Quantitative Structure-Property Relationship for pH-Triggered Drug Release Performance of Acid-Responsive Four/Six-Arms Star Polymeric Micelles.

PURPOSE: The pH-responsive copolymer micelles are widely used as carriers in drug delivery system, but there are few micro-level mechanistically explorations on the pH-triggered drug release. Here we elucidate the relationship between drug release behavior of four/six-arms star copolymer micelles and the copolymer structures. METHOD: The net cumulative drug release percentage (En) was taken as the dependent variables, block unit autocorrelation descriptors as independent variables. The quantitative structure-property relationship models of drug release from block copolymers were developed at pH 7.4 and 5.0 of two periods (stage I: 0~12 h, stage II: 12~96 h). RESULTS: The models built are of good fitting ability, internal predictive ability, stability and statistically significance. Drug diffusion is mainly influenced by the intra-block force, and micellar erosion by inter-block force. At pH 5.0, lowest unoccupied molecular orbital energy of copolymer unit is the main factor influencing the En. Stage I of drug release is affected by hydrophobic property and stage II by regional polar of copolymer molecules. CONCLUSION: The models present good performance, factors affecting drug release behavior at different pH conditions can offer guidance for the design of copolymer structures to control the drug release behavior of micelles in a targeted and quantitatively way.

Synthesis and evaluation of cholesterol-grafted PEGylated peptides with pH-triggered property as novel drug carriers for cancer chemotherapy.

Multifunctional core/shell micelles were self-assembled from triblock copolymers poly(ethylene glycol) methyl ether-b-peptide-g-cholesterol (mPEG-b-P-g-Chol) and used as the doxorubicin delivery carriers for cancer chemotherapy. The copolymers were designed and synthesized successfully based on peptides containing histidine residues (pH-trigger) with different topological structures. The peptides were modified by mPEG (hydrophilic) and cholesterol motifs (hydrophobic) on the terminus, resulting in pH-sensitive amphiphilic copolymers. The critical micelle concentrations (CMCs) of the micelles were determined as 4.79, 2.50 and 1.86mg/L for the linear, Y-shape and fork-shape copolymers, respectively, demonstrating the formation of micelle even at low concentration. The pKb values of three copolymers were found to be around 6.1-6.3 by potentiometric titration test, showing the satisfied pH-sensitivity. The average diameter and zeta potential of blank micelles were 170nm and +20mV at pH 7.4, and increased to 250nm and +35mV at pH 5.0. DOX was loaded into the core of polymeric micelles by dialysis method, and the drug loading capacity slightly increased when the copolymer topological structure changed from linear to Y- and fork-shape. The drug release rate from the system was obviously influencing by the pH values according to the results of in vitro DOX release experiment. Moreover, to investigate the structure-property relationship, the drug release mechanism was preliminarily explored by the semi-empirical equations. Toxicity test showed that three copolymers had bare toxicity whereas the DOX-loaded micelles remained high cytotoxicity for tumor cells. The results indicate the synthesized copolymers might be a potential hydrophobic drug delivery carrier for cancer targeting therapy with controlled drug release.

Dissipative particle dynamics studies of doxorubicin-loaded micelles assembled from four-arm star triblock polymers 4AS-PCL-b-PDEAEMA-b-PPEGMA and their pH-release mechanism.

Dissipative particle dynamics (DPD) simulation was applied to investigate the microstructures of the micelles self-assembled from pH-sensitive four-arm star triblock poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) (4AS-PCL-b-PDEAEMA-b-PPEGMA). In the optimized system, the micelles have a core-mesosphere-shell three-layer structure. The drug-loading process and its distribution at different formulations in the micelles were studied. The results show that DOX molecules distributed in the core and the interface between the core and the mesosphere, suggesting the potential encapsulation capacity of DOX molecules. More drugs were loaded in the micelles with the increase in DOX, and the size of micelles became larger. However, some openings start to generate on the PEG shell when the DOX reaches a certain concentration. By changing the pH values of the system, different morphologies of the micelles were acquired after the pH-sensitive blocks PDEAEMA were protonated, the mechanism of which was also analyzed through correlating functions. The results indicated that the sudden increase in solubility parameter of the pH-sensitive blocks and the swelling of the micelles were the key factors on the change of morphologies. Furthermore, with the decrease in pH value, the number and size of the cracks on the surface of the micelles were larger, which may have a direct effect on the drug release. In conclusion, 4AS-PCL-b-PDEAEMA-b-PPEGMA has great promising applications in delivering hydrophobic anticancer drugs for improved cancer therapy.

[A short term clinical evaluation of IPS e.max Press all-ceramic crowns].

PURPOSE: The aim of this study was to evaluate the clinical effect of IPS e.max Press crowns. METHODS: A total of 127 IPS e.max Press crowns was placed in forty-one patients from 2007 to 2009. The crowns were evaluated with a modified USPHS criteria for color match, marginal discoloration, fracture, secondary caries, marginal adaptation and gingival health for a period of 12 to 42 months, with a mean of 28 months after insertion. A,B,C and D ratings were assigned. RESULTS: 94.49% of the crowns were rated as A and 5.51% rated as B for color match and marginal adaptation. 1.57% of the crowns was detected with marginal discoloration and one crown(0.79%) was detected with veneer chipping. No secondary caries was detected, and 93.70% of the crowns were rated as A, 4.72% rated as B and 1.58% rated as C for gingival health. CONCLUSION: IPS e.max Press crowns exhibit excellent clinical performance over a mean evaluation period of 28 months.