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Alginate hydrogels are currently being employed and explored for a broad range of medical applications including cell encapsulation, drug delivery, and tissue engineering. In these capacities, knowledge of the mechanical and material properties of the hydrogels and the properties that govern and influence them is necessary to adequately design and effectively use these systems. Although much is known about the mechanical properties of alginate in compression and shear, little is known about the tensile characteristics. Thus, an extensive tensile assessment of alginate hydrogels was completed as a function of alginate type, formulation, gelling conditions, incubation, and strain rate. In general, the initial tensile behavior and properties of alginate hydrogels were highly dependent on the choice of the alginate polymer and how it was processed. Specifically, high guluronic acid containing alginate polymers yielded stronger, more ductile hydrogels than high mannuronic acid containing alginates. The ultimate stress, ultimate strain, and tensile modulus were decreased by increased phosphate concentrations, solution reconstitution with phosphate buffered saline instead of culture media, and peptide modification. Incubation of hydrogels for at least 7 days diminished many of the initial tensile property differences associated with formulation and gelling conditions. Overall, by controlling the specific alginate polymer and processing methods, a wide range of tensile properties are available from these hydrogels.

The use of zirconia in medicine and dentistry has rapidly expanded over the past decade, driven by its advantageous physical, biological, esthetic, and corrosion properties. Zirconia orthopedic hip replacements have shown superior wear-resistance over other systems; however, risk of catastrophic fracture remains a concern. In dentistry, zirconia has been widely adopted for endosseous implants, implant abutments, and all-ceramic crowns. Because of an increasing demand for esthetically pleasing dental restorations, zirconia-based ceramic restorations have become one of the dominant restorative choices. Areas covered: This review provides an updated overview of the applications of zirconia in medicine and dentistry with a focus on dental applications. The MEDLINE electronic database (via PubMed) was searched, and relevant original and review articles from 2010 to 2016 were included. Expert commentary: Recent data suggest that zirconia performs favorably in both orthopedic and dental applications, but quality long-term clinical data remain scarce. Concerns about the effects of wear, crystalline degradation, crack propagation, and catastrophic fracture are still debated. The future of zirconia in biomedical applications will depend on the generation of these data to resolve concerns.

It is generally accepted that the human neutrophil can be mechanically represented as a droplet of polymeric fluid enclosed by some sort of thin slippery viscoelastic cortex. Many questions remain however about the detailed rheology and chemistry of the interior fluid and the cortex. To address these quantitative issues, we have used a finite element method to simulate the dynamics of neutrophils during micropipet aspiration using various plausible assumptions. The results were then systematically compared with aspiration experiments conducted at eight different combinations of pipet size and pressure. Models in which the cytoplasm was represented by a simple Newtonian fluid (i.e., models without shear thinning) were grossly incapable of accounting for the effects of pressure on the general time scale of neutrophil aspiration. Likewise, models in which the cortex was purely elastic (i.e., models without surface viscosity) were unable to explain the effects of pipet size on the general aspiration rate. Such models also failed to explain the rapid acceleration of the aspiration rate during the final phase of aspiration nor could they account for the geometry of the neutrophil during various phases of aspiration. Thus, our results indicate that a minimal mechanical model of the neutrophil needs to incorporate both shear thinning and surface viscosity to remain valid over a reasonable range of conditions. At low shear rates, the surface dilatation viscosity of the neutrophil was found to be on the order of 100 poise-cm, whereas the viscosity of the interior cytoplasm was on the order of 1000 poise. Both the surface viscosity and the interior viscosity seem to decrease in a similar fashion when the shear rate exceeds approximately 0.05 s(-1). Unfortunately, even models with both surface viscosity and shear thinning studied are still not sufficient to fully explain all the features of neutrophil aspiration. In particular, the very high rate of aspiration during the initial moments after ramping of pressure remains mysterious.