Micromechanical Models for FDM 3D-Printed Polymers: A Review.

Due to its large number of advantages compared to traditional subtractive manufacturing techniques, additive manufacturing (AM) has gained increasing attention and popularity. Among the most common AM techniques is fused filament fabrication (FFF), usually referred to by its trademarked name: fused deposition modeling (FDM). This is the most efficient technique for manufacturing physical three-dimensional thermoplastics, such that FDM machines are nowadays the most common. Regardless of the 3D-printing methodology, AM techniques involve layer-by-layer deposition. Generally, this layer-wise process introduces anisotropy into the produced parts. The manufacturing procedure creates parts possessing heterogeneities at the micro (usually up to 1 mm) and meso (mm to cm) length scales, such as voids and pores, whose size, shape, and spatial distribution are mainly influenced by the so-called printing process parameters. Therefore, it is crucial to investigate their influence on the mechanical properties of FDM 3D-printed parts. This review starts with the identification of the printing process parameters that are considered to affect the micromechanical composition of FDM 3D-printed polymers. In what follows, their (negative) influence is attributed to characteristic mechanical properties. The remainder of this work reviews the state of the art in geometrical, numerical, and experimental analyses of FDM-printed parts. Finally, conclusions are drawn for each of the aforementioned analyses in view of microstructural modeling.

Controls on late-Holocene drift-sand dynamics: The dominant role of human pressure in the Netherlands.

Holocene drift-sand activity in the northwest European sand belt is commonly directly linked to population pressure (agricultural activity) or to climate change (e.g. storminess). In the Pleistocene sand areas of the Netherlands, small-scale Holocene drift-sand activity began in the Mesolithic, whereas large-scale sand drifting started during the Middle Ages. This last phase not only coincides with the intensification of farming and demographic pressure but also is commonly associated with a colder climate and enhanced storminess. This raises the question to what extent drift-sand activity can be attributed to either human activities or natural forcing factors. In this study, we compare the spatial and temporal patterns of drift-sand occurrence for the four characteristic Pleistocene sand regions in the Netherlands for the period between 1000 BC and AD 1700. To this end, we compiled a new supra-regional overview of drift-sand activity based on age estimates (14C, optically stimulated luminescence (OSL), archaeological and historical ages). The occurrence of sand drifting was then compared in time and space with historical-route networks, relative vegetation openness and climate. Results indicate a constant but low drift-sand activity between 1000 BC and AD 1000, interrupted by a remarkable decrease in activity around the BC/AD transition. It is evident that human pressure on the landscape was most influential on initiating sand drifting: this is supported by more frequent occurrences close to routes and the uninterrupted increase of drift-sand activity from AD 900 onwards, a period of high population density and large-scale deforestation. Once triggered by human activities, this drift-sand development was probably further intensified several centuries later during the cold and stormier 'Little Ice Age' (LIA; AD 1570-1850).

Monomelic amyotrophy with late progression.

Monomelic amyotrophy is a sporadic juvenile-onset disease that presents with gradual onset of weakness and atrophy in the hand muscles unilaterally. Generally, this disease is considered a 'benign' and non-progressive motor neuron disease, which stabilizes within five years of onset. We discuss a case that illustrates that monomelic amyotrophy may rarely exhibit late clinical progression to the lower extremities after a prolonged period of disease stability.

Prominent inflammatory changes on muscle biopsy in patients with Miyoshi myopathy.

Miyoshi myopathy is a rare autosomal recessive distal myopathy characterized by early and prominent involvement of the posterior compartment of the legs. We describe two patients with the clinical diagnosis of Miyoshi myopathy who demonstrated marked inflammatory changes on muscle biopsy of clinically less affected muscles. This report illustrates the importance of recognizing the marked variability in histopathology of Miyoshi myopathy which may include an inflammatory infiltrate on muscle biopsy which mimics the histopathologic picture of an inflammatory myopathy.

Mycophenolate mofetil in dermatomyositis: is it safe?

The authors report 10 patients with idiopathic dermatomyositis treated with mycophenolate mofetil in combination with corticosteroids. Successful steroid taper without disease relapse was achieved in six patients; however, in three patients, treatment was associated with opportunistic infections, leading to death in one patient. The disproportionately high rate of opportunistic infections in this group is considered.

Copper deficiency myeloneuropathy and pancytopenia secondary to overuse of zinc supplementation.

The haematological complications of acquired copper deficiency have been well documented, but the neurological complications have only recently been reported. An illustrative case of copper deficiency myeloneuropathy with pancytopenia is presented and the potential aetiologies and neurological manifestations of this deficiency state discussed.

Complex repetitive discharges: cause or effect of neurogenic muscle hypertrophy?

We report a patient with adult-onset spinal muscular atrophy (SMA) of the scapulohumeral type with neurogenic muscle hypertrophy (NMH) in markedly weakened biceps muscles in association with continuous complex repetitive discharges (CRDs). This is an apparently unique case due to the bilaterality of the NMH associated with CRDs as well as the well-circumscribed symmetric upper extremity distribution of the hypertrophy. The possible mechanisms of NMH in association with spontaneous motor activity are discussed.

Chronic inflammatory demyelinating polyneuropathy after treatment with interferon-alpha.

Treatment with interferon-alpha (IFN-alpha) has been associated with the occurrence of a number of autoimmune disorders. We report a case of chronic inflammatory demyelinating polyneuropathy (CIDP) occurring in a patient with a chronic viral hepatitis C infection who received a novel, long-acting form of IFN-alpha. After withdrawal of the interferon treatment, this patient responded to a single extended course of plasma exchange that resulted in a complete clinical remission of symptoms without relapse.

Electrodiagnostic significance of supramaximally stimulated A-waves.

A-waves are generally considered a nonspecific finding of unclear electrodiagnostic and clinical significance. We systematically identified A-waves during routine F-wave studies and defined them as supramaximally elicited reproducible intermediate to late responses that are clearly separate from the M-responses. In patients with A-waves, we noted electrophysiologic diagnoses, the nerve in which the A-wave was identified, the presence of A-waves in multiple nerves, and A-wave morphology. In 54 of 1,258 studies performed, A-waves were present in one or more nerves. Electrophysiologic diagnoses in patients with A-waves included diffuse axonal neuropathy (11.5%), demyelinating neuropathy (66.7%), motor neuron disease (6.5%), radiculopathy (3.6%), mononeuropathy (3.9%), and normal (tibial nerve only) 0.7%. A-waves were abnormal when found in any nerve except the tibial nerve. They were particularly prevalent and present in multiple nerves in acquired and hereditary demyelinating neuropathies, and they more often had a complex morphology. We postulate that demyelination is the crucial underlying pathophysiologic correlate of the supramaximally stimulated A-wave.

Treatment of myasthenia gravis with mycophenolate mofetil: a case report.

We report a patient with myasthenia gravis (MG) who had marked clinical benefit in response to treatment with mycophenolate mofetil as documented by serial quantitative measures of strength and muscle fatigue. Our patient had experienced either adverse side effects or a suboptimal response to the usual immunosuppressive agents used in MG. Mycophenolate mofetil was used in combination with cyclosporine and prednisone and allowed for significant reductions in dosage of these immunosuppressants. We conclude that mycophenolate mofetil deserves further study as a therapeutic agent in MG. In particular, its role as a steroid-sparing agent and as a drug to be used in combination immunotherapy in more severe or refractory cases of MG should be investigated.

Distinguishing clinical and electrodiagnostic features of X-linked bulbospinal neuronopathy.

X-linked bulbospinal neuronopathy (XLBSN) or Kennedys disease is a rare inherited neuromuscular disease characterized by adult-onset muscle weakness, usually in a limb-girdle distribution. It is frequently misdiagnosed despite a distinctive clinical presentation, usually due to the absence of a clear family history, and perhaps also due to failure of recognition. Accurate diagnosis is crucial for genetic counseling purposes and because alternative diagnoses usually carry a poorer prognosis. We evaluated 4 patients with XLBSN and one symptomatic female heterozygote patient. Based on our clinical observations in these patients and a systematic review of previously reported cases, the following clinical and electrophysiologic features when present in the setting of adult-onset muscle weakness, are strongly suggestive of the disorder: 1) facial weakness, 2) facial twitching or fasciculations, 3) tongue weakness and atrophy, 4) postural hand tremor, 5) hypo- or areflexia, and 6) absent or low-amplitude sensory nerve action potentials despite clinically normal sensation. We also hypothesize regarding the possibility of partial expression of the abnormal XLBSN gene in a symptomatic heterozygote female patient.

Etanercept treatment in corticosteroid-dependent myasthenia gravis.

The authors report a prospective pilot trial of etanercept in corticosteroid-dependent autoimmune myasthenia gravis. Eleven patients were enrolled, with eight completing the 6-month trial. Two patients were withdrawn owing to disease worsening, and one patient was withdrawn because of an erythematous skin rash. Six of the eight patients who completed the trial improved, based on quantitative measures of muscle strength and lowering of corticosteroid requirement.

HMG-CoA Reductase Inhibitor Myopathy: Clinical, Electrophysiological, and Pathologic Data in Five Patients.

OBJECTIVES: To define the clinical, electrophysiological, and pathologic features of the myopathy associated with the use of HMG CoA reductase inhibitors. METHODS: Five patients with myopathy associated with HMG CoA reductase inhibitors were evaluated. Complete histories, physical examinations, manual muscle testing, serum creatine kinase, urine myoglobin measurements, electrodiagnostic studies, and muscle biopsy were performed. RESULTS: Consistent features in our patients included a subacute onset of myalgias and weakness, electromyography demonstrating electrical myotonia, elevated creatine kinase levels, and in some patients myoglobinuria despite a relative lack of muscle necrosis on muscle biopsy and preserved myofibrillatory architecture by electron microscopy. All patients experienced resolution of symptoms within 3 weeks of drug discontinuation. CONCLUSIONS: We postulate that the constellation of clinical, electrophysiological, and pathologic findings among our patients with HMG CoA reductase inhibitor myopathy may be explained by the early toxic effects of HMG CoA reductase inhibitors on muscle membrane organelles and sarcolemmal function. Patients on concurrent therapy with cyclosporine, gemfibrozil, and antifungal agents of the azole groups are at an increased risk of developing this toxic myopathy.

Mycophenolate mofetil for myasthenia gravis: an analysis of efficacy, safety, and tolerability.

The authors report a retrospective analysis of the use of mycophenolate mofetil (MyM) in 85 patients with autoimmune myasthenia gravis. The Myasthenia Gravis Foundation of America (MGFA) postintervention status (PIS) was used to characterize the treatment response in each patient. Sixty-two patients (73%) achieved a PIS status indicating improvement. Quantitative strength testing performed on the majority of patients before and after treatment also improved. Side effects to MyM were observed in 27% of patients but required discontinuation in only 6%.