Entity

Time filter

Source Type

Germantown, MD, United States

With constrained transportation budgets there is a great need to increase the service life of bridges. Typically the deck is the weak link in the durability of a bridge with the corrosion of the reinforcing being the primary deterioration mechanism. Using Glass Fiber Reinforced Polymer (GFRP) to replace the traditional steel reinforcing eliminates reinforcing-related corrosion and should significantly increase the service life of the deck. The I-635 Bridges over State Ave in Kansas City, KS were built in the late 60's and had an extensive history of repairs and overlays. In 2013 KDOT decided to replace the decks with traditional epoxy coated steel in the northbound bridge and GFRP reinforcing in the southbound bridge. There was a small premium to use GFRP rebar over traditional steel reinforcing which is expected to be offset by an increase in the service life of the deck. A picture of the reinforcing for the new bridge deck is shown in Figure 1. Source


Sundaramurthi P.,University of Minnesota | Sundaramurthi P.,Hughes Inc. | Suryanarayanan R.,University of Minnesota
Journal of Physical Chemistry B | Year: 2011

Macromolecules and other thermolabile biologicals are often buffered and stored in frozen or dried (freeze-dried) state. Crystallization of buffer components in frozen aqueous solutions and the consequent pH shifts were studied in carboxylic (succinic, malic, citric, tartaric acid) and amino acid (glycine, histidine) buffers. Aqueous buffer solutions were cooled from room temperature (RT) to -25 °C and the pH of the solution was measured as a function of temperature. The thermal behavior of frozen solutions was investigated by differential scanning calorimetry (DSC), and the crystallized phases were identified by X-ray diffractometry (XRD). Based on the solubility of the neutral species of each buffer system over a range of temperatures, it was possible to estimate its degree of supersaturation at the subambient temperature of interest. This enabled us to predict its crystallization propensity in frozen systems. The experimental and the predicted rank orderings were in excellent agreement. The malate buffer system was robust with no evidence of buffer component crystallization and hence negligible pH shift. In the citrate and tartrate systems, at initial pH < pKa2, only the most acidic buffer component (neutral form) crystallized on cooling, causing an increase in the freeze-concentrate pH. In glycine buffer solutions, when the initial pH was ∼3 units < isoelectric pH (pI = 5.9), β-glycine crystallization caused a small decrease in pH, while a similar effect but in the opposite direction was observed when the initial pH was ∼3 units > pI. In the histidine buffer system, depending on the initial pH, either histidine or histidine HCl crystallized. © 2011 American Chemical Society. Source


Sundaramurthi P.,University of Minnesota | Sundaramurthi P.,Hughes Inc. | Suryanarayanan R.,University of Minnesota
Pharmaceutical Research | Year: 2010

Purpose: To study the influence of crystallizing and non-crystallizing cosolutes on the crystallization behavior of trehalose in frozen solutions and to monitor the phase behavior of trehalose dihydrate and mannitol hemihydrate during drying. Methods: Trehalose (a lyoprotectant) and mannitol (a bulking agent) are widely used as excipients in freeze-dried formulations. Using differential scanning calorimetry (DSC) and X-ray diffractometry (XRD), the crystallization behavior of trehalose in the presence of (i) a crystallizing (mannitol), (ii) a non-crystallizing (sucrose) solute and (iii) a combination of mannitol and a model protein (lactose dehydrogenase, catalase, or lysozyme) was evaluated. By performing the entire freeze-drying cycle in the sample chamber of the XRD, the phase behavior of trehalose and mannitol were simultaneously monitored. Results: When an aqueous solution containing trehalose (4% w/v) and mannitol (2% w/v) was cooled to -40°C at 0.5°C/min, hexagonal ice was the only crystalline phase. However, upon warming the sample to the annealing temperature (-18°C), crystallization of mannitol hemihydrate was readily evident. After 3 h of annealing, the characteristic XRD peaks of trehalose dihydrate were also observed. The DSC heating curve of frozen and annealed solution showed two overlapping endotherms, attributed by XRD to the sequential melting of trehalose dihydrate - ice and mannitol hemihydrate - ice eutectics, followed by ice melting. While mannitol facilitated trehalose dihydrate crystallization, sucrose completely inhibited it. In the presence of protein (2 mg/ml), trehalose crystallization required a longer annealing time. When the freeze-drying was performed in the sample chamber of the diffractometer, drying induced the dehydration of trehalose dihydrate to amorphous anhydrate. However, the final lyophiles prepared in the laboratory lyophilizer contained trehalose dihydrate and mannitol hemihydrate. Conclusions: Using XRD and DSC, the sequential crystallization of ice, mannitol hemihydrate, and trehalose dihydrate was observed in frozen solutions. Mannitol, by readily crystallizing as a hemihydrate, accelerated trehalose dihydrate crystallization in frozen solutions. However, by remaining amorphous, sucrose completely inhibited trehalose dihydrate crystallization. Crystallization of the lyoprotectantt in the model protein formulations might have serious implications on protein stability. © 2010 Springer Science+Business Media, LLC. Source


Sundaramurthi P.,University of Minnesota | Sundaramurthi P.,Hughes Inc. | Suryanarayanan R.,University of Minnesota
Pharmaceutical Research | Year: 2011

Purpose: To effectively inhibit succinate buffer crystallization and the consequent pH changes in frozen solutions. Methods: Using differential scanning calorimetry (DSC) and X-ray diffractometry (XRD), the crystallization behavior of succinate buffer in the presence of either (i) a crystallizing (glycine, mannitol, trehalose) or (ii) a non-crystallizing cosolute (sucrose) was evaluated. Aqueous succinate buffer solutions, 50 or 200 mM, at pH values 4.0 or 6.0 were cooled from room temperature to -25°C at 0.5°C/min. The pH of the solution was measured as a function of temperature using a probe designed to function at low temperatures. The final lyophiles prepared from these solutions were characterized using synchrotron radiation. Results: When the succinic acid solution buffered to pH 4.0, in the absence of a cosolute, was cooled, there was a pronounced shift in the freeze-concentrate pH. Glycine and mannitol, which have a tendency to crystallize in frozen solutions, remained amorphous when the initial pH was 6.0. Under this condition, they also inhibited buffer crystallization and prevented pH change. At pH 4.0 (50 mM initial concentration), glycine and mannitol crystallized and did not prevent pH change in frozen solutions. While sucrose, a non-crystallizing cosolute, did not completely prevent buffer crystallization, the extent of crystallization was reduced. Sucrose decomposition, based on XRD peaks attributable to β-D-glucose, was observed in frozen buffer solutions with an initial pH of 4.0. Trehalose completely inhibited crystallization of the buffer components when the initial pH was 6.0 but not at pH 4.0. At the lower pH, the crystallization of both trehalose dihydrate and buffer components was evident. Conclusion: When retained amorphous, sucrose and trehalose effectively inhibited succinate buffer component crystallization and the consequent pH shift. However, when trehalose crystallized or sucrose degraded to yield a crystalline decomposition product, crystallization of buffer was observed. Similarly, glycine and mannitol, two widely used bulking agents, inhibited buffer component crystallization only when retained amorphous. In addition to stabilizing the active pharmaceutical ingredient, lyoprotectants may prevent solution pH shift by inhibiting buffer crystallization. © 2010 Springer Science+Business Media, LLC. Source


Sundaramurthi P.,University of Minnesota | Sundaramurthi P.,Hughes Inc. | Patapoff T.W.,Genentech | Suryanarayanan R.,University of Minnesota
Pharmaceutical Research | Year: 2010

Purpose: (i) To study the crystallization of trehalose in frozen solutions and (ii) to understand the phase transitions during the entire freeze-drying cycle. Method: Aqueous trehalose solution was cooled to -40°C in a custom-designed sample holder. The frozen solution was warmed to -18°C and annealed, and then dried in the sample chamber of the diffractometer. XRD patterns were continuously collected during cooling, annealing and drying. Results: After cooling, hexagonal ice was the only crystalline phase observed. However, upon annealing, crystallization of trehalose dihydrate was evident. Seeding the frozen solution accelerated the solute crystallization. Thus, phase separation of the lyoprotectant was observed in frozen solutions. During drying, dehydration of trehalose dihydrate yielded a substantially amorphous anhydrous trehalose. Conclusions: Crystallization of trehalose, as trehalose dihydrate, was observed in frozen solutions. The dehydration of the crystalline trehalose dihydrate to substantially amorphous anhydrate occurred during drying. Therefore, analyzing the final lyophile will not reveal crystallization of the lyoprotectant during freeze-drying. The lyoprotectant crystallization can only become evident by continuous monitoring of the system during the entire freeze-drying cycle. In light of the phase separation of trehalose in frozen solutions, its ability to serve as a lyoprotectant warrants further investigation. © 2010 Springer Science+Business Media, LLC. Source

Discover hidden collaborations