Silica-calcium phosphate nanocomposite (SCPC) has a superior bone regenerative capacity and resorbability when compared to hydroxyapatie (HA) and bioactive glass [1–2]. Synthesis of SCPC bioceramics with superior mechanical properties has been an important and challenging issue. Ideally, the mechanical strength of the orthopedic implantat should be comparable to that of the host-bone in order to provide structural support and minimize stress shielding. The compressive strength of trabecular bone ranges from 2–12 MPa and that of cortical bone varies in the range of 100–230 MPa [3]. The aim of the present study is to study the effect of processing parameters on the mechanical properties of SCPC cylinders prepared by powder metallurgy technique. The mechanical properties were correlated to the microstructure of SCPC prepared under different processing conditions.

Tissue mechanics is one of the key courses of the Biomechanics subtrack of the undergraduate curriculum. The aims of the course include: 1) To understand the concepts of stress, strain, viscoelasticity and how these concepts apply to musculoskeletal tissues. 2) The ability to infer the state of stress and strain at a given point in a biological structure under torsional, axial, bending and other types of loads. 3) To understand the anatomy of musculoskeletal tissues. Accomplishment of these aims requires a holistic understanding of statics, strength of materials and microanatomy of connective tissues. Conveying this wide range of topics in one class is a major challenge and most textbooks on this subject lack depth either in engineering or in physiology. The purpose of this abstract is to describe the benefits of the integration of theory with experimental practice for bridging the difficult topics of statics, strength of materials and tissue anatomy within the framework of undergraduate biomedical engineering curriculum.

Genetic engineering of protein-based materials provides material scientists with high levels of control in material microstructures, properties, and functions [1]. For example, multi-block protein copolymers in which individual block may possess distinct mechanical or biological properties have been biosynthesized [2, 3]. Polypeptide sequences derived from well-studied structural proteins (e.g., collagen, silk, elastin) are often used as motifs in the design and synthesis of new protein-based material, in which new functional groups may be incorporated. In this fashion, we have produced a series of silk-elastin-like proteins (SELPs) consisting of polypeptide sequences derived from silk of superior mechanical strength and elastin that is extremely durable and resilient [2, 4]. Notably, the silk-like blocks are capable of crystallizing to form virtual cross-links between elastin-mimetic sequences, which, in turn, lower the crystallinity of the silk-like blocks and thus enhance the solubility of SELPs. Consequently, SELPs may be fabricated into useful structures for biomedical applications, including drug delivery. In this study, we will characterize viscoelastic properties of SELPs, which are particularly relevant to tissue engineering applications.

Despite recent progress, mechanical properties of tissue engineered heart valves still lack mechanical strength compared to native aortic valves [1]. Although cyclic tissue straining in bioreactor systems is known to enhance tissue formation [2], specific optimal loading protocols have not yet been defined. To get a better insight in the effects of mechanical loading on tissue development, mechanical behavior of tissue constructs should be monitored and controlled during culture. However, currently used methods for mechanical characterization (e.g. tensile tests, indentation tests) are destructive and can therefore only be performed at the end stage of tissue culture. An experimental-numerical approach was previously proposed by which leaflet deformation was assessed during culture in a bioreactor system, real-time and non-invasively [3]. Further development of this approach now enables a non-invasive and non-destructive assessment of mechanical properties of engineered heart valve leaflets.

The use of processed structural allografts for treatment of massive segmental defects in long bones can be complicated by poor incorporation and remodeling of the devitalized graft, foreign-body reaction and micro-damage accumulation which often leads to catastrophic graft failure [1]. It is therefore useful to develop a bioengineered, biodegradable scaffold that is able to stimulate healing of the defect region. The use of bioengineered scaffolds has been limited due to their poor mechanical strength that does not permit withstanding large in vivo loads and due to their poor osteoinductive properties. We therefore investigated the use of rigid polylactic acid/beta-tricalcium phosphate (PLA/βTCP) composites used in conjunction with osteoinductive factors such as growth hormones (parathyroid hormone (PTH)) and growth factors (bone morphogenic protein-2 (BMP-2) & vascular endothelial growth factor (VEGF)) to stimulate bone formation and vessel ingrowth in the segmental defect region. We examined the physical characteristics of the scaffolds, and evaluated their osteoinductive potential in a clinically-relevant mouse model of a femoral segmental defect with or without PTH treatment. Finally, we used an ectopic bone formation model to assess the efficacy of the scaffold in site-specific delivery of bone anabolic factors.

The sclera is the outer shell and principal load-bearing tissue of the eye, which consists primarily of avascular lamellae of collagen fibers. Ninety percent of the collagen fibers in the sclera are Type I, which provide the eye with necessary mechanical strength to sustain intraocular pressure (IOP). In the posterior sclera, there is a fenestrated canal, called the optic nerve head (ONH), through which the retinal ganglion cell axons pass transmitting visual signals from the retina to the brain. The opening of the ONH is structurally supported by a fenestrated connective tissue called the lamina cribrosa.

Collagen is one of the most abundant proteins in the human body. Due to its biological significance and omnipresence, it has been intensely studied for several decades both at the molecular and at the tissue level. A single collagen molecule is a rope like super helix of three α-chains. Collagen molecules self assemble in an orderly fashion to form different suprastructures such as fibrils and networks, providing mechanical strength to the tissue. Collagen density and suprastructural organization determines the local mechanical tension in a particular region of the tissue. Cells sense the tension and in turn trigger a controlled process of growth and remodeling of tissues through secretion or degradation of extracellular components including collagen. Tissue homeostasis is a complex process and adding to such complexity, a single collagen molecule is unstable at body temperature [1], but its stability increases after self-assembly and cross-linking.

Loss of mechanical strength of arteries can manifest itself in many ways including rupture of a vulnerable atherosclerotic plaques, burst of saccular aneurisms, rupture of artery/graft anastomosis, and traumatic rupture of aorta by impact loading due to automobile accidents. In all cases the fracture of the tissue leads to sudden cardiovascular events that often have a lethal end. To date there are insufficient experimental data on the mechanical strength of healthy and diseased vascular tissue. Most of the results refer to the failure properties from uniaxial quasi-static tensile tests on strips and rings. It was found that the tensile strength is different in the circumferential and longitudinal direction especially when it is determined from strain controlled dynamic tests [1]. Results form load-controlled fatigue tests have shown a gradual softening of the arterial tissue, development of a residual (plastic) deformation, and existence of S-N curve [2]. However, the information from uniaxial tests is not sufficient to predict the damage of tubular segments due to coupling between circumferential and longitudinal stress via constitutive equations and deformed geometry. Moreover, the mechanisms of arterial tissue failure remain unknown.

Cardiovascular disease is still the number one cause of death in the industrialized world. Diseased small diameter blood vessels are frequently replaced by native grafts. However, these vessels have a limited life time [1], for example the patency at 10 year after coronary artery bypass grafting of saphenous vein grafts is 57% [2]. Tissue engineering (TE) of small diameter blood vessels seems a promising approach to overcome these shortcomings or address the increasing need for substitutes during follow up surgery. Mechanical conditioning of myofibroblast (MFs) seeded constructs appears to be beneficial for functional tissue properties, such as cell proliferation, ECM production and mechanical strength [3,4]. Without a functional endothelial cell (ECs) layer however, patency may be compromised by thrombogenecity. Construction of an EC layer might on the other hand affect the tissue composition during culture, as was shown for bovine ECs, which influenced proliferation and ECM production of smooth muscle cells [5].

Contemporary tissue engineered heart valves seem to have sufficient mechanical strength for implantation [1]. Nevertheless, mechanical properties, tissue structure and architecture still need to be improved. Recent studies indicate enhancement of mechanical properties by applying cyclic diastolic pressure loads to the developing tissue in a bioreactor system [2]. However, current bioreactors operate with a preset transvalvular pressure applied to the tissue. Mechanical properties of the engineered construct may vary during culturing and consequently, the pressure-induced deformations are unknown. To systematically study the effects of mechanical straining on tissue development and to design an optimal conditioning protocol, real-time measurement and control of local tissue strains are desired.

A small but significant fraction of screw placement in the proximal femur for hip fractures results in iatrogenic fractures associated with the screw hole [1]. There is evidence that the failure occurs under fatigue, and it is likely that those individuals experiencing failure have greater stresses in the proximal femur as dictated by key morphometric variables, such as cortical thickness and bone size. Finite element analysis (FEA) could greatly facilitate fracture risk assessment in the presurgical phase by predicting the local stresses, however, executing FEM in a patient customized fashion would be costly, time consuming, and technically difficult for surgeons to perform.

Osteoarthritis (OA), commonly known as ‘wear and tear’ in human joints, affects over 27 million people in the United States [1]. There is currently no encompassing solution for the regeneration of damaged articular cartilage. One potential solution involves the close emulation of the native structure of articular cartilage, with special consideration given to maintaining the distinct organized zonal ultrastructure, characterized by both random and highly aligned zones of collagen fibrils, in order to preserve mechanical and cell signaling properties of the extracellular matrix [2]. Techniques such as electrospinning achieve high degrees of alignment, but do so at the cost of denaturing the collagen molecule [3] that may lead to inferior cell recognition and mechanical strength.

Development of a small-diameter vascular graft (<6 mm) have been challenging due to thrombosis and intimal hyperplasia [1]. To overcome this problem, cardiovascular tissue engineers have attempted to construct a highly porous and biocompatible fibrous scaffold providing a sufficient mechanical strength for the regeneration of a functional tissue [2–5]. Herein, we present a 3D tubular-shaped micro/nanofibrous composite-layered scaffold for vascular tissue engineering. The surface of scaffold has high surface roughness by introducing nanofibrous layer and the biophysical properties have been fulfilled by using microfibrous layer. Moreover, the atomized spraying technique is applied to spray elastin proteins, which is well known as an antithrombogenic material, on the surface of micro/nanofibrous composite-layered scaffold to introduce an appropriate antithrombogenic surface.

Conditions such as diabetes and obesity have been found to affect the mechanical integrity of bone. Studies have shown that diabetic rodent models exhibit lower levels of new bone formation during fracture healing 1 , lower bone mineral density (BMD) 2 , and increased risk of fracture 3 . There are differences, however, in the bone integrity of bone samples from type I and type II diabetics, which is most likely due to obesity 2 . Findings from research on obesity’s effects on bone integrity have been controversial; although there is an increase in bone mineral density (BMD) with increasing body mass index (BMI) and a decrease in fracture incidence in the central body regions in obese women compared to healthy weight women due to soft tissue padding, there is an increase in fracture incidence at extremeties 4 . Other studies have shown that while cortical bone strength may not be adversely affected by high-fat diets, cancellous bone BMD and mechanical strength was significantly lower in high-fat diet mice than low-fat diet mice 5 . In addition, extreme obesity has been associated with lower BMD despite the general trend of increased BMD with higher BMI 6 .

Native articular cartilage exhibits tension-compression nonlinearity (TCN), where the compressive modulus is lower than its relatively high tensile modulus [1–2]. TCN produces in restricted lateral expansion of the tissue upon axial compression. We previously demnostrated that osmotic swelling can be used to measure the TCN of engineered cartilage by placing the tissue in an initial state of tensile strain. Incremental application of compression can be used to study the tissue’s mechanical properties as it transitions from tension to compression [3]. Although engineered cartilage is able to achieve the Young’s modulus (E Y ) and glycosaminoglycan (GAG) content of native tissue, the collagen content and dynamic modulus (G*) consistently underperform the native tissue. Removing GAG with chondroitinase ABC (cABC) has been shown to significantly decrease the tissue properties immediately after digestion but the properties rebound, with improved collagen content and G* compared to undigested controls [4]. Furthermore, we have previously shown that cABC digestion significantly increases TCN in engineered cartilage [3]. Dynamic loading (DL) has been shown to significantly increase the mechanical properties without significantly altering biochemical composition of engineered cartilage, however the mechanism through which DL modulates the mechanical strength of engineered cartilage may be due in part to improved extracellular matrix (ECM) organization [5]. We therefore hypothesize that cABC digestion and DL will improve the tensile properties of engineered cartilage.

The cervix plays an important role in pregnancy as a mechanical barrier to prevent preterm birth (PTB). The material strength of the cervix can be attributed to its extracellular matrix (ECM), a network of cross-linked collagens (types I and III) embedded within a viscous matrix of glycosaminoglycans (GAG). GAGs are negatively charged polysaccharides that provide a fixed charge density (FCD) within the tissue to maintain hydration. Throughout gestation, the ECM of the cervix undergoes a remodeling process characterized by three stages: gradual softening in early pregnancy, a rapid increase in tissue distensibility termed ripening in late pregnancy, and repair at post partum 1 . As the cervix softens and ripens, mature collagen cross-links break down while GAG content increases 2,3 . Previous research has shown that these changes in collagen and GAGs correlate to a mechanically softer cervix at term 4 .

Nowadays approximately 3–6% of the population is estimated to have unruptured cerebral aneurysms. The rupture risk of aneurysms can be predicted by using computational tools and patient-specific models. As an ideal method, we can assess the risk factors by determining the blood tension and the material strength of the wall tissue in the aneurisms. Although it is hard to obtain aneurismal material strength without invasive measurement, it is possible to estimate the wall tension by numerical simulation [1].

Silk may possess superior mechanical strength while its resilience is very poor. In contrast, elastin in human arteries is very soft but extremely durable with an estimated half-life of 70 years. By combing polypeptide sequences derived from native silk and elastin, we have produced a series of silk-elastin-like proteins (SELPs), which have displayed a set of outstanding properties such as good biocompatibility and controllable biodegradation rates [1]. In this study, we will examine the crystallization of the silk-like blocks and the crosslinking of the elastin-like blocks, as well as their influences on the mechanical behavior of SELPs. The ultimate goal of this study is to explore the potential of SELPs for applications in the engineering of load-bearing tissues such as arteries.

Dynamic mechanotransduction, particularly under high frequency, low amplitude signals, has been proven effective in mediating bone loss and improving mechanical strength for tissues affected by estrogen deficient osteopenia. Ultrasound, which behaves as an alternating pressure wave in bone, may offer an effective, non-invasive technology for delivery of anabolic signals. In vitro, dynamic mechanical signals delivered using ultrasound have been shown to increase osteoblast proliferation [1], and in vivo studies have established ultrasound as an effective treatment for delayed and non-union fractures [2]. Previously, we showed that ultrasound signals similar to those currently used in a clinical setting for fracture healing were effective in mediating decreases in bone volume and mechanical strength at the millimeter length-scale in response to estrogen deficient osteopenia [3]. Due to bone’s inherent viscoelasticity and the dynamic nature of the applied ultrasound signals, it is particularly important to consider both elastic and viscous components of bone’s adaptive response to applied loads. In light of these findings, the goal of this study was to determine the role of therapeutic ultrasound signal intensity in modulating changes in bone’s nanoscale elastic and viscoelastic material properties associated with estrogen deficient osteopenia. We hypothesize that bone is sensitive to dynamic mechanical signals delivered via ultrasound and that bone’s tissue level nano-scale material properties, particularly nonlinear viscoelastic properties, are sensitive to ultrasound signal intensity.

Recent studies have shown that its necessary for synthetic matrix to provide similar mechanical response as cell’s host environment in the body for desired tissue growth [1,2]. Osteoblast cells reside in the rigid matrix made of collagen fibers and hydroxyapatite crystals. Therefore for the growth of proper functional bone tissue, its utmost necessary that scaffolds provide mechanical response similar to bone matrix. Bone also serves as a mechanical support to the body. Thus scaffolds used for bone tissue engineering should also provide adequate mechanical support to prevent collapse of the neonatal tissue. The mechanical response of scaffolds decreases significantly as porosity increases. The porosity of scaffold around 90% has been considered optimal for tissue engineering. At such high porosity, the mechanical strength and elastic modulus decreases significantly. Various polymers both of synthetic and biological origin have been investigated as a material for scaffold [3]. Synthetic polymers are biodegradable, biocompatible, and can be easily formed into different shapes and sizes. However, hydrophobicity, lack of functional groups and release of acidic products on degradation are causes of concern. Biopolymers such as collagen, chitin, chitosan etc. promote cell adhesion, proliferation and differentiation, and evoke minimal foreign body reaction on implantation [4]. But, they have inadequate mechanical properties for bone regeneration and tend to loose structural integrity under wet and body fluid conditions. The quest for scaffold materials which, not only promote cell adhesion, proliferation and differentiation but also have adequate mechanical strength to support bone tissue growth is still on. In the current work, we discuss the synthesis and characterizations of nanocomposites based on biopolymers and hydroxyapatite. The biopolymers used are chitosan and polygalacturonic acid. These two biopolymers are biocompatible, biodegradable and electrostatically complementary to each other. We have also investigated the molecular mechanics involved in their mechanical behavior. Their in vitro response have been investigated by seeding human Osteoblast cells and studying their adhesion, proliferation and differentiation. Synthesis and characterizations of nanostructured fibers based on chitosan and polygalacturonic acid will also be discussed here.