Controlled release of 5-fluorouridine from radiation-crosslinked poly(ethylene-co-vinyl acetate) films

Modeling diffusion-based drug release inside a nerve conduit in vitro and in vivo validation study

The objective of this work was to develop a model and understand the diffusion of a drug into and throughout a drug delivering nerve conduit from a surrounding reservoir through a hole in the wall separating the lumen of the conduit and the reservoir. A mathematical model based on Fick's law of diffusion was developed using the finite difference method to understand the drug diffusion and the effect of varying device parameters on the concentration of drug delivered from a hole-based drug delivery device. The mathematical model was verified using a physical microfluidic (μFD) model and an in vitro/in vivo release test using prototype devices. The results of the mathematical model evaluation and microfluidic device testing offered positive insight into the reliability and function of the reservoir and hole-based drug delivering nerve conduit. The mathematical model demonstrated how changing device parameters would change the drug concentration inside the device. It was observed that the drug release in the conduit could be tuned by both concentration scaling and changing the hole size or number of holes. Based on the results obtained from the microfluidic device, the error in the mathematical drug release model was shown to be less than 10% when comparing the data obtained from mathematical model and μFD model. The data highlights the flexibility of having a hole-based drug delivery system, since the drug release can be scaled predictably by changing the device parameters or the concentration of the drug in the reservoir. Graphical abstract .

Design, synthesis, characterization and biological evaluation of Thieno[2,3-b]pyridines-chitosan nanocomposites as drug delivery systems for colon targeting

Thieno[2,3-b]pyridine derivatives DATP_a-c have been synthesized based on Thorpe-Ziegler Cyclization. The reaction of arylidene malononitrile derivatives (I_a-c) with thiocyanoacetamide (II) in basic medium (piperidine) followed by alkylation using ethyl chloroacetate and finally, cyclization in sodium ethoxide yielded DATP_a-c. Thieno[2,3-b]pyridine-chitosan nanocomposites CS-DATP_a-c were prepared from the DATP_a-c and CS nanoparticles using sodium tripolyphosphate (TPP). CS-DATP_a-c nanocomposites were characterized using FTIR, TEM and XRD techniques and showed a relatively narrow size distribution of monodispersed nanoparticles with the average size of 14-78 nm. The in vitro release studies of CS-DAΤP_a-c nanocomposites were investigated and showed that the drug release rate is pH-dependent and the trend is as follows: basic > neutral > acidic. The faster release rate in basic medium effectively prolongs drug delivery in gastric pH. Additionally, the antibacterial investigation showed that DATP_a-c and CS-DATP_a-c nanocomposites exhibited antibacterial activity against both Gram-positive and Gram-negative bacteria but CS-DATP_a-c nanocomposites showed much higher antibacterial activity compared to the DATP_a-c, which in agreement with the particle size measurements as DATP_a-c are in the bulky structure whereas, CS-DATP_a-c are in the nanostructure. The results may have applications of drug design for colon targeting.

Hot-Melt Preparation of a Non-Biodegradable Peptide Implant: A Proof of Principle

BACKGROUND

Both biodegradable and non-biodegradable peptide-loaded implants are already developed for the long-term treatment of patients, thereby reducing the frequency of drug administration. To further improve peptide formulation, extending the scope of implant-based drug delivery systems towards other polymers and processing techniques is highly interesting.

OBJECTIVE

In this study, as a proof-of-principle, the feasibility of hot-melt processing of a peptide active pharmaceutical ingredient was assessed by developing a non-biodegradable poly(ethylenevinyl acetate) (33% VA) implant loaded with 20% (w/w) buserelin acetate.

METHODS

Cross-sectional implant characterization was performed by Raman microscopy. The stability of buserelin acetate in the polymeric matrix was evaluated for 3 months under ICH stability conditions and the quantity as well as the degradation products analyzed using LC-UV methods. An in vitro dissolution study was performed as well and buserelin acetate and its degradants analyzed using the same chromatographic methods.

RESULTS

No significant quantities of buserelin acetate-related degradation products were formed during the hot-melt preparation as well as during the stability study. Together with the consistent buserelin acetate assay values over time, chemical peptide stability was thus demonstrated. The in vitro buserelin acetate release from the implant was found to be diffusion-controlled after an initial burst release, with stable release profiles in the stability study, demonstrating the functional stability of the peptide implant.

CONCLUSION

These results indicate the feasibility of preparing non-biodegradable peptide-loaded implants using the hot-melt production method and may act as a proof of principle concept for further innovation in peptide medicinal formulations.

The effect of polyethylene glycol structure on paclitaxel drug release and mechanical properties of PLGA thin films

Thin films of poly(lactic acid-co-glycolic acid) (PLGA) incorporating paclitaxel typically have slow release rates of paclitaxel of the order of 1 μg day(-1) cm(-2). For implementation as medical devices a range of zero order release rates (i.e. 1-15 μg day(-1) cm(-2)) is desirable for different tissues and pathologies. Eight and 35 kDa molecular weight polyethylene glycol (PEG) was incorporated at 15%, 25% and 50% weight ratios into PLGA containing 10 wt.% paclitaxel. The mechanical properties were assessed for potential use as medical implants and the rates of release of paclitaxel were quantified as per cent release and the more clinically useful rate of release in μg day(-1) cm(-2). Paclitaxel quantitation was correlated with the release of PEG from PLGA, to further understand its role in paclitaxel/PLGA release modulation. PEG release was found to correlate with paclitaxel release and the level of crystallinity of the PEG in the PLGA film, as measured by Raman spectrometry. This supports the concept of using a phase separating, partitioning compound to increase the release rates of hydrophobic drugs such as paclitaxel from PLGA films, where paclitaxel is normally homogeneously distributed/dissolved. Two formulations are promising for medical device thin films, when optimized for tensile strength, elongation, and drug release. For slow rates of paclitaxel release an average of 3.8 μg day(-1) cm(-2) using 15% 35k PEG for >30 days was achieved, while a high rate of drug release of 12 μg day(-1) cm(-2) was maintained using 25% 8 kDa PEG for up to 12 days.

Drug release kinetics and transport mechanisms of non-degradable and degradable polymeric delivery systems

IMPORTANCE OF THE FIELD

The advancement in material design and engineering has led to the rapid development of new materials with increasing complexity and functions. Both non-degradable and degradable polymers have found wide applications in the controlled delivery field. Studies on drug release kinetics provide important information into the function of material systems. To elucidate the detailed transport mechanism and the structure-function relationship of a material system, it is critical to bridge the gap between the macroscopic data and the transport behavior at the molecular level.

AREAS COVERED IN THIS REVIEW

The structure and function information of selected non-degradable and degradable polymers have been collected and summarized from literature published after the 1990s. The release kinetics of selected drug compounds from various material systems is discussed in case studies. Recent progress in the mathematical models based on different transport mechanisms is highlighted.

WHAT THE READER WILL GAIN

This article aims to provide an overview of structure-function relationships of selected non-degradable and degradable polymers as drug delivery matrices.

TAKE HOME MESSAGE

Understanding the structure-function relationship of the material system is key to the successful design of a delivery system for a particular application. Moreover, developing complex polymeric matrices requires more robust mathematical models to elucidate the solute transport mechanisms.