Design and synthesis of pH-sensitive polymeric micelles for oral delivery of poorly water-soluble drugs

pH-sensitive polymer poly (polylactide-co-methacrylic acid)–b-poly (acrylic acid) was synthesized using atom transfer radical polymerization and ring-opening polymerization and characterized by gel permeation chromatography and ¹H NMR. The polymers can self-assemble to form micelles in aqueous medium, which respond rapidly to pH change within the gastrointestinal relevant pH range. Critical micelle concentrations and pH response behavior of the polymeric micelle were investigated. Water-insoluble drug nifedipine was loaded and the drug-loading content can be controlled by tuning the composition of the polymers. The in vitro release studies indicate pH sensitivity enabled rapid drug release at the environment of simulated intestinal fluid (pH 7.36), the cumulative released amount of NFD reached more than 80% within 24 h, while only 35% in the simulated gastric fluid (pH 1.35). All the results showed that the pH-sensitive P(PLAMA-co-MAA)–b-PAA micelle may be a prospective candidate as oral drug delivery carrier for hydrophobic drugs with controlled release behavior.     

A thermosensitive chitosan-based hydrogel barrier for post-operative adhesions' prevention

Post-operative peritoneal adhesions are common and serious complications for surgeons. They can cause pelvic pain, infertility, and potentially lethal bowel obstruction. We synthesized injectable hydrogels that formed by chemical modification through grafted hydrobutyl groups to chitosan chains. Gelation of hydroxybutyl chitosan (HBC) occurs in less than 60 s. Once formed, it can also be recovered completely. The residue time of hydrogels can extend to 4 weeks in Kunming mice. HBC hydrogels showed mild cytotoxicity to mice fibroblast cell (L929) and human vascular endothelial cell (ECV-304) in vitro and were biocompatible in the murine muscles, causing no adhesions for 4 weeks. HBC gels can form a durable barrier between defected cecum and abdominal wall. In a mice sidewall defect-bowel abrasion model, HBC gels showed significant efficacy in reducing adhesion formation.     

A pH-sensitive chitosan-tripolyphosphate hydrogel beads for controlled glipizide delivery

A chitosan(CS)-tripolyphosphate (TPP) hydrogel bead was prepared by the ionic gelation method for the controlled delivery of glipizide. The structure and surface morphology of the beads were characterized by FT-IR and SEM, separately. Factors influencing the swelling behavior of the hydrogel beads were also investigated, such as CS concentration (X(1)), TPP concentration (X(2)), the weight ratio of drug to polymer (X(3)), crosslinking time (X(4)), and the volume ratio of CS to TPP (X(5)). In addition, the swelling property and the delivery behavior of the hydrogel bead was studied as well. With decreasing of pH value, the swelling ratio of the bead was increasing. The swelling ratio of hydrogel bead at pH 1.5 was relatively high, while this value was low at pH 6.8. The amount of glipizide released from the hydrogel bead at pH 1.5 was about 90%, while this value approached 36% at pH 6.8. The results clearly suggested that the CS-TPP hydrogel beads were used as a pH-sensitive controlled release system for the delivery of glipizide.     

A new injectable radiopaque chitosan-based sclerosing embolizing hydrogel for endovascular therapies

Endovascular repair of abdominal aortic aneurysms with a stent graft is limited by the persistence or recurrence of endoleaks. These are believed to be related to the recanalization of the aneurismal sac by endothelialized neochannels, which could lead to late type I and II endoleaks. Embolization has been proposed to treat or prevent endoleaks, but presently commercialized embolizing materials have several drawbacks and do not fully prevent endoleak recurrence. A novel chitosan hydrogel that is injectable, radiopaque and contains sodium tetradecyl sulfate (STS), a well-known sclerosing agent, was developed in order to combine blood flow occlusion and endothelium ablation properties. chitosan/STS hydrogels were characterized and optimized using rheometry, scanning electron microscopy, swelling and ex vivo embolization assay. They were shown to exhibit rapid gelation and good mechanical properties, as well as sclerosing properties. Their potential for the embolization of aneurysms was subjected to preliminary in vivo evaluation in a bilateral iliac aneurysm model (three dogs) reproducing persistent endoleaks after endovascular aneurysm repair (EVAR). At 3 months no endoleak was detected in any of the three aneurysms treated with chitosan/STS hydrogels. In contrast, type I endoleaks were detected in two of the three aneurysms treated with chitosan hydrogels. Generally, chitosan/STS hydrogels have great potential as embolizing and sclerosing agents for EVAR and possibly other endovascular therapies.     

温敏性壳聚糖水凝胶复合细胞因子修复兔关节软骨缺损

背景：单独以细胞因子修复软骨缺损时局部很难保持有效浓度,且维持时间非常有限。 目的：观察负载基质细胞衍生因子1β、转化生长因子β1温敏性壳聚糖水凝胶修复兔关节软骨缺损的可行性。 方法：通过京尼平的交联作用制备温敏性壳聚糖水凝胶,并负载基质细胞衍生因子1β、转化生长因子β1。取24只兔制作双侧膝关节软骨全层缺损模型,随机分为3组：结合组软骨下骨钻孔后以负载基质细胞衍生因子1β、转化生长因子β1的温敏性壳聚糖水凝胶充填软骨缺损,钻孔组行软骨下骨钻孔,对照组不做任何处理。 结果与结论：温敏性壳聚糖水凝胶在37 ℃凝胶时间为3 min,结构致密,为多孔三维支架,能缓慢释放基质细胞衍生因子1β、转化生长因子β1。结合组软骨修复在组织细胞形态、超微结构、Ⅱ型胶原含量等方面均明显优于钻孔组和对照组(P < 0.05)。说明负载基质细胞衍生因子1β、转化生长因子β1温敏性壳聚糖水凝胶结合软骨下骨钻孔能有效修复兔膝关节软骨全层缺损。     

A novel chitosan-based thermosensitive hydrogel containing doxorubicin liposomes for topical cancer therapy

Thermosensitive hydrogel containing drug-loaded liposomes delivery system offers the possibility of reduced dosing frequency and sustained drug action. In the study, a soluble chitosan derivative, N-[(2-hydroxy-3-trimethylammonium) propyl] chitosan chloride, was used and interacted with glycerophosphate to produce a thermosensitive hydrogel as the matrix of doxorubicin-loaded liposomes. The formulation could retain the liquid state with good fluidity below or at room temperature for long time but turn into a nonflowing gel after exposing to body temperature for no more than 5?min. The mean size of liposomes was increased when dispersed into the hydrogel, while the entrapment efficiency of doxorubicin in liposomes was not discounted by the hydrogel, which was over 90%. The in vitro release experiment performed with a dialysis membrane model showed that the liposomes-containing hydrogel exhibited an excellent sustained-release behavior, which eliminated the initial burst release occuring in the liposomal formulation and only released about 22% loaded drug in 9?days. In vivo antitumor activity was evaluated by the survival time of H22-bearing mice treated with various doxorubicin formulation, which showed that the hydrogel enhanced the antitumor activity and reduced the systemic toxicity. Thus, all these results demonstrated that the thermosensitive hydrogel with embedded liposomes is a promising antitumor drug carrier for topical cancer therapy.     

Drug nanoparticles: formulating poorly water-soluble compounds

More than 40% of compounds identified through combinatorial screening programs are poorly soluble in water. These molecules are difficult to formulate using conventional approaches and are associated with innumerable formulation-related performance issues. Formulating these compounds as pure drug nanoparticles is one of the newer drug-delivery strategies applied to this class of molecules. Nanoparticle dispersions are stable and have a mean diameter of less than 1 micron. The formulations consist of water, drug, and one or more generally regarded as safe excipients. These liquid dispersions exhibit an acceptable shelf-life and can be postprocessed into various types of solid dosage forms. Drug nanoparticles have been shown to improve bioavailability and enhance drug exposure for oral and parenteral dosage forms. Suitable formulations for the most commonly used routes of administration can be identified with milligram quantities of drug substance, providing the discovery scientist with an alternate avenue for screening and identifying superior analogs. For the toxicologist, the approach provides a means for dose escalation using a formulation that is commercially viable. In the past few years, formulating poorly water-soluble compounds using a nanoparticulate approach has evolved from a conception to a realization whose versatility and applicability are just beginning to be realized.     

Anti-biofouling and functionalizable bioinspired chitosan-based hydrogel coating via surface photo-immobilization

Zwitterionic polymer is a new generation of anti-fouling materials with its good resistance to protein and bacterial adhesion. Constructing the anti-fouling surfaces with zwitterionic polymer has been regarded as an effective approach for improving the biocompatibility and biofunctionality of clinic devices. Herein, we reported a facile approach to construct a biodegradable anti-biofouling and functionalizable hydrogel coating via photo-immobilization using commercial polyethylene terephthalate (PET) films as the substrate, based on zwitterionic glycidyl methacrylate-phosphorylcholine-chitosan (PCCs-GMA). The surface structure and physicochemical properties of zwitterionic PCCs-GMA hydrogel coating were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM) and static water contact angle measurement, and its functionalizable sites were detected by fluorescence labeling. Compared with the pristine PET and cationic chitosan - GMA and hydroxypropyltrimethyl ammonium chloride chitosan (HTCC) - GMA hydrogel coatings, zwitterionic PCCs-GMA hydrogel coating exhibited excellent biocompatibility, and significantly reduced protein adsorption for three model proteins of fibrinogen, immunoglobulin and lysozyme, repelled platelet adhesion, as well as showed a high resistance to bacterial attachment of Escherichia coli and Staphylococcus aureus and superior anti-fouling properties to MRC-5 cells. The results indicated that photo-immobilized zwitterionic PCCs-GMA hydrogel coating has perspective as a dual functional platform with integrated antifouling and further biofunctional properties for various biomedical applications.     

Ethyl acetate Salix alba leaves extract-loaded chitosan-based hydrogel film for wound dressing applications

High toxicity and multidrug resistance associated with various standard antimicrobial drugs have necessitated search for safer alternatives in plant-derived materials. In this study, we performed biological examination of chitosan-based hydrogel film loaded with ethyl acetate Salix alba leaves extract against 11 standard laboratory strains. FTIR showed regeneration of saccharide peak in CP1A at 1047 cm^?1 and increased in height of other peaks. DSC exothermic decomposition peaks at 112 °C, 175 °C and 251 °C reveal the effect of extract on hydrogel film. From FESEM images, three-dimensional cross-linking and extract easily seen in the globular form from the surface. MTT assay on HEK 293 cells showed that CP1A was non-toxic. Minimum inhibitory concentration ranges from 4000 μg/ml to 125 μg/ml. Enterococcus faecium, Candida glabrata and Candida tropicalis were the most resistant, while Salmonella typhi and Candida guilliermondii were the most susceptible micro-organisms.     

Self-assembled nanoparticles made from a new PEGylated poly(aspartic acid) graft copolymer for intravaginal delivery of poorly water-soluble drugs

New amphiphilic PEGylated poly(aspartic acid) graft copolymer (PASP-PEG-Ph) was synthesized as a nanocarrier for intravaginal drug delivery of poorly water-soluble drugs. PASP-PEG-Ph self-assembled into negatively charged spherically shaped nanoparticles in the presence of pH 4.5 and pH 7.0 vaginal fluid simulants with a diameter of approximately 200 nm as evidenced by Zeta-potentiometer, scanning electron microscope (SEM), dynamic light scattering (DLS) analysis. A significant number of stable NPs could be maintained at pH 4.5, 37 °C for 13 days. The PASP-PEG-Ph NP showed no significant cytotoxicity toward the T-cell line SupT1 and human vaginal epithelial cell line Vk2/E6E7 up to 1 mg/mL. The highest encapsulation efficiency of the model drug coumarin 6 (C6) by PASP-PEG-Ph was 92.0 ± 5.7%. The sustained release profile of the encapsulated C6 was demonstrated by an in vitro release study. An in vitro cellular uptake study revealed strong cellular uptake of the C6 loaded NP by SupT1 cells within 2 h.     

Synthesis and characterization of a pH-sensitive hydrogel made of pyruvic-acid-modified chitosan

Pyruvic-acid-type chitosan (PA-CS) was prepared by the reaction of an amine group on chitosan with a carbonyl group on pyruvic acid. Then, a novel hydrogel film was obtained via cross-linking of poly(ethylene glycol) diglycidyl ether (PEGDE) with PA-CS. 1H-NMR and FT-IR spectrometry were applied for the verification of the CS and PA-CS structure. The degree of swelling was studied by changing the molar ratio of PEGDE and PA-CS. Moreover, the swelling ratio of cross-linked membrane in different pH buffer solutions was measured. The result showed that the swelling of hydrogel exhibited obvious pH-sensitivity. The swelling ratio was higher at pH 1-4 and pH 7-12, but lower at pH 5-6.     

Synthesis and characterization of in situ chitosan-based hydrogel via grafting of carboxyethyl acrylate

We developed and characterized a novel in situ chitosan-poly(ethylene oxide) (PEO) hydrogel via two steps: 2-carboxyethyl acrylate molecules were grafted to the primary amine functional groups in chitosan in the first step and then Michael type addition reaction was processed between the grafted acrylate end groups and the thiol end groups in the PEO. Grafting of acrylate molecules to the amine groups in the deacetylated water soluble chitosan was confirmed by observing the new acrylate peaks by the FTIR and NMR spectra of the acrylated chitosan samples, as well as changes in relative viscosities of chitosan and acrylated chitosan. Formation of the chitosan-PEO hydrogel was visually observed with digital images after both gelation and hydration. Rheological analyses of the hydrogel formation were performed to detect its gelation time, phase angle changes, and visco-elastic properties over frequency and strain percentage. Their results indicated that the gelation process was completed within 10 min after mixing the precursor liquid solutions. An extent of water swelling, mechanical strength against compression and the morphologies of the hydrogel surface and cross sections after dehydration process were analyzed by microbalance measurement, texture analyzer, and scanning electron microscopy observation, respectively. Biological activities of the hydrogels were evaluated by observing smooth muscle cell behaviors such as cell adhesion and viability as well as by measuring the number of adhered cells on their surfaces.     

Spontaneously forming hydrogel from water-soluble random- and block-type phospholipid polymers

The mixed aqueous solutions of two water-soluble phospholipid polymers, such as poly[2-methacryloyloxyethyl phosphorylcholine(MPC)-co-methacrylic acid(MA)] (rPMA) and poly[MPC-co-n-butyl methacrylate(BMA)] (PMB), spontaneously form a hydrogel at room temperature without any chemical treatment due to hydrogen bonding formation between the carboxyl groups. With the objective of enhancing the hydrogen bonding efficiency, we have focused on the density of the carboxyl groups by controlling the chemical structure and monomer unit sequence. Thus, a random and an ABA-block-type MPC copolymer having carboxylic acids, poly[MPC-co-4-(2-methacryloyloxyethyl) trimellitic acid(MET)] (rPMT) and poly(MA)-poly(MPC)-poly(MA) (bPMA), have been designed. The purpose of this study is to investigate the gelation mechanism and physical properties of a hydrogel composed of rPMA and PMB (ABgel), one of bPMA and PMB (bABgel), and one of rPMT and poly(MPC-co-benzyl methacrylate) (PMBz) (TZgel). The Raman spectroscopic analysis and the rheological study of the dissolution behaviors indicated that the TZgel formation occurred due to inter- and intra-molecular hydrogen bonding formation between the carboxyl groups in the rPMT. The gelation mechanism of the bABgel was investigated by the dynamic light scattering measurement, the scanning electron microscopy observation and the rheological study. The results showed that the bPMA chains aggregate in the aqueous medium and transform into a hydrogel network structure. The bPMA needed much more gelation time than the rPMA due to this transformation. There was no difference between the gelation periods of the ABgel and the TZgel. The compression strengths of the ABgel and the bABgel showed no significant difference, while that of TZgel was lower than ABgel. The reason for this is that the polymer chains and bulky side chains of rPMT inhibit rearranging into a planar conformation and forming hydrogen bondings. These results lead to the conclusion that the properties of these MPC polymer hydrogels can be controlled by not only the chemical structure of the polymer but also the monomer unit sequence containing carboxyl groups.     

Release profile of insulin from pH-sensitive hydrogel and its hypoglycemic effect by oral administration

The purpose of this study was to investigate the release profile and in vivo hypoglycemic effect of insulin (INS)-loaded pH-sensitive hydrogel (INS-TPM950) administrated by oral route. TPM950 was fabricated via a free polymerization method and its inner morphology was observed with a scanning electron microscope (SEM). INS was encapsulated into TPM950 by an adsorption method, and the in vitro release profiles of INS from INS-TPM950 were revealed in pH 1.2 and 6.8. To investigate the hypoglycemic effect of INS-TPM950, Male Wistar rats were used in modeling of diabetes mellitus by multiple intraperitoneal injection of alloxan. The in vivo hypoglycemic effect of oral INS-TPM950 was studied, and the optimal dosage was also determined. SEM photograph showed that abundant 3D meshes were distributed in the inner of TPM950 hydrogel. INS release profile suggested that only 18.2 ± 11.3% INS was released in pH 1.2, but over 88.8 ± 4.9% was delivered into phosphate buffer solution in pH 6.8. After injection to the diabetic rats, the released INS solution from INS-TPM950 exhibited an obvious hypoglycemic effect. Oral administration of 50.0 I.U./kg of INS-TPM950 showed a slow but effective hypoglycemic effect, and the lowest blood glucose level was reached to 47.5 ± 5.5% of the original level. Therefore, this formulation had a potential application in diabetes treatment via oral ingestion.     

Development of disposable PDMS micro cell culture analog devices with photopolymerizable hydrogel encapsulating living cells

Microscale cell culture devices with two or more cell types, such as the micro cell culture analog (microCCA), are promising devices to predict mammalian response to toxic drug and chemical exposure. A polydimethylsiloxane (PDMS) version of such microfluidic devices has been challenging to construct due to the difficulty of patterning multi cell types directly into designated individual cell culture chambers in an oxygen plasma bonded PDMS device. Approaches with micro-valves for flow control are complex, expensive and inconvenient to use. In this study, an alternative approach using polyethylene glycol diacrylate (PEG-DA) for spatially controlled multi-cell type patterning inside a bonded microCCA device is described. We constructed a three-cell type PDMS microCCA following a human physiologically based pharmacokinetic (PBPK) modeling, and applied continuous cell culture medium recirculation within the device as a blood surrogate. A fluorescence microscope based direct pattern writing method was used to form cell/hydrogel microstructures with higher cell viability than the traditional UV lamp based method. The positive effect of mixed molecular weight PDG-DA on hydrogel-encapsulated cell membrane integrity was also studied. This prototype PDMS microCCA device was then tested with Triton X-100 as a model toxicant. The combination of hydrogel photo-patterning and the microfluidic cell culture platform enables the fabrication of simple and low cost multi-cell type biosensors for drug development, toxicity study and clinical diagnosis.     

A nanoscale drug-entrapment strategy for hydrogel-based systems for the delivery of poorly soluble drugs

The hydrophilic nature of hydrogel matrices makes them disadvantageous to entrap poorly soluble therapeutic agents and greatly restricts their applications as drug-delivery systems. In this study, we demonstrated that sustained delivery of lipophilic drugs in hydrogel-based devices can be readily achieved by enhancing retention of drugs within micelles. This nanoscale drug-entrapment strategy was applied to develop a polymeric drug-eluting stent. Sirolimus, a lipophilic anti-proliferative/immunosuppressive drug, was entrapped into the hydrophobic core of Pluronic L121 micelles and then blended in a chitosan-based strip and crosslinked by an epoxy compound to fabricate test stents. It was found that the use of such a nanoscale drug-entrapment strategy was able to significantly increase the loading efficiency of lipophilic drugs, prevent the drug from aggregation and beneficially reduce its initial burst release; thus, the duration of drug release was extended considerably. When implanting the stent in rabbit infrarenal abdominal aortas, in-stent restenosis was markedly reduced and less inflammatory reaction was observed, while unfavorable effects such as delayed endothelial healing caused by the overdose of sirolimus could be significantly evaded.     

Novel anti-obesity drugs

Obesity is a chronic disease with a worldwide increasing incidence. The mainstay of therapy consists in modification of behaviour related to obesity such as overeating and physical inactivity. When these life-style modifying attempts fail, the use of anti-obesity drugs is warranted. Public health efforts and current anti-obesity agents have not controlled the increasing epidemic of obesity, which has led to an extensive research on novel anti-obesity agents. This review presents an overview on potential future candidates.     

Preparation and characterization of pH-sensitive hydrogel of chitosan/poly(acrylic acid) co-polymer

A pH-sensitive co-polymer hydrogel of chitosan/poly(acrylic acid) (CS/PAAc) was prepared by irradiating the aqueous solution mixture of chitosan and acrylic acid with 60Co gamma-ray irradiation. The effect of the composition of chitosan and AAc on the properties of the hydrogel, such as swelling ratio and pH-sensitivity, were determined. Fourier Transform Infrared (FT-IR) spectrometry was applied in the attenuated total reflectance (ATR) mode for analyzing the structure change of the hydrogels after the treatment in different pH buffer solutions.     

Preparation and characterization of pH-sensitive hydrogel of chitosan/poly(acrylic acid) co-polymer

A pH-sensitive co-polymer hydrogel of chitosan/poly(acrylic acid) (CS/PAAc) was prepared by irradiating the aqueous solution mixture of chitosan and acrylic acid with ⁶⁰Co γ-ray irradiation. The effect of the composition of chitosan and AAc on the properties of the hydrogel, such as swelling ratio and pH-sensitivity, were determined. Fourier Transform Infrared (FT-IR) spectrometry was applied in the attenuated total reflectance (ATR) mode for analyzing the structure change of the hydrogels after the treatment in different pH buffer solutions.     

Tuning the dependency between stiffness and permeability of a cell encapsulating hydrogel with hydrophilic pendant chains

The mechanical stiffness of a hydrogel plays a significant role in regulating the phenotype of cells that adhere to its surface. However, the effect of hydrogel stiffness on cells cultured within its matrix is not well understood, because of the intrinsic inverse dependency between the permeability and stiffness of hydrogels. This study therefore presents an advanced biomaterial design strategy to decrease the inverse dependency between permeability and stiffness of a cell encapsulating hydrogel. Hydrogels were made by cross-linking poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) monoacrylate (PEGMA), with PEGMA acting as a pendant polymer chain. Increasing the mass fraction of PEGMA while keeping the total polymer concentration constant led to a decrease in the elastic modulus (E) of the hydrogel, but caused a minimal increase in the swelling ratio (Q). The size and hydrophobicity of the end groups of pendant PEG chains further fine tuned the dependency between Q and E of the hydrogel. Pure PEGDA hydrogels with varying molecular weights, which show the same range of E but a much greater range of Q, were used as a control. Fibroblasts encapsulated in PEGDA–PEGMA hydrogels displayed more significant biphasic dependencies of cell viability and vascular endothelial growth factor (VEGF) expression on E than those encapsulated in pure PEGDA hydrogels, which were greatly influenced by Q. Overall, the hydrogel design strategy presented in this study will be highly useful to better regulate the phenotype and ultimately improve the therapeutic efficacy of a wide array of cells used in various biology studies and clinical settings.