Implanted drug delivery devices

Polyelectrolytes have been widely investigated as components of biocompatible materials. Biomaterials come into contact with blood when used as components in invasive instruments, implant devices, extracorporeal devices in contact with blood flow, implanted parts of hard structural elements, implanted parts of organs, implanted soft tissue substitutes and drug delivery devices. Approaches to the development of blood compatible materials include surface modification to give blood compatibility, polyelectrolyte-based systems which adsorb and/or release heparin as well as polyelectrolytes which mimic the biological activity of heparin. 

Demand pacemakers are very low current devices, requiring only 25-50 jiW for sensing and 60-100 pW for stimulation. In contrast, implanted ventricular defibrillators (Fig. 1.3) must be able to deliver short electric pulses of 25-40 J (e.g. 2 A at 2 V for 10 s) which can shock the heart into normal rhythm, and hence require a much higher rate battery. The most common system is a lithium-silver vanadium oxide cell with a liquid-organic based electrolyte. More than 80 000 such units have been implanted. Implanted drug delivery devices also use lithium primary batteries, as do neurostimulators and bone growth stimulators. 

Microminiature drug delivery device. This is the heart of the implanted medication systems. The drug delivery device often consists of a diaphragm-operated infusion pump that supplies drug at a constant predetermined rate to the body. The pump is connected to the drug reservoir, which, in some cases, may be recharged when exhausted. Today, the available electronic components are so miniature that they can be implanted comfortably even in newborn babies. The pump can be programmed for a constant or variable basal infusion of medication with a repetitive period of from 1 hour to 60 days. By far the most frequently used basal period is 24 hours. A period of 28 days is available, particularly for the infusion of sex hormones to mimic the female menstrual cycle. 

Dziubla TD, Lowman, AM, Toqman MC, and Joseph JI. Implantable drug delivery devices. In Dillow AK and Lowman AM, eds. Biomimetic Materials and Design. New York, Basel Marcel Dekker, 2002, pp. 507-531. 

Permanent implants, prostheses, vascular grafts, catheters, and drug delivery devices... 

One of the most obvious ways to provide sustained-release medication is to place the drug in a delivery device and implant the system into body tissue. A classification of drug delivery devices is shown in Table 1.8. 

The concept of drug delivery devices is old, but new technologies are being applied. Surgical techniques and special injection devices are sometimes required for implantation. The materials used for these implants must be biocompatible. 

Table 1.8 Classification of drug delivery devices Surgically implanted devices for prolonged sustained drug release Drug reservoirs...

The physician then uploads itinerant agent software modules into the microbot to monitor other conditions. The mobile intelligent agent technology allows physicians to launch or upload software programs with specific itinerary or mission to a remote system such as the implanted microbot. The newly uploaded itinerant software module then activates the implantable drug delivery device (IDDD) to release the drug compounds into Jane s blood stream. 

It is critical to demonstrate consistent release rates. Regulatory agencies have suggested that release rates should be within 10% of that specified. These release rates can be checked in vitro however, some in vivo data confirming the release rates are desirable, since the human vitreous has unique characteristics that can affect drug release from many drug delivery devices. If one embarked on a clinical development plan, demonstrated preclinical safety, and clinical safety and efficacy with an implant later shown to release drug outside of the specifications, the initial studies could be invalid. 

Biodegradability is often an important consideration in the development of biomedical, pharmaceutical, and agricultural products for a number of applications. Biodegradable polymers have been formulated for uses such as controlled release and drug-delivery devices, surgical sutures, scaffolds for tissue regeneration, vascular grafts and stents, artificial skin, and orthopedic implants. 

Conductive polymers (CPs) are an emerging teehnology in the field of biomaterials. While CPs retain a predominantly investigative role in the field of medical implants, they have shown potential across a wide range of applications, including neural interfaces, biosensors, nerve grafts, and drug-delivery devices. 

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