Picosecond Laser Ablation of Polyhydroxyalkanoates (PHAs): Comparative Study of Neat and Blended Material Response

Polyhydroxyalkanoates (PHAs) have emerged as a promising biodegradable and biocompatible material for scaffold manufacturing in the tissue engineering field and food packaging. Surface modification is usually required to improve cell biocompatibility and/or reduce bacteria proliferation. Picosecond laser ablation was applied for surface micro structuring of short- and medium-chain length-PHAs and its blend. The response of each material as a function of laser energy and wavelength was analyzed. Picosecond pulsed laser modified the surface topography without affecting the material properties. UV wavelength irradiation showed halved ablation thresholds compared to visible (VIS) wavelength, revealing a greater photochemical nature of the ablation process at ultraviolet (UV) wavelength. Nevertheless, the ablation rate and, therefore, ablation efficiency did not show a clear dependence on beam wavelength. The different mechanical behavior of the considered PHAs did not lead to different ablation thresholds on each polymer at a constant wavelength, suggesting the interplay of the material mechanical parameters to equalize ablation thresholds. Blended-PHA showed a significant reduction in the ablation threshold under VIS irradiation respect to the neat PHAs. Picosecond ablation was proved to be a convenient technique for micro structuring of PHAs to generate surface microfeatures appropriate to influence cell behavior and improve the biocompatibility of scaffolds in tissue engineerin

The decoherence criterion

The decoherence mechanism signals the limits beyond which the system dynamics approaches the classical behavior. We show that in some cases decoherence may also signal the limits beyond which the system dynamics has to be described by quantum field theory, rather than by quantum mechanics.Comment: revised paper, in print on Mod. Phys. Lett.

Multiscale understanding of tricalcium silicate hydration reactions

Tricalcium silicate, the main constituent of Portland cement, hydrates to produce crystalline calcium hydroxide and calcium-silicate-hydrates (C-S-H) nanocrystalline gel. This hydration reaction is poorly understood at the nanoscale. The understanding of atomic arrangement in nanocrystalline phases is intrinsically complicated and this challenge is exacerbated by the presence of additional crystalline phase(s). Here, we use calorimetry and synchrotron X-ray powder diffraction to quantitatively follow tricalcium silicate hydration process: i) its dissolution, ii) portlandite crystallization and iii) C-S-H gel precipitation. Chiefly, synchrotron pair distribution function (PDF) allows to identify a defective clinotobermorite, Ca11Si9O28(OH)2.8.5H2O, as the nanocrystalline component of C-S-H. Furthermore, PDF analysis also indicates that C-S-H gel contains monolayer calcium hydroxide which is stretched as recently predicted by first principles calculations. These outcomes, plus additional laboratory characterization, yielded a multiscale picture for C-S-H nanocomposite gel which explains the observed densities and Ca/Si atomic ratios at the nano- and meso- scales.This work has been supported by Spanish MINECO through BIA2014-57658-C2-2-R, which is co-funded by FEDER, BIA2014-57658-C2-1-R and I3 (IEDI-2016-0079) grants. We also thank CELLS-ALBA (Barcelona, Spain) for providing synchrotron beam time at BL04-MSPD beamline

Recovery of Water and Salt from Hyper-Saline Mine Water using Freeze Crystallization

The Freezerbacks researched, designed, and economically evaluated a full-scale freeze crystallization process as well as two alternative full-scale processes: 5 stage multiple effect evaporation and reverse osmosis. All three processes were designed to treat hyper-saline mine water that was sent into evaporation pond systems. These systems were designed for Freeport-McMoRan’s mines that need to treat impacted water. The Freeport-McMoRan copper mine in Miami, Arizona was visited in order to gain insight about the problem. The mine is no longer actively mining copper and is in the process of reclaiming land used. An essential part of restoring the land is treating impacted water that is currently being recirculated throughout the process before discharging. Current methods, evaporation ponds, are neither time nor cost effective. Ultimately, the water needs to be purified to the EPA standard of the maximum concentration level of sulfates (250 mg/L). After the feed has been processed, a waste stream will be disposed of via existing evaporation ponds. The deciding factor between the processes is the economics and total recovery. Multiple effect evaporation can be modified to recover more than 50% of water therefore reducing the footprint for the evaporation ponds. Although the heat of vaporization for water is about six times greater (40.65 kJ/mol) than the heat of fusion for water (6.02 kJ/mol), the capital cost for freeze crystallization is greater, and the process is unused on an industrial scale. Reverse osmosis will purify 50% of the water with a simpler system and cheaper overall cost. All processes are being presented as viable, with preference for the reverse osmosis. A batch bench scale system was constructed to model freeze crystallization. It was designed to process one gallon of salt solution in a single vessel. The bench scale process overall recovered 72% of the water with a final salt composition that ranges from 1.44 wt.% to 5.10 wt.%. For full-scale design purposes, 2.5 wt.% recovery was assumed. Reverse osmosis further purified the melted ice to EPA standards. A thorough evaluation was conducted by generating a full-scale economic analysis for each process, taking into consideration the advantages and disadvantages of each. Important factors taken into consideration were capital and operating costs, complexity, total recovery of water, and concentration of sulfates in the water recovered. In the freeze crystallization process, impacted water is pumped through two units in a semi-batch process where ice is formed on concentric plate coils in vessels. A total of 75% water is first recovered by crystallization and then the recovered water is passed through a reverse osmosis membrane (RO) to recover 50% of the initial brine water at environmental specifications. The net present value (NPV) after 10 years of operation is $(21.4 million) with a 50$(9.44 million). The reverse osmosis process will require two stages and a total of 21 elements. Reverse osmosis proved to be the most economical with an NPV of $(2.96 million) and a 50% purified water recovery compared to the other two processes

Influence of the 3-Hydroxyvalerate Content on the Processability, Nucleating and Blending Ability of Poly(3-Hydroxybutyrate-co-3-hydroxyvalerate)-Based Materials

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate (P(3HB-co-3HV) copolymers are an attractive class of biopolymers whose properties can be tailored by changing the 3-hydroxyvalerate monomer (3HV) concentration, offering the possibility of counteracting problems related to high crystallinity, brittleness, and processability. However, there are few studies about the effects of 3HV content on the processability of copolymers. The present study aims to provide new insights into the effect of 3HV content on the processing step including common practices like compounding, addition of nucleation agents and/or amorphous polymers as plasticizers. P(3HB-co-3HV)-based films containing 3, 18, and 28 mol % 3HV were processed into films by extrusion and subsequent molding. The characterization results confirmed that increasing the 3HV content from 3 to 28 mol % resulted in a decrease in the melting point (from 175 to 100 °C) and an improvement in mechanical properties (i.e., elongation at break from 7 ± 1% to 120 ± 3%). The behavior of P(3HB-co-3HV) in the presence of additives was also investigated. It was shown that an increase in the 3HV content leads to better miscibility with amorphous polymers

Effects of isothermal crystallization on the mechanical properties of a elastomeric medium chain length polyhydroxyalkanoate

In the present study, the relationship between molecular structure and mechanical properties for a medium chain length polyhydroxyalkanoate (mcl-PHA) composed of 3-hydroxyoctanoate and 3-hydroxyhexanoate was elucidated. The mcl-PHA was crystallized from the melt at four different temperatures between its glass transition and melting point (37, 21, 3 and −21 °C) and its molecular structure was analysed by means of differential scanning calorimetry (DSC) and wide-angle X-ray diffractometry (WAXD). The mechanical properties, which were analysed via tensile-tests and dynamic mechanical analysis (DMA), were clearly affected by the selected crystallization temperature and corresponding molecular structure of the polymer. In this sense, samples crystallized at 37, 21 and 3 °C displayed higher secant moduli calculated at 2% (E2% ∼ 20 MPa) than the sample crystallized at −21 °C (E2% ∼ 7 MPa) due to their higher crystallinity. Even if samples crystallized at 37, 21 and 3 °C had very similar degree of crystallinity, their secant moduli calculated at 50, 100 and 200% (E50%, E100% and E200%) and yield strength (σy) were clearly affected by the selected crystallization temperature, showing a positive correlation (i.e., higher crystallization temperatures and corresponding more ordered crystalline domains with narrower crystal distributions resulted in higher E50%, E100% and E200% values).The authors are thankful for funds from the Basque Government, Department of Education, Universities and Research (GIC12/161-IT-632-13) and the Spanish Ministry of Innovation and Competitiveness MINECO (MAT2013-45559-P)

Novel Polyhydroxyalkanoate blends: their characterisation and possible applications

Polyhydroxyalkanoates (PHAs) are polyesters consisting of 3-hydroxyalkanoic acids synthesised by numerous bacteria as storage compounds, in the presence of excess carbon, under nutrient limiting conditions. PHAs are biodegradable and biocompatible polymers that exhibit a variety of properties ranging from being thermoplastic to elastomeric in nature. For the first part of this study, the production of PHA in Bacillus cereus SPV and Pseudomonas mendocina was investigated. Nutrient limitations play a major role in PHA production hence, studies were carried out on the effect of nitrogen, potassium and magnesium limitations on the short chain length PHA accumulation by B. cereus SPV. The organism was grown in the Kannan and Rehacek medium using sucrose as the carbon source and accumulated PHA with a maximum yield of 38.0% dcw was observed in the shaken flask cultures. The study was continued with batch fermentation studies in 2 litre fermenters and an enhanced PHA yield was observed with an optimum yield of 44.6% dcw. Further, an enrichment media (MEM media) for B. cereus SPV was modified, with three simultaneous nutrient limitations for the production of PHA. A further improved yield of the polymer (52.64% dcw) was observed in this novel media. Chemical analysis of the extracted polymer was carried out using NMR and it was found that the organism accumulated the homopolymer of P(3HB). When Pseudomonas mendocina was grown in the mineral salt media (MSM) with a sodium octanoate as sole carbon source, medium chain length PHA accumulation was observed with a maximum polymer yield of 29.43% dcw in shaken flask cultures. The study continued with batch fermentation studies on the production of the PHAs, which was carried out using 2 Litre fermenters and an improved yield of the polymer (33.5 wt% dcw) was noted. Fed batch fermentation was also explored and a further increase in polymer accumulation was obtained, giving a maximum yield of 37.09% dcw. Chemical analysis of the polymer using NMR proved that the organism accumulated a homopolymer of Poly(3-hydroxyoctanoate) P(3HO), a rare occurrence. P. mendocina was also grown in MSM media with sucrose as carbon source and PHA accumulation was observed with a yield of 27.19% dcw. The polymer was structurally analysed by NMRand identified as the homopolymer of P(3HB).This is the first time that an absolute homopolymer of P(3HB) has been produced by P.mendocina using sucrose as the carbon source. A detailed study on the effects of different extraction methods on the yield of the PHAs was carried out. Among different extraction methods used for PHA extraction the dispersion method gave the highest PHA yield of 30% dcw. The chloroformextraction showed the polymer yield of 28% dcw.The soxhlet extraction, gave the lowest yield of 12% dcw.A novel PHA recovery and purification method based on the osmotic and detergent based lysis and purification was also successfully developed. Higher purity (25%)of the extracted PHA compared to dispersion method, was confirmed by GC analysis. The blending of the flexible and soft P(3HO) extracted from P.medochina with the brittle and stiff P(3HB) from Bacills cereusSPV was carried out in two ratios, 5:1 and 1:5. The thermal analysis of P(3HB) showed that the polymer sample had a high melting temperature Tm of 167.39°C, a glass transition temperature, Tg of 2.43°C and a crystallisation temperature Tc value of 54.33°C. The thermal analysis of P(3HO) showed that the polymer exhibited low melting temperature of 50.36°C, a Tg of -32.86°C), and no Tc value. The P(3HB)/P(3HO) 5:1 blend showed two melting temperature 164.91°C and 157.22 °C, single lower glass transition temperature of 5.84°C and raised Tc of 69.58°C as compared to neat P(3HB).The P(3HO)/P(3HB) 5:1 blend on the other hand higher melting temperature of (164.85°C), lower glass transition temperature of -36.990C as compared to P(3HO) and no Tc was observed. The P(3HO)/P(3HB) (5:1) blend showed an Young modulus value of 37 MPa with a tensile strength of 1.5 MPa and elongation to break of 160%. Increasing the amount of P(3HB) as in the case of P(3HB)/P(3HO) (5:1) increased the Young modulus value to 4.99 MPa indicating an increase in the stiffness. The percentage of elongation of the film was reduced to just 35.81%. The incorporation of P(3HB) into the biopolymer matrix of P(3HO) or P(3HO) into a predominantly P(3HB) matrix thus resulted in a change in the mechanical properties of the neat PHAs. P(3HB) served the purpose of increasing the tensile strength of the blend, whereas P(3HO) served the purpose of increasing the elasticity of the material. The flexible and strong nature of the P(3HO)/P(3HB) (5:1) blend would make it suitable for a variety of application including the preparation of nerve conduits. The water contact angle value for neat P(3HB) film was 70.37o and for P(3HO) was 99.94o. In the case of blend films P(3HO)/P(3HB) (5:1) and P(3HB)/P(3HO)(5:1), the θH2O was 90.39o and 80.0o respectively. The water contact angle studies showed that both the neat and blend PHAs are hydrophobic in nature. Both the neat and blend films were able to support the attachment, growth and proliferation of the HaCaT cells. However, biocompatibility was better for the P(3HO)/P(3HB) 5:1 film and the topological features of this film led to improved cell attachment and proliferation. SEM analysis confirmed that the HaCaT cells had been able to grow and mature faster on the P(3HO)/P(3HB) (5:1) blendfilm. In conclusion, this work has led to the development of novel PHA blends with new properties, which can be exploited in a variety of applications including nerve tissue engineering

Binary Polyhydroxyalkanoate Systems for Soft Tissue Engineering

Progress in tissue engineering is dependent on the availability of suitable biomaterials. In an effort to overcome the brittleness of poly(3-hydroxybutyrate), P(3HB), a natural biodegradable polyester, and widen its biomedical applications, plasticising of P(3HB) with oligomeric substances of related structure has been studied. A biosynthesised medium-chain-length polyhydroxyalkanoate (mcl-PHA) copolymer, the plasticizer precursor, was obtained using vegetable waste frying oil as a sole carbon source. The mcl-PHA was transformed into an oligomeric derivative by acid hydrolysis. The plasticising effect of the oligomeric mcl-PHA on P(3HB) was studied via characterisation of thermal and mechanical properties of the blends in the course of ageing at ambient conditions. Addition of oligomeric mcl-PHA to P(3HB) resulted in softer and more flexible materials based entirely on PHAs. It was shown that the oligomeric mcl-PHA transformed highly crystalline P(3HB) into materials with a dominant amorphous phase when the content of oligomeric mcl-PHA exceeded 10wt%. In vitro biocompatibility studies of the new binary PHA materials showed high viability and proliferation of C2C12 myoblast cells. Thus, the proposed approach for P(3HB) plasticisation has the potential for the generation of more pliable biomaterials based on P(3HB) which can find application in unique soft tissue engineering applications where a balance between stiffness, tensile strength and ductility is required