Fibroblast growth factor (FGF) is a polypeptide that has been shown to have a stimulatory effect on osseous tissues in vitro. This study characterized the release of FGF from plaster of Paris (PLP) and measured the dissolution of PLP in various solutions with the aim of developing a reliable carrier system for the release of FGF in vivo. The study consisted of five experiments: (I) FGF diffusion from PLP pellets, (II) FGF diffusion from PLP discs, (III) PLP dissolution in saline, (IV) PLP dissolution in serum, and (V) FGF adsorption by commercially pure titanium. FGF was observed to be released at a rate directly proportional to the rate of dissolution of the PLP carrier, suggesting that either the FGF binds to the PLP; or, alternatively, the FGF may be entrapped by the PLP. Dissolution rate, and thus release rate, could be varied by varying the mass of the carrier. Greater diffusion of FGF was observed in larger, more slowly dissolving PLP carriers. Dissolution of PLP was observed to be slower in serum than in saline, apparently due to stabilization by factors in the serum but not due to a concentration gradient effect. Titanium coupons did not adsorb significant amounts of FGF. These results indicate that PLP, which has been shown in the past neither to aggravate inflammatory response nor to interfere with bone ingrowth, may serve as delivery vehicle for FGF to osseous tissues in vivo.
Multistage hydraulic fracturingturing treatments in unconventional wells have greatly increased the number and magnitude of stress cycles that must be withstood by primary cement jobs. The stress cycling of hydraulic fracturingturing on Portland Cement, with its intrinsic mechanical properties, may present a risk to long-term well integrity. By modifying the mechanical properties of the set-cement to make it more flexible, the risk of compromising well integrity during hydraulic fracturingturing treatments can be reduced. The mechanical properties of set-cement designs can be tested in a laboratory setting. This allows quantification of the compressive strength, tensile strength, Young's modulus, and Poisson's ratio of the set cement. Hydraulic fracturingturing design software can be used to quantify the pressure and temperature cycles to which the inner diameter of the primary casing string will be subjected. A mathematical model is used to predict the potential risk of mechanical failure of the set cement based on the mechanical properties and the pressure and temperature cycles of the expected treatment. The mathematical model identifies risk of failure in tension, compression, and de-bonding. By adding flexible materials to Portland Cement in a reduced water, tri-modal particle-size-distribution blend, the Young's modulus can be reduced while relatively high compressive and tensile strength is maintained. According to the mathematical model, a cement sheath with these properties is at a low risk of mechanical failure in any of the three failure modes up to a certain hydraulic fracturingturing pressure. Wireline logging tools use ultrasonic waves to measure acoustic impedance and flexural attenuation for cement evaluation. These readings are used to assess the integrity of the cement sheath in a 360° solid/liquid/gas map around the casing. These logging data can be used to determine the presence and extent of damage to the cement sheath during the hydraulic fracturingturing operation. A hydraulic fracturingturing treatment was applied to a well cemented with optimized flexible and trimodal properties. Cement evaluation logs were run before and after treatment for comparison. The post-fracturingturing log showed no damage to the annular cement sheath.
Pure calcium sulfate (CS) is an excellent bone graft material because it is biocompatible, completely biodegradable, osteoconductive, safe, nontoxic and angiogenic. It also has barrier properties. However, its rapid degradation limits its use as a bone graft material. A nanocomposite of CS and poly (l lactic acid) (PLLA) in a ratio of 96:4 was developed to overcome this problem. This composite underwent slower degradation. It took 16 weeks for complete degradation whereas pure CS takes only 4 weeks. When implanted in bone defects in rabbits, it underwent complete degradation and stimulated vigorous bone formation.
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