biological materials often presents similar solutions, since the number of materials available in nature is fairly limited and therefore resourceful combinations of them have to be developed to address specifi c environmental constraints. We have identifi ed these common designs and named them "structural design elements."In the emerging fi eld of biological materials science, there is a great need for systematizing these observations and to describe the underlying mechanics principles in a unifi ed manner. This is necessary as similar designs are often reported under various names. As an example, the presence of numerous interfaces within a composite that introduce a signifi cant property mismatch, which we suggest be named a "layered" structure, has been previously referred to as "lamella" in bone [ 2 ] and fi sh scales, [ 3 ] "brick and mortar" in abalone, [4][5][6] and a "laminated structure" in sea sponges [ 7 ] despite providing most if not all of the same structural advantages. We propose herein a new system of eight structural design elements that are most common amongst a wide variety of animal taxa. These structural elements have each evolved to improve the mechanical properties, namely strength, stiffness, fl exibility, fracture toughness, wear resistance, and energy absorption of different biological materials for specifi c multi-functions (e.g., body support, joint movement, impact protection, mobility, weight reduction). These structural design elements are visually displayed in Figure 1 : • Fibrous structures; offering high tensile strength when aligned in a single direction, with limited to nil compressive strength.• Helical structures; common to fi brous or composite materials, offering toughness in multiple directions and in-plane isotropy.• Gradient structures; materials and interfaces that accommodate property mismatch (e.g., elastic modulus) through a gradual transition in order to avoid interfacial mismatch stress buildup, resulting in an increased toughness.• Layered structures; complex composites that increase the toughness of (most commonly) brittle materials through the introduction of interfaces.• Tubular structures; organized porosity that allows for energy absorption and crack defl ection.• Cellular structures; lightweight porous or foam architectures that provide directed stress distribution and energy absorption.Eight structural elements in biological materials are identifi ed as the most common amongst a variety of animal taxa. These are proposed as a new paradigm in the fi eld of biological materials science as they can serve as a toolbox for rationalizing the complex mechanical behavior of structural biological materials and for systematizing the development of bioinspired designs for structural applications. They are employed to improve the mechanical properties, namely strength, wear resistance, stiffness, fl exibility, fracture toughness, and energy absorption of different biological materials for a variety of functions (e.g., body support, joint movement, impact protection, ...

Comprehensive studies comparing tensile properties of sutures are over 25 years old and do not include recent advances in suture materials. Accordingly, the objective of this article is to investigate the tensile properties of commonly used sutures in cutaneous surgery. Thirteen 3-0 sized modern sutures (four nonabsorbable and nine absorbable) were tensile tested in both straight and knotted configurations according to the procedures outlined by the United States Pharmacopeia. Glycomer 631 was found to have the highest failure load (56.1 N) of unknotted absorbable sutures, while polyglyconate (34.2 N) and glycomer 631 (34.3 N) had the highest failure loads of knotted absorbable sutures. Nylon (30.9 N) and polypropylene (18.9 N) had the greatest failure loads of straight and knotted nonabsorbable sutures, respectively. Polydioxane was found to have the most elongation prior to breakage (144%) of absorbable sutures. Silk (8701 MPa) and rapid polyglactin 910 (9320 MPa) had the highest initial modulus of nonabsorbable and absorbable sutures, respectively. The new data presented in the study provide important information for guiding the selection of suture materials for specific surgeries.

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Objectives Secondary caries is the most common reason for composite restoration replacement and usually forms between dentin and the filling. The objective of this study was to investigate the combined effect of cyclic loading and bacterial exposure on bacterial penetration into gaps at the interface between dentin and resin composite restorative material using a novel bioreactor system and test specimen design. Methods Human molars were machined into 3 mm thick disks with 2 mm deep × 5 mm diameter cavity preparations into which composite restorations were placed. A ∼15-30 micrometer (small) or ∼300 micrometer wide (large) dentin-restoration gap was introduced along half of the interface between the dentin and restoration. Streptococcus mutans UA 159 biofilms were grown on each sample prior to testing in a bioreactor both with and without cyclic loading. Both groups of samples were tested for 2 weeks and post-test biofilm viability was confirmed with a live-dead assay. Samples were fixed, mounted and cross-sectioned to reveal the gaps and observe the depth of bacterial penetration. Results It was shown that for large gap samples the bacteria easily penetrated to the full depth of the gap independent of loading or non-loading conditions. The results for all cyclically loaded small gap samples show a consistently deep bacterial penetration down 100% of the gap while the average penetration depth was only 67% for the non-loaded samples with only two of six samples reaching 100%. Significance A new bioreactor was developed that allows combining cyclic mechanical loading and bacterial exposure of restored teeth for bacterial biofilm and demineralization studies. Cyclic loading was shown to aid bacterial penetration into narrow marginal gaps, which could ultimately promote secondary caries formation.

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