abundant classes were short-chain siloxanes, fluorinated compounds, and hydrocarbons. To quantify the siloxanes present in the samples, a targeted HS-GS-MS was optimized using a central composite design and validated according to guidelines for bioanalytical methods. Lower limits of quantification in the low μg/L range, good precision with RSD% < 12% and accuracy with recovery rates in the 81 ( ± 7) - 96 ( ± 4) % range were achieved. Short-chain siloxanes were quantified in both commercial and post-operative tamponades, being the RS-OIL ECS5000 characterized by the highest concentration levels of the investigated analytes. By contrast, Densiron Xtra tamponades showed the lowest amount of short-chain siloxanes, observing a general decrease in their concentration levels according to the residence time in the eyes.

Enhancing Chlorobenzene Biodegradation by Delftia tsuruhatensis Using a Water-Silicone Oil Biphasic System

In this study, a water-silicone oil biphasic system was developed to enhance the biodegradation of monochlorobenzene (CB) by Delftia tsuruhatensis LW26. Compared to the single phase, the biphasic system with a suitable silicone oil fraction (v/v) of 20% allowed a 2.5-fold increase in the maximum tolerated CB concentration. The CB inhibition on D. tsuruhatensis LW26 was reduced in the presence of silicone oil, and the electron transport system activity was maintained at high levels even under high CB stress. Adhesion of cells to the water-oil interface at the water side was observed using confocal laser scanning microscopy. Nearly 75% of cells accumulated on the interface, implying that another interfacial substrate uptake pathway prevailed besides that initiated by cells in the aqueous phase. The 8-fold increase in cell surface hydrophobicity upon the addition of 20% (v/v) silicone oil showed that silicone oil modified the surface characteristics of D. tsuruhatensis LW26. The protein/polysaccharide ratio of extracellular polymeric substances (EPS) from D. tsuruhatensis LW26 presented a 3-fold enhancement. These results suggested that silicone oil induced the increase in the protein content of EPS and rendered cells hydrophobic. The resulting hydrophobic cells could adhere on the water-oil interface, improving the mass transfer by direct CB uptake from silicone oil.

Quantification of Silicone Oil and Its Degradation Products in Aqueous Pharmaceutical Formulations by 1H-NMR Spectroscopy

During the past years, there has been an increasing focus on the presence of silicone oil as a contaminant in pharmaceutical formulations kept in prefilled syringes (PFSs). As the PFSs are coated on the inner wall with silicone oil (polydimethylsiloxane), there is a potential risk that the oil can migrate from the inner surface of the primary packing material into the aqueous solution. Several studies have demonstrated that presence of silicone oil as droplets in a high-concentrated protein formulation can cause protein aggregation. Hence, because the use of silicone-coated primary packing material for protein formulations are increasing, the call for an easy and quantitative method for determination of silicone oil and its degradation products in pharmaceutical formulations is therefore needed. Several analytical techniques have in the past been developed with the aim of detecting the presence of silicone oil and degradation products hereof. Most of these methods require hydrolyzation, derivatization, and extraction steps followed by, for example, gas chromatography-mass spectrometry analysis. Applying these methods can cause a loss in detection or an overestimation of the hydrolytic degradation products of silicone oil, that is, trimethylsilanol and dimethylsilanediol. The 2 silanols are highly hydrophilic and prefers the aqueous environment. Analysis of an aqueous formulation obtained from a PFS by ¹H-NMR spectroscopy provides data about the content and levels of silicone oil and the 2 silanols even in levels below 10 ppm. The ¹H-NMR method offers an easy and direct, quantitative measurement of samples intended for clinical use and samples kept at elevated temperature for a prolonged time (i.e., stability studies). The result of the study presented here showed dimethylsilanediol to be the main silicone compound present in the aqueous formulation when kept in baked-on PFSs. The degradation product dimethylsilanediol, in full accordance with expected hydrolytic degradation of silicone oil, increased during storage and with elevated temperature. In addition, the method can be applied to aqueous samples where polydimethylsiloxane has been added as, for example, the major constituent of antifoam.

Characterization of the initial level and migration of silicone oil lubricant in empty prefilled syringes for biologics using infrared spectroscopy

Glass prefillable syringes are lubricated with silicone oil to ensure functionality and a consistent injection for the end user. If excessive silicone is applied, droplets could potentially result in aggregation of sensitive biopharmaceuticals or clouding of the solution. Therefore, monitoring and optimization of the applied silicone layer is critical for prefilled syringe development. The hydrophobic properties of silicone oil, the potential for assay interference, and the very small quantities applied to prefilled syringes present a challenge for the development of a suitable assay. In this work we present a rapid and simple Fourier transform infrared (FTIR) spectroscopy method for quantitation of total silicone levels applied to prefilled syringes. Level-dependent silicone oil migration occurred over time for empty prefilled syringes stored tip-up. However, migration from all prefilled syringes with between 0.25 and 0.8 mg of initial silicone oil resulted in a stable limiting minimum level of between 0.15 and 0.26 mg of silicone in the syringe reached after 1 to 4 years of empty tip-up storage. The results of the FTIR assay correlated well with non-destructive reflectometry characterization of the syringes. This assay can provide valuable data for selection of a robust initial silicone oil target and quality control of prefilled syringes intended for biopharmaceuticals.

LAY ABSTRACT

Glass prefillable syringes are lubricated with silicone oil to ensure functionality and a consistent injection for the end user. If excessive silicone is applied, droplets could potentially result in aggregation of sensitive biopharmaceuticals or clouding of the solution. Therefore, monitoring and optimization of the applied silicone layer is critical for prefilled syringe development. The hydrophobic properties of silicone oil, the potential for assay interference, and the very small quantities applied to prefilled syringes present a challenge for the development of a suitable assay. In this work we present a rapid and simple Fourier transform infrared (FTIR) spectroscopy method for quantitation of total silicone levels applied to prefilled syringes. Level-dependent silicone oil migration occurred over time for empty prefilled syringes stored tip-up. However, migration from all prefilled syringes with between 0.25 and 0.8 mg of initial silicone oil resulted in a stable limiting minimum level of between 0.15 and 0.26 mg of silicone in the syringe reached after 1 to 4 years of empty tip-up storage. The results of the FTIR assay correlated well with non-destructive reflectometry characterization of the syringes. This assay can provide valuable data for selection of a robust initial silicone oil target and quality control of prefilled syringes intended for biopharmaceuticals.

Particle size coarsening induced by valve silicone in a metered dose inhaler

The objective of this study was to evaluate the effect of valve silicone on the delivered particle size distribution of a suspension metered dose inhaler (MDI). Valves were manufactured with distinct levels of silicone, which could be differentiated with Fourier transform infrared spectroscopy (FT-IR). The amount of silicone in the valve was proportional to the amount of silicone that entered the formulation and the subsequent decrease in fine particle fraction (FPF) of the active pharmaceutical ingredient (API) measured by Andersen cascade impaction. The effect of silicone content was not linear as even small amounts of silicone made a significant contribution to particle size coarsening. This coarsening was also a function of storage time and temperature. Accelerated stability conditions greatly increased coarsening kinetics as 1 month at 40 degrees C and 75% RH induced significantly more coarsening than 12 months at room temperature. Field emission scanning electron micrograph images suggest that the primary mechanism of particle size change may be aggregation as particle clusters were seen. This study indicates that silicone can be a critical process parameter for particle size distribution of a suspension MDI product. Thus, the amount of silicone in the valves needs to be minimized and controlled.

Hazard assessment of silicone oils (polydimethylsiloxanes, PDMS) used in antifouling-/foul-release-products in the marine environment

Non-eroding silicone-based coatings can effectively reduce fouling of ship hulls and are an alternative to biocidal and heavy metal-based antifoulings. The products, whose formulations and make up are closely guarded proprietary knowledge, consist of a silicone resin matrix and may contain unbound silicone oils (1-10%). If these oils leach out, they can have impacts on marine environments: PDMS are persistent, adsorb to suspended particulate matter and may settle into sediment. If oil films build up on sediments, infiltration may inhibit pore water exchange. PDMS do not bioaccumulate in marine organisms and soluble fractions have low toxicity to aquatic and benthic organisms. At higher exposures, undissolved silicone oil films or droplets can cause physical-mechanic effects with trapping and suffocation of organisms. These 'new' effects are not covered by current assessment schemes. PDMS make the case that very low water solubility and bioavailability do not necessarily preclude damage to marine environments.

Depósito subconjuntival de óleo de silicone após cirurgia vitreorretiniana

PURPOSE

To assess the histopathological findings of conjunctival specimens from patients submitted to vitreoretinal surgery with intraocular silicone oil injection.

METHODS

Prospective analyses of 30 eyes of 30 patients were evaluated. Before the patients underwent removal of the intraocular silicone oil, conjunctival excision was performed and submitted to histopathologic examination.

RESULTS

The presence of empty spaces corresponding to silicone oil location was positive in 10 (33%) specimens. The presence of inflammatory cells, vascular congestion, leukostasis, lymphocyte and monocyte infiltrates were positive in 27 (90%) specimens. The presence of silicone oil was positive in 10 (33%) specimens. Therefore, in those patients who undergo vitreoretinal surgery, silicone oil may be present in the conjunctiva or subconjunctival space, even if biomicroscopic examination seems to be normal. According to our knowledge, this is the first study with the purpose to assess the histopathological findings of conjunctival specimens from patients submitted to vitreoretinal surgery with intraocular silicone oil injection.

CONCLUSION

Ophthalmologists should be aware of this possible complication after intraocular use of silicone oil after vitreoretinal surgery.

In situ measurement of the infrared absorption and extinction of chemical and biologically derived aerosols using flow-through photoacoustics

In an effort to establish a more reliable set of optical cross sections for a variety of chemical and biological aerosol simulants, we have developed a flow-through photoacoustic system that is capable of measuring absolute, mass-normalized extinction and absorption cross sections. By employing a flow-through design we avoid issues associated with closed aerosol photoacoustic systems and improve sensitivity. Although the results shown here were obtained for the tunable CO2 laser waveband region, i.e., 9.20-10.80 microm, application to other wavelengths is easily achievable. The aerosols considered are categorized as biological, chemical, and inorganic in origin, i.e., Bacillus atrophaeus endospores, dimethicone silicone oil (SF-96 grade 50), and kaolin clay powder (alumina and silicate), respectively. Results compare well with spectral extinction measured previously by Fourier-transform infrared spectroscopy. Comparisons with Mie theory calculations based on previously published complex indices of refraction and measured size distributions are also presented.

Silicone oil in the subarachnoidal space--a possible route to the brain?

Using this case report, we sought evidence that silicone oil may infiltrate the subarachnoidal space. Vitrectomy combined with silicone oil implantation was performed on the right eye of a 72-year-old woman. The silicone oil was removed 2 months later, because the patient had developed elevated intraocular pressure. The blind and painful eye was subsequently enucleated. By light microscopy, presumed silicone oil bubbles were identified in the optic nerve and the subarachnoidal space of the enucleated eye. These vacuoles were examined by energy-dispersive X-ray analysis (EDAX). In addition, in the vacuoles, immunohistochemistry was used to test for the presence of CD 68-positive macrophages. Silicone oil infiltration sites in the optic nerve, in the central retinal artery, and in the subarachnoidal space were located by light microscopy and confirmed by EDAX. CD 68-positive macrophages were found in the silicone-filled vacuoles. Silicone oil used for endotamponade may infiltrate the optic nerve and even the subarachnoidal space. This supports the assumption that silicone oil, under special circumstances, may even migrate into the brain.

Silicone oil content in ophthalmic viscosurgical devices

PURPOSE

To examine the silicone oil content in 5 brands of ophthalmic viscoelastic devices (OVDs).

SETTING

Department of Ophthalmology, Central Hospital of Vasteras, Vasteras, Sweden.

METHODS

Phacoemulsification with intraocular lens (IOL) implantation was performed in 250 patients. Five brands of OVD were used, each one in 50 procedures. From each brand, 5 separate batches, each consisting of 10 syringes, were used. The 250 samples from identical batches were sent for spectrophotometric analysis, and 250 samples were used during surgery.

RESULTS

The silicone oil content varied significantly between the OVD brands.

CONCLUSIONS

Silicone oil is a common contaminant in many OVDs. Ophthalmic viscosurgical devices with relatively low silicone oil content are available.

The fate of silicone oil during heat-curing glass siliconization--changes in molecular parameters analyzed by size exclusion and high temperature gas chromatography

The siliconization of pharmaceutical glass containers, usually for parenteral formulations, is performed in a so-called heat-curing process using diluted aqueous emulsions of medical grade silicone oils. To do this, the emulsion film is spread on the inner container surface, followed by an application of dry heat at temperatures above 300 degrees C. Water and surfactants are removed by degradation and vaporization, while the thermostable poly(dimethylsiloxane) (PDMS) is left on the surface. In the present study, heat-cured siliconized glass containers of two different types were solvent-extracted to obtain material of heat-treated PDMS. These samples were analyzed by size exclusion chromatography (SEC) and high-temperature gas chromatography (GC) with special respect to low molecular-weight siloxanes (LMWS). By comparison with the untreated starting materials, significant changes in the molecular weight distribution (MWD) of the silicone oil were revealed. Almost all of the LMWS present in untreated materials were not detectable in the heat-cured extract of a 100 cSt. Baysilone silicone oil. Small amounts of PDMS-molecules, with chain lengths of 25 up 45 siloxane units, were traceable. The examination of a second product of higher viscosity yielded unexpected results. The heat-treated extract contained none of the siloxanes that were detected in the starting material. Siloxanes of chain lengths of up to 45 units having molecular weights of over 3000 g/mol could not be found after the siliconization process. This led to the conclusion that not only vaporization effects must be responsible for their absence, but also that silicone suffers from a heat-induced degradation. The results of SEC and GC analysis were supported by each other. The whole molecular weight distribution and four distinct fractions were characterized by SEC, while the GC analysis was capable of a high-resolution view into the LMWS fraction below 3500 g/mol. In conclusion, the benefit of the heat treatment is that no LMWS, a source of toxicological concern, remain in the respective containers. On the other hand, an increase in molecular weight and viscosity of the silicone oil, and thus a possible change of the lubricating properties, is likely to happen through removal of LMWS. But these changes probably have no impact on the hydrophobic surface behavior of silicone-treated glass.

29Si imaging of silicone breast implants and intraocular silicone oil

Silicon-29 (29Si) imaging was investigated as a potential imaging modality for monitoring silicone prostheses in humans. The 29Si relaxation times of several silicone gels were measured and found to average T1 = 21.2 +/- 1.5 s and T2 = 207 +/- 40 ms, with no significant difference between virgin and explanted gels. A single-shot half-Fourier rapid acquisition with relaxation enhancement (RARE) and a refocused gradient-echo sequence were used for acquiring 29Si images with 5 x 5 mm2 resolution and no slice selection. Three volunteers with silicone-gel-filled breast implants and one subject with an intraocular silicone oil injection were thus examined in a total acquisition time of 10-15 min per image. On all 29Si images, the shape of the silicone object was well depicted. Although at present, conventional proton images are superior in resolution and signal-to-noise ratio, 29Si imaging has the advantage of optimal specificity, since only the silicone itself is visible.

Quality evaluation of radiographic contrast media in large-volume prefilled syringes and vials

RATIONALE AND OBJECTIVES

The authors compared the particle contaminations of radiographic contrast media packaged in large-volume prefilled syringes and vials.

MATERIALS AND METHODS

Particle counting was performed for four contrast media packaged in large-volume prefilled syringes (iohexol, ioversol, ioversol for angiography, and ioxaglate) and three contrast media packaged in vials (iohexol, ioversol, and ioxaglate). X-ray emission spectrometry was performed to characterize the individual particles. The amount of silicone oil in the syringe was quantified with infrared spectrophotometry.

RESULTS

The particle contamination in syringes containing ioversol was higher than that in syringes containing iohexol or ioxaglate. Particle contamination in the vials was relatively low, except with ioxaglate. X-ray emission spectrometry of the components of the syringe and vial showed that the source of particles was internal material released from the rubber stopper or inner surface.

CONCLUSION

The particle counts for contrast media packaged in syringes and vials varied considerably among the different contrast media and were related to the amount of silicone oil on the inner surface and rubber piston of the syringe.

[Toxic substances with silicone oil after intraocular injections]

In articles about the analysis of intraocular silicone oil, mostly the amount and toxicity of low-molecular-weight components (LMWC) have been investigated. This study was intended to analyze the components of silicone oil following a longer intraocular application. We analyzed silicone oil removed from human eyes with PVR a few months postoperatively. The fraction of LMWC was further investigated and we separated 16 different components belonging to hexachlorhexanes (HCH), polybiphenyls (PCB) and dichlor-diphenyl-trichlorethane (DDT). All these substances are said to have a toxic and cancerogenic effect as well as weakening the immune system. The concentration of these organic chloride components measured in intraocular injected silicone oil is about the same as fatty tissue but exceeds the concentration in human blood enormously. Possible damage to the retina by these toxic substances is another reason for early removal of silicone oil if the situation of the retina is stable.

Release of Ofloxacin from silicone gel sheet

From a drug delivery system using silicone gel, the amount of Ofloxacin (OFLX) released or transferred to a wound and blood was measured over 2 weeks. From three types of silicone gel containing 2, 0.2 and 0.02% OFLX respectively, levels from that with 2% OFLX were highest, approximately two to five times higher than that with 0.02% OFLX. Statistically significant differences were found between the three types (P < 0.01, Student's t-test). When used in partial thickness skin wounds on rats, only an extremely small amount of OFLX was detected in the serum, being higher under gel containing 2% OFLX. In a clinical study, however, no drug was detected either in the blood or the wound after 1 week.

The influence of silicone oil in toothpastes on abrasion in vitro

The influence of addition of silicone oil to toothpastes was investigated in vitro using a laser reflexion technique and a profilometer. Acrylic plates were subjected to brushing in a brushing machine containing a toothpaste-water slurry. Four different toothpastes were used with and without the addition of 10% silicone oil. The results showed that the addition of silicone oil to a toothpaste decreased the abrasion rate and made the surface of the treated material smoother than after brushing with the original toothpaste.

Identification of silicone oil in the retina after intravitreal injection

Retinal tissue obtained from 2 eyes that had been injected with silicone oil for 2 years was stained with monoclonal antibodies against macrophages and studied by light and electron microscopy and energy-dispersive x-ray analysis. Both specimens showed areas with a relatively intact architecture as well as parts with loss of normal structure. In both areas, immunostaining showed single intraretinal macrophages. Energy-dispersive x-ray results clearly demonstrated that some of the intracellular and extracellular vacuoles within the retina represented the storage sites of silicone.

Fourier transform infrared spectroscopic analysis of organic oil mastitis

The prevalent use of "medical grade" silicone oils, gels, and elastomers in medical practice has largely obscured the fact that other (illicit) materials also are still in use. Injection fluids used for tissue augmentations are sometimes composed of adulterated silicone oil formulations containing a variety of organic oils. The differential diagnosis between silicone mastitis and other organic oil mastitis in biopsy and mastectomy specimens cannot be resolved by oral history and histopathologic examination alone. In two of three specimens clinically and histopathologically diagnosed initially as silicone mastitis at the authors' institution, examination by Fourier transform infrared spectroscopy revealed that the principal organic oils were mineral oil and soy or olive oil. Only one specimen of mastitis contained silicone oil. In view of the significant prognostic as well as medicolegal implications of the pathologic diagnosis, the generic term "organic oil mastitis" should be used in the absence of additional objective data.

Ocular toxicity of low-molecular-weight components of silicone and fluorosilicone oils

Silicone oil (SiO) and fluorosilicone oil (FSiO) are injected into the vitreous cavity in difficult cases of retinal detachment surgery. SiO and FSiO contain linear and cyclic low-molecular-weight components (LMWC) that are thought to cause ocular toxicity. Using the purified oils (without LMWC) and some of the individual LMWC, the authors evaluated the relation of the LMWC to the short-term ocular toxicity of the oils. When octamethylcyclotetrasiloxane or other single small species of linear and cyclic LMWC of SiO were injected into the rabbit anterior chamber, severe inflammation and corneal edema were induced. The ocular responses to the single species of the LMWC of SiO decreased with an increase of the molecular weights. Cyclic LMWC of FSiO (a mixture of trimethyl-3,3,3-trifluoropropylcyclotrisiloxane and tetramethyl-3,3,3-trifluoropropylcyclotetrasiloxane) also induced inflammation and corneal edema. However, unpurified SiO and FSiO, as well as purified oils (via solvent fractionation), did not cause significant adverse ocular response, presumably because the amounts of LMWC (especially the smallest species) in the oils were relatively small. Using gas chromatography, the authors analyzed SiO and FSiO recovered from rabbit and human vitreous cavities up to 2 yr after injection. In most of the cases, the concentrations of LMWC in SiO decreased after injection. This is consistent with the possibility that LMWC diffused from the oils into the ocular tissues. The long-term effect of LMWC in intraocular SiO and FSiO has not been determined. However, diffusion of LMWC into ocular tissues may relate to the chronic ocular toxicity of the oils.

Analysis and fractionation of silicone and fluorosilicone oils for intraocular use

Silicone oil (SiO) and fluorosilicone oil (FSiO) are useful in difficult cases of retinal detachment surgery. Unidentified low-molecular-weight components (LMWC) and residual catalysts in SiO and FSiO have been implicated in the adverse reactions of the oils in the eye. The authors analyzed LMWC of SiO and FSiO using a gas chromatograph (GC) equipped with a 6-ft x 2-mm column packed with 3% SP-2250 and a flame-ionization detector. By commercially available standards and a homologous series plot, MD3M to MD23M (linear LMWC) and D4 to D30 (cyclic LMWC) were positively identified in commercial-grade 1000-centistokes (cs) SiO. Commercial-grade 12,500-cs SiO contained GC-detectable LMWC (up to MD28M and D30) at higher concentrations than commercial-grade 1000 cs SiO, although the weight percent of acetone-extractable LMWC (including those larger than MD28M and D30) was less in the former than in the latter. The GC-detectable LMWC in most medical-grade SiO were less than those in commercial-grade SiO. Tetramethylammonium siloxanolate (a residual catalyst) and tributylphosphine oxide (a heat-decomposition product of a polymerization catalyst) were tentatively identified in commercial- and medical-grade 12,500-cs SiO, respectively. Commercial-grade 1000- and 10,000-cs FSiO also contained LMWC, including F3 and/or F4 (cyclic LMWC). To eliminate LMWC from the oils, the authors developed a solvent fractionation method using acetone for SiO and hexane for FSiO. After continuous solvent extraction of SiO for 2 weeks and FSiO for 3 weeks, all measurable LMWC were eliminated from the oils.

Precipitate analysis from an indwelling total parenteral nutrition catheter

The composition of a precipitate obtained from a silastic right atrial catheter was determined. The precipitate was collected and washed with deionized water thoroughly before subjecting portions of it to organic and inorganic analysis. Inorganic analysis was conducted using scanning electron microscopy and x-ray spectroscopy for sodium, aluminum, silicone, sulfur, chlorine, and calcium. Phosphorus analysis was conducted by a commercial laboratory. Organic analysis was conducted by thin layer chromatography with cholesterol, phosphatidyl serine, phosphatidyl choline, phosphatidyl ethanolamine, and sphingomyelin as standards. Silicone, calcium, and phosphorus and three organic compounds, which could not be conclusively identified, were found. The precipitate was most likely calcium phosphate intermixed with silicone oil lubricant and residual total parenteral nutrition (TPN) solution. This formed in the catheter at body temperature probably due to incomplete catheter flushing.

Peritoneal reaction to liquid silicone: an experimental study

Silicone oils (polymethylsiloxanes) with different viscosities (200, 1000 and 5000 cSt) and a fluorinated silicone oil (5000 cSt) were injected into the peritoneum of CBA mice. Three weeks after the injection, peritoneal exudates were obtained and investigated using light and electron microscopy. For each silicone-oil type, light-microscopic examination revealed the presence of abundant extracellular lipid-like droplets and a dense cellular infiltrate composed of macrophages, lymphocytes and multinucleated giant cells. Lipid-like inclusions were observed in macrophages and multinucleated giant cells. These intracellular inclusions were revealed to be membrane bound by transmission electron microscopy. We observed no differences with respect to the amount of phagocytotic activity for the different silicone-oil types tested. Purified silicone oils of lower viscosity (OP 200 and OP 1000) resulted in the mildest chronic inflammatory reaction. Our results suggest that emulsification, phagocytosis and granulomatous inflammation are associated with intraocular silicone-oil implantation. The question of which properties would make a silicone oil most suitable for clinical use requires further investigation.