Reinforcements in avian wing bones: Experiments, analysis, and modeling.

Almost all species of modern birds are capable of flight; the mechanical competency of their wings and the rigidity of their skeletal system evolved to enable this outstanding feat. One of the most interesting examples of structural adaptation in birds is the internal structure of their wing bones. In flying birds, bones need to be sufficiently strong and stiff to withstand forces during takeoff, flight, and landing, with a minimum of weight. The cross-sectional morphology and presence of reinforcing structures (struts and ridges) found within bird wing bones vary from species to species, depending on how the wings are utilized. It is shown that both morphology and internal features increases the resistance to flexure and torsion with a minimum weight penalty. Prototypes of reinforcing struts fabricated by 3D printing were tested in diametral compression and torsion to validate the concept. In compression, the ovalization decreased through the insertion of struts, while they had no effect on torsional resistance. An elastic model of a circular ring reinforced by horizontal and vertical struts is developed to explain the compressive stiffening response of the ring caused by differently oriented struts.

Axial compression of a hollow cylinder filled with foam: a study of porcupine quills.

Porcupines use their lightweight quills, which are strong enough to support significant compression and flexure loads, for defense. Hystrix, with long and thick quills, belongs to the family of Hystricidae (Old World porcupines), while Erethizon, with smaller quills, belongs to the Erethizontidae family (New World porcupines). The objective of this work is to compare the structure and compressive properties of quills from Hystrix and Erethizon. Both quills have a thin keratinous cortex filled with closed-cell foam that has cell diameters decreasing from the center to the cortex. Hystrix quills have stiffeners that extend from the cortex towards the center. The local buckling strength is larger for Hystrix, and very good agreement is found between the predicted values and the experimental ones for both quills. The foam shows extensive deformation, both tensile and compressive, around the buckled cortex.

Elastic moduli of untreated, demineralized and deproteinized cortical bone: validation of a theoretical model of bone as an interpenetrating composite material.

A theoretical experimentally based multi-scale model of the elastic response of cortical bone is presented. It portrays the hierarchical structure of bone as a composite with interpenetrating biopolymers (collagen and non-collagenous proteins) and minerals (hydroxyapatite), together with void spaces (porosity). The model involves a bottom-up approach and employs micromechanics and classical lamination theories of composite materials. Experiments on cortical bone samples from bovine femur include completely demineralized and deproteinized bones as well as untreated bone samples. Porosity and microstructure are characterized using optical and scanning electron microscopy, and micro-computed tomography. Compression testing is used to measure longitudinal and transverse elastic moduli of all three bone types. The characterization of structure and properties of these three bone states provides a deeper understanding of the contributions of the individual components of bone to its elastic response and allows fine tuning of modeling assumptions. Very good agreement is found between theoretical modeling and compression testing results, confirming the validity of the interpretation of bone as an interpenetrating composite material.

Correlation of the mechanical and structural properties of cortical rachis keratin of rectrices of the Toco Toucan (Ramphastos toco).

Mechanical characterization of the cortex of rectrices (tail feathers) of the Toco Toucan (Ramphastos toco) has been carried out by tensile testing of the rachis cortex in order to systematically determine Young's modulus and maximum tensile strength gradients on the surfaces and along the length of the feather. Of over seventy-five samples tested, the average Young's modulus was found to be 2.56±0.09 GPa, and maximum tensile strength was found to be 78±6 MPa. The Weibull modulus for all sets is greater than one and less than four, indicating that measured strength is highly variable. The highest Weibull moduli were reported for dorsal samplings. Dorsal and ventral surfaces of the cortex are both significantly stiffer and stronger than lateral rachis cortex. On the dorsal surface, cortex sampled from the distal end of the feather was found to be least stiff and weakest compared to that sampled from proximal and middle regions along the length of the feather. Distinctive fracture patterns correspond to failure in the superficial cuticle layer and the bulk of the rachis cortex. In the cuticle, where supramolecular keratinous fibers are oriented tangentially, evidence of ductile tearing was observed. In the bulk cortex, where the fibers are bundled and oriented longitudinally, patterns suggestive of near-periodic aggregation and brittle failure were observed.

Mechanistic aspects of the fracture toughness of elk antler bone.

Bone is an adaptive material that is designed for different functional requirements; indeed, bones have a variety of properties depending on their role in the body. To understand the mechanical response of bone requires the elucidation of its structure-function relationships. Here, we examine the fracture toughness of compact bone of elk antler, which is an extremely fast-growing primary bone designed for a totally different function than human (secondary) bone. We find that antler in the transverse (breaking) orientation is one of the toughest biological materials known. Its resistance to fracture is achieved during crack growth (extrinsically) by a combination of gross crack deflection/twisting and crack bridging via uncracked "ligaments" in the crack wake, both mechanisms activated by microcracking primarily at lamellar boundaries. We present an assessment of the toughening mechanisms acting in antler as compared to human cortical bone, and identify an enhanced role of inelastic deformation in antler which further contributes to its (intrinsic) toughness.

Comparison of the structure and mechanical properties of bovine femur bone and antler of the North American elk (Cervus elaphus canadensis).

Antler and limb bone have a similar microstructure and chemical composition. Both are primarily composed of type I collagen and a mineral phase (carbonated apatite), arranged in osteons in compact (cortical bone) sections and a lamellar structure in the cancellous (spongy or trabecular bone) sections. The mineral content is lower in antler bone and it has a core of cancellous bone surrounded by compact bone running through the main beam and tines. The mineral content is higher in the compact compared with the cancellous bone, although there is no difference in ratios of the mineral elements with calcium. Mechanical tests (bend and compression) on longitudinal and transverse orientations of dry and rehydrated compact bone of North American elk (Cervus elaphus canadensis) antlers are compared with known data on other antlers as well as bovine femora. Both dry and rehydrated bones are highly anisotropic, with the bending and compressive strength and elastic modulus higher in the longitudinal than in the transverse direction. There is no significant difference between the bend strength and elastic modulus between dry and rehydrated samples tested in the transverse direction. The elastic modulus measured from the bending tests is compared with composite models. The elastic modulus and bend strengths are lower in the rehydrated condition, but the strain to failure and fracture toughness is much higher compared with dry samples. All antler bone mechanical properties are lower than that of bovine femora. The antler has a much higher fracture toughness compared with bovine femora, which correlates with their main function in intraspecific combat as a high impact resistant, energy absorbent material. A model of compression deformation is proposed, which is based on osteon sliding during shear.

Structure and mechanical properties of selected biological materials.

Mineralized biological tissues offer insight into how nature has evolved these components to optimize multifunctional purposes. These mineral constituents are weak by themselves, but interact with the organic matrix to produce materials with unexpected mechanical properties. The hierarchical structure of these materials is at the crux of this enhancement. Microstructural features such as organized, layered organic/inorganic structures and the presence of porous and fibrous elements are common in many biological components. The organic and inorganic portions interact at the molecular and micro-levels synergistically to enhance the mechanical function. In this paper, we report on recent progress on studies of the abalone and Araguaia river clam shells, arthropod exoskeletons, antlers, tusks, teeth and bird beaks.

Retrograde aortic dissection after bilateral iliac artery stenting: a case report and review of the literature.

We report a case of retrograde aortic dissection after bilateral iliac artery stenting. A 63-year-old black woman underwent aortography with balloon angioplasty of bilateral common iliac artery lesions and subsequent vascular stent placement. The patient developed an acute aortic dissection from the level of the aortic bifurcation to the left subclavian artery. This case is presented to call attention to the previously unreported complication of retrograde aortic dissection after bilateral iliac artery angioplasty and stent placement presenting as acute chest pain.

Are both color-flow duplex scanning and cerebral arteriography required prior to carotid endarterectomy?

In an attempt to eliminate the morbidity, mortality, and cost associated with arteriography, surgeons are relying increasingly on duplex scanning of the extracranial arteries as the primary preoperative evaluation prior to carotid endarterectomy (CEA). This study was initiated to evaluate the need for cerebral arteriography in the preoperative evaluation of patients for CEA. One hundred five patients undergoing 114 CEA procedures are included in a retrospective review to determine whether the addition of cerebral arteriography changed the operative management of these patients. In 58 of 105 patients (55%), color-flow duplex scanning and cerebral arteriography were performed in the workup prior to CEA. In four patients a discrepancy was found between the duplex results and the arteriogram, leading to a change in the operative approach in two. The remaining 47 patients (45%) underwent color-flow duplex scanning as the definitive preoperative study; the surgical management was altered because of the operative findings in one patient. Although color-flow duplex scanning does not provide absolute concordance with cerebral arteriography, in most instances it can be used as the definitive preoperative study prior to CEA. We define the indications for cerebral arteriography in patients undergoing CEA.

Simple surgical treatment of nonparasitic hepatic cysts.

Benign nonparasitic liver cysts are uncommon lesions. Incidental diagnosis is increasing with the advent of routine abdominal computed tomography and ultrasound scanning. Cysts that attain massive proportions often become symptomatic and require therapeutic intervention. Surgical resection and Roux-en-Y cystojejunostomy drainage have been the treatments of choice, but simpler unroofing techniques without drainage have recently been employed with success. Three patients with symptomatic, large, nonparasitic cysts were surgically treated in such a fashion without complication and form the basis of this report. The technique of wide unroofing involves excision of the nonhepatic cyst wall with oversewing of communicating biliary radicals. No recurrences have been detected in follow-up screening. Wide unroofing is a simple and yet reliable surgical option for the treatment of symptomatic hepatic cysts.

Paraplegia following intra-aortic balloon support. Report of a case.

A case is presented of paraplegia associated with the intra-aortic balloon pump used in a post-operative patient. The published experience with this complication is reviewed.

Carotid endarterectomy in patients with contralateral carotid occlusion: is the risk increased?

Many vascular surgeons believe the risk of carotid endarterectomy is greater if the patient has a contralateral carotid occlusion, and thus believe intraoperative shunting is mandatory. Five hundred and eleven carotid endarterectomies were performed over the last 11 years by two of us (JEM and RAL). Of these, 370 had charts available for detailed analysis. Twenty-seven of these patients had complete occlusion of the contralateral carotid artery. Eight of these 27 patients were asymptomatic and 16 patients had transient ischemic attacks prior to surgery. Two patients had strokes which were stable at the time of surgery. One patient with a previous stroke was operated upon emergently with a new stroke in evolution. All were operated upon under general anesthesia and only three had intraoperative shunting. Occlusion time averaged 17.1 minutes varying from 11 to 34 minutes. There were two deaths, one cardiac and one pulmonary, and no postoperative strokes either temporary or permanent. Of the 343 patients without contralateral occlusion, three patients (.87%) died, and there were 19 (5.5%) neurologic complications of which seven (2%) were present at the time of hospital discharge. It appears that contralateral carotid occlusion does not increase the risk of stroke after carotid endarterectomy even when intraoperative shunting is not used.

Surgical approach to the treatment of popliteal aneurysm.

Seventeen popliteal artery aneurysms were repaired at the Santa Barbara Cottage Hospital from 1975 to 1987. Fourteen patients were involved, with three having bilateral lesions. All but one were men with an average age of 67 years. Four of the aneurysms (three patients) presented with asymptomatic masses while the others were associated with arterial or venous obstructive symptoms. The aneurysms were repaired and there was no mortality. One patient developed a transient foot-drop. All patients with symptoms caused by their aneurysm were improved or became asymptomatic, postoperatively. We are impressed that the posterior approach to an uncomplicated popliteal artery aneurysm has several advantages over the bypass technique. The distal anastomosis can frequently be kept proximal to the knee joint, and since exposure of the aneurysm is excellent, aneurysmectomy is often possible thus eliminating pressure symptoms as well as the possibility of late rupture.

Indications for contralateral carotid endarterectomy: role of the noninvasive laboratory.

In 1,733 patients, 2,054 carotid phonoangiographic and oculoplethysmographic studies were performed. Seventy of these patients required carotid endarterectomy either for symptoms or for severely ulcerated plaques. Of these, 12 had bilateral procedures. This review suggests that noninvasive studies can be helpful in determining which patients should undergo contralateral carotid endarterectomy and when. The decision to correct the other side was based on generally accepted indications, development of symptoms and the presence of severely ulcerated plaques. In addition, positive results on carotid phonoangiography and oculoplethysmography, whenever they develop, are a strong indication for the contralateral procedure. The stenotic lesion that appears significant on arteriograhy may not be hemodynamically significant on noninvasive studies. These patients may be followed expectantly with serial carotid phonoangiograhic and oculoplethysmographic studies until hemodynamically significant flow delays appear or symptoms develop.

The pajaroello tick bite. The frightening folklore and the mild disease.

The pajaroella tick (Ornithodoros coriaceus) has a fairly wide distribution in the coastal and mountainous areas of California and Mexico. Persons engaged in outdoor activities there, are frequently bitten. Little is written in the medical literature concerning the tick and its bite. What has been written is liberally injected with frightening folklore that sometimes results in overzealous treatment. Conservative and supportive therapy is advisable and only rarely should one have to resort to such treatment as excision of an area of tissue necrosis to prevent ulceration and prolongation of healing.