Pharmaceutical Polymeric Controlled Drug Delivery Systems

Complex calcium carbonate/polymer microparticles as carriers for aminoglycoside antibiotics

Composite microparticles of CaCO₃ and two pectin samples (which differ by the functional group ratio) or corresponding nonstoichiometric polyelectrolyte complexes with different molar ratios (0.5, 0.9 and 1.2) are obtained, characterized and tested for loading and release of streptomycin and kanamycin sulphate. The synthesized carriers were characterized before and after drug loading in terms of morphology (by SEM using secondary electron and energy selective backscattered electron detectors), porosity (by water sorption isotherms) and elemental composition (by elemental mapping using energy dispersive X-ray and FTIR spectroscopy). The kinetics of the release mechanism from the microparticles was investigated using Higuchi and Korsmeyer–Peppas mathematical models.

Self-assembled microparticles of CaCO₃ and pectin/polyelectrolyte complexes as carriers for streptomycin and kanamycin sulfates by transformation into calcium phosphates.

Autotemplate Microcapsules of CaCO3/Pectin and Nonstoichiometric Complexes as Sustained Tetracycline Hydrochloride Delivery Carriers

New types of composites were obtained by an autotemplate method for assembling hollow CaCO₃ capsules by using pH-sensitive polymers. Five pectin samples, which differ in the methylation degree and/or amide content, and some nonstoichiometric polyelectrolyte complex dispersions, prepared with the pectin samples and poly(allylamine hydrochloride), were used to control the crystal growth. The morphology of the composites was investigated by scanning electron microscopy, and the polymorphs characteristics were investigated by FTIR spectroscopy. The presence of the polymer in the composite particles was evidenced by X-ray photoelectron spectroscopy, particle charge density, and zeta-potential. The new CaCO₃/pectin hollow capsules were tested as a possible matrix for a tetracycline hydrochloride carrier. The kinetics of the drug release mechanism was followed using Higuchi and Korsmeyer-Peppas mathematical models.

Nanoparticles of biodegradable polymers for new-concept chemotherapy

The current regimen of chemotherapy is far from satisfactory--its efficiency is limited and patients suffer from serious side effects. Various drug delivery devices have been under intensive investigation in the past few decades in attempts to develop controlled and targeted methods of chemotherapy administration. This article reviews the latest developments in nanoparticles of biodegradable polymers for chemotherapy of cancer and other diseases such as cardiovascular restenosis. The preliminary results obtained in the author's laboratory are used to demonstrate the concept. This review is written with the belief that engineering, in particular, chemical engineering principles, can be applied and further developed to solve the problems in the current practice of chemotherapy and promote a new concept of chemotherapy - chemotherapy at home.

Dexamethasone-releasing cochlear implant coatings: application of artificial neural networks for modelling of formulation parameters and drug release profile

Objectives

Over the past few decades, mathematical modelling and simulation of drug delivery systems has been steadily gained interest as a focus for academic and industrial attention. Here, simulation of dexamethasone (DEX, a corticosteroid anti-inflammatory agent) release profile from drug-eluting cochlear implant coatings is reported using artificial neural networks.

Methods

The devices were fabricated as monolithic dispersions of the pharmaceutically active ingredient in a silicone rubber matrix. A two-phase exponential model was fitted on the experimentally obtained DEX release profiles. An artificial neural network (ANN) was trained to determine formulation parameters (i.e. DEX loading percentage, the devices surface area and their geometry) for a specific experimentally obtained drug release profile. In a reverse strategy, an ANN was trained for determining expected drug release profiles for the same set of formulation parameters.

Key findings

An algorithm was developed by combining the two previously developed ANNs in a serial manner, and this was successfully used for simulating the developed drug-eluting cochlear implant coatings. The models were validated by a leave-one-out method and performing new experiments.

Conclusions

The developed ANN algorithms were capable to bilaterally predict drug release profile for a known set of formulation parameters or find out the levels for input formulation parameters to obtain a desired DEX release profile.

Copolymer nanoparticles composed of sulfobetaine and poly(ε-caprolactone) as novel anticancer drug carriers

Novel ABA type amphiphilic copolymers (PCL-APS-PCL) consisting of polycaprolactone (PCL) (A) as hydrophobic block and N,N'-bis (2-hydroxyethyl) methylamine ammonium propane sulfonate (APS) (B) as hydrophilic segment, self-assembled into nanoparticles (NPs) with solvent evaporation method. The sizes and size distributions of NPs were characterized by dynamic light scattering. The morphology of NPs was observed by scanning electron microscopy (SEM). The critical micelle concentration (CMC) was determined by fluorescent probe. The drug loading content (DLC) and the drug release amount were characterized by UV-visible spectrophotometer. The cytotoxicity of the NPs was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenylte-trazoliumbromide (MTT) assay. It was found that the NPs were spherical in shape with sizes around 100 nm. The CMCs of the copolymers were quite low (×10(-4) mg/mL). The DLC decreased with lengthening of hydrophobic PCL block. In vitro drug release experiment demonstrated that the release rate of paclitaxel sped with the decrease of PCL length. MTT results showed that NPs were nontoxic to osteoblast and human epithelial carcinoma (hela) cells. After drug loading, NPs could restrain the growth of hela or even kill hela cells. Therefore, these preliminary studies suggest that the novel PCL-APS-PCL NPs have a great potential application as anticancer drug-delivery carriers.

Hydrogels cross-linked by native chemical ligation

We describe the use of native chemical ligation (NCL) reaction to covalently cross-link soluble polymers into hydrogels. Macromonomers consisting of a four-armed poly(ethylene glycol) (PEG) core end-functionalized with either thioester or N-terminal cysteine peptide were designed and synthesized. Upon mixing aqueous solutions of the thioester and N-terminal cysteine macromonomers, rigid hydrogels formed within minutes. The gelation time was affected by choice of buffer, pH, polymer concentration, reaction temperature, and chemical composition of the N-terminal cysteine conjugate. The kinetics of gel formation and the viscoelastic behavior of selected hydrogels were further studied by oscillatory rheology, which demonstrated a minimum gel formation time of approximately two minutes and the formation of an elastic cross-linked hydrogel via the NCL reaction. A useful feature of this hydrogel strategy is the regeneration of thiol functional groups as a result of the NCL reaction, thereby allowing functionalization of the polymer hydrogel with biomolecules. This was demonstrated by conjugation of a maleimide-GRGDSPG-NH(2) peptide to an NCL hydrogel, permitting the attachment of human mesenchymal stem cells (hMSCs) on the hydrogel. Due to the mild reaction conditions, chemoselectivity, and potential for biological functionalization, our approach may prove useful as a general method for hydrogel formation, including hydrogels intended for biomedical applications.

Microspheres from new biodegradable poly(ester amide)s with different ratios ofL- andD-alanine for controlled drug delivery

A series of biodegradable poly (ester amide)s composed of sebacic acid, dodecanediol and different ratios of the stereoisomers of L- and D-alanine were synthesized for applications in drug delivery systems. Microspheres loaded with diclofenac sodium salt, triclosan and clofazimine were prepared with the solvent evaporation technique. No influence of polymer constitution in the drug release rate was found in vitro and no degradation occurred during the period of drug release. It was shown that a sustained delivery of the hydrophilic diclofenac sodium salt in Sörensen media occurred and it was controlled by diffusion. However, exhaustion of microspheres was feasible only from the most porous matrices where channelling had an important contribution.

Control of burst release from nanogels via layer by layer assembly

Undesirable burst release phenomenon is commonly encountered in nanostructured delivery systems, and should be addressed. The present study demonstrates a simple and practical way to reduce or minimize high burst release associated with nanoparticulate delivery systems. Drug loaded nanogels of size less than 200 nm were successfully coated with alternating layers of poly(allylamine hydrochloride) (PAH, cationic) and poly(sodium 4-styrenesulfonate) (PSS, anionic) polyelectrolytes. With every layer of polyelectrolyte, the radius increased by 2 nm, and the zeta-potential alternated between positive and negative values. PSS coated nanogels were stable at all pH, while PAH coated nanogels were only stable up to pH of 8. A drug selective electrode (DSE) was used to directly measure the concentration of procaine hydrochloride (PrHy) from MAA-EA coated nanogels. The high burst release was reduced or minimized when the number of layers of polyelectrolyte was increased. An empirical relationship describing the number of polyelectrolyte layers and time to attain steady-state drug concentration (tau(D)) was developed, where tau(D) increased with increasing polyelectrolyte layers.

Mineralization of radiation-crosslinked polyvinyl alcohol/polyvinyl pyrrolidone hydrogels

A study of the calcification of the polyvinyl alcohol/polyvinyl pyrrolidone (PVA/PVP) hydrogels during their exposure to a calcium chloride solution or a simulated body fluid has been carried out. On the basis of the experiments, using a two-compartment permeation cell, the diffusion of calcium ions and their subsequent deposition in the hydrogels were elucidated. Steady-batch experiments were also performed to further elaborate the deposition pattern and the types of calcium deposits. It was demonstrated that Fick's second law of diffusion can describe the diffusion of calcium ions through PVA/PVP hydrogels at 310 K. The diffusion coefficient was determined to be (4.4+/-0.1)x10(-10) m2/s and the partition coefficient for the hydrogels was 0.06. Formation of calcium deposits was noticed taking place both on the surface and inside the hydrogels. The deposits formed on the surface have flake morphology, while the deposits inside the hydrogels are more like globular aggregates. Both types of deposits have been characterized as being comprised calcium and hydroxyl ion deficient apatites with chloride ions the most likely substituting species at the hydroxyl sites.

Synthesis and in vitro drug release behavior of amphiphilic triblock copolymer nanoparticles based on poly (ethylene glycol) and polycaprolactone

Novel BAB type amphiphilic triblock copolymers consisting of poly (ethylene glycol) (PEG) (B) as hydrophilic segment and poly (epsilon-caprolactone) (PCL) (A) as hydrophobic block were prepared by coupling reaction using L-lysine methyl ester diisocyanate (LDI) as the chain extender. The triblock copolymers obtained were characterized by FT-IR, 1H NMR, GPC, and DSC. Core-shell type nanoparticles were prepared by nanoprecipitation method and below 100 nm nanoparticles were obtained due to their specific structure. Transmission electron microscopy image demonstrated that these nanoparticles were spherical in shape. Stability of the nanoparticles in biological media was evaluated. Poorly water-soluble anticancer drug 4'-demethyl-epipodophyllotoxin (DMEP) was chosen for controlled drug release because it was easily encapsulated into polymeric nanoparticles via hydrophobic interaction. In vitro release behavior of DMEP from polymeric nanoparticles was investigated, the results showed that the drug release rate can be modulated by the variation of the copolymer composition.

Enzymatically cross-linked hydrogels and their adhesive strength to biosurfaces

OBJECTIVES

To design an in-situ gelling hydrogel capable of solidifying rapidly under physiologic conditions into a hydrogel capable of adhering tissue surfaces together.

DESIGN

Multifunctional polymers containing covalently bound peptide substrates of transglutaminase were designed.

EXPERIMENTAL VARIABLE

Enzyme cross-linked hydrogels were compared with commercial fibrin tissue adhesive.

OUTCOME MEASURE

The shear strength between tissue surfaces or type 1 collagen membranes bonded with hydrogel was measured.

RESULTS

The shear adhesive strength of transglutaminase cross-linked hydrogels was found to be equal to or better than fibrin sealant for tissue and collagen surfaces, respectively.

CONCLUSION

Transglutaminase cross-linked hydrogels are injectable, in-situ formed, biodegradable, and expected to be useful in a variety of applications including sustained drug delivery, medical and dental adhesives, tissue repair and engineering as polymeric scaffolds, and gene therapy.

Styrenic block copolymers for biomaterial and drug delivery applications

The use of styrenic block copolymers has undergone a renaissance as a biomaterial and drug delivery matrix. The early promise posed by the physical and biological properties of these block copolymers for implantable medical devices was not met. However, there has been an increased understanding of the role of microphase separation on the mediation of the biological response. Poly (styrene-b-isobutylene-b-styrene) (SIBS) block copolymer has critical enabling properties related to processing, vascular compatibility and bio-stability that has resulted in its use as the matrix for paclitaxel delivery from Boston Scientific's TAXUS coronary stent. These enabling properties will allow the continuing development of medical devices based on SIBS that meet demanding physical and biological requirements.

Physical characterization of controlled release of paclitaxel from the TAXUS? Express2? drug-eluting stent

The polymer carrier technology in the TAXUS drug-eluting stent consists of a thermoplastic elastomer poly(styrene-b-isobutylene-b-styrene) (SIBS) with microphase-separated morphology resulting in optimal properties for a drug-delivery stent coating. Comprehensive physical characterization of the stent coatings and cast film formulations showed that paclitaxel (PTx) exists primarily as discrete nanoparticles embedded in the SIBS matrix. Thermal and chemical analysis did not show any evidence of solubility of PTx in SIBS or of any molecular miscibility between PTx and SIBS. Atomic force microscope data images revealed for the first time three-dimensional stent coating surfaces at high spatial resolutions in air and in situ under phosphate-buffered saline as drug was released. PTx release involves the initial dissolution of drug particles from the PTx/SIBS coating surface. Morphological examination of the stent coatings in vitro supported an early burst release in most formulations because of surface PTx followed by a sustained slower release of PTx from the bulk coating. The in vitro PTx release kinetics were dependent on the formulation and correlated to the drug-to-polymer ratio. Atomic force microscopy analysis confirmed this correlation and further supported the concept of a matrix-based drug-release coating.

Biodegradable plastics from renewable sources

Plastic waste disposal is a huge ecotechnological problem and one of the approaches to solving this problem is the development of biodegradable plastics. This review summarizes data on their use, biodegradability, commercial reliability and production from renewable resources. Some commercially successful biodegradable plastics are based on chemical synthesis (i.e. polyglycolic acid, polylactic acid, polycaprolactone, and polyvinyl alcohol). Others are products of microbial fermentations (i.e. polyesters and neutral polysaccharides) or are prepared from chemically modified natural products (e.g., starch, cellulose, chitin or soy protein).