Volumetric Growth Research Articles

Personalized Volumetric Tissue Generation by Enhancing Multiscale Mass Transport through 3D Printed Scaffolds in Perfused Bioreactors.

Engineered tissues provide an alternative to graft material, circumventing the use of donor tissue such as autografts or allografts and non-physiological synthetic implants. However, their lack of vasculature limits the growth of volumetric tissue more than several millimeters thick which limits their success post-implantation. Perfused bioreactors enhance nutrient mass transport inside lab-grown tissue but remain poorly customizable to support the culture of personalized implants. Here, a multiscale framework of computational fluid dynamics (CFD), additive manufacturing, and a perfusion bioreactor system are presented to engineer personalized volumetric tissue in the laboratory. First, microscale 3D printed scaffold pore geometries are designed and 3D printed to characterize media perfusion through CFD and experimental fluid testing rigs. Then, perfusion bioreactors are custom-designed to combine 3D printed scaffolds with flow-focusing inserts in patient-specific shapes as simulated using macroscale CFD. Finally, these computationally optimized bioreactor-scaffold assemblies are additively manufactured and cultured with pre-osteoblast cells for 7, 20, and 24days to achieve tissue growth in the shape of human calcaneus bones of 13mL volume and 1cm thickness. This framework enables an intelligent model-based design of 3D printed scaffolds and perfusion bioreactors which enhances nutrient transport for long-term volumetric tissue growth in personalized implant shapes. The novel methods described here are readily applicable for use with different cell types, biomaterials, and scaffold microstructures to research therapeutic solutions for a wide range of tissues.

Current Understanding of the Genetics and Molecular Mechanisms Regulating Wood Formation in Plants.

Unlike herbaceous plants, woody plants undergo volumetric growth (a.k.a. secondary growth) through wood formation, during which the secondary xylem (i.e., wood) differentiates from the vascular cambium. Wood is the most abundant biomass on Earth and, by absorbing atmospheric carbon dioxide, functions as one of the largest carbon sinks. As a sustainable and eco-friendly energy source, lignocellulosic biomass can help address environmental pollution and the global climate crisis. Studies of Arabidopsis and poplar as model plants using various emerging research tools show that the formation and proliferation of the vascular cambium and the differentiation of xylem cells require the modulation of multiple signals, including plant hormones, transcription factors, and signaling peptides. In this review, we summarize the latest knowledge on the molecular mechanism of wood formation, one of the most important biological processes on Earth.

Evaluating growth trends of residual sporadic vestibular schwannomas: a systematic review and meta-analysis.

Gross total resection remains the gold-standard approach for vestibular schwannomas (VS) when surgery is indicated. In select cases, incomplete resection (IR) becomes a desired alternative to preserve the facial nerve function and the patient's quality of life. While a lot of earlier studies described incompletely resected sporadic VSs as dormant, more recent studies reported a higher growth rate following IR, therefore an evaluation of the residual VS growth rates could have important implications for the follow-up treatment protocols and provide relevant information for neurosurgeons, neuro-otologists, neuropathologists, and radiologists. Although prognostic factors predicting preoperative VS growth have been previously investigated, these factors have not been investigated following IR. Our review aims to examine the growth rate of residual sporadic VS following IR and to examine variables associated with the regrowth of residual VS. The review was conducted in accordance with the PRISMA guidelines. Six databases (MEDLINE (Ovid), Embase (Ovid), CINAHL Plus (EBSCO), Cochrane Central Register of Controlled Trials (CENTRAL), WHO International Clinical Trials Registry Platform and UK Clinical Trials Gateway (WHO ICTRP) were searched. Full-text articles analysing growth rates in at least ten patients who had residual VS after IR were assessed. We conducted a meta-analysis using a random-effects model via RevMan. 14 studies totalling 849 patients were included in the analysis. The mean planimetric growth rate was 1.57mm/year (range 0.16-3.81mm/year). The mean volumetric growth rate was 281.725 mm3/year (range 17.9-530.0 mm3/year). Age, sex, pre-operative tumour size/volume, cystic tumour sub-type, MIB-1 index, and intracanalicular tumour location were not associated with residual growth. Residual tumour size/volume was statistically significant to growth (OR = 0.65, 95% CI 0.47-0.90, p = 0.01). Radiological re-growth occurred in an average of 26.6% of cases (range 0-54.5%). From our analysis, only the residual tumour volume/size was associated with residual VS growth. Therefore, close postoperative surveillance for the first year, followed by an annual MRI scan for at least 5years, and subsequently extended interval surveillance remains of utmost importance to monitor disease progression and provide timely surgical and adjuvant interventions. Our study shows that future work should be aimed at molecular and histological characteristics of residual VSs to aid prognostic understanding of growth.

Orchestrated neuronal migration and cortical folding: A computational and experimental study.

Brain development involves precisely orchestrated genetic, biochemical, and mechanical events. At the cellular level, neuronal proliferation in the innermost zone of the brain followed by migration towards the outermost layer results in a rapid increase in brain surface area, outpacing the volumetric growth of the brain, and forming the highly folded cortex. This work aims to provide mechanistic insights into the process of brain development and cortical folding using a biomechanical model that couples cell division and migration with volumetric growth. Unlike phenomenological growth models, our model tracks the spatio-temporal development of cohorts of neurons born at different times, with each cohort modeled separately as an advection-diffusion process and the total cell density determining the extent of volume growth. We numerically implement our model in Abaqus/Standard (2020) by writing user-defined element (UEL) subroutines. For model calibration, we apply in utero electroporation (IUE) to ferret brains to visualize and track cohorts of neurons born at different stages of embryonic development. Our calibrated simulations of cortical folding align qualitatively with the ferret experiments. We have made our experimental data and finite-element implementation available online to offer other researchers a modeling platform for future study of neurological disorders associated with atypical neurodevelopment and cortical malformations.

P69: Extracting mural and volumetric growth patterns of platelet aggregates on engineered surfaces by use of an entity tracking algorithm

P69: Extracting mural and volumetric growth patterns of platelet aggregates on engineered surfaces by use of an entity tracking algorithm

Growth of Myriangium sp. in sabouraud medium: a new approach to the definition of kinetic parameters / Crescimento de Myriangium sp. em meio sabouraud: uma nova abordagem para a definição de parâmetros cinéticos

In this study, the yeast growth process was mathematically modeled and growth kinetic parameters were defined for two strains of Myriangium sp. (Y6511 and Y6512) in Sabouraud medium at temperatures of 26, 30 and 34 °C at time t varying from t0 = 0 h, tf = 36 h. Maximum cell concentrations were 30.50 g/L (Y6511 at 34°C) and 34.00 g/L (Y6512 at 34°C). The maximum specific growth rates calculated for strains Y6511 and Y6512 were respectively 0.30 and 0.28 h-1 in the growth condition at 26 °C after 11.5 h of growth (for Y6511) and 9.5 h of growth (for Y6512). Maximum biomass volumetric growth rates were 2.75 and 2.63 g/L.h for strains Y6511 and Y6512, respectively, at 26 °C. For strain Y6511, the unit increase in temperature (g/L.°C) raises the cell concentration to a maximum value of 0.27 g/L.°C in the process time of 9.55 h and temperature of 29.5 °C. Similarly, for strain Y6512, the unit increase in temperature raises the cell concentration to a maximum value of 0.45 g/L.°C in the process time of 7.35 h and temperature of 26.8 °C. The observed parameters can be used for the production of cell mass, in batch or continuous process, enzymes and other bioproducts of commercial interest.

Development of regional brain gray matter volume across the first 13 years of life is associated with childhood math computation ability for children born very preterm and full term

Very preterm birth (VP; <32 weeks’ gestation) is associated with altered brain gray matter development and lower math ability. In typically developing children, the neural correlates of math ability may change dynamically with age, though evidence in VP children is limited. In a prospective longitudinal cohort of children born VP and full term (FT), we aimed to investigate associations between 1) concurrent regional brain volumes and math ability at 7 (n = 148 VP; n = 34 FT) and 13-years (n = 130 VP; n = 46 FT), and 2) regional volumetric growth across childhood (term-equivalent age (TEA) to 7-years; 7 to 13-years) and math ability from 7 to 13-years, and improvement in ability from 7 to 13 years. For both aims we investigated whether associations differed between birth groups. Cross-sectionally, frontal, temporal and subcortical regional volumes were positively associated with math ability for both birth groups. For FT children, greater growth of specific temporal regions was associated with higher math ability, and greater improvements. For VP children, similar associations were only observed for growth from TEA to 7-years with 13-year ability and improvements in ability. In conclusion, VP birth appears to alter associations of brain development across the first 13 years with childhood math ability.

Egr1 is a 3D matrix-specific mediator of mechanosensitive stem cell lineage commitment.

While extracellular matrix (ECM) mechanics strongly regulate stem cell commitment, the field’s mechanistic understanding of this phenomenon largely derives from simplified two-dimensional (2D) culture substrates. Here, we found a 3D matrix–specific mechanoresponsive mechanism for neural stem cell (NSC) differentiation. NSC lineage commitment in 3D is maximally stiffness sensitive in the range of 0.1 to 1.2 kPa, a narrower and more brain-mimetic range than we had previously identified in 2D (0.75 to 75 kPa). Transcriptomics revealed stiffness-dependent up-regulation of early growth response 1 (Egr1) in 3D but not in 2D. Egr1 knockdown enhanced neurogenesis in stiff ECMs by driving β-catenin nuclear localization and activity in 3D, but not in 2D. Mechanical modeling and experimental studies under osmotic pressure indicate that stiff 3D ECMs are likely to stimulate Egr1 via increases in confining stress during cell volumetric growth. To our knowledge, Egr1 represents the first 3D-specific stem cell mechanoregulatory factor.

Relationship Between Coronary Artery Calcium and Atherosclerosis Progression Among Patients With Suspected Coronary Artery Disease

BackgroundAmong symptomatic patients, it remains unclear whether a coronary artery calcium (CAC) score alone is sufficient or misses a sizeable burden and progressive risk associated with obstructive and nonobstructive atherosclerotic plaque. ObjectivesAmong patients with low to high CAC scores, our aims were to quantify co-occurring obstructive and nonobstructive noncalcified plaque and serial progression of atherosclerotic plaque volume. MethodsA total of 698 symptomatic patients with suspected coronary artery disease (CAD) underwent serial coronary computed tomographic angiography (CTA) performed 3.5 to 4.0 years apart. Atherosclerotic plaque was quantified, including by compositional subgroups. Obstructive CAD was defined as ≥50% stenosis. Multivariate linear regression models were used to measure atherosclerotic plaque progression by CAC scores. Cox proportional hazard models estimated CAD event risk (median of 10.7 years of follow-up). ResultsAcross baseline CAC scores from 0 to ≥400, total plaque volume ranged from 30.4 to 522.4 mm3 (P < 0.001) and the prevalence of obstructive CAD increased from 1.4% to 49.1% (P < 0.001). Of those with a 0 CAC score, 97.9% of total plaque was noncalcified. Among patients with baseline CAC <100, nonobstructive CAD was prevalent (40% and 89% in CAC scores of 0 and 1-99), with plaque largely being noncalcified. On the follow-up coronary CTA, volumetric plaque growth (P < 0.001) and the development of new or worsening stenosis (P < 0.001) occurred more among patients with baseline CAC ≥100. Progression varied compositionally by baseline CAC scores. Patients with no CAC had disproportionate growth in noncalcified plaque, and for every 1 mm3 increase in calcified plaque, there was a 5.5 mm3 increase in noncalcified plaque volume. By comparison, patients with CAC scores of ≥400 exhibited disproportionate growth in calcified plaque with a volumetric increase 15.7-fold that of noncalcified plaque. There was a graded increase in CAD event risk by the CAC with rates from 3.3% for no CAC to 21.9% for CAC ≥400 (P < 0.001). ConclusionsCAC imperfectly characterizes atherosclerotic disease burden, but its subgroups exhibit pathogenic patterns of early to advanced disease progression and stratify long-term prognostic risk.

Management of Sporadic Vestibular Schwannomas in Children-Volumetric Analysis and Clinical Outcome Assessment.

Vestibular schwannomas (VS) usually manifest between the 5th and 8th decade of life. Most pediatric cases are associated with Neurofibromatosis type 2 and sporadic VS are rare in this age group. Few case series have been published. We report on our institutional series of sporadic VS in children. We included all cases between 2003 and 2021; 28 of 1635 patients harbored a sporadic VS and were younger than 21 years old. A retrospective review of clinical parameters and surgical data as well as outcomes was performed. All procedures were performed via a retrosigmoid approach. Preoperative imaging was assessed, and tumor volumetry was performed. Mean follow-up was 28 months, symptomatology was diverse. Most children and adolescents presented with hearing loss and tinnitus. All cases with multiple preoperative magnetic resonance imaging scans showed volumetric tumor growth between 1 and 18%/month (mean 8.9 ± 5.6%). Cystic tumor morphology and bone erosion was seen in larger tumors. Gross total resection was possible in 78% of patients and no recurrence was observed. All patients with subtotal resection showed tumor regrowth. Sporadic VS in children are rare and present with a high clinical variability. Surgical resection is the primary therapy and is feasible with favorable results comparable to the adult age group.

Patient age at time of reverse shoulder arthroplasty remains stable over time: a 7.5-year trend evaluation.

There is a common belief among some shoulder surgeons that the increased utilization of reverse shoulder arthroplasty (RSA) is driven by the operation being performed in younger patients. The primary purpose of this study was to evaluate the change in patient age at the time of primary RSA in the USA. All patients undergoing primary RSA (January 2011-June 2018) were identified in the Mariner database. The mean age at the time of primary RSA was evaluated for each patient and assessed in 6-month intervals. A longitudinal comparison over time was performed for all patients. A total of 56,141 primary RSA were evaluated, with the mean age increasing from 69 in the 2011 to 71 in 2018 (p < 0.001). The largest increase in RSA utilization occurred in patients > 70 (1092 in 2011 to 3499 in 2018), with patients < 50years demonstrating the slowest growth (13 in 2011 to 65 in 2018). However, when evaluated by percentage increase from 2011 to 2018, RSA volumes for patients < 60 have increased 390% compared to 220% for those > 70years (p < 0.001). RSA continues to be performed at a similar mean age despite expanded indications and surgeon comfort. However, patients < 60years have had a greater increase in utilization compared to patients > 70years. The volumetric growth of RSA has largely been driven by the older population, but younger patients have shown a higher percentage of growth, which may explain the generalized observation that RSA is performed in younger patients. Level III; Retrospective comparative study; Treatment study.

Hearing loss and volumetric growth rate in untreated vestibular schwannoma.

In this study, the authors aimed to clarify the relationship between hearing loss and tumor volumetric growth rates in patients with untreated vestibular schwannoma (VS). Records of 128 treatment-naive patients diagnosed with unilateral VS between 2012 and 2018 with serial audiometric assessment and MRI were reviewed. Tumor growth rates were determined from initial and final tumor volumes, with a median follow-up of 24.3 months (IQR 8.5-48.8 months). Hearing changes were based on pure tone averages, speech discrimination scores, and American Academy of Otolaryngology-Head and Neck Surgery hearing class. Primary outcomes were the loss of class A hearing and loss of serviceable hearing, estimated using the Kaplan-Meier method and with associations estimated from Cox proportional hazards models and reported as hazard ratios. Larger initial tumor size was associated with an increased risk of losing class A (HR 1.5 for a 1-cm3 increase; p = 0.047) and serviceable (HR 1.3; p < 0.001) hearing. Additionally, increasing volumetric tumor growth rate was associated with elevated risk of loss of class A hearing (HR 1.2 for increase of 100% per year; p = 0.031) and serviceable hearing (HR 1.2; p = 0.014). Hazard ratios increased linearly with increasing growth rates, without any evident threshold growth rate that resulted in a large, sudden increased risk of hearing loss. Larger initial tumor size and faster tumor growth rates were associated with an elevated risk of loss of class A and serviceable hearing.

Volumetric growth rates of untreated cavernous sinus meningiomas.

Meningiomas that arise primarily within the cavernous sinus are often believed to be more indolent in their growth pattern. Despite this perceived growth pattern, disabling symptoms can arise even with small tumors. While research has been done on cavernous sinus meningiomas (CSMs) and their treatment, very little is known about their natural growth rates. With a better understanding of the growth rate of CSM, patient treatment and guidance can be can optimized and individualized. The goal of this study was to determine volumetric growth rates of untreated CSMs. Thirty-seven patients with 166 MR images obtained between May 2004 and September 2019 were reviewed, with a range of 2-13 MR images per patient (average of 4.5 MR images per patient). These scans were obtained over an average follow-up period of 45.9 months (median 33.8, range 2.8-136.9 months). All imaging prior to any intervention was included in this analysis. Volumetric measurements were performed and assessed over time. The estimated volumetric growth rate was 23.3% per year (95% CI 10.2%-38.0%, p < 0.001), which is equivalent to an estimated volume doubling time (VDT) of 3.3 years (95% CI 2.1-7.1 years). There was no significant relationship between growth rate and patient age (p = 0.09) or between growth rate and patient sex (p = 0.78). The median absolute growth rate was 41% with a range of -1% to 1793%. With a definition of "growth" as an increase of greater than 20% during the observed period, 65% of tumors demonstrated growth within their observation interval. Growth rates for each tumor were calculated and tumors were segmented based on growth rate. Of 37 patients, 22% (8) demonstrated no growth (< 5% annual growth, equivalent to a VDT > 13.9 years), 32% (12) were designated as slow growth (annual growth rate 5%-20%, VDT 3.5-13.9 years), 38% (14) were found to have medium growth (annual growth rate 20%-100%, VDT 0.7-3.5 years), and 8% were considered fast growing (annual growth rate > 100%, VDT < 0.7 years). This study evaluated CSM volumetric growth rates. A deeper understanding of the natural history of untreated CSMs allows for better counseling and management of patients.

Characterization of volumetric growth of intracranial meningiomas in Māori and Pasifika populations in New Zealand.

Māori and Pasifika populations in New Zealand have a higher incidence and prevalence of intracranial meningioma (IM). We sought to evaluate the volumetric growth rate of meningiomas under surveillance in these populations. From July 2002 to October 2020, 336 patients with a total of 408 IM underwent conservative management with serial radiological surveillance at Auckland City Hospital and met the criteria for the study. Inclusion criteria included: age >16 at diagnosis, ≥2 appropriate scans one or more years apart. Exclusion criteria included previous cranial irradiation, a diagnosis of Neurofibromatosis and prior treatment of meningioma. Demographic and clinical data were obtained from the electronic medical records. Imaging data were recorded from the first and last scans. We utilized open-source image processing software (3D Slicer) for semi-automated segmentation and volume calculation. Consistent with previous literature, we calculated the relative growth rate (RGR, %/year) and annual volume change (AVC, cm3 /year) over time. Four hundred and eight meningiomas were volumetrically characterized for a mean duration of 6.2 years. The Māori and Pasifika populations (n= 134/393) demonstrated a higher RGR (31.41 versus 14.33%/year) (P= 0.026) and AVC (2.05 versus 0.95 cm3 ) (P= 0.025) compared to the control population. They also presented at a younger age and had a higher rate of tumour multiplicity. Males represented only 17.6% of the cohort but exhibited a higher growth rate (AVC=2.52 cm3 /year) than females (AVC=0.99 cm3 /year) (P= 0034). Māori and Pasifika populations in New Zealand have a higher incidence and volumetric growth rate of IM compared to a control population. This warrants further clinical, histopathological and genomic analysis.

Growth kinetics and progression rates of cystic renal masses on active surveillance.

298 Background: The Bosniak classification is used to risk stratify the probability of cancer among cystic renal masses using CT or MRI and assigns a class ranging from I-IV. Bosniak III and IV masses have the highest probabilities of cancer and are treated similarly to solid renal masses per 2021 American Urological Association (AUA) Guidelines. The purpose of this study was to determine the growth kinetics and progression rates of unresected Bosniak III and IV masses defined by Bosniak Classification, version 2019 (v2019). Methods: In this retrospective and IRB-approved study, CT and MRI images of 107 cystic renal masses from 100 patients (34 women, 66 men; range 28-92 years) with unresected Bosniak III and IV masses from 2005-2021 were reviewed. Cystic renal masses on baseline imaging were assigned a category based on v2019 by two abdominal radiologists, with discrepancies resolved by a third, such that each mass had a single Bosniak class assignment. Mass dimensions over serial imaging were measured using orthogonal planes by a radiologist with 3D laboratory training. Linear growth rate (mm/year) and volumetric growth rate (mL/year) were calculated. “Progression” off of active surveillance was defined as any of the following: linear growth rate &gt; 5 mm a year, volume doubling rate ≤ 1 year, or increased stage based on TNM. Results: 107 cystic renal masses were categorized as 51 Bosniak III and 56 Bosniak IV masses on baseline exam. Median follow-up time was 406 days. Linear growth rate for Bosniak III masses was 0.4 ± 4.3 mm/year while linear growth rate for Bosniak IV masses was 2.3 ± 4.9 mm/year (p = 0.036; Student’s t-test). 12/51 (24%) Bosniak III masses progressed based on above definitions while 26/56 (46%) Bosniak IV masses progressed (p = 0.016; Fisher’s exact test). 13 masses upgraded from a Bosniak III to IV during surveillance, but category upgrades were not associated with progression (p = 0.131; Fisher’s exact test). 2 patients developed lung metastases; both masses were Bosniak IV and were biopsy proven papillary and clear cell renal cell carcinomas. Conclusions: Although currently treated similarly by AUA Guidelines, unresected Bosniak IV masses grow faster than Bosniak III masses and are more likely to progress off of active surveillance.

Abstract WP12: Evolution Of Regional Flair White Matter Hyperintensities After Ischemic Stroke: A Voxel-wise Approach

Background: White matter (WM) degeneration after ischemic stroke may herald post-stroke cognitive decline. FLAIR WM hyperintensity (WMH) reflects tissue injury and accumulates around the infarct and in remote regions. But WMH volumetry is insensitive to regional progression. We compared WMH volumetry to a voxel-wise (VW) approach for detecting FLAIR WMH change longitudinally after stroke. Methods: Ischemic stroke patients enrolled in an observational cohort study underwent serial MRI acutely, at 1 month and every 3 months thereafter. Patients with 6 to 12-month follow-up were included. WMH lesion volumes were automatically segmented on serial FLAIR MRI. In the hemisphere contralateral to the infarct after 30 days, we compared longitudinal change in WMH volume to a VW regression of FLAIR signal change over time. Serial FLAIR images were nonlinearly aligned using a T1 intermediate. FLAIR intensities were normalized, corrected for local expansion/contraction, and smoothed. Within voxels identified as lesion at any timepoint, significant WMH change was determined relative to the normal appearing WM and converted to percent of total intracranial volume (TICV). Results: 22 stroke patients (mean age 73, NIHSS 4, infarct volume 10.3cc) had on average 3 follow-ups over 343 days. In the non-stroke hemisphere, volumetry revealed lesion growth in 12 participants (55%) while VW analysis revealed FLAIR signal increase in 15 (68%). For volumetry, mean lesion increase was 0.01 ± 0.20% of TICV per year while VW FLAIR intensity increased in mean 0.11 ± 0.23% of total intracranial voxels. Volumetric growth was associated with the volume of VW signal increase (Std Beta = 0.51, p = 0.02). In the stroke hemisphere, WMH expansion of peri-infarct tissue, consistent with Wallerian degeneration, was present in 10 participants (45%). WMH regression, consistent with atrophy or infarct cavitation, was present in 14 participants (64%). Stroke hemisphere WMH expansion was associated with higher NIHSS (Std B = 0.58, p = 0.009) while regression was associated with larger infarct volumes (Std B = 0.80, p &lt; 0.001). Conclusions: In early chronic stroke, VW longitudinal WMH analysis detects progressive WM degradation with regional variation and may be more sensitive than gross volumetry.

Adsorption and deformation characteristics of coal under liquid nitrogen cold soaking

The research on gas adsorption deformation characteristics of coal under liquid nitrogen cold soaking deserves investigation, as most of the investigation efforts in this field are in a preliminary stage. In this article, the experiments of coal adsorption deformation under different times of liquid nitrogen cold soaking (0, 1, 3, 5, 7 and 9) were carried out. The variation of coal gas adsorption capacity and volumetric strain under different times of liquid nitrogen cold soaking were investigated. Based on thermodynamics, the adsorption strain model of coal was developed, and the relationship between coal adsorption capacity and volumetric strain was discussed. The research results show that: (i) the coal adsorption capacity and volumetric strain both gradually decrease with the increase of the number of liquid nitrogen cold soaking; (ii) the saturated gas adsorption capacity and limit volume strain of coal both show a decreasing trend with the increase of liquid nitrogen cold soaking times; (iii) the volumetric strain of coal under the different times of liquid nitrogen cold soaking first accelerates and then slowly rises with the increase of adsorption capacity. After liquid nitrogen cold soaking, the volumetric strain growth rate of coal gradually decreases; (iv) the coal under different cold soaking times reaches the limit volumetric strain at a pressure (P) that is higher than the pressure (p) required to reach the saturation adsorption capacity, and the values of p and P both show a decreasing trend with the increase of liquid nitrogen cold soaking times; (v) the model results have good predictive effect.

Volumetric growth of soft tissues evaluated in the current configuration

The growth and remodelling of soft tissues plays a significant role in many physiological applications, particularly in understanding and managing many diseases. A commonly used approach for soft tissue growth and remodelling is volumetric growth theory, introduced in the framework of finite elasticity. In such an approach, the total deformation gradient tensor is decomposed so that the elastic and growth tensors can be studied separately. A critical element in this approach is to determine the growth tensor and its evolution with time. Most existing volumetric growth theories define the growth tensor in the reference (natural) configuration, which does not reflect the continuous adaptation processes of soft tissues under the current configuration. In a few studies where growth from a loaded configuration was considered, simplifying assumptions, such as compatible deformation or geometric symmetries, were introduced. In this work, we propose a new volumetric growth law that depends on fields evaluated in the current configuration, which is residually stressed and loaded, without any geometrical restrictions. We illustrate our idea using a simplified left ventricle model, which admits inhomogeneous growth in the current configuration. We compare the residual stress distribution of our approach with the traditional volumetric growth theory, that assumes growth occurring from the natural reference configuration. We show that the proposed framework leads to qualitative agreements with experimental measurements. Furthermore, using a cylindrical model, we find an incompatibility index that explains the differences between the two approaches in more depth. We also demonstrate that results from both approaches reach the same steady solution published previously at the limit of a saturated growth. Although we used a left ventricle model as an example, our theory is applicable in modelling the volumetric growth of general soft tissues.

A macroscopic approach for stress-driven anisotropic growth in bioengineered soft tissues

The simulation of growth processes within soft biological tissues is of utmost importance for many applications in the medical sector. Within this contribution, we propose a new macroscopic approach for modelling stress-driven volumetric growth occurring in soft tissues. Instead of using the standard approach of a-priori defining the structure of the growth tensor, we postulate the existence of a general growth potential. Such a potential describes all eligible homeostatic stress states that can ultimately be reached as a result of the growth process. Making use of well-established methods from visco-plasticity, the evolution of the growth-related right Cauchy–Green tensor is subsequently defined as a time-dependent associative evolution law with respect to the introduced potential. This approach naturally leads to a formulation that is able to cover both, isotropic and anisotropic growth-related changes in geometry. It furthermore allows the model to flexibly adapt to changing boundary and loading conditions. Besides the theoretical development, we also describe the algorithmic implementation and furthermore compare the newly derived model with a standard formulation of isotropic growth.

Lateral forces determine dimensional accuracy of the narrow-kerf sawing of wood

The shrinking global forest area limits the supply of industrially usable raw resources. This, in combination with the ever-increasing consumption of timber due to population growth can lead to the lack of a positive balance between the annual volumetric growth and consumption of wood. An important innovation toward increasing environmental and economic sustainability of timber production is to reduce the volume of wood residues by minimizing the sawing kerf. It results in higher material yield but may impact the dimensional accuracy of derived products. Therefore, the cutting tool geometry as well as the sawing process as a whole must be carefully optimized to assure optimal use of resources. The goal of this study is to better understand the causes of machining errors that occur when sawing wood with saws of varying thickness of kerf, with a special focus on re-sawing thin lamellae performed on the gang saw. Numerical simulations were tested against experimental results, considering influence of diverse components of cutting forces, in addition to the initial and operating stiffness coefficients of the saw blade. It has been demonstrated that asymmetric loads from the cutting process for the scraper saw blade can cause sawing inaccuracies. The simulation methodology developed in this research can be straightforwardly extended towards determination of optimal geometry of other cutting tools, particularly with the reduced sawing kerf. This may lead to more sustainable use of natural resources as well as an increase in economic gain for the wood processing industries.