Biotrapping Ureolytic Bacteria on Sand to Improve the Efficiency of Biocementation

Microbially induced calcium carbonate precipitation (MICP) has emerged as a novel technology with the potential to produce building materials through lower-temperature processes. The formation of calcium carbonate bridges in MICP allows the biocementation of aggregate particles to produce biobricks. Current approaches require several pulses of microbes and mineralization media to increase the quantity of calcium carbonate minerals and improve the strength of the material, thus leading to a reduction in sustainability. One potential technique to improve the efficiency of strength development involves trapping the bacteria on the aggregate surfaces using silane coupling agents such as positively charged 3-aminopropyl-methyl-diethoxysilane (APMDES). This treatment traps bacteria on sand through electrostatic interactions that attract negatively charged walls of bacteria to positively charged amine groups. The APMDES treatment promoted an abundant and immediate association of bacteria with sand, increasing the spatial density of ureolytic microbes on sand and promoting efficient initial calcium carbonate precipitation. Though microbial viability was compromised by treatment, urea hydrolysis was minimally affected. Strength was gained much more rapidly for the APMDES-treated sand than for the untreated sand. Three injections of bacteria and biomineralization media using APMDES-treated sand led to the same strength gain as seven injections using untreated sand. The higher strength with APMDES treatment was not explained by increased calcium carbonate accrual in the structure and may be influenced by additional factors such as differences in the microstructure of calcium carbonate bridges between sand particles. Overall, incorporating pretreatment methods, such as amine silane coupling agents, opens a new avenue in biomineralization research by producing materials with an improved efficiency and sustainability.

Experimental studies suggest differences in the distribution of thorax elasticity between insects with synchronous and asynchronous musculature

Insects have developed diverse flight actuation mechanisms, including synchronous and asynchronous musculature. Indirect actuation, used by insects with both synchronous and asynchronous musculature, transforms thorax exoskeletal deformation into wing rotation. Though thorax deformation is often attributed exclusively to muscle tension, the inertial and aerodynamic forces generated by the flapping wings may also contribute. In this study, a tethered flight experiment was used to simultaneously measure thorax deformation and the inertial/aerodynamic forces acting on the thorax generated by the flapping wing. Compared to insects with synchronous musculature, insects with asynchronous muscle deformed their thorax 60% less relative to their thorax diameter and their wings generated 2.8 times greater forces relative to their body weight. In a second experiment, dorsalventral thorax stiffness was measured across species. Accounting for weight and size, the asynchronous thorax was on average 3.8 times stiffer than the synchronous thorax in the dorsalventral direction. Differences in thorax stiffness and forces acting at the wing hinge led us to hypothesize about differing roles of series and parallel elasticity in the thoraxes of insects with synchronous and asynchronous musculature. Specifically, wing hinge elasticity may contribute more to wing motion in insects with asynchronous musculature than in those with synchronous musculature.

The impacts of biomineralization and oil contamination on the compressive strength of waste plastic-filled mortar

Researchers have made headway against challenges of increasing cement infrastructure and low plastic recycling rates by using waste plastic in cementitious materials. Past studies indicate that microbially induced calcium carbonate precipitation (MICP) to coat plastic in calcium carbonate may improve the strength. The objective of this study was to increase the amount of clean and contaminated waste plastic that can be added to mortar and to assess whether MICP treatment enhances the strength. The performance of plastic-filled mortar was investigated at 5%, 10%, and 20% volume replacement for cement. Untreated, clean plastics at a 20% cement replacement produced compressive strengths acceptable for several applications. However, a coating of MICP on clean waste plastic did not improve the strengths. At 10% replacement, both MICP treatment and washing of contaminated plastics recovered compressive strengths by approximately 28%, relative to mortar containing oil-coated plastics. By incorporating greater volumes of waste plastics into mortar, the sustainability of cementitious composites has the potential of being improved by the dual mechanisms of reduced cement production and repurposing plastic waste.

Biomineralization of Plastic Waste to Improve the Strength of Plastic-Reinforced Cement Mortar

The development of methods to reuse large volumes of plastic waste is essential to curb the environmental impact of plastic pollution. Plastic-reinforced cementitious materials (PRCs), such as plastic-reinforced mortar (PRM), may be potential avenues to productively use large quantities of low-value plastic waste. However, poor bonding between the plastic and cement matrix reduces the strength of PRCs, limiting its viable applications. In this study, calcium carbonate biomineralization techniques were applied to coat plastic waste and improved the compressive strength of PRM. Two biomineralization treatments were examined: enzymatically induced calcium carbonate precipitation (EICP) and microbially induced calcium carbonate precipitation (MICP). MICP treatment of polyethylene terephthalate (PET) resulted in PRMs with compressive strengths similar to that of plastic-free mortar and higher than the compressive strengths of PRMs with untreated or EICP-treated PET. Based on the results of this study, MICP was used to treat hard-to-recycle types 3-7 plastic waste. No plastics investigated in this study inhibited the MICP process. PRM samples with 5% MICP-treated polyvinyl chloride (PVC) and mixed type 3-7 plastic had compressive strengths similar to plastic-free mortar. These results indicate that MICP treatment can improve PRM strength and that MICP-treated PRM shows promise as a method to reuse plastic waste.

Rational Control of Calcium Carbonate Precipitation by Engineered Escherichia coli

Ureolytic bacteria ( e.g., Sporosarcina pasteurii) can produce calcium carbonate (CaCO₃). Tailoring the size and shape of biogenic CaCO₃ may increase the range of useful applications for these crystals. However, wild type Sporosarcina pasteurii is difficult to genetically engineer, limiting control of the organism and its crystal precipitates. Therefore, we designed, constructed, and compared different urease operons and expression levels for CaCO₃ production in engineered Escherichia coli strains. We quantified urease expression and calcium uptake and characterized CaCO₃ crystal phase and morphology for 13 engineered strains. There was a weak relationship between urease expression and crystal size, suggesting that genes surrounding the urease gene cluster affect crystal size. However, when evaluating strains with a wider range of urease expression levels, there was a negative relationship between urease activity and polycrystal size (e.g., larger crystals with lower activity). The resulting range of crystal morphologies created by the rationally designed strains demonstrates the potential for controlling biogenic CaCO₃ precipitation.

Knee Function Assessment in Patients With Meniscus Injury: A Preliminary Study of Reproducibility, Response to Treatment, and Correlation With Patient-Reported Questionnaire Outcomes

Background:

Outcomes of meniscus surgery are typically assessed with patient questionnaires that help capture symptoms and functional limitations but may not provide an accurate representation of underlying joint health. There are currently no performance-based measures of knee function in patients with symptomatic meniscus injury.

Purpose:

To assess the reproducibility, response to partial meniscectomy, and correlation with patient-reported questionnaire outcomes of novel performance-based knee function tests.

Study Design:

Cohort study (diagnosis); Level of evidence, 2.

Methods:

A battery of 9 tests for activities that require knee movements essential for everyday living was developed. Intra- and interrater reproducibility was assessed in 50 meniscus tear patients completing the battery at 2 preoperative assessments with either the same or different examiners. Response to arthroscopic partial meniscectomy was evaluated in 35 of these patients 6 weeks after surgery. Subjects also completed the Knee Injury and Osteoarthritis Outcome Score (KOOS) and International Knee Documentation Committee (IKDC) questionnaires pre- and postoperatively.

Results:

The intrarater intraclass correlation coefficients (ICCs) were excellent for all tests (ICC > 0.8). Interrater ICC > 0.8 was observed for step-down, stair descent, star lunges, and timed treadmill travel. Performance on all tests improved significantly with surgery (P < .05), with the greatest improvement in sit-to-stand and stair ascent and descent. A greater percentage response to surgery was seen on questionnaire outcomes (20%-65%) than on performance-based tests (3%-15%). Moderate to poor correlations existed between the KOOS activities of daily living subscale and the performance-based tests (all ICCs ≤ 0.4).

Conclusion:

Performance-based knee function tests demonstrated good reproducibility and responsiveness in patients undergoing partial meniscectomy.

Clinical Relevance:

As both patient perception and functional performance are determinants of patient outcomes, questionnaires and performance-based tests could be used simultaneously to provide complementary data to monitor short- and long-term outcomes after meniscus surgery.