Intranasal Drug Delivery of Olanzapine-Loaded Chitosan Nanoparticles

The aim of this study was to investigate olanzapine (OZ) systemic absolute bioavailability after intranasal (i.n.) administration in vivo to conscious rabbits. Furthermore, the study investigated the potential use of chitosan nanoparticles as a delivery system to enhance the systemic bioavailability of olanzapine following intranasal administration. Olanzapine-loaded chitosan nanoparticles were prepared through ionotropic gelation of chitosan with tripolyphosphate anions and studied in terms of their size, drug loading, and in vitro release. The OZ nanoparticles were administered i.n. to rabbits, and OZ plasma concentration at predetermined time points was compared to i.n. administration of OZ in solution. The concentrations of OZ in plasma were analyzed by ultra performance liquid chromatography mass spectroscopy (UPLC/MS). OZ-loaded chitosan nanoparticles significantly (p < 0.05) enhanced systemic absorption with 51 ± 11.2% absolute bioavailability as compared to 28 ± 6.7% after i.n. administration of OZ solution. The results of the present study suggest that intranasal administration of OZ-loaded chitosan nanoparticles formulation could be an attractive modality for delivery of OZ systemically.KEY WORDS: bioavailability, intranasal, nanoparticles, olanzapine, pharmacokinetic     

Preparation and Evaluation of Miconazole Nitrate-Loaded Solid Lipid Nanoparticles for Topical Delivery

The purpose of this study was to prepare miconazole nitrate (MN) loaded solid lipid nanoparticles (MN-SLN) effective for topical delivery of miconazole nitrate. Compritol 888 ATO as lipid, propylene glycol (PG) to increase drug solubility in lipid, tween 80, and glyceryl monostearate were used as the surfactants to stabilize SLN dispersion in the SLN preparation using hot homogenization method. SLN dispersions exhibited average size between 244 and 766 nm. All the dispersions had high entrapment efficiency ranging from 80% to 100%. The MN-SLN dispersion which showed good stability for a period of 1 month was selected. This MN-SLN was characterized for particle size, entrapment efficiency, and X-ray diffraction. The penetration of miconazole nitrate from the gel formulated using selected MN-SLN dispersion as into cadaver skins was evaluated ex-vivo using franz diffusion cell. The results of differential scanning calorimetry (DSC) showed that MN was dispersed in SLN in an amorphous state. The MN-SLN formulations could significantly increase the accumulative uptake of MN in skin over the marketed gel and showed a significantly enhanced skin targeting effect. These results indicate that the studied MN-SLN formulation with skin targeting may be a promising carrier for topical delivery of miconazole nitrate.     

Solid Lipid Nanoparticles as Delivery Systems for Bioactive Food Components

The inclusion of bioactive compounds, such as carotenoids, omega-3 fatty acids, or phytosterols, is an essential requisite for the production of functional foods designed to improve the long-term health and well-being of consumers worldwide. To incorporate these functional components successfully in a food system, structurally sophisticated encapsulation matrices have to be engineered, which provide maximal physical stability, protect ingredients against chemical degradation, and allow for precise control over the release of encapsulated components during mastication and digestion to maximize adsorption. A novel encapsulation system initially developed in the pharmaceutical industries to deliver lipophilic bioactive compounds is solid lipid nanoparticles (SLN). SLN consist of crystallized nanoemulsions with the dispersed phase being composed of a solid carrier lipid–bioactive ingredient mixture. Contrary to larger colloidal solid lipid particles, specific crystal structures can be “dialed-in” in SLN by using specific surfactant mixtures and ensuring that mean particle sizes are below 100–200 nm. Moreover, in SLN, microphase separations of the bioactive compound from the solidifying lipid matrix can be prevented resulting in an even dispersion of the encapsulated compound in the solid matrix thereby improving chemical and physical stability of the bioactive. In this review article, we will briefly introduce the structure, properties, stability, and manufacturing of solid lipid particles and discuss their emerging use in food science.     

Quetiapine Nanoemulsion for Intranasal Drug Delivery: Evaluation of Brain-Targeting Efficiency

To evaluate the possibility of improved drug delivery of quetiapine fumarate (QTP), a nanoemulsion system was developed for intranasal delivery. Effects of different HLBs of Emalex LWIS 10, PEG 400 and Transcutol P, as co-surfactants, were studied on isotropic region of pseudoternary-phase diagrams of nanoemulsion system composed of capmul MCM (CPM) as oil phase, Tween 80 as surfactant and water. Phase behaviour, globule size, transmission electron microscope (TEM) photographs and brain-targeting efficiency of quetiapine nanoemulsion were investigated. In vitro dissolution study of optimised nanoemulsion formulation, with mean diameter 144?±?0.5 nm, showed more than twofold increase in drug release as compared with pure drug. According to results of in vivo tissue distribution study in Wistar rats, intranasal administration of QTP-loaded nanoemulsion had shorter T _max compared with that of intravenous administration. Higher drug transport efficiency (DTE%) and direct nose-to-brain drug transport (DTP%) was achieved by nanoemulsion. The nanoemulsion system may be a promising strategy for brain-targeted delivery of QTP.     

Development of Timolol-Loaded Galactosylated Chitosan Nanoparticles and Evaluation of Their Potential for Ocular Drug Delivery

This study was conducted to develop timolol maleate (TM)-loaded galactosylated chitosan (GC) nanoparticles (NPs) (TM-GC-NPs) followed by optimization via a four-level and three-factor Box–Behnken statistical experimental design. The optimized nanoparticles showed a particle size of 213.3?±?6.83 nm with entrapment efficiency of 38.58?±?1.31% and drug loading of 17.72?±?0.28%. The NPs were characterized with respect to zeta potential, pH, surface morphology, and differential scanning calorimetry (DSC). The determination of the oil–water partition coefficient demonstrated that the TM-GC-NPs had a high liposolubility at pH 6 as compared to timolol-loaded chitosan nanoparticles (TM-CS-NPs) and commercial TM eye drops. The in vitro release study indicated that TM-GC-NPs had a sustained release effect compared with the commercial TM eye drops. Ocular tolerance was studied by the hen’s egg chorioallantoic membrane (HET-CAM) assay and the formulation was non-irritant and could be used for ophthalmic drug delivery. The in vitro transcorneal permeation study and confocal microscopy showed enhanced penetration, and retention in the cornea was achieved with TM-GC-NPs compared with the TM-CS-NPs and TM eye drops. Preocular retention study indicated that the retention of TM-GC-NPs was significantly longer than that of TM eye drops. The in vivo pharmacodynamic study suggested TM-GC-NPs had a better intraocular pressure (IOP) lowering efficacy and a prolonged working time compared to commercial TM eye drops (P?≤?0.05). The optimized TM-GC-NPs could be prepared successfully promising their use as an ocular delivery system.     

Development, Optimization, and Characterization of Solid Self-Nanoemulsifying Drug Delivery Systems of Valsartan Using Porous Carriers

The present studies entail formulation development of novel solid self-nanoemulsifying drug delivery systems (S-SNEDDS) of valsartan with improved oral bioavailability, and evaluation of their in vitro and in vivo performance. Preliminary solubility studies were carried out and pseudoternary phase diagrams were constructed using blends of oil (Capmul MCM), surfactant (Labrasol), and cosurfactant (Tween 20). The SNEDDS were systematically optimized by response surface methodology employing 3^3-Box–Behnken design. The prepared SNEDDS were characterized for viscocity, refractive index, globule size, zeta potential, and TEM. Optimized liquid SNEDDS were formulated into free flowing granules by adsorption on the porous carriers like Aerosil 200, Sylysia (350, 550, and 730) and Neusilin US2, and compressed into tablets. In vitro dissolution studies of S-SNEDDS revealed 3–3.5-fold increased in dissolution rate of the drug due to enhanced solubility. In vivo pharmacodynamic studies in Wistar rats showed significant reduction in mean systolic BP by S-SNEDDS vis-à-vis oral suspension (p < 0.05) owing to the drug absorption through lymphatic pathways. Solid-state characterization of S-SNEDDS using FT-IR and powder XRD studies confirmed lack of any significant interaction of drug with lipidic excipients and porous carriers. Further, the accelerated stability studies for 6 months revealed that S-SNEDDS are found to be stable without any change in physiochemical properties. Thus, the present studies demonstrated the bioavailability enhancement potential of porous carriers based S-SNEDDS for a BCS class II drug, valsartan.KEY WORDS: BCS, bioavailability, in vitro dissolution, porous carriers, XRD     

Recent Advances in Lipid Nanoparticle Formulations with Solid Matrix for Oral Drug Delivery

Lipid nanoparticles based on solid matrix have emerged as potential drug carriers to improve gastrointestinal (GI) absorption and oral bioavailability of several drugs, especially lipophilic compounds. These formulations may also be used for sustained drug release. Solid lipid nanoparticle (SLN) and the newer generation lipid nanoparticle, nanostructured lipid carrier (NLC), have been studied for their capability as oral drug carriers. Biodegradable, biocompatible, and physiological lipids are generally used to prepare these nanoparticles. Hence, toxicity problems related with the polymeric nanoparticles can be minimized. Furthermore, stability of the formulations might increase than other liquid nano-carriers due to the solid matrix of these lipid nanoparticles. These nanoparticles can be produced by different formulation techniques. Scaling up of the production process from lab scale to industrial scale can be easily achieved. Reasonably high drug encapsulation efficiency of the nanoparticles was documented. Oral absorption and bioavailability of several drugs were improved after oral administration of the drug-loaded SLNs or NLCs. In this review, pros and cons, different formulation and characterization techniques, drug incorporation models, GI absorption and oral bioavailability enhancement mechanisms, stability and storage condition of the formulations, and recent advances in oral delivery of the lipid nanoparticles based on solid matrix will be discussed.     

A New Brain Drug Delivery Strategy: Focused Ultrasound-Enhanced Intranasal Drug Delivery

Central nervous system (CNS) diseases are difficult to treat because of the blood-brain barrier (BBB), which prevents most drugs from entering into the brain. Intranasal (IN) administration is a promising approach for drug delivery to the brain, bypassing the BBB; however, its application has been restricted to particularly potent substances and it does not offer localized delivery to specific brain sites. Focused ultrasound (FUS) in combination with microbubbles can deliver drugs to the brain at targeted locations. The present study proposed to combine these two different platform techniques (FUS+IN) for enhancing the delivery efficiency of intranasally administered drugs at a targeted location. After IN administration of 40 kDa fluorescently-labeled dextran as the model drug, FUS targeted at one region within the caudate putamen of mouse brains was applied in the presence of systemically administered microbubbles. To compare with the conventional FUS technique, in which intravenous (IV) drug injection is employed, FUS was also applied after IV injection of the same amount of dextran in another group of mice. Dextran delivery outcomes were evaluated using fluorescence imaging of brain slices. The results showed that FUS+IN enhanced drug delivery within the targeted region compared with that achieved by IN only. Despite the fact that the IN route has limited drug absorption across the nasal mucosa, the delivery efficiency of FUS+IN was not significantly different from that of FUS+IV. As a new drug delivery platform, the FUS+IN technique is potentially useful for treating CNS diseases.     

综述——纳米材料与药物输递：脂质纳米粒在口服给药系统中的应用

脂质纳米粒是由固体脂肪酸或其酯类制成的一类纳米制剂,其生物相容性好、安全性好,所以在药物递送领域受到广泛关注．难溶性药物、多肽及蛋白质药物由于溶解度、跨膜能力以及稳定性等问题,导致口服生物利用度低,而利用脂质纳米粒作为其载体,口服给药后能显著改善药物的生物利用度,这使得脂质纳米粒在口服给药系统中得到了广泛的应用与研究．本文从口服脂质纳米粒的处方、制备工艺、吸收机制以及应用四个方面对其进行了详细的综述．     

Preparation,Characterization, and Optimization of Folic Acid-Chitosan-Methotrexate Core-Shell Nanoparticles by Box-Behnken Design for Tumor-Targeted Drug Delivery

The objective of this study was to investigate the combined influence of independent variables in the preparation of folic acid-chitosan-methotrexate nanoparticles (FA-Chi-MTX NPs). These NPs were designed and prepared for targeted drug delivery in tumor. The NPs of each batch were prepared by coaxial electrospray atomization method and evaluated for particle size (PS) and particle size distribution (PSD). The independent variables were selected to be concentration of FA-chitosan, ratio of shell solution flow rate to core solution flow rate, and applied voltage. The process design of experiments (DOE) was obtained with three factors in three levels by Design expert software. Box-Behnken design was used to select 15 batches of experiments randomly. The chemical structure of FA-chitosan was examined by FTIR. The NPs of each batch were collected separately, and morphologies of NPs were investigated by field emission scanning electron microscope (FE-SEM). The captured pictures of all batches were analyzed by ImageJ software. Mean PS and PSD were calculated for each batch. Polynomial equation was produced for each response. The FE-SEM results showed the mean diameter of the core-shell NPs was around 304 nm, and nearly 30% of the produced NPs are in the desirable range. Optimum formulations were selected. The validation of DOE optimization results showed errors around 2.5 and 2.3% for PS and PSD, respectively. Moreover, the feasibility of using prepared NPs to target tumor extracellular pH was shown, as drug release was greater in the pH of endosome (acidic medium). Finally, our results proved that FA-Chi-MTX NPs were active against the human epithelial cervical cancer (HeLa) cells.     

中空硅纳米药物递送体系的线粒体靶向性探究

目的:探究中空硅纳米粒在细胞线粒体内的定位。方法:以阿霉素为模型药物及荧光影像分子,通过激光共聚焦显微镜,考察中空硅纳米粒与线粒体分子探针在线粒体内的共定位。通过差速离心法提取线粒体,进一步确认硅纳米粒在线粒体内的聚集。结果:与线粒体分子探针为共定位参照,中孔硅纳米粒在线粒体中分布的皮尔逊系数为0.758±0.033,线粒体提取结果显示,进入细胞的纳米粒有90.01±3.89%分布于线粒体。结论:中空硅纳米粒具有自发聚集于线粒体的能力,可以作为药物靶向递送载体,为线粒体类疾病的治疗提供新的平台。     

Physical-Chemical Characterization and Formulation Considerations for Solid Lipid Nanoparticles

Pure glyceryl mono-oleate (GMO) (lipid) and different batches of GMO commonly used for the preparation of GMO-chitosan nanoparticles were characterized by modulated differential scanning calorimetry (MDSC), cryo-microscopy, and cryo-X-ray powder diffraction techniques. GMO-chitosan nanoparticles containing poloxamer 407 as a stabilizer in the absence and presence of polymers as crystallization inhibitors were prepared by ultrasonication. The effect of polymers (polyvinyl pyrrolidone (PVP), Eudragits, hydroxyl propyl methyl cellulose (HPMC), polyethylene glycol (PEG)), surfactants (poloxamer), and oils (mineral oil and olive oil) on the crystallization of GMO was investigated. GMO showed an exothermic peak at around ?10°C while cooling and another exothermic peak at around ?12°C while heating. It was followed by two endothermic peaks between 15 and 30 C, indicative of GMO melting. The results are corroborated by cryo-microscopy and cryo-X-ray. Significant differences in exothermic and endothermic transition were observed between different grades of GMO and pure GMO. GMO-chitosan nanoparticles resulted in a significant increase in particle size after lyophilization. MDSC confirmed that nanoparticles showed similar exothermic crystallization behavior of lipid GMO. MDSC experiments showed that PVP inhibits GMO crystallization and addition of PVP showed no significant increase in particle size of solid lipid nanoparticle (SLN) during lyophilization. The research highlights the importance of extensive physical-chemical characterization for successful formulation of SLN.     

Multiunit Floating Drug Delivery System of Rosiglitazone Maleate: Development, Characterization, Statistical Optimization of Drug Release and In Vivo Evaluation

A multiunit floating drug delivery system of rosiglitazone maleate has been developed by encapsulating the drug into Eudragit® RS100 through nonaqueous emulsification/solvent evaporation method. The in vitro performances of microspheres were evaluated by yield (%), particle size analysis, drug entrapment efficiency, in vitro floating behavior, surface topography, drug–polymer compatibility, crystallinity of the drug in the microspheres, and drug release studies. In vitro release was optimized by a {3, 3} simplex lattice mixture design to achieve predetermined target release. The in vivo performance of the optimized formulation was evaluated in streptozotocin-induced diabetic rats. The results showed that floating microspheres could be successfully prepared with good yields (69–75%), high entrapment (78-97%), narrow size distribution, and desired target release with the help of statistical design of experiments from very small number of formulations. In vivo evaluation in albino rats suggested that floating microspheres of rosiglitazone could be a promising approach for better glycemic control.     

Paliperidone-Loaded Nanolipomer System for Sustained Delivery and Enhanced Intestinal Permeation: Superiority to Polymeric and Solid Lipid Nanoparticles

Paliperidone (PPD) is the most recent second-generation atypical antipsychotic approved for the treatment of schizophrenia. An immediate release dose causes extrapyramidal side effects. In this work, a novel nanolipomer carrier system for PPD with enhanced intestinal permeability and sustained release properties has been developed and optimized. PPD was successfully encapsulated into a lipomer consisting of a specific combination of biocompatible materials including poly-ε-caprolactone as a polymeric core, Lipoid S75, and Gelucire® 50/13 as a lipid shell and polyvinyl alcohol as a stabilizing agent. The lipomer system was characterized by dynamic light scattering, TEM, DSC, and FTIR. An optimized lipomer formulation possessed a particle size of 168 nm, PDI of 0.2, zeta potential of ?23 mV and an encapsulation efficiency of 87.27%?±?0.098. Stability in simulated gastrointestinal fluids investigated in terms of particle size, zeta potential, and encapsulation efficiency measurements ensured the integrity of the nanoparticles upon oral administration. PPD-loaded nanolipomers demonstrated a superior sustained release behavior up to 24 h and better ex vivo intestinal permeation for PPD compared to the corresponding polymeric and solid lipid nanoparticles and drug suspension. The in vitro hemocompatibility test on red blood cells revealed no hemolytic effect of PPD-loaded lipomers which reflects its safety. The elaborated nanohybrid carrier system represents a promising candidate for enhancing the absorption of PPD providing a 2.6-fold increase in the intestinal permeation flux compared to the drug suspension while maintaining a sustained release behavior. It is a convenient alternative to the commercially available dosage form of PPD.     

Development and Evaluation of Artesunate-Loaded Chitosan-Coated Lipid Nanocapsule as a Potential Drug Delivery System Against Breast Cancer

Artesunate (ART)—a well-known hydrophobic anti-malarial agent was incorporated in a polymer-lipid hybrid nanocolloidal system for anti-cancer therapeutic. The lipid negatively charged nanoemulsion was formulated by modified hot homogenization method then covered with positively charged chitosan via electrostatic interaction to obtain chitosan-coated lipid nanocapsule (ART-CLN). Physical properties of the system were characterized in terms of size, charge, morphology, drug loading capacity, and physical state. In addition, anti-cancer activities were confirmed by conducting MTT assay for ART and ART-CLN on different cancer cell lines. Obtained ART-CLN after coating chitosan revealed positive charge (13.2 ± 0.87 mV), small particle size (160.9 ± 3.5 nm), and spherical shape. High drug entrapment efficiency (95.49 ± 1.13%) and sustained release pattern were observed. Moreover, the good cellular uptake was recorded by flow cytometry as well as confocal image. Finally, ART-CLN exhibited stronger anti-cancer activity than free ART on breast cancer cell lines (MCF-7, MDA-MB-231). These results suggested that by loading ART into lipid core of polymer-lipid hybrid carrier, the activity and physical stability of ART can be significantly increased for cancer chemotherapy.KEY WORDS: anti-cancer, artesunate, breast cancer, chitosan, lipid nanoparticles     

Effects of Formulation Variables on the Particle Size and Drug Encapsulation of Imatinib-Loaded Solid Lipid Nanoparticles

Imatinib (IMT), an anticancer agent, inhibits receptor tyrosine kinases and is characterized by poor aqueous solubility, extensive first-pass metabolism, and rapid clearance. The aims of the current study are to prepare imatinib-loaded solid lipid nanoparticles (IMT-SLN) and study the effects of associated formulation variables on particle size and drug encapsulation on IMT-SLN using an experimental design. IMT-SLN was optimized by use of a “combo” approach involving Plackett-Burman design (PBD) and Box-Behnken design (BBD). PBD screening resulted in the determination of organic-to-aqueous phase ratio (O/A), drug-to-lipid ratio (D/L), and amount of Tween® 20 (Tw20) as three significant variables for particle size (S _z), drug loading (DL), and encapsulation efficiency (EE) of IMT-SLN, which were used for optimization by BBD, yielding an optimized criteria of O/A?=?0.04, D/L?=?0.03, and Tw20?=?2.50%?w/v. The optimized IMT-SLN exhibited monodispersed particles with a size range of 69.0?±?0.9 nm, ζ-potential of ?24.2?±?1.2 mV, and DL and EE of 2.9?±?0.1 and 97.6?±?0.1%?w/w, respectively. Results of in vitro release study showed a sustained release pattern, presumably by diffusion and erosion, with a higher release rate at pH 5.0, compared to pH 7.4. In conclusion, use of the combo experimental design approach enabled clear understanding of the effects of various formulation variables on IMT-SLN and aided in the preparation of a system which exhibited desirable physicochemical and release characteristics.     

Diazepam-Loaded Solid Lipid Nanoparticles: Design and Characterization

The aim of the present study was to investigate the feasibility of the inclusion of a water-insoluble drug (diazepam, DZ) into solid lipid nanoparticles (SLNs), which offer combined advantages of rapid onset and prolonged release of the drug. This work also describes a new approach to prepare suppositories containing DZ-loaded SLN dispersions, as potential drug carrier for the rectal route. Modified high-shear homogenization and ultrasound techniques were employed to prepare SLNs. The effect of incorporation of different concentrations of Compritol® ATO 888 or Imwitor® 900K and Poloxamer 188 or Tween 80 was investigated. Results showed that varying the type or concentration of lipid matrix or surfactant had a noticeable influence on the entrapment efficiencies, particle size, and release profiles of prepared SLNs. Differential scanning calorimetry and X-ray diffraction measurements showed that the majority of SLNs possessed less ordered arrangements of crystals than the corresponding bulk lipids, which was favorable for increasing the drug loading capacity. Transmission electron microscopy and laser diffractometry studies revealed that the prepared nanoparticles were round and homogeneous and 60% of the formulations were less than 500 nm. Additionally, SLN formulations showed significant (P?in vitro release of DZ from the suppositories prepared using DZ-loaded SLN dispersions (equivalent to 2 mg DZ) was significantly (P?相似文献   

Inorganic Porous Nanoparticles for Drug Delivery in Antitumoral Therapy

The use of nanoparticles in oncology to deliver chemotherapeutic agents has received considerable attention in the last decades due to their tendency to be passively accumulated in solid tumors. Besides this remarkable property, the surface of these nanocarriers can be decorated with targeting moieties capable to recognize malignant cells which lead to selective nanoparticle uptake mainly in the diseased cells, without affecting the healthy ones. Among the different nanocarriers which have been developed with this purpose, inorganic porous nanomaterials constitute some of the most interesting due to their unique properties such as excellent cargo capacity, high biocompatibility and chemical, thermal and mechanical robustness, among others. Additionally, these materials can be engineered to present an exquisite control in the drug release behavior placing stimuli-responsive pore-blockers or sensitive hybrid coats on their surface. Herein, the recent advances developed in the use of porous inorganic nanomedicines will be described in order to provide an overview of their huge potential in the look out of an efficient and safe therapy against this complex disease. Porous inorganic nanoparticles have been designed to be accumulated in tumoral tissues; once there to recognize the target cell and finally, to release their payload in a controlled manner.     

Design and Characterization of Metformin-Loaded Solid Lipid Nanoparticles for Colon Cancer

Colorectal cancer is a global concern, and its treatment is fraught with non-selective effects including adverse side effects requiring hospital visits and palliative care. A relatively safe drug formulated in a bioavailability enhancing and targeting delivery platform will be of significance. Metformin-loaded solid lipid nanoparticles (SLN) were designed, optimized, and characterized for particle size, zeta potential, drug entrapment, structure, crystallinity, thermal behavior, morphology, and drug release. Optimized SLN were 195.01?±?6.03 nm in size, ?17.08?±?0.95 mV with regard to surface charge, fibrous in shape, largely amorphous, and release of metformin was controlled. The optimized size, charge, and shape suggest the solid lipid nanoparticles will migrate and accumulate in the colon tumor preventing its proliferation and subsequently leading to tumor shrinkage and cell death.     

固体脂质纳米粒制备方法的研究进展

固体脂质纳米粒是近年来备受关注的一种新型给药系统,本文对近年来固体脂质纳米粒的新型制备方法:薄膜接触器法、超声-挤压过滤法、微通道法、纳米反应嚣法的制备原理,方法及特点进行了讨论,并对现阶段存在的问题及今后的研究方向进行了展望.