Disulfide Cross‐Linked Polypeptide Nanogel Conjugated with a Fluorescent Probe as a Potential Image‐Guided Drug‐Delivery Agent

A disulfide cross‐linked PEGylated polypeptide nanogel with a near infrared fluorescence (NIRF) group has been synthesized. At first, a NIRF nanogel precursor is prepared by a ring‐opening polymerization of L ‐cystine‐N‐carboxy anhydride with azide‐functionalized poly(ethylene glycol) methyl ether. Alkyne cyanine is then conjugated to the nanogel by a click chemical reaction. The formation of the targeted nanogel is confirmed by a series of characterizations. The anticancer drug doxorubicin can be loaded into the NIRF nanogel by physical encapsulation, and the obtained drug‐loaded NIRF nanoparticle shows reduction‐promoted drug‐release behavior in the presence of 10 mM glutathione. The as‐prepared drug‐loaded NIRF nanoparticle has potential applications in the real‐time imaging of drug delivery in vivo.     

Facile one-pot synthesis of glucose-sensitive nanogel via thiol-ene click chemistry for self-regulated drug delivery

A novel glucose-sensitive nanogel was conveniently prepared through one-pot thiol-ene copolymerization of pentaerythritol tetra(3-mercaptopropionate), poly(ethylene glycol) diacrylate, methoxyl poly(ethylene glycol) acrylate and N-acryloyl-3-aminophenylboronic acid. The formation of core–shell nanogel was verified by proton nuclear magnetic resonance, dynamic laser scattering (DLS) and transmission electron microscopy. The successful incorporation of phenylboronic acid (PBA) in the nanogel was confirmed through Fourier transform infrared spectroscopy, inductively coupled plasma mass spectrometry and fluorescence technology. Owing to the presence of PBA, the nanogel exhibited high glucose sensitivity in phosphate-buffered saline determined by DLS and fluorescence technology. The increased amount of glucose causes an increase in the hydrodrodynamic radius and a decrease in the fluorescence intensity of PBA–alizarin red S (ARS) complex in the nanogel at pH 7.4 because of the competitive substitution of ARS to form the hydrophilic PBA–glucose complex. ARS and insulin were loaded into this glucose-sensitive nanogel. In vitro release profiles revealed that the drug release from the nanogel could be triggered by the presence of glucose. The more glucose in the release medium, the more drug was released and the faster the release rate. Furthermore, in vitro methyl thiazolyl tetrazolium assay, lactate dehydrogenase assay and hemolysis test suggested that the nanogel was biocompatible. Therefore, the PBA-incorporated nanogel with high glucose-sensitivity and good biocompatibility may have great potential for self-regulated drug release.     

Nanostructured hybrid hydrogels prepared by a combination of atom transfer radical polymerization and free radical polymerization

A new method to prepare nanostructured hybrid hydrogels by incorporating well-defined poly(oligo (ethylene oxide) monomethyl ether methacrylate) (POEO₃₀₀MA) nanogels of sizes 110–120 nm into a larger three-dimensional (3D) matrix was developed for drug delivery scaffolds for tissue engineering applications. Rhodamine B isothiocyanate-labeled dextran (RITC-Dx) or fluorescein isothiocyanate-labeled dextran (FITC-Dx)-loaded POEO₃₀₀MA nanogels with pendant hydroxyl groups were prepared by activators generated electron transfer atom transfer radical polymerization (AGET ATRP) in cyclohexane inverse miniemulsion. Hydroxyl-containing nanogels were functionalized with methacrylated groups to generate photoreactive nanospheres.¹H NMR spectroscopy confirmed that polymerizable nanogels were successfully incorporated covalently into 3D hyaluronic acid-glycidyl methacrylate (HAGM) hydrogels after free radical photopolymerization (FRP). The introduction of disulfide moieties into the polymerizable groups resulted in a controlled release of nanogels from cross-linked HAGM hydrogels under a reducing environment. The effect of gel hybridization on the macroscopic properties (swelling and mechanics) was studied. It is shown that swelling and nanogel content are independent of scaffold mechanics. In-vitro assays showed the nanostructured hybrid hydrogels were cytocompatible and the GRGDS (Gly–Arg–Gly–Asp–Ser) contained in the nanogel structure promoted cell–substrate interactions within 4 days of incubation. These nanostructured hydrogels have potential as an artificial extracellular matrix (ECM) impermeable to low molecular weight biomolecules and with controlled pharmaceutical release capability. Moreover, the nanogels can control drug or biomolecule delivery, while hyaluronic acid based-hydrogels can act as a macroscopic scaffold for tissue regeneration and regulator for nanogel release.     

Fabrication of a novel pH-sensitive glutaraldehyde cross-linked pectin nanogel for drug delivery

A novel pH-sensitive nanogel based on pectin cross-linked with glutaraldehyde (PT-GA) was designed and synthesized for drug delivery. Transmission electron microscope observation shows that the nano-sized gel particles exhibit a spherical morphology. The optical absorbance study of nanogel suspension reveals its pH sensitivity. Cytotoxicity study shows that the nanogel has no apparent inhibitory effect on cells. The in vitro drug-release behavior of the drug-loaded nanogel particles in three kinds of media, i.e., simulated gastric fluid, simulated intestine fluid and simulated colon fluid, was studied. PT-GA nanogel exhibits a faster release at a high pH, and the release could be further accelerated in the presence of pectinolytic enzyme, indicating that the nanogel may be used for colon-specific drug delivery.     

Carbon nanotube nanoreservior for controlled release of anti-inflammatory dexamethasone

On demand release of anti-inflammatory drug or neurotropic factors have great promise for maintaining a stable chronic neural interface. Here we report the development of an electrically controlled drug release system based on conducting polymer and carbon nanotubes. Drug delivery research using carbon nanotubes (CNTs) has taken advantage of the ability of CNTs to load large amounts of drug molecules on their outer surface. However, the utility of the inner cavity of CNTs, which can increase the drug loading capacity, has not yet been explored. In this paper, the use of multi-wall CNTs as nanoreserviors for drug loading and controlled release is demonstrated. The CNTs are pretreated with acid sonication to open their ends and make their outer and inner surfaces more hydrophilic. When dispersed and sonicated in a solution containing the anti-inflammatory drug dexamethasone, experiments show that the pretreated CNTs are filled with the drug solution. To prevent the unwanted release of the drug, the open ends of the drug-filled CNTs are then sealed with polypyrrole (PPy) films formed through electropolymerization. The prepared electrode coating significantly reduced the electrode impedance, which is desired for neural recording and stimulation. More importantly, the coating can effectively store drug molecules and release the bioactive drug in a controlled manner using electrical stimulation. The dexamethasone released from the PPy/CNT film was able to reduce lipopolysaccharide induced microglia activation to the same degree as the added dexamethasone.     

Modified n-HA/PA66 scaffolds with chitosan coating for bone tissue engineering: cell stimulation and drug release

The dipping-drying procedure and cross-linking method were used to make drug-loaded chitosan (CS) coating on nano-hydroxyapatite/polyamide66 (nHA/PA66) composite porous scaffold, endowing the scaffold controlled drug release functionality. The prefabricated scaffold was immersed into an aqueous drug/CS solution in a vacuum condition and then crosslinked by vanillin. The structure, porosity, composition, compressive strength, swelling ratio, drug release and cytocompatibility of the pristine and coating scaffolds were investigated. After coating, the scaffold porosity and pore interconnection were slightly decreased. Cytocompatibility performance was observed through an in vitro experiment based on cell attachment and the MTT assay by MG63 cells which revealed positive cell viability and increasing proliferation over the 11-day period in vitro. The drug could effectively release from the coated scaffold in a controlled fashion and the release rate was sustained for a long period and highly dependent on coating swelling, suggesting the possibility of a controlled drug release. Our results demonstrate that the scaffold with drug-loaded crosslinked CS coating can be used as a simple technique to render the surfaces of synthetic scaffolds active, thus enabling them to be a promising high performance biomaterial in bone tissue engineering.     

Novel composite fiber structures to provide drug/protein delivery for medical implants and tissue regeneration

A novel class of bioresorbable composite (core/shell) fiber structures loaded with bioactive agents was developed and studied. These unique polymeric structures are designed to combine good mechanical properties with a desired controlled release profile, in order to serve as scaffolds for tissue regeneration applications and as basic elements of medical implants. These core/shell fiber structures were formed by "coating" core polymer fibers with drug/protein-containing poly(dl-lactic-co-glycolic acid) porous structures. The shell preparation ("coating") was performed by the freeze-drying of water-in-oil emulsions. Both water soluble and water insoluble agents can be incorporated in these structures and their activity is preserved, since the fiber fabrication requires neither high temperatures nor harsh solvents in the vicinity of the bioactive agents. Examples for release profiles of protein (horseradish peroxidase) and drug (paclitaxel) are presented. We have demonstrated that appropriate selection of the emulsion's parameters can yield a variety of new core/shell fiber structures with desirable drug/protein release behavior. This will lead to the engineering of new implants and scaffolds, and will advance the field of tissue regeneration and medical implants.     

纤维素薄膜包衣缓释剂的设计和性能考察

背景：乙基纤维素是常用的不溶性高分子材料,具有良好的成膜性能和机械性能,可用于缓释包衣材料。 目的：制备美斯地浓纤维素薄膜包衣缓释剂,并考察其性能。 方法：以羟丙甲基纤维素为缓释材料,以体外累计释放度为指标,运用单因素考察确定片芯处方,以乙基纤维素为薄膜包衣材料,采用正交实验设计优选出包衣处方,制备美斯地浓纤维素薄膜包衣缓释剂,考察其体外释放性能及对光和热的稳定性能。 结果与结论：通过单因素考察确定以羟丙甲纤维素 K15M作为缓释材料,体积分数95%乙醇溶液为黏合剂制备缓释片片芯,正交实验设计优选出包衣处方为：包衣增重为10%、致孔剂用量为3%、抗黏剂用量为0.1%,纤维素薄膜包衣缓释剂在2,4,8 h的体外累计释放度为(19.52±0.72)%,(42.31±0.61)%,(86.50±0.72)%,具有良好的缓释特征,且对光和热稳定。     

单硝酸异山梨酯脉冲控释微丸的制备及体外释药影响因素的研究

制备单硝酸异山梨酯脉冲控释微丸并对影响释药的因素进行考察.采用挤出滚圆法制备载药丸芯,以水溶胀性材料为内包衣溶胀层,乙基纤维素水分散体为外包衣控释层制备脉冲控释微丸,并考察溶胀层材料类型、溶胀层和控释层包衣增重、介质pH值等对药物释放的影响.结果表明,该包衣微丸可脉冲释药,药物释放情况不受pH值的影响,低取代羟丙基纤维素与羟丙基甲基纤维素以一定比例混合作为内包衣层,乙基纤维素水分散体为外包衣层制备的脉冲控释微丸,当内包衣层增重为15%和外包衣层增重为13%时,达到了时滞为5 h、时滞后1.5 h累积释药80%以上的脉冲释药效果.     

Light‐Switchable Supramolecular Self‐Assembly of Soft Colloids

Self‐assembly is an efficient strategy of constructing microgel‐based intelligent materials. However, it remains a challenge to realize the reversible self‐assembly of microgels. Herein, a method to guide the self‐assembly of soft colloids with light‐stimuli is proposed, utilizing the light‐responsive host–guest interaction between an azobenzene functionalized nanogel (the guest colloid) and an α‐cyclodextrin functionalized microgel (the host colloid). The two colloids can form a stable colloid cluster when the surface of the host colloid is fully packed with the guest colloids. The colloid cluster can disassemble when irradiated with UV light and reassemble when irradiated with visible light. The reversible colloidal self‐assembly can be controlled by the interplay between the supramolecular and covalent crosslinking, and can also be adjusted by the addition of competitive host molecules. Besides the light‐sensitivity, the colloid cluster inherits the deformability and temperature‐sensitivity from its parent colloids. These features are different from the supramolecular self‐assembly of hard colloids or macroscopic gels, and manifest the as‐prepared colloid cluster potential building blocks of light‐responsive materials.     

Doxorubicin‐Loaded Nanogel Assemblies with pH/Thermo‐triggered Payload Release for Intracellular Drug Delivery

For improving intracellular doxorubicin (DOX) delivery, DOX‐encapsulated nanogel assemblies with pH/thermo‐responsive drug release are developed. DOX and a graft copolymer comprising acrylic acid (AAc) and 2‐methacryloyloxyethyl acrylate (MEA) units as the backbone and with poly(N‐isopropylacrylamide) (PNIPAAm) and monomethoxy poly(ethylene glycol) as the grafts at pH 7.4 and 4 °C undergo electrostatically induced co‐association into copolymer/DOX nanocomplexes. After being crosslinked by polymerization of the MEA moieties, the complex nanoconstructs exhibit a unique nanogel‐like architecture. Taking advantage of the extensive electrostatic attraction of the DOX molecules with ionized AAc residues and π–π stacking among copolymer‐bound DOX molecules, the DOX‐loaded nanogels show a relatively high payload content. With the milieu pH being reduced from 7.4 to 4.7, the drug release is appreciably promoted due to the massive disruption of ionic AAc/DOX pairings. The thermo‐evolved phase transition of the PNIPAAm grafts further accelerates drug elution, particularly at pH 4.7. In vitro characterization indicates that the DOX‐embedded nanogels endocytosed by HeLa cells can progressively release DOX within acidic organelles. As a result, the viability of cancer cells treated with DOX‐loaded nanoparticles can be further reduced by prolonging incubation time. This work demonstrates the great potential of the DOX‐loaded nanogel assemblies for effective intracellular drug delivery.

     

Surface studies of coated polymer microspheres and protein release from tissue-engineered scaffolds

The controlled release of growth factors from porous, polymer scaffolds is being studied for potential use as tissue-engineered scaffolds. Biodegradable polymer microspheres were coated with a biocompatible polymer membrane to permit the incorporation of the microspheres into tissue-engineered scaffolds. Surface studies with poly(D,L-lactic-co-glycolic acid) [PLGA], and poly(vinyl alcohol) [PVA] were conducted. Polymer films were dip-coated onto glass slides and water contact angles were measured. The contact angles revealed an initially hydrophobic PLGA film, which became hydrophilic after PVA coating. After immersion in water, the PVA coating was removed and a hydrophobic PLGA film remained. Following optimization using these 2D contact angle studies, biodegradable PLGA microspheres were prepared, characterized, and coated with PVA. X-ray photoelectron spectroscopy was used to further characterize coated slides and microspheres. The release of the model protein bovine serum albumin from PVA-coated PLGA microspheres was studied over 8 days. The release of BSA from PVA-coated PLGA microspheres embedded in porous PLGA scaffolds over 24 days was also examined. Coating of the PLGA microspheres with PVA permitted their incorporation into tissue-engineered scaffolds and resulted in a controlled release of BSA.     

Layer‐by‐Layer Formation of Polyamine‐Salt Aggregate/Polyelectrolyte Multilayers. Loading and Controlled Release of Probe Molecules from Self‐Assembled Supramolecular Networks

The use of soft materials as building blocks in layer‐by‐layer (LbL) assemblies represent a very appealing and useful approach to enhance the loading capacity of thin films. Here, the capacity of positively charged polyamine‐salt aggregates (PSAs) based on ionically crosslinked poly(allylamine hydrochloride) (PAH) with phosphate anions (Pi) is explored to act as building blocks in construction of multilayers by alternated deposition with poly(sodium 4‐styrenesulfonate). Hybrid thin films are successfully prepared by the LbL technique with a highly regular growth and a material deposition rate higher than the traditional full polyelectrolyte LbL. The loading of bromophenol blue (BPB) is evaluated by integration into PSAs followed by LbL deposition and monitored with UV–vis spectroscopy. Finally, the release of the dye molecules is carried out by exposing the film to different aqueous solutions. It is shown that a fully controlled release can be achieved by simply varying the media pH obtaining total BPB release over periods between minutes and months. The data obtained reveal that this new LbL construction strategy using ionically crosslinked PAH/Pi colloids allows to obtain nanoarchitectures with high loading capacity and remarkable properties for controlled release.     

Controlling drug release from acrylic polymers: in vitro studies with potential oral inserts

The use of a drug modified polymer system which can release drugs such as hydrocortisone sodium succinate and chlorhexidine acetate has been explored. By partially coating the drug loaded acrylic, such that it acts as a core with an impermeable membrane covering most of the surface, the rapid releases of the drug can be prevented and near zero-order rates of release achieved. For chlorhexidine acetate the release time was extended from around 20 d to 80 d with at least 60% of the drug being released. A similar potential for the controlled release of hydrocortisone sodium succinate is described and represents an important stage in the development of an intra-oral insert for drug delivery.     

Surface studies of coated polymer microspheres and protein release from tissue-engineered scaffolds

The controlled release of growth factors from porous, polymer scaffolds is being studied for potential use as tissue-engineered scaffolds. Biodegradable polymer microspheres were coated with a biocompatible polymer membrane to permit the incorporation of the microspheres into tissueengineered scaffolds. Surface studies with poly(D,L-lactic-co-glycolic acid) [PLGA], and poly(vinyl alcohol) [PVA] were conducted. Polymer films were dip-coated onto glass slides and water contact angles were measured. The contact angles revealed an initially hydrophobic PLGA film, which became hydrophilic after PVA coating. After immersion in water, the PVA coating was removed and a hydrophobic PLGA film remained. Following optimization using these 2D contact angle studies, biodegradable PLGA microspheres were prepared, characterized, and coated with PVA. X-ray photoelectron spectroscopy was used to further characterize coated slides and microspheres. The release of the model protein bovine serum albumin from PVA-coated PLGA microspheres was studied over 8 days. The release of BSA from PVA-coated PLGA microspheres embedded in porous PLGA scaffolds over 24 days was also examined. Coating of the PLGA microspheres with PVA permitted their incorporation into tissue-engineered scaffolds and resulted in a controlled release of BSA.     

A novel strontium-doped calcium polyphosphate/erythromycin/poly(vinyl alcohol) composite for bone tissue engineering

It is our goal to develop bactericidal bone scaffolds with osteointegration potential. In this study, poly(vinyl alcohol) (PVA) coating (7%) was applied to an erythromycin (EM)-impregnated strontium-doped calcium polyphosphate (SCPP) scaffold using a simple slurry dipping method. MicroCT analysis showed that PVA coating reduced the average pore size and the percentage of pore interconnectivity to some extent. Compressive strength tests confirmed that the PVA coating significantly increased material elasticity and slightly enhanced the scaffold mechanical strength. It was also confirmed that the PVA coatings allowed a sustained EM release that is controlled by diffusion through the intact PVA hydrogel layer, irrespective of the drug solubility. PVA coating did not inhibit the EM bioactivity when the scaffolds were immersed in simulated body fluid for up to 4 weeks. EM released from SCPP-EM-PVA composite scaffolds maintained its capability of bacterial growth (S. aureus) inhibition. PVA coating is biocompatible and nontoxic to MC3T3 preosteoblast cells. Furthermore, we found that SCPP-EM-PVA composite scaffolds and their eluants remarkably inhibited RANKL-induced osteoclastogenesis in a murine RAW 264.7 macrophage cell line. Thus, this unique multifunctional bioactive composite scaffold has the potential to provide controlled delivery of relevant drugs for bone tissue engineering.     

Sustained release of a model macromolecule from preparations with erodible core

A series of sustained release tablets were prepared which consisted of a water-soluble core and a highly hydrophobic coat. Release of a macromolecule, Spectrum Orange, from this preparation was studied. It was found that release was controlled by the coat composition and coating solution viscosity. SEM and optical microscopy of the tablets indicated that the coats contained pores on the surface which penetrated in towards the centre of the core. It was deduced that the almost zero order release of macromolecules from these tablets was basically through these pores and not by diffusion through the polymer matrix.     

Novel bioresorbabale composite fiber structures loaded with proteins for tissue regeneration applications: microstructure and protein release

Novel bioresorbable core/shell composite fiber structures loaded with proteins were developed and studied. These unique polymeric structures are designed to combine good mechanical properties with a desired controlled protein-release profile, to serve as scaffolds for tissue regeneration applications. Core/shell fiber structures were formed by "coating" poly(L-lactic acid) fibers with protein-containing poly(DL-lactic-co-glycolic acid) porous structures. Shell preparation (coating) was performed by the freeze-drying of water in oil emulsions. The present study focused on the effect of the emulsion's formulation on the porous shell structure and on the resulting cumulative protein release from the composite fibers for 90 days. Horseradish peroxidase (HRP) was used as the protein source. The release profiles usually exhibited an initial burst effect, accompanied by a decrease in release rate with time, as is typical for diffusion-controlled systems. The HRP content and the emulsion's organic:aqueous phase ratio exhibited significant effects on both the shell microstructure and the HRP release profile from the composite fibers, whereas the polymer content of the emulsion's organic phase only affected these fiber characteristics in certain cases. Proper selection of the emulsion's parameters can yield core/shell fiber structures with the desired protein release behavior and other useful physical properties.     

Nanogel scavengers for drugs: local anesthetic uptake by thermoresponsive nanogels

The use of functional nanogels based on poly(N-isopropylacrylamide) for effectively scavenging compounds (here, the model drug bupivacaine) is demonstrated using an in vitro cell-based assay. Nanogels containing higher loadings of acidic functional groups or more core-localized functional group distributions bound more bupivacaine, while nanogel size had no significant effect on drug binding. Increasing the dose of nanogel applied also facilitated more bupivacaine binding for all nanogel compositions tested. Binding was driven predominantly by acid-base interactions between the nanogels (anionic) and bupivacaine (cationic) at physiological pH, although both non-specific absorption and hydrophobic partitioning also contributed to drug scavenging. Nanogels exhibited minimal cytotoxicity to multiple cell types and were well tolerated in vivo via peritoneal injections, although larger nanogels caused limited splenic toxicity at higher concentrations. The cell-based assay described herein is found to facilitate more robust drug uptake measurements for nanogels than conventional centrifugation-based assays, in which nanogels can be compressed (and thus drug released) during the measurement.     

Accurate Targeting and Controllable Release of Hybrid Liposome Containing a Stretchable Copolymer

Developing an intelligent drug delivery/release system, which can transport drugs to the target tissues precisely and release drugs timely, is an important challenge in chemotherapy. A multistage sensitive drug delivery system is designed by inserting a folate (FA) modified lipid and a pH/temperature dual‐sensitive amphiphilic copolymer into a liposome bilayer. The stretchable copolymer plays a role in protection on FA ligand for more accurate targeting. Then, the stretch ability of the copolymer in the liposome bilayer is verified by using the Langmuir–Blodgett film technique. The interaction between the 1,2‐dipalmitoyl‐sn‐glycerol‐3‐phosphocholine (DPPC) monolayer and hybrid liposomes is found to increase, indicating the FA ligand is exposed due to the copolymer shrinking with increasing temperature. Fluorescence polarization measurements demonstrate that the insertion of the copolymer improves the stability of the liposome and offers pH‐controllability for drug release. As a result, the drug leakage of the hybrid liposome is restrained significantly at pH 7.4, while at an acidic pH, the drug release is accelerated. The designed pH/temperature dual‐sensitive copolymer is expected to provide more precise targeting and environmentally controlled drug release to drug delivery systems based on liposomes.