How suture networks improve the protective function of natural structures: A multiscale investigation.

Myriad natural protective structures consist of bone plates joined by convoluted unmineralized (soft) collagenous sutures. Examples of such protective structures include: shells of turtles, craniums of almost all animals (including humans), alligator armour, armadillo armour, and others. The function of sutures has been well researched. However, whether, and if so how, sutures improve protective performance during a predator attack has received limited attention. Sutures are ubiquitous in protective structures, and this motivates the question as to whether sutures optimize the protective function of the structure. Hence, in this work the behaviour of structures that contain sutures during predator attacks is investigated. We show that sutures decrease the maximum strain energy density that turtle shells experience during predator attacks by more than an order of magnitude. Hence, sutures make turtle shells far more resilient to material failure, such as, fracture, damage, and plastic deformations. Additionally, sutures increase the viscous behaviour of the shell causing increased dissipation of energy during predator attacks. Further investigations into the influence of sutures on behaviour during locomotion and breathing are also presented. The results presented in this work motivate the inclusion of sutures in biomimetically designed protective structures, such as helmets and protective clothing. STATEMENT OF SIGNIFICANCE: Myriad bony protective structures contain networks of sutures, that is con- voluted soft collagenous tissue. Their ubiquity motivates the question, whether, and if so how, sutures improve protective performance. Hence, this work inves- tigates how sutures affect protective performance using computational experi- ments. Due to the length scale of sutures being far smaller than the structures in which they reside, classical modelling approaches are prohibitively expensive. Hence, in this work, a multiscale approach is taken. To our knowledge, this is the first multiscale investigation of structures that contain sutures. Among other insights, we show that sutures decrease the maximum strain energy density in structures during predator attacks by over an order of mag- nitude. Hence, sutures make structures far more resilient to failure.

Computationally modelling the mechanical behaviour of turtle shell sutures-A natural interlocking structure.

Sutures, the soft collagenous tissue joining interdigitating bony protrusions on the edges of bone plates, play a significant mechanical role in allowing a turtle shell to respond optimally to a range of loading regimes. In this contribution, qualitative and quantitative aspects of the mechanical behaviour of turtle shell suture regions are investigated by means of mathematical modelling. Notable features of the model include: (i) a geometrically realistic three dimensional model for the suture geometry; (ii) taking the hyperelastic, anisotropic and incompressible nature of the suture material into account; and (iii) a novel method for defining the collagen fibre directions within the suture. The model is validated against a physical three point bending test and replicates many of the qualitative and quantitative aspects of the mechanical behaviour. The model is then used to elucidate the effect that sutures have on the shell's mechanical behaviour during a predator attack. It is found that the sutures increase the energy required from a predator during an attack whilst cushioning the brittle bone, and so protecting it from fracture. Additionally, longer bony protrusions increase strain energy absorption but also increase the likelihood of fracture.

Treatment of progressive pulmonary sarcoidosis with cyclosporin A. A randomized controlled trial.

Conventional treatment of sarcoidosis is often only partially effective. We examined the effect of cyclosporin A (CsA) combined with prednisone for the treatment of sarcoidosis. Thirty-seven patients with biopsy-proven sarcoidosis were treated with either prednisone 20 mg/d in a prospectively tapered regimen (P) or with combination therapy consisting of prednisone 20 mg/d in a prospectively tapered regimen and cyclosporin A, 5 to 7 mg/kg/d (P-CsA) for up to 18 mo in an open-label randomized controlled trial. Evaluation was done at baseline and at 3, 9, and 18 mo of the degree of dyspnea, pulmonary function, chest radiographs, bronchoalveolar lavage (BAL), and adverse events. Criteria for a good therapeutic response, improvement, treatment failure, and relapse were defined. Thirty-seven patients were treated for at least 9 mo and 18 mo. Six patients in remission were included in an intention-to-treat-analysis at 18 mo. The groups did not differ significantly with respect to therapeutic response from baseline. A significant (p < 0.05) improvement was observed in dyspnea until 9 mo (P) and 18 mo (P-CsA), and in lung function until 9 mo (P) and 3 mo (P-CsA). BAL results showed a significant decrease in lymphocyte counts at 9 mo for the P group only (p < 0.05). More side effects were observed in the P-CsA group than in the P group, including elevation of the mean serum creatinine concentration at 3 and 9 mo (p < 0.05), and a doubling of the number of infections in this group. Relapse after an initially good therapeutic response occurred in two of nine patients in the P group and five of seven patients in the P-CsA group (p < 0.07). Although CsA may have theoretical benefits in the treatment of sarcoidosis, our results do not support its use in this disease.

Static bone histomorphometry in preterm and term babies.

The nature and pathophysiology of the bone loss which occurs in term and especially preterm neonates are poorly understood, and it is unclear whether this neonatal osteopenia results from impaired bone formation or increased bone resorption. This study compared the static bone histomorphometry of preterm and term babies, employing iliac crest bone biopsy specimens obtained postmortem. All the babies died within the first 6 days of life and none had any clinical, biochemical or radiologic evidence of metabolic bone disease. The trabecular bone volume, as well as static parameters of bone formation (OV/TV, OV/BV, OS/BS, OB.S/BS) did not differ significantly in preterm and term babies. Although time-spaced tetracycline labelling could not be employed in the present study, evidence of rickets was not apparent. Parameters of bone resorption in preterm babies were, however, significantly higher (p = 0.01) than those of term babies, suggesting that increased bone resorption and not impaired formation, underlies the development of osteopenia in the preterm neonate.

High turnover osteopenia in preterm babies.

Osteopenia is common in preterm babies, but its pathogenesis is uncertain. In this study bone density in babies was quantitated, postnatal bone mineralization compared to expected intrauterine bone mineralization and the pathogenesis of osteopenia investigated. Healthy babies (103 term, 76 preterm) were examined clinically, biochemically and radiologically the day after birth and at a time corresponding to expected full term gestation. Appendicular bone density was quantitated by magnification radiogrammetry, using the humeral cortical index (CI). The CI of preterm and term babies was similar the day after birth. In preterm babies elevated serum alkaline phosphatase and high urinary hydroxyproline indicated increased bone turnover. The CI of preterm babies at expected full term gestation was lower (p = 0.0001) than that of term babies at birth, implying that postnatal bone mineralization lagged behind expected intrauterine bone mineralization. Radiologic data suggested increased endosteal resorption rather than decreased bone formation. At expected full term gestation the preterm babies had higher serum alkaline phosphatase and urinary calcium, phosphate, c-AMP and hydroxyproline (p = 0.0001) than term babies at birth, and 15% had periosteal reactions. The biochemical as well as the radiologic data therefore indicated high turnover osteopenia in preterm babies. We conclude that postnatal bone mineralization in preterm babies lagged significantly behind expected intrauterine bone mineralization and that the osteopenia observed in preterm babies is caused by increased bone resorption and not by decreased bone formation. The cause(s) of this high turnover osteopenia, however, remains to be ascertained.

Ventilation-perfusion imaging in evaluating regional lung function in nonpenetrating injury to the chest.

The extent of chest wall and lung injury after nonpenetrating injury to the chest (NIC) determine how aggressive and invasive management modalities should be. We investigated the value of ventilation (133Xe) and perfusion (99mTc) studies as indicators of extent of lung injury in 28 patients with moderate to severe unilateral NIC. The ventilation-perfusion (V/Q) abnormalities were compared with parameters conventionally used to evaluate NIC. All studies were carried out within 24 h of NIC and repeated 24 h later. Ventilation (p less than 0.001) and perfusion (p less than 0.01) abnormalities were more extensive soon after NIC than suggested by chest roentgenograms. Chest x-ray film changes lagged behind V/Q changes on admission and also after 24 h. The extent of ventilation, perfusion, and chest x-ray film abnormalities on admission were all predictors of increased morbidity. V/Q studies may be useful to define the extent as well as the changes in regional lung function following NIC.

Neurocysticercosis: correlative pathomorphology and MR imaging.

CT and MR images of 32 patients with neurocysticercosis were correlated with pathomorphology. Gross morphological features of cystic larvae, complex arachnoid cysts, granulomatous abscesses, basal meningitis and mineralised nodules correlated closely with the images obtained, especially on MR, where resolution permitted visualisation of larval protoscolices. Our material indicates three forms of the natural history of neurocysticercosis related chiefly to anatomic location, and provides details of the evolution of large, complex arachnoid cysts.

Nuclear magnetic resonance imaging. Experience with the first 100 cases at Tygerberg Hospital.

Facilities for magnetic resonance imaging (MRI) have been available in South Africa since November 1985. This article summarizes our experience with this new imaging modality, illustrates normal anatomical features and pathological conditions in sagittal, coronal and axial planes, and compares MRI with computed tomography scans of the same regions.

Obstruction-strangulation of post-traumatic diaphragmatic hernia--delayed diagnosis and fatal outcome.

The radiological and clinical features of 9 cases of obstructed post-traumatic diaphragmatic hernia are reviewed. In none of these patients was the diagnosis of a diaphragmatic hernia considered before radiography, all cases being clinically diagnosed as 'acute abdomen', most frequently pancreatitis or perforated peptic ulcer. Even after radiographs had shown opacity at the left base in all 9 cases, together with a distended proximal bowel in 6, the correct diagnosis was made in only 4. Through lack of correct radiological diagnosis, there was a delay of at least 1 day between admission and operation in 6 patients, and 3 of the 4 deaths occurred in this group. Obstruction-strangulation of diaphragmatic hernia should be considered as a possible cause of 'acute abdomen' in the presence of a left basal abnormality, especially in patients from areas with a high incidence of assault. Confirmatory contrast studies should be done only if they can be done immediately and quickly. Pregnancy can cause hernias to become obstructed and strangulated, but this can be averted by obtaining a history of previous trauma early in the pregnancy.