Tubular Constructs Research Articles

A vertical additive-lathe printing system for the fabrication of tubular constructs using gelatin methacryloyl hydrogel

Reproducing both the mechanical and biological performance of native blood vessels remains an ongoing challenge in vascular tissue engineering. Additive-lathe printing offers an attractive method of fabricating long tubular constructs as a potential vascular graft for the treatment of cardiovascular diseases. Printing hydrogels onto rotating horizontal mandrels often leads to sagging, resulting in poor and variable mechanical properties. In this study, an additive-lathe printing system with a vertical mandrel to fabricate tubular constructs is presented. Various concentrations of gelatin methacryloyl (gelMA) hydrogel were used to print grafts on the rotating mandrel in a helical pattern. The printing parameters were selected to achieve the bonding of consecutive gelMA filaments to improve the quality of the printed graft. The hydrogel filaments were fused properly under the action of gravity on the vertical mandrel. Thus, the vertical additive-lathe printing system was used to print uniform wall thickness grafts, eliminating the hydrogel sagging problem. Tensile testing performed in both circumferential and longitudinal direction revealed that the anisotropic properties of printed gelMA constructs were similar to those observed in the native blood vessels. In addition, no leakage was detected through the walls of the gelMA grafts during burst pressure measurement. Therefore, the current printing setup could be utilized to print vascular grafts for the treatment of cardiovascular diseases.

Utilizations of Steel-Reinforced Concrete-Filled Steel Tubular (SRCFST) Constructions

In recent times, there has been a significant amount of research dedicated to traditional concrete-filled steel tubular (CFST) structures. This research has been broad and includes both practical testing and theoretical analysis. As of late, scholars have redirected their attention toward introducing innovations in the domain of steel-concrete composite systems. This piece delves into investigations involving experiments and simulations, as well as the underlying mechanisms and interplays of constraints. The focus is on rectangular columns made of Steel-Reinforced Concrete Filled Square Tubular (SRCFST), subjected to combined compression and torsion forces. By building upon previous investigations, the article not only provides a summary but also evaluates the pathways that research on SRCFST columns has taken. Additionally, it offers a glimpse into the potential directions for future studies. This comprehensive strategy not only serves as a point of reference for upcoming research endeavors but also furnishes practical insights for their real-world implementation.

Densified collagen tubular grafts for human tissue replacement and disease modelling applications

There is a significant need across multiple indications for an off-the-shelf bioengineered tubular graft which fulfils the mechanical and biological requirements for implantation and function but does not necessarily require cells for manufacture or deployment. Herein, we present a tissue-like tubular construct using a cell-free, materials-based method of manufacture, utilizing densified collagen hydrogel. Our tubular grafts are seamless, mechanically strong, customizable in terms of lumen diameter and wall thickness, and display a uniform fibril density across the wall thickness and along the tube length. While the method enables acellular grafts to be generated rapidly, inexpensively, and to a wide range of specifications, the cell-compatible densification process also enables a high density of cells to be incorporated uniformly into the walls of the tubes, which we show can be maintained under perfusion culture. Additionally, the method enables tubes consisting of distinct cell domains with cellular configurations at the boundaries which may be useful for modelling aortic disease. Further, we demonstrate additional steps which allow for luminal surface patterning. These results highlight the universality of this approach and its potential for developing the next generation of bioengineered grafts.

Zein-based 3D tubular constructs with tunable porosity for 3D cell culture and drug delivery

Manufacturing tubular constructs with tunable porosity can mimic the vascular structure, not only for supplying nutrients and removing metabolites to support long-term 3D cell culture but also for delivering bioactive components and drugs to tissues. There are few reports on the second purpose through 3D printing. In this study, bio-inspired tubular constructs with permeability were achieved using zein-based ink, forming structures with tunable porosity via the 3D printing technique. The parameters, e.g., zein content, with/without the addition of porogen, and drying conditions, were optimized to control the porous structure and porosity of the printed tubes. The inner wall of the resultant tube supported the adhesion of endothelial cells. A perfusion system was designed, and the penetrability of zein-based tubular constructs was demonstrated by the dialysis test. Moreover, perfusion of cell culture media and the anti-cancer drug in cell-laden hydrogels with tubular structure resulted in 3-day of 3D cell culture with a higher survival rate, and the drug was delivered to local cells around the tubular constructs, respectively. This is a new report on the preparation of 3D-printed tubular constructs using zein as the biomaterial inks with tunable porosity and porous structure, providing a general system for 3D cell culture, 3D drugs screening/pharmacokinetics in vitro, and tissue engineering.

Fabrication of 3D cylindrical thermosensitive hydrogels as supports for cell culture and detachment of tubular cell sheets

Pseudo interpenetrating vinyl-caprolactam (VCL) based thermosensitive tubular hydrogels with a volume phase transition temperature, VPTT, around 35 °C, have been prepared by combining two different crosslinkers, a di-methacrylate (C1) and a di-vinyl urea (C2). The molar ratio between the two crosslinkers (for a global crosslinker molar percentage of 1.9) has shown to play a key role on the properties of the hydrogel. Increasing the amount of di-vinyl urea, leads to transparent but rather fragile materials and to a lower extent of thermosensitivity, that is, to a lower variation in the hydrogel swelling upon temperature change. However, tubes prepared with a selected crosslinker molar ratio C1/C2 of 65/35 provided a compromise between transparency, thermosensitivity and maneuverability and were, thus, evaluated as supports for cell culture using premyoblastic cells. These hydrogels, used as supports, allow for surface adhesion and cell proliferation until confluence, and eventually an efficient monolayer detachment (and transplant to a 3D-printed polylactic acid (PLA) support) through a controlled drop in temperature. As a result, this method permits to obtain tubular tissue constructs with potential applications in tissue engineering such as in the elaboration of vascular grafts.

Bioengineering strategies for 3D bioprinting of tubular construct using tissue-specific decellularized extracellular matrix

The goal of the current study is to develop an extracellular matrix bioink that could mimic the biochemical components present in natural blood vessels. Here, we have used an innovative approach to recycle the discarded varicose vein for isolation of endothelial cells and decellularization of the same sample to formulate the decellularized extracellular matrix (dECM) bioink. The shift towards dECM bioink observed as varicose vein dECM provides the tissue-specific biochemical factors that will enhance the regeneration capability. Interestingly, the encapsulated umbilical cord mesenchymal stem cells expressed the markers of vascular smooth muscle cells because of the cues present in the vein dECM. Further, in vitro immunological investigation of dECM revealed a predominant M2 polarization which could further aid in tissue remodeling. A novel approach was used to fabricate vascular construct using 3D bioprinting without secondary support. The outcomes suggest that this could be a potential approach for patient- and tissue-specific blood vessel regeneration.

4D Biofabrication of Mechanically Stable Tubular Constructs Using Shape Morphing Porous Bilayers for Vascularization Application.

This study reports the fabrication of highly porous electrospun self-folding bilayers, which fold into tubular structures with excellent mechanical stability, allowing them to be easily manipulated and handled. Two kinds of bilayers based on biocompatible and biodegradable soft (PCL, polycaprolactone) and hard (PHB, poly-hydroxybutyrate) thermoplastic polymers have been fabricated and compared. Multi-scroll structures with tunable diameter are obtained after the shape transformation of the bilayer in aqueous media, where PCL-based bilayer rolled longitudinally and PHB-based one rolled transversely with respect to the fiber direction. A combination of higher elastic modulus and transverse orientation of fibers with respect to rolling direction allowed precise temporal control of shape transformation of PHB-bilayer - stress produced by swollen methacrylated hyaluronic acid (HA-MA) do not relax with time and folding is not affected by the fact that bilayer is fixed in unfolded state in cell culture medium for more than 1h. This property of PHB-bilayer allowed cell culturing without a negative effect on its shape transformation ability. Moreover, PHB-based tubular structure demonstrated superior mechanical stability compared to PCL-based ones and do not collapse during manipulations that happened to PCL-based one. Additionally, PHB/HA-MA bilayers showed superior biocompatibility, degradability, and long-term stability compared to PCL/HA-MA.

Mechanical alterations of electrospun poly(ϵ-caprolactone) in response to convective thermobonding.

Vascular graft failure has persisted as a major clinical problem. Mechanical, structural, and transport properties of vascular grafts are critical factors that substantially affect their function and thus the outcome of implantation. The manufacturing method, post-processing technique, and material of choice have a significant impact on these properties. The goal of this work is to use thermal treatment to modulate the transport properties of PCL-based vascular engineered constructs. To this end, we electrospun PCL tubular constructs and thermally bonded the electrospun fibers in a convective oven at various temperatures (54, 57, and 60°C) and durations of treatment (15, 30, and 45 s). The effects of fiber thermal bonding (thermobonding) on the transport, mechanical, and structural properties of PCL tubular constructs were characterized. Increasing the temperature and treatment duration enhanced the degree of thermobonding by removing the interconnected void and fusing the fibers. Thermobonding at 57°C and 60°C for longer than 30 s increased the median tangential modulus (E=126.1 MPa, [IQR=20.7]), mean suture retention (F=193.8 g, [SD=18.5]), and degradation rate while it decreased the median permeability (kA =0 m/s), and median thickness (t=60 μm, [IQR=2.5]). In particular, the thermobonding at 57°C allowed a finer modulation of permeability via treatment duration. We believe that the thermobonding method can be utilized to modulate the properties of vascular engineered constructs which can be useful in designing functional vascular grafts.

Facile fabrication of Bi-layered perfusable hydrogel tubes as biomimetic 3D arterial construct

Small-diameter arterial conduits with native physiological and biological equivalence continues to be a constant global demand posing critical challenges in fabrication. Advent of various strategies towards mimicking the structural hierarchy of a native blood vessel, often involve complex instrumentation and template-assistance with post-processing complications eventually compromising structural fidelity. In the present research, we report a template-free, facile strategy- ‘3D wet writing’ by peripheral-core differential ionic gelation to fabricate perfusable customizable constructs of any dimension, thickness and length in <5 mins. Dual-crosslinking using di-diol complexation of borax with Alginate- poly (vinyl alcohol) was performed to enhance the stability of fabricated bi-layered tubular constructs (BLT). These fabricated BLTs demonstrated non-linear mechanical characteristics of native blood vessels in withstanding physiological (120/80 mmHg) hemodynamic loading conditions with cyclic strain (5.82 ± 0.88%). The BLTs also ensured adequate longitudinal (0.176 ± 0.03 MPa) & circumferential (0.29 ± 0.012 MPa) tensile strength and burst pressure strength of 353.875 ± 22.69 mmHg. Hemocompatible characteristics of BLT were clearly evident with lower hemolytic index (0.21 ± 0.03%) and maintenance of erythrocyte structural integrity under dynamic conditions. Further, non-thrombogenic and non-inflammatory characteristics of BLTs were confirmed by in-activated platelets and monocytes under dynamic conditions. The developed wet-writing technique exhibited facile integration of layer-specific cells concurrently with the BLT fabrication. The spatial cell-specific expressions of smooth muscle (α-SMA) and endothelial (CD-31) cells in BLT were comparable to native hierarchical cellular organization with the multi-layered medial and mono-layered intimal layers. Further, ex-vivo dynamic studies on anastomotic interface between BLT and rat abdominal aorta clearly evidenced the functional efficacy of fabricated BLTs as physiologically relevant small-diameter vascular construct.

3D bioprinting of multi-layered segments of a vessel-like structure with ECM and novel derived bioink.

3D-Bioprinting leads to the realization of tridimensional customized constructs to reproduce the biological structural complexity. The new technological challenge focuses on obtaining a 3D structure with several distinct layers to replicate the hierarchical organization of natural tissues. This work aims to reproduce large blood vessel substitutes compliant with the original tissue, combining the advantages of the 3D bioprinting, decellularization, and accounting for the presence of different cells. The decellularization process was performed on porcine aortas. Various decellularization protocols were tested and evaluated through DNA extraction, quantification, and amplification by PCR to define the adequate one. The decellularized extracellular matrix (dECM), lyophilized and solubilized, was combined with gelatin, alginate, and cells to obtain a novel bioink. Several solutions were tested, tuning the percentage of the components to obtain the adequate structural properties. The geometrical model of the large blood vessel constructs was designed with SolidWorks, and the construct slicing was done using the HeartWare software, which allowed generating the G-Code. The final constructs were 3D bioprinted with the Inkredible + using dual print heads. The composition of the bioink was tuned so that it could withstand the printing of a segment of a tubular construct up to 10 mm and reproduce the multicellular complexity. Among the several compositions tested, the suspension resulting from 8% w/v gelatin, 7% w/v alginate, and 3% w/v dECM, and cells successfully produced the designed structures. With this bioink, it was possible to print structures made up of 20 layers. The dimensions of the printed structures were consistent with the designed ones. We were able to avoid the double bioink overlap in the thickness, despite the increase in the number of layers during the printing process. The optimization of the parameters allowed the production of structures with a height of 20 layers corresponding to 9 mm. Theoretical and real structures were very close. The differences were 14% in height, 20% internal diameter, and 9% thickness. By tailoring the printing parameters and the amount of dECM, adequate mechanical properties could be met. In this study, we developed an innovative printable bioink able to finely reproduce the native complex structure of the large blood vessel.

Tyramine-Functionalized Alginate-Collagen Hybrid Hydrogel Inks for 3D-Bioprinting.

Extrusion-based 3D-bioprinting using hydrogels has exhibited potential in precision medicine; however, researchers are beset with several challenges. A major challenge of this technique is the production of constructs with sufficient height and fidelity to support cellular behavior in vivo. In this study, we present the 3D-bioprinting of cylindrical constructs with tunable gelation kinetics by controlling the covalent crosslinking density and gelation time of a tyramine-functionalized alginate hydrogel (ALG-TYR) via enzymatic reaction by horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). The extruded filament was crosslinked for a second time on a support bath containing H2O2 to increase fidelity after printing. The resulting tubular construct, with a height of 6 mm and a wall thickness of 2 mm, retained its mechanical properties and had a maximum 2-fold swelling after 2 d. Furthermore, collagen (COL) was introduced into the ALG-TYR hydrogel network to increase the mechanical modulus and cell cytocompatibility, as the encapsulated fibroblast cells exhibited a higher cell viability in the ALG-TYR/COL construct (92.13 ± 0.70%) than in ALG-TYR alone (68.18 ± 3.73%). In summary, a vascular ECM-mimicking scaffold was 3D-bioprinted with the ALG-TYR/COL hybrid hydrogel, and this scaffold can support tissue growth for clinical translation in regenerative and personalized medicine.

Melt Electrowriting of a Photo‐Crosslinkable Poly(ε‐caprolactone)‐Based Material into Tubular Constructs with Predefined Architecture and Tunable Mechanical Properties

Front Cover: Melt electrowriting (MEW) is a novel additive manufacturing technique currently limited by the material selection. The cover image, by Tomasz Jungst and co-workers in article number 2200097, depicts a construct made during the approach to establish new materials for MEW based on an acrylate-endcapped urethane-based polymer (AUP). Blending AUP with the gold-standard material in MEW, poly-(ε-caprolacton), enables tailoring mechanical properties of constructs via photo-crosslinking.

Comparative Study on the Influence of Different Forms of New Tubular Roof Method Construction on Railway Tracks

Through the research on the effect of underpass construction using the New Tubular Roof Method on the overlying strata and railway tracks, the characteristics and pros/cons of three forms of the New Tubular Roof Method are analyzed. Based on the geological conditions and structural dimensions of the Taiyuan Yingze Street Underpass Project, by analogy to the structural sections of Shenyang Metro Xinle Ruins Station and Seoul Metro Lot 923 Station, three research cases were designed: “Taiyuan method”, “Shenyang method” and “Seoul method”. The numerical models are established, and the construction process of three cases are simulated. The results show that the three forms of the New Tubular Roof Method have different characteristics. The impact of construction on the rail is mainly reflected in the absolute settlement, while the offset of the rail and the relative displacement between the rails are small, which are not enough to pose a threat to the driving safety. “Taiyuan method” has the best control effect on the deformation of the rails in general, but there is a complex superimposed interference effect during tube jacking, and the settlement in the tube jacking stage accounts for a large proportion. “Taiyuan method” and “Shenyang method” adopt the integrated inner-connecting tube roof structure to cover the entire excavation area, which have excellent effect of isolating excavation disturbance. However, “Shenyang method” has the problem of excessive settlement during the stage of steel tube incision. The settlement caused by the construction of “Seoul method” in the tube jacking stage is relatively small, and there is no need to perform the complicated and dangerous tube incision. However, the excavation disturbance of “Seoul method” will partially escape from the side of the structure, and the excavation influence range is significantly larger than other methods.

A Real-time Monitoring Method of Prestressed Tubular Piles Construction Based on Machine Vision

Prestressed tubular piles are a kind of workpiece commonly used in infrastructure construction of oil and other industries. The prestressed tubular piles shall be vertical to the ground at all times during installation. In engineering practice, professionals are usually required to monitor at all times. This method is easy to lead to personnel fatigue and error. Aiming to this, in this paper, a real-time monitoring method of prestressed tubular piles construction state based on machine vision is proposed and verified with the field data. The proposed method can realize the real-time vertical monitoring of prestressed tubular piles during installation. The research results can provide a reference for the assistance and automatic monitoring of the prestressed tubular piles installation process.

Design of an electrospun tubular construct combining a mechanical and biological approach to improve tendon repair

Hand tendon injuries represent a major clinical problem and might dramatically diminish a patient’s life quality. In this study, a targeted solution for flexor tendon repair was developed by combining a mechanical and biological approach. To this end, a novel acrylate-endcapped urethane-based polymer (AUP) was synthesized and its physico-chemical properties were characterized. Next, tubular repair constructs were developed using electrospinning of the AUP material with incorporated naproxen and hyaluronic acid (i.e. anti-inflammatory and anti-adhesion compounds, respectively), and with a tubular braid as mechanical reinforcement. Tensile testing of the repair constructs using ex vivo sheep tendons showed that the developed repair constructs fulfilled the required mechanical properties for tendon repair (i.e. minimal ultimate stress of 4 MPa), with an ultimate stress of 6.4 ± 0.6 MPa. Moreover, in vitro biological assays showed that the developed repair tubes and the incorporated bioactive components were non-cytotoxic. In addition, when equine tenocytes and mesenchymal stem cells were co-cultured with the repair tubes, an increased production of collagen and non-collagenous proteins was observed. In conclusion, this novel construct in which a mechanical approach (fulfilling the required mechanical properties) was combined with a biological approach (incorporation of bioactive compounds), shows potential as flexor tendon repair application.Graphical abstract

Manufacturing of self-standing multi-layered 3D-bioprinted alginate-hyaluronate constructs by controlling the cross-linking mechanisms for tissue engineering applications

Three-dimensional (3D) bioprinting of self-supporting stable tissue and organ structure is critically important in extrusion-based bioprinting system, especially for tissue engineering and regenerative medicine applications. However, the development of self-standing bioinks with desired crosslinking density, biocompatibility, tunable mechanical strength and other properties like self-healing, in situ gelation, drug or protein incorporation is still a challenge. In this study, we report a hydrogel bioink prepared from alginate (Alg) and hyaluronic acid (HA) crosslinked through multiple crosslinking mechanisms, i.e. acyl-hydrazone, hydrazide interactions and calcium ions. These Alg-HA gels were highly dynamic and shear-thinning with exceptional biocompatibility and tunable mechanical properties. The increased dynamic nature of the gels is mainly chemically attributed to the presence of acyl-hydrazone bonds formed between the amine groups of the acyl-hydrazide of alginate and the monoaldehyde of the HA. Among the different combinations of Alg-HA gel compositions prepared, the A5H5 (Alginate-acyl-hydrazide:HA-monoaldehyde, ratio 50:50) gel showed a gelation time of ∼60 s, viscosity of ∼400 Pa s (at zero shear rate), high stability in various pH solutions and increased degradation time (>50 days) than the other samples. The A5H5 gels showed high printability with increased post-printing stability as observed from the 3D printed structures (e.g. hollow tube (∼100 layers), porous cube (∼50 layers), star, heart-in, meniscus and lattice). The scanning electron microscopy analysis of the 3D constructs and hydrogels showed the interconnected pores (∼181 µm) and crosslinked networks. Further, the gels showed sustained release of 5-amino salicylic acid and bovine serum albumin. Also, the mechanical properties were tuned by secondary crosslinking via different calcium concentrations. In vitro assays confirmed the cytocompatibility of these gels, where the 3D bioprinted lattice and tubular (∼70 layers) constructs demonstrated high cell viability under fluorescence analysis. In in vivo studies, Alg-HA gel showed high biocompatibility (>90%) and increased angiogenesis (threefolds) and reduced macrophage infiltration (twofold decrease), demonstrating the promising potential of these hydrogels in 3D bioprinting applications for tissue engineering and regenerative medicine with tunable properties.

Melt Electrowriting of a Photo‐Crosslinkable Poly(ε‐caprolactone)‐Based Material into Tubular Constructs with Predefined Architecture and Tunable Mechanical Properties

AbstractMelt electrowriting (MEW) is an additive manufacturing process that produces highly defined constructs with elements in the micrometer range. A specific configuration of MEW enables printing tubular constructs to create small‐diameter tubular structures. The small pool of processable materials poses a bottleneck for wider application in biomedicine. To alleviate this obstacle, an acrylate‐endcapped urethane‐based polymer (AUP), using a poly(ε‐caprolactone) (PCL) (molar mass: 20 000 g mol−1) (AUP PCL20k) as backbone material, is synthesized and utilized for MEW. Spectroscopic analysis confirms the successful modification of the PCL backbone with photo‐crosslinkable acrylate endgroups. Printing experiments of AUP PCL20k reveal limited printability but the photo‐crosslinking ability is preserved post‐printing. To improve printability and to tune the mechanical properties of printed constructs, the AUP‐material is blended with commercially available PCL (AUP PCL20k:PCL in ratios 80:20, 60:40, 50:50). Print fidelity improves for 60:40 and 50:50 blends. Blending enables modification of the constructs' mechanical properties to approximate the range of blood vessels for transplantation surgeries. The crosslinking‐ability of the material allows pure AUP to be manipulated post‐printing and illustrates significant differences in mechanical properties of 80:20 blends after crosslinking. An in vitro cell compatibility assay using human umbilical vein endothelial cells also demonstrates the material's non‐cytotoxicity.

Utilization of an Acellular Cartilage Matrix‐Based Photocrosslinking Hydrogel for Tracheal Cartilage Regeneration and Circumferential Tracheal Repair

AbstractAcellular cartilage matrix (ACM)‐based hydrogels hold promise for use in the context of tracheal cartilage regeneration owing to the ease with which they can be molded into specific shapes and their intrinsic cartilage‐specific microenvironmental properties. In this report, an acrylic anhydride‐modified ACM (Ac‐matrix) hydrogel is fabricated for utilization in the context of tracheal cartilage regeneration and circumferential tracheal repair. Hydrogels are successfully prepared with a range of Ac‐matrix concentrations (4%, 6%, and 8%) and found that mechanical strength increases with rising Ac‐matrix concentrations whereas swelling and degradation ratio values decline. These Ac‐matrix hydrogels exhibit satisfactory cytocompatibility when loaded with chondrocytes. Chondrocyte‐loaded 6% hydrogels are able to support cartilage formation both in vitro and in vivo across a range of chondrocyte densities (5, 10, 20, and 40 million chondrocytes per mL), with increasing density being conducive to more homogenous cartilage formation. A homogeneously tubular tracheal cartilage construct is additionally generated and supports circumferential tracheal reconstruction in a rabbit tracheal lesion model system, with a biological structure and function consistent with those of the native trachea. These results suggest that this Ac‐matrix hydrogel platform is well‐suited to use in the context of tracheal cartilage regeneration, thus offering the potential to support circumferential tracheal reconstruction.

Biomechanical Evaluation of a Tubular Braided Construct for Primary Deep Flexor Tendon Surgery

Immediate postoperative mobilization has been shown to avoid adhesion formation and improve range of motion after flexor tendon repair. A tubular braided construct was designed to allow for these rehabilitation protocols. In this exvivo study, 92 ovine flexor tendons were divided randomly into 2 equal groups. After creating a transection, the tendons of the first group were repaired using a tubular braided construct. This construct, consisting of a tubular braid of polypropylene and polyethylene terephthalate fibers, exerts a grasping effect on the tendon ends. The control group received a multistrand modified Kessler repair with a looped polydioxanone suture (PDS) 4-0 suture and a Silfverskiöld epitendinous repair using an Ethilon 6-0 suture. After the repair, a static and an incremental cyclic tensile test was performed until failure. During the static test, the tubular braid resulted in a significantly higher load at 3 mm gap formation (86.3 N ± 6.0 vs 50.1 N ± 11.6), a higher ultimate load at failure (98.3 N ± 12.7 vs 63 N ± 11.1), higher stress at ultimate load (11.8 MPa ± 1.2 vs 8.1 MPa ± 3.1), and higher stiffness (7.1 N/mm ± 2.9 vs 8.7 N/mm ± 2.2). For the cyclic tests, survival analyses for 1-, 2- and 3-mm gap formation and failure demonstrated significant differences in favor of the tubular braided construct. The tubular braided construct withstands the required loads for immediate rehabilitation not only in static tests, but also during cyclic tests. This is in contrast with the control group, where sufficient strength is reached during static tests, but failures occur below the required loads during cyclic testing. The tubular braided construct provides a larger safety margin for immediate intensive rehabilitation protocols.

Design and physical validation of a non-planar interlocking element for tubular structures

An interlocking topological structure represents an arrangement of parts designed so that the degrees of freedom of each component are takeover by the surrounding neighbours. For the planar arrangements, there are multiple possibilities to design such assemblies via platonic solids such as tetrahedron, cube, octahedron and osteomorphic geometries. This paper describes the geometrical modelling process of a non-planar interlocking element that can be used to produce tubular structures. The geometric element was defined by two curved surfaces identified with the inner and outer shell of the tubular structure and joined by six curved surfaces, providing through those the interlocking design. The virtual geometry was produced using an additive manufacturing process generating the physical model of a tubular construction assembled from non-planar interlocking elements.