There is a strong need for biomedical implant coatings which can act to deliver the appropriate therapeutics, including sensitive biologic drugs, to localized areas in the body with a level of precision and control. The current state-of-art for drug-coated implants is essentially limited to those which elute a single drug over a given time period, usually with a drug release profile based on the rate of diffusion of the drug component from the thin film coating or the rate of degradation of a homogeneous bulk polymer. In either case, it is not possible to introduce complex release profiles such as the sequential release or two or more drugs utilizing standard methods;yet there are many situations in which more than one therapeutic is needed, and must be introduced at different times during the lifetime of the implant. Furthermore, it is considerably more difficult to deliver pH or solvent sensitive recombinant protein drugs or growth factors often needed for implant applications using traditional degradable polymers such as PLGA, which can expose the drug to low pH and harsh processing conditions. The primary aim of this work is to utilize the enabling nanofabrication tool of electrostatic multilayer assembly to create coatings one nanoscale layer at a time by alternating drugs with degradable polyions such that complex, multicomponent, sequential or graduated release of drugs takes place from implant surfaces in a layer-by-layer fashion. This method is simple, low cost, and allows infinite tuning of film composition using an alternate electrostatic assembly process, resulting in films that degrade under biological conditions to release series of drugs layers at a time.
Specific Aims i nclude the control of degradable polyion composition, multilayer film assembly conditions, and manipulation of nanometer scale structure of the thin films to ensure delivery in inverse order to construction of the film. In vitro cell culture studies of release of antibacterial agents and growth factors will be used to determine efficacy and optimal dose levels of these systems. Animal models that include a small animal large scale rabbit study will be used to determine efficacy of antibacterial, growth factor, and combination coatings that delivery 2 or 3 agents will be performed. A large animal goat model that better replicates human bone mechanics will be performed on the most promising nanoscale coatings. Preservation of sensitive biologic drug efficacy will be key to these studies. This novel approach has several important high- impact applications, including coatings of stents, sutures, bone and other surgical implants. The focus of this work will be on orthopedic implants, an area where the controlled delivery of multiple therapeutics could eliminate additional surgeries and promote rapid healing. We will investigate the coating of prostheses with therapeutic quantities of antibiotics, angipgenic factors, and bone morphogenetic growth factors that can be released sequentially to enable disinfection of the joint area, bone healing and growth respectively. The concept of highly controlled, passive coatings on implants is both commercially feasible and disruptive, and promises molecular level control of delivery from the device surface, which should lead to broader applications for a number of implant devices.
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