Design of a core-shelled polymer cylinder for potential programmable drug delivery

Repetitive on-demand drug release from polymeric matrices containing a macroscopic spherical iron core

A system for multiple on-demand drug release has been prepared that can be activated with an alternating magnetic field as external trigger. The core/shell samples have been developed based on a macroscopic spherical iron core coated with a thermoresponsive polymer, poly(styrene-stat-butyl methacrylate), containing ibuprofen as a model drug. During exposure of the samples to the magnetic field (ON state), the release rate of ibuprofen is significantly increased, up to 35 times the release rate without the magnetic field (OFF state). Using one sample or two samples in line with the magnetic field does not influence the ON/OFF ratio of the system, showing the possibility of using multiple samples to increase and tune the drug dose. Increasing the concentration of ibuprofen in the polymer layer is shown to increase the release rate in both the ON and OFF states. Increasing the size of the iron core and, consequently, decreasing the polymer thickness, was found to only increase the release rate during exposure resulting in higher ON/OFF ratios. The developed on demand drug delivery systems represents a promising development towards on demand drug delivery implants.

REFLECTIONS ON CAREER GOALS

During my chemical engineering studies, it was only during my master thesis work that I decided to continue with PhD research as I really enjoyed doing original research. When coming to the end of my PhD research under supervision of Prof. Ulrich S. Schubert, I developed the ambition to pursue an academic career. Fortunately, I got the opportunity to stay with Prof. Schubert as project leader for the Dutch Polymer Institute (DPI). Within this position, I supervised ten researchers and was able to start developing my independent research lines. Despite that I now advise students to not stay in the same laboratory, this first position allowed me to gain some initial independence and to publish a large number of papers that has been a great benefit in my further career. After two and a half years I needed a new challenge that I found by taking up a part-time position at a start-up company in Eindhoven, Dolphys Medical BV, while I also continued as part-time group leader for the DPI. As senior product developer, I was in charge of the research and learned to focus on the application rather than scientific curiosity. This experience made me realize that I prefer the freedom to do academic blue sky research and decided to fully go for an academic position. After personal discussions with some prominent professors in the Netherlands, I applied for a postdoc fellowship in the Netherlands with Prof. Roeland Nolte as well as a Humboldt fellowship in Germany with Prof. Martin Möller, which I both got. As a result, I went one year 'abroad' to Aachen and returned to Nijmegen where I intended to start my independent career. However, another opportunity came along. Via my personal network I was informed that I would make a good chance if I applied for a new professor scheme in Ghent. So I applied and the rest is history. Picture of the Supramolecular Chemistry Group (2017).

Vaccine adjuvants: current challenges and future approaches

For humans, companion animals, and food producing animals, vaccination has been touted as the most successful medical intervention for the prevention of disease in the twentieth century. However, vaccination is not without problems. With the development of new and less reactogenic vaccine antigens, which take advantage of molecular recombinant technologies, also comes the need for more effective adjuvants that will facilitate the induction of adaptive immune responses. Furthermore, current vaccine adjuvants are successful at generating humoral or antibody mediated protection but many diseases currently plaguing humans and animals, such as tuberculosis and malaria, require cell mediated immunity for adequate protection. A comprehensive discussion is presented of current vaccine adjuvants, their effects on the induction of immune responses, and vaccine adjuvants that have shown promise in recent literature.

Preparation of Novel Cationic Copolymer Microspheres and Evaluation of Their Function by In Vitro and In Vivo tests as Ph-Sensitive Drug Carrier Systems

Novel pH-sensitive copolymer microspheres containing methylacrylic acid and styrene cross-linking with divinylbenzene were synthesized by free radical polymerization. The microspheres that were formed were then characterized by Fourier-Transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), size analysis, and X-ray analysis. The copolymer microspheres showed pulsatile swelling behavior when the pH of the media changed. The pH-sensitive microspheres were loaded with diltiazem hydrochloride (DH). The release characteristics of the free drug and the drug-loaded microspheres were studied under both simulated gastric conditions and intestinal pH conditions. The in vivo evaluation of the pulsatile preparation was subsequently carried out using beagle dogs as experimental subjects. The results demonstrated that the drug release exhibited a pulsatile character both in vitro and in vivo.

Polymers as biomaterials for tissue engineering and controlled drug delivery

The advent of biodegradable polymers has significantly influenced the development and rapid growth of various technologies in modern medicine. Biodegradable polymers are mainly used where the transient existence of materials is required and they find applications as sutures, scaffolds for tissue regeneration, tissue adhesives, hemostats, and transient barriers for tissue adhesion, as well as drug delivery systems. Each of these applications demands materials with unique physical, chemical, biological, and biomechanical properties to provide efficient therapy. Consequently, a wide range of degradable polymers, both natural and synthetic, have been investigated for these applications. Furthermore, recent advances in molecular and cellular biology, coupled with the development of novel biotechnological drugs, necessitate the modification of existing polymers or synthesis of novel polymers for specific applications. This review highlights various biodegradable polymeric materials currently investigated for use in two key medical applications: drug delivery and tissue engineering.

Detection and modelling of DNA hybridization by EIS measurements. Mention of a polythiophene matrix suitable for electrochemically controlled gene delivery

A conducting polymer sensor for direct label-free DNA detection based on a polythiophene bearing an electroactive linker group is investigated. DNA hybridization is studied by electrochemical impedance spectroscopy (EIS) and quartz crystal microbalance (QCM) techniques. Modelling of DNA hybridization by EIS measurements exhibits the contribution of nucleic acid to a superficial p-doping process. A 675-mer single-stranded DNA is produced using asymmetric PCR from a DNA sequence of a transposable element mariner and hybridized to the previously immobilized probe. Electrochemical stimulus leads to the release "on demand" of DNA fragments and the amount delivery permits to do PCR amplification.

Polymer actuator valves toward controlled drug delivery application

A novel controlled drug delivery system in which drug release is achieved by electrochemically actuating an array of polymeric valves on a set of drug reservoirs has been developed. The valves are bilayer structures, made in shape of a flap hinged on one side to a valve seat, consisting of thin films of evaporated gold and electrochemically deposited polypyrrole (PPy). Drugs (dry or wet) were pre-stored in an array of these reservoirs and their release is accomplished by bending the bilayer flaps away from the substrate with a small applied bias. In vitro color dye release experiment has been conducted. Seventy-five percent less energy consumption was achieved with this bilayer polymer valve design to open a same size reservoir compared to metal-corrosion based valves. Complex release patterns such as multiple drug pulsatile release and continuous linear release have been successfully implemented through flexible control of valve actuation sequence. These valves can be actuated under closed-loop-control of sensors responding to a specific biological or environmental stimulus, leading to potential applications in advanced responsive drug delivery systems.

Multi-pulse drug delivery from a resorbable polymeric microchip device

Controlled-release drug delivery systems have many applications, including treatments for hormone deficiencies and chronic pain. A biodegradable device that could provide multi-dose drug delivery would be advantageous for long-term treatment of conditions requiring pulsatile drug release. In this work, biodegradable polymeric microchips were fabricated that released four pulses of radiolabelled dextran, human growth hormone or heparin in vitro. Heparin that was released over 142 days retained on average 96 +/- 12% of its bioactivity. The microchips were 1.2 cm in diameter, 480-560 microm thick and had 36 reservoirs that could each be filled with a different chemical. The devices were fabricated from poly(L-lactic acid) and had poly(D,L-lactic-co-glycolic acid) membranes of different molecular masses covering the reservoirs. A drug delivery system can be designed with the potential to release pulses of different drugs at intervals after implantation in a patient by using different molecular masses or materials for the membrane.

In vitro release of sodium diclofenac from a central core matrix tablet aimed for colonic drug delivery

The present study was aimed at developing a novel sodium diclofenac formulation for colonic release. The proposed delivery system consisted in a polymeric matrix tablet containing a drug central core purposely designed for obtaining a time-controlled release profile characterized by an initial phase of lag-time followed by a controlled release phase, according to zero order kinetics. The spheric central core was formed by a solid dispersion of the drug into the hydrophilic polymer PEG 4000, which enabled an improvement of drug dissolution properties with respect to other carriers such as lactose. Eudragit RS100 was used as inert polymeric matrix for the core coating, mixed (50:50, w/w) with sodium chloride and Emdex as channeling agents. Tablets containing the drug central core were prepared by direct compression, without any other excipient, and tested for dissolution properties according to the USP paddle method, under pH-gradient conditions. For both series of formulations, lag times increased with decreasing the channeling agent particle size, as a consequence of the smaller pores formed by its dissolution. However, formulations containing sodium chloride always showed longer lag times than the corresponding with Emdex and were more effective in providing prolonged zero-order release periods. This was mainly attributed to the plastic deformation properties under compression shown by sodium chloride, leading to a less porous, more compact network which more strictly controlled solvent penetration and drug dissolution and release rates. By varying the sodium chloride/Eudragit w/w ratio, it was possible to suitably modulate the length of both the lag time (for achieving colonic targeting) and zero-order release phases.

Implantable, polymeric systems for modulated drug delivery

The ability to deliver therapeutic agents to a patient in a pulsatile or staggered release profile has been a major goal in drug delivery research over the last two decades. This review will cover methods that have been developed to control drug delivery profiles with implantable polymeric systems. Externally and internally controlled systems will be discussed, spanning a range of technologies that include pre-programmed systems, as well as systems that are sensitive to modulated enzymatic or hydrolytic degradation, pH, magnetic fields, ultrasound, electric fields, temperature, light and mechanical stimulation. Implantable systems have the potential to improve the quality of life for patients undergoing therapy with a variable dosing regime by eliminating the need for multiple intravenous injections. Ideally, these systems would also result in increased patient compliance with a given therapy due to the relative ease of self-dosing.