Less Is More: Hollow-Truss Microlattice Metamaterials with Dual Sound Dissipation Mechanisms and Enhanced Broadband Sound Absorption

Being a lightweight material with high design freedoms, there are increasing research interests in microlattice metamaterials as sound absorbers. However, thus far, microlattices are limited to one sound dissipation mechanism, and this inhibits their broadband absorption capabilities. Herein, as opposed to improving performances via the addition of features, a dissipation mechanism is subtractively introduced by hollowing out the struts of the microlattice. Then, a class of hollow-truss metamaterial (HTM) that is capable of harnessing dual concurrent dissipation mechanisms from its complex truss interconnectivity and its hollow interior is presented. Experimental sound absorption measurements reveal superior and/or customizable absorption properties in the HTMs as compared to their constitutive solid-trusses. An optimal HTM displays a high average broadband coefficient of 0.72 at a low thickness of 24 mm. Numerically derived, a dissipation theorem based on the superimposed acoustic impedance of the critically coupled resistance and reactance of the outer-solid and inner-hollow phases, across different frequency bands, is proposed in the HTM. Complementary mechanical property studies also reveal improved compressive toughness in the HTMs. This work demonstrates the potential of hollow-trusses, where they gain the dissipation mechanism through the subtraction of the material and display excellent acoustic properties.

Preformed silastic silos in the management of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is sometimes complicated by abdominal compartment syndrome, a clinical syndrome characterized by multiple organ dysfunction that arises as a consequence of increased intra-abdominal pressure. The evolving clinical picture of NEC sometimes requires "second-look" operations done after initial abdominal exploration to more accurately gauge the optimal extent of surgery. Placing intestines in a preformed, spring-loaded, transparent Silastic silo, traditionally used in the staged treatment of gastroschisis, addresses both situations: decompression of the abdomen and allowing periodic inspection of the intestines. Standard silos were used in three infants with advanced (Bell Class 3) NEC without perforation before definitive surgery. Clinical indices and laboratory values were recorded during the patients' hospital courses. All three infants had extensive areas of intestinal ischemia and necrosis. FiO2, acidosis, and urinary output remained stable or improved in two patients. Silo placement corrected abdominal compartment syndrome in the third patient. Intestinal resection was required in all infants, each achieving surgical resolution of NEC. Two patients ultimately died from respiratory and neurologic complications. Application of a silo addresses abdominal compartment syndrome as a complication of NEC and allows continual inspection of the intestines. Physiological indices may improve the patient's overall clinical status.

Privates on parade: soldiers, medicine and the treatment of inguinal hernias in Georgian England

Hernias were prevalent among servicemen, typically recruited from amongst the malnourished. Civilian medical practice deemed the rupture incurable, taking a palliative approach. For the military this was unacceptable: wastage rates due to ruptures were high, servicemen were valuable commodities. Examples here are used to illustrate that experimentation was a contentious activity, reliant on the whims of patronage and war-time budgets. Although military hospitals provided a good venue to engage in experimentation it was contested.

[Laparoscopic incisional hernia repair as first therapeutic choice]

AIM

Incisional hernias are one of the most frequent complications of open abdominal surgery. Historically, the best results have been obtained with the open rives-stoppa approach. This is done by fixing a large piece of prosthetic mesh behind the rectus muscle. Laparoscopic approach allows similar mesh placement with minimal dissection and lower recurrence rate compared to the open mesh repair.

METHODS

Between October 2001 to September 2003, 75 consecutive patients were scheduled to undergo laparoscopic incisional hernia repair with ePTFE mesh (Gore-Tex Dualmesh Plus). Postoperative complications were recorded and analysed.

RESULTS

Most were obese affected by multiple wall defects Conversion to open surgery was required in 1 case Postoperative complications occurred 13.3%. Recurrence occurred in one only case.

CONCLUSIONS

The key to the success of this procedure is avoidance of complications. The laparoscopic approach is safe, effective and relatively complication-free option in the management of patients presenting with a first time or recurrent incisional hernia and recommended as the treatment of choice.

Trusses in the management of hernia today

In the UK an estimated 40,000 trusses are issued annually. The rate of 700 per million is higher than that presently found in other countries and may be because of reduced access to surgery. Despite the high use of trusses little has been published on their effectiveness, complication rates and value. This review summarizes current knowledge, and concludes that further studies on the benefits and effectiveness of trusses need to be performed to enable patients to receive appropriate advice and guidance.

Use of a truss to maintain inguinal hernia reduction in a very low birth weight infant

Trusses are not usually used in management of inguinal hernia of the very low birth weight infant. A potential benefit of this therapy is maintenance of hernia reduction, thus delaying operative repair until the infant is larger and healthier. We designed a safe and effective truss with supplies found in most neonatal intensive care units.

Inguinal mass in a college football player: a case study

A 22-yr-old male college football player presented with a 3-wk history of a mass in his right inguinal area. Originally thought by the athlete to be a groin strain, evaluation revealed a large indirect inguinal hernia. Surgical evaluation was obtained to confirm the diagnosis of a 4-cm opening at the external inguinal ring. The hernia completely and spontaneously reduced in the supine position. The athlete was successfully allowed to participate with the use of a truss and underwent an uneventful surgical repair at the end of the season. The diagnosis and treatment of inguinal hernias are reviewed.

Trusses

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When is surgery necessary for a groin hernia?

Hernias are one of the most common causes of symptoms in the groin. Surgery is needed for all femoral and indirect inguinal hernias to prevent incarceration and strangulation. Asymptomatic direct hernias can be observed if they are not enlarging. Atypical symptoms in a patient with a hernia must be evaluated to exclude other disease. Fortunately, most groin hernias can be repaired electively.

Use of rib belts in acute rib fractures

The current treatment for uncomplicated rib fractures is the exclusion of associated injuries followed by symptomatic treatment with analgesics. Encouragement of deep breathing is also recommended to avoid secondary or delayed pulmonary complications. The use of circumferential rib belts in treating patients with acute rib fractures has been discouraged because of possible complications from restricted ventilation. A review of the literature revealed no previous clinical studies to support this view. We designed and conducted a controlled, prospective, randomized pilot study to determine if there was any increased morbidity associated with the use of rib belts in the treatment of patients with acute rib fractures. Twenty-five adult patients with radiographically proven acute rib fractures were randomized into two groups. The first group was treated with analgesics and a standard circumferential rib belt (Zimmer Universal Rib Belt). The second group was treated with oral analgesics alone. Patients were contacted by telephone three days after the initial injury and then reexamined 14 days postinjury. Rates of pain resolution, compliance, and delayed complications were determined. Rib belts were not found to significantly reduce the severity of pain. Four complications (one case of bloody pleural effusion requiring hospitalization, two cases of asymptomatic discoid atelectasis, and one case of allergic contact dermatitis) were identified, all occurring in the group of patients receiving rib belts. This pilot study indicates that while rib belts are widely accepted by patients for control of pain, they appear to be associated with an increased incidence of complications. Clinical studies with larger sample sizes will be needed to confirm these findings.

[Functional principles of the lumbotrain harness. A clinical and experimental study]

This paper presents the results of pressure measurements on the truss pad of the lumbotrain harness. As compared to the pressure measurements carried out previously on truss pads of rigid orthotic devices by the same authors, a much more uniform pressure distribution was found.

Letter: Hernias in children

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Truss designed by Locke

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