Erodable polymeric matrix

In some conditions, the normalized gel layer thickness (=(S — R)/a) may reach a constant value because the synchronization of the swelling and eroding fronts generates pseudo-order release of a solute incorporated in the polymeric matrix. Experimental results concern mixes made of the drug diclofenac sodium and the excipient poly(vinyl alcohol), HPMC type 2208 or NaCMC (Fig. 9). 

It was also discovered that ultrasound could affect the release of substances from polymers. The ultrasound system has a potential advantage over many other systems in that no additional substance (e.g., a magnetic bead) is required in the polymeric matrix. Furthermore, in the case of ultrasound the polymer can be injected, and since it can be erodible there is no need for surgical removal. The application of ultrasound in humans, both for diagnostic and therapeutic purposes, has been extensively studied and is considered a safe practice. 

Physically dissolved in nonporous polymeric matrix Nonerodible Erodible... 

Erodible inserts contain drug dispersed throughout a polymeric matrix (polylactic, polyglycolic, alginic acid, polypeptides, etc.) the drug is gradually leached from the matrix as it slowly erodes and disintegrates in the cul-de-sac. Devices of this kind have been... 

The drug may be incorporated in a slowly eroding matrix of waxy materials, embedded in a plastic matrix, complexed with anion exchange resins or incorporated in a water-insoluble hydrophilic matrix. Drug release from these systems occurs by several mechanisms diffusion, dissolution, ionic exchange or osmotic pressure [1,2], depending on the type of polymeric excipient present and the formulation used. 

Polymeric carriers are biodegradable or water-soluble polymer matrices, typically in the form of colloidal-sized particles (microspheres or nanospheres), rods, or films. The active agent is entrapped within but not chemically bonded to the matrix. The drug is released in a sustained fashion as the polymer is dissolved or degraded, eroded, and finally resorbed [24,30,58-62]. 

The controlled release of macromolecules from non-erodible, hydrophobic polymeric matrices is modelled as a discrete diffusion process with the release of solute occuring through distinct pores in the polymer which are formed as solid particles of molecule dissolve. In order to formulate predictive models of the release behavior of these devices, quantitative information on the microgeometry of the system is required. We present a computer-based system for obtaining estimates of the system porosity, isotropy, particle shape, and particle size distribution from observations on two-dimensional sections from the polymer matrix. 

Microbial mats and biofilms, defined as surface layers of microbes entrained in a matrix of extracellular polymeric substances (EPS) (Characklis and Marshall, 1989), are also important in changing the surface texture and erodibility of sediments in estuaries (de Beer and Kiihl, 2001). The EPS are primarily composed of cellular-derived polysaccharides, polyuronic acids, proteins, nucleic acids, and lipids (Decho and Lopez, 1993 Schmidt and Ahring, 1994). The EPS can serve as a cementing agent for surface sediment particles, thereby affecting the erodibility of sediments as well as the flux of dissolved constituents across the sediment-water interface (de Beer and Kiihl, 2001). 

Any sol-gel phase reversible system described above can be used as an erodible matrix system. All the components of the system in the sol state are essentially in the dissolved state, and thus they can be released to the environment in the absence of protecting membranes. During the process of gel to sol transition by the addition of glucose, the incorporated insulin can be released as a function of glucose concentration. There are of course other polymeric systems which can be used in glucose-sensitive erodible insulin delivery. 

Release from Polymeric Matrices. In nonsmface erodible matrix systems diffusion of the active ingredient occurs from the interior of the particle to the surface. This gives rise to a declining rate of release according to the square root of time as shown by curve B in Figure 3. In practice, the approximate... 

However, the data revealed several interesting characteristics of a combined matrix system. Firstly, it was found that an additive such as maleic anhydride could facilitate the release of MB from the otherwise seemingly impermeable PCL matrix without erosion by ester hydrolysis. Secondly, as indicated by MB release and analyses of the composition, at 20% by weight or less, a polymeric component of low solubility, such as partially hydrolyzed PVA, could be released from a PCL pellet disc which did not erode and acted as a passive structural component. Finally, the passive component could essentially be selected from any compound, polymeric or otherwise, as well as being permanently or even temporarily insoluble. Therefore, it was inferred that a bioactive polypeptide like insulin or somatotropin could also be safely delivered on a sustained basis from an implant made of a passive structural component as aforementioned. 

With nanoparticles, the architectnre of the particle shell or matrix can be formulated and fine-tuned to offer controlled release of its contents, ranging from constant but prolonged release to zero release. The particles can be formulated with desired characteristics via key structural features, such as CToss-tmking density, hydrophilic-hydrophobic balance of the copolymer units, and stiffness of the polymeric network. Furthermore, erodible or biodegradable particles can be used to combine the release mechanisms of diffusion and erosion. In addition, the particles can be designed to respond to different stimuh from the external environment by adjusting a number of parameters, such as pH, temperature, ionic strength, cosolvent composition, pressure, or electric field. 

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