- Research article
- Open Access
Influence of emulsifiers on the characteristics of polyurethane structures used as drug carrier
© Heghes et al.; licensee Chemistry Central Ltd. 2013
- Received: 10 January 2013
- Accepted: 1 April 2013
- Published: 10 April 2013
Emulsifiers have a significant role in the emulsion polymerization by reducing the interfacial tension thus increasing the stability of colloidal dispersions of polymer nanostructures. This study evaluates the impact of four emulsifiers on the characteristics of polyurethane hollow structures used as drug delivery system.
Polyurethane (PU) structures with high stability and sizes ranging from nano- to micro-scale were obtained by interfacial polyaddition combined with spontaneous emulsification. The pH of PU aqueous solutions (0.1% w/w) was slightly acidic, which is acceptable for products intended to be used on human skin. Agglomerated structures with irregular shapes were observed by scanning electron microscopy. The synthesized structures have melting points between 245-265°C and reveal promising results in different evaluations (TEWL, mexametry) on murine skin.
In this study hollow PU structures of reduced noxiousness were synthesized, their size and stability being influenced by emulsifiers. Such structures could be used in the pharmaceutical field as future drug delivery systems.
- Hollow structures
- Hexamethylene diisocyanate
- Zeta potential
Several varieties of structures (polymeric and metal nano- and micro-particles, liposomes, micelles, quantum dots, dendrimers, lipoproteins, nanotubs) were used as drug carriers in order to reduce drug metabolism, drug toxicity and to prolong in vivo drug activity . The liver isoenzymes known as cytochrome P450 are involved in phase I of drug metabolism . During a study of drug elimination pathways it was established that the cytochrome P450 is responsible for complete removal from the human body of more than a half of 400 drugs marketed in Europe and US . Toxicity studies for polymer-methotrexate conjugate vs. free methotrexate on murine rheumatoid arthritis model indicate that the free compound starts to cause animals’death at the maximum tolerated dose and is highly toxic at LD50 level, while the polymer-methotrexate conjugate shows no toxicity at the same equivalent concentrations . The drug carriers can prolong the in vivo drug activity, both by their controlled drug-release technology and a long-lasting target binding and rebinding mechanism .
Polyurethanes are commonly used in medical applications and their use continues to expand due to their versatility, biocompatibility and hemocompatibility. There are several types of PU, including the following: liquid PU for hollow-fiber devices, PU for dip-molding, PU coatings, biostable PU and thermoplastic PU . Sivak WN  synthesized a novel PU drug delivery system based on lysine diisocyanate and glycerol using various tertiary amines and organometallic urethane as catalysts. The use of LDI-glycerol PU foams as drug carriers for the controlled release of 7-tert-butyldimethylsilyl-10-hydroxy-camptothecin (DB-67) revealed that such foams were capable of delivering therapeutic concentrations of DB-67 in vitro over an 11 weeks trial period .
The purpose of the present investigation was to develop aliphatic PU structures with a diameter in the range of 100-300 nm in the absence of a catalyst. We also studied the effect of four emulsifiers on the structures’ size and stability and also their noxiousness on murine skin model.
The development of novel targeted nano-polymers in the drug delivery field is currently a research topic of high interest [9, 10]. In our research the main aim was to avoid the potentially toxic additional raw materials. Only aliphatic compounds were used even if it is well-known that these compounds lead to final products of poor physical and mechanical properties . In this synthesis the presence of a chains’ initiator was not necessary and the reaction went without catalyst. Unlike previous studies  a single surfactant has been used instead of a mixture (lipophilic or hydrophilic) and only in a small amount.
The pH values of PU solutions were determined using a Schott TitroLine at 25°C as described in the literature . The measurements were made in triplicate and data were expressed as mean and standard deviation. The obtained samples show slightly acidic pH values (5.88±0.11 for sample PuS-1, 6.07±0.09 for sample PuS-2, 5.98±0.16 for PuS-3 and 6.24±0.09 for sample PuS-4). The above pH values are appropriate for products intended for skin application considering that skin pH is around 5.80 for men and around 5.54 for women . Variable skin pH values were reported in the literature, all in the acidic domain, but varying from 4.0 to 7.0 depending on the purpose of using . These slightly acidic solutions are acceptable for dermal applications because they do not cause dry skin as a regular soap does and also maintain the normal skin microflora.
The PU structures characteristics obtained by Zetasizer Nano ZS
Particle size (nm)
Zeta potential (mV) mean ± SD
Mean ± SD
164 ± 12
33.9 ± 5.0
201 ± 19
37.5 ± 4.4
298 ± 11
23.0 ± 4.8
379 ± 23
29.7 ± 3.1
Zeta potential values are used to predict particles’ stability, stable particles presenting a zeta potential more negative than -30 mV or more positive than +30 mV . All this considered, the PU structures obtained in the first two experiments (using Cremophor EL and Cremophor A6 as emulsifiers) are considered the most stable products.
In this research PU structures were synthesized using a well-known procedure, the interfacial polyaddition combined with spontaneous emulsification. HMDI in acetone was used as isocyanate component and a mixture of MEG, 1,4-BD and PEG 200 in water was used as hydroxylic component. Four different emulsifiers were used and the synthesis was done without any chain initiator or catalyst. The PU structures showed a good stability, melting points between 245-265°C, and sizes between 150-400 nm. The PU structures were embedded in a cream for topical applications on murine skin. Evolution of TEWL, melanin content and skin erythema were recorded for a period of 30 days. The comparative analysis revealed that PU structures based on Cremophor A6 present the best toxicological profile and can be used as drug carriers for therapeutic purposes.
Hexamethylene diisocyanate (HMDI), polyethylene glycol (PEG 200) and acetone were obtained from Merck (Germany). Emulsifiers (Cremophor EL, Cremophor A6, Cremophor A25, and Cremophor RH40) were kindly donated by our colleagues from University of Szeged (Hungary). Mono-ethylene glycol (MEG) was purchased from Lach-Ner s.r.o. (Czech Rep.) while 1,4-butanediol (1,4-BD) was purchased from Carl Roth GmbH (Germany). All substances were used as received.
The influence of the aqueous components ratio , isocyanate component , and influence of stirring speed  were already studied by our team in order to optimize the structures sizes and stability.
Isocyanate and hydroxyl components were used in a 1:1.1 molar ratio in order to reduce the amount of secondary products (amines) and to ensure an easier washing of products by using distilled water.
Phases preparation – HMDI in acetone 0.5 mM solution (organic phase) was heated at 40°C; MEG, 1,4-BD and PEG 200 (1:1:2, molar ratio) in distilled water 0.5 mM solution (aqueous phase) was mixed with different emulsifiers and heated at 40°C.
The organic phase was injected into the aqueous phase at 40°C under magnetic stirring (500 rpm). The stirring was maintained for 4 hours at 40°C in order to ensure the maturation of the PU structures walls, even if the structures were formed in the first three minutes.
Acetone and a part of water were removed by slow evaporation in the oven, keeping the suspensions as thin layers (approx. 3 mm) in Petri dishes at 60°C for 12 hours. Products were purified by three cycles of centrifugation and dispersion in a mixture of water-acetone (1:1, v/v) in order to eliminate possible secondary products or unreacted raw materials.
The previously described procedure was repeated four times with different emulsifiers, which were chosen in order to study their effects on the PU characteristics (samples: PuS-1 with Cremophor EL, 1.5 ml; PuS-2 with Cremophor A6, 0.2 g; PuS-3 with Cremophor A25, 0.2 g; PuS-4 with Cremophor RH40, 0.2 g). The samples were carefully dried and the pH of PU aqueous solutions was measured at the same concentration.
Physical and chemical characterization
The shape and morphology of the final PU structures were examined with a Hitachi 2400S SEM as already described in the literature .
Thermal analysis was carried out using a Mettler-Toledo 821e instrument between 30-300°C because most of the urethane groups (-NH-COO-) are stable in this temperature range .
Particles size and charge were measured using a Zetasizer Nano series equipment Nano-Zs, Malvern Instruments. Samples were diluted in distilled water at a ratio of 1:5000 v/v. The measurements were carried out in duplicate for each sample.
In vitro characterization of similar PU structures was already done by our team by testing of mesenchymal stem cells (MSCs) viability. There were obtained good results after 48 hours based on the Alamar Blue test .
Ten CD1Nu/Nu eight weeks old female mice were purchased from Charles River (Sulzfeld, Germany). The protocol followed all National Institute of Animal Health (NIAH) rules: during the experiment animals were maintained in standard conditions of 12 hours light-dark cycle, food and water ad libitum, 24±1°C, humidity above 55%. Mice were divided into five equal groups (2 mice for blank cream and each PU structures type, respectively).
Evaluation of skin parameters
PU structures were included in a cream prepared as previously described in the literature by Pavicic T et al.  in order to observe how they affect skin parameters. The blank cream used was an oil-in-water emulsion containing water, hydrogenated polydecene, steareth-2, cetearyl alcohol, phenoxyethanol, methylparaben, diazolidinyl urea and disodium EDTA; the other formulations contain the same ingredients and additionally 0.2% PU structures. The cream was stretched with a gentle massage till it was totally absorbed into the back skin every third day (1 ml / application).
After each application, determination of skin parameters was performed within 30 minutes. All the measurements were carried out according to the published guidelines  with a Multiprobe Adapter System (MPA5) from Courage&Khazaka Electronics, Germany, equipped with a Tewameter®TM300 probe and a Mexameter®MX18 probe. All measurements were done at the same moment of the day, by the same operator, in a narrow range of temperature (24±1°C) and air humidity (45±3%).
The nude mice have been used in many studies in immunology, pathology, genetics, virology, parasitology, endocrinology, dermatology, radiology and many other areas . Nude mice are not bald but instead show an 'abortive' reduced hair growth on different sites of the integument . In this research, CD1Nu/Nu female mice skin was chosen to study newly synthesized PU structures’ noxiousness; their skin is sensitive to experimentally induced infections or to other diseases, the lack of hair being the most significant predisposing factor .
Skin is the soft outer layer of humans and most animals. The skin plays a crucial role in protecting the body against pathogens . Another main role is the function as a barrier to water permeation, a phenomenon of normal transfer of water through the stratum corneum into the atmosphere, known as transepidermal water loss (TEWL), which represents part of insensible water loss . TEWL may increase due to disruption of the skin barrier (wounds, scratches, burns, exposure to solvents or surfactants, extreme dryness) and is affected by humidity, temperature, season and moisture content of the skin (hydration level) .
Transepidermal water loss (TEWL) was reported to predict the irritation potential of a given compound, e.g. a notable increase of TEWL, meaning a significant reduction of the skin barrier function, was recorded when sodium laurylsulfate (SLS) was applied on the skin . In the last years, TEWL studies focused on the benefits of phytocompounds used in cosmetology  and of the anti-aging skin products . In this research, the measurements with Tewameter®TM300 probe were accomplished following a procedure previously described in the literature : the probe was recalibrated in the first day of the trial according to the manufacturer’s indications  while room humidity and temperature were continuously monitored and kept in a narrow range of values.
Mexametry is an easy, quick and inexpensive technique used to determine the two components mainly responsible for the colour of the skin: melanin and haemoglobin (erythema) . In this study, a Mexameter®MX18 probe with three light-emitting diodes for green, red and infrared light was used. Instrumental evaluations of skin colour were performed after each cream application (every third day). The probe was maintained on the application spot until the device software displayed the measured values on the computer screen (1-3 seconds).
All measurements using the Courage&Khazaka MPA5 device were done in triplicate and data were expressed as mean and standard deviation of the differences between the current day and the first day of the trial for the same mouse.
Paired Student’s t tests or One-way Anova followed by Bonferroni’s post-tests were used to determine the statistical difference between different experimental and blank groups: *, ** and *** indicate p<0.05, p<0.01 and <0.001.
We would like to thank to Srinivas Ganta and Mansoor M Amiji from the Department of Pharmaceutical Sciences (Northeastern University, Boston, US) for the measurement of particle size and charge.
- Torchilin VP: Introduction. Nanocarriers for drug delivery: needs and requirements. Nanoparticulates As Drug Carriers. Edited by: Torchilin VP. 2006, London: Imperial College Press, 1-8.View ArticleGoogle Scholar
- Ogu CC, Maxa JL: Drug interactions due to cytochrome P450. Proc (Bayl Univ Med Cent). 2000, 13 (4): 421-423.Google Scholar
- Clarke SJ, BC: Human cytochromes P450 and their role in metabolism-based drug-drug interactions. Drug-drug interactions. 2002, New York: Marcel Dekker, Inc, 55-88.Google Scholar
- Pachence JM, Simon P: Novel methods for site-directed drug delivery. Drug Delivery Technol. 2003, 3 (1): 40-Google Scholar
- Vauquelin G, Charlton SJ: Long-lasting target binding and rebinding as mechanisms to prolong in vivo drug action. Br J Pharmacol. 2010, 161 (3): 488-508. 10.1111/j.1476-5381.2010.00936.x.View ArticleGoogle Scholar
- Wright J: Using Polyurethanes in Medical Applications. Medical Device & Diagnostic Industry. 2006, 28 (3): 98-109.Google Scholar
- Sivak WN: Synthesis and Characterization of Novel Polyurethane Drug Delivery Systems. 2007, Doctoral Dissertation: University of PittsburghGoogle Scholar
- Sivak WN, Pollack IF, Petoud S, Zamboni WC, Zhang J, Beckman EJ: Catalyst-dependent drug loading of LDI-glycerol polyurethane foams leads to differing controlled release profiles. Acta Biomater. 2008, 4 (5): 1263-1274. 10.1016/j.actbio.2008.01.008.View ArticleGoogle Scholar
- Kim D, Kim E, Lee J, Hong S, Sung W, Lim N, Park CG, Kim K: Direct synthesis of polymer nanocapsules: self-assembly of polymer hollow spheres through irreversible covalent bond formation. J Am Chem Soc. 2010, 132 (28): 9908-9919. 10.1021/ja1039242.View ArticleGoogle Scholar
- Liu X, Basu A: Core functionalization of hollow polymer nanocapsules. J Am Chem Soc. 2009, 131 (16): 5718-5719. 10.1021/ja809619w.View ArticleGoogle Scholar
- Polyurethanes types. http://www.merquinsa.com/whats/FPPUtypes1.pdf.
- Bouchemal K, Briancon S, Perrier E, Fessi H, Bonnet I, Zydowick N: Synthesis and characterization of polyurethane and poly(ether urethane) nanocapsules using a new technique of interfacial polycondensation combined to spontaneous emulsification. Int J Pharm. 2004, 269: 89-100. 10.1016/j.ijpharm.2003.09.025.View ArticleGoogle Scholar
- Redes L, Borcan F, Lonescu D, Ambrus R, Galuscan A, Popovici I: Synthesis and characterization of a polyurethane transdermal carrier for lupeol. J Agroaliment Process Technol. 2011, 17 (3): 321-325.Google Scholar
- Ehlers C, Ivens UI, Møller ML, Senderovitz T, Serup J: Females have lower skin surface pH than men. A study on the surface of gender, forearm site variation, right/left difference and time of the day on the skin surface pH. Skin Res Technol. 2001, 7 (2): 90-94. 10.1034/j.1600-0846.2001.70206.x.View ArticleGoogle Scholar
- Lambers H, Piessens S, Bloem A, Pronk H, Finkel P: Natural skin surface pH is on average below 5, which is beneficial for its resident flora. Int J Cosmet Sci. 2006, 28 (5): 359-370. 10.1111/j.1467-2494.2006.00344.x.View ArticleGoogle Scholar
- Gallardo V, Morales ME, Ruiz MA, Delgado AV: An experimental investigation of the stability of ethylcellulose latex. Correlation between zeta potential and sedimentation. Eur J Pharm Sci. 2005, 26: 170-175. 10.1016/j.ejps.2005.05.008.View ArticleGoogle Scholar
- Champion JA, Katare YK, Mitragotri S: Particle shape: A new design parameter for micro- and nanoscale drug delivery carriers. J Control Release. 2007, 121: 3-9. 10.1016/j.jconrel.2007.03.022.View ArticleGoogle Scholar
- Zhang XD, Macosko CW, Davis HT, Nikolov AD, Wasan DT: Role of Silicone Surfactant in Flexible Polyurethane Foam. J. Coll. Interface Sci. 1999, 215: 270-279. 10.1006/jcis.1999.6233.View ArticleGoogle Scholar
- Differential Scanning Calorimetry - Science @ Stanislaus. http://science.csustan.edu/perona/4012/dsc_exp.pdf.
- Royall PG, Craig DQM, Doherty C: Characterisation of the Glass Transition of an Amorphous Drug Using Modulated DSC. Pharm Res. 1998, 15: 1117-1121. 10.1023/A:1011902816175.View ArticleGoogle Scholar
- Hentschel T, Munstedt H: Kinetics of the molar mass decrease in a polyurethane melt: a rheological study. Polymer. 2001, 42: 3195-3203. 10.1016/S0032-3861(00)00489-4.View ArticleGoogle Scholar
- Tanriverdi F, Borlu M, Atmaca H, Koc CA, Unluhizarci K, Utas S, Kelestimur F: Investigation of the skin characteristics in patients with severe GH deficiency and the effects of 6 months of GH replacement therapy: a randomized placebo controlled study. Clin Endocrinol. 2006, 65: 579-585. 10.1111/j.1365-2265.2006.02631.x.View ArticleGoogle Scholar
- Agar N, Young AR: Melanogenesis: a photoprotective response to DNA damage?. Mutat Res. 2005, 571 (1–2): 121-132.View ArticleGoogle Scholar
- Atlas SW, Braffman BH, LoBrutto R, Elder DE, Herlyn D: Human malignant melanomas with varying degrees of melanin content in nude mice: MR imaging, histopathology, and electron paramagnetic resonance. J Comput Assist Tomogr. 1990, 14 (4): 547-554. 10.1097/00004728-199007000-00009.View ArticleGoogle Scholar
- Dadachova E, Revskaya E, Sesay MA, Damania H, Boucher R, Sellers RS, Howell RC, Burns L, Thornton GB, Natarajan A, Mirick GR, DeNardo SJ, DeNardo GL, Casadevall A: Pre-clinical evaluation and efficacy studies of a melanin-binding IgM antibody labeled with 188Re against experimental human metastatic melanoma in nude mice. Cancer Biol Ther. 2008, 7 (7): 1116-1127. 10.4161/cbt.7.7.6197.View ArticleGoogle Scholar
- Curtis A, Calabro K, Galarneau JR, Bigio IJ, Krucker T: Temporal Variations of Skin Pigmentation in C57Bl/6 Mice Affect Optical Bioluminescence Quantitation. Mol Imaging Biol. 2011, 13 (6): 1114-1123. 10.1007/s11307-010-0440-8.View ArticleGoogle Scholar
- Costin GE, Hearing VJ: Human skin pigmentation: melanocytes modulate skin color in response to stress. FASEB J. 2007, 21 (4): 976-994. 10.1096/fj.06-6649rev.View ArticleGoogle Scholar
- The American Heritage medical dictionary, Editors of the American Heritage Dictionaries: Boston, MA: Houghton Mifflin HarcourtGoogle Scholar
- Wilhelm KP, Freitag G, Wolff HH: Surfactant-induced skin irritation and skin repair. Evaluation of the acute human irritation model by noninvasive techniques. J Am Acad Dermatol. 1994, 30 (6): 944-949. 10.1016/S0190-9622(94)70114-8.View ArticleGoogle Scholar
- Borcan F, Dehelean CA, Anghel A: Obtaining and Characterization of Polyether-Urethane Nanostructures – A Possible Drug Carrier System. Ann. West Univ. Timisoara, Series Chem. 2011, 20 (1): 41-46.Google Scholar
- Borcan F, Soica CM, Ganta S, Amiji MM, Dehelean CA, Munteanu MF: Synthesis and preliminary in vivo evaluations of polyurethane microstructures for transdermal drug delivery. Chem Cent J. 2012, 6 (1): 87-10.1186/1752-153X-6-87.View ArticleGoogle Scholar
- Borcan F, Soica CM, Dehelean CA, Ganta S, Amiji MM: Size and Stability Optimization for Polyurethane Nanostructures used as Transdermal Drug Vehicle. Rev. Chim. Bucharest. 2012, 63 (11): 1164-1166.Google Scholar
- Soica CM, Peev CI, Ciurlea S, Ambrus R, Dehelean CA: Physico-chemical and toxicological evaluations of betulin and betulinic acid interactions with hydrophilic cyclodextrins. Farmacia. 2010, 58 (5): 611-619.Google Scholar
- Simon J, Barla F, Kelemen-Haller A, Farkas F, Kraxner M: Thermal stability of polyurethanes. Chromatographia. 1988, 25 (2): 99-106. 10.1007/BF02259024.View ArticleGoogle Scholar
- Pavicic T, Gauglitz GG, Lersch P, Schwach-Abdellaoui K, Malle B, Korting HC, Farwick M: Efficacy of Cream-Based Novel Formulations of Hyaluronic Acid of Different Molecular Weights in Anti-Wrinkle Treatment. J Drugs Dermatol. 2011, 10 (9): 990-1000.Google Scholar
- Rogiers V, EEMCO Group: EEMCO guidance for the assessment of transepidermal water loss in cosmetic sciences. Skin Pharmacol Appl Skin Physiol. 2001, 14 (2): 117-128. 10.1159/000056341.View ArticleGoogle Scholar
- Sharkey FE, Fogh J: Considerations in the use of nude mice for cancer research. Cancer Metastasis Rev. 1984, 3: 341-360. 10.1007/BF00051459.View ArticleGoogle Scholar
- Militzer K: Hair growth pattern in nude mice. Cells Tissues Organs. 2001, 168 (4): 285-294. 10.1159/000047845.View ArticleGoogle Scholar
- Fox JG, Barthold SW, Davisson MT, Newcomer CE, Quimby FW, Smith AL: The Mouse in Biomedical Research. 2006, Burlington MA: Academic Press, 2Google Scholar
- Proksch E, Brandner JM, Jensen JM: The skin: an indispensable barrier. Exp Dermatol. 2008, 17 (12): 1063-1072. 10.1111/j.1600-0625.2008.00786.x.View ArticleGoogle Scholar
- Madison KC: Barrier function of the skin: "la raison d'être" of the epidermis. J Invest Dermatol. 2003, 121 (2): 231-241. 10.1046/j.1523-1747.2003.12359.x.View ArticleGoogle Scholar
- Chemistry of skin: Trans-epidermal water loss (TEWL). http://swiftcraftymonkey.blogspot.ro/2010/03/chemistry-of-skin-trans-epidermal-water.html.
- Antoine JL, Contreras JL, van Neste D: ph Influence on surfactant-induced skin irritation. Dermatosen in Beruf und Umwelt. 1989, 37 (3): 96-100.Google Scholar
- Dell’Acqua G, Schweikert K, Calloni G: Oak, Green Tea and Orange Derivatives to Disrupt JAK/STAT, NF-kB Irritation Pathways. Cosmetics & Toiletries. 2011, 126 (1): 30-39.Google Scholar
- Thibodeau A: Anti-aging Skin Care Benefits of Saccharina longicruris Extract. Cosmetics & Toiletries. 2011, 126 (3): 208-216.Google Scholar
- Mündleina M, Valentina B, Chabicovskya R, Nicolicsa J, Weremczukb J, Tarapatab G, Jachowicz R: Comparison of transepidermal water loss (TEWL) measurements with two novel sensors based on different sensing principles. Sensors and Actuators A: Physical. 2008, 142 (1): 67-72. 10.1016/j.sna.2007.04.012.View ArticleGoogle Scholar
- MPA5-TM300 Manual. http://www.courage-khazaka.de.
- MPA5-MX18 Manual. http://www.courage-khazaka.de.
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