乳酸-羟基乙酸共聚物载药纳米粒的制备及体外释药性

背景:医用纳米粒作为药物传递的新型载体,目前已经成为医药领域研究的重点。目的:构建以生物可降解材料乳酸-羟基乙酸共聚物为载体,负载抗肿瘤药物5-氟尿嘧啶的载药纳米粒。方法:利用复乳-溶剂挥发法制备乳酸-羟基乙酸共聚物载药纳米粒。场发射扫描电子显微镜观察纳米粒表面形态;激光粒度分析仪测定粒径分布并计算成球率;紫外分光光度计测定5-氟尿嘧啶载药量、包封率,并对体外释药进行评估。结果与结论:纳米粒呈球性,平均粒径为(186±14)nm,成球率、载药量和包封率分别为70.8%、6.6%、28.1%,体外释药有突释现象,24h内5-氟尿嘧啶累积释药量达36.2%,10d达83.6%。提示成功制备乳酸-羟基乙酸共聚物载药纳米粒,其具有缓释效应。     

Molecular design of biodegradable polymeric micelles for temperature-responsive drug release.

We designed thermo-responsive and biodegradable polymeric micelles for an ideal drug delivery system whose target sites are where external stimuli selectively release drugs from the polymeric micelles. The thermo-responsive micelles formed from block copolymers that were composed both of a hydrophobic block and a thermo-responsive block. Poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) showing a lower critical solution temperature (LCST) around 40 degrees C was synthesized for the thermo-responsive block, while biodegradable poly(D,L-lactide), poly(epsilon-caprolactone), or poly(D,L-lactide-co-epsilon-caprolactone) was used for the hydrophobic block. By changing both the block lengths of the poly(D,L-lactide)-containing block copolymers, physical parameters such as micelle diameter and critical micelle concentration were varied. On the other hand, the choice of the hydrophobic block was revealed to be critical in relation to both on the thermo-responsive release of the incorporated anti-cancer drug, doxorubicin, and the temperature-dependent change of the hydrophobicity of the micelles' inner core. One polymeric micelle composition successfully exhibited rapid and thermo-responsive drug release while possessing a biodegradable character.     

乳酸-羟基乙酸共聚物载药纳米粒的制备及体外释药性

背景：医用纳米粒作为药物传递的新型载体,目前已经成为医药领域研究的重点。目的：构建以生物可降解材料乳酸-羟基乙酸共聚物为载体,负载抗肿瘤药物5-氟尿嘧啶的载药纳米粒。方法：利用复乳-溶剂挥发法制备乳酸-羟基乙酸共聚物载药纳米粒。场发射扫描电子显微镜观察纳米粒表面形态;激光粒度分析仪测定粒径分布并计算成球率;紫外分光光度计测定5-氟尿嘧啶载药量、包封率,并对体外释药进行评估。结果与结论：纳米粒呈球性,平均粒径为（186±14）nm,成球率、载药量和包封率分别为70.8%、6.6%、28.1%,体外释药有突释现象,24h内5-氟尿嘧啶累积释药量达36.2%,10d达83.6%。提示成功制备乳酸-羟基乙酸共聚物载药纳米粒,其具有缓释效应。     

“刚／柔”可控的新型聚氨酯材料的制备与表征

背景：生物可降解聚氨酯是生物医用材料领域研究的-个热点。基于聚乳酸的智能型聚聚氨在生物医学领域具有广阔的应用前景。目的：以D，L-丙交酯、1，6-六亚甲基二异氰酸酯、1，4-丁二醇和1，4-丁二胺作为原料，从分子设计角度出发，制备-种基于聚乳酸的“刚，柔”可控多嵌段聚氨酯材料。方法：采用熔融聚合法首先合成羟基封端聚（D，L-乳酸），加入六亚甲基二异氰酸酯作为交联剂，再聚合得到基于聚（D，L-乳酸）的聚氨酯。通过红外光谱仪、核磁共振波谱仪、热重，差热综合热分析仪、万能材料试验机等仪器对羟基封端聚（D，L-乳酸）及基于聚（D，L-乳酸）的聚氨酯进行结构表征和性能测试。结果与结论：实验发现，经熔融聚合后的产物与预期分子结构设计相符，通过调节材料中反应物的比例调节硬段和软段的比例，从而实现调控该材料“刚，柔”转变程度（断裂伸长率从472％-112％）和“刚，柔”转变温度（玻璃化转变温度从36．33-44．04℃）。结果表明由可降解生物材料制备的基于聚（D，L-乳酸）的聚氨酯材料具备热敏效应，且其断裂伸长率和玻璃化转变温度可控，具备应用于生物医学工程领域的基础。     

New biodegradable polymers for injectable drug delivery systems.

Many biodegradable polymers were used for drug delivery and some are successful for human application. There remains fabrication problems, such as difficult processability and limited organic solvent and irreproducible drug release kinetics. New star-shaped block copolymers, of which the typical molecular architecture is presented, results from their distinct solution properties, thermal properties and morphology. Their unique physical properties are due to the three-dimensional, hyperbranched molecular architecture and influence microsphere fabrication, drug release and degradation profiles. We recently synthesized thermosensitive biodegradable hydrogel consisting of polyethylene oxide and poly(L-lactic acid). Aqueous solution of these copolymers with proper combination of molecular weights exhibit temperature-dependent reversible sol-gel transition. Desired molecular arrangements provide unique behavior that sol (at low temperature) form gel (at body temperature). The use of these two biodegradable polymers have great advantages for sustained injectable drug delivery systems. The formulation is simple, which is totally free of organic solvent. In sol or aqueous solution state of this polymer solubilized hydrophobic drugs prior to form gel matrix.     

Modulated release of IdUrd from poly (D,L-lactide-co-glycolide) microspheres by addition of poly (D,L-lactide) oligomers.

This paper reports the release characteristics of a radiosensitizer, 5-iodo-2'-deoxyuridine (IdUrd), from poly (D,L-lactide-co-glycolide) 50: 50 (PLGA) microparticles obtained by a phase separation technique. Poly (D,L-lactide) oligomers (D,L-PLA) were incorporated into the PLGA matrix in order to accelerate the overall drug release rate and regulate the triphasic release profile exhibited by the standard PLGA microparticles. For D,L-PLA (800), the burst effect was large and the IdUrd release was complete between 28 and 35 days. These results were attributed to rapid pore formation on the periphery of the microsphere in the early stages of incubation, due to hydrosolubility of the smallest oligomers (D,L-PLA (800)). In the case of D,L-PLA (1,100), drug release occurred over a six week period, the standard time course of conventional radiation therapy. The period during which the radiosensitizer was incorporated in human brain tumor cell nuclei after its entrapment in biodegradable microspheres was determined by using an organotypical tissue culture. The presence of radiosensitizer in the DNA of tumor cell nuclei was detected by immunohistochemical labelling of tumor fragments. IdUrd release from standard microspheres (7+/-0.5 weeks) was longer than from oligomer-containing batches. For D,L-PLA (800)-containing microspheres, the radiosensitizer was entirely released within 4. 5+/-0.5 weeks. The microspheres containing D,L-PLA (1,100) allowed an IdUrd release over a 5 to 6 week period. The ex vivo data were consistent with the in vitro findings in terms of release duration.     

Characterization and in vitro degradation of poly(2,3-(1,4-diethyl tartrate)-co-2,3-isopropyliden tartrate).

In the present study, a less known polyester based on tartaric acid was characterized with respect to its degradation mechanism. Poly(2,3-(1,4-diethyl tartrate)-co-2,3-isopropyliden tartrate) (PTA) differs from commonly used biodegradable polyesters, such as poly(lactides-co-glycolides) (PLGA) by the presence of additional cleavable bonds in the polymer side chains. This modification results in different polymer properties and influences polymer degradation. The hydrolytic degradation of PTA was studied in parallel to PLGA using disc-shape matrices, which were obtained by compression-molding. The discs were incubated in pH 7.4 phosphate buffer solution at 37 degrees C. The degraded samples were characterized for percentage mass loss, water absorption, decay of molecular weight and change in glass transition temperature. The results demonstrate that the degradation of PTA proceeds via bulk erosion similar to PLGA. However, the degradation of PTA implants is characterized by a rapid mass loss within a short period of time appearing after a definite lag phase without remarkable mass loss. This makes the polymer promising for pulsatile drug release systems.     

Thermo-responsive drug delivery from polymeric micelles constructed using block copolymers of poly(N-isopropylacrylamide) and poly(butylmethacrylate).

To achieve a combination of spatial specificity in a passive manner with a stimuli-responsive targeting mechanism, a temperature-responsive polymeric micelle is prepared using block copolymers of (poly(N-isopropylacrylamide-b-butylmethacrylate) (PIPAAm-PBMA)). The micelle inner core formed by self-aggregates of PBMA segments successfully loaded with a drug (adriamycin), and the outer shell of PIPAAm chains played a role of stabilization and initiation of micellar thermo-response. Optimum conditions were investigated for the micelle formation and drug loading into the inner cores in a view of micellar stability and function as drug carriers. Outer shell hydrophilicity that prevents inner core interaction with biocomponents and other micelles can be suddenly switched to hydrophobic at a specific site by local temperature increase beyond the LCST (lower critical solution temperature) (32.5 degrees C). These micelles showed reversible structural changes allowing drug release upon heating/cooling thermal fluctuations through the LCST. Polymeric micelles incorporated with adriamycin showed a dramatic thermo-responsive on/off switching behavior for both drug release and in vitro cytotoxicity according to the temperature responsive structural changes of a micellar shell structure. The reversible and sensitive thermo-response of the micelle opens up opportunities to construct a novel drug delivery system in conjunction with localized hyperthermia.     

Poly(D,L-lactide-co-ethyl ethylene phosphate)s as new drug carriers.

Many biodegradable polymers have been developed for controlled drug delivery. The plethora of drug therapies and types of drugs demand different formulations, fabrications conditions and release kinetics. No one single polymer can satisfy all the requirements. To extend the properties of poly(D,L-lactide) (PLA), we synthesized copolymers of PLA and poly(ethylethylene phosphate) (PEEP) by ring-opening polymerization using Al(Oipr)3 as the initiator. The copolymers were structurally characterized by IR and 1H NMR. DSC data confirmed the formation of random microphase structure in all the copolymers, and showed a decrease of Tg from 43.2 to -22.6 degrees C when the molar content of ethylethylene phosphate (EEP) increased from 5 to 40%. The hydrophilicity of the copolymers increased with EEP content. In contrast to the degradation behavior of PLA, disc samples made of PLAEEP90 showed a linear weight loss profile in PBS (pH 7.4) at 37 degrees C. BSA microspheres using PLAEEP90 were prepared by double-emulsion method, yielding a loading level of 4.3% and a loading efficiency of 75%. The BSA release profile consisted of an initial burst (9%) on the first day, followed by a daily 4% release for the following 40 days, resulting in 91% of the BSA release in a near linear manner. The released BSA remained intact according to SDS-PAGE data. Cytotoxicity and histopathology studies showed low toxicity in HeLa cells and good tissue biocompatibility in mouse brain, respectively. PLAEEP is a promising biodegradable polymer for controlled drug delivery.     

Protein release microparticles based on the blend of poly(D,L-lactic-co-glycolic acid) and oligo-ethylene glycol grafted poly(L-lactide).

Bovine serum albumin (BSA), a model protein drug, was encapsulated with a microparticle based on the blend of poly(D,L-lactic-co-glycolic acid) (PLGA) and poly(L-lactide)-g-oligo(ethylene glycol) (PLLA-g-oligoEG). Effects of PLLA-g-oligoEG in the blend on degradation, characteristic properties, and release behavior of the microparticle were studied. Drug loading efficiency increased with increase in the graft frequency of oligoEG in the graft copolymer in the blend. The release of BSA was found to be more efficient for microparticles based on the blend than on the PLGA, which is due to the faster protein diffusion through the swollen phase of the hydrogel-like structure. The microparticles based on the blend showed a slower degradation and a lower pH shift compared to that of PLGA.     

A poly(ethylene glycol)-based surfactant for formulation of drug-loaded mucus penetrating particles

Mucosal surfaces are protected by a highly viscoelastic and adhesive mucus layer that traps most foreign particles, including conventional drug and gene carriers. Trapped particles are eliminated on the order of seconds to hours by mucus clearance mechanisms, precluding sustained and targeted drug and nucleic acid delivery to mucosal tissues. We have previously shown that polymeric coatings that minimize adhesive interactions with mucus constituents lead to particles that rapidly penetrate human mucus secretions. Nevertheless, a particular challenge in formulating drug-loaded mucus penetrating particles (MPP) is that many commonly used surfactants are either mucoadhesive, or do not facilitate efficient drug encapsulation. We tested a novel surfactant molecule for particle formulation composed of Vitamin E conjugated to 5 kDa poly(ethylene glycol) (VP5k). We show that VP5k-coated poly(lactide-co-glycolide) (PLGA) nanoparticles rapidly penetrate human cervicovaginal mucus, whereas PLGA nanoparticles coated with polyvinyl alcohol or Vitamin E conjugated to 1 kDa PEG were trapped. Importantly, VP5k facilitated high loading of paclitaxel, a frontline chemo drug, into PLGA MPP, with controlled release for at least 4 days and negligible burst release. Our results offer a promising new method for engineering biodegradable, drug-loaded MPP for sustained and targeted delivery of therapeutics at mucosal surfaces.     

Double-walled microspheres for the sustained release of a highly water soluble drug: characterization and irradiation studies.

Composite double-walled microspheres with biodegradable poly(L-lactic acid) (PLLA) shells and poly(D,L-lactic-co-glycolic acid) (PLGA) cores were fabricated with highly water-soluble etanidazole entrapped within the core as solid crystals. This paper discusses the characterization, in vitro release and the effects of irradiation on this class of microsphere. Through the variation of polymer mass ratios, predictable shell and core dimensions could be fabricated and used to regulate the release rates. A direct and simple method was devised to determine the composition of the shell and core polymer based on the different solubilities of the polymer pair in ethyl acetate. A distribution theory based on solubility parameter explains why highly hydrophilic etanidazole has the tendency to be distributed consistently to the more hydrophilic polymer. Release profiles for normal double-walled samples have about 80% of drug released over 10 days after the initial time lag, while for irradiated double-walled samples, the sustained release lasted for more than 3 weeks. Although sustained release was short of the desired 6-8 weeks required for therapy, a low initial burst of less than 5% and time lags that can be manipulated, allows for administration of these microspheres together with traditional ones to generate pulsatile or new type of releases. The effects of irradiation were also investigated to determine the suitability of these double-walled microspheres as delivery devices to be used in conjunction with radiotherapy. Typical therapeutic dosage of 50 Gy was found to be too mild to have noticeable effects on the polymer and its release profiles, while, sterilization dosages of 25 kGy, lowered the glass transition temperatures and crystalline melting point, indirectly indicating a decrease in molecular weight. This accelerated degradation of the polymer, hence releasing the drug.     

Programmable delivery of hydrophilic drug using dually responsive hydrogel cages.

Micro-capsules normally encapsulate therapeutic agents only inside their cavities. In this paper, we report on the synthesis of dually responsive poly(N-isopropylacrylamide) (PNiPAM)-co-acrylic acid (AA) hydrogel cages sub-micrometer in size and the use of these cages as drug carriers. The cavity structure of the cages can enhance volume phase transition compared to solid gel particles, thus favoring drug loading and release. TEM images and FT-IR spectra confirmed that the model drug isoniazid (INH) is located in two regions: within the shell and inside the cavity of the cages. The drugs residing in the shell can form hydrogen bonds with the cage matrix, while the drugs in the cavity are interaction free with the carrier. This difference from the residency of drugs exploited to a structure induced drug release which was programmable controlled by external pH and temperature. In vitro drug release studies showed that in a neutral medium (pH=7.4), major drugs were preserved within the shell, while in an acidic medium (pH=1.2), nearly all of the drugs were released due to the dissociation of hydrogen bonds.     

Localization of bovine serum albumin in double-walled microspheres.

Phase separation of binary blends of various combinations of poly (L-lactide) (PLA), and poly (D,L-lactide-co-glycolide) (PLGA), was investigated using differential scanning calorimetry (DSC). Based on this phase separation phenomenon, double-walled microspheres were fabricated. A model agent, bovine serum albumin (BSA) labeled with fluorescein isothiocyanate (FITC-BSA) was localized in each layer. Scanning electron microscopy (SEM) and fluorescence microscopy (FM) were used to assess the formation of double-walled microspheres and the localization of the drug, respectively. When a 1:1 polymer ratio was used, the FITC-BSA was localized in the outer layer. When the relative ratio of PLGA to PLA was increased to 3:1 using the same overall polymer concentration, the FITC-BSA was localized in the inner core. Release studies were carried out to evaluate the advantage of double-walled microspheres compared to single walled microspheres. Microspheres made with FITC-BSA localized in the inner core exhibited a significantly lower initial release rate compared to microspheres where the drug was located in the outer layer, or compared to microspheres made from PLA only. Hence microspheres with a double-walled morphology have the potential for therapeutic use where a high burst might be detrimental.     

Biodegradable polymeric microspheres with "open/closed" pores for sustained release of human growth hormone.

A new approach for attaining sustained release of protein is introduced, involving a pore-closing process of preformed porous PLGA microspheres. Highly porous biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres were fabricated by a single water-in-oil emulsion solvent evaporation technique using Pluronic F127 as an extractable porogen. Recombinant human growth hormone (rhGH) was incorporated into porous microspheres by a simple solution dipping method. For their controlled release, porous microspheres containing hGH were treated with water-miscible solvents in aqueous phase for production of pore-closed microspheres. These microspheres showed sustained release patterns over an extended period; however, the drug loading efficiency was extremely low. To overcome the drug loading problem, the pore-closing process was performed in an ethanol vapor phase using a fluidized bed reactor. The resultant pore-closed microspheres exhibited high protein loading amount as well as sustained rhGH release profiles. Also, the released rhGH exhibited structural integrity after the treatment.     

Anti-tumor drug delivery of pH-sensitive poly(ethylene glycol)-poly(L-histidine-)-poly(L-lactide) nanoparticles

pH-sensitive poly(ethylene glycol)-poly(l-histidine)-poly(L-lactide) (PEG-PH-PLLA) nanoparticles were prepared and used as carriers for anti-tumor drug delivery. The morphology and properties of the nanoparticles such as pH sensitivity, zeta potential and mean diameters were investigated. The cytotoxicity of PEG-PH-PLLA nanoparticles was evaluated. Doxorubicin (DOX) was encapsulated in the nanoparticles to explore the release profile. The drug-loaded nanoparticles were incubated with HepG2 cells to study the in vitro anti-tumor effect. The results showed the sizes of both blank nanoparticles and drug-loaded nanoparticles in pH 7.4 were smaller than those of nanoparticles in pH 5.0, and the mean diameter of drug-loaded nanoparticles was much bigger than that of blank nanoparticles. The PEG-PH-PLLA nanoparticles were nontoxic to both NIH 3T3 fibroblasts and HepG2 cells. The release profile showed that the release of DOX in pH 5.0 was much faster than that in pH 7.4. The in vitro experiments demonstrated that the anti-tumor effect of drug-loaded nanoparticles was preferable to free doxorubicin. The pH-sensitive PEG-PH-PLLA nanoparticles are promising carriers for anti-tumor drug delivery.     

载5-氟尿嘧啶纳米微球治疗荷H22腹水瘤小鼠的实验研究

目的 观察自制载5-氟尿嘧啶(5-FU)纳米微粒对荷H22小鼠恶性腹水的治疗作用以及对小鼠生存期、小鼠体重、H22细胞周期、小鼠肝脏毒性的影响.方法 168只荷H22腹水瘤昆明小鼠随机分为7组,即空白对照组、溶剂对照组、辅料对照组、5-FU阳性药组(5 d共3 mg),低(5 d共0.12 mg)、中(5 d共0.6 mg)、高(5 d共3 mg)剂量微粒缓释组.药物经腹腔注入,微粒缓释组只给药一次,其他组均为连续给药5 d,每天一次.观察各组小鼠生存情况,比较各组小鼠平均生存时间、小鼠体重、细胞增殖指数(PI)以及肝脏毒性.结果 与对照组比较,微粒缓释组能明显提高小鼠的生存时间(P<0.05)、减小小鼠体重(P<0.05)和增殖指数(PI)、减小肝毒性.与阳性药物组比较,中、高剂量微粒缓释组对小鼠H22腹水瘤的抑制作用增加,表现为明显延长生存时间(P<0.05)、减缓小鼠体重增长(P<0.05)和减小增殖指数(PI),药物对肝脏毒性影响也有减小,表现为中剂量组肝脏毒性明显降低,高剂量组肝脏毒性与阳性药物组相当.结论 5-FU载药缓释纳米微球在治疗荷H22腹水瘤小鼠时可以在小鼠体内持续释放,与阳性药物组相比减少了给药次数,增加了药物对H22肿瘤细胞的抑制作用,并减小对肝脏的毒性.     

Protein encapsulation into biodegradable microspheres by a novel S/O/W emulsion method using poly(ethylene glycol) as a protein micronization adjuvant.

A new method for preparing protein-loaded biodegradable microspheres by a process involving solid-in-oil-in-water (S/O/W) emulsion was established using poly(ethylene glycol) (PEG). In the first step, a protein solution was lyophilized with PEG, which resulted in the formation of spherical protein microparticles, less than 5 microm in diameter, dispersed in a continuous PEG phase. This process was well explained by the aqueous phase separation phenomenon induced by freezing-condensation. Since this lyophilizate could be directly dispersed in an organic phase containing biodegradable polymer by dissolving PEG with methylene chloride, a conventional in-water drying method could be adopted in the second step. Through this S/O/W emulsion process, horseradish peroxidase was effectively entrapped into monolithic-type microspheres of poly(DL-lactic-co-glycolic acid) (PLGA), without significant loss of activity. Bovine superoxide dismutase (bSOD), as another model protein, could be encapsulated into reservoir-type microspheres by the 'polymer-alloys method' using both poly(DL-lactic acid) (PLA) and PLGA. The initial release of bSOD from this reservoir-type microsphere was efficiently reduced. Further, the bSOD release kinetics could be suitably modified by adjusting the loading amounts of PEG or polymer composition. In this study, the multi-functional nature of PEG was successfully utilized in the preparation and designing of protein-loaded microspheres.     

Synthesis and characterization of poly(ethyl-2-cyanoacrylate) nanoparticles with a magnetic core.

A method is described to prepare composite colloidal nanoparticles, consisting of a magnetic core (magnetite) and a biodegradable polymeric shell (poly(ethyl-2-cyanoacrylate) or PE-2-CA). The method is based on the so-called anionic polymerization procedure, often used in the synthesis of PE-2-CA nanospheres designed for drug delivery. In the present work, the heterogeneous structure of the particles can confer both magnetic-field responsiveness and potential applicability as a drug carrier. In order to investigate to what extent this target is achieved, we compare the structure, chemical composition, and surface properties of the core/shell particles with those of both the nucleus and the coating material. This preliminary study shows that the synthetic new material displays an intermediate behavior between that of magnetite and PE-2-CA spheres. Thus, electrophoresis measurements as a function of pH and as a function of KNO3 concentration, show great similarity between the core/shell and pure polymer nanoparticles. A similar conclusion is reached when a surface thermodynamic study is performed on the three types of particles: the electron-donor component of the surface free energy of the solids is the quantity that appears to be most sensitive to the surface composition. The fact that PE-2-CA is close to being a non-polar material gives rise to a measurable decrease in the electron-donor component of the surface free energy of core/shell particles as compared to magnetite.     

In-vivo and clinical evaluations of poly(L-lactide) plates and screws for use in maxillofacial traumatology

The possible application of biodegradable osteosynthesis material presents many advantages over conventional metallic devices. This study was concerned with the in-vivo evaluation of poly(L-lactide) with different molecular weights, in particular in regard to their mechanical strength, changes of molecular weight and their tissue response. It was found that poly(L-lactide) has acceptable mechanical strength for use in maxillofacial traumatology. In another trial, mandibular fractures of 12 dogs were successfully stabilized with resorbable plates and screws made of this polymer. Finally, the results of a pilot study of its clinical application in the treatment of zygomatic fractures have been presented.