1
|
Zalloum IO, Jafari Sojahrood A, Paknahad AA, Kolios MC, Tsai SSH, Karshafian R. Controlled Tempering of Lipid Concentration and Microbubble Shrinkage as a Possible Mechanism for Fine-Tuning Microbubble Size and Shell Properties. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:17622-17631. [PMID: 38016673 DOI: 10.1021/acs.langmuir.3c01599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2023]
Abstract
The acoustic response of microbubbles (MBs) depends on their resonance frequency, which is dependent on the MB size and shell properties. Monodisperse MBs with tunable shell properties are thus desirable for optimizing and controlling the MB behavior in acoustics applications. By utilizing a novel microfluidic method that uses lipid concentration to control MB shrinkage, we generated monodisperse MBs of four different initial diameters at three lipid concentrations (5.6, 10.0, and 16.0 mg/mL) in the aqueous phase. Following shrinkage, we measured the MB resonance frequency and determined its shell stiffness and viscosity. The study demonstrates that we can generate monodisperse MBs of specific sizes and tunable shell properties by controlling the MB initial diameter and aqueous phase lipid concentration. Our results indicate that the resonance frequency increases by 180-210% with increasing lipid concentration (from 5.6 to 16.0 mg/mL), while the bubble diameter is kept constant. Additionally, we find that the resonance frequency decreases by 260-300% with an increasing MB final diameter (from 5 to 12 μm), while the lipid concentration is held constant. For example, our results depict that the resonance frequency increases by ∼195% with increasing lipid concentration from 5.6 to 16.0 mg/mL, for ∼11 μm final diameter MBs. Additionally, we find that the resonance frequency decreases by ∼275% with increasing MB final diameter from 5 to 12 μm when we use a lipid concentration of 5.6 mg/mL. We also determine that MB shell viscosity and stiffness increase with increasing lipid concentration and MB final diameter, and the level of change depends on the degree of shrinkage experienced by the MB. Specifically, we find that by increasing the concentration of lipids from 5.6 to 16.0 mg/mL, the shell stiffness and viscosity of ∼11 μm final diameter MBs increase by ∼400 and ∼200%, respectively. This study demonstrates the feasibility of fine-tuning the MB acoustic response to ultrasound by tailoring the MB initial diameter and lipid concentration.
Collapse
Affiliation(s)
- Intesar O Zalloum
- Department of Physics, Toronto Metropolitan University, Toronto M5B 2K3, Ontario, Canada
- Institute for Biomedical Engineering, Science and Technology (iBEST), A Partnership between Toronto Metropolitan University and St. Michael's Hospital, 209 Victoria Street, Toronto M5B 1T8, Ontario, Canada
- Keenan Research Centre for Biomedical Science, Unity Health Toronto, 209 Victoria Street, Toronto M5B 1W8, Ontario, Canada
| | - Amin Jafari Sojahrood
- Department of Physics, Toronto Metropolitan University, Toronto M5B 2K3, Ontario, Canada
- Institute for Biomedical Engineering, Science and Technology (iBEST), A Partnership between Toronto Metropolitan University and St. Michael's Hospital, 209 Victoria Street, Toronto M5B 1T8, Ontario, Canada
- Keenan Research Centre for Biomedical Science, Unity Health Toronto, 209 Victoria Street, Toronto M5B 1W8, Ontario, Canada
| | - Ali A Paknahad
- Department of Mechanical and Industrial Engineering, Toronto Metropolitan University, 350 Victoria Street, Toronto M5B 2K3, Ontario, Canada
- Institute for Biomedical Engineering, Science and Technology (iBEST), A Partnership between Toronto Metropolitan University and St. Michael's Hospital, 209 Victoria Street, Toronto M5B 1T8, Ontario, Canada
- Keenan Research Centre for Biomedical Science, Unity Health Toronto, 209 Victoria Street, Toronto M5B 1W8, Ontario, Canada
| | - Michael C Kolios
- Department of Physics, Toronto Metropolitan University, Toronto M5B 2K3, Ontario, Canada
- Institute for Biomedical Engineering, Science and Technology (iBEST), A Partnership between Toronto Metropolitan University and St. Michael's Hospital, 209 Victoria Street, Toronto M5B 1T8, Ontario, Canada
- Keenan Research Centre for Biomedical Science, Unity Health Toronto, 209 Victoria Street, Toronto M5B 1W8, Ontario, Canada
| | - Scott S H Tsai
- Department of Mechanical and Industrial Engineering, Toronto Metropolitan University, 350 Victoria Street, Toronto M5B 2K3, Ontario, Canada
- Institute for Biomedical Engineering, Science and Technology (iBEST), A Partnership between Toronto Metropolitan University and St. Michael's Hospital, 209 Victoria Street, Toronto M5B 1T8, Ontario, Canada
- Keenan Research Centre for Biomedical Science, Unity Health Toronto, 209 Victoria Street, Toronto M5B 1W8, Ontario, Canada
- Graduate Program in Biomedical Engineering, Toronto Metropolitan University, 350 Victoria Street, Toronto M5B 2K3, Ontario, Canada
| | - Raffi Karshafian
- Department of Physics, Toronto Metropolitan University, Toronto M5B 2K3, Ontario, Canada
- Institute for Biomedical Engineering, Science and Technology (iBEST), A Partnership between Toronto Metropolitan University and St. Michael's Hospital, 209 Victoria Street, Toronto M5B 1T8, Ontario, Canada
- Keenan Research Centre for Biomedical Science, Unity Health Toronto, 209 Victoria Street, Toronto M5B 1W8, Ontario, Canada
| |
Collapse
|
2
|
Gupta I, Su X, Jonnalagadda US, Das D, Pramanik M, Kwan JJ. Investigating the Acoustic Response and Contrast Enhancement of Drug-Loadable PLGA Microparticles with Various Shapes and Morphologies. ULTRASOUND IN MEDICINE & BIOLOGY 2021; 47:1844-1856. [PMID: 33810888 DOI: 10.1016/j.ultrasmedbio.2021.02.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 01/07/2021] [Accepted: 02/16/2021] [Indexed: 06/12/2023]
Abstract
Polymer nanoparticles and microparticles have been used primarily for drug delivery. There is now growing interest in further developing polymer-based solid cavitation agents to also enhance ultrasound imaging. We previously reported on a facile method to produce hollow poly(lactic-co-glycolic acid) (PLGA) microparticles with different diameters and degrees of porosity. Here, we investigate the cavitation response from these PLGA microparticles with both therapeutic and diagnostic ultrasound transducers. Interestingly, all formulations exhibited stable cavitation; larger porous and multicavity particles also provided inertial cavitation at elevated acoustic pressure amplitudes. These larger particles also achieved contrast enhancement comparable to that of commercially available ultrasound contrast agents, with a maximum recorded contrast-to-tissue ratio of 28 dB. Therefore, we found that multicavity PLGA microparticles respond to both therapeutic and diagnostic ultrasound and may be applied as a theranostic agent.
Collapse
Affiliation(s)
- Ipshita Gupta
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
| | - Xiaoqian Su
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
| | - Umesh Sai Jonnalagadda
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
| | - Dhiman Das
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
| | - Manojit Pramanik
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
| | - James J Kwan
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459.
| |
Collapse
|
3
|
Song R, Peng C, Xu X, Wang J, Yu M, Hou Y, Zou R, Yao S. Controllable Formation of Monodisperse Polymer Microbubbles as Ultrasound Contrast Agents. ACS APPLIED MATERIALS & INTERFACES 2018; 10:14312-14320. [PMID: 29637761 DOI: 10.1021/acsami.7b17258] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Microbubbles have been widely used as ultrasound contrast agents in clinical diagnosis and hold great potential for ultrasound-mediated therapy. However, polydispersed population and short half-life time (<10 min) of the microbubbles still limit their applications in imaging and therapy. To tackle these problems, we develop a microfluidic flow-focusing approach to produce monodisperse microbubbles stabilized by Poly(lactic-co-glycolic acid) (PLGA) as the polymer shell. The size of PLGA microbubbles can be tightly controlled from ∼600 nm to ∼7 μm with a coefficient of variation less than 4% in size distribution for ensuring highly homogeneous echogenic behavior of PLGA polymer microbubbles in ultrasound fields. Both in vitro and in vivo experiments showed that the monodisperse PLGA microbubbles had excellent echogenicity and elongated sonographic duration time (>3 times) for ultrasound imaging in comparison with the commercial lipid microbubbles.
Collapse
Affiliation(s)
| | - Chuan Peng
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center of Cancer Medicine, Department of Ultrasound , Sun Yat-sen University Cancer Center , 510060 Guangzhou , China
| | | | - Jianwei Wang
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center of Cancer Medicine, Department of Ultrasound , Sun Yat-sen University Cancer Center , 510060 Guangzhou , China
| | | | | | - Ruhai Zou
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center of Cancer Medicine, Department of Ultrasound , Sun Yat-sen University Cancer Center , 510060 Guangzhou , China
| | | |
Collapse
|
4
|
Kandadai MA, Mukherjee P, Shekhar H, Shaw GJ, Papautsky I, Holland CK. Microfluidic manufacture of rt-PA -loaded echogenic liposomes. Biomed Microdevices 2016; 18:48. [PMID: 27206512 PMCID: PMC4920071 DOI: 10.1007/s10544-016-0072-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Echogenic liposomes (ELIP), loaded with recombinant tissue-type plasminogen activator (rt-PA) and microbubbles that act as cavitation nuclei, are under development for ultrasound-mediated thrombolysis. Conventional manufacturing techniques produce a polydisperse rt-PA-loaded ELIP population with only a small percentage of particles containing microbubbles. Further, a polydisperse population of rt-PA-loaded ELIP has a broadband frequency response with complex bubble dynamics when exposed to pulsed ultrasound. In this work, a microfluidic flow-focusing device was used to generate monodisperse rt-PA-loaded ELIP (μtELIP) loaded with a perfluorocarbon gas. The rt-PA associated with the μtELIP was encapsulated within the lipid shell as well as intercalated within the lipid shell. The μtELIP had a mean diameter of 5 μm, a resonance frequency of 2.2 MHz, and were found to be stable for at least 30 min in 0.5 % bovine serum albumin. Additionally, 35 % of μtELIP particles were estimated to contain microbubbles, an order of magnitude higher than that reported previously for batch-produced rt-PA-loaded ELIP. These findings emphasize the advantages offered by microfluidic techniques for improving the encapsulation efficiency of both rt-PA and perflurocarbon microbubbles within echogenic liposomes.
Collapse
Affiliation(s)
- Madhuvanthi A Kandadai
- Department of Emergency Medicine, University of Cincinnati, 231 Albert Sabin Way, Suite 1551, Cincinnati, OH, 45267, USA.
- Department of Emergency Medicine, 231 Albert Sabin Way, CVC 3974, Cincinnati, OH, 45267-0769, USA.
| | - Prithviraj Mukherjee
- Department of Electrical Engineering and Computing Systems, University of Cincinnati, 812 Rhodes Hall, Cincinnati, OH, 45221, USA
| | - Himanshu Shekhar
- Department of Internal Medicine, Division of Cardiovascular Health and Diseases, University of Cincinnati, 231 Albert Sabin Way, Cincinnati, OH, 45267, USA
| | - George J Shaw
- Department of Emergency Medicine, University of Cincinnati, 231 Albert Sabin Way, Suite 1551, Cincinnati, OH, 45267, USA
| | - Ian Papautsky
- Department of Electrical Engineering and Computing Systems, University of Cincinnati, 812 Rhodes Hall, Cincinnati, OH, 45221, USA
| | - Christy K Holland
- Department of Internal Medicine, Division of Cardiovascular Health and Diseases, University of Cincinnati, 231 Albert Sabin Way, Cincinnati, OH, 45267, USA
| |
Collapse
|
5
|
Xia L, Porter TM, Sarkar K. Interpreting attenuation at different excitation amplitudes to estimate strain-dependent interfacial rheological properties of lipid-coated monodisperse microbubbles. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2015; 138:3994-4003. [PMID: 26723353 DOI: 10.1121/1.4938234] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Broadband attenuation of ultrasound measured at different excitation pressures being different raises a serious theoretical concern, because the underlying assumption of linear and independent propagation of different frequency components nominally requires attenuation to be independent of excitation. Here, this issue is investigated by examining ultrasound attenuation through a monodisperse lipid-coated microbubble suspension measured at four different acoustic excitation amplitudes. The attenuation data are used to determine interfacial rheological properties (surface tension, surface dilatational elasticity, and surface dilatational viscosity) of the encapsulation according to three different models. Although different models result in similar rheological properties, attenuation measured at different excitation levels (4-110 kPa) leads to different values for them; the dilatation elasticity (0.56 to 0.18 N/m) and viscosity (2.4 × 10(-8) to 1.52 × 10(-8) Ns/m) both decrease with increasing pressure. Numerically simulating the scattered response, nonlinear energy transfer between frequencies are shown to be negligible, thereby demonstrating the linearity in propagation and validating the attenuation analysis. There is a second concern to the characterization arising from shell properties being dependent on excitation amplitude, which is not a proper constitutive variable. It is resolved by arriving at a strain-dependent rheology for the encapsulation. The limitations of the underlying analysis are discussed.
Collapse
Affiliation(s)
- Lang Xia
- Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, USA
| | - Tyrone M Porter
- Department of Mechanical Engineering, Boston University, Boston, Massachusetts 02215, USA
| | - Kausik Sarkar
- Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, USA
| |
Collapse
|
6
|
Helfield BL, Leung BYC, Huo X, Goertz DE. Scaling of the viscoelastic shell properties of phospholipid encapsulated microbubbles with ultrasound frequency. ULTRASONICS 2014; 54:1419-24. [PMID: 24746478 DOI: 10.1016/j.ultras.2014.03.014] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Revised: 03/22/2014] [Accepted: 03/22/2014] [Indexed: 05/11/2023]
Abstract
Phospholipid encapsulated microbubbles are widely employed as clinical diagnostic ultrasound contrast agents in the 1-5 MHz range, and are increasingly employed at higher ultrasound transmit frequencies. The stiffness and viscosity of the encapsulating "shells" have been shown to play a central role in determining both the linear and nonlinear response of microbubbles to ultrasound. At lower frequencies, recent studies have suggested that shell properties can be frequency dependent. At present, there is only limited knowledge of how the viscoelastic properties of phospholipid shells scale at higher frequencies. In this study, four batches of in-house phospholipid encapsulated microbubbles were fabricated with decreasing volume-weighted mean diameters of 3.20, 2.07, 1.82 and 1.61 μm. Attenuation experiments were conducted in order to assess the frequency-dependent response of each batch, resulting in resonant peaks in response at 4.2, 8.9, 12.6 and 19.5 MHz, respectively. With knowledge of the size measurements, the attenuation spectra were then fitted with a standard linearized bubble model in order to estimate the microbubble shell stiffness Sp and shell viscosity Sf, resulting in a slight increase in Sp (1.53-1.76 N/m) and a substantial decrease in Sf (0.29×10(-6)-0.08×10(-6) kg/s) with increasing frequency. These results performed on a single phospholipid agent show that frequency dependent shell properties persist at high frequencies (up to 19.5MHz).
Collapse
Affiliation(s)
- B L Helfield
- Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; Sunnybrook Research Institute, Toronto, Ontario, Canada.
| | - Ben Y C Leung
- Sunnybrook Research Institute, Toronto, Ontario, Canada
| | - Xuan Huo
- Sunnybrook Research Institute, Toronto, Ontario, Canada
| | - D E Goertz
- Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; Sunnybrook Research Institute, Toronto, Ontario, Canada
| |
Collapse
|
7
|
Paul S, Nahire R, Mallik S, Sarkar K. Encapsulated microbubbles and echogenic liposomes for contrast ultrasound imaging and targeted drug delivery. COMPUTATIONAL MECHANICS 2014; 53:413-435. [PMID: 26097272 PMCID: PMC4470369 DOI: 10.1007/s00466-013-0962-4] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Micron- to nanometer-sized ultrasound agents, like encapsulated microbubbles and echogenic liposomes, are being developed for diagnostic imaging and ultrasound mediated drug/gene delivery. This review provides an overview of the current state of the art of the mathematical models of the acoustic behavior of ultrasound contrast microbubbles. We also present a review of the in vitro experimental characterization of the acoustic properties of microbubble based contrast agents undertaken in our laboratory. The hierarchical two-pronged approach of modeling contrast agents we developed is demonstrated for a lipid coated (Sonazoid™) and a polymer shelled (poly D-L-lactic acid) contrast microbubbles. The acoustic and drug release properties of the newly developed echogenic liposomes are discussed for their use as simultaneous imaging and drug/gene delivery agents. Although echogenicity is conclusively demonstrated in experiments, its physical mechanisms remain uncertain. Addressing questions raised here will accelerate further development and eventual clinical approval of these novel technologies.
Collapse
Affiliation(s)
- Shirshendu Paul
- Department of Mechanical Engineering, University of Delaware, Newark DE 19716, USA
| | - Rahul Nahire
- Department of Pharmaceutical Sciences, North Dakota State University, Fargo ND 58108, USA
| | - Sanku Mallik
- Department of Pharmaceutical Sciences, North Dakota State University, Fargo ND 58108, USA
| | - Kausik Sarkar
- Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, USA
| |
Collapse
|
8
|
Wang CH, Yeh CK. Controlling the size distribution of lipid-coated bubbles via fluidity regulation. ULTRASOUND IN MEDICINE & BIOLOGY 2013; 39:882-892. [PMID: 23453628 DOI: 10.1016/j.ultrasmedbio.2013.01.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2012] [Revised: 01/06/2013] [Accepted: 01/15/2013] [Indexed: 06/01/2023]
Abstract
Lipid-coated bubbles exhibit oscillation responses capable of enhancing the sensitivity of ultrasound imaging by improving contrast. Further improvements in performance enhancement require control of the size distribution of bubbles to promote correspondence between their resonance frequency and the frequency of the ultrasound. Here we describe a size-controlling technique that can shift the size distribution using a currently available agitation method. This technique is based on regulating the membrane dynamic fluidity of lipid mixtures and provides a general size-controlling variable that could also be applied in other fabrication methods. Three materials (1,2-dihexadecanoyl-sn-glycero-3-phosphocholine, 1,2-dioctadecanoyl-sn-glycero-3-phospho-(1'-rac-glycerol) and polyethylene glycol 40 stearate) with distinct initial fluidities and phase behaviors were used to demonstrate the use of fluidity regulation to control bubble sizes. Bubble size distributions of different formulations were determined by electrical impedance sensing, and bubble volumes and surface areas were calculated. To confirm the relationship between regulated fluidity and mean bubble size, the membrane fluidity of each composition was determined by fluorescence anisotropy, with the results indicating linear relations in the compositions with similar main transition temperatures. Compositions with a higher molar proportion of polyethylene glycol 40 stearate showed higher fluidities and larger bubbles. B-mode ultrasound imaging was performed to investigate the echogenicity and lifetime of the fabricated bubbles, with the results indicating that co-mixing a high-transition-temperature charged lipid (i.e., 1,2-dioctadecanoyl-sn-glycero-3-phospho-(1'-rac-glycerol)) extends the tailoring range of this fluidity regulation technique, allowing refined and continuous changes in mean bubble size (from 0.93 to 2.86 μm in steps of ∼0.5 μm), and also prolongs bubble lifetime. The polydispersity of each composition was also determined to evaluate practicality in particular applications. Our study demonstrates a feasible approach to naturally controling bubble size distribution and provides a practical reference for other fabrication systems and ultrasound imaging applications.
Collapse
Affiliation(s)
- Chung-Hsin Wang
- Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan
| | | |
Collapse
|
9
|
Zhushma A, Lebedeva N, Sen P, Rubinstein M, Sheiko SS, Dayton PA. A system for acoustical and optical analysis of encapsulated microbubbles at ultrahigh hydrostatic pressures. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:055105. [PMID: 23742587 DOI: 10.1063/1.4803158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Acoustics are commonly used for borehole (i.e., oil well) imaging applications, under conditions where temperature and pressure reach extremes beyond that of conventional medical ultrasonics. Recently, there has been an interest in the application of encapsulated microbubbles as borehole contrast agents for acoustic assessment of fluid composition and flow. Although such microbubbles are widely studied under physiological conditions for medical imaging applications, to date there is a paucity of information on the behavior of encapsulated gas-filled microbubbles at high pressures. One major limitation is that there is a lack of experimental systems to assess both optical and acoustic data of micrometer-sized particles data at these extremes. In this paper, we present the design and application of a high-pressure cell designed for acoustical and optical studies of microbubbles at hydrostatic pressures up to 27.5 MPa (271 atm).
Collapse
Affiliation(s)
- Aleksandr Zhushma
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
| | | | | | | | | | | |
Collapse
|
10
|
Paul S, Russakow D, Nahire R, Nandy T, Ambre AH, Katti K, Mallik S, Sarkar K. In vitro measurement of attenuation and nonlinear scattering from echogenic liposomes. ULTRASONICS 2012; 52:962-9. [PMID: 22652364 PMCID: PMC3889870 DOI: 10.1016/j.ultras.2012.03.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Revised: 01/18/2012] [Accepted: 03/16/2012] [Indexed: 05/09/2023]
Abstract
Echogenic liposomes (ELIP) are an excellent candidate for concurrent imaging and drug delivery applications. They combine the advantages of liposomes-biocompatibility and ability to encapsulate both hydrophobic and hydrophilic drugs-with strong reflections of ultrasound. The objective of this study is to perform a detailed in vitro acoustic characterization - including nonlinear scattering that has not been studied before - along with an investigation of the primary mechanism of echogenicity. Both components are critical for developing viable clinical applications of ELIP. Mannitol, a cryoprotectant, added during the preparation of ELIP is commonly believed to be critical in making them echogenic. Accordingly, here ELIP prepared with varying amount of mannitol concentration are investigated for their pressure dependent linear and non-linear scattered responses. The average diameter of these liposomes is measured to be 125-185nm. But they have a broad size distribution including liposomes with diameters over a micro-meter as observed by TEM and AFM. These larger liposomes are critical for the overall echogenicity. Attenuation through liposomal solution is measured with four different transducers (central frequencies 2.25, 3.5, 5, 10MHz). Measured attenuation increases linearly with liposome concentration indicating absence of acoustic interactions between liposomes. Due to the broad size distribution, the attenuation shows a flat response without a distinct peak in the range of frequencies (1-12MHz) investigated. A 15-20dB enhancement with 1.67 μg/ml of lipids is observed both for the scattered fundamental and the second harmonic responses at 3.5MHz excitation frequency and 50-800kPa amplitude. It demonstrates the efficacy of ELIP for fundamental as well as harmonic ultrasound imaging. The scattered response however does not show any distinct subharmonic peak for the acoustic excitation parameters studied. Small amount of mannitol proves critical for echogenicity. However, mannitol concentration above 100mM shows no effect.
Collapse
Affiliation(s)
- Shirshendu Paul
- Mechanical Engineering, University of Delaware, Newark, DE 19716
| | - Daniel Russakow
- Mechanical Engineering, University of Delaware, Newark, DE 19716
| | | | - Tapas Nandy
- North Dakota State University, Fargo, ND 58108
| | | | | | | | - Kausik Sarkar
- Mechanical Engineering, University of Delaware, Newark, DE 19716
- Mechanical and Aerospace Engineering, George Washington University, Washington, DC 20052
| |
Collapse
|