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- Gene delivery using dendrimer/pDNA complexes immobilized in electrospun fibers using the Layer-by-Layer techniquePublication . Ramalingam, Kirthiga; Castro, Rita; Pires, Pedro; Shi, Xiangyang; Rodrigues, João; Xiao, Shili; Tomás, HelenaA gene delivery platform for potential use in tissue engineering applications was developed by surface functionalization of biodegradable electrospun poly(lactic-co-glycolic acid) (PLGA) fibers with nanolayers of chitosan (cationic polymer) and alginate (anionic polymer) using the Layer-by-Layer (LbL) technique. The developed system not only supported the attachment and growth of human Mesenchymal Stem Cells (hMSCs), but also was capable of delivering pDNA/dendrimer complexes and inducing cell differentiation towards the osteogenic lineage when a pDNA codifying for human Bone Morphogenetic Protein-2 (BMP-2) was used. Beyond providing a means for pDNA/dendrimer complex immobilization, the polyelectrolyte coating conferred sustained release properties to the scaffold that resulted in pDNA protection from degradation. The polyelectrolyte coating, by itself, also contributed to enhance cell differentiation.
- Recent advances in β-galactosidase and fructosyltransferase immobilization technologyPublication . Ureta, Maria Micaela; Martins, Gonçalo Nuno; Figueira, Onofre; Pires, Pedro Filipe; Castilho, Paula Cristina; Gomez-Zavaglia, AndreaThe highly demanding conditions of industrial processes may lower the stability and affect the activity of enzymes used as biocatalysts. Enzyme immobilization emerged as an approach to pro mote stabilization and easy removal of enzymes for their reusability. The aim of this review is to go through the principal immobilization strategies addressed to achieve optimal industrial proc esses with special care on those reported for two types of enzymes: b-galactosidases and fructo syltransferases. The main methods used to immobilize these two enzymes are adsorption, entrapment, covalent coupling and cross-linking or aggregation (no support is used), all of them having pros and cons. Regarding the support, it should be cost-effective, assure the reusability and an easy recovery of the enzyme, increasing its stability and durability. The discussion provided showed that the type of enzyme, its origin, its purity, together with the type of immobilization method and the support will affect the performance during the enzymatic synthesis. Enzymes’ immobilization involves interdisciplinary knowledge including enzymology, nanotechnology, molecular dynamics, cellular physiology and process design. The increasing availability of facilities has opened a variety of possibilities to define strategies to optimize the activity and re-usability of b-galactosidases and fructosyltransferases, but there is still great place for innovative developments.
- The speed of sound and isentropic compressibility of liquid difluoromethane (HFC32) fromT=(248 to 343) K and pressures up to 65 MPaPublication . Pires, P. F.; Guedes, H. J. R.This work reports experimental data on the speed of sound in liquid difluoromethane ŽHFC32, or R32. from T s Ž248 to 343. K and pressures up to 65 MPa. The results were obtained using a newly-built apparatus, calibrated with toluene over the whole experimental region, and show good agreement with two available data sets. The uncertainties are "0.01 K in the temperature, "0.025 MPa in the pressure up to 35 MPa, and "0.2 MPa above this value. The final uncertainty on the speed of sound is estimated to be "0.2 per cent. The data were fitted using a simple analytical equation and the results are discussed. The isentropic compressibility was calculated over the Ž p, T. surface where the reported speed of sound values and the corresponding literature densities overlap.
- Acoustic determination of thermophysical properties and critical parameters for R404A and critical line of x CO2+(1− x) R404APublication . Esperança, José M. S. S.; Pires, Pedro F.; Guedes, Henrique J. R.; Ribeiro, Nuno; Costa, Tânia; Aguiar-Ricardo, AnaThe thermophysical properties and critical parameters for the alternative refrigerant R404A (52 wt % of 1,1,1- trifluoroethane (R143a) + 44 wt % of pentafluoroethane (R125) + 4 wt % of 1,1,1,2-tetrafluoroethane (R134a)) were investigated using two different acoustic techniques. The critical behavior of the system xCO2 + (1 - x)R404A was also investigated. Experimental data of speed of sound in liquid R404A from 258 K to 338 K and pressures up to 65 MPa were measured using a pulse-echo method. Derived thermodynamic properties are calculated, combining our experimental data with density and isobaric heat capacity values published by other authors. Measurements of the critical temperature Tc and pressure pc on (R404A) and mixtures of xCO2 + (1 - x)R404A were performed using another simple ultrasonic time-delay technique. The binary critical line was determined over the whole composition range showing that this system deviates only slightly from ideality since the critical line is a continuous line. The Peng-Robinson equation of state with conventional mixing and combining rules was used to correlate the binary experimental data.
- The speed of sound, and derived thermodynamic properties of liquid trifluoromethane (HFC23) fromT=(258 to 303)K at pressures up to 65MPaPublication . Pires, P. F.; Guedes, H. J. R.This work reports experimental data of the speed of sound in liquid trifluoromethane (HFC23, or R23) from T = (258 to 303) K at pressures up to 65 MPa, measured with a pulse-echo method adapted from Papadakis(1) and Guedes et al.(2) The results are fitted to a rational approximant and compared with literature data.(3) Derived thermodynamic properties such as the isentropic compressibility κs, the isothermal compressibility κT , the cubic expansion coefficient αp, and the specific heat capacity at constant pressure cp are calculated by combining the present experimental data with the density values published by other authors.(4–11) The estimated properties are compared, where possible, with literature data.
- A novel non-intrusive microcell for sound-speed measurements in liquids. Speed of sound and thermodynamic properties of 2-propanone at pressures up to 160 MPaPublication . Azevedo, R. Gomes de; Szydlowski, J.; Pires, P. F.; Esperança, J. M. S. S.; Guedes, H. J. R.; Rebelo, L. P. N.A novel high-pressure, ultrasonic cell of extremely reduced internal dimensions ( 0.8 10 6 m3) and good precision for the determination of the speed of propagation of sound in liquids was conceived and built. It makes use of a non-intrusive methodology where the ultrasonic transducers are not in direct contact with the liquid sample under investigation. The new cell was used to carry out speed of sound measurements in 2-propanone (acetone) in broad ranges of temperature (265 < T =K < 340) and pressure (0:1 < p=MPa < 160). (p; q; T ) data for acetone were also determined but in a narrower T ; p range (298 to 333 K; 0.1 to 60 MPa). In this interval, several thermodynamic properties were thus calculated, such as: isentropic (js) and isothermal (jTÞ compressibility, isobaric thermal expansivity (ap), isobaric (cp) and isochoric (cv) specific heat capacity, and the thermal pressure coefficient (cv). Comparisons with values found in the literature generally show good agreement.
- Acoustic determination of thermophysical properties and critical parameters for R410A and critical line of x CO2+(1− x) R410APublication . Ribeiro, Nuno; Costa, Tânia; Aguiar-Ricardo, Ana; Esperança, José M. S. S.; Pires, Pedro F.; Guedes, Henrique J. R.The thermophysical properties and critical parameters for the alternative refrigerant R410A (a near azeotropic refrigerant mixture containing difluoromethane (R32) and pentafluoroethane (R125) (50 wt % of each)) were investigated using two different acoustic techniques. The critical behavior of the system xCO2 + (1 - x)R410A was also investigated. Experimental data of speed of sound in liquid R410A from (253 to 338) K and pressures up to 65 MPa were measured using a pulse-echo method. Derived thermodynamic properties were calculated, combining our experimental data with density and isobaric heat capacity values published by other authors. Measurements of the critical temperature Tc and pressure pc on (R410A) and mixtures of xCO2 + (1 - x)R410A were performed using another simple ultrasonic time-delay technique. The binary critical line was determined over the whole composition range, showing that this system deviates only slightly from ideality since the critical line is a continuous line. The Peng-Robinson equation of state with conventional mixing and combining rules was used to correlate the binary experimental data.
- Acoustic determination of thermophysical properties and critical parameters for the mixture (51 wt% R143a+ 49 wt% R125) and critical line of x CO2+(1− x)(51 wt% R143a+ 49 wt% R125)Publication . Esperança, José M. S. S.; Pires, Pedro F.; Guedes, Henrique J. R.; Ribeiro, Nuno; Costa, Tânia; Aguiar-Ricardo, AnaThe thermophysical properties and critical parameters for the alternative refrigerant (51 wt % of 1,1,1-trifluoroethane (R143a) + 49 wt % of pentafluoroethane (R125))svery close to the composition of R507 (50 wt % of each mixture component)swere investigated using two different acoustic techniques. The critical behavior of the system xCO2 + (1 - x)(51 wt % R143a + 49 wt % R125) was also investigated. Experimental data of speed of sound in liquid (51 wt % R143a + 49 wt % R125) from T ) (253 to 338) K and pressures up to 65 MPa were measured using a pulse-echo method. Derived thermodynamic properties were calculated, combining our experimental data with density and isobaric heat capacity values published by other authors. Measurements of the critical temperature Tc and pressure pc on (51 wt % R143a + 49 wt % R125) and mixtures of xCO2 + (1 - x)(51 wt % R143a + 49 wt % R125) were performed using another simple ultrasonic time-delay technique. The binary critical line was determined over the whole composition range showing that this system deviates only slightly from ideality since the critical line is a continuous line. The Peng-Robinson equation of state with conventional mixing and combining parameters was used to correlate the binary experimental data.
- Thermophysical and thermodynamic properties of ionic liquids over an extended pressure range: [bmim][NTf2] and [hmim][NTf2]Publication . Azevedo, R. Gomes de; Esperança, J. M. S. S.; Szydlowski, J.; Visak, Z. P.; Pires, P. F.; Guedes, H. J. R.; Rebelo, L. P. N.The current study focuses on 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [bmim][NTf2], and 1-hexyl-3- methylimidazolium bis(trifluoromethylsulfonyl)amide, [hmim][NTf2]. The objective is to study the influence of pressure as well as that of the cation s alkyl chain length on several properties of this type of ionic liquids. Speed of propagation of ultrasound waves and densities in pure ionic liquids (ILs) as a function of temperature and pressure have been determined. Several other thermody namic properties such as compressibilities, expansivities and heat capacities have been obtained. Speed of sound measurements have been carried out in broad ranges of temperature (283 < T/K < 323) and pressure (0.1 < p/MPa < 150), using a non-intrusive micro cell. Density measurements have been performed at broad ranges of temperature (298 < T/K < 333) and pressure (0.1 < p/MPa < 60) using a vibrating tube densimeter. The pressure dependence of heat capacities, which is generally mild, is highly dependent on the curvature of the temperature dependence of density.
- Ultrasonic speed of sound and derived thermodynamic properties of liquid 1, 1, 1, 2, 3, 3, 3-heptafluoropropane (HFC227ea) from 248 K to 333 K and pressures up to 65 MPaPublication . Pires, P. F.; Esperança, J. M. S. S.; Guedes, H. J. R.This work reports experimental data of the speed of sound in liquid 1,1,1,2,3,3,3-heptafluoropropane (HFC227ea) from 248 K to 333 K and pressures up to 65 MPa, measured with a pulse-echo method. The results are fitted with a rational approximant. Derived thermodynamic properties are calculated, combining our experimental data with density and isobaric heat capacity values published by other authors. The results were compared with the data available in the literature.