Temperature- and pH-sensitive terpolymers for modulated delivery of streptokinase

Therapeutic delivery systems for rheumatoid arthritis based on hydrogel carriers

Rheumatoid arthritis (RA) is an autoimmune disease suffered by millions of people worldwide. It can significantly affect the patient's quality of life by damaging not only the joints but also organs such as the lungs and the heart. RA is normally treated using nonsteroidal anti-inflammatory drugs (NSAIDs), glucocorticoids, disease-modifying antirheumatic drugs (DMARDs), and biologics. These active agents often cause side effects and offer low efficacy due to their lack of specificity and limited retention time. In an attempt to improve RA treatments, hydrogel-based systems have been proposed as drug delivery carriers. Due to their exceptional adaptability and biocompatibility, hydrogels have the potential of enhancing the delivery of RA therapy through different administration routes in an efficient and effective manner. In this review, we explore the application of hydrogel systems as potential carriers in RA treatment. Additionally, we discuss recent work in the field and highlight the required hydrogel properties, depending on the administration route. The outstanding potential of hydrogel systems as carriers for RA was demonstrated; however, there is extensive research yet to be done to improve available treatments for RA.

Photoactive hydrogels for pre-concentration, labelling, and controlled release of proteins

We report a novel hydrogel for pre-concentration, fluorescent labelling, and light-triggered release of proteins for detection of low abundance biomarkers. The hydrogel was a co-polymer of acrylamide/bisacrylamide and methacrylamide attached to fluorescein isothiocyanate via a light cleavable bond and a poly(ethylene glycol) spacer arm of molecular weight of 3400 g mol-1. Unlike previous work, proteins were captured by an irreversible chemical reaction rather than by non-covalent affinity binding or physical entrapment. Because the protein-reactive group was attached to fluorescein, which in turn was coupled to the hydrogel by a photocleavable bond, on release the protein was labelled with fluorescein. Our hydrogel offered a pre-concentration factor of up to 236 for a model protein, streptavidin. Each protein molecule was labelled with 85 fluorescein molecules, and 50% of the proteins in the hydrogel were released after UV exposure for ∼100 s. The proteins released from the hydrogel were captured in biotinylated microtitre plates and detected by fluorescence, allowing measurement of at least 0.01 ppm (or ∼166 pM) of protein in sample solutions. The reported hydrogel is promising for detection of low abundance proteins while being less laborious than enzyme-linked immunosorbent assay and less affected by changes in environmental conditions than label-free biosensors.

Electrospun nanofibers in cancer research: from engineering of in vitro 3D cancer models to therapy

Electrospinning is historically related to tissue engineering due to its ability to produce nano-/microscale fibrous materials with mechanical and functional properties that are extremely similar to those of the extracellular matrix of living tissues. The general interest in electrospun fibrous matrices has recently expanded to cancer research both as scaffolds for in vitro cancer modelling and as patches for in vivo therapeutic delivery. In this review, we examine electrospinning by providing a brief description of the process and overview of most materials used in this process, discussing the effect of changing the process parameters on fiber conformations and assemblies. Then, we describe two different applications of electrospinning in service of cancer research: firstly, as three-dimensional (3D) fibrous materials for generating in vitro pre-clinical cancer models; and secondly, as patches encapsulating anticancer agents for in vivo delivery.

Conjugate of Doxorubicin with a Thermosensitive Polymer Drug Carrier

A temperature-responsive drug delivery system that is soluble in aqueous solutions below its phase transition temperature but hydrophobically collapsing and aggregating at higher temperatures was prepared. A ternary copolymer of N-isopropylmethacrylamide, N-propylmethacrylamide and 4-nitrophenyl N-methacryloylglycylglycinate was synthesized. The reaction of the 4-nitrophenyl ester groups with hydrazine resulted in a polymer hydrazide which enabled the attachment of doxorubicin (DOX) via a pH-sensitive hydrazone bond. The system exhibited phase separation in aqueous solutions at a temperature of about 41'C and released free DOX at pH 5.0 at a rate higher by one order of magnitude than at pH 7.4. In combination with local hyperthermia, the system is expected to be valuable for the delivery of chemotherapeutic agents in the treatment of solid tumors. The relation between the temperature of the phase transition of the system and the cloud point temperature (CPT) as well as the necessity to distinguish between the CPT and the lower critical solution temperature (LCST) is discussed and the factors influencing the results of determination of the CPT (its definition, concentration of the polymer solution, rate of heating, presence of cosolutes, chemical structure of polymer and its heterogeneity) are analysed in detail.

Synthesis and characterization of acrylic acid-2-hydroxyethyl methacrylate IPN hydrogels

Three different methods have been developed to crosslink the poly(acrylic acid-2-hydroxyethyl methacrylate) to form the hydrogels having tunable swelling, rheological and morphological properties with applicability in dye and heavy metal removal.

Thermoresponse improvement of poly(N-isopropylacrylamide) hydrogels via formation of poly(sodium p-styrenesulfonate) nanophases

The block copolymer networks composed of poly(N-isopropylacrylamide) (PNIPAM) and poly(sodium p-styrenesulfonate) were synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization with α,ω-didithiobenzoate-terminated poly(sodium p-styrenesulfonate) (PSSNa) as the macromolecular chain transfer agent. It was found that the block copolymer networks were microphase-separated as evidenced by means of transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). In the block copolymer networks, spherical or cylindrical PSSNa microdomains were finely dispersed into continuous PNIPAM matrixes. In comparison with unmodified PNIPAM hydrogel, the nanostructured hydrogels displayed improved thermoresponsive properties. In addition, the swelling ratios of the PSSNa-modified PNIPAM hydrogels were significantly higher than that of plain PNIPAM hydrogel. The improvement of thermoresponse was attributable to the formation of the PSSNa nanophases, which promoted the transportation of water molecules in the cross-linked networks.

Poly(N-isopropylacrylamide)-based semi-interpenetrating polymer networks for tissue engineering applications. Effects of linear poly(acrylic acid) chains on rheology

Semi-interpenetrating polymer networks (semi-IPNs), comprised of poly(N-isopropylacrylamide-co-acrylic acid) (p(NIPAAm-co-AAc)) hydrogels and linear p(AAc) chains, were synthesized, and the effects of the p(AAc) chains on semi-IPN rheology were examined. Oscillatory shear rheometry studies were performed and the rheological data were analyzed as a function of temperature, frequency, and p(AAc) chain amount (weight average molecular weight (Mw) 4.5 x 10(5) g/mol). At 22 degrees C, the semi-IPNs, as well as control p(NIPAAm-co-AAc) hydrogels, demonstrated rheological data that were representative of soft, loosely cross-linked solids. Furthermore, only the highest p(AAc) chain amount tested affected the rigidity of the p(NIPAAm-co-AAc)-based semi-IPNs, as compared to the p(NIPAAm-co-AAc) hydrogels. At 37 degrees C, the complex shear moduli (G*) demonstrated by the p(NIPAAm-co-AAc)-based semi-IPNs were significantly greater than G* exhibited by the p(NIPAAm-co-AAc) hydrogels, and the semi-IPN G* values significantly increased with increasing p(AAc) chain amount. These results can be used to develop p(NIPAAm)-based semi-IPNs with tailored mechanical properties that may function as scaffolds in tissue engineering initiatives.

Stimuli-sensitive hydrogels: ideal carriers for chronobiology and chronotherapy

The development of solid-phase peptide synthesis in the early 1960s and recombinant DNA technology in the early 1970s boosted the scientific interest of utilizing proteins and peptides as potential therapeutic agents to battle poorly controlled diseases. While there has been rapid progress in the development and synthesis of new proteins and peptides as potential therapeutic agents, the formulation and development of the associated delivery systems is lacking. The development of delivery systems is equally important due to the problems of stability, low bioavailability and short half-life of proteins and peptides. The main problem in this field is that low stability leads to low bioavailability. In this review we draw attention to chrono-pharmacological drug-delivery systems, which can be used to match the delivery of therapeutic agents with the biological rhythm. They are very important especially in endocrinology and in vaccine therapy. We show that the treatment of hypopituitary dwarfism by administration of human growth-hormone-releasing hormone (GHRH) is more effective when GHRH is administered in a pulsatile manner that exhibits a period characteristic of the patient's circadian rhythm. Here we examine how to design novel chrono-pharmacological drug-delivery systems that should be able to release the therapeutic agents at predetermined intervals.

Morphologically Well-defined Gold Nanoparticles Embedded in Thermo-Responsive Hydrogel Matrices

Nanocomposite materials consisting of colloidal gold (Au) nanoparticles embedded in thermo-responsive poly(N-isopropylacrylamide) (PNIPAm) hydrogels are synthesized. Thiol groups that bind to both Au3+ ions and colloidal Au are incorporated into the side-chains of the PNIPAm hydrogels through copolymerization. This report describes formation of morphologically well-defined Au nanoparticles with varying long-term stability inside the hydrogel matrices containing adjustable concentrations of thiols. Compared with the non-Au containing PNIPAm hydrogels, the Au-PNIPAm nanocomposite hydrogels have shown higher degrees of equilibrium swelling and different temperature-triggered phase transitions. It is hypothesized that these remarkable changes in hydrogel bulk properties are related to the different morphologies and sizes, and possibly the amount of surface charges, of the Au nanoparticles.

Swelling and Mechanical Properties of Modified HEMA-based Superporous Hydrogels

Superporous hydrogels (SPHs), based on poly(2-hydroxyethyl methacrylate) (PHEMA), were prepared by adding minute amounts of an ion-complexable hydrophilic acrylic acid. PHEMA SPHs are generally strong, but their swelling is minimal. To improve the swelling, different poly(HEMA-co-acrylic acid) hydrogels were polymerized and crosslinked, then physically treated with divalent calcium and trivalent aluminum cations. The incorporation of acrylic acid copolymer into the SPH, followed by crosslinking of the copolymer with calcium or aluminum ions produced SPHs with improved swelling and strength. Cells in the presence of hydrogel showed high viability indicating the absence of cytotoxicity and stimulatory effect.

Novel platforms for oral drug delivery

The aim of this review is to provide the reader general and inspiring prospects on recent and promising fields of innovation in oral drug delivery. Nowadays, inventive drug delivery systems vary from geometrically modified and modular matrices, more close to "classic" pharmaceutical manufacturing processes, to futuristic bio micro-electro-mechanical systems (bioMEMS), based on manufacturing techniques borrowed from electronics and other fields. In these technologies new materials and creative solutions are essential designing intelligent drug delivery systems able to release the required drug at the proper body location with the correct release rate. In particular, oral drug delivery systems of the future are expected to have a significant impact on the treatment of diseases, such as AIDS, cancer, malaria, diabetes requiring complex and multi-drug therapies, as well as on the life of patients, whose age and/or health status make necessary a multiple pharmacological approach.

Hydrogel nanoparticles in drug delivery

Hydrogel nanoparticles have gained considerable attention in recent years as one of the most promising nanoparticulate drug delivery systems owing to their unique potentials via combining the characteristics of a hydrogel system (e.g., hydrophilicity and extremely high water content) with a nanoparticle (e.g., very small size). Several polymeric hydrogel nanoparticulate systems have been prepared and characterized in recent years, based on both natural and synthetic polymers, each with its own advantages and drawbacks. Among the natural polymers, chitosan and alginate have been studied extensively for preparation of hydrogel nanoparticles and from synthetic group, hydrogel nanoparticles based on poly (vinyl alcohol), poly (ethylene oxide), poly (ethyleneimine), poly (vinyl pyrrolidone), and poly-N-isopropylacrylamide have been reported with different characteristics and features with respect to drug delivery. Regardless of the type of polymer used, the release mechanism of the loaded agent from hydrogel nanoparticles is complex, while resulting from three main vectors, i.e., drug diffusion, hydrogel matrix swelling, and chemical reactivity of the drug/matrix. Several crosslinking methods have been used in the way to form the hydrogel matix structures, which can be classified in two major groups of chemically- and physically-induced crosslinking.

Enhanced intratumoral uptake of quantum dots concealed within hydrogel nanoparticles

Effective nanomedical devices for tumor imaging and drug delivery are not yet available. In an attempt to construct a more functional device for tumor imaging, we have embedded quantum dots (which have poor circulatory behavior) within hydrogel nanoparticles made of poly-N-isopropylacrylamide. We found that the hydrogel encapsulated quantum dots are more readily taken up by cultured tumor cells. Furthermore, in a melanoma model, hydrogel encapsulated quantum dots also preferentially accumulate in the tumor tissue compared with normal tissue and have ∼16-fold greater intratumoral uptake compared to non-derivatized quantum dots. Our results suggest that these derivatized quantum dots, which have greatly improved tumor localization, may enhance cancer monitoring and chemotherapy.

Chronobiology, drug delivery, and chronotherapeutics

Biological processes and functions are organized in space, as a physical anatomy, and time, as a biological time structure. The latter is expressed by short-, intermediate-, and long-period oscillations, i.e., biological rhythms. The circadian (24-h) time structure has been most studied and shows great importance to the practice of medicine and pharmacotherapy of patients. The phase and amplitude of key physiological and biochemical circadian rhythms contribute to the known predictable-in-time patterns in the occurrence of serious and life-threatening medical events, like myocardial infraction and stroke, and the manifestation and severity of symptoms of chronic diseases, like allergic rhinitis, asthma, and arthritis. Moreover, body rhythms can significantly affect responses of patients to diagnostic tests and, most important to the theme of this special issue, medications. Rhythmicity in the pathophysiology of disease is one basis for chronotherapeutics--purposeful variation in time of the concentration of medicines in synchrony with biological rhythm determinants of disease activity--to optimize treatment outcomes. A second basis is the control of undesired effects of medications, especially when the therapeutic range is narrow and the potential for adverse effects high, which is the case for cancer drugs. A third basis is to meet the biological requirements for frequency-modulated drug delivery, which is the case for certain neuroendocrine peptide analogues. Great progress has been realized with hydrogels, and they offer many advantages and opportunities in the design of chronotherapeutic systems for drug delivery via the oral, buccal, nasal, subcutaneous, transdermal, rectal, and vaginal routes. Nonetheless, innovative delivery systems will be necessary to ensure optimal application of chronotherapeutic interventions. Next generation drug-delivery systems must be configurable so they (i) require minimal volitional adherence, (ii) respond to sensitive biomarkers of disease activity that often vary in time as periodic (circadian rhythmic) and non-periodic (random) patterns to release medication to targeted tissue(s) on a real time as needed basis, and (iii) are cost-effective.

Hydrogels in controlled release formulations: network design and mathematical modeling

Over the past few decades, advances in hydrogel technologies have spurred development in many biomedical applications including controlled drug delivery. Many novel hydrogel-based delivery matrices have been designed and fabricated to fulfill the ever-increasing needs of the pharmaceutical and medical fields. Mathematical modeling plays an important role in facilitating hydrogel network design by identifying key parameters and molecule release mechanisms. The objective of this article is to review the fundamentals and recent advances in hydrogel network design as well as mathematical modeling approaches related to controlled molecule release from hydrogels. In the first section, the niche roles of hydrogels in controlled release, molecule release mechanisms, and hydrogel design criteria for controlled release applications are discussed. Novel hydrogel systems for drug delivery including biodegradable, smart, and biomimetic hydrogels are reviewed in the second section. Several mechanisms have been elucidated to describe molecule release from polymer hydrogel systems including diffusion, swelling, and chemically-controlled release. The focus of the final part of this article is discussion of emerging hydrogel delivery systems and challenges associated with modeling the performance of these devices.

[New intelligent and targetted drug delivery systems. Pharmaceutical and biomedical applications]

Biomaterials are widely used in numerous medical applications. Chemical engineering has played a central role in this research and development. We review herein polymers as biomaterials, materials and approaches used in drug and protein delivery systems, materials used as scaffolds in tissue engineering, and nanotechnology and microfabrication techniques applied to biomaterials.

Novel Method Using a Temperature-Sensitive Polymer (Methylcellulose) to Thermally Gel Aqueous Alginate as a pH-Sensitive Hydrogel

A novel method using a temperature-sensitive polymer (methylcellulose) to thermally gel aqueous alginate blended with distinct salts (CaCl2, Na2HPO4, or NaCl), as a pH-sensitive hydrogel was developed for protein drug delivery. It was noted that the salts blended in hydrogels may affect the structures of an entangled network of methylcellulose and alginate and have an effect on their swelling characteristics. The methylcellulose/alginate hydrogel blended with 0.7 M NaCl (with a gelation temperature of 32 degrees C) demonstrated excellent pH sensitivity and was selected for the study of release profiles of a model protein drug (bovine serum albumin, BSA). In the preparation of drug-loaded hydrogels, BSA was well-mixed to the dissolved aqueous methylcellulose/alginate blended with salts at 4 degrees C and then gelled by elevating the temperature to 37 degrees C. This drug-loading procedure in aqueous environment at low temperature may minimize degradation of the protein drug while achieving a high loading efficiency (95-98%). The amount of BSA released from test hydrogels was a function of the amount of alginate used in the hydrogels. The amount of BSA released at pH 1.2 from the test hydrogel with 2.5% alginate was relatively low (20%), while that released at pH 7.4 increased significantly (86%). In conclusion, the methylcellulose/alginate hydrogel blended with NaCl could be a suitable carrier for site-specific protein drug delivery in the intestine.

The influence of the copolymer composition on the diltiazem hydrochloride release from a series of pH-sensitive poly[(N-isopropylacrylamide)-co-(methacrylic acid)] hydrogels

A series of poly[(N-isopropylacrylamide)-co-(methacrylic acid)] (P[(N-iPAAm)-co-(MAA)]) hydrogels was investigated to determine the composition that exhibits a better pH-modulated release of diltiazem hydrochloride (DIL.HCl). For this purpose hydrogel slabs were loaded with DIL.HCl by the immersion method, and its release under acidic medium (0.1N HCl, pH 1.2) and in phosphate buffer pH 7.2, using United States Pharmacopeia (USP) 24 Apparatus 1, was investigated. According to the results from the slabs, copolymers with 85% mol N-iPAAm content were selected to prepare tablets with different particle size. The effect of pH and particle size changes on DIL.HCl release from these last hydrogel tablets was investigated by a stepwise pH variation of the dissolution medium. The amount of DIL.HCl released from high N-iPAAm content copolymer slabs under acidic pH medium was not only very low but it was also released at a slow rate. In the 85% N-iPAAm tablets, significant differences between and within release profiles were found as a function of particle size and pH, respectively. A relationship between particle size and release rate has been found. The lower DIL.HCl release at acidic pH from enriched N-iPAAm copolymers is interpreted by a cooperative thermal- and pH-collapse. Although for the whole range of copolymer composition a dependence of the equilibrium of swelling on the pH was found, DIL.HCl release experiments indicated that hydrogels with 85% mol N-iPAAm are the more adequate to be used for modulated drug delivery systems. Additionally, the particle size of the tablet can be used to tailor the release rate.

Morphology of poly(methacrylic acid)/poly(N-isopropyl acrylamide) interpenetrating polymeric networks

The morphology of interpenetrating polymeric networks (IPNs) composed of the temperature-sensitive poly(N-isopropyl acrylamide) (PNIPAAm) and the pH-sensitive poly(methacrylic acid) (PMAA) were investigated by scanning electron microscopy (SEM). The IPN hydrogels were prepared by a sequential UV polymerization method. SEM studies were conducted on IPN hydrogel samples dried by different methods, and the influence on the IPN structure was discussed. The environmental conditions induced morphological changes for these dual sensitive IPN hydrogels which were studied by cryogenic SEM, when the gels were analyzed in their wet state. The results showed that the porous size in the IPN was strongly influenced by the environmental pH and temperature. Decrease in pH and increase in temperature resulted in significant pore size decrease for the swollen IPNs hydrogels.

Thermo-responsive peptide-modified hydrogels for tissue regeneration

Loosely cross-linked hydrogels consisting of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) were synthesized, characterized, and used as model scaffolds for studying cell-material interactions in three-dimensions (3D). The AAc groups were functionalized with peptides containing the -RGD- and -FHRRIKA- sequences found in bone sialoprotein. Chemical modification of the hydrogels was verified via solid-state (1)H nuclear magnetic resonance spectroscopy, lower critical solution temperature studies, and volume change studies. The peptide-modified hydrogels were pliable at 22 degrees C and could be injected through a small-diameter aperture. Rat calvarial osteoblasts (RCO) seeded into the peptide-modified hydrogels were viable for at least 21 days of in vitro culture. The RCO spread more and demonstrated significantly greater proliferation when cultured within the peptide-modified hydrogels, as compared to control hydrogels. These peptide-modified P(NIPAAm-co-AAc) hydrogels serve as useful tools for studying cell-material interactions within 3D structures and have the potential to be used as injectable scaffolds for tissue engineering applications.

Poly(N-isopropylacrylamide)-based semi-interpenetrating polymer networks for tissue engineering applications. 1. Effects of linear poly(acrylic acid) chains on phase behavior

Poly(N-isopropylacrylamide)-based [P(NIPAAm)-based] semi-interpenetrating polymer networks (semi-IPNs), consisting of P(NIPAAm)-based hydrogels and linear poly(acrylic acid) [P(AAc)] chains, were synthesized, and the effects of the P(AAc) chains on semi-IPN injectability and phase behavior were analyzed. In P(NIPAAm)- and P(NIPAAm-co-AAc)-based semi-IPN studies, numerous reaction conditions were varied, and the effects of these factors on semi-IPN injectability, transparency, phase transition, lower critical solution temperature (LCST), and volume change were examined. The P(AAc) chains did not significantly affect the LCST or volume change of the semi-IPNs, compared to control hydrogels. However, the P(AAc) chains affected the injectability, transparency, and phase transition of the matrices, and these effects were dependent on chain amount and molecular weight (MW) and on interactions between the P(AAc) chains and the solvent and/or copolymer chains in P(NIPAAm-co-AAc) hydrogels. These results can be used to design "tailored" P(NIPAAm)-based semi-IPNs that have the potential to serve as functional scaffolds in tissue engineering applications.

Reversible adsorption by a pH- and temperature-sensitive acrylic hydrogel

Thermo- and pH-sensitive hydrogels were synthesized using N-isopropylacrylamide (NIPA) and N-aminopropylmethacrylamide, cross-linked with N,N'-methylenebis(acrylamide). The dependence of the degree of swelling on the cross-linking density was analyzed according to the Flory-Huggins theory and a master curve obtained. To optimize the efficiency of these hydrogels in controlled release, we studied the loading and release of a divalent molecule (naphthalenedisulfonic acid, NS-2) in media of different ionic strengths and pH. The uptake process followed the Langmuir adsorption isotherm model. The highest loading occurred when the amino groups in the gel were protonated (acidic pH) and could come close each other to form a binding site for the two sulfonic groups of NS-2, i.e. low degree of cross-linking and collapsed state. Below the phase transition temperature (33 degrees C), NS-2 loaded hydrogels quickly released a significant amount of adsorbate until a new equilibrium between free NS-2 and adsorbed NS-2 was achieved. Above that temperature, hydrogels not only stopped the release but were even able to take free NS-2 up again from the medium, showing that the loading/release process was reversible and reproducible after several temperature cycles. At 37 degrees C, the release rate was independent of the degree of cross-linking (NIPA caused the hydrogel to collapse), but was strongly affected by the pH and salt concentrations of the medium, which condition the strength of the interaction between the hydrogel amino groups and the NS-2 sulfonic groups. In an acidic medium, the protonated amino groups bind NS-2 strongly and the amount released is small. In contrast, at pH 7.4 or in the presence of a high salt concentration, the hydrogel loses its affinity for NS-2 and the release rate increases, giving pH- or salt-sensitive delivery systems. Additionally, since the hydrogel is collapsed, the release can be prolonged for a long period of time.