Characterization of Mechanical and Biological Properties of 3-D Scaffolds Reinforced with Zinc Oxide for Bone Tissue Engineering

A scaffold for bone tissue engineering should have highly interconnected porous structure, appropriate mechanical and biological properties. In this work, we fabricated well-interconnected porous β-tricalcium phosphate (β-TCP) scaffolds via selective laser sintering (SLS). We found that the mechanical and biological properties of the scaffolds were improved by doping of zinc oxide (ZnO). Our data showed that the fracture toughness increased from 1.09 to 1.40 MPam^1/2, and the compressive strength increased from 3.01 to 17.89 MPa when the content of ZnO increased from 0 to 2.5 wt%. It is hypothesized that the increase of ZnO would lead to a reduction in grain size and an increase in density of the strut. However, the fracture toughness and compressive strength decreased with further increasing of ZnO content, which may be due to the sharp increase in grain size. The biocompatibility of the scaffolds was investigated by analyzing the adhesion and the morphology of human osteoblast-like MG-63 cells cultured on the surfaces of the scaffolds. The scaffolds exhibited better and better ability to support cell attachment and proliferation when the content of ZnO increased from 0 to 2.5 wt%. Moreover, a bone like apatite layer formed on the surfaces of the scaffolds after incubation in simulated body fluid (SBF), indicating an ability of osteoinduction and osteoconduction. In summary, interconnected porous β-TCP scaffolds doped with ZnO were successfully fabricated and revealed good mechanical and biological properties, which may be used for bone repair and replacement potentially.     

Bioresorbable Scaffolds Based on Fibroin for Bone Tissue Regeneration

Using the tissue-engineered constructs based on scaffolds that imitate the extracellular matrix of living tissues unveils new opportunities in the treatment of various pathologies and injuries associated with tissue and organ damage. Silk fibroin of silkworm Bombyx mori is a biocompatible and bioresorbable polymer with high mechanical strength and elasticity that allows creating scaffolds on its basis for regeneration of various tissues, including bone. In the present work, fibroin scaffolds were obtained. They were designed in the form of porous sponges, films, and hybrid scaffolds of a bilayer structure in which the porous sponge threedimensional structure is limited on one side by a film. The structure of the scaffolds and their biocompatibility were studied: immortalized and primary fibroblasts, as well as the osteoblast-like cells, have been shown to successfully adhere and proliferate on the surface of the studied scaffolds. Numerous osteogenesis foci have been observed in the implant region 4 weeks after the fibroin porous scaffold implantation in the in vivo experiments in a rat femoral bone defect model indicating the osteoconduction of the scaffolds.     

The Effect of Processing Temperature on Mechanical Properties of Novel Silk Fibroin and Chitosan Blend Scaffolds for Musculoskeletal Regeneration

This article has no abstract.     

Theoretical Prediction and Experimental Testing of Mechanical Properties for 3D Printed Silk Fibroin-Type II Collagen Scaffolds for Cartilage Regeneration

Silk fibroin-typeⅡcollagen scaffold was made by 3D printing technique and freeze-drying method, and its mechanical properties were studied by experiments and theoretical prediction. The results show that the three-dimensional silk fibroin-typeⅡ collagen scaffold has good porosity and water absorption, which is (89.3%+3.26%) and (824.09%+93.05%), respectively. With the given strain value, the stress of scaffold decreases rapidly firstly and then tends to be stable during the stress relaxation. Both initial and instantaneous stresses increase with increase of applied strain value. The creep strains of scaffold with different stress levels show the two stages: the rapidly increasing stage and the second stable stage. It is noted that the scaffold with compressive stress of less than 35 kPa can recover when the compressive stress is removed. However when the compressive stress is higher than 50 kPa, the scaffold is damaged and its structure is destroyed. Not only the compressive property but tensile property of scaffold are dependent on the applied displacement rate or strain rate. Its compressive elastic modulus and tensile modulus increase with increase of strain rate or displacement rate. The nonlinear relaxation model and creep model were constructed respectively and applied to predict the stress relaxation behavior and creep behavior of scaffold. It is found that there are good agreements between the experimental data and predictions, which mean that the built theoretical model can predict the mechanical behavior of scaffold.     

Porous Silk Scaffolds for Delivery of Growth Factors and Stem Cells to Enhance Bone Regeneration

Stem cell-based tissue engineering shows promise for bone regeneration and requires artificial microenvironments to enhance the survival, proliferation and differentiation of the seeded cells. Silk fibroin, as a natural protein polymer, has unique properties for tissue regeneration. The present study aimed to evaluate the influence of porous silk scaffolds on rat bone marrow stem cells (BMSCs) by lenti-GFP tracking both in vitro and in vivo in cranial bone defects. The number of cells seeded within silk scaffolds in rat cranial bone defects increased from 2 days to 2 weeks after implantation, followed by a decrease at eight weeks. Importantly, the implanted cells survived for 8 weeks in vivo and some of the cells might differentiate into endothelial cells and osteoblasts induced by the presence of VEGF and BMP-2 in the scaffolds to promote angiogenesis and osteogenesis. The results demonstrate that porous silk scaffolds provide a suitable niche to maintain long survival and function of the implanted cells for bone regeneration.     

Comparative Mechanical Properties and Histology of Bone

Different bone tissues differ in their amounts of porosity,mineralization,reconstruction, and preferred orientation. Allthese have important effects on mechanical properties. Veryporous, cancellous bone is always weaker and morecompliant thancompact bone on a weight for weight basis, yet it occurs inplaceswhere its energyabsorbing ability, or its low density,is advantageous. Bonevaries considerably in its mineralization,and such variations have quite disproportionate effects on mechanicalproperties. These variations can be shown to be adaptive. Inparticular, there must always be a compromise between stiffnessandresistanceto fracture; these two properties run contrary to each other.The reason for secondary remodeling is an unresolved problem,though in a few places the role of such remodeling in changingthe grain of the bone is clearly mechanically adaptive. Themechanical properties of non-mammalian bone are obscure, andas the histology of such bone is often quite different fromthat of mammalian bone, we are no doubt in for some surpriseswhen the mechanical properties ofnonmammalian bone are discovered.     

Tensile Mechanical Properties of Swine Cortical Mandibular Bone

Temporary orthodontic mini implants serve as anchorage devices in orthodontic treatments. Often, they are inserted in the jaw bones, between the roots of the teeth. The stability of the mini implants within the bone is one of the major factors affecting their success and, consequently, that of the orthodontic treatment. Bone mechanical properties are important for implant stability. The aim of this study was to determine the tensile properties of the alveolar and basal mandible bones in a swine model. The diametral compression test was employed to study the properties in two orthogonal directions: mesio-distal and occluso-gingival. Small cylindrical cortical bone specimens (2.6 mm diameter, 1.5 mm thickness) were obtained from 7 mandibles using a trephine drill. The sites included different locations (anterior and posterior) and aspects (buccal and lingual) for a total of 16 specimens from each mandible. The load-displacement curves were continuously monitored while loading half of the specimens in the oclluso-gingival direction and half in the mesio-distal direction. The stiffness was calculated from the linear portion of the curve. The mesio-distal direction was 31% stiffer than the occluso-gingival direction. The basal bone was 40% stiffer than the alveolar bone. The posterior zone was 46% stiffer than the anterior zone. The lingual aspect was stiffer than the buccal aspect. Although bone specimens do not behave as brittle materials, the diametral compression test can be adequately used for determining tensile behavior when only small bone specimens can be obtained. In conclusion, to obtain maximal orthodontic mini implant stability, the force components on the implants should be oriented mostly in the mesio-distal direction.     

Donor Age-Related Biological Properties of Human Dental Pulp Stem Cells Change in Nanostructured Scaffolds

The aim of the present work is to study how biological properties, such as proliferation and commitment ability, of human adult dental pulp stem cells (DPSCs) relate to the age of the donor. Human dental pulps were extracted from molars of healthy adult subjects aged 16 to >66 years. DPSCs were isolated and cultured in the presence of osteogenic, neurogenic, or vasculogenic differentiation medium. Proliferation ability was evaluated by determining doubling time, and commitment ability was evaluated by gene expression and morphological analyses for tissue-specific markers. The results confirm a well-defined proliferative ability for each donor age group at an early in vitro passage (p2). DPSCs from younger donors (up to 35 years) maintain this ability in long-term cultures (p8). Stem cells of all age donor groups maintain their commitment ability during in vitro culture. In vivo tests on the critical size defect repair process confirmed that DPSCs of all donor ages are a potent tool for bone tissue regeneration when mixed with 3D nanostructured scaffolds.     

MSCs在自组装多肽纳米纤维支架中的三维培养及脂向分化研究

拟采用自组装多肽RADA16水凝胶建市MSCs的三维培养体系,以观察MSCs在RADA16中的黏附、形态及脂向分化情况.将第3代细胞置于RADA16水凝胶中进行三维培养.实验组细胞-材料复合物以脂向诱导液诱导,对照组以DMEM培养液培养,然后进行形态学观察,油红O染色及Western blot检测.荧光染色显示,绝大多数MSCs在RADA16水凝胶中能存活,且在不同的三维平面上生长.经诱导后,细胞内有大量油红O染色阳性的脂滴聚集,Western blot分析结果显示有脂肪细胞特异的蛋白PPARγ表达,且表达量随诱导时间的延长而增加.以上结果表明,RADA16水凝胶支架为MSCs的黏附、生长提供良好的三维环境,经定向诱导后支架内的MSCs可向脂肪组织方向分化.     

Pairwise Assembly Determines the Intrinsic Potential for Self-Organization and Mechanical Properties of Keratin Filaments

Most type I and II keratin genes are spatially and temporally regulated in a pairwise manner in epithelial tissues, where they represent the major structural proteins. Epithelia can be partitioned into simple (single-layered) and complex (multilayered) types. We compared the structural and mechanical properties of natural keratin polymers occurring in complex (K5-K14) and simple (K8-K18) epithelia. The intrinsic properties of these distantly related keratin filaments, whether dispersed or bundled in vitro, were surprisingly similar in all respects when at high polymer concentration. When type I and II assembly partners were switched to give rise to mismatched polymers (K5-K18; K8-K14), the interfilament interactions, which determine the structural and mechanical properties of keratin polymers, were significantly altered. We also show that a K5-K16 polymer exhibits lesser elasticity than K5- K14, which may help explain the inability of K16 to fully rescue the skin blistering characteristic of K14 null mice. The property of self-interaction exhibited by keratin filaments is likely to assist their function in vivo and may account for the relative paucity of cytoplasmic and keratin-specific cross-linkers. Our findings underscore the fundamental importance of pairwise polymerization and have implications for the functional significance of keratin sequence diversity.     

Changes in the Mechanical Properties and Composition of Bone during Microdamage Repair

Under normal conditions, loading activities result in microdamage in the living skeleton, which is repaired by bone remodeling. However, microdamage accumulation can affect the mechanical properties of bone and increase the risk of fracture. This study aimed to determine the effect of microdamage on the mechanical properties and composition of bone. Fourteen male goats aged 28 months were used in the present study. Cortical bone screws were placed in the tibiae to induce microdamage around the implant. The goats were euthanized, and 3 bone segments with the screws in each goat were removed at 0 days, 21 days, 4 months, and 8 months after implantation. The bone segments were used for observing microdamage and bone remodeling, as well as nanoindentation and bone composition, separately. Two regions were measured: the first region (R1), located 1.5 mm from the interface between the screw hole and bone; and the second region (R2), located>1.5 mm from the bone-screw interface. Both diffuse and linear microdamage decreased significantly with increasing time after surgery, with the diffuse microdamage disappearing after 8 months. Thus, screw implantation results in increased bone remodeling either in the proximal or distal cortical bone, which repairs the microdamage. Moreover, bone hardness and elastic modulus decreased with microdamage repair, especially in the proximal bone tissue. Bone composition changed greatly during the production and repair of microdamage, especially for the C (Carbon) and Ca (Calcium) in the R1 region. In conclusion, the presence of mechanical microdamage accelerates bone remodeling either in the proximal or distal cortical bone. The bone hardness and elastic modulus decreased with microdamage repair, with the micromechanical properties being restored on complete repair of the microdamage. Changes in bone composition may contribute to changes in bone mechanical properties.     

自组装短肽水凝胶支架三维培养环境对骨髓间充质干细胞生物学特性及心肌方向分化的影响

目的:探究短肽GFS-4自组装形成的水凝胶作为支架材料构建三维微环境对BMSCs生物学特性及向心肌细胞方向诱导分化过程的影响。方法:刚果红染色、红细胞膜裂解实验检测短肽GFS-4自组装效果及对细胞膜是否具有裂解作用;CCK8和AO/EB染色分别检测对BMSCs活性和凋亡的影响;Real-time PCR分析BMSCs诱导分化后MLC-2v、GATA-4基因表达情况。结果:GFS-4自组装后形成致密凝胶,自组装前后对细胞膜无损伤;三维培养环境细胞呈球形生长,细胞活力和凋亡速度均低于二维培养环境。三维培养组在诱导分化过程中的第5天和第7天MLC-2v、GATA-4基因表达均显著高于二维组(P0.05)。结论:短肽GFS-4自组装水凝胶构建的三维微环境延缓了BMSCs的增殖速度和凋亡速度,并促进向心肌方向诱导分化过程中MLC-2v、GATA-4基因的表达。     

骨髓间充质干细胞复合支架材料的骨组织工程研究进展

近年来,组织工程技术飞速发展,将种子细胞与支架材料相复合的骨组织工程研究已成为热点,并日趋走向成熟。这一全新的治疗方案将成为解决临床上各种原因造成的骨组织缺损的最有效途径之一。骨组织工程技术包括种子细胞、支架材料和生长因子三个方面。其中,BMSCs因具有多向分化能力、强大的增殖能力以及低免疫源性被认为是最理想的种子细胞,而支架材料的种类有很多种,目前对支架材料的选择也尚有分歧。如何找到理想的支架材料是骨组织工程研究中亟待解决的重要问题。本文就组织工程中与骨髓间充质干细胞(BMSCs)相复合的各类支架材料的研究现状进行综述,这些支架材料的研究将为骨组织工程支架材料的选择提供有效依据。     

Effects of Hydrogen Peroxide Cleaning Procedures on Bone Graft Osteoinductivity and Mechanical Properties

Bone allografts are frequently used during orthopaedic trauma cases or other reconstructive procedures. Most allografts are processed and cleaned before use. Our goals were to determine if an improved cleaning procedure compromises the strength or osteoinductivity of a graft. We compared our improved cleaning procedure to our standard cleaning procedure on cortical bone allograft. The cleaning procedures are generally composed of a series of chemical steps with nonionic detergents, hydrogen peroxide, and alcohol under time and temperature control, subjected to ultrasonic agitation. We tested the compressive strength, impact strength, and shear strength following the standard and improved cleaning procedures. Osteoinductivity was tested in 4 groups, using the improved cleaning procedure with four different hydrogen peroxide cleaning times: 0, 1, 3, and 5 h. Osteoinductivity was evaluated in vivo, using a 28-day implant in the hamstring muscle of an athymic, nude mouse. Results demonstrated that osteoinductivity is maintained with cleaning in hydrogen peroxide for up to 1 h, and that compressive strength, impact strength, and shear strength were all unaffected by the improved cleaning procedure. The improved cleaning procedure therefore did not compromise the strength or osteoinductivity of cortical bone allografts in comparison to the standard procedure.     

Fabrication of Porous Scaffolds for Bone Tissue Engineering Using a 3-D Robotic System: Comparison with Conventional Scaffolds Fabricated by Particulate Leaching

This article has no abstract.     

The Mechanical Properties of RNA-DNA Hybrid Duplex Stretched by Magnetic Tweezers

RNA can anneal to its DNA template to generate an RNA-DNA hybrid (RDH) duplex and a displaced DNA strand, termed R-loop. RDH duplex occupies up to 5% of the mammalian genome and plays important roles in many biological processes. The functions of RDH duplex are affected by its mechanical properties, including the elasticity and the conformation transitions. The mechanical properties of RDH duplex, however, are still unclear. In this work, we studied the mechanical properties of RDH duplex using magnetic tweezers in comparison with those of DNA and RNA duplexes with the same sequences. We report that the contour length of RDH duplex is ～0.30 nm/bp, and the stretching modulus of RDH duplex is ～660 pN, neither of which is sensitive to NaCl concentration. The persistence length of RDH duplex depends on NaCl concentration, decreasing from ～63 nm at 1 mM NaCl to ～49 nm at 500 mM NaCl. Under high tension of ～60 pN, the end-opened RDH duplex undergoes two distinct overstretching transitions; at high salt in which the basepairs are stable, it undergoes the nonhysteretic transition, leading to a basepaired elongated structure, whereas at low salt, it undergoes a hysteretic peeling transition, leading to the single-stranded DNA strand under force and the single-stranded RNA strand coils. The peeled RDH is difficult to reanneal back to the duplex conformation, which may be due to the secondary structures formed in the coiled single-stranded RNA strand. These results help us understand the full picture of the structures and mechanical properties of nucleic acid duplexes in solution and provide a baseline for studying the interaction of RDH with proteins at the single-molecule level.     

Influence of Nano-HA Coated Bone Collagen to Acrylic (Polymethylmethacrylate) Bone Cement on Mechanical Properties and Bioactivity

Objective

This research investigated the mechanical properties and bioactivity of polymethylmethacrylate (PMMA) bone cement after addition of the nano-hydroxyapatite(HA) coated bone collagen (mineralized collagen, MC).

Materials & Methods

The MC in different proportions were added to the PMMA bone cement to detect the compressive strength, compression modulus, coagulation properties and biosafety. The MC-PMMA was embedded into rabbits and co-cultured with MG 63 cells to exam bone tissue compatibility and gene expression of osteogenesis.

Results

15.0%(wt) impregnated MC-PMMA significantly lowered compressive modulus while little affected compressive strength and solidification. MC-PMMA bone cement was biologically safe and indicated excellent bone tissue compatibility. The bone-cement interface crosslinking was significantly higher in MC-PMMA than control after 6 months implantation in the femur of rabbits. The genes of osteogenesis exhibited significantly higher expression level in MC-PMMA.

Conclusions

MC-PMMA presented perfect mechanical properties, good biosafety and excellent biocompatibility with bone tissues, which has profoundly clinical values.     

Preparation,Mechanical and Biological Properties of Inkjet Printed Alginate/Gelatin Hydrogel

3D printing has made remarkable progress in soft tissue reconstruction enabling the custom design of complex material implants with patient specific geometry.Th...