Film Formation from Colloidal Dispersions Stabilized by Sugar

Lectin-Recognizable Colloidal Dispersions Stabilized by n-Dodecyl β-d-Maltoside: Particle−Particle and Particle−Surface Interactions. Woo-Sung Ba...
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Biomacromolecules 2005, 6, 2615-2621

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Film Formation from Colloidal Dispersions Stabilized by Sugar Derivatives and Their Controllable Release for Selective Protein Adsorption Woo-Sung Bae,† David J. Lestage,† Michael Proia,‡ Sabine Heinhorst,‡ and Marek W. Urban*,† School of Polymers and High Performance Materials and Department of Chemistry and Biochemistry, The University of Southern Mississippi, Hattiesburg, Mississippi 39406 Received May 17, 2005; Revised Manuscript Received June 20, 2005

Although the use of sugar and sugar derivatives has been documented in polymer research for many years, there are no reports that would utilize these species as polymerization sites of colloidal polymeric particles that, later on, may be released during particle coalescence to form films with surfaces that differentiate protein adsorption. These studies show that, when n-dodecyl-β-D-maltoside (DDM) is utilized for the synthesis and stabilization of poly[methyl methacrylate-co-(n-butyl acrylate)] (p-MMA/nBA) colloidal particles, upon particle coalescence DDM stratifies near the film-air (F-A) interface. By using attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy and internal reflection infrared imaging (IRIRI), comparative adsorption studies on p-MMA/nBA surfaces exposed to globulin (Glo), fibrinogen (Fib), and bovine serum albumin (BSA) reveal that the presence of DDM selectively inhibits Glo and Fib adsorption, but does not affect BSA. The presence of DDM also enhances the rate of mobility of sodium dioctylsulfosuccinate (SDOSS) resulting from interactions between DDM and SDOSS moieties, and the surface morphologies change as a result of concentration variations of DDM in the colloidal dispersions. Introduction Recently, we reported1,2 that biologically active molecules such as phospholipids (PL) may effectively serve as dispersing agents in the synthesis of stable colloidal dispersions. While one function of these species is to stabilize colloidal dispersions, other studies also showed that PL are capable of self-stratifying near the surfaces during coalescence.3,4 The apparent ability to form unique morphological features near the film-air (F-A) interface may be controlled by such stimuli as pH, ionic strength of the colloidal solution, and temperature.5,6 As one would anticipate, the formation of surface morphological and crystallographic features also depend on PL’s chemical structures, a colloidal particle polymer matrix, and coalescence conditions.6,7 Since stratified PL near the F-A interface may serve numerous surface bioprocesses, sensing devices, or biorafts, there is an increasing interest in the development of polymeric surfaces with stimuli-responsive characteristics. Another avenue is the development of polymeric films with surfaces that are capable of feeding or destroying biologically active species8 in contact, and one of such entities is sugar derivatives. Although it is well-known that diverse functions of sugars and their derivatives in metabolism of living organisms and other biological processes9 make these species unique candidates for utilization and incorporation into man-made * To whom all correspondence should be addressed. † School of Polymers and High Performance Materials. ‡ Department of Chemistry and Biochemistry.

polymers, the primary focus of the past efforts was copolymerizing sugar derivatives using a free radical polymerization process10,11 or polymerization of nanospheres containing sugar derivatives and other polymer entities.12 These approaches, although promising, exhibit certain limitations, as an ultimate goal is to create functional surfaces containing controllable amounts of active stimuli-responsive species. Although the simplest approach would be the addition of these species to already complex formulations containing colloidal particles, the goal is to develop stimuli-responsive properties that will allow the control of colloidal stability and serve as adsorption/disorption surface sites for bioactive species after coalescence. Since adsorbed fibrinogen (Fib) and globulin (Glo) are known to induce platelet aggregation,13 and their hydrophilicity is the primary factor controlling surface adsorption,13-15 we will examine their adsorption properties on polymeric films obtained from methyl methacrylate (MMA) and n-butyl acrylate (nBA) colloidal particles stabilized by DDM and sodium dioctylsulfosuccinate (SDOSS). Experimental Section MMA, nBA, DDM, SDOSS, and potassium persulfate (KPS) were purchased from Aldrich Chemical Co. Fib, Glo, bovine serum albumin (BSA), and 2-morpholinoethanesulfonic acid (MES) were utilized in the protein adsorption test and were purchased from Sigma. MMA/nBA copolymer emulsions were synthesized using a semicontinuous process

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outlined elsewhere16 and adapted for small-scale emulsion polymerization. The reaction flask was immersed in a water bath preheated to 74 °C and purged with N2 gas. The reactor was charged with 10 mL of deionized and distilled (DDI) water, and while N2 purging for 30 min to remove oxygen, the content was stirred at 300 rpm. DDM and SDOSS concentrations were 5% (w/w) of the total monomer, and the ratio of DDM and SDOSS was 0, 10, 30, and 50% (w/ w) DDM of the total surfactant concentration. Such prepared pre-emulsion contained 41.95% (w/w) of MMA/nBA ) 1/1 dispersed in water. After 30 min of N2 purging, pre-emulsion and initiator solutions were fed at 0.333 and 0.095 mL/min into the vessel over periods of 3 and 3.5 h, respectively. After pre-emulsion feeding was completed, bath temperature was raised to 80 °C while a 5 mL initiator chaser solution was added. Upon cooling, the emulsion was filtered twice. The particle size analysis was performed using a Microtrac particle size analyzer model UPA250, and it was determined that the addition of DDM increases the size of colloidal particles up to 30% compared to those not containing DDM; however, particle size is not exactly proportional to DDM concentrations. In a typical experiment, 0.5 mL of colloidal dispersions were cast onto a poly(tetrafluoroethylene) (PTFE) substrate to obtain a film thickness of 300 µm. Aqueous colloidal dispersions of MMA/nBA copolymers containing 0% (MB-DDM-0), 10% (MB-DDM-10), 30% (MB-DDM30), and 50% DDM (MB-DDM-50) were allowed to coalesce under 50% relative humidity (RH) and 30 °C for 5 days. Polarized attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectra were collected using a BioRad FTS-6000 FT-IR single-beam spectrometer set at 4 cm-1 resolution equipped with a ZnSe polarizer. A 45° face angle Ge crystal with 50 × 20 × 3 mm3 dimensions was used. This configuration allows the analysis of the F-A and filmsubstrate (F-S) interfaces at approximately 0.5 µm from each interface upon removal of the film from the mold. The use of a ZnSe polarizer facilitates orientation studies by utilizing transverse electric (TE) and transverse magnetic (TM) modes of polarized IR light. Each spectrum represents 200 coadded scans ratioed against the same number of reference scans collected using an empty ATR cell. All spectra were corrected for spectral distortions and optical effects using Q-ATR software.17 To verify the band assignments resulting from interactions between SDOSS and water, we conducted model experiments where SDOSS, SDOSS/H2O, and 9:1, 7:3, and 1:1 ratios of SDOSS/DDM in water were analyzed spectroscopically. Figure 1 (traces A-E) illustrates the results of these experiments, and the origin of the 1073, 1068, 1050, 1046, 1043, 1023, and 1021 cm-1 bands is summarized in Table 1. It is apparent that the S-O symmetric stretching vibrations due to SDOSS shift toward lower wavenumbers as the DDM concentration increases, whereas the C-O stretching band due to DDM shifts toward higher wavenumbers. Glass transition temperatures (Tg) of colloidal films were measured using differential scanning calorimetry (TA Instruments, DSC Q 100) in a modulated mode at (2 °C/40 s during increasing average temperature at 3 °C/min up to 100

Bae et al.

Figure 1. ATR FT-IR spectra of (A) SDOSS, (B) SDOSS in H2O, (C) SDOSS/DDM ) 9:1 in H2O, (D) SDOSS/DDM ) 7:3 in H2O, and (E) SDOSS/DDM ) 1:1 in H2O.

°C. Table 2 provides compositions of colloidal dispersions prepared in these studies. Optical image and internal reflection IR imaging (IRIRI) experiments18 were obtained using a Digilab FTS 6000 Stingray imaging system with an internal reflection element (IRE). This system consists of a Digilab FTS 6000 spectrometer, a UMA 500 microscope, an ImagIR focal plane array (FPA) image detector, and a semispherical Ge IRE. IRIR images were collected using the following spectral acquisition parameters: undersampling ratio of 4, step-scan speed of 2.5 Hz, 1777 spectrometer steps, 64 images per step, and 8 cm-1 spectral resolution. In a typical experiment, spectral data set acquisition time was approximately 20 min. Image processing was performed using the Environment for Visualizing Images (ENVI) software (Research Systems, Inc., version 3.5). Appropriate baseline correction algorithms were applied to compensate for baseline deviations. The adsorption of protein on MB-DDM-50 and MBDDM-0 was evaluated using ATR FT-IR spectroscopy and IRIRI. The coalesced film was rinsed with DDI water, immersed, and equilibrated in the protein solution (initial concentration of protein: 500 mg/dm3) at ambient temperature for 24 h at pH 6.2, 5.6, and 5.6 MES buffer solution for Glo, Fib, and BSA, respectively. Latex films were then immersed in excess water for 15 min and rinsed to remove excess of unattached protein, followed by drying in a desiccator. Such films were placed on a Ge crystal and analyzed immediately using ATR FT-IR. The amount of adsorbed protein was determined by measuring the absorbance at ∼1705-1585 cm-1 due to the amide I bands characteristic of each protein. Surface heterogeneities were analyzed by IRIRI. Results and Discussion In an effort to create responsive and functional surfaces from colloidal particles containing sugar derivatives, SDOSS and DDM were introduced into an aqueous phase, followed

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Table 1. IR Bands of MMA/nBA in the Presence of DDM and SDOSS and Their Assignment surfactants

functional group -Na+

SDOSS

SO3 SO3-Na+- - -H2O SO3-Na+- - -H2O- - -H-O-DDM SDOSS/DDM ) 9:1 C-O (cyclic) C-O (-CH2-O-H) SDOSS/DDM ) 1:1 C-O (cyclic) C-O (-CH2-O-H)

DDM

Table 2. Composition and the Glass Transition Temperature (Tg) of MMA/nBA Colloidal Dispersions coalesced films MB-DDM-0 MB-DDM-10 MB-DDM-30 MB-DDM-50

starting components (wt. %) water MMA 69.12 69.12 69.12 69.12

14.40 14.40 14.40 14.40

nBA 14.40 14.40 14.40 14.40

SDOSS DDM K2S2O8 1.44 1.29 1.00 0.72

0 0.14 0.44 0.72

0.63 0.63 0.63 0.63

Tg 8 °C 5 °C -3 °C -4 °C

by free radical polymerization of MMA/nBA copolymer particles stabilized by SDOSS/DDM. Such dispersions were allowed to coalesce to form continuous films. As listed in Table 2, the total amount of SDOSS/DDM in an aqueous phase is 1.44% (w/w), which corresponds to 5% (w/w) of the total solids content, and MMA/nBA copolymer films prepared with different SDOSS/DDM percent (w/w) ratios exhibit variations of the Tg values. This behavior results from the enhanced free volume of the MMA/nBA polymer matrix by DDM as well as the reduced ionic content resulting from smaller amounts of SDOSS, thus smaller content of localized ionic clusters (LICs),5,6,19 although copolymer compositional drifts resulting from the presence of different SDOSS/DDM ratios cannot be ruled out. In an effort to determine the role of DDM in the synthesis of p-MMA/nBA and film formation, we utilized ATR FT-IR spectroscopy which, similarly to the previous studies,1,5-7,20,21 allows us to analyze the F-A and filmsubstrate (F-S) interfaces. Figure 2a,b shows spectra recorded from the F-A and F-S interfaces of coalesced films containing SDOSS and DDM. Although the total amount of DDM and SDOSS in the colloidal solution is 5% (w/w), it is quite apparent that the F-A and F-S interfaces exhibit different and rather unexpected levels of DDM and SDOSS. As seen in Figure 2, for MB-DDM-0 and MBDDM-10, SDOSS migrates toward the F-A interface, which is manifested by the increased intensity of the 1046 cm-1 (S-O symmetric stretch) band along with the bands at 1299 (S-O asymmetric stretch) and 1261 cm-1 (C-O stretch) (not shown).22 As the ratio of SDOSS to DDM changes from 1/0 to 1/1, when going from MB-DDM-0 to MB-DDM-50, while maintaining the total content of 5% (w/w), the band intensities due to SDOSS as well as DDM also change. Along with the results of the model studies shown in Figure 1, Figure 2 shows that SDOSS mainly migrates toward the F-A interface under 30 °C and 50% RH coalescence conditions and DDM facilitates migration of SDOSS toward the F-A interface. This is manifested by enhanced band intensities of the bands at 1046-1043 cm-1. These observations are in agreement with the recent studies,6 where migration of SDS was facilitated by the presence of

IR band (cm-1)

assignment

1050 1046 1043 1068 1021 1073 1023

S-O sym. stretch S-O sym. stretch SDOSS S-O sym. stretch C-O stretch

propylene glycol as a result of surface-interfacial interactions during coalescence, since earlier studies23,24 indicated that the presence of surfactant molecules on polymeric surfaces might often result in their preferential orientation. ATR FT-IR polarization experiments were conducted on p-MMA/nBA films containing DDM and SDOSS and showed that there are significant intensity differences for the bands recorded at TE and TM polarizations. These observation indicate that the dichroic ratio (R ) A|/A⊥, where A| is the absorbance for parallel (TE) polarized light and A⊥ is the absorbance for perpendicular (TM) polarized light) values are significantly smaller or greater than 1 (R ) 1 would indicate random orientation), and thus, in-plane SDOSS orientation is predominant. This is illustrated in Figure 2c, and these observations also indicate that significant orientations of SDOSS at the F-A interface with increasing DDM content occur at high concentration levels of SDOSS. Although we anticipated that the migration of DDM to the F-A interface will be significant because of favorable solubility in water, which upon evaporation will cause DDM migration to the F-A interface, as illustrated in Figure 2, DDM also facilitates mobilization of SDOSS to the F-A interfaces; thus, DDM-SDOSS interactions are surprisingly strong. As result of stratification of DDM-SDOSS at the F-A interface, let us examine surface heterogeneity. To illustrate morphological features resulting from stratification to the F-A interface, Figure 3a shows an optical image of the F-A interface of MB-DDM-50 films which appears to be optically heterogeneous. Because IRIRI allows us to obtain chemical information resulting from heterogeneities, we tuned in to the C-O stretching vibrations of -CH2-O-H groups on maltoside moieties of DDM (1023 cm-1) and C-O-C stretching vibrations of the nBA polymer matrix (1159 cm-1). As shown in Figure 3b, IRIRI experiments were performed on the regions that correspond to the designated optical areas with heterogeneities. Figure 3c illustrates IR spectra recorded from the areas labeled A and B in Figure 3b. As shown, the C-O stretching vibrations due to DDM at 1023 cm-1 exhibit higher band intensities at the area A. In contrast, the distribution of the 1159 cm-1 band due to C-O-C stretching vibrations of p-nBA diminishes, indicating its lower concentrations. These measurements also indicate that DDM stratifies near the p-MMA component of the p-MMA/n-BA matrix. Although one would anticipate the random copolymer formation, the presence of p-MMA and p-nBA components at the F-A interface of MB-DDM-50 results from compositional drifts that occur during emulsion polymerization. It is well-known that due-to-reactivity ratio differences between

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Figure 2. ATR FT-IR spectra recorded from the F-A and F-S interfaces in the 1100-950 cm-1 region for MMA/nBA prepared with various SDOSS/DDM ratios: (a) F-A (A, B) and F-S (A′, B′) of the MB-DDM-0 and MB-DDM-10, (b) F-A (A, B) and F-S (A′, B′) of the MB-DDM-30 and MB-DDM-50, (c) TE (A, B) and TM (A′, B′) of the MB-DDM-30 and MB-DDM-50.

Figure 3. (a) Optical images for the F-A interface of MB-DDM-50 film, (b) IRIR image recorded from the specified regions of optical images, and (c) IR spectra recorded from areas labeled A and B in IRIR image.

MMA and nBA (r1 ) 1.7 and r2 ) 0.38, MMA (M1)/n-BA (M2))25 as well as solubility in water (1.5 wt. % for MMA and 0.16 wt. % for nBA),26 MMA/nBA polymerization results in the formation of localized small blocks of each homopolymer.27-29 This feature results in heterogeneous surfaces and DDM, being soluble in an aqueous phase, migrates toward the F-A interface to form surface islands

near the p-MMA domains due to higher p-MMA hydrophilicity. As indicated in the Introduction, the primary objective of these studies is to develop surfaces that will be responsive to protein adsorption, which is one of the fundamental concerns regarding platelet adhesion and blood clotting.9,15,30 Because plasma protein adsorption plays a major role in vivo for the initiation of thrombus formation at the blood-material interface, the control of protein adsorption is of significance. Earlier studies indicated31 that poly[(2-glucosyloxyethyl methacrylate)-co-styrene] microspheres with hydrophilic surfaces suppress adsorption of bovine serum albumin (BSA) and globulin (Glo) more than the polystyrene microspheres; our efforts focused on Glo, Fib, and BSA adsorption to MMA/nBA. To determine interactions between polymeric films containing DDM and proteins, we exposed MMA/nBA films containing DDM to aqueous solutions containing Glo, Fib, and BSA proteins, and examined their F-A and F-S interfaces. Since the hydrophilic part of DDM is composed of two R-linked glucose units (maltose), the F-A interfaces containing high concentrations of DDM are expected to suppress protein adsorption. Furthermore, biocompatibility of saccharide moieties of DDM also plays an important role in polymeric surface-protein adhesion. To follow the protein adsorption process, ATR FT-IR spectroscopy was utilized, and as shown in Figure 4a, amide I bands32 due to Glo are detected in the 1705-1585 cm-1 regions after protein exposure. While traces A and B illustrate ATR FT-IR spectra recorded from the F-S and F-A interfaces of MB-DDM-0, respectively, traces C and D are spectra recorded from the F-S and F-A interfaces of films containing a 1:1 ratio of SDOSS/DDM. As seen, similar protein adsorption is detected, with the exception of the F-A interface (trace D) of MB-DDM-50 with a significantly reduced amide I band indicating that the presence of DDM, which migrated toward the F-A interface, suppresses Glo adsorption at this interface. For reference, trace E illustrates ATR FT-IR spectrum recorded from the F-A interface of the MB-DDM-series, which were exposed to the MES buffer

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Figure 4. ATR FT-IR spectra recorded from protein-adsorbed MB-DDM-0 film and MB-DDM-50 film in the 1705-1585 cm-1 region (amide I group of each protein): (a) Glo adsorption test on film interfaces (A-E), (b) Fib adsorption test on film interfaces (A-E), and (c) BSA adsorption test on film interfaces (A-E). For reference purposes, the IR spectra of MES buffer solution exposed MB-DDM-50 film without proteins (trace E). Same spectra were obtained in the case of the MMB-DDM-0 film.

solution without the protein. Similar behavior is observed for Fib protein which is manifested by spectroscopic changes illustrated in Figure 4b, although Fib protein adsorption is higher, as manifested by enhanced intensities of the 1659 and 1632 cm-1 bands for amide I. However, there is marginal discrimination between the F-A and F-S interfaces exhibited by Fib in the presence of DDM. In contrast to Glo and Fib, BSA appears not to exhibit selectivity for adsorption on the MMA/nBA interfaces, as demonstrated by unchanged band intensities due to amide I (1659 cm-1) in traces A-D of Figure 4c. Studies are in progress to determine each protein adsorption characteristics. In an effort to determine heterogeneity of the protein adsorption, optical and IRIR images were obtained and analyzed. As illustrated in Figure 5a,b, after Glo was allowed to adsorb onto the F-A interface of MB-DDM-0, darker areas of the inset square of the optical image represent adsorbed Glo proteins, whereas lighter regions have no Glo moieties. Again, heterogeneous adsorption occurs at the F-A interface, and chemical conformation of the presence of Glo is shown in Figure 5c, which illustrates higher concentration levels of Glo in area A. Similarly, Fib adsorption onto the F-A interface of MB-DDM-0 is also heterogeneous, and as shown in Figure 6 which illustrate the surface optical image, IRIRI and IR spectra were recorded from areas A and B. Again, adsorption of Fib in area A is higher, thus indicating that the protein adsorption occurs and these heterogeneities are present on the entire film surface. It should be noted that regardless of whether DDM is utilized or not in the synthesis of colloidal dispersions, BSA adsorption is homogeneous, and thus, this protein exhibits no selective adsorption onto the surface. This is illustrated in Figure 4c, in ATR measurements where the 1659 cm-1 band remains constant, and consequently, IRIR images (not shown) are homogeneous. Mechanisms leading to selective or nonselective adsorption of Glo, Fib, and BSA are under investigation. IRIRI experiments were also performed at the F-A interface of MB-DDM-50 coalesced films. Figure 7 illustrates IRIR images obtained from the same area of the bands at 1068 (Figure 7a) and 1632 (Figure 7b) cm-1, which are due to C-O stretching vibrations of DDM (Note: The band due to DDM of MB-DDM-50 is expected to be detected at 1073

Figure 5. (a) Optical images of Glo adsorbed at the F-A interface of MB-DDM-0 film, (b) IRIR Image recorded from the specified regions of optical images, and (c) IR spectra recorded from areas labeled A and B in IRIR image.

cm-1. However, protein adsorption tests involve washing a specimen with an aqueous solution which partially removes DDM from the film surface. Therefore, the band due to DDM is shifted and detected at 1068 cm-1. Model studies are shown in Figure 1.) and amide I in Glo, respectively. Analysis of the spectra recorded from the areas labeled A and B on images shown in Figure 7a,b shows that, when higher concentrations of DDM are present, which is manifested by higher band intensity of the band due to DDM (Figure 7a, area A; trace B), no bands due to Glo are detected from the same area (Figure 7b, area B; trace B). In contrast,

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Figure 8. Schematic representation of (a) migration of DDM during coalescence, (b) DDM stratification, (c) protein adsorption, and (d) molecular orientation of SDOSS in the presence of water and DDM.

Figure 6. (a) Optical images of Fib adsorbed at the F-A interface of MB-DDM-0 film, (b) IRIR Image recorded from the specified regions of optical images, and (c) IR spectra recorded from areas labeled A and B in IRIR image.

is sufficient to alter protein adsorption of polymeric surfaces due not only to intrinsic biological properties of R-glucose moieties, but also to the higher hydrophilicity of hydroxyl groups of sugar derivatives. These two characteristics of DDM suppress protein surface interactions. In summary, mechanisms responsible for generating surface heterogeneities and protein adsorption are schematically illustrated in Figure 8. As shown in Figure 8a, DDM migration occurs during coalescence, thus resulting in heterogeneous surfaces such as those shown in Figure 8b. Upon exposure to Glo and Fib, the areas that contain DDM diminish Glo and Fib adsorption. This is illustrated in Figure 8c. Finally, dichroic ratio measurements allowed us to estimate orientation of DDM and SDOSS at the F-A interface. Figure 8d illustrates preferential molecular orientation of SDOSS in the presence of water and DDM, where in-plane orientation at the F-A interface is observed, which is a function of concentration, and SDOSS molecules take preferentially in-plane orientation.24 Conclusions

Figure 7. IRIR image recorded from Glo adsorbed at the F-A interface of the MB-DDM-50 film obtained by tuning into the 1069 cm-1 (a) and 1632 cm-1 (b) bands and IR spectra recorded from areas labeled A and B.

when DDM concentration is diminished (Figure 7a, area A; trace A), enhanced Glo content is detected, which is manifested by the presence of the amide I band at 1632 cm-1 (Figure 7b, area A; trace A). Thus, only 2.5% (w/w) of DDM

When sugar derivatives serve as polymerization sites as well as polymer particle stabilizing agents, colloidal particles are stabilized in an aqueous environment and upon coalescence form uniform polymeric films, sugar derivatives are released from the particle surfaces and, under suitable conditions, selectively stratify in the areas of the excess of interfacial energy regions of a polymer matrix or driven by other stimuli. Since particle surface area diminishes during coalescence and the excess of interfacial energy forces the mobilization of surface active species to migrate to the F-A and F-S interfaces, saccharide molecules, being watersoluble, selectively stratify, thus creating active sites for adsorption. These studies showed that DDM migrates mainly

Colloidal Dispersions Stabilized by Sugar Derivatives

toward the F-A interface during coalescence of MMA/nBA particles and also DDM enhances the rate of mobility of SDOSS resulting from interactions between DDM and SDOSS moieties. Such MMA/nBA surfaces are heterogeneous, and the access of DDM suppresses Glo and Fib protein adsorption. In contrast, the same surfaces do not affect adsorption of BSA. These studies also show surface morphology changes as a result of concentration change of DDM in the colloidal dispersion. Acknowledgment. This work was supported primarily by the MRSEC Program of the National Science Foundation under award no. DMR 0213883. References and Notes (1) Yacoub, A.; Urban, M. W. Biomacromolecules 2003, 4, 52-56. (2) Lestage, D. J.; Urban, M. W. Langmuir 2005, 21, 4266-4267. (3) Lestage, D. J.; Schleis, D. J.; Urban, M. W. Langmuir 2004, 20, 7027-7035. (4) Lestage, D. J.; Yu, M.; Urban, M. W. Biomacromolecules 2005, 6, 1561-1572. (5) Lestage, D. J.; Urban, M. W. Langmuir 2004, 20, 6443-6449. (6) Dreher, W. R.; Urban, M. W.; Porzio, R. S.; Zhao, C. L. Langmuir 2003, 19, 10254-10259. (7) Zhao, Y.; Urban, M. W. Macromolecules 2000, 33, 8426-8434. (8) Bae, W.-S.; Urban, M. W. Langmuir 2004, 20, 8372-8378. (9) Serizawa, T.; Yasunaga, S.; Akashi, M. Biomacromolecules 2001, 2, 469-475. (10) Mortell, K. H.; Gingras, M.; Kiessling, L. L. J. Am. Chem. Soc. 1994, 116, 12053-12054. (11) Bovin, N. V.; Gabius, H. J. Chem. Soc. ReV. 1995, 24, 413-421. (12) Takeuchi, S.; Oike, M.; Kowitz, C.; Shimasaki, C.; Hasegawa, K.; Kitano, H. Makromol. Chem. 1993, 194, 551-558. (13) Nojiri, C.; Okano, T.; Koyanagi, H.; Nakahama, S.; Park, K. D.; Kim, S. W. J. Biomater. Sci. Polym. Ed. 1992, 4, 75-88.

Biomacromolecules, Vol. 6, No. 5, 2005 2621 (14) Okano, T.; Nishiyama, S.; Shinohara, I.; Akaike, T.; Sakurai, Y. Polym. J. 1978, 10, 223-228. (15) Takahara, A.; Jo, N. J.; Kajiyama, T. J. Biomater. Sci. Polym. Ed. 1989, 1, 17-29. (16) Davis, S. D.; Hadgraft, J.; Palin, K. J. Encylopedia of Emulsion Technology; Marcel Dekker: New York, 1985; Vol. 2. (17) Huang, J. B.; Urban, M. W. Appl. Spectrosc. 1992, 46, 1666-1672. (18) Otts, D. B.; Zhang, P.; Urban, M. W. Langmuir 2002, 18, 64736477. (19) Tant, M. R.; Mauritz, K. A.; Wilkes, G. L. Ionomers; Synthesis, Structure, Properties, and Applications; Blackie Academic and Professional: New York, 1997. (20) Urban, M. W. Vibrational Spectroscopy of Molecules and Macromolecules on Surfaces; John Wiley & Sons: New York, 1993; Vol. 81. (21) Urban, M. W. Attenuated Total Reflectance Spectroscopy of Polymerss Theory and Practice; American Chemical Society: Washington, DC, 1996. (22) Evanson, K. W.; Urban, M. W. J. Appl. Polym. Sci. 1991, 42, 23092320. (23) Urban, M. W.; Evanson, K. W. Polym. Commun. 1990, 31, 279282. (24) Zhao, Y.; Urban, M. W. Langmuir 2001, 17, 6961-6967. (25) Brandrup, J.; Immergut, E. H. Polymer Handbook, 3rd ed.; John Wiley and Sons: New York, 1989. (26) Bassett, D. R. J. Coat. Technol. 2001, 73, 43. (27) Dreher, W. R.; Urban, M. W. Langmuir 2004, 20, 10455-10463. (28) Lovell, P. A.; El-Aasser, M. S. Emulsion polymerization and emulsion polymers; John Wiley & Sons Ltd.: West Sussex, England, 1997; p 242. (29) Odian, G. Principles of Polymerization, 3rd ed.; John Wiley & Sons: New York, 1991; p 335. (30) Sugiyama, K.; Kato, K.; Kido, M.; Shiraishi, K.; Ohga, K.; Okada, K.; Matsuo, O. Macromol. Chem. Phys. 1998, 199, 1201-1208. (31) Sugiyama, K.; Oku, T. Polym. J. 1995, 27, 179-188. (32) van de Weert, M.; Haris, P. I.; Hennink, W. E.; Crommelin, D. J. A. Anal. Biochem. 2001, 297, 160-169.

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