Self-repair of a biological fiber guided by an ordered elastic framework.

Incorporating sacrificial cross-links into polymers represents an exciting new avenue for the development of self-healing materials, but it is unclear to what extent their spatial arrangement is important for this functionality. In this respect, self-healing biological materials, such as mussel byssal threads, can provide important chemical and structural insights. In this study, we employ in situ small-angle X-ray scattering (SAXS) measurements during mechanical deformation to show that byssal threads consist of a partially crystalline protein framework capable of large reversible deformations via unfolding of tightly folded protein domains. The long-range structural order is destroyed by stretching the fiber but reappears rapidly after removal of load. Full mechanical recovery, however, proceeds more slowly, suggesting the presence of strong and slowly reversible sacrificial cross-links. One likely role of the highly ordered elastic framework is to bring sacrificial binding sites back into register upon stress release, facilitating bond reformation and self-repair.

Tubular frameworks guiding orderly bone formation in the antler of the red deer (Cervus elaphus).

Deer antler is a bony tissue which re-grows every year after shedding. Growth speed and material properties of this tissue are truly remarkable, making it an interesting model for bone regeneration. Surprisingly, not much is known about the ultrastructure of the calcified tissues and the temporal sequence of their development during antler growth. We use a combination of imaging tools based on light and electron microscopy to characterize antler tissue at various stages of development. We observe that mineralized cartilage is first transformed into a bone framework with low degree of collagen fibril ordering at the micron level. This framework has a honeycomb-like appearance with the cylindrical pores oriented along the main antler axis. Later, this tissue is filled with primary osteons, whose collagen fibrils are mainly oriented along the pores, thus improving the antler's mechanical properties. This strongly suggests that to achieve very fast organ growth it is advantageous to have a longitudinal porous framework as an intermediate step in bone formation. The example of antler shows that geometric features of this framework are crucial, and a tubular geometry with a diameter in the order of hundred micrometers seems to be a good solution for fast framework-mediated bone formation.

On the importance of a motivational agency variable: Being a formal business in developing countries is only helpful for growth if business owners show a high degree of personal initiative.

This article advances the understanding of when and how formal status of small-scale entrepreneurs can contribute to higher growth in comparison to their informal counterparts. Our integrative framework suggests that both formal status and personal initiative (PI) behavior have a common pathway to predict firm growth. More importantly, formal firms improve their growth perspectives only if the entrepreneurs show a high degree of PI. The integrative framework was tested using longitudinal data with 2 measurement points with a total of 190 formal and informal entrepreneurs in the Sub-Saharan African country of Zimbabwe. Results show that both formal status and PI have indirect effects on firm growth through available resources. Further, PI has a dual-path moderating effect on the indirect effect of formal status to firm growth such that the indirect effect of formal status on firm growth via available resources is strongest when entrepreneurs have high PI, but there is no indirect effect when PI is low. Our research shows the importance of considering the interplay of institutional and psychological factors for explaining firm growth in developing countries. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Heart-focused anxiety before and after cardiac surgery.

OBJECTIVE: We investigated the degree and course of heart-focused anxiety (HFA) in patients with cardiac diseases before and after cardiac surgery. METHODS: We examined 90 patients undergoing coronary bypass, valve replacement, or combined surgery before surgery, 6 weeks after surgery, and 6 months after surgery. Patients completed the Cardiac Anxiety Questionnaire (CAQ), which assesses heart-focused fear, attention, and avoidance, and a set of other questionnaires assessing general anxiety, depression, and quality of life. Data were compared with an age- and sex-controlled contrast group of 72 orthopedic patients with no history of cardiac disease. RESULTS: All dimensions of HFA were elevated in patients before surgery. CAQ-Fear was significantly reduced 6 weeks after surgery and at 6-month follow-up. CAQ-Avoidance was stable after surgery but declined on follow-up, while there was only a statistical tendency indicating reduction in CAQ-Attention. Approximately 20% of patients continued to experience clinically elevated levels of HFA at 6-month follow-up. Furthermore, we found decreases in global anxiety and depression, and an increase in quality of life after surgery. CONCLUSIONS: In contrast to global psychosocial indicators, the more specific assessment of HFA may help identify individuals with elevated levels of HFA who might benefit from interventions to help them adjust to the effects of surgery and lingering cardiac problems.

Business owners' action planning and its relationship to business success in three African countries.

A model of business success was developed with motivational resources (locus of control, self-efficacy, achievement motivation, and self-reported personal initiative) and cognitive resources (cognitive ability and human capital) as independent variables, business owners' elaborate and proactive planning as a mediator, and business size and growth as dependent variables. Three studies with a total of 408 African micro and small-scale business owners were conducted in South Africa, Zimbabwe, and Namibia. Structural equation analyses partially supported the hypotheses on the importance of psychological planning by the business owners. Elaborate and proactive planning was substantially related to business size and to an external evaluation of business success and was a (partial) mediator for the relationship between cognitive resources and business success. The model carries important implications for selection, training, and coaching of business owners.

Accelerated growth plate mineralization and foreshortened proximal limb bones in fetuin-A knockout mice.

The plasma protein fetuin-A/alpha2-HS-glycoprotein (genetic symbol Ahsg) is a systemic inhibitor of extraskeletal mineralization, which is best underscored by the excessive mineral deposition found in various tissues of fetuin-A deficient mice on the calcification-prone genetic background DBA/2. Fetuin-A is known to accumulate in the bone matrix thus an effect of fetuin-A on skeletal mineralization is expected. We examined the bones of fetuin-A deficient mice maintained on a C57BL/6 genetic background to avoid bone disease secondary to renal calcification. Here, we show that fetuin-A deficient mice display normal trabecular bone mass in the spine, but increased cortical thickness in the femur. Bone material properties, as well as mineral and collagen characteristics of cortical bone were unaffected by the absence of fetuin-A. In contrast, the long bones especially proximal limb bones were severely stunted in fetuin-A deficient mice compared to wildtype littermates, resulting in increased biomechanical stability of fetuin-A deficient femora in three-point-bending tests. Elevated backscattered electron signal intensities reflected an increased mineral content in the growth plates of fetuin-A deficient long bones, corroborating its physiological role as an inhibitor of excessive mineralization in the growth plate cartilage matrix--a site of vigorous physiological mineralization. We show that in the case of fetuin-A deficiency, active mineralization inhibition is a necessity for proper long bone growth.

Inhomogeneous fibril stretching in antler starts after macroscopic yielding: indication for a nanoscale toughening mechanism.

Antler is a unique mineralized tissue, with extraordinary toughness as well as an ability to annually regenerate itself in its entirety. The high fracture resistance enables it to fulfill its biological function as a weapon and defensive guard during combats between deer stags in the rutting season. However, very little is quantitatively understood about the structural origin of the antler's high toughness. We used a unique combination of time-resolved synchrotron small angle X-ray diffraction together with tensile testing of antler cortical tissue under physiologically wet conditions. We measured the deformation at the nanoscale from changes in the meridional diffraction pattern during macroscopic stretch-to-failure tests. Our results show that on average fibrils are strained only half as much as the whole tissue and the fibril strain increases linearly with tissue strain, both during elastic and inelastic deformation. Most remarkably, following macroscopic yielding we observe a straining of some fibrils equal to the macroscopic tissue strain while others are hardly stretched at all, indicating an inhomogeneous fibrillar strain pattern at the nanoscale. This behavior is unlike what occurs in plexiform bovine bone and may explain the extreme toughness of antler compared to normal bone.