Methods of preparing gaseous precursor-filled microspheres

Abstract

Methods of and apparatus for preparing gas-filled microspheres are described. Gas-filled microspheres prepared by these methods are particularly useful, for example, in ultrasonic imaging applications and in therapeutic drug delivery systems.

Description

RELATED APPLICATIONS [0001] This application is a divisional of copending U.S. Ser. No. 09 / 118,329, filed Jul. 17, 1998, now allowed, which in turn is a divisional of U.S. Ser. No. 08 / 487,230, filed Jun. 6, 1995, now U.S. Pat. No. 5,853,752, which is a divisional of U.S. Ser. No. 08 / 159,687, filed Nov. 30, 1993, now U.S. Pat. No. 5,585,112, which is a continuation-in-part of U.S. Ser. No. 08 / 160,232 filed Nov. 30, 1993, now U.S. Pat. No. 5,542,935, and a continuation-in-part of U.S. Ser. No. 08 / 159,674, filed Nov. 30, 1993, now abandoned. Said 08 / 160,232 and 08 / 159,674 are continuations-in-part of U.S. Ser. No. 08 / 076,239 filed Jun. 11, 1993, now U.S. Pat. No. 5,469,854, which is a continuation-in-part of U.S. Ser. No. 07 / 717,084, now U.S. Pat. No. 5,228,446, and U.S. Ser. No. 07 / 716,899, now abandoned, both of which were filed Jun. 18, 1991. Said 07 / 717,084 and 07 / 716,899 are continuations-in-part of U.S. Ser. No. 07 / 569,828, filed Aug. 20, 1990, now U.S. Pat. No. 5,088,499, which ...

AI Technical Summary

Benefits of technology

[0024] The present invention provides methods and apparatus for preparing temperature activated gaseous precursor-filled liposomes suitable for use as contrast agents for ultrasonic imaging or as drug delivery agents. The methods of the present invention provide the advantages, for example, of simplicity and potential cost savings during manufacturing of temperature activated gaseous precursor-filled liposomes.

[0026] Unexpectedly, the temperature activated gaseous precursor-filled liposomes prepared in accordance with the methods of the present invention possess a number of surprising yet highly beneficial characteristics. For example, gaseous precursor-filled liposomes are advantageous due to their biocompatibility and the ease with which lipophilic compounds can be made to cross cell membranes after the liposomes are ruptured. The liposomes of the invention also exhibit intense echogenicity on ultrasound, are highly stable to pressure, and / or generally possess a long storage life, either when stored dry or suspended in a liquid medium. The echogenicity of the liposomes is of importance to the diagnostic and therapeutic applications of the liposomes made according to the invention. The gaseous precursor-filled liposomes also have the advantages, for example, of stable particle size, low toxicity and compliant membranes. It is believed that the flexible membranes of the gaseous precursor-filled liposomes may be useful in aiding the accumulation or targeting of these liposomes to tissues such as tumors.

[0027] The temperature activated gaseous precursor-filled liposomes made according to the present invention thus have superior characteristics for ultrasound contrast imaging. When inside an aqueous or tissue media, the gaseous precursor-filled liposome creates an interface for the enhanced absorption of sound. The gaseous precursor-filled liposomes are therefore useful in imaging a patient generally, and / or in diagnosing the presence of diseased tissue in a patient as well as in tissue heating and the facilitation of drug release or activation.

Problems solved by technology

X-rays, however, are known to be somewhat dangerous, since the radiation employed in X-rays is ionizing, and the various deleterious effects of ionizing radiation are cumulative.

This technique, however, has various drawbacks such as expense and the fact that it cannot be conducted as a portable examination.

In addition, MRI is not available at many medical centers.

Nuclear medicine techniques, however, suffer from poor spatial resolution and expose the animal or patient to the deleterious effects of radiation.

Furthermore, the handling and disposal of radionuclides is problematic.

However, despite these various technological improvements, ultrasound is still an imperfect tool in a number of respects, particularly with regard to the imaging and detection of disease in the liver and spleen, kidneys, heart and vasculature, including measuring blood flow.

The methods and materials in the prior art for introduction of genetic materials, for example, to living cells is limited and ineffective.

These methods have all been relatively ineffective in vivo and only of limited use for cell culture transfection.

None of these methods potentiate local release, delivery and integration of genetic material to the target cell.

Great strides have been made in characterizing genetic diseases and in understanding protein transcription but relatively little progress has been made in delivering genetic material to cells for treatment of human and animal disease.

A principal difficulty has been to deliver the genetic material from the extracellular space to the intracellular space or even to effectively localize genetic material at the surface of selected cell membranes.

Whole virus has been used but the amount of genetic material that can be placed inside of the viral capsule is limited and there is concern about possible dangerous interactions that might be caused by live virus.

Despite extensive work on viral vectors, it has been difficult to develop a successfully targeted viral mediated vector for delivery of genetic material in vivo.

Conventional, liquid-containing liposomes have been used to deliver genetic material to cells in cell culture but have mainly been ineffective in vivo for cellular delivery of genetic material.

For example, cationic liposome transfection techniques have not worked effectively in vivo.

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