Acclimation to wind loads and/or contact stimuli? A biomechanical study of peltate leaves of Pilea peperomioides.

Plants are exposed to various environmental stresses. Leaves immediately respond to mechano-stimulation, such as wind and touch, by bending and twisting or acclimate over a longer time period by thigmomorphogenetic changes of mechanical and geometrical properties. We selected the peltate leaves of Pilea peperomioides for a comparative analysis of mechano-induced effects on morphology, anatomy, and biomechanics of petiole and transition zone. The plants were cultivated for 6 weeks in a phytochamber divided into four treatment groups: control (no stimulus), touch stimulus (brushing every 30 s), wind stimulus (constant air flow of 4.6 m s-1), and a combination of touch and wind stimuli. Comparing the four treatment groups, neither the petiole nor the transition zone showed significant thigmomorphogenetic acclimations. However, comparing the petiole and the transition zone, the elastic modulus (E), the torsional modulus (G), the E/G ratio, and the axial rigidity (EA) differed significantly, whereas no significant difference was found for the torsional rigidity (GK). The twist-to-bend ratios (EI/GK) of all petioles ranged between 4.33 and 5.99, and of all transition zones between 0.67 and 0.78. Based on the twist-to-bend ratios, we hypothesize that bending loads are accommodated by the petiole, while torsional loads are shared between the transition zone and petiole.

Biomechanics of the parasite-host interaction of the European mistletoe.

The European mistletoe (Viscum album) is an epiphytic hemiparasite that attaches to its host by an endophytic system. Two aspects are essential for its survival: the structural integrity of the host-parasite interface must be maintained during host growth and the functional integrity of the interface must be maintained during ontogeny and under mechanical stress. We investigated the mechanical properties of the mistletoe-host interaction. Intact and sliced mistletoe-host samples, with host wood as reference, were subjected to tensile tests up to failure. We quantified the rough fractured surface by digital microscopy and analysed local surface strains by digital image correlation. Tensile strength and deformation energy were independent of mistletoe age but exhibited markedly lower values than host wood samples. Cracks initiated at sites with a major strain of about 30%, especially along the mistletoe-host interface. The risk of sudden failure was counteracted by various sinkers and a lignification gradient that smooths the differences in the mechanical properties between the two species. Our results improve the understanding of the key mechanical characteristics of the host-mistletoe interface and show that the mechanical connection between the mistletoe and its host is age-independent. Thus, functional and structural integrity is ensured over the lifetime of the mistletoe.

Functional morphology of plants - a key to biomimetic applications.

Learning from living organisms has emerged from a mainly curiosity-driven examination, where helpful functions of biological structures have been copied, into systematic biomimetic approaches that transfer a targeted function and its underlying principles from the biological model to a technical product. Plant biomimetics is based on functional morphology, which combines the knowledge gained from the morphology, anatomy and mechanics of plants and makes a statement about their form-structure-function relationship. Since the functional morphology of plants has become key to biomimetic applications, we present its central role in deciphering the functional principles that can be applied to engineering solutions. We consider that the future of biomimetics will include bioinspired developments that will contribute to better sustainability than that achieved by conventional products.

Peak values of twist-to-bend ratio in triangular flower stalks of Carex pendula: a study on biomechanics and functional morphology.

PREMISE: Because of their own weight and additional wind forces, plants are exposed to various bending and torsional loads that sometimes require contradictory structural characteristics and mechanical properties. The resulting trade-off between flexural and torsional rigidity can be quantified and compared using the dimensionless twist-to-bend ratio. METHODS: The flexural rigidity of the stems of Carex pendula was determined by 2-point bending tests. Additionally, 4-point bending tests and torsional tests were carried out on segments of two internodes directly below the inflorescences to measure flexural and torsional rigidity. Anatomical investigations were performed to quantify the cross-sectional distribution of their tissues. RESULTS: The flexural rigidity of the stems, segments of the apical internode 1, and the more basal internode 2 differed significantly from each other, whereas the bending elastic moduli were not significantly different. The torsional rigidity of segments of internode 2 was a factor of 3.3 higher than that of internode 1, whereas the torsional moduli did not differ significantly. The twist-to-bend ratios of segments of internode 1 and 2 reached values between 85 and 403. Light microscopic investigations revealed a triangular stem possessing individual sclerenchyma strands, with internode 2 having significantly more strands than internode 1. CONCLUSIONS: In the case of Carex pendula, flexural and torsional rigidity are adapted to the given mechanical constraints by significant changes in morphometric variables (axial and polar second moment of area, number of sclerenchyma strands), whereas the material properties (bending and torsional modulus) do not change markedly along the stem.

Self-Repair in Cacti Branches: Comparative Analyses of Their Morphology, Anatomy, and Biomechanics.

Damage-repair is particularly important for the maintenance of the water-storing abilities of succulent plants such as cacti. Comparative morphological, anatomical, and biomechanical analyses of self-repair were performed on artificially wounded branches of Opuntia ficus-indica and Cylindropuntia bigelovii. Macroscopic observations, contrast staining, and lignin-proof staining were used to investigate morphological and anatomical responses after wounding at various time intervals. Two-point bending tests were repeatedly performed on the same branches under unwounded, freshly wounded, and healed conditions by using customized 3D-printed clamping jaws. Morphologically, both species showed a rolling-in of the wound edges, but no mucilage discharge. Anatomically, ligno-suberized peridermal layers developed that covered the wound region, and new parenchyma cells formed, especially in O. ficus-indica. In all samples, the wounding effect directly after damage caused a decrease between 18% and 37% in all the tested mechanical parameters, whereas a positive healing effect after 21 days was only found for C. bigelovii. Based on our data, we hypothesize a high selection pressure on the restoration of structural integrity in the wound area, with a focus on the development of efficient water-retaining mechanisms, whereas the concept of "sufficient is good enough" seems to apply for the restoration of the mechanical properties.

Comparative Analyses of the Self-Sealing Mechanisms in Leaves of Delosperma cooperi and Delosperma ecklonis (Aizoaceae).

Within the Aizoaceae, the genus Delosperma exhibits a vast diversification colonizing various ecological niches in South-Africa and showing evolutionary adaptations to dry habitats that might include rapid self-sealing. Leaves of Delosperma react to external damage by the bending or contraction of the entire leaf until wound edges are brought into contact. A study of leaf morphology and anatomy, biomechanics of entire leaves and individual tissues and self-sealing kinematics after a ring incision under low and high relative humidity (RH) was carried out comparing the closely related species Delosperma cooperi and Delosperma ecklonis, which are indigenous to semi-arid highlands and regions with an oceanic climate, respectively. For both species, the absolute contractions of the examined leaf segments ("apex", "incision", "base") were more pronounced at low RH levels. Independent of the given RH level, the absolute contractions within the incision region of D. cooperi were significantly higher than in all other segments of this species and of D. ecklonis. The more pronounced contraction of D. cooperi leaves was linked mainly to the elastic properties of the central vascular strand, which is approximately twice as flexible as that of D. ecklonis leaves.

Drooping of Gerbera flower heads: mechanical and structural studies of a well-known phenomenon.

Gerbera, one of the most loved cut flowers, is (in)famous for the drooping of its flower heads under dehydration. This effect has been quantified by analysing both fully turgescent and wilting peduncles of Gerbera jamesonii 'Nuance'. Wilting peduncles display pronounced bending in the region directly below the inflorescence after 24 h of dehydration, while the rest of the peduncle remains upright. Using anatomical measurements and three-point bending tests, we have analysed whether this phenomenon is caused by mechanical and/or geometrical alterations. We have found that both the flexural rigidity and the axial second moment of area are significantly decreased in the apical part of wilting peduncles, whereas the bending elastic modulus shows no significant change. Moreover, cross-sections of wilting peduncles ovalize significantly more than those of turgescent peduncles and exhibit considerable shrinkage of the parenchyma, taking up the majority of the cross-sectional area. Generally, the drooping of wilting Gerbera flowers can be regarded as a temporary instability of a rod-shaped cellular solid caused by anatomical differences (tissue arrangement, existence or the absence of a pith cavity) and geometrical changes (the decrease of axial second moment of area, cross-sectional ovalization, shrinkage of tissues) between the apical and basal regions of their peduncles.

Finite element modelling of complex movements during self-sealing of ring incisions in leaves of Delosperma cooperi.

A numerical computer model was developed in order to describe the complex self-sealing mechanism of injured Delosperma cooperi leaves. For this purpose, the leaf anatomy was simplified to a model consisting of five concentric tissue layers. Specific parameters (modulus of elasticity, permeability, porosity, etc.) were assigned to each tissue type for modelling its physical properties. These parameters were either determined experimentally from living plant material or taken from literature. The developed computer model considers the leaf as a liquid-filled porous body within a continuum approach in order to determine the governing equations. The modelling of the wound accounts for both the injury of peripheral tissues and the free surfaces caused by the incision. The loss of water through these free surfaces initiates the self-sealing process. It is further shown that the tissue permeability and the reflection coefficient (relative permeability of a cell membrane for solutes) are the determining parameters of the self-sealing process, whereas the modulus of elasticity has a negligible influence. Thus, the self-sealing mechanism is a hydraulically driven process which leads to a local (incision region) and global (total leaf) contraction of the leaf. The accuracy of the modelled self-sealing process was validated by comparing simulation results with experiments conducted on natural plant leaves. The results will serve as valuable input for developing novel, bio-inspired technical products with self-sealing function.

Adaptive spatiotemporal changes in morphology, anatomy, and mechanics during the ontogeny of subshrubs with square-shaped stems.

PREMISE OF THE STUDY: Plant stems can be regarded as fiber-reinforced structures characterized by anatomical heterogeneity, mechanical anisotropy, and adaptability to changing internal and external constraints. Our study focused on adaptive spatiotemporal changes in morphology, anatomy, and mechanical properties during the ontogeny of Leonurus cardiaca L. (Lamiaceae) internodes, proving considerable functional adaptability. METHODS: Four-point bending tests and torsional tests were carried out on the same internodes to measure flexural and torsional stiffness. Axial and polar second moments of area for entire cross sections and for individual tissues were determined from transverse stem sections immediately after testing. Based on these data, additional relevant mechanical parameters such as bending elastic modulus, torsional modulus and twist to bend ratio were calculated. KEY RESULTS: Leonurus cardiaca is characterized by a square-shaped hollow stem in transverse section with an outer frame of various strengthening tissues and an inner ring of parenchyma. Statistical analyses of axial and polar second moment of area, flexural stiffness, torsional stiffness, bending elastic modulus, and torsional modulus revealed significant differences for all comparisons with respect to spatial resolution (two adjacent internodes) and temporal resolution (in June before flowering and in September after fruit formation). The twist to bend ratios of the internodes, however, always remain in the same range. CONCLUSIONS: With respect to spatiotemporal development, stems of the subshrub L. cardiaca show a marked increase in flexural and torsional stiffness during ontogeny. Strikingly, changes in stem mechanics are more influenced by variations in mechanical tissue properties than by changes in relative proportion of different tissue types.

Association Between Body Mass Index and Clinical and Endoscopic Features of Eosinophilic Esophagitis.

BACKGROUND: Because eosinophilic esophagitis (EoE) causes dysphagia, esophageal narrowing, and strictures, it could result in low body mass index (BMI), but there are few data assessing this. AIM: To determine whether EoE is associated with decreased BMI. METHODS: We conducted a prospective study at the University of North Carolina from 2009 to 2013 enrolling consecutive adults undergoing outpatient EGD. BMI and endoscopic findings were recorded. Incident cases of EoE were diagnosed per consensus guidelines. Controls had either reflux or dysphagia, but not EoE. BMI was compared between cases and controls and by endoscopic features. RESULTS: Of 120 EoE cases and 297 controls analyzed, the median BMI was lower in EoE cases (25 vs. 28 kg/m2, p = 0.002). BMI did not differ by stricture presence (26 vs. 26 kg/m2, p = 0.05) or by performance of dilation (26 vs. 27 kg/m2 for undilated; p = 0.16). However, BMI was lower in patients with narrow caliber esophagus (24 vs. 27 kg/m2, p < 0.001). EoE patients with narrow caliber esophagus also had decreased BMI compared to controls with narrow caliber esophagi (24 vs. 27 kg/m2, p = 0.001). On linear regression after adjustment for age, race, and gender, narrowing decreased BMI by 2.3 kg/m2 [95% CI -4.1, -0.6]. CONCLUSIONS: BMI is lower in EoE cases compared to controls, and esophageal narrowing, but not focal stricture, is associated with a lower BMI in patients with EoE. Weight loss or low BMI in a patient suspected of having EoE should raise concern for esophageal remodeling causing narrow caliber esophagus.

Gastric adenocarcinoma microRNA profiles in fixed tissue and in plasma reveal cancer-associated and Epstein-Barr virus-related expression patterns.

MicroRNA expression in formalin-fixed paraffin-embedded tissue (FFPE) or plasma may add value for cancer management. The GastroGenus miR Panel was developed to measure 55 cancer-specific human microRNAs, Epstein-Barr virus (EBV)-encoded microRNAs, and controls. This Q-rtPCR panel was applied to 100 FFPEs enriched for adenocarcinoma or adjacent non-malignant mucosa, and to plasma of 31 patients. In FFPE, microRNAs upregulated in malignant versus adjacent benign gastric mucosa were hsa-miR-21, -155, -196a, -196b, -185, and -let-7i. Hsa-miR-18a, 34a, 187, -200a, -423-3p, -484, and -744 were downregulated. Plasma of cancer versus non-cancer controls had upregulated hsa-miR-23a, -103, and -221 and downregulated hsa-miR-378, -346, -486-5p, -200b, -196a, -141, and -484. EBV-infected versus uninfected cancers expressed multiple EBV-encoded microRNAs, and concomitant dysregulation of four human microRNAs suggests that viral infection may alter cellular biochemical pathways. Human microRNAs were dysregulated between malignant and benign gastric mucosa and between plasma of cancer patients and non-cancer controls. Strong association of EBV microRNA expression with known EBV status underscores the ability of microRNA technology to reflect disease biology. Expression of viral microRNAs in concert with unique human microRNAs provides novel insights into viral oncogenesis and reinforces the potential for microRNA profiles to aid in classifying gastric cancer subtypes. Pilot studies of plasma suggest the potential for a noninvasive addition to cancer diagnostics.

Lymphocytic Esophagitis: An Emerging Clinicopathologic Disease Associated with Dysphagia.

BACKGROUND: Lymphocytic esophagitis (LyE) is a recently described clinicopathological condition, but little is known about its features and clinical associations. AIM: The aim of this study was to characterize patients with LyE, compare them to non-LyE controls, and identify risk factors. METHODS: We conducted a retrospective study of all patients ≥18 years old who underwent upper endoscopy with esophageal biopsy between January 1, 2000, and June 1, 2012. Archived pathology slides were re-reviewed, and LyE was diagnosed if there was lymphocyte-predominant esophageal inflammation with no eosinophils or granulocytes. Three non-LyE controls groups were also defined: reflux, eosinophilic esophagitis (EoE), and normal. Clinical data were extracted from electronic medical records, and LyE cases were compared to non-LyE controls. RESULTS: Twenty-seven adults were diagnosed with LyE, and the majority were female (63 %). The most common symptom was dysphagia (70 %). Fifty-two percentage had a prior or current diagnosis of reflux. Endoscopic findings included strictures (37 %), erosive esophagitis (33 %), rings (26 %), and hiatal hernia (26 %); 33 % of patients required dilation. After histology re-review, 78 % of LyE patients were found to have more than 20 lymphs/hpf. In comparison with the normal, reflux and EoE controls, patients with LyE tended to be nonwhite (p < 0.01), were more commonly tobacco users (p = 0.02) and less likely to have seasonal allergies (p = 0.02). CONCLUSION: LyE commonly presents with dysphagia due to esophageal strictures which require dilation. Smoking was associated with LyE, whereas atopy was not. LyE should be considered as a diagnostic possibility in patients with these characteristics undergoing upper endoscopy.

Utility of a Noninvasive Serum Biomarker Panel for Diagnosis and Monitoring of Eosinophilic Esophagitis: A Prospective Study.

OBJECTIVES: Noninvasive biomarkers would be valuable for diagnosis and monitoring of eosinophilic esophagitis (EoE). The aim of this study was to determine the utility of a panel of serum biomarkers for the diagnosis and management of EoE. METHODS: We conducted a prospective cohort study of consecutive adults undergoing outpatient esophagogastroduodenoscopy. Incident cases of EoE were diagnosed per consensus guidelines; controls had gastroesophageal reflux disease (GERD) or dysphagia and did not meet the EoE criteria. EoE cases were treated with topical steroids and had repeat endoscopy. Pre- and post-treatment serum samples were analyzed in a blinded manner for interleukin (IL)-4, IL-5, IL-6, IL-9, IL-13, transforming growth factor (TGF)-α, TGF-ß, tumor necrosis factor-α, eotaxin-1, -2, and -3, thymic stromal lymphopoietin (TSLP), major basic protein, and eosinophil-derived neurotoxin. Cases and controls were compared at baseline, and pre- and post-treatment assays were compared in cases. RESULTS: A total of 61 incident EoE cases and 87 controls were enrolled; 51 EoE cases had post-treatment serum analyzed. There were no significant differences in any of the biomarkers between EoE cases and controls at baseline. IL-13 and eotaxin-3 for cases and controls were 85 ± 160 vs. 43 ± 161 pg/ml (P=0.12) and 41 ± 159 vs. 21 ± 73 (P=0.30). There were no significant differences in assay values among cases before and after treatment. There were also no differences after stratification by atopic status or treatment response. CONCLUSIONS: A panel of inflammatory factors known to be associated with EoE pathogenesis were not increased in the serum, nor were they responsive to therapy. None of these biomarkers are likely candidates for a serum test for EoE. Histologic analysis for diagnosis and management of EoE continues to be necessary, and novel, less invasive, biomarkers are needed.

A Clinical Prediction Tool Identifies Cases of Eosinophilic Esophagitis Without Endoscopic Biopsy: A Prospective Study.

OBJECTIVES: Eosinophilic esophagitis (EoE) is difficult to distinguish from gastroesophageal reflux (GERD) and other causes of dysphagia. We assessed the utility of a set of clinical and endoscopic features for predicting EoE without obtaining esophageal biopsies. METHODS: We prospectively enrolled consecutive adults undergoing outpatient upper endoscopy at the University of North Carolina from July 2011 through December 2013. Incident cases of EoE were diagnosed per consensus guidelines. Non-EoE controls had either GERD- or dysphagia-predominant symptoms. A predictive model containing clinical and endoscopic, but no histological, data was assessed. Receiver operator characteristic curves were constructed and the area under the curve (AUC) was calculated. RESULTS: A total of 81 EoE cases (mean age 38 years; 60% male; 93% white; 141 eosinophils per high-power field (eos/hpf)) and 144 controls (mean age 52, 38% male; 82% white; 3 eos/hpf) were enrolled. A combination of clinical (age, sex, dysphagia, food allergy) and endoscopic (rings, furrows, plaques, hiatal hernia) features was highly predictive of EoE. The AUC was 0.944, with sensitivity, specificity, and accuracy of 84, 97, and 92%. Similar values were seen after limiting controls to those with only reflux or dysphagia or to those with esophageal eosinophilia not due to EoE. CONCLUSIONS: We validated a set of clinical and endoscopic features to predict EoE with a high degree of accuracy and allow identification of those at very low risk of disease. Use of these predictors at the point-of-care will avoid the effort and expense of low-yield histological examinations for EoE.

Distribution and variability of esophageal eosinophilia in patients undergoing upper endoscopy.

The variability of eosinophilic infiltrates in eosinophilic esophagitis is not well described. This study aimed to determine the distribution of esophageal eosinophilia and the utility of histologic cut-points for eosinophilic esophagitis diagnosis in subjects undergoing endoscopy. We performed a prospective study of adults undergoing outpatient endoscopy. Research protocol esophageal biopsies were obtained from all subjects. Incident cases of eosinophilic esophagitis were diagnosed per consensus guidelines. Biopsies were interpreted following a validated protocol, and maximum eosinophil counts (eosinophils per high-power field; eos/hpf) were determined. Histologic analyses were performed on a per-patient, per-biopsy, and per-hpf basis. There were 213 patients, yielding 923 esophageal biopsies with 4588 hpfs. Overall, 48 patients (23%), 165 biopsy fragments (18%), and 449 hpfs (10%) had ≥15 eos/hpf; most subjects had no or low levels of eosinophils. In the eosinophilic esophagitis cases, 119 biopsy fragments (63%) and 332 hpfs (36%) had ≥15 eos/hpf. There was a mean 104-fold difference between the lowest and highest hpf eosinophil count for the eosinophilic esophagitis patients; 85% of the biopsies from eosinophilic esophagitis cases also had at least one hpf with <15 eos/hpf. The cut-point of 15 eos/hpf had a sensitivity of 100% and a specificity of 96% for diagnosis of eosinophilic esophagitis. In conclusion, most patients have little to no esophageal eosinophilia. In patients with eosinophilic esophagitis, there was marked variability in the eosinophil counts by biopsy and by hpf within a given biopsy. Additionally, the 15 eos/hpf cut-point was highly sensitive and specific for eosinophilic esophagitis. Multiple esophageal biopsies from different locations should be obtained to optimize eosinophilic esophagitis diagnosis.

Markers of eosinophilic inflammation for diagnosis of eosinophilic esophagitis and proton pump inhibitor-responsive esophageal eosinophilia: a prospective study.

BACKGROUND & AIMS: Distinguishing between eosinophilic esophagitis (EoE), gastroesophageal reflux disease, and proton pump inhibitor-responsive esophageal eosinophilia (PPI-REE) is challenging. We assessed whether immunohistochemical analysis of esophageal tissues for major basic protein (MBP), eotaxin-3, and tryptase can be used for diagnosis of EoE and to differentiate EoE from PPI-REE. METHODS: We conducted a prospective study of 196 consecutive adults who underwent outpatient endoscopy at the University of North Carolina from 2009 through 2012. Incident cases of EoE were diagnosed per consensus guidelines. Patients with gastroesophageal reflux disease or dysphagia served as controls. PPI-REE was defined as a symptomatic and histologic response to a PPI. Immunohistochemistry was performed to quantify MBP, eotaxin-3, and tryptase. The maximum density of epithelial staining was determined for each assay; levels were compared between EoE and control groups and then EoE and PPI-REE groups, and receiver operating characteristic curves were constructed. RESULTS: Esophageal tissues from patients with EoE (n = 50) had a median 951 MBP-positive cells/mm(2), whereas those from controls (n = 123) had a median 2 MBP-positive cells/mm(2) (P < .001). Samples from patients with EoE had a median 155 eotaxin-3-positive cells/mm(2), and those from controls (n = 123) had 18 eotaxin-3-positive cells/mm(2) (P < .001). Samples from patients with EoE had a median 249 tryptase-positive cells/mm(2), and those from controls (n = 123) had 11 tryptase-positive cells/mm(2) (P < .001). Levels of MBP, eotaxin-3, tryptase, and the combination of all 3 identified patients with EoE with area under the receiver operating characteristic curve values of 0.99, 0.94, 0.99, and 1.00. Analyses of only samples with eosinophil counts of 10-100 eosinophils per high-power field produced similar results. No marker distinguished EoE from PPI-REE. Esophageal tissues from patients with PPI-REE (n = 23) had 987 MBP-positive cells/mm(2) (P = .18, compared with EoE), 160 eotaxin-3-positive cells/mm(2) (P = .33), and 243 tryptase-positive cells/mm(2) (P = .28). CONCLUSIONS: Esophageal tissues from patients with EoE have substantially higher levels of MBP, eotaxin-3, and tryptase than controls on the basis of immunohistochemical analysis. Assays for the 3 markers identify patients with EoE with 100% accuracy but cannot distinguish EoE from PPI-REE.

Is a Forest Fire a Natural Disaster? Investigating the Fire Tolerance of Various Tree Species-An Educational Module.

Wildfires are unplanned conflagrations perceived as a threat by humans. However, fires are essential for the survival of fire-adapted plants. On the one hand, wildfires cause major damage worldwide, burning large areas of forests and landscapes, threatening towns and villages, and generating high levels of air pollution. On the other hand, fire-adapted plants (pyrophytes) in the fire landscapes of the Earth are able to survive exposure to heat (e.g., because of their thick bark, which protects their living tissue) and benefit from fire directly (e.g., fire initiates cone opening and seed release) or indirectly (e.g., fewer competing plants of fire-sensitive species remain, seeds germinate in the ash-fertilized soil). We present the experimental set-up and results of a fire experiment on bark samples used as a basis to assess the fire tolerance of various trees. Fire tolerance is defined as the ability of a tree to survive a surface fire (up to 200 °C and 5 min duration). The measure of the fire tolerance for a tree species is the time taken for the vascular cambium under the insulating bark to reach the critical temperature of 60 °C. Within an educational module, we provide worksheets for teachers and students enabling them to analyze the fire tolerance of various tree barks.

Bio-Inspired Pressure-Dependent Programmable Mechanical Metamaterial with Self-Sealing Ability.

Self-sealing is one of the fascinating functions in nature that enables living material systems to respond immediately to damage. A prime plant model is Delosperma cooperi, which can rapidly self-seal damaged succulent leaves by systematically deforming until the wound closes. Inspired by this self-sealing principle, a novel programmable mechanical metamaterial has been developed to mimic the underlying damage management concept. This material is able to react autonomously to changes in its physical condition caused by an induced damage. To design this ability into the programmable metamaterial, a permeable unit cell design has been developed that can change size depending on the internal pressure. The parameter space and associated mechanical functionality of the unit cell design is simulated and analyzed under periodic boundary conditions and various pressures. The principles of self-sealing behavior in designed metamaterials are investigated, crack closure efficiency is identified for different crack lengths, the limitations of the proposed approach are discussed, and successful crack closure is experimentally demonstrated in the fabricated metamaterial. Although this study facilitates the first step on the way of integrating new bio-inspired principles in the metamaterials, the results show how programmable mechanical metamaterials might extend materials design space from pure properties to life-like abilities.

The Basics of Evolution Strategies: The Implementation of the Biomimetic Optimization Method in Educational Modules.

With a focus on education and teaching, we provide general background information on bioinspired optimization methods by comparing the concept of optimization and the search for an optimum in engineering and biology. We introduce both the principles of Darwinian evolution and the basic evolutionary optimization procedure of evolution strategies. We provide three educational modules in work sheets that can be used by teachers and students to improve their understanding of evolution strategies. The educational module "Optimization of a Milk Carton" shows that the material consumption in producing a milk carton can be minimized using an evolution strategy with a mutative step size control. The use of a standard dice and a pocket calculator enables new milk cartons to be generated, with the offspring having the lowest material consumption becoming the parent of the next generation. The other educational modules deal with the so-called brachistochrone problem. The module "Fastest and Shortest Marble Track" provides a construction plan for a marble track whereby students can experimentally compare the "path of shortest length" with the "path of shortest time". The EvoBrach software, is used in the module "Various Marble Track Shapes" to compare the running times of a marble on a straight line, a parabola, and a brachistochrone. In conclusion, the introduction to the biomimetic method of evolution strategies and the educational modules should deepen the understanding of both optimization problems and biological evolution.