Sufficient Mechanical Support Research Articles

Hillslope Processes Affect Vessel Lumen Area and Tree Dimensions.

The height growth of the trees depends on sufficient mechanical support given by the stem and an effective hydraulic system. On unstable slopes, tree growth is affected by soil pressure from above and potential soil erosion from below the position of tree. The necessary stabilization is then provided by the production of mechanically stronger wood of reduced hydraulic conductivity. Unfortunately, the interaction between tree growth (both radial and axial) and stabilization in the soil is still insufficiently understood. Therefore, in this study, we aimed to quantify the impact of hillslope dynamics on the degree of tree growth and hydraulic limitation, and the potential effect on tree height growth and growth plasticity. To evaluate this effect, we took four cores from 80 individuals of Quercus robur and Fraxinus excelsior and measured tree-ring widths (TRWs) and vessel lumen areas (VLAs). The tree heights were evaluated using a terrestrial laser scanner, and local soil depth was measured by a soil auger. Our data showed a significant limitation of the tree hydraulic system related with the formation of eccentric tree-rings. The stem eccentricity decreased with increasing stem diameter, but at the same time, the negative effect of stem eccentricity on conduit size increased with the increasing stem diameter. Even though this anatomical adaptation associated with the effect of stem eccentricity differed between the tree species (mainly in the different degree of limitations in conduit size), the trees showed an increase in the proportion of hydraulically inactive wood elements and a lowered effectiveness of their hydraulic system. In addition, we observed a larger negative effect of stem eccentricity on VLA in Quercus. We conclude that the stabilization of a tree in unstable soil is accompanied by an inability to create sufficiently effective hydraulic system, resulting in severe height-growth limitation. This affects the accumulation of aboveground biomass and carbon sequestration.

Surface coating prolongs the degradation and maintains the mechanical strength of surgical suture in vivo

Biodegradable and absorbable sutures have been widely used in surgical procedures. However, for the repair of ligament and tendon injures, the biodegradable suture cannot provide sufficient mechanical support to close the wound for a long period of time which is important to completely heal the tissue. Herein, we develop a simple method that makes a surface coating to prolong the degradation of the suture in vivo. Polylactic acid (PLLA) and Polycaprolactone (PCL) were successfully coated to a commercial degradable polydioxanone (PDO) suture in this study, which was confirmed by Fourier transform infrared spectra (FTIR). Scanning electron microscopy (SEM) was used to observe the smooth surface of the coated sutures. Moreover, live/dead assay of human fibroblasts after co-culturing with the modified/unmodified sutures showed fairly good cellular activity. In vivo study demonstrates the degradation properties of sutures were significantly changed after the surface coating. The raw suture exhibited the fastest degradation in 12 weeks, showing significantly decline in mechanical strength. Interestingly, the PCL-coated suture was able to maintain more than 20% of its original tensile strength after 12 weeks' implantation. In addition, in vivo results of PCL-coated sutures also showed less inflammatory cell infiltration and less surface inflammation. These findings indicate the one step suture-coating method could be feasibly for the development of clinical equipment.

Pliable, Scalable, and Degradable Scaffolds with Varying Spatial Stiffness and Tunable Compressive Modulus Produced by Adopting a Modular Design Strategy at the Macrolevel.

Clinical results obtained when degradable polymer-based medical devices are used in breast reconstruction following mastectomy are promising. However, it remains challenging to develop a large scaffold structure capable of providing both sufficient external mechanical support and an internal cell-like environment to support breast tissue regeneration. We propose an internal-bra-like prototype to solve both challenges. The design combines a 3D-printed scaffold with knitted meshes and electrospun nanofibers and has properties suitable for both breast tissue regeneration and support of a silicone implant. Finite element analysis (FEA) was used to predict the macroscopic and microscopic stiffnesses of the proposed structure. The simulations show that introduction of the mesh leads to a macroscopic scaffold stiffness similar to the stiffness of breast tissue, and mechanical testing confirms that the introduction of more layers of mesh in the modular design results in a lower elastic modulus. The compressive modulus of the scaffold can be tailored within a range from hundreds of kPa to tens of kPa. Biaxial tensile testing reveals stiffening with increasing strain and indicates that rapid strain-induced softening occurs only within the first loading cycle. In addition, the microscopic local stiffness obtained from FEA simulations indicates that cells experience significant heterogeneous mechanical stimuli at different places in the scaffold and that the local mechanical stimulus generated by the strand surface is controlled by the elastic modulus of the polymer, rather than by the scaffold architecture. From in vitro experiments, it was observed that the addition of knitted mesh and an electrospun nanofiber layer to the scaffold significantly increased cell seeding efficiency, cell attachment, and proliferation compared to the 3D-printed scaffold alone. In summary, our results suggest that the proposed design strategy is promising for soft tissue engineering of scaffolds to assist breast reconstruction and regeneration.

A novel substrate based on electrospun polyurethane nanofibers and electrosprayed polyvinyl alcohol microparticles for recombinant human erythropoietin delivery.

After myocardial infarction caused by a heart attack, endothelial cells need to be preserved in order to regenerate new capillaries. Moreover, sufficient mechanical support is necessary for the infarcted myocardium to pump the blood. Herein, we designed a novel substrate containing polyurethane (PU) nanofibrous layers and recombinant human erythropoietin (rhEPO)-loaded microparticles for both controlled releases of rhEPO and mechanical support of myocardium. In this system, the single-layer (SL) and double-layer (DL) PU nanofibers were electrospun, and then microparticles with different rhEPO:polyvinyl alcohol (PVA) ratios were electrosprayed on the layers. The in vitro release behavior of rhEPO from SL substrates was not satisfactory, and then the study focused on DL patches in which the release profile was in accordance with Korsmeyer-Peppas model. The release exponent of 0.89 for the DL PU/120PVA:1rhEPO represented zero-order release. The results inferred that these substrates possessed highly tailored mechanical properties; Young's modulus and ultimate tensile strength of the substrates were 74-172 kPa and 7.4-9.9MPa, respectively. The rhEPO release from the substrates was leading to the proper adhesion of endothelial cells and more than 95% cell viability. The results indicated that the patch of elastic nanofibers and microparticles offered a potential substrate for simultaneous rhEPO delivery to endothelial cells and also mechanically supporting the infarcted myocardium.

Soil Moisture Levels Affect the Anatomy and Mechanical Properties of Basil Stems (Ocimum basilicum L.).

As plants would benefit from adjusting and optimizing their architecture to changing environmental stimuli, ensuring a strong and healthy plant, it was hypothesized that different soil moisture levels would affect xylem and collenchyma development in basil (Ocimum basilicum L. cv. Marian) stems. Four different irrigation set-points (20, 30, 40 and 50% VWC), corresponding respectively to pF values of 1.95, 1.65, 1.30 and 1.15, were applied. Basil plants grown near the theoretical wilting point (pF 2) had a higher xylem vessel frequency and lower mean vessel diameter, promoting water transport under drought conditions. Cultivation at low soil moisture also impacted the formation of collenchyma in the apical stem segments, providing mechanical and structural support to these fast-growing stems and vascular tissues. The proportion of collenchyma area was significantly lower for the pF1.15 treatment (9.25 ± 3.24%) compared to the pF1.95 and pF1.30 treatments (16.04 ± 1.83% and 13.28 ± 1.38%, respectively). Higher fractions of collenchyma resulted in a higher mechanical stem strength against bending. Additionally, tracheids acted as the major support tissues in the basal stem segments. These results confirm that the available soil moisture impacts mechanical stem strength and overall plant quality of basil plants by impacting xylem and collenchyma development during cultivation, ensuring sufficient mechanical support to the fast-growing stem and to the protection of the vascular tissues. To our knowledge, this study is the first to compare the mechanical and anatomical characteristics of plant stems cultivated at different soil moisture levels.

Highly porous Sr-doped TiO2 ceramics maintain compressive strength after grain boundary corrosion

Maintaining sufficient mechanical support during bone healing is an essential property for ceramic bone scaffolds. However, grain boundary (GB) dissolution may compromise the mechanical strength of polycrystalline ceramics in the physiological environment. Therefore, we investigated the GB formation and its impact on the compressive strength and corrosion behavior in TiO2 scaffolds doped with calcium and strontium. To alter the GB composition and densification process, sintering conditions were altered. Prolonged sintering times and increased sintering temperature led to improved densification and increased strength in Ca-doped scaffolds. However, dissolution of the resulting amorphous GBs caused a significant loss of compressive strength when exposed to an acidic environment. In contrast, a crystalline SrTiO3 GB phase present in Sr-doped scaffolds, for which increased sintering temperature combined with rapid cooling led to a significantly improved compressive strength. Formation of SrTiO3 crystals in the GBs maintained the strength for over 4 weeks in an acidic environment.

Rapid Self‐Expansion Behavior of the PMMA‐Based Bone Cement with P(MMA‐AA)‐GO Nano‐Units

AbstractThe volume shrinkage of polymethylmethacrylate (PMMA) bone cement is typically addressed by incorporating additives into the matrix. However, the maximum water absorption and swelling capacity of the composite bone cement are not sufficiently improved due to its rapid solidification. In this work, poly(methyl methacrylate‐acrylic acid)‐grafted graphene oxide [P(MMA‐AA)‐GO] nano‐units with the microsphere‐lamellar structure are synthesized, and then P(MMA‐AA)‐GO bone cement (PGBC) is fabricated. The rate of absorption and swelling of PGBC are significantly promoted by the microsphere–lamellar structure of P(MMA‐AA)‐GO nano‐units, achieving maximum absorption and swelling capacity of PGBC before its solidification. PGBC 4 exhibits the maximum equilibrium simulate body fluid (SBF) absorption ratio and equilibrium swelling ratio of 90.2% ± 1.7% and 92.5% ± 4.5%, respectively. Interestingly, the maximum compression strength of the composite before immersion is also observed in PGBC 4 with a value of 77.2 ± 1.1 MPa. The enhanced compression strength of PGBC overcomes the bottleneck of the decreased compression strength resulting from the enhanced absorption behavior. Therefore, PGBC with rapid self‐expansion behavior and improved mechanical properties can not only reduce the injection volume to avoid leakage in the clinic but also provide sufficient mechanical support, which has promising application potential in the clinical setting.

Long-term survival and clinical outcomes of non-vascularized autologous and allogeneic fibular grafts are comparable for treating osteonecrosis of the femoral head

BackgroundOsteonecrosis of the femoral head (ONFH) is a disabling disease, which often involves young patients. Recently, various hip-preserving surgeries were recommended to delay total hip arthroplasty (THA).Questions/purposesThis study aimed to compare clinical outcomes and survival rate in the long-term follow-up between core decompression combined with a non-vascularized autologous fibular graft (group A) and an allogeneic fibular graft (group B) for the treatment of ONFH.Patients and methodsWe retrospectively evaluated 117 patients (153 hips) with ONFH (Association Research Circulation Osseous [ARCO] stages IIa to IIIc) who underwent the abovementioned hip-preserving surgeries between January 2003 and June 2012. The mean (range) follow-up times (years) were 12.9 (7–16) and 9.3 (6–16) in groups A and B, respectively. Clinical outcomes were assessed using the Harris Hip Score (HHS), visual analog scale (VAS) score, and forgotten joint score (FJS). A survival analysis was performed using the Kaplan-Meier method. The end point was THA.ResultsGroups A and B showed postoperative improvements, respectively, in HHS from 65 ± 7.2 to 80.3 ± 14.5 and from 66 ± 5.9 to 82.4 ± 13.6 (p < 0.05), and in VAS score from 6.3 ± 1.1 to 2.3 ± 1.6 and from 6.1 ± 1 to 2.2 ± 2.2 (p < 0.05). However, no significant differences in the HHS, VAS score, and hip FJS at the last follow-up (p > 0.05) and 15-year survival rate (84.1% and 86%, respectively, p > 0.05) were found between groups A and B.ConclusionsAutologous and allogeneic fibular grafts can attain equally good clinical outcomes and high survival rates in long-term follow-up, and thus can greatly delay THA owing to good bone osseointegration and sufficient mechanical support. Notably, the ratio of failure will increase when patients were more than 37 years old.Level of evidenceLevel III, therapeutic study

Enhanced regeneration of bone defects using sintered porous Ti6Al4V scaffolds incorporated with mesenchymal stem cells and platelet-rich plasma.

A new highly controlled powder sintering technique was used for the fabrication of a porous Ti6Al4V scaffold. The platelet-rich plasma (PRP) was prepared using whole blood. The PRP was used as a cell carrier to inject bone marrow mesenchymal stem cells (MSC) into the pores of the Ti6Al4V scaffold in the presence of calcium chloride and thrombin, and then the composite construct of porous Ti6Al4V loaded with PRP gel and MSC was obtained. The bare Ti6Al4V scaffold and the Ti6Al4V scaffold loaded with MSC were used as controls. The characteristics and mechanical properties of the scaffold, and the biological properties of the constructs were evaluated by a series of in vitro and in vivo experiments. The results show that the sintered porous Ti6Al4V has good biocompatibility, and high porosity and large pore size, which can provide sufficient space and sufficient mechanical support for the growth of cells and bones without an obvious stress shielding effect. However, Ti6Al4V/MSC/PRP showed a significantly higher cell proliferation rate, faster bone growth speed, more bone ingrowth, and higher interfacial strength. Therefore, the porous Ti6Al4V scaffolds incorporated with MSC and PRP may be more effective at enhancing bone regeneration, and is expected to be used for bone defect repair.

Biodegradable magnesium implants: a potential scaffold for bone tumor patients

Relapse and metastasis of tumor may occur for osteosarcoma (OS) patients after clinical resection. Conventional metallic scaffolds provide sufficient mechanical support to the defected bone but fail to eradicate recurring tumors. Here we report that biodegradable magnesium (Mg) wire-based implant can inhibit OS growth. In brief, the Mg wires release Mg ions to activate the transport of zinc finger protein Snail1 from cytoplasm to cell nucleus, which induces apoptosis and inhibits proliferation of OS cells through a parallel antitumor signaling pathway of miRNA-181d-5p/TIMP3 and miRNA-181c-5p/NLK downstream. Simultaneously, the hydrogen gas evolution from Mg wires eliminates intracellular excessive reactive oxygen species, by which the growth of bone tumor cells is suppressed. The subcutaneous tumor-bearing experiment of OS cells in nude mice further confirms that Mg wires can effectively inhibit the growth of tumors and prolong the survival of tumor-bearing mice. In addition, Mg wires have no toxicity to normal cells and tissues. These results suggest that Mg implant is a potential anti-tumor scaffold for OS patients.

The mechanical property and corrosion resistance of Mg-Zn-Nd alloy fine wires in vitro and in vivo

Titanium and its alloy are commonly used as surgical staples in the reconstruction of intestinal tract and stomach, however they cannot be absorbed in human body, which may cause a series of complications to influence further diagnosis. Magnesium and its alloy have great potential as surgical staples, because they can be degraded in human body and have good mechanical properties and biocompatibility. In this study, Mg-2Zn-0.5Nd (ZN20) alloy fine wires showed great potential as surgical staples. The ultimate tensile strength and elongation of ZN20 alloy fine wires were 248 MPa and 13%, respectively, which could be benefit for the deformation of the surgical staples from U-shape to B-shape. The bursting pressure of the wire was about 40 kPa, implying that it can supply sufficient mechanical support after anastomosis. Biochemical test and histological analysis illustrated good biocompatibility and biological safety of ZN20 alloy fine wire. The residual tensile stress formed on the outside of ZN20 fine wire during drawing would accelerate the corrosion. The second phase had a negative influence on corrosion property due to galvanic corrosion. The corrosion rate in vitro was faster than that in vivo due to the capsule formed on the surface of ZN20 alloy fine wire.

Collagen Membrane for Guided Bone Regeneration in Dental and Orthopedic Applications.

Treatment of cortical bone defects is a clinical challenge. Guided bone regeneration (GBR), commonly used in oral and maxillofacial dental surgery, may show promise for orthopedic applications in repair of cortical bone defects. However, a limitation in the use of GBR for cortical bone defects is the lack of an ideal scaffold that provides sufficient mechanical support to bridge the cortical bone with minimal interference in the repair process. We have developed a new collagen membrane, CelGro™, for use in GBR. We report the material characterization of CelGro and evaluate the performance of CelGro in translational preclinical and clinical studies. The results show CelGro has a bilayer structure of different fiber alignment and is composed almost exclusively of type I collagen. CelGro was found to be completely acellular and free from xenoantigen, α-gal (galactose-alpha-1,3-galactose). In the preclinical study of a rabbit cortical bone defect model, CelGro demonstrated enhanced bone-remodeling activity and cortical bone healing. Microcomputed tomography evaluation showed early bony bridging over the defect area 30 days postoperatively, and nearly complete restoration of mature cortical bone at the bone defect site 60 days postoperatively. Histological analysis 60 days after surgery further confirmed that CelGro enables bridging of the cortical bone defect by induction of newly formed cortical bone. Compared to a commercially available collagen membrane, Bio-Gide®, CelGro showed much better cortical alignment and reduced porosity at the defect interface. As selection of orthopedic patients with cortical bone defects is complex, we conducted a clinical study evaluating the performance of CelGro in guided bone regeneration around dental implants. CelGro was used in GBR procedures in a total of 16 implants placed in 10 participants. Cone-beam computed tomography images show significantly increased bone formation both horizontally and vertically, which provides sufficient support to stabilize implants within 4 months. Together, the findings of our study demonstrate that CelGro is an ideal membrane for GBR not only in oral and maxillofacial reconstructive surgery but also in orthopedic applications (Clinical Trial ID ACTRN12615000027516).

Fabrication of piezoelectric porous BaTiO3 scaffold to repair large segmental bone defect in sheep.

Porous titanium scaffolds can provide sufficient mechanical support and bone growth space for large segmental bone defect repair. However, they fail to restore the physiological environment of bone tissue. Barium titanate (BaTiO3) is considered a smart material that can produce an electric field in response to dynamic force. Low-intensity pulsed ultrasound stimulation (LIPUS), as a kind of micromechanical wave, can not only promote bone repair but also induce BaTiO3 to generate an electric field. In our studies, BaTiO3 was coated on porous Ti6Al4V and LIPUS was externally applied to observe the influence of the piezoelectric effect on the repair of large bone defects in vitro and in vivo. The results show that the piezoelectric effect can effectively promote the osteogenic differentiation of bone marrow stromal cells (BMSCs) in vitro as well as bone formation and growth into implants in vivo. This study provides an optional alternative to the conventional porous Ti6Al4V scaffold with enhanced osteogenesis and osseointegration for the repair of large bone defects.

A pure zinc membrane with degradability and osteogenesis promotion for guided bone regeneration: In vitro and in vivo studies

Selection of an appropriate membrane material for guided bone regeneration (GBR) is still ongoing among resorbable and nonresorbable membranes with different characteristics. The major problem with nonresorbable membranes is the inevitable secondary surgery, while resorbable polymer membranes have limitations in providing sufficient mechanical support during the bone repair period due to premature loss of mechanical strength. Pure magnesium foil has been evaluated to explore its feasibility as a resorbable GBR membrane. It exhibited better mechanical properties, whereas poor formability and fast degradation rate were noted. In light of this, pure zinc membrane was developed as a pilot research in this paper. We designed three types of pure zinc membranes: pure Zn without pores, pure Zn with 300µm diameter and 1000µm diameter pores, and pure titanium without pores as a control. The mechanical property, in vitro immersion tests, and MC3T3-E1 cell viability assays were tested. Moreover, in vivo behaviors of three type zinc membranes were evaluated by using a rat calvarial critical-sized bone defect model. The experimental results indicated that pure Zn membrane with 300µm pores showed the most favorable osteogenic capability, comparable to that of titanium membrane without pores. Therefore, considering appropriate degradation rate, adequate mechanical maintenance, and profitable osteogenic capacity, metallic pure zinc is believed to be a promising candidate for barrier membranes in GBR therapy for bone regeneration, and its mechanical property can be enhanced with further alloying. STATEMENT OF SIGNIFICANCE: Metallic element zinc plays a pivotal role in the growth and mineralization of bone tissues. As a pilot research, three type of guided bone regeneration (GBR) membranes were developed in the present work: pure Zn without pores, pure Zn with 300µm-diameter and 1000µm-diameter pores respectively. The mechanical property, in vitro immersion tests and MC3T3-E1 cell viability assays were tested, with pure titanium without pores as a control, thereafter the in vivo performance were evaluated by using a rat calvarial critical-sized bone defect model. It indicated that pure Zn membrane with 300µm pores showed the most favorable osteogenic capability, comparable to that of titanium membrane control, and is believed to be a promising material candidate as barrier membrane in GBR therapy for bone regeneration.

A Comparative Study on the Influence of Chromium on the Phase Fraction and Elemental Distribution in As-Cast High Chromium Cast Irons: Simulation vs. Experimentation

The excellent abrasion resistance of high chromium cast irons (HCCIs) stems from the dispersion of the hard iron-chromium eutectic carbides. The surrounding matrix on the other hand, provides sufficient mechanical support, improving the resistance to cracking deformation and spalling. Prior knowledge of the microstructural characteristics is imperative to appropriately design subsequent heat treatments, and in this regard, employing computational tools is the current trend. In this work, computational and experimental results were correlated with the aim of validating the usage of MatCalc simulations to predict the eutectic carbide phase fraction and the elemental distribution in two HCCI alloys, in the as-cast condition. Microstructural observations were carried out using optical microscopy and SEM. The chemical composition and fraction of each phase was measured by electron probe microanalysis and image analysis, respectively. In all cases, the values predicted by the pseudo-equilibrium diagrams, computed with MatCalc, were in accordance with the experimentally determined values. Consequently, the results suggest that time and resource intensive experimental procedures can be replaced by simulation techniques to determine the phase fraction and especially, the individual phase compositions in the as-cast state.

Design and Development of High Current Pulse Shaping Inductor Based on Bitter Magnet Configuration for Electro Magnetic Launcher

A unique pulse shaping inductor was designed and developed using a modified Bitter magnet configuration, to operate at peak current of 150 kA for duration of 5-10 ms in a Pulse Forming Network (PFN). The inductor was designed with a stack of parallel copper plates in the form of circular discs with a central hole, with GRP insulation plates in between. The design is optimized by electromagnetic finite element techniques for inductance and structural stability. The conducting discs and insulators are clamped together with tie rods between two endplates to provide adequate contact pressure and sufficient mechanical support. The conducting, inter connecting and insulating components were modeled and optimised parametrically for the desired performance and structural integrity. The device was fabricated, assembled and tested with 24 bitter plates for 28 μH inductance. The inductor was integrated with 400 kJ capacitor bank module and tested under static and dynamic condition. Current pulse of peak above 100 kA was generated, with consistent arc-free performance, high reliability and structural stability.

Development of three-dimensional printing polymer-ceramic scaffolds with enhanced compressive properties and tuneable resorption

In this study, bone tissue engineered scaffolds fabricated via powder-based 3D printing from hydroxyapatite (HA) and calcium sulphate (CaSO4) powders were investigated. The combination of using a fast resorbing CaSO4 based powder and the relatively slower HA powder represents a promising prospect for tuning the bioresorption of 3D printed (3DP) scaffolds. These properties could then be tailored to coincide with tissue growth rate for different surgical procedures. The manufactured scaffolds were infiltrated with poly(ε‑caprolactone) (PCL). The PCL infiltrated the inter-particle spacing within the 3DP structures due to the nature of a loosely-packed powder bed and also covered the surface of ceramic-based scaffolds. Consequently, the average compressive strength, compressive modulus and toughness increased by 314%, 465% and 867%, respectively. The resorption behaviour of the 3DP scaffolds was characterised in vitro using a high-throughput system that mimicked the physiological environment and dynamic flow conditions relevant to the human body. A rapid release of CaSO4 between Day 0 and 28 was commensurate with a reduction in scaffold mass and compressive properties, as well as an increase in medium absorption. In spite of this, HA particles, connected by PCL fibrils, remained within the microstructure after 56 days resorption under dynamic conditions. Consequently, a high level of structural integrity was maintained within the 3DP scaffold. This study presented a porous PCL-HA-CaSO4 3DP structure with the potential to encourage new tissue growth during the initial stages of implantation and also offering sufficient structural and mechanical support during the bone healing phase.

A high-strength mineralized collagen bone scaffold for large-sized cranial bone defect repair in sheep.

Large-sized cranial bone defect repair presents a great challenge in the clinic. The ideal cranioplasty materials to realize the functional and cosmetic recovery of the defect must have sufficient mechanical support, excellent biocompatibility, good osseointegration and biodegradability as well. In this study, a high-strength mineralized collagen (MC) bone scaffold was developed with biomimetic composition, microstructure and mechanical properties for the repair of sheep large-sized cranial bone defects in comparison with two traditional cranioplasty materials, polymethyl methacrylate and titanium mesh. The compact MC scaffold showed no distinct pore structure and therefore possessed good mechanical properties. The strength and elastic modulus of the scaffold were much higher than those of natural cancellous bone and slightly lower than those of natural compact bone. In vitro cytocompatibility evaluation revealed that the human bone marrow mesenchymal stem cells (hBMSC) had good viability, attachment and proliferation on the compact MC scaffold indicating its excellent biocompatibility. An adult sheep cranial bone defect model was constructed to evaluate the performances of these cranioplasty materials in repairing the cranial bone defects. The results were investigated by gross observation, computed tomography scanning as well as histological assessments. The in vivo evaluations indicated that compact MC scaffold showed notable osteoconductivity and osseointegration with surrounding cranial bone tissues by promoting bone regeneration. Our results suggested that the compact MC scaffold has a promising potential for large-sized cranial bone defect repair.

An innovative Mg/Ti hybrid fixation system developed for fracture fixation and healing enhancement at load-bearing skeletal site

Magnesium (Mg) is a potential biomaterial suitable for developing biodegradable orthopaedic implants, especially as internal fixators for fracture fixation at non-load bearing skeletal sites. However, Mg alone cannot provide sufficient mechanical support for stable fracture fixation at load bearing sites due to its rapid degradation in the early stage after implantation. In consideration of the strengths and weaknesses of Mg, we developed an innovative magnesium/titanium (Mg/Ti) hybrid fixation system for long bone fracture fixation and investigated the fixation efficacy. The finite element analysis (FEA) results indicated that the Mg/Ti hybrid fixation system provided sufficient mechanical support for fracture fixation at load-bearing skeletal site. As a proof-of-concept, we performed a “Z-shaped” open osteotomy at the mid-shaft of rabbit tibia. For comparison, the animals were divided into two groups: Mg/Ti group (fixated with Mg screws and Ti fixators) and Ti control group (fixated with Ti screws and Ti fixators). The radiographic, four-point bending mechanical test, histological and histomorphometric analysis were postoperatively performed in a temporal manner up to 12 weeks. Both X-ray and micro-CT images of the Mg/Ti group showed a larger callus (14.7% at 3rd week and 24.8% at 6th week, n = 5–7, p < 0.05) in the regions of interest (ROIs) over time, especially at the opposite cortex of the fixation plate. At the 12th week post-operation, the biomechanical test result indicated that the rabbit tibia in the Mg/Ti group healed better and the overall mechanical strength was approximately 3-fold higher (n = 8, p < 0.05) than that at 6th week. Furthermore, the FEA revealed that the Mg/Ti group had a higher mechanical strength (19.5% at week 6 and 31.5% at week 12) at the specified ROI and resulted in an earlier and faster endochondral ossification (68.0% at week 3 and 71.4% at week 6) with a higher expression of osteocalcin (54.0%) and collagen I (34.2%) than the Ti control group (n = 4, p < 0.05). Further evaluation suggested that a higher expression of calcitonin gene-related peptide (CGRP), a known osteogenic neuron peptide, in the fracture callus of the Mg/Ti group might be a major underlying mechanism of enhanced fracture healing attributed to the release of Mg ions during the degradation of Mg screws.

Current Concepts in Carious Tissue Removal

To summarize current concepts in carious tissue removal. Traditionally, caries has been seen as an infectious disease and was treated by attempted complete removal of all cariogenic bacteria. The logical traditional aim of carious tissue removal—removing all bacteria from carious lesions—no longer applies. The contemporary aim of carious tissue removal is to maximize restoration longevity, without unnecessarily removing sound or remineralizable dentin. This is based on recent perspectives that dental caries is a biofilm-based and lifestyle-mediated disorder. In shallow lesions, as much carious tissue as possible should be removed, with removal until hard dentin is felt around the periphery of a cavity (to maximize restoration survival and seal the cavity) while centrally firm dentin is left (to retain remineralizable dentin). For deep lesions in teeth with vital pulps (without irreversible pulpitis or pulp necrosis), maintaining pulp vitality is the priority. Dentists should aim to avoid pulp exposure and accept leaving soft or leathery dentin in areas close to the dental pulp, while at the periphery, carious tissue should be removed until hard tissue is felt, ensuring that any remaining bacteria are sealed and inactivated and that the restoration has sufficient mechanical support against masticatory forces. An alternative for deep lesions is stepwise removal. Carious tissue strategies where no carious tissue removal at all is performed include sealing using plastic materials or stainless steel crowns, or non-restorative cavity control. A range of carious tissue removal strategies are available and should be applied according to lesion characteristics, pulp vitality, and other patient related factors. Always striving to remove carious tooth tissue until hard dentin remains is not in line with current evidence and not recommended.