Polymers for Drug Controlled-Delivery Systems

1. Introduction

Controlled release drug delivery is a new way to treat illnesses. The term controlled release refers to the ability of a drug delivery system to release a drug over an extended period of time at a controlled rate. It generally involves implanting an engineered polymer directly into the organ or system that is affected by a disease. Since the polymer is implanted directly into the tissues affected by disease, the side effects are often small compared to systemic drug delivery (i.e. taking a pill or getting a shot).

Interest in drug delivery research is increasing for a number of reasons: the need for systems to deliver novel, genetically engineered pharmaceuticals, the need to target delivery of anticancer drugs to specific tumors, the need to develop patentable sustained delivery systems, and the need to increase patient compliance. Polymers are essential for all the new delivery systems, including transdermal patches, microspheres, pumps, aerosols, ocular implants, and contraceptive implants. The major disease areas that are expected to benefit from development of new delivery systems include chronic degenerative diseases, such as central nervous system disorders associated with aging, cancer, cardiovascular and respiratory diseases, chemical imbalances, and cellular dysfunction.

Brain diseases are particularly good candidates for controlled release techniques because of a physiological feature known as the blood-brain barrier. The blood-brain barrier refers to a tight sheath of cells that surround the blood vessels in your brain. These cells make sure that only specific types of molecules get into the brain. More specifically, only small, water insoluble molecules can get into the brain. Consequently, the types of drugs that are developed for brain disease must fit this criteria, which is unfortunate because many promising drugs are water soluble or large. The use of controlled release techniques has led to tremendous breakthroughs in treating people brain diseases.

2. General Information

Polymers

Importance and uses

Polymers are abundant in biological materials and are increasingly important in health, medicine, and biotechnology. Examples include implants, medical devices and diagnostics, controlled drug release, biological methods and mechanisms, and the techniques of biotechnology. This is an area of rapidly expanding understanding and application.

Growing use of polymers as biomaterials

o Seasickness patches

o Prostheses—hip cups, lenses, blood vessels, orthopedic implants, denture bases, fillings, sutures, heart valves, organs, vascular grafts, hernia mesh, catheters, syringes, diapers, blood bags, artificial limbs, ligaments, packaging

o Controlled release

o Diagnostics

Emerging electronic properties of polymers

o Dielectrics

o Synthetic metals and battery materials

o Sensors

o Lithographic resists

o Photonic materials

o Light-emitting diodes and displays

o Electrophotography

o Holography

o Fuel cells

o Solar cells

Emergence of synthetic means for control of polymer structures

o Coordination catalysts

o Biocatalysis, enzyme synthesis, biological organisms for synthesizing monomers and polymers

o Ring-opening metathesis polymerization

o Hybrid organic-inorganic materials synthesis, sol gel formation

o Dendritic polymers

o Composites with tailored transport, electrical, or optical properties

Growing use of blends and composites to obtain “tailored” properties

o High-strength, high-modulus fibers

o Enhanced matrix choices

o “Tailored” mechanical properties

o High-stability toughening additives

o High-temperature options

o Understanding of failure mechanisms

Enhanced characterization capability through computer and electronic advances

o Molecular: colligative, light scattering, centrifuged separation, NMR, UV, FTIR, RAMAN

o Solutions, melts: rheology, diffusion, neutron scattering

o Solid state: synchrotron x-ray and electron spectroscopy, TEM, soft x-ray microscopy, mechanical testing

o Surface analysis: XPS, depth profiling, SIMS, SFA, AMF, LFM

o Folding: NMR

o New microscopies: confocal and scanning tunneling

Evolution of polymer theory with emphasis on computer modeling and simulation

o States of matter: solutions, crystalline, amorphous, LCs, blends, block polymers, copolymers, interfaces, surfaces

Dynamic properties: rheology, mechanical properties, electroactive

Continuing search for viable recycling strategies

o Collection problems: separation, contamination

o Blending: properties of mixtures

o Processing: to return to monomer or other feedstock type

o Other means of disposal: incineration, landfill

Enhanced process control through computer and sensor applications

o Molding

o Extrusion

o Film blowing

o Coating

Continuing substitution of polymers for metals and other materials

o Aircraft, space vehicles

o Automobiles

o Clothing

o Machined parts

o Construction

o Electronics

o Marine structures and vehicles

Growing use of polymeric materials for wide variety of military items

o Bullet-proof clothing

o Uniforms

o Aircraft weight reduction

Growing understanding of structure-property relationships

o Finite-element analysis

o Flow modeling, rheology

o Simulation of structures of composites, blends, crystalline polymers