Physical hydrogels with self-assembled nanostructures as drug delivery systems

Introduction: As an essential complement to chemically crosslinked hydrogels, drug delivery systems based on physical hydrogels with self-assembled nanostructures are gaining increasing attention, owing to potential advantages of reduced toxicity, convenience of in situ gel formation, stimuli-responsiveness, reversible sol-gel transition, and improved drug loading and delivery profiles.

Areas covered: In this review, drug delivery systems based on physical hydrogels are discussed according to their self-assembled nanostructures, such as micelles, layer-by-layer constructs, supramolecular inclusion complexes, polyelectrolyte complexes and crystalline structures. The driving forces of the self-assembly include hydrophobic interaction, hydrogen bonding, electrostatic interaction, π–π stacking and weak van der Waals forces. Stimuli-responsive properties of physical hydrogels, including thermo- and pH-sensitivity, are considered with particular focus on self-assembled nanostructures.

Expert opinion: Fabricating self-assembled nanostructures in drug delivery hydrogels, via physical interactions between polymer–polymer and polymer–drug, requires accurately controlled macro- or small molecular architecture and a comprehensive knowledge of the physicochemical properties of the therapeutics. A variety of nanostructures within hydrogels, with which payloads may interact, provide useful means to stabilize the drug form and control its release kinetics.     

Design of stimuli-responsive dendrimers

Importance of the field: Dendrimers are synthetic macromolecules with well-defined structures, many terminal functional groups, and an inner space to hold small molecules. These properties make them potential drug carriers. Recently, stimuli-responsive drug delivery systems have become attractive because of the reduction of side effects and maximum expression of drug action.

Areas covered in this review: This paper reviews dendrimer nanoparticles that are sensitive to temperature, light, pH and redox state.

What the reader will gain: Strategies to design these dendritic polymers are provided in this review.

Take home message: By adding stimuli-responsive properties to the dendrimers, dendritic polymers capable of controlled release can be produced. These stimuli-responsive dendrimers are a potential next generation drug carrier.     

HPAN/SPI水凝胶纤维的PH刺激响应性能

探索了聚丙烯腈(PAN)和大豆分离蛋白(SPI)在NaOH水溶液中进行PAN碱解，然后挤到凝固浴中凝固、交联，制备水解聚丙烯腈(HPAN)／SPI水凝胶纤维的方法。通过测定凝胶纤维的平衡溶胀伸长率和溶胀伸长率，观察到HPAN／SPI水凝胶纤维的滞后和可逆的伸长／收缩行为，同时在不同组成的凝胶纤维中，随着PAN含量的逐渐增大，水凝胶纤维的响应速率呈现由小到大然后减小的变化规律，当mPAN／mspt=6／4时有最好的响应性能。     

pH敏感性生物医用材料在药物传递中的研究与进展

目的：概述几类常见的pH敏感性生物医用材料在药物传递中的研究与进展,为其在后续pH敏感性生物材料的研究与开发提供参考。方法：通过文献研究,总结归纳常见的四类pH敏感性生物材料的作用机理和在药物传递中的应用,探讨其在临床转化上存在的挑战与研究方向。结果与结论：pH敏感性生物医用材料可根据人体内不同组织器官环境的酸碱性来使药物到达并作用于病灶部位,达到治疗的效果。但其在产品的研究与开发中还存在很多问题,而面临最大的挑战即是选择、修饰以及整合相应材料,设计并制备出安全有效的pH敏感性生物医用材料。解决因不同生物材料结构特点而产生的技术难题,才能实现真正的产品化和临床化。     

Self-assembly pH-sensitive chitosan/alginate coated polyelectrolyte complexes for oral delivery of insulin

Polyelectrolyte complexes (PEC) provide new opportunities for controlled release system of drugs, and have potentials to address challenges on the way to effective oral insulin delivery. Here, an innovative pH-sensitive PEC for insulin oral administration was developed, which was formed by self-assembly of two oppositely charged nanoparticles (chitosan-coated nanoparticles and alginate-coated nanoparticles) through electrostatic interaction via optimised double emulsion method. The encapsulation efficiency of insulin-loaded alginate-coated and chitosan-coated nanoparticles were 81.5?±?7.4% and 55.2?±?7.0%, respectively, and the particle size of these nanoparticles were in 200–300?nm range. The pH-dependent morphology of PEC was observed by transmission electron microscopy. The PEC exhibited insulin release profile triggered by pH in vitro and was non-cytotoxicity against Caco-2 cell. The insulin-loaded PEC could decrease blood glucose levels effectively and prolong insulin release after oral administration to diabetic rats. The results illustrated that the as-prepared PEC may be employed as a potential oral insulin delivery system.     

雷替曲塞pH敏感脂质体的制备研究

目的 制备雷替曲塞pH敏感脂质体，并优化其处方和制备工艺，对所优化的pH敏感脂质体进行评价。方法 采用单因素考察和正交设计试验优化处方，考察最优处方制得的雷替曲塞pH敏感脂质体的粒径、Zeta电位、外观形态、包封率、体外释放度和细胞毒性作用。结果 按最优处方制备的雷替曲塞pH敏感脂质体，平均粒径为(227.0±21.4)nm，PDI为0.223±0.061，Zeta电位为(-44.2±3.6)mv，包封率为(58.3±2.1)%；体外释放结果表明载药脂质体在pH5.0和pH6.0的释放介质中释放快速，在pH7.4的释放介质中释放缓慢，pH敏感作用明显；细胞毒性试验证实脂质体载体本身安全性较高，而载药脂质体制剂有较高的细胞毒性。结论 本研究表明，优化得到的雷替曲塞pH敏感脂质体具有简便的制备方法、适宜的理化性质和较高的安全性，具有广阔的临床应用前景。     

Modifying matrix micro-environmental pH to achieve sustained drug release from highly laminating alginate matrices

Lamination of alginate matrix tablet at acidic pH can compromise its function as a sustained release carrier. This phenomenon is associated with the conversion of sodium alginate to alginic acid. An innovative approach for controlling the release of a highly water-soluble drug from such matrices is presented in this paper. Inclusion of pH-modifiers was employed to raise the micro-environmental pH within matrices undergoing dissolution at gastric pH. The changes in micro-environmental pH of hydrating alginate matrices were visualized with the aid of a pH-indicator and subsequently quantified using image analysis. Transient elevation in micro-environmental pH impeded alginate protonation and minimized or prevented matrix lamination, contributing to preservation of drug diffusion barrier. Significant reduction in the rate of drug release at pH 1.2 was achieved in the presence of such additives. The action of pH-modifiers was synergistically enhanced in the presence of a carbon dioxide barrier formed by effervescing sodium bicarbonate, reducing drug release in the acidic medium from 60 to 20%. Further insight into the influence of lamination on drug release from alginate compacts was given.     

Monitoring intracellular pH changes in response to osmotic stress and membrane transport activity using 5-chloromethylfluorescein

Intracellular free H⁺ concentration (pHi) responds to numerous extracellular stimuli. The use of fluorescent indicator dyes to measure pHi is strongly influenced by the ability of target cells to retain activated dye within the cytoplasmic compartment. Here, 3 pH-sensitive indicator dyes—acetoxymethyl (AM) esters of SNARF-1 and BCECF, and the thiol-reactive 5-chloromethyfluorescein (CMFDA)—were examined for monitoring pHi. The stability of pH measurements was strongly affected by temperature, cell type, indicator dye, and use of transport inhibitors to prevent dye export. Cellular retention of CMFDA, which forms covalent complexes, was sufficient to permit monitoring of transient pHi changes over extended time periods in a multi-well plate assay format. In human embryonic kidney (HEK293) and Chinese hamster ovary (CHO) cells, increasing osmotic pressure caused a significant rise in pHi. In contrast, activation of native or transfected β-adrenergic, cholinergic, and d and m opioid receptors did not measurably affect pHi in HEK293 cells. Decreases in pHi were observed in CHO cells expressing the human H⁺/peptide transporter PEPT1 upon addition of dipeptide substrates. The use of CMFDA in multi-well formats should facilitate study of osmotic and transport activity and screening for drugs that affect pHi.     

加替沙星pH敏感眼用原位凝胶体外释放的研究

目的研究加替沙星pH敏感眼用原位凝胶的体外释药特性与机制。方法采用改良桨法考察加替沙星pH敏感眼用原位凝胶的释药规律,并用无膜溶出法研究其释放机制。结果凝胶溶蚀和药物释放随着振荡频率和释放面积的增加而加快。其溶蚀度与释放度有明显相关性。结论体外的溶蚀行为与释放行为遵循零级动力学方程,凝胶溶蚀是决定药物释放的主要因素。     

Long-circulating, pH-sensitive liposomes sterically stabilized by copolymers bearing short blocks of lipid-mimetic units

A major hurdle towards in vivo utilization of pH-sensitive liposomes is their prompt sequestration by reticuloendothelial system and hence short circulation time. Prolonged circulation of liposomes is usually achieved by incorporation of pegylated lipids, which have been frequently reported to deteriorate the acid-triggered release. In this study we evaluate the ability of four novel nonionic copolymers, bearing short blocks of lipid-mimetic units to provide steric stabilization of DOPE:CHEMs liposomes. The vesicles were prepared using the lipid film hydration method and extrusion, yielding liposomes of 120–160 nm in size. Their pH-sensitivity was monitored via the release of encapsulated calcein. The incorporation of the block copolymers at concentration up to 10 mol% did not deteriorate the pH-sensitivity of the liposomes. A selected formulation was tested for stability in presence of 25% human plasma and proved to significantly outclass the plain DOPE:CHEMs liposomes. The ability of calcein-loaded liposomes to deliver their cargo inside EJ cells was investigated using fluorescent microscopy and the results show that the surface-modified vesicles are as effective to ensure intracellular delivery as plain liposomes. The pharmacokinetics and organ distribution of a selected formulation, containing a copolymer bearing four lipid anchors was investigated in comparison to plain liposomes and PEG (2000)–DSPE stabilized liposomes. The juxtaposition of the blood clearance curves and the calculated pharmacokinetic parameters show that the block copolymer confers superior longevity in vivo. The block copolymers utilized in this study can be consider as promising sterically stabilizing agents for pH-sensitive liposomes.