Poly(N-vinylcaprolactam) and Salicylic Acid Polymeric Prodrug Grafted onto Medical Silicone to Obtain a Novel Thermo- and pH-Responsive Drug Delivery System for Potential Medical Devices

New medical devices with anti-inflammatory properties are critical to prevent inflammatory processes and infections in medical/surgical procedures. In this work, we present a novel functionalization of silicone for medical use with a polymeric prodrug and a thermosensitive polymer, by graft polymerization (gamma rays), for the localized release of salicylic acid, an analgesic, and anti-inflammatory drug. Silicone rubber (SR) films were functionalized in two stages using graft polymerization from ionizing radiation (⁶⁰Co). The first stage was grafting poly(N-vinylcaprolactam) (PNVCL), a thermo-sensitive polymer, onto SR to obtain SR-g-PNVCL. In the second stage, poly(2-methacryloyloxy-benzoic acid) (P2MBA), a polymeric prodrug, was grafted to obtain (SR-g-PNVCL)-g-P2MBA. The degree of functionalization depended on the concentrations of monomers and the irradiation dose. The films were characterized by attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM–EDX), thermogravimetric analysis (TGA), and contact angle. An upper critical solution temperature (UCST) of the films was demonstrated by the swelling degree as a temperature function. (SR-g-PNVCL)-g-P2MBA films demonstrated hydrolysis-mediated drug release from the polymeric prodrug, pH, and temperature sensitivity. GC–MS confirmed the presence of the drug (salicylic acid), after polymer hydrolysis. The concentration of the drug in the release media was quantified by HPLC. Cytocompatibility and thermo-/pH sensitivity of functionalized medical silicone were demonstrated in cancer and non-cancer cells.

Radiation Grafting of a Polymeric Prodrug onto Silicone Rubber for Potential Medical/Surgical Procedures

Silicone rubber (SR) is a material used for medical procedures, with a common example of its application being in implants for cosmetic or plastic surgeries. It is also an essential component for the development of medical devices. SR was functionalized with the polymeric prodrug of poly(2-methacryloyloxy-benzoic acid) (poly(2MBA)) to render the analgesic anti-inflammatory drug salicylic acid by hydrolysis. The system was designed by functionalizing SR films (0.5 cm × 1 cm) with a direct grafting method, using gamma irradiation (⁶⁰Co source) to induce the polymerization process. The absorbed dose (from 20 to 100 kGy) and the monomer concentration (between 0.4 and 1.5 M) were critical in controlling the surface and the bulk modifications of SR. Grafting poly(2MBA) onto SR (SR-g-2MBA) were characterized by attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy/energy-dispersive X-ray spectrometry, fluorescence microscopy, the contact angle, and the swelling. SR-g-2MBA demonstrated the drug’s sustained and pH-dependent release in simulated physiological mediums (pH = 5.5 and 7.4). The drug’s release was quantified by high-performance liquid chromatography and confirmed by gas chromatography–mass spectrometry. Finally, cytocompatibility was demonstrated in murine fibroblast and human cervical cancer cell lines. The developed systems provide new polymeric drug release systems for medical silicone applications.

Covalently-controlled drug delivery via therapeutic methacrylic tissue adhesives

Therapeutic methacrylic (TMA) monomers lend local, covalently-controlled release of therapeutics, tunable mechanical properties, and increased cytocompatibility to cyanoacrylate medical adhesives.

Polymeric prodrug-functionalized polypropylene films for sustained release of salicylic acid

Medical devices decorated with salicylic acid-based polymer chains (polymeric prodrug) that slowly release this anti-inflammatory and anti-biofilm drug at the implantation site were designed. A "grafting from" method was implemented to directly grow chains of a polymerizable derivative of salicylic acid (2-methacryloyloxy-benzoic acid, 2MBA) onto polypropylene (PP). PP was modified both at bulk and on the surface with poly(2MBA) by means of an oxidative pre-irradiation method ((60)Co source), in order to obtain a grafted polymer in which salicylic acid units were linked by means of labile ester bonds. The grafting percent depended on absorbed dose, reaction time, temperature and monomer concentration. The functionalized films were analyzed regarding structure (FTIR-ATR, SEM-EDX, fluorescence microscopy), temperature stability (TGA), interaction with aqueous medium (water contact angle and swelling), pH-responsive release and cytocompatibility (fibroblasts). In the obtained poly(2MBA)-grafted biomaterial, poly(2MBA) behaved as a polymeric prodrug that regulates salicylic acid release once in contact with aqueous medium, showing pH-dependent release rate.

Core Cross-linked Star Polymers for Temperature/pH Controlled Delivery of 5-Fluorouracil

RAFT polymerization with cross-linking was used to prepare core cross-linked star polymers bearing temperature sensitive arms. The arms consisted of a diblock copolymer containingN-isopropylacrylamide (NIPAAm) and 4-methacryloyloxy benzoic acid (4MBA) in the temperature sensitive block and poly(hexyl acrylate) forming the second hydrophobic block, while ethyleneglycol dimethacrylate was used to form the core. The acid comonomer provides pH sensitivity to the arms and also increases the transition temperature of polyNIPAAm to values in the range of 40 to 46°C. Light scattering and atomic force microscopy studies suggest that loose core star polymers were obtained. The star polymers were loaded with 5-fluorouracil (5-FU), an anticancer agent, in values of up to 30 w/w%.In vitrorelease experiments were performed at different temperatures and pH values, as well as with heating and cooling temperature cycles. Faster drug release was obtained at 42°C or pH 6, compared to normal physiological conditions (37°C, pH 7.4). The drug carriers prepared acted as nanopumps changing the release kinetics of 5-FU when temperatures cycles were applied, in contrast with release rates at a constant temperature. The prepared core cross-linked star polymers represent advanced drug delivery vehicles optimized for 5-FU with potential application in cancer treatment.

Structure–property relationships of DEAEM-containing bone cements: effect of the substitution of a methylene group by an aromatic ring

New aromatic methacrylates were prepared by substitution of a methylene group from diethylaminoethyl methacrylate (DEAEM) by an aromatic ring at two different positions. Diethylamino benzyl methacrylate (DEABM) and N-methacryloyloxyethyl)-N-ethyl-m-toluidine (MEET) were polymerized and incorporated as co-monomers in bone cement formulations. Cements were evaluated in terms of curing and mechanical properties in addition to changes in their glass transition temperature by DSC and surface properties by contact angle measurements. The immediate effect of the presence of an aromatic ring within the amino methacrylate was that it modified the bone cements' physical appearance, as colored products were obtained. It was also observed that peak temperature increased and setting time decreased by the use of DEABM and MEET instead of DEAEM. Simultaneously, both tensile and compressive strength of bone cements were improved; this effect was related to a higher glass transition temperature. In addition, surface properties of cements were modified by the incorporation of the aromatic ring, being more hydrophilic at low molar fractions and more hydrophobic at high molar fractions. Based on these studies, it is concluded that the position of the aromatic ring within the amino methacrylate modified not only the cement's appearance, but also the setting and mechanical properties.

Synthesis of pH and temperature sensitive, core-shell nano/microgels, by one pot, soap-free emulsion polymerization

The synthesis and properties of thermal/pH-sensitive core-shell copolymer nano/microgels were investigated. The crosslinked core consisted of N-isopropylacrylamide (NIPAAm) while the shell was stabilized by poly(ethylene glycol) methyl ether methacrylate (PEGMA) and 2-methacryloyloxybenzoic acid (2MBA) using a "one pot" soapless emulsion polymerization method. Monodisperse particles were produced with average hydrodynamic diameters ranging from 40 to 880 nm, as determined by dynamic light scattering (DLS) in water at 25°C, depending on the synthetic recipe used. The influence of PEGMA and 2MBA content on size and temperature transition at different pH values was studied. Zeta potential measurements and acid-base titration studies demonstrated almost complete incorporation of acid comonomer (2MBA) into the nano/microgels. Two different crosslinkers, a stable and an acid labile, were compared. The crosslinker used has a major influence on the size and charge density of the nano/microgels produced. Microscopic studies confirmed the core-shell morphology of the nano/microgels.

Drug release from complexes with a series of poly(carboxyalkyl methacrylates), a new class of weak polyelectrolytes

Carboxyalkyl methacrylates, a new class of non-cross-linked, hydrophobic weak polyelectrolytes, were synthesized, and then bound to cationic drugs (propranolol.HCl, diltiazem.HCl and verapamil.HCl) to form water-insoluble complexes that release the bound drug only in ionic media (pH 7.4). Compressed tablets were prepared from these cation exchange polyelectrolytes. Release profiles followed zero order kinetics (n>0.90; n is the release exponent). As the hydrophobicity of the polyelectrolytes increased, the rate of release decreased and deviated from linearity (n=0.7). Both the ionic strength of the medium as well as the solubility of the drug affected the rate of release. In acidic media (pH 1.2) a burst of drug was released but the release was halted by a layer of non-ionized polymer precipitated on the surface of the tablets. The results indicate that it is possible to "tailor-make" the release kinetics by using a polyelectrolyte from the series with the suitable hydrophobicity.

Comparative study on the properties of acrylic bone cements prepared with either aliphatic or aromatic functionalized methacrylates

Bone cements prepared with methacrylic acid (MAA) and diethyl amino ethyl methacrylate (DEAEM) were compared with formulations employing 4-methacryloyloxybenzoic acid (MBA) and 4-diethyaminobenzyl methacrylate (DEABM) as comonomer. The influence of these new aromatic monomers on various physicochemical, setting and mechanical properties was assessed. Surface characterization demonstrated that bone cements prepared with any of the functionalized monomers exhibited increasing hydrophilicity with monomer concentration and that the aromatic monomers provided more hydrophilic cements than their aliphatic counterparts for low concentrations of the functional monomer. It was also found that bone cements prepared with high amounts of the acidic aliphatic monomer provided the highest exotherm of reaction and their setting times were shorter than MBA based cements. On the other hand, DEABM containing bone cements exhibited shorter setting times than DEAEM formulations and slightly higher peak temperatures. In general, it was found that the glass transition temperature increased with the presence of acidic comonomer and decreased when alkaline comonomers were present, especially aliphatic ones. When aromatic methacrylates were used at 0.05 molar fraction, the highest tensile and compressive strength were achieved i.e. 46 and 118 MPa for MBA and 51 and 108 MPa for DEABM formulations. A further increase in the aromatic monomer concentration led to cements of low mechanical properties due to solubility problems as revealed by SEM.