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The deep continental crust represents a vast potential habitat for microbial life where its activity remains poorly constrained. Organic acids like acetate are common in these ecosystems, but their role in the subsurface carbon cycle - including the mechanism and rate of their turnover - is still unclear. Here, we develop an isotope-exchange 'clock' based on the abiotic equilibration of H-isotopes between acetate and water, which can be used to define the maximum in situ acetate residence time. We apply this technique to the fracture fluids in Birchtree and Kidd Creek mines within the Canadian Precambrian crust. At both sites, we find that acetate residence times are <1 million years and calculated a rate of turnover that could theoretically support microbial life. However, radiolytic water-rock reactions could also contribute to acetate production and degradation, a process that would have global relevance for the deep biosphere. More broadly, our study demonstrates the utility of isotope-exchange clocks in determining residence times of biomolecules with possible applications to other environments., (© 2024. The Author(s).)

Stable hydrogen isotope compositions ( 2 H/ 1 H ratios) have been an invaluable tool for studying biogeochemical processes in nature, but the diversity of molecular targets amenable to such analysis is limited. Here, we demonstrate a new technique for measuring δ 2 H of biomolecules via Orbitrap mass spectrometry (MS) using acetate as a model analyte. Acetate was chosen as a target molecule because its production and consumption are central to microbial carbon cycling, yet the mechanisms behind acetate turnover remain poorly understood. δ 2 H of acetate could provide a useful constraint on these processes; however, it remains uncharacterized in nature due to analytical challenges. Electrospray ionization (ESI)-Orbitrap MS circumvents these challenges and delivers methyl-specific H-isotope compositions of acetate with nanomole sensitivity, enough to enable analyses of environmental samples. This approach quantifies the methyl-specific δ 2 H and molecular-average δ 13 C of acetate simultaneously while achieving <3 and <0.5‰ uncertainty, respectively. Using optimized ionization and Orbitrap parameters, this level of precision is obtained within 15 min using only 15 nmol of acetate. As a demonstration of our analytical approach, we cultured three acetogenic bacteria and found a large 2 H-fractionation between acetate and water (>310‰ depletion) associated with the Wood-Ljungdahl pathway, while fermentation expressed a muted (∼80‰) fractionation. With its high precision and sensitivity, Orbitrap MS is a promising tool for investigating these signals in nature after offline purification. Furthermore, the ESI-Orbitrap method presented here could be applied to other molecules amenable to ESI, including central metabolites and sugars, greatly expanding the molecular targets used in hydrogen isotope biogeochemistry.

Calves inoculated with Escherichia coli O157:H7 and fed either a high-roughage or high-concentrate diet were evaluated for rumen proliferation and fecal shedding of E. coli O157:H7. Calves fed the high-roughage diet had lower mean rumen volatile fatty acid concentrations and higher rumen pH values than did calves fed the high-concentrate diet. Despite these differences in rumen conditions, the calves fed the high-roughage diet did not have greater rumen populations of E. coli O157: H7 and did not exhibit increased or longer fecal shedding compared with the calves fed the high-concentrate diet. Two calves shedding the highest mean concentrations of E. coli O157:H7 were both fed the high-concentrate diet. There was a significant (P < 0.05) positive correlation between fecal shedding and rumen volatile fatty acid concentration in calves fed a high-concentrate diet. The effects of diet on E. coli O157:H7 proliferation and acid resistance were investigated using an in vitro rumen fermentation system. Rumen fluid collected from steers fed a high-roughage diet, but not from steers fed a high-concentrate diet, supported the proliferation of E. coli O157:H7. Rumen fluid from steers fed a high-concentrate diet rapidly induced acid resistance in E. coli O157:H7. The impact of diet on fecal shedding of E. coli O157:H7 is still unclear and may depend on dietary effects on fermentation in the colon and on diet-induced changes in the resident microflora. However, rapid development of acid tolerance by E. coli O157:H7 in the rumens of calves fed high-concentrate diets, allowing larger populations to survive passage through the acidic abomasum to proliferate in the colon, may be one factor that influences fecal shedding in cattle on feed.

The international use of medical device standards is expanding for both economic and regulatory reasons. It is no longer adequate to have standards that only specify measurement methods and labeling for a product. An effort needs to be put forth between industry, academia and government to promote standards that also include a minimum set of acceptable performance criteria. This will allow for a less subjective evaluation of the conformance of the medical device to the appropriate standard as well as promote a uniform set of minimal performance expectations for a class of products among consumers.

High-energy irradiation sterilization of medical devices and implants composed of polymeric biomaterials that are in contact with tissue and/or blood, may adversely affect their long-term mechanical and/or biological performance (tissue and/or blood compatibility). Since many polymeric implants may contain trace quantities of catalysts and/or other additives, the effect of high-energy radiation on these additives, and possible synergistic effects with the polymer chains under the influence of high-energy radiation, must be considered. It is essential to indicate whether polymeric implants are used in short-term (acute) or long-term (chronic) applications. Relatively small changes in their physicochemical, mechanical, and biological properties may be tolerable in the short term, whereas similar changes may lead to catastrophic failures in long-term applications. Therefore, polymeric implants which are to be sterilized by high-energy irradiation should be carefully evaluated for long-term property changes which may be induced by the radiation.

Two techniques, focal spot projection and fringe projection, have been developed for profiling the edges of anterior-chamber style intraocular lenses (IOL). The techniques are based on measurement of the trajectory of reflected light when an incident beam is focused and stepped across the edge surface (spot projection) or when two focused beams combine to form an optical interference pattern on the edge (fringe projection). The optical configurations for performing the projection techniques are described along with the mathematical relationship between the reflected-beam trajectories and the edge profile. An automated system for the implementation of focal spot projection was developed. The system has the capability of positioning the IOL edge at the focal point of the incident beam, acquiring trajectory data via stepper motors and a TV camera, processing the data to generate a profile, and displaying the profile on the computer video monitor or in hard-copy form via a printer. On one lens tested, three profiles corresponding to different locations along the IOL edge could be generated without user intervention. However, the user has the option of manually positioning the IOL to permit greater versatility. The typical 300-microm wide IOL edges are profiled to a resolution of approximately 20 microm. To constrain optical and microprocessor hardware costs, compromises were made in operating speeds so that approximately 20 min is required per profile. With current trends in integrated circuit technology future generations of the system could be made faster and prove useful as a QC tool for the IOL industry. Furthermore, the present device can be used in determining appropriate IOL profile standards.

The reliability of the leads of the entire pacemaker system is vital as the risks of failure include: (1) loss of pacing due to the deterioration of the polymeric insulator in the physiological environment; (2) thromboembolism due to inadequate blood compatibility of the insulator; (3) tissue reactions at the electrode/tissue interface; (4) general foreign body rejection phenomena; (5) perforation of the leads; and (6) excessive stress applied by sutures causing abrasion and stress cracking. Although silicone has been used widely, some years ago Pellethane (a segmented polyetherurethane-urea) has been introduced as an alternate lead insulator, chiefly because it can be extruded using additives into smooth and thin tubes. The additives (antioxidants), extrusion aids, and low molecular weight polymer chains (oligomers) together represent up to approximately 8% by weight of leachables, depending on the extraction medium. The in vivo degradation of Pellethane is biologic in nature and is most likely associated with the absorption and premeation of body fluids from the surrounding physiologic environment leading to stress cracking via the formation of microvoids. Thermally and biologically unstable biuret and allophonate groups in this polyurethane, exposure of the polymer to high extrusion temperatures, and stresses created within the polymer also play key roles in the degradation process. In the case of electrodes, some corrosion can occur even with noble metals and ions formed with the involvement of penetrating body fluids which may combine with the urethane and/or urea groups of the polyurethane, leading to its further degradation in vivo. The totality of the situation indicates a need for the development of a standard guideline for the uniform and consistent pre-clinical testing and evaluation of new materials and fabrication processes of implantable pacemaker leads. Such guidelines should take into consideration, among others, the physiological environment, species-differences between test animals and humans, and observe reliable statistical interpretations based on sufficient data.

An optical correlation technique has been shown to accurately measure leak conduction rates from 10(-1) to 10(-6) atm cc/sec. Using hybrid microcircuit packages with glass capillary leakers, dimensional changes were detected as the packages were exposed to a small increase in external pressure. The rate at which the package returns to its original dimensions is measured and used, along with the internal free volume, to compute the leak rate. Because of its several advantages, the technique has the potential to become a useful nondestructive quality-control technique.

The physico-chemical and biological aspects of polymeric materials represent vital areas in the reliable, safe, and efficacious functioning of controlled drug-delivery devices. In the case of implantable systems, potential biological problems include incompatibility of the polymers and their degradation products with the physiological environment, adverse metabolic consequences of the degradation products, and occlusion of the drug conduits (catheters) with thrombi and/or drugs, (i.e., insulin aggregates). In the case of transcutaneous drug delivery systems, proper consideration must be given to avoid skin irritation and allergic responses as well as other toxic effects. With biodegradable systems that may follow simple hydrolysis and/or enzyme-catalyzed degradation of labile chemical side-chains that hold the drug molecule and/or the main polymer chain, increased attention must be given not only to the short-term but also the long-term metabolic consequences of the degradation products. Although the term "biodegradation" is often used for in vitro situations it should be reserved only for in vivo circumstances as, at the present time, no in vitro experiments can completely simulate the in vivo environment. The misuse of this term may lead to premature predictions as to the performance of a device in vivo, a situation that ought to be avoided. Appropriate attention must also be given to the effect of drugs on polymers as drug/polymer interactions may influence the stability of both the polymers and drugs and may result in altered therapeutic performance. Standards are needed to clearly differentiate between controlled drug delivery systems and older "sustained" and "time-release" preparations.

Medical implant materials that come in contact with tissues, body fluids (including blood) constitute an area in medical devices where reliability and clinical performance limitations are vital. Polymeric implant materials differ in important aspects from metals and alloys, and ceramics (including glasses and carbons) with respect to their atomic and molecular structures and morphology. It is suggested that four categories of 'standards' be developed: (1) certified primary reference materials to be used for calibration purposes, (2) reference materials to be used for the comparative evaluation of physico-chemical and biological properties, (3) 'fabrication-grade' reference materials for intercomparative evaluation of processing conditions, and (4) reference implants aimed at the intercomparative evaluation of possible synergistic effects of additives, processing aids, and fabrication processes on in vivo service life, including biological and mechanical performance.