The use of SIMS, XPS and in situ AFM to probe the acid catalysed hydrolysis of poly(orthoesters)

Due to poly(orthoesters) being susceptible to acid catalysed hydrolysis, these polymers have attracted considerable interest for the controlled delivery of therapeutic agents within biodegradable matrices. The pH-sensitivity of the poly (orthoesters) has lead to several drug delivery systems being developed, whose rate of drug release is predominantly controlled by the rate of polymer hydrolysis. This study reports on the use of X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and atomic force microscopy (AFM) in a multitechnique approach to probe the effect of acid catalysed hydrolysis at the interface of poly(orthoesters). The molecular specificity of SIMS was successfully employed, suggesting that the preferred mechanism for hydrolysis was via the cleavage of an exocyclic alkoxy bond in the 3,9,-diethylidene-2,4,8,10-tetraoxaspiro [5,5] undecane(DETOSU) unit. The resulting change in the surface chemical structure of the partially hydrolysed poly(orthoester) is such that it was not detectable by XPS analysis. Images acquired from an in situ AFM study of the hydrolysis ofa poly(orthoester), showed changes in the surface morphology, seen as the formation of pits, and an overall thinning of the polymer film. The use of SIMS, XPS and AFM has enabled changes in surface chemistry to be compared with changes in surface morphology. These complementary data, on the behaviour of the polymer during degradation have important implications for the further design of novel biodegradable materials.     

Biodegradable interlocking nails for fracture fixation

Serious problems such as stress shielding, allergic reactions, and corrosion are associated with the use of metallic fracture fixation devices in fractured long bones. Metal implants often are removed during a second retrieval operation after fracture healing has completed. A biocompatible implant that degrades slowly during implantation would obviate the need for a second operation and save the patient from considerable physical, psychologic, and financial discomfort. The biodegradable implant must provide the fractured limb sufficient support for a certain time, allowing early loading. A gradual transfer of load from the biodegradable implant to the bone would result in a better product of bone healing and avoid stress shielding. In an animal model using adult sheep, two types of biodegradable polymer interlocking nails were tested in comparison with a stainless steel interlocking nail. Fracture healing, mechanical properties of the bones, degradation behavior in vivo and in vitro, and tissue response were monitored during a 2 1/2-year followup study. To detect shifts in acid base relations caused by the release of acid compounds, pH measurements were performed. Fracture healing was unimpaired, and the mechanical test results of all three groups were excellent. Histologic analysis showed a mild inflammatory response, but no pH shifts were observed. The results of this study justify additional research on these promising materials.     

Antigen-releasing polymer rings and microspheres stimulate mucosal immunity in the vagina

Several recent studies suggest that direct application of antigen to the vaginal surface may enhance local IgA secretion, but the most effective methods for stimulating immunity at the vaginal surface have not been identified. We used antigen-loaded, biocompatible, vaginal rings to provide controlled and sustained antigen delivery directly to the vaginal mucosal surface. Mice were primed with ferritin, either subcutaneously or orally by ferritin-loaded polymer microspheres, and vaginally boosted by insertion of a ferritin-loaded polymer ring. We found that the vaginal rings were a convenient method for providing controlled antigen delivery to the vagina. Subcutaneously primed mice receiving ferritin-loaded vaginal rings had ferritin-specific IgA in their mucus secretions, while mice receiving blank rings did not. Oral priming with ferritin-loaded poly(lactic acid) microspheres also produced significant levels of ferritin-specific IgA in the vaginal secretions, but required the presence of cholera toxin. Controlled ferritin delivery to mucosal surfaces, either by oral, biodegradable microspheres or vaginal rings, provides a convenient and reliable method for enhancing vaginal IgA production in mice.     

Nodules precipitated by methotrexate in chronic juvenile polyarticular arthritis

Poly-L-lactic acid (PLLA), a biodegradable polymer, is generally considered to be gradually degraded without causing any severe tissue reaction. However, we encountered a patient who developed foreign body gonitis caused by screw breakage after fixation of an intercondylar prominence fracture with PLLA screws. This case suggests that care should be taken when PLLA materials are used to fix intraarticular fractures.     

Interstitial delivery of carboplatin via biodegradable polymers is effective against experimental glioma in the rat

PURPOSE: Carboplatin has shown promise experimentally as an antineoplastic agent against both primary central nervous system (CNS) tumors and several solid tumors that frequently metastasize to the brain. Unfortunately, carboplatin is limited in its clinical use for tumors in the CNS by systemic toxicity and poor penetration through the blood brain barrier. Recent advances in polymer technology have made feasible the intracranial implantation of a biodegradable polymer capable of local sustained delivery of chemotherapy for brain neoplasms. This study assessed the toxicity and efficacy of carboplatin delivered from intracranial sustained release polymers in the treatment of experimental gliomas in rodents. METHODS: Two biodegradable anhydride polymer systems were tested: a copolymer of 1,3-bis-(p-carboxyphenoxy propane) and sebacic acid, and a copolymer of fatty acid dimer and sebacic acid. The polymers were loaded with carboplatin and dose escalation studies evaluating toxicity were performed by implanting carboplatin-loaded polymers into the brains of rats. Next, efficacy was tested. F-98 glioma cells were injected intracranially into rats, and 5 days later polymers containing the highest tolerated doses were implanted at the site of tumor growth. The survival of animals receiving carboplatin-loaded polymer was compared with that of animals receiving intraperitoneal doses of the same agent. RESULTS: Carboplatin-polymer was well tolerated at doses up to 5% loading in both polymer systems. Locally delivered carboplatin effectively prolonged survival of rats with F98 gliomas. Maximal treatment effect was seen with 5% loading of either polymer, with median survival increased threefold over control (P < 0.004). Systemic carboplatin also significantly prolonged survival, but the best intracranial polymer dose was significantly more effective than the best systemic dose tested. CONCLUSIONS: Carboplatin can be safely delivered intracranially by biodegradable sustained- release polymers. This treatment improves survival in rodents with experimental gliomas, with locally delivered carboplatin being more effective than systemic carboplatin.     

Influence of the microencapsulation method and peptide loading on poly(lactic acid) and poly(lactic-co-glycolic acid) degradation during in vitro testing

Three methods were used, namely spray drying, w/o/w solvent evaporation and the aerosol solvent extraction system (ASES), for the preparation of microparticles having the same size range, to study the influence of the preparation method on polymer degradation in vitro (PBS, 37 degrees C, one month). The following five polymers of the biodegradable poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) group were selected: L-PLA, MW 81 200; DL-PLGA 75:25, MW 64-300; DL-PLGA 50:50 MW 52 600; DL-PLGA 50:50 MW 14 500, AND DL-PLGA 50:50, MW 3400, to prepare drug-free and drug-loaded microparticles. Tetracosactide was selected as model peptide. When microparticles were prepared by solvent evaporation, the mean diameter and, more markedly, the drug encapsulation efficiency tended to decrease when decreasing the molecular weight and increasing the proportion of glycolic acid in the polymer. In contrast, no direct influence of the polymer nature on these parameters was observed in spray dried microparticles. Polymer degradation was heterogenous in L-PLA and DL-PLGA 75:25 microparticles and was not influenced by the presence of the drug at a nominal loading of 1% (w/w), when prepared by the three methods (note that with ASES, only L-PLA could be used for microencapsulation). In batches made of DL-PLGA 50:50 MW 52 600, the degradation rate decreased slightly when increasing the drug loading. Only in the case of DL-PLGA 50:50 MW 14 500, the polymer degradation rate for spray dried microparticles was higher compared to that for microparticles prepared by the w/o/w solvent evaporation method. Generally, the degradation rates of the different microparticles followed the expected order: L-PLA相似文献   

Effects of protein-surface interactions on protein ion signals in MALDI mass spectrometry

The influence of polymer surface-protein binding affinity on protein ion signals in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is examined. The surfaces of poly(vinylidene fluoride) and poly(ethylene terephthalate) polymer substrates are modified by pulsed rf plasma deposition of allylamine. By varying the on/off duty cycle of the pulsed rf plasma, the polymer substrate surfaces are coated with thin films having varying densities of surface amine groups. The varying surface amine density is shown to lead to systematic changes in the surface binding affinity for the 125I-radiolabeled peptides angiotensin I and porcine insulin. Unlabeled angiotensin I and porcine insulin are then deposited on the pulsed rf plasma-modified substrates and analyzed by MALDI mass spectrometry. The experimental approach involves applying the peptide to the modified polymer surface in an aqueous phosphate-buffered saline solution and allowing the peptide solution to dry completely under ambient conditions. Subsequently, the MALDI matrix alpha-cyano-4-hydroxycinnamic acid in methanol and 10% trifluoroacetic acid in water are added to the peptide-coated modified polymer surfaces. The results of these studies demonstrate that, for the sample preparation method employed, increases in the surface peptide binding affinity lead to decreases in the peptide MALDI ion signal.     

Excretion of a radiolabelled anticancer biodegradable polymeric implant from the rabbit brain

The elimination of a clinically used anticancer biodegradable polymer implant (Gliadel) in the rabbit brain was studied. The implant is composed of N,N-bis(2-chloroethyl)-N-nitrosourea (BCNU) (1.6 wt%) dispersed in a copolyanhydride matrix of 1,3-bis(p-carboxyphenoxypropane) (CPP) and sebacic acid (SA) in a 20:80 molar ratio. Four groups of rabbits were implanted with wafers loaded with BCNU, one in a 14C-SA-labelled polymer, another in a 14C-CPP-labelled polymer and two groups with 14C-BCNU in a non-labelled polymer, one for BCNU disposition study and one for residual drug study. In the rabbits implanted with the 14C-SA-labelled polymer, approximately 10% of the radioactivity was found in the urine and 2% in the faeces, and about 10% remained in the device 7 d after implantation. In contrast, only 4% of the radioactivity of the 14C-CPP-labelled polymer was found in urine and faeces during this period. However, a drastic increase in the CPP excretion was found after 9 d, and at 21 d, 64% of the implanted 14C-CPP was found in the urine and faeces, and 29% was still in the recovered wafers. Approximately 50% of the BCNU in the wafers was released in 3 d, and over 95% was released after 6 d in the rabbit brain. This study demonstrates that BCNU-loaded polyanhydride is biodegradable and is excreted from the body primarily through the renal system. The water-soluble components SA and BCNU were rapidly excreted, while the insoluble CPP was gradually eliminated after a lag time of 9 d.     

In vivo performance of a new biodegradable polyester urethane system used as a nerve guidance channel

Biodegradable nerve guidance channels (NGCs) represent a promising alternative to current clinical nerve repair procedures. To be suitable as a NGC material, the polymer system should possess elastomeric properties and degrade at a defined rate without interfering with the regenerating environment. Polymers made of non-crystallizable blocks of poly[glycolide-co-(epsilon-caprolactone)]-diol and crystallizable blocks of poly[(R)-3-hydroxybutyric acid-co-(R)-3-hydroxyvaleric acid]-diol (PHB) can be modulated so as to respond to those criteria. Tubular structures were fabricated from three different types of materials containing either 41, 17 or 8 wt% PHB. Nerve regeneration through a 10 mm long NGC using a transected sciatic nerve model with an 8 mm gap was studied in rats at 4, 12 and 24 weeks. Out of 26 implanted NGCs, 23 contained regenerated tissue cables centrally located within the channel lumen and composed of numerous myelinated axons and Schwann cells. No significant difference in the degree of regeneration was observed between the various channel types. The inflammatory reaction associated with the polymer degradation had not interfered with the nerve regeneration process. Macrophages and giant cells surrounded polymer material remnants. A weight loss of 33, 74 and 88% for polymers containing 41, 17 and 8 wt% PHB was observed after 24 weeks by nuclear magnetic resonance (NMR) anaylsis, respectively. In all cases, the polymer fragments had a porous appearance with multiple surface cracks as evidenced by scanning electron microscopical analysis. Guidance channels made of 8 wt% PHB containing polymer displayed the highest degree of degradation at 24 weeks with only small polymer fragments remaining. The present study suggests that this new biodegradable elastomeric polymeric material holds promises for its utilization as nerve guidance channels.     

Spatially controlled cell engineering on biodegradable polymer surfaces

Controlling receptor-mediated interactions between cells and template surfaces is a central principle in many tissue engineering procedures (1-3). Biomaterial surfaces engineered to present cell adhesion ligands undergo integrin-mediated molecular interactions with cells (1, 4, 5), stimulating cell spreading, and differentiation (6-8). This provides a mechanism for mimicking natural cell-to-matrix interactions. Further sophistication in the control of cell interactions can be achieved by fabricating surfaces on which the spatial distribution of ligands is restricted to micron-scale pattern features (9-14). Patterning technology promises to facilitate spatially controlled tissue engineering with applications in the regeneration of highly organized tissues. These new applications require the formation of ligand patterns on biocompatible and biodegradable templates, which control tissue regeneration processes, before removal by metabolism. We have developed a method of generating micron-scale patterns of any biotinylated ligand on the surface of a biodegradable block copolymer, polylactide-poly(ethylene glycol). The technique achieves control of biomolecule deposition with nanometer precision. Spatial control over cell development has been observed when using these templates to culture bovine aortic endothelial cells and PC12 nerve cells. Furthermore, neurite extension on the biodegradable polymer surface is directed by pattern features composed of peptides containing the IKVAV sequence (15, 16), suggesting that directional control over nerve regeneration on biodegradable biomaterials can be achieved.     

Porous-coated titanium implant impregnated with a biodegradable protein delivery system

Tissue ingrowth into porous-coated orthopedic and dental implants is commonly used as a means to achieve long-term fixation of these prostheses. However, the degree of tissue ingrowth is often inadequate and inconsistent. If the pores of these implants are impregnated with a controlled drug release system delivering relevant growth factors, then it might be possible to stimulate more tissue ingrowth. The present study introduces such a system based on biodegradable polymers and investigates its protein release profile and polymer degradation characteristics. Porous coated titanium implants were impregnated with a mixture of a 50%-50% polylactic acid-polyglycolic acid copolymer and a model protein, soybean trypsin inhibitor. Control implants contained only the polymer and no protein. The implants were subjected to hydrolytic degradation in phosphate buffered saline at 37 degrees C for periods of 3, 6, and 11 weeks. The protein release and the mass and molecular weight of the polymer were monitored. The results indicate that the protein is released in three distinct phases and the polymer loses almost all its mass and molecular weight by 11 weeks. There was a significant difference in the polymer degradation characteristics between the control and test implants, which might be the result of some complex polymer-protein interactions.     

Manufacture of porous biodegradable polymer conduits by an extrusion process for guided tissue regeneration

We have fabricated porous, biodegradable tubular conduits for guided tissue regeneration using a combined solvent casting and extrusion technique. The biodegradable polymers used in this study were poly(DL-lactic-co-glycolic acid) (PLGA) and poly(L-lactic acid) (PLLA). A polymer/salt composite was first prepared by a solvent casting process. After drying, the composite was extruded to form a tubular construct. The salt particles in the construct were then leached out leaving a conduit with an open-pore structure. PLGA was studied as a model polymer to analyze the effects of salt weight fraction, salt particle size, and processing temperature on porosity and pore size of the extruded conduits. The porosity and pore size were found to increase with increasing salt weight fraction. Increasing the salt particle size increased the pore diameter but did not affect the porosity. High extrusion temperatures decreased the pore diameter without altering the porosity. Greater decrease in molecular weight was observed for conduits manufactured at higher temperatures. The mechanical properties of both PLGA and PLLA conduits were tested after degradation in vitro for up to 8 weeks. The modulus and failure strength of PLLA conduits were approximately 10 times higher than those of PLGA conduits. Failure strain was similar for both conduits. After degradation for 8 weeks, the molecular weights of the PLGA and PLLA conduits decreased to 38% and 43% of the initial values, respectively. However, both conduits maintained their shape and did not collapse. The PLGA also remained amorphous throughout the time course, while the crystallinity of PLLA increased from 5.2% to 11.5%. The potential of seeding the conduits with cells for transplantation or with biodegradable polymer microparticles for drug delivery was also tested with dyed microspheres. These porous tubular structures hold great promise for the regeneration of tissues which require tubular scaffolds such as peripheral nerve, long bone, intestine, or blood vessel.     

Taurine in rat posterior pituitary: localization in astrocytes and selective release by hypoosmotic stimulation

The design of biomaterials containing specific ligands on the surface offers the possibility of creating materials that can interact with and potentially control mammalian cell behavior. Biodegradable materials further provide the significant advantage that the polymer will disappear in vivo, obviating long-term negative tissue responses as well as the need for retrieval. In earlier studies we synthesized and characterized arginine-glycine-aspartic acid (RGD) peptide-modified poly(lactic acid-co-lysine) (PLAL). In this study, both bulk properties and surface features have been characterized, with a focus on surface analysis as a means of interpreting observed changes in cell behavior. Bulk peptide attachments were performed using 1,1'-carbonyldiimidazole (CDI). Amino groups were measured using colorimetric assays and X-ray photoelectron spectroscopy (XPS). Peptides were measured by incorporating iodine into the peptide as a distinct elemental marker for use with XPS. Typical samples contained 13 +/- 4 pmol/cm2 of amino groups and 4 +/- 0.2 pmol/ cm2 of peptides, as calculated from XPS measurements of nitrogen and iodine. The wettability and crystallinity of the samples were determined by contact angles and differential scanning calorimetry, respectively. Wettability and crystallinity were not altered by the incorporation of lysine or peptides. After incubating bovine aortic endothelial (BAE) cells for 4 h on surfaces with RGD-containing peptides, the mean spread cell area increased from 77 +/- 2 microns2 to 405 +/- 29 microns2 compared to 116 +/- 11 microns2 on poly(lactic acid), 87 +/- 4 microns2 on PLAL, and 105 +/- 4 microns2 on surfaces with RDG-containing (control) peptides. The significance of this work is that the first synthetic interactive, resorbable biomaterial has been developed, and use of this material to control cell behavior has been demonstrated.     

A tissue-engineered conduit for peripheral nerve repair

BACKGROUND: Peripheral nerve repair using autograft material has several shortcomings, including donor site morbidity, inadequate return of function, and aberrant regeneration. Recently, peripheral nerve research has focused on the generation of synthetic nerve guidance conduits that might overcome these phenomena to improve regeneration. In our laboratory, we use the unique chemical and physical properties of synthetic polymers in conjunction with the biological properties of Schwann cells to create a superior prosthesis for the repair of multiply branched peripheral nerves, such as the facial nerve. OBJECTIVES: To create a polymeric facial nerve analog approximating the fascicular architecture of the extratemporal facial nerve, to introduce a population of Schwann cells into the analog, and to implant the prosthesis into an animal model for assessment of regeneration. RESULTS: Tubes of poly-L-lactic acid (molecular weight, 100000) or polylactic-co-glycolic acid copolymer were formed using a dip-molding technique. They were created containing 1, 2, 4, or 5 sublumina, or "fascicular analogs." Populations of Schwann cells were isolated, expanded in culture, and plated onto these polymer films, where they demonstrated excellent adherence to the polymer surfaces. Regeneration was demonstrated through several constructs. CONCLUSIONS: A tubular nerve guidance conduit possessing the macroarchitecture of a polyfascicular peripheral nerve was created. The establishment of resident Schwann cells onto poly-L-lactic acid and polylactic-co-glycolic acid surfaces was demonstrated, and the feasibility of in vivo regeneration through the conduit was shown. It is hypothesized that these tissue-engineered devices, composed of widely used biocompatible, biodegradable polymer materials and adherent Schwann cells, will be useful in promoting both more robust and more precisely directed peripheral nerve regeneration.     

Synthesis and characterization of biodegradable alpha,beta-poly (3-hydroxypropyl, propyl)-DL-asparamide

A biodegradable condensation polymer alpha,beta-poly (3-hydroxypropyl, propyl)-DL-asparamide has been synthesized. Its monomer is DL-aspartic-acid and its spacers are mixture of 3-amino-propanol-1 and propylamine. The polymers thus synthesized are characterized by 1H-NMR, water sorption and intrinsic viscosity. For the purpose of applicability, we have synthesized the polymers with different properties in reference to the molar ratios of propyl amine to 3-amino-hydroxypropyl in polymer synthesis.     

Covalent immobilization of hirudin improves the haemocompatibility of polylactide-polyglycolide in vitro

A biodegradable polymer, poly(D,L-lactide-co-glycolide) RESOMER RG756, was modified by surface immobilization of recombinant hirudin (r-Hir) with glutaraldehyde as coupling reagent to improve the blood contacting properties of the polymer. The activity of immobilized hirudin on the polymer was estimated by a chromogenic assay to about 2.5 ATU r-Hir cm-2. The improvement of the haemocompatibility of the modified RG756 was evaluated in terms of platelet adhesion/activation, whole blood clotting times and clot formation rate. Fluorescence microscopy revealed that surface modification with r-Hir resulted in decreased platelet adhesion and activation. An ELISA for P-selectin, a marker of platelet activation, was used to confirm this result. Clotting time experiments demonstrated significantly prolonged non-activated partial thromboplastin times, and a decreased clot formation rate of whole blood in contact with r-Hir modified RG756 compared with the plain polymer. Comparison of immobilized r-Hir with bound heparin yielded equivalent improvement of blood-contacting properties of the investigated polymers. These in vitro investigations indicate that the immobilization of r-Hir on RG756 is a useful method to improve the blood contacting properties of polylactides/polyglycolides and other polymers as well.     

The potentiation of the effect of radiation treatment by intratumoral delivery of cisplatin

PURPOSE: To compare potentiation of the effects of acute or fractionated radiation by cisplatin when the drug was delivered intratumorally by implanted biodegradable polymer, by intraperitoneal injection, or by intraperitoneal osmotic pump. METHODS AND MATERIALS: Radiation was delivered to a mouse tumor (RIF-1) either in a single dose or in a fractionated regime in conjunction with cisplatin delivered either as a bolus injection, with an osmotic pump, or with a biodegradable polymer rod containing cisplatin. The osmotic pump was implanted in the intraperitoneal cavity of the mouse while the polymer implants were placed directly in the tumor. As the polymer degrades, the drug is released at the treatment site leading to high local concentrations. The osmotic pump, in contrast, leads to prolonged systemic exposure to the drug at low concentrations. Tumor growth delay (TGD) was used as an endpoint in these experiments. RESULTS: The most effective treatment protocol, in terms of potentiating the effects of radiation was cisplatin delivered by polymer implanted 2 days before an acute dose of radiation (growth modification factor [DMF] = 2.2). Comparison of single and multifraction regimes where polymer implant was on the same day as the commencement of treatment showed greater potentiation of the effect of fractionated than of acute radiation treatment with the DMF for fractionated treatment remaining relatively constant (1.5-1.9) for 5, 8, and 12 fraction treatments. Cisplatin delivered via the osmotic pump did not deliver a high enough dose of cisplatin to produce therapeutic effect in this mouse tumor model and had little impact on response to treatment. CONCLUSIONS: Our results indicated that cisplatin delivered intratumorally by biodegradable polymer implant was effective in potentiating the effect of both acute and fractionated radiation. For the fractionated treatments the effect was maintained with increasing fraction numbers and treatment time.     

聚乳酸/羟基磷灰石复合型多孔状可降解生物材料

以乳酸和乙醇酸为原料分别合成了丙交酯(LA)和乙交酯(GA)2种单体,并用单体聚合成了聚丙交酯(PLA)和丙交酯乙交酯共聚物(PLGA),结合用粉末冶金的方法制得的纳米羟基磷灰石粉末(HA),制得了聚乳酸/羟基磷灰石复合型生物可降解的多孔材料。研究结果表明,PLA和PLGA聚合物的产率同聚合过程中的氮压有关,控制造孔剂的粒度,可以得到理想的多孔材料。     

THE AMPHIPHILIC MULTIARM COPOLYMERS BASED ON HYPERBRANCHED POLYESTER AND LYSINE: SYNTHESIS AND SELF-ASSEMBLY

The amphiphilic multiarm copolymers were synthesized through the modification of commercially available hyperbranched polyesters (Boltorn H40) with N-ε-carbobenzoxy-L-Lysine N-carboxyanhydride (ZLys-NCA). After being condensed with N-Boc-phenylalanine (Boc-Nphe) and deprotected the Boc-groups in trifluoroacetic acid (TFA), the original terminal hydroxyl groups were transformed into the amino groups and then initiated the ring-opening polymerization of ZLys-NCA. The hydrophilic poly(L-lysine) was grafted to the surface of Boltorn H40 successfully after the protecting benzyl groups were removed by the HBr solution in glacial acetic acid (33 wt%). The resulting multiarm copolymers were characterized by the 1H-NMR, GPC and FTIR. The arm length calculated by NMR and GPC analysis was about 3 and 13 lysine-units for H40-Phe-PLys1 and H40-Phe-PLys2 respectively. Due to the amphiphilic molecular structure, they displayed ability to self-assemble into spherical micelles in aqueous solution with the average diameter in the range from 70 nm to 250 nm. The CMC of H40-Phe-PLys1 and H40-Phe-PLys2 was 0.013 mg/mL and 0.028 mg/mL, respectively,indicating that H40-Phe-PLysl with shorter ann length is easier to self-assemble than H40-Phe-PLys2 with longer arm length.     

Preparation and characterization of nanocapsules from preformed polymers by a new process based on emulsification-diffusion technique

PURPOSE: The aim of this study was to investigate whether biodegradable nanocapsules could be obtained by the emulsification-diffusion technique. METHODS: This technique consists of emulsifying an organic solution containing an oil, a polymer, and a drug in an aqueous solution of a stabilizing agent. The subsequent addition of water to the system induces solvent diffusion into the external phase, resulting in the formation of colloidal particles. Nanoparticles obtained in this way were characterized by their particle size, zeta potential, isopycnic density and drug entrapment. The shape, surface and structure of the nanocapsules were evaluated by freeze fracture scanning electron microscopy (SEM) and by atomic force microscopy (AFM). RESULTS: Density gradient centrifugation confirmed the formation of nanocapsules. The density was found to be intermediate between those of nanoemulsions and nanospheres. The existence of a unique density band indicated high yields. Nanocapsule density was a function of the original oil/polymer ratio, revealing that the polymer content and, consequently, the wall thickness, can be controlled by this method. SEM and AFM showed the presence of capsular structures with smooth homogeneous walls. The versatility and effectiveness of the method were demonstrated using different lipophilic drug/oil core/wall polymer/partially water-miscible solvent systems. The mechanism of nanocapsule formation was explained as a chemical instability (diffusion stranding) generated during diffusion. CONCLUSIONS: This study demonstrated that the emulsification-diffusion technique enables the preparation of nanocapsules in a simple, efficient, reproducible and versatile manner.