Crystallization,morphology, and mechanical behavior of polylactide/poly(ε‐caprolactone) blends

Optically pure polylactides, poly(L ‐lactide) (PLLA) and poly(D ‐lactide) (PDLA), were blended across the range of compositions with poly(ε‐caprolactone) (PCL) to study their crystallization, morphology, and mechanical behavior. Differential scanning calorimetry and dynamic mechanical analysis (DMA) of the PLA/PCL blends showed two T_gs at positions close to the pure components revealing phase separation. However, a shift in the tan δ peak position by DMA from 64 to 57°C suggests a partial solubility of PCL in the PLA‐rich phase. Scanning electron microscopy reveals phase separation and a transition in the phase morphology from spherical to interconnected domains as the equimolar blend approaches from the outermost compositions. The spherulitic growth of both PLA and PCL in the blends was followed by polarized optical microscopy at 140 and 37°C. From tensile tests at speed of 50 mm/min Young's modulus values between 5.2 and 0.4 GPa, strength values between 56 and 12 MPa, and strain at break values between 1 and 400% were obtained varying the blend composition. The viscoelastic properties (E′ and tan δ) obtained at frequency of 1 Hz by DMA are discussed and are found consistent with composition, phase separation, and crystallization behavior of the blends. POLYM. ENG. SCI., 46:1299–1308, 2006. © 2006 Society of Plastics Engineers     

Advances and Perspectives in Dental Pulp Stem Cell Based Neuroregeneration Therapies

Human dental pulp stem cells (hDPSCs) are some of the most promising stem cell types for regenerative therapies given their ability to grow in the absence of serum and their realistic possibility to be used in autologous grafts. In this review, we describe the particular advantages of hDPSCs for neuroregenerative cell therapies. We thoroughly discuss the knowledge about their embryonic origin and characteristics of their postnatal niche, as well as the current status of cell culture protocols to maximize their multilineage differentiation potential, highlighting some common issues when assessing neuronal differentiation fates of hDPSCs. We also review the recent progress on neuroprotective and immunomodulatory capacity of hDPSCs and their secreted extracellular vesicles, as well as their combination with scaffold materials to improve their functional integration on the injured central nervous system (CNS) and peripheral nervous system (PNS). Finally, we offer some perspectives on the current and possible future applications of hDPSCs in neuroregenerative cell therapies.     

Novel poly(vinyl alcohol)-g-poly(hydroxy acid) copolymers: Synthesis and characterization

Poly(vinyl alcohol) (PVA) was reacted with three hydroxy acids (HA), namely D,L-lactic acid (LA), glycolic acid (GA) and D,L-3-hydroxybutyric acid (HB). The graft copolymers obtained were thoroughly characterized by ¹H and ¹³C NMR, FTIR, and DSC. Copolymer compositions were in the range 14–45 mol% HA with average lateral chain lengths in the range 1.1–1.3. The CO stretching band, arising from the lateral polyester chains, presents significant differences from that of pure polyesters. In case of the VALA and VAGA copolymers, carbonyl groups are almost completely interassociated with hydroxyl groups and as a result the carbonyl band presents a single contribution; however, splitting appears in VAHB. The band at about 1735 cm^?1 already observed for Poly(3-hydroxybutyrate) P3HB was reexamined in the light of molecular models for VAHB and the splitting observed was attributed to C–H???OC and to O–H???OC hydrogen bonding. The thermal analysis of copolymers demonstrates that esterification suppresses crystallinity and increases free volume, both accounting for a Tg reduction with regard to PVA. The stronger intermolecular hydrogen bonding interactions found in PVA with the chemically modified PVAs opens an interesting way towards miscibility with polyesters and other polymer systems containing carbonyl groups.     

Predictive-collaborative model as recovery and validation tool. Case of study: Psychiatric emergency department decision support

There is a frequent situation in data mining where data collected must be used in real time to support decisions and they could present missing or non consistent values. The objective of this proposal consists of the recovery of missing values and verifies the consistency and integrity of the provided, in order to increase the information to support decisions. To address this, a predictive-collaborative model has been designed. It is composed of different predictive models generated by means of a training set and classifier selection algorithm. The combined suggestions of these predictive models are offered to support decisions. As case of study, the psychiatric emergency department at the Doce de Octubre Hospital in Madrid has been considered, where the response time is critical and the data are acquired in a stress situation which affects the quality of data significantly.     

Psychological treatment of chronic posttraumatic stress disorder in victims of sexual aggression

The aim of this research was to test the comparative effectiveness of two therapeutic modalities in the treatment of chronic posttraumatic stress disorder in victims of sexual aggression: (a) self-exposure and cognitive restructuring and (b) progressive relaxation training. The sample consisted of 20 patients (victims of rape in adulthood or adult victims of childhood sexual abuse) selected according to DSM-III-R criteria. A multigroup experimental design with repeated measures (pretreatment, posttreatment, and 1-, 3-, 6-, and 12-month follow-up) was used. Most treated patients improved, but the success rate was higher in all measures in the exposure and cognitive restructuring group immediately on posttreatment and at follow-up. Implications of this study for clinical practice and future research in this field are commented on.     

Crystallinity assessment and in vitro cytotoxicity of polylactide scaffolds for biomedical applications

Bioresorbable polylactides are one of the most important materials for tissue engineering applications. In this work we have prepared scaffolds based on the two optically pure stereoisomers: poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA). The crystalline structure and morphology were evaluated by DSC, AFM and X-ray diffraction. PLLA and PDLA crystallized in the α form and the equimolar PLLA/PDLA blend, crystallized in the stereocomplex form, were analyzed by a proliferation assay in contact with mouse L-929 and human fibroblasts and neonatal keratinocytes for in vitro cytotoxicity evaluation. SEM analysis was conducted to determine the cell morphology, spreading and adhesion when in contact with the different polymer surfaces. The preserved proliferation rate showed in MTT tests and the high colonization on the surface of polylactides observed by SEM denote that PLLA, PDLA and the equimolar PLLA/PDLA are useful biodegradable materials in which the crystalline characteristics can be tuned for specific biomedical applications.     

Crystallinity and mechanical properties of optically pure polylactides and their blends

Nonisothermal solidifications of medical‐grade polylactides were conducted on compression molding sheets, resulting in a variety of crystalline forms and different amounts of crystallinity. Both optically pure polylactides, poly (L‐lactide) (PLLA) and poly (D‐lactide) (PDLA), were found to crystallize at a low melting temperature α crystalline form. PLLA/PDLA blends were found to yield both α homocrystallites and 50°C higher melting temperature stereocomplex crystallites. The effects of processing conditions and blend composition on crystal heterogeneity and degree of crystallinity were studied. Tensile tests reveal for these polylactides Young's modulus values of 3.5–4.2 GPa, strength values of 62–71 MPa, and elongations at break of 1–5%, depending on blend composition and crystallinity. POLYM. ENG. SCI. 45:745–753, 2005. © 2005 Society of Plastics Engineers     

Tool for Rural and Statewide Multimodal Transportation Planning

The Georgia Department of Transportation's Multi-modal Transportation Planning Tool (MTPT) facilitates multimodal planning in rural areas. Using open databases that are available agencywide, the tool can aid in the analysis of transportation requirements of rural areas, identify potential implementation constraints early in the planning process, and develop a prioritized project list by mode for an analysis region. The MTPT addresses highways, transit, intercity bus, commuter and passenger rail, aviation, and bicycles. An integrated geographic information system plays an important role in the presentation of the results. This paper discusses the development of the MTPT and describes program functionality. The paper will be of particular interest to state transportation agencies interested in using statewide databases for multimodal planning purposes. Described techniques identify how data that are typically collected and maintained for an entire state (e.g., traffic volumes, posted speeds, designated bike routes, roadway functional classes, crash information, and county-based socioeconomic data) can be combined with field verified default factors, widely accepted planning and analysis methods, and additional regionally calibrated planning algorithms to perform system-level planning at the city, county, multicounty, or state levels.     

Rheological and mechanical behaviour of tetraglycidyldiaminodiphenylmethane (TGDDM)/anhydride epoxy systems

The curing of tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) cured with hexahydrophthalic anhydride, tetrahydrophthalic anhydride and nadic methyl anhydride was studied using static rheological techniques under isothermal conditions in different temperature ranges for each system. 1:1 and 1:0.5 stoichiometric ratios were used in all three TGDDM/anhydride systems analysed. From the gelation times of each system at the different conditions employed activation energies were calculated. Flexural mechanical properties, such as elastic modulus, strength and strain to break, were also investigated for all the three TGDDM/anhydride systems employed for different anhydride weight contents which ranged from 0.5 to 1.34 parts of the anhydride weight corresponding to the stoichiometric composition. Possible reasons to explain the mechanical behaviour shown are discussed.     

Molecular dynamics study of the influence of functionalization on the elastic properties of single and multiwall carbon nanotubes

The effect of carboxylation on axial Young’s modulus of carbon nanotubes is investigated using a molecular dynamics (MD) approach. COMPASS force field is used to model the interatomic interactions in single wall (SWCNT) and multiwall carbon (MWCNT) with different amounts of –COOH groups attached to their surfaces. The results of the MD simulations show how an increase of the number of carboxylic groups on the CNT surface leads to a decrease on the Young moduli of the CNTs. The decrease of MWCNT Young’s modulus is found to be lower than in the case of SWCNT.