Derek Halverson

Validation of High Gradient Magnetic Field Based Drug Delivery to Magnetizable Implants Under Flow

The drug-eluting stents increasingly frequent occurrence late stage thrombosis have created a need for new strategies for intervention in coronary artery disease. This paper demonstrates further development of our minimally invasive, targeted drug delivery system that uses induced magnetism to administer repeatable and patient specific dosages of therapeutic agents to specific sites in the human body. Our first aim is the use of magnetizable stents for the prevention and treatment of coronary restenosis; however, future applications include the targeting of tumors, vascular defects, and other localized pathologies. Future doses can be administered to the same site by intravenous injection. This implant-based drug delivery system functions by placement of a weakly magnetizable stent or implant at precise locations in the cardiovascular system, followed by the delivery of magnetically susceptible drug carriers. The stents are capable of applying high local magnetic field gradients within the body, while only exposing the body to a modest external field. The local gradients created within the blood vessel create the forces needed to attract and hold drug-containing magnetic nanoparticles at the implant site. Once these particles are captured, they are capable of delivering therapeutic agents such as antineoplastics, radioactivity, or biological cells.

Magnetostatic interactions between carbon nanotubes filled with magnetic nanoparticles

The magnetostatic interactions between carbon nanotubes filled with magnetic particles have been experimentally and theoretically studied. By making nanotubes uniformly magnetized, one eliminates the attraction caused by periodicity of nanoparticles in magnetic chains. The discreteness of individual nanoparticles in the nanoneedles is not observed and these nanoneedles interact by their magnetic poles. Since the attraction/repulsion events are predictable, the suspensions of magnetic nanotubes are attractive candidates for active elements in changeable diffraction gratings, filters, and polarizers.

Manipulation of nonmagnetic nanobeads in dilute ferrofluid

Patterns of submicron Co islands in conjunction with a uniform, static, or rotating magnetic field are used to demonstrate the possibility of assembling 100–300nm nonmagnetic latex beads in designated locations and manipulating their movements on surfaces.

Arraying Nonmagnetic Colloids by Magnetic Nanoparticle Assemblers

We review our recent work on the manipulation and assembly of nonmagnetic colloidal materials above magnetically programmable surface templates. The nonmagnetic materials are manipulated by a fluid dispersion of magnetic nanoparticles, known as ferrofluid. Particle motion is guided by a program of magnetic information stored in a substrate in the form of a lithographically patterned template of micromagnets. We show how dynamic control over the motion of nonmagnetic particles can be accomplished by applying rotating external magnetic field. This unexpectedly large degree of control over particle motion can be used to manipulate large ensembles of particles in parallel, potentially with local control over particle trajectory

Local approximation matching for open boundary problems

A local approximation matching method is used to derive a computational scheme for static field problems with open boundaries. This scheme results in a conventional finite difference method applied in the interior and a new difference scheme applied to nodes on the exterior boundary. Numerical examples are provided indicating that errors due to mesh truncation are low.

Magnetic Field Assisted Fractionation of Nonmagnetic Colloids in Ferrofluid

Flocculation of nonmagnetic colloidal particles in ferrofluid while in the presence of an external uniform magnetic field is investigated experimentally. Magnetic nanoparticles in ferrofluid create magnetic interactions between nonmagnetic colloidal particles. It is demonstrated that nonmagnetic particles can be fractionated by size much more efficiently in the presence of these magnetic interactions

Locally targeted drug delivery to magnetic stents for therapeutic applications

The ability to safely and effectively deliver high dosages of drugs to specific sites in the human body is fundamental to the advancement of drug delivery research. Drugs with proven effectiveness under in vitro investigation often reach a major roadblock under in vivo testing due to a lack of an effective delivery strategy. In addition, many clinical scenarios require delivery of agents that are therapeutic at the desired delivery point, but otherwise systemically toxic. This paper proposes a method for targeted drug delivery by applying high magnetic field gradients within the body to an injected superparamagnetic colloidal fluid carrying a drug, without relying on magnetic coils held external to the body to provide the force. The experimental flow model presented gives insight into the use of magnetic carriers for site-specific delivery of therapeutic agents

Arranging Matter by Magnetic Nanoparticle Assembly

The transporting colloidal particles, large molecules, cells, and other materials across surfaces and for assembling them into highly regular patterns are introduced through a method, where nonmagnetic materials are manipulated by a fluid dispersion of magnetic nanoparticles. Manipulation of materials is guided by a program of magnetic information stored in a substrate. Dynamic control over the motion of nonmagnetic particles can be achieved by reprogramming the substrate magnetization on the fly. We have developed methods for magnetically manipulating materials in a programmable fashion without requiring their attachment to magnetic particle carriers, which is the most common magnetic manipulation scheme. This developed manipulation techniques are not a stand-alone process, and they must be assisted by surface forces, based on molecular recognition, morphological templating, and/or photo-initiated chemical reactions.

Manipulation of Non-Magnetic Materials in Ferrofluid Containing Media

A novel method is proposed whereby non-magnetic objects can be moved along a surface at the microscale and nanoscale. It uses a negative magnetophoretic force, explained in the caption for figure one, on the non-magnetic objects which results from stabilized 10nm diameter iron oxide particles (ferrofluid) being attracted to regions of field maxima around magnetic islands on a surface, which pushes the non-magnetic objects to regions of field minima. By varying an external magnetic field we can control where these minima are and thus control how objects will position themselves with static fields and by using rotating time varying fields we can control how they move across the surface. This method does not require the objects to be initially in contact with the surface, as they will be pulled down to the surface from solution. While this paper deals with beads, any arbitrarily shaped object should be manipuable using this method. Additionally, while we address non-magnetic objects in this work similar methods could easily manipulate objects that are magnetic.