Sonochemically produced fluorocarbon microspheres: a new class of magnetic resonance imaging agent

Update of ultrasound-assembling fabrication and biomedical applications for heterogeneous polymer composites

As a power-driving approach, ultrasound irradiation is very appealing to the preparation or modification of new materials. In the review, we overviewed the latest development of ultrasound-mediated effects or reactions in polymer composites, and demonstrated its unique and powerful aspects on the polymerization or aggregation. The review generalized the different categories of heterogeneous polymer composites by defining the constituents, and described the shapes, sizes and basic properties of various purpose-specific or site-specific products. Importantly, the review paid more attention to the main biomedicine applications of heterogeneous polymer composites, such as drug or bioactive substance entrapment, delivery, release, imaging, and therapy, and emphasized many advantages of ultrasound-assembling approaches and heterogeneous polymer composites in biology and medicine fields. In addition, the review also indicated the prospective challenges of heterogeneous polymer composites both in ultrasound-assembling designs and in biomedical applications.

Characterization of sonochemically prepared human serum albumin nanocapsules using different plant oils as core component for targeted drug delivery

The focus of this study is the preparation of proteinaceous human serum albumin (HSA) nanocapsules with biocompatible plant oil cores avoiding toxic cross-linker and noxious non-aqueous liquids. The sonochemical preparation of HSA capsules with different plant oils yields particles with narrow size distribution forming suspensions stable for at least 14 days and enabling long-term storage by freezing. Furthermore, wheat germ agglutinin (WGA) as a targeting molecule was successfully embedded into the proteinaceous particle shell at a molar ratio of 7:1 (HSA/WGA). As urothelial cell binding studies revealed up to 55% higher cell binding potential of WGA-grafted particles than those without a targeter, targeted protein nanocapsules represent the first step towards new and innovative formulations.

Very low field 19F MRI of perfluoro-octylbromide: Minimizing chemical shift effects and signal loss due to scalar coupling

¹⁹F images have been obtained from perflurooctylbromide (PFOB) at very low magnetic field (50 mT). The small spectral dispersion (in Hz) means that all fluorine nuclei contribute to the signal without chemical shift artifacts or the need for specialized imaging sequences. Turbo spin echo trains with short interpulse intervals and full 180° refocussing pulses suppress scalar coupling, leading to long apparent T₂ values and highly efficient data collection. Overall, the detection efficiency of PFOB is very similar that of water in tissue.

Sonochemically modified ovalbumin enhances enantioenrichment of some amino acids

As part of our efforts to develop a new method for chiral resolution of amino acids with sonochemically modified proteins, we present result that indicates how ovalbumin microspheres (OAMS) interact specifically with l-amino acids from a racemate in solution, leaving an excess of d-enantiomer in the permeate solution. Among different amino acids that interacted with the OAMS, tryptophan (Trp) was the most successfully resolved with 65% enantiomeric excess. A control experiment with native ovalbumin in solution did not show any chiral resolution of amino acids. Interestingly, when the OAMS were pretreated with racemic lysine (Lys) solution and then used for resolution of tryptophan the enantiomeric enrichment of d-tryptophan was raised to 98%. This unanticipated positive effect is discussed in terms of the structural correlation between Trp and Lys, which is less apparent in other amino acids such as phenylalanine.

Characterization of Magnetic Nanoparticle-Seeded Microspheres for Magnetomotive and Multimodal Imaging

Magnetic iron-oxide nanoparticles have been developed as contrast agents in magnetic resonance imaging (MRI) and as therapeutic agents in magnetic hyperthermia. They have also recently been demonstrated as contrast and elastography agents in magnetomotive optical coherence tomography and elastography (MM-OCT and MM-OCE, respectively). Protein-shell microspheres containing suspensions of these magnetic nanoparticles in lipid cores, and with functionalized outer shells for specific targeting, have also been demonstrated as efficient contrast agents for imaging modalities such as MM-OCT and MRI, and can be easily modified for other modalities such as ultrasound, fluorescence, and luminescence imaging. By leveraging the benefits of these various imaging modalities with the use of only a single agent, a magnetic microsphere, it becomes possible to use a widefield imaging method (such as MRI or small animal fluorescence imaging) to initially locate the agent, and then use MM-OCT to obtain dynamic contrast images with cellular level morphological resolution. In addition to multimodal contrast-enhanced imaging, these microspheres could serve as drug carriers for targeted delivery under image guidance. Although the preparation and surface modifications of protein microspheres containing iron oxide nanoparticles has been previously described and feasibility studies conducted, many questions regarding their production and properties remain. Since the use of multifunctional microspheres could have high clinical relevance, here we report a detailed characterization of their properties and behavior in different environments to highlight their versatility. The work presented here is an effort for the development and optimization of nanoparticle-based microspheres as multi-modal contrast agents that can bridge imaging modalities on different size scales, especially for their use in MM-OCT and MRI imaging.

Sonochemistry-Assembled Stimuli-Responsive Polymer Microcapsules for Drug Delivery

Stimuli-responsive polymer microcapsules (PMs) fabricated by the sonochemical method have emerged for developing useful drug delivery systems, and the latest developments are mainly focusing on the synthetic strategies and properties such as structure, size, stability, loading capacity, drug delivery, and release. There, the primary attribution of sonochemistry is to offer a simple and practical approach for the preparation of PMs. Structure, size, stability, and properties of PMs are designed mainly according to synthetic materials, implementation schemes, or specific demands. Numerous functionalities of PMs based on different stimuli are demonstrated: targeting motion in a magnetic field or adhering to the living cells with sensitive sites through molecular recognition, and stimuli-triggered release including enzymatic catalysis, chemical reaction as well as physical or mechanical process. The current review discusses the basic principles and mechanisms of stimuli effects, and describes the progress in the application such as targeted drug systems and controlled drug systems, and also gives an outlook on the future challenges and opportunities for drug delivery and theranostics.

Sonochemistry: Science and Engineering

Sonochemistry offers a simple route to nanomaterial synthesis with the application of ultrasound. The tiny acoustic bubbles, produced by the propagating sound wave, enclose an incredible facility where matter interact among at energy as high as 13 eV to spark extraordinary chemical reactions. Within each period - formation, growth and collapse of bubbles, lies a coherent phase of material formation. This effective yet highly localized method has facilitated synthesis of various chemical and biological compounds featuring unique morphology and intrinsic property. The benign processing lends to synthesis without any discrimination towards a certain group of material, or the substrates where they are grown. As a result, new and improved applications have evolved to reach out various field of science and technology and helped engineer new and better devices. Along with the facile processing and notes on the essence of sonochemistry, in this comprehensive review, we discuss the individual and mutual effect of important input parameters on the nanomaterial synthesis process as a start to help understand the underlying mechanism. Secondly, an objective discussion of the diversely synthesized nanomaterial follows to divulge the easiness imparted by sonochemistry, which finally blends into the discussion of their applications and outreach.

Preparation of multifunctional polysaccharide microcontainers for lipophilic bioactive agents

Chitosan/xanthan gum microcontainers with a core-shell structure formed due to chemical interactions between polysaccharide chains induced by ultrasonication are presented. Containers were prepared by sonication of water-immiscible (oil-like) liquids in the solution of polysaccharides. One-step fabrication of the container permanent shell is possible, because of the contribution of ultrasonically caused formation of hydrogen bonds and amide linkages. We synthesized containers in a wide size range from 350 nm to 7500 nm, varying in oil/water ratio. The microcontainers were modified with oppositely charged polyelectrolytes and microparticles, which could be used to impart the specified properties to the system. The biocide 4,5-dichloro-2-n-octyl-4-isothiazoline-3-one (DCOIT) was loaded into the proposed containers by utilizing its solution as an oil phase. The following incorporation of the DCOIT containers into the polymer coating demonstrated more sustained antimicrobial activity (∼30%) of the biocide in the encapsulated state, compared to its non-encapsulated form.

Sonochemical synthesis of nanomaterials

High intensity ultrasound can be used for the production of novel materials and provides an unusual route to known materials without bulk high temperatures, high pressures, or long reaction times. Several phenomena are responsible for sonochemistry and specifically the production or modification of nanomaterials during ultrasonic irradiation. The most notable effects are consequences of acoustic cavitation (the formation, growth, and implosive collapse of bubbles), and can be categorized as primary sonochemistry (gas-phase chemistry occurring inside collapsing bubbles), secondary sonochemistry (solution-phase chemistry occurring outside the bubbles), and physical modifications (caused by high-speed jets or shock waves derived from bubble collapse). This tutorial review provides examples of how the chemical and physical effects of high intensity ultrasound can be exploited for the preparation or modification of a wide range of nanostructured materials.

Fragrance release profile from sonochemically prepared protein microsphere containers

Protein microspheres have been prepared by sonicating a mixture of pure fragrant oil (amyl acetate (AA)) with an aqueous protein (bovine serum albumin) solution. The prepared protein spheres are nano- to micrometer sized with an encapsulation efficiency of approx. 97% for the AA present on the surface and inside the BSA capsule. Containers were found stable for more than 6 months when stored sealed at 4°C and 20°C. For the release profile measurements, we used a simple, automated and direct method. We continuously weighed the encapsulated microspheres and measured the evaporation rates. The release profiles at 15°C and 25°C display two different evaporation rates. The higher rate is the sum of a few evaporation rates, including water molecules, while the slower rate is due to the evaporation of pure AA. The changes in the evaporation rates occur upon the collapse of the container. This event coincides with the full evaporation of water. For morphological characterization we dyed the AA with Nile red, and used SEM, ESEM, Cryo-SEM, light microscopy, and confocal laser scanning microscopy measurements.

Sonochemically born proteinaceous micro- and nanocapsules

The use of proteins as a substrate in the fabrication of micro- and nanoparticulate systems has attracted the interest of scientists, manufactures, and consumers. Albumin-derived particles were commercialized as contrast agents or anticancer therapeutics. Food proteins are widely used in formulated dietary products. The potential benefits of proteinaceous micro- and nanoparticles in a wide range of biomedical applications are indisputable. Protein-based particles are highly biocompatible and biodegradable structures that can impart bioadhesive properties or mediate particle uptake by specific interactions with the target cells. Currently, protein microparticles are engineered as vehicles for covalent attachment and/or encapsulation of bioactive compounds, contrast agents for magnetic resonance imaging, thermometric and oximetric imaging, sonography and optical coherence tomography, etc. Ultrasound irradiation is a versatile technique which is widely used in many and different fields as biology, biochemistry, dentistry, geography, geology, medicine, etc. It is generally recognized as an environmental friendly, cost-effective method which is easy to be scaled up. Currently, it is mainly applied for homogenization, drilling, cleaning, etc. in industry, as well for noninvasive scanning of the human body, treatment of muscle strains, dissolution of blood clots, and cancer therapy. Proteinaceous micro- and nanocapsules could be easily produced in a one-step process by applying ultrasound to an aqueous protein solution. The origin of this process is in the chemical changes, for example, sulfhydryl groups oxidation, that takes place as a result of acoustically generated cavitation. Partial denaturation of the protein most probably occurs which makes the hydrophobic interactions dominant and also responsible for the formation of stable capsules. This chapter aims to present the current state-of-the-art in the field of sonochemically produced protein micro- and nanocapsules, paying special attention to the proposed mechanisms for their formation, the factors that influence the capsules characteristics as well to the current applications of these particles. Current challenges in the field are also outlined as, for example, the ultrasound-protein interaction and other possible aspects of the mechanism of their formation.

Applications of ultrasound to the synthesis of nanostructured materials

Recent advances in nanostructured materials have been led by the development of new synthetic methods that provide control over size, morphology, and nano/microstructure. The utilization of high intensity ultrasound offers a facile, versatile synthetic tool for nanostructured materials that are often unavailable by conventional methods. The primary physical phenomena associated with ultrasound that are relevant to materials synthesis are cavitation and nebulization. Acoustic cavitation (the formation, growth, and implosive collapse of bubbles in a liquid) creates extreme conditions inside the collapsing bubble and serves as the origin of most sonochemical phenomena in liquids or liquid-solid slurries. Nebulization (the creation of mist from ultrasound passing through a liquid and impinging on a liquid-gas interface) is the basis for ultrasonic spray pyrolysis (USP) with subsequent reactions occurring in the heated droplets of the mist. In both cases, we have examples of phase-separated attoliter microreactors: for sonochemistry, it is a hot gas inside bubbles isolated from one another in a liquid, while for USP it is hot droplets isolated from one another in a gas. Cavitation-induced sonochemistry provides a unique interaction between energy and matter, with hot spots inside the bubbles of approximately 5000 K, pressures of approximately 1000 bar, heating and cooling rates of >10(10) K s(-1); these extraordinary conditions permit access to a range of chemical reaction space normally not accessible, which allows for the synthesis of a wide variety of unusual nanostructured materials. Complementary to cavitational chemistry, the microdroplet reactors created by USP facilitate the formation of a wide range of nanocomposites. In this review, we summarize the fundamental principles of both synthetic methods and recent development in the applications of ultrasound in nanostructured materials synthesis.

Sonochemical synthesis of liquid-encapsulated lysozyme microspheres

Liquid-encapsulated lysozyme microspheres were successfully synthesized using a sonochemical method. The encapsulation of four different liquids, namely, sunflower oil, tetradecane, dodecane and perfluorohexane on the formation, stability and morphology of the lysozyme microspheres was studied. Among the four different liquids used for encapsulation, perfluorohexane-filled microspheres were found to be most stable in the dried state with a narrow size distribution. In order to explore the possibility of encapsulating biofunctional molecules (e.g., drugs) within these microspheres, liquids containing a fluorescent dye (Nile red) were encapsulated and the ultrasound-induced release of these dye-loaded liquids was studied. The fluorescence data for the liquid-filled lysozyme microspheres demonstrated the potential use of the sonochemical technique for synthesizing these "vehicles" for the encapsulation and the controlled delivery of dyes, flavours, fragrances or drugs.

Liquid perfluorocarbons as contrast agents for ultrasonography and (19)F-MRI

Perfluorocarbons (PFCs) are fluorinated compounds that have been used for many years in clinics mainly as gas/oxygen carriers and for liquid ventilation. Besides this main application, PFCs have also been tested as contrast agents for ultrasonography and magnetic resonance imaging since the end of the 1970s. However, most of the PFCs applied as contrast agents for imaging were gaseous. This class of PFCs has been recently substituted by liquid PFCs as ultrasound contrast agents. Additionally, liquid PFCs are being tested as contrast agents for (19)F magnetic resonance imaging (MRI), to yield dual contrast agents for both ultrasonography and (19)F MRI. This review focuses on the development and applications of the different contrast agents containing liquid perfluorocarbons for ultrasonography and/or MRI: large and small size emulsions (i.e. nanoemulsions) and nanocapsules.

Characterization and activity of sonochemically-prepared BSA microspheres containing Taxol--an anticancer drug

Proteinaceous microspheres of BSA (Bovine Serum Albumin) containing an anticancer drug, Taxol (paclitaxel) were fabricated using a sonochemical procedure and then assayed for chemical and biological activity. The sonochemical reaction did not compromise the drug, which became encapsulated in the BSA microspheres. The amount of the anticancer drug in the microspheres was determined by HPLC. Anticancer activity of the proteinaceous microspheres encapsulating the Taxol was tested on Mouse Multiple Myeloma cell line MPC-11. The influence of the Taxol microspheres on the cancer cells was different from pristine Taxol. It was found that Taxol in combination with the organic solvent causes the death of cancer cells.

Are sonochemically prepared alpha-amylase protein microspheres biologically active?

Using high-intensity ultrasound, we have synthesized alpha-amylase microspheres. The paper presented characterization as well as catalytic experiments of the sonochemically-produced microspheres. It also provided an estimate of the efficiency of the sonochemical process in converting the native protein to microspheres. These microspheres showed a very good enzymatic activity compared with the native alpha-amylase. The enzymatic activity of the amylase microspheres was 27% of that of the native protein after a short reaction time (3 min), while over a longer reaction time (1 h) it reached 56% of the activity of the native protein.

Self-assembled microspheres from f-block elements and nucleoamphiphiles

Hollow microspheres featuring a hybrid lipid-cation multilamellar shell are prepared by hydration of a nucleoside based amphiphile with an aqueous solution containing either actinide or lanthanide salts. The physico-chemical data collected clearly indicate that the formation of these microspheres is a consequence of the following concomitant stabilizing factors: (i) hydrophobic interactions, (ii) nucleobase dimer formation and (iii) phosphate/f-block element salt binding.

The preparation of avidin microspheres using the sonochemical method and the interaction of the microspheres with biotin

Avidin microspheres were prepared using the sonochemical method. It was found that avidin microspheres can bind biotin, but to a lesser degree than the native protein. The binding of the biotin molecules to the avidin microspheres was probed primarily by TPD measurements.

Catheter tracking and visualization using 19F nuclear magnetic resonance

This work presents an investigation into catheter visualization and localization using 19F nuclear magnetic resonance (NMR) in conjunction with proton imaging. For this purpose, the imaging capabilities of a standard system were extended to allow for 19F excitation and signal detection. Two modes of operation were implemented: 1) a real-time tracking mode that provides tip tracking and automatic slice position updates interleaved with real-time, interactive proton imaging; and 2) a non-real-time catheter length visualization mode in which the entire length of a catheter can be assessed. Initial phantom experiments were conducted with the use of an angiographic balloon catheter filled with the blood substitute perfluorooctylbromide (PFOB). Using limited bandwidth excitation centered at the resonances of the CF2 groups of PFOB, we found that sufficient signal could be received to facilitate tip tracking during catheter motion and length visualization for various catheter configurations. The present approach is considered a promising alternative to existing methods, which either are associated with safety concerns (if active markers are employed) or suffer from insufficient, direction-dependent contrast (if passive visualization is used). Furthermore, our approach enables visualization of the entire length of the catheter. The proposed method provides a safe technique that, unlike electrical or optical devices, does not require modification of commercially available catheters.

Heat-activated Liposomal MR Contrast Agent: Initial in Vivo Results in Rabbit Liver and Kidney

PURPOSE

To evaluate by using in vivo magnetic resonance (MR) imaging the functionality of a liposomal paramagnetic contrast agent with T1 relaxivity that rapidly and markedly increases at temperatures above the gel-to-liquid crystalline phase transition temperature (T(c)) of the liposome membrane.

MATERIALS AND METHODS

Liposomal gadolinium diethylenetriaminepentaacetic acid bis(methylamide) was injected intravenously at a dose of 0.4 or 1.2 mL (containing 10 or 30 micromol of gadolinium, respectively) per kilogram of body weight shortly before the application of focused ultrasound in liver (seven rabbits) or kidney (three rabbits). VX2 tumors had been implanted in liver in four of the rabbits. Eighteen locations in liver (13 in normal tissue, five in tumor) and 12 locations in kidney were sonicated. MR thermometry was performed during sonications. Signal intensity enhancement was evaluated on T1-weighted images acquired after the tissue cooled, and enhanced zones were compared with isotherms at T(c) of the liposome membrane (approximately 57 degrees C) by using Bland-Altman analysis. In liver, enhanced zones also were compared with areas of histologically verified thermal damage. The threshold temperature of enhancement at T1-weighted imaging was verified by monitoring the signal intensity increase after 10 sonications at varied powers in two locations in normal liver tissue.

RESULTS

Persistent enhancement was observed on T1-weighted images at all sonicated liver locations. In liver, enhanced zones on T1-weighted images were contiguous both with 57 degrees C isotherms (25 measurements; mean difference +/- SD, 0.4 mm +/- 1.2) and with histologically verified areas of necrosis (seven measurements; mean difference +/- SD, 0.1 mm +/- 0.9). The threshold temperature of enhancement at T1-weighted imaging in normal liver was 53 degrees -57 degrees C. In kidney, enhanced zones on T1-weighted images did not match the isotherms.

CONCLUSION

The liposomal contrast agent was effective at in vivo MR thermometry in liver but not in kidney.

An Easy Sonochemical Route for the Encapsulation of Tetracycline In Bovine Serum Albumin Microspheres

A one-step sonochemical process starting with the native BSA and tetracycline was employed to encapsulate the antibiotic drug in microspheres of BSA. The tetracycline loading studies showed that the maximum tetracycline loading capacity was found to be 65%. The antimicrobial activity of the tetracycline loaded in BSA microspheres was demonstrated on two bacterial strains that are sensitive to tetracycline.

The preparation of magnetic proteinaceous microspheres using the sonochemical method

Using high-intensity ultrasound, we have developed a method for the synthesis of magnetic microspheres. The microspheres are composed of iron oxide-filled and coated globular bovine serum albumin (BSA). The magnetic microspheres are prepared from BSA and iron pentacarbonyl, or from BSA and iron acetate. Transmission electron microscopy and scanning electron microscopy show spherical particles. The particle size distributions are gaussian, with a mean diameter of a few micrometers. Using chemical analysis, it was found that the total percentage of iron oxide in the microspheres is between 39% and 42%. Mössbauer measurements were also performed.

Thermosensitive paramagnetic liposomes for temperature control during MR imaging-guided hyperthermia: in vitro feasibility studies

RATIONALE AND OBJECTIVES

Magnetic resonance (MR) imaging-based temperature monitoring has gained interest for use in general hyperthermia treatment of tumors. Such therapy requires an accurate control of the temperature, which should range from 41 degrees to 45 degrees C. A novel type of thermosensitive MR agent is proposed: liposome-encapsulated gadolinium chelates whose temperature response is linked to the phase-transition properties of the liposome carrier. In vitro relaxometry and MR imaging were used to evaluate the thermosensitivity of the contrast properties of liposomal gadolinium diethylenetriaminepentaacetic acid bis(methylamide) (Gd-DTPA-BMA).

MATERIALS AND METHODS

T1 relaxivity (rl) measurements of liposomal Gd-DTPA-BMA were undertaken at 0.47 T and at temperatures of 20 degrees-48 degrees C. MR imaging was performed at 2.0 T with a gel phantom containing inserts of liposomes. Diffusion-weighted and T1-weighted gradient-recalled echo images were acquired as the phantom was heated from 22 degrees to about 65 degrees C.

RESULTS

At ambient temperature, the r1 of liposomal Gd-DTPA-BMA was exchange limited due to slow water exchange between the liposome interior and exterior. A sharp, marked increase in r1 occurred as the temperature reached and exceeded the gel-to-liquid crystalline phase-transition temperature (Tm) of the liposomes (42 degrees C). The relaxation enhancement was mainly attributable to the marked increase in transmembrane water permeability, yielding fast exchange conditions. There was good correlation between the relaxometric and imaging results; the signal intensity on T1-weighted gradient-recalled echo images increased markedly as the temperature approached Tm. The temperature sensitivity of the diffusion-weighted technique differed from that of the liposome-based T1-weighted approach, with an apparent water diffusion coefficient increasing linearly with temperature.

CONCLUSION

Since the transition from low to high signal intensity occurred in the temperature range of 38 degrees - 42 degrees C, the investigated paramagnetic liposomes have a potential role as "off-on" switches for temperature control during hyperthermia treatment.

19F-MRI in vivo determination of the partial oxygen pressure in perfluorocarbon-loaded alginate capsules implanted into the peritoneal cavity and different tissues

Semipermeable hydrogels formed with a biocompatible alginate solution and Ba(2+) ions protect encapsulated cells and tissues from a foreign immune system. For the viability and metabolic activity of the encapsulated materials, a sufficient oxygen supply inside the capsules is necessary. Quantitative (19)F-MRI was performed on perfluorocarbon-loaded alginate capsules implanted into the peritoneal cavity, the musculus quadriceps femoris, and beneath the kidney capsule of rats, in order to determine in vivo the partial oxygen pressure (pO(2)) inside the capsules at these implantation sites. The temporal behavior of the pO(2) values was observed for at least 3 months. The most stable values over time were observed in the kidney, where inter-rat pO(2) differences were considerable. In the muscle, the values were very high directly after implantation and decreased to nearly zero after 2 weeks. In the peritoneal cavity, values changed randomly over a wide range between different rats and over time. Magn Reson Med 42:1039-1047, 1999.