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Design and development of a fibrous structure for the potential treatment of spinal cord injury using parametric modelling in Rhinoceros 3D®

  • Ivis de Aguiar Souza ORCID logo EMAIL logo , Lais Kohan ORCID logo , Joana M. Rocha ORCID logo , Maurício José da Silva Filho ORCID logo , Joaquim Jorge Peixoto ORCID logo , Raul Fangueiro ORCID logo and Diana S. P. Ferreira ORCID logo
Published/Copyright: June 11, 2025
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AUTEX Research Journal
From the journal AUTEX Research Journal Volume 25 Issue 1

Abstract

Spinal cord injury (SCI) consists of partial or complete damage to the organ’s functions. Injuries can be traumatic or non-traumatic. New investigations have pointed out different paths in terms of spinal cord regeneration. Among these, the use of scaffolds has grown, structures created based on biomaterials and synthetic materials, aimed at remodelling the injured area, promoting tissue growth, regenerating damaged axons, and vascularizing the affected region. This work developed a fibrous scaffold using a vertical braider to produce Maypole structures from Polyamide 6 fibres, known for their strong mechanical properties, 3D architecture, and porosity, which support cell growth. The scaffold structures were evaluated based on porosity, mechanical strength, and dimensional stability under compression. Among the tested models, the T2/A8B40/E16B50 structure demonstrated superior performance, withstanding a tensile strength of 1,674 N, surpassing other samples. Its external layer of 16 yarns (0.50 mm) and internal layer of 0.40 mm yarns provided greater rigidity and load-bearing capacity. It also showed high elastic recovery (96.47%) after 10 compression cycles, maintaining excellent recovery despite its high load capacity. With 50.7% porosity and 49.3% coverage, the T2/A8B40/E16B50 scaffold balanced mechanical strength with permeability, making it the most promising candidate for SCI treatment and future implant testing.

Keywords: Braided; fibrous structures; grasshopper; parametric design; Rhinoceros 3D® ; scaffold; spinal cord injury

1 Introduction

The spinal cord is directly responsible for regulating specific body functions, such as respiratory, circulatory, excretory, sexual, and homeostatic functions. Additionally, the cord is crucial for conducting nerve stimuli, directly affecting sensory-motor capacity through afferent and efferent pathways [1,2]. The spinal cord injury (SCI) consists of partial or complete impairment of organ activities. In this regard, injuries can be classified as traumatic or non-traumatic. Traumatic injuries arise from various accidents, sports, and violence, while non-traumatic injuries result from diseases affecting individuals such as tumours/cancer, multiple sclerosis, degenerations, and myelitis [3,4,5].

Researchers define a set of contemporary strategies for treating SCIs, focusing on the following [6,7,8,9,10]: (1) Spinal stabilization, a strategy aimed at achieving greater decompression of the spinal cord [11,12]; (2) Administration of antibiotics such as Minocycline, a tetracycline medication demonstrating neuroprotective effects in animal models of acute SCI. Specifically, antibiotics regulate cytokine expression, reduce cell death, lesion size, and improve functional recovery [6]; (3) Administration of high doses of corticosteroids, an intervention aimed at reducing inflammatory processes and inhibiting lipid peroxidation that generates free radicals. Radicals are released due to the interaction of myelin sheaths from damaged neurons with oxygen [13]; (4) Local injection of neurotrophic factors, which promote the reduction or prevention of apoptosis and aid in axon regeneration [14]; (5) Implantation of three-dimensional scaffolds to alleviate spinal cord compression. These supports serve as structures that can stimulate neuronal growth in affected areas, aiding in spinal cord regeneration, as supported by previous studies [15–17].

Recent studies have elucidated a series of pathways concerning spinal cord regeneration, with particular emphasis on the utilization of scaffolds – structures fabricated from biomaterials, which may be natural or synthetic. The primary objectives of these scaffolds are to remodel the injured area, foster tissue growth, regenerate damaged axons, and promote vascularization in the affected region. In this context, the physicochemical properties of these structures have become fashionable, focusing on biocompatibility, the controlled release of bioactive compounds, and the promotion of cell growth and differentiation [18]. Three-dimensional scaffold structures have garnered special attention, particularly those employed in suture applications [19], ligament and tendon scaffolds [20,21], cardiac stents [22,23], and for the oesophagus and airways [24,25]. The three-dimensional supports, known as Cell-Free Scaffolds – devoid of stem cells or totipotent structures – are exclusively composed of polymers [26,27]. These polymers can be synthesized for the fabrication of various 3D structures, including impressed structures, hydrogels, or textile fibres [28]. The literature showcases promising examples of such resources utilising diverse materials such as polycaprolactone (PCL), polylactic acid (PLA), poly(lactic acid-co-glycolic acid) (PLGA), polyethylene glycol (PEG), poly(2-hydroxyethyl methacrylate) (PHEMA), N-(2-hydroxypropyl) methacrylamide) (PHPMA) [26,27,29], and polyamide (PA), with applications ranging from bone repair scaffolds [30], hernia containment knitting [31], to cardiac stents [22,23,32].

A recent literature review on polymeric fibres as scaffolds for spinal cord lesions highlights the versatility of structure production using electrospinning, phase separation, self-assembly, and 3D printing methods [33]. This investigation underscores the efficacy of polymeric fibres and their electrical properties as a stimulus for regeneration. Electrified nanofibres, resembling extracellular matrix, can facilitate cell growth and proliferation [10]. Furthermore, approaches have emerged focusing on developing structures for bone fracture repair [34,35,36]. Studies employing PA6 scaffolds for bone repair have shown high efficiency regarding bone regeneration due to their biocompatibility and osteoconductive [37].

Furthermore, the construction of PA nanofibrous membranes to analyse central nervous system cell growth yielded results indicating that PA-based structures increased the secretion of fibroblast growth factor-2 – a growth factor that aids in wound healing – and promoted neurite growth. The study demonstrates the material’s efficiency in replicating the morphology of central nervous system tissue, as it supported the growth of astrocyte extensions and the secretion of fibroblast growth factors [38].

Considering the aforementioned information, textile-based scaffolds represent a promising avenue for collaborative treatment. These scaffolds possess fundamental characteristics such as three-dimensionality (3D), porosity [32,36,39,40], rigidity, elasticity, mechanical strength, and biocompatibility [41,42,43,44,45]. In addition to promoting nerve cell growth and regeneration, scaffolds facilitate the release of bioactive compounds and can reduce cystic cavities and subsequent glial scarring [10,29,46].

In this manner, this study developed a potential fibrous framework with the potential for application in the treatment of SCIs. Initially, in previous study [47] structures were generated through parametric modelling using algorithmic modelling in Rhinoceros 3D® software (version 6) and the Grasshopper plugin, wherein various structural designs were constructed. In this regard, yarns measuring 0.30, 0.40, and 0.50 mm were employed, and the respective structures were constructed with 8 and 16 yarns in the external layer and 8 yarns in the internal layer.

The prototyping of the structure was achieved using a vertical Trenz-Export braider, which produces Maypole braided structures. The structure was crafted from synthetic fibres of Polyamide 6 (PA6), which exhibits high resistance to extremely low temperatures (−40 to −60°C) and a melting temperature of 223°C. PA6 also boasts good mechanical properties, including a compressive strength of 68 MPa, tensile strength ranging from 45–85 MPa, and tensile elongation of 100–150%. Additionally, it possesses a moisture absorption rate of 4–4.5% and chemical resistance to solvents such as water, alcohol, and esters [48,49]. The PA6 implantable structure demonstrates biocompatibility and biodegradability, albeit at a slow rate (1 year). Furthermore, it facilitates good cell adhesion and growth and finds extensive application in scaffold structures [22,50,51,52].

The structures inherently exhibit significant characteristics for scaffold structure design, including good porosity, permeability, and robust mechanical and physical properties [10,45,53]. Scaffold structures also possess a three-dimensional architecture [17]. Additionally, the study presents a less financially burdensome process in terms of costs and design, building upon the various structures already produced in textile material and their effective outcomes as demonstrated in existing scientific literature.

2 Methods and techniques

2.1 Methods

The parametric design differs from that commonly used in traditional design practices. Initially, shapes are not explicitly declared; instead, parameters are defined, from which various shapes of objects or configurations can emerge. The equations of algorithmic thinking are utilized to describe relationships between objects and geometries, encompassing elements such as lines, points, and shapes. Consequently, designers can utilize the same shapes and lines to generate a multitude of objects by manipulating variables and their interrelationships. For instance, variables such as material quantity, density, and structural components guide the development of complex structures within parametric design. This approach focuses on the process of creating objects rather than the objects themselves [54,55,56].

The parametric design can be used to simulate and reproduce objects, despite being possible to evaluate properties and structures, in this research, also experimental tests were compared in order to prototype these objects.

2.1.1 Parameters used in the construction of a braided structure employed in the algorithm for the external and internal layers of the structure.

I. Type of structure chosen – model among the three most common structures: Diamond (1/1), Regular (2/2), and Hercules (3/3) (Figure 1).

Figure 1 1. Algorithm structure for generating the external layer. 2. Section of the algorithm responsible for defining the parameters/type of structure related to the ligament. 3. The resulting structure types based on ligament definition: Diamond (1/1), Regular (2/2), and Hercules (3/3).
Figure 1

1. Algorithm structure for generating the external layer. 2. Section of the algorithm responsible for defining the parameters/type of structure related to the ligament. 3. The resulting structure types based on ligament definition: Diamond (1/1), Regular (2/2), and Hercules (3/3).

II. Number of yarns – The quantity of strands used, considering that the greater the number of strands, the more complex the geometry becomes. Additionally, it is possible to control the quantity of interlacing per centimetres (Figure 2).

Figure 2 1. Full structure of the algorithm. 2. Section of the structure responsible for defining the number of braids and the number of yarns in the braided configuration. 3. Types of structures resulting from variations in the number of yarns and braids parameters.
Figure 2

1. Full structure of the algorithm. 2. Section of the structure responsible for defining the number of braids and the number of yarns in the braided configuration. 3. Types of structures resulting from variations in the number of yarns and braids parameters.

III. Yarn diameter – The yarn diameter holds significant importance concerning the production of a braid as it implies modifications in the architecture of the structure and the angles formed in the braiding, besides, of course, the potential to make the structure stiffer and mechanically resistant (Figure 3).

Figure 3 1. Full structure of the algorithm. 2. Section of the structure responsible for the “extrusion” process and regulation of yarns diameter. 3. Types of yarns with different dimensions: 0.30 and 0.60 mm, respectively.
Figure 3

1. Full structure of the algorithm. 2. Section of the structure responsible for the “extrusion” process and regulation of yarns diameter. 3. Types of yarns with different dimensions: 0.30 and 0.60 mm, respectively.

IV. Structure diameter – The structure diameter also affects the geometry of the structure and consequently the angle (Figure 4).

Figure 4 1. Full structure of the algorithm. 2. Section of the structure responsible for defining the diameter and height of the braided structure. 3. Heights of the braided structure: 10 and 5 cm. 4. Diameters of the braided structure: 1.5 and 0.5 cm.
Figure 4

1. Full structure of the algorithm. 2. Section of the structure responsible for defining the diameter and height of the braided structure. 3. Heights of the braided structure: 10 and 5 cm. 4. Diameters of the braided structure: 1.5 and 0.5 cm.

V. Extraction – The extraction in the algorithm can be controlled through parameters such as braid height, number of braids per centimetres, and yarn diameter (Figures 2–4).

The initial construction starts from a point in the Grasshopper software; this point is initially connected and then duplicated. Subsequently, the duplicated points are moved to a set of defined positions along the Z-axis and are arranged around a cylindrical structure that simulates the role of a mould. Additionally, a series of horizontal subdivisions are created along the Z-axis; these layers are responsible for forming the braiding/crossing in the braided structures. A point positioning system was also devised to modify the types of braided structures produced. The points were connected to form the yarn structures with the aid of NURBS curves, and a command was inserted to control the yarn diameter. The model was replicated, and a mechanism was created based on duplicating the structure through the subdivision of a circle (Figure 5).

Figure 5 1. Creation of the point for the development of the braided structure along the Z-axis; 2. Braiding structure of the internal layer; 3. Braiding structure of the external layer; 4. Duplication mechanism of the structure produced in 2 based on the division of a circle into points; 5. Analysis model of the structures regarding established criteria for selecting the best model (porosity criterion). (a) Internal structure built with 8 yarns and external with 8 yarns. (b) Internal structure with 8 yarns and external with 16 yarns.
Figure 5

1. Creation of the point for the development of the braided structure along the Z-axis; 2. Braiding structure of the internal layer; 3. Braiding structure of the external layer; 4. Duplication mechanism of the structure produced in 2 based on the division of a circle into points; 5. Analysis model of the structures regarding established criteria for selecting the best model (porosity criterion). (a) Internal structure built with 8 yarns and external with 8 yarns. (b) Internal structure with 8 yarns and external with 16 yarns.

In the parametric design developed in this study, parameters such as scaffold diameter and yarn diameter significantly impact the mechanical characteristics and functionality of the final structure. For example, yarn diameter directly influences stiffness and mechanical strength. Yarns with larger diameters cover a greater area, resulting in increased structural rigidity and reduced porosity, as well as modifications to the geometric structure, as shown in Figures 5 and 7 – a and b. Scaffold diameter, on the other hand, affects the interlacing angle and, consequently, the compaction and mechanical stability. These correlated parameters are essential in applications such as fibrous scaffolds for spinal cord regeneration, as they allow for balancing porosity, strength, and flexibility to promote optimal cell adhesion and growth.

2.1.2 Winding

Initially, the first part of the construction process consisted of selecting 16 bobbins, which were then inserted into the Trenz-Export model PR810 parallel winding winder. Subsequently, the machine, upon yarn passage, is programmed to initiate a rotational movement of the coupled bobbins. Concurrently, a metallic sheath containing the yarn undergoes a translational movement responsible for loading the bobbin (Figure 6).

Figure 6 Trenz-Export winding machine model PR810 winding a PA yarn.
Figure 6

Trenz-Export winding machine model PR810 winding a PA yarn.

2.1.3 Feeding of the braiding machine

The braiding machine can be fed in various ways. In the case of the Trenz-Export vertical braiding machine model 16/100 with 16 bobbins, it is possible to produce braids with 4, 6, 8, 10, 12, 14, or 16 strands. In the braiding process of this study, we tested braids with 16 and 8 strands. The braided structures produced consist of two layers. In Figure 7a, the manufacturing of the braid with an external layer of 16 strands and cores of 8 strands can be identified, while in Figure 7b, the braid is shown with an external layer of 8 strands and cores of 8 strands. Figure 8 depicts the Trenz-Export vertical braiding machine model 16/100, where it can be observed supplied with both 8 and 16 bobbins, with braids on the upper part.

Figure 7 External structure designed and prototyped on a braiding machine: (a) braided structure with 16 PA strands, (b) braided structure with 8 PA strands. Both structures were prototyped using 0.50 mm PA strands.
Figure 7

External structure designed and prototyped on a braiding machine: (a) braided structure with 16 PA strands, (b) braided structure with 8 PA strands. Both structures were prototyped using 0.50 mm PA strands.

Figure 8 Machine supplied with 8 bobbins and 16 bobbins.
Figure 8

Machine supplied with 8 bobbins and 16 bobbins.

The following structures were built – T1/A8B30/E16B50 (internal layer with a braid of 8 yarns with a diameter of 0.30 mm, covered by an external layer of 16 yarns with a diameter of 0.50 mm); T2/A8B40/E16B50 (internal layer with a braid of 8 yarns with a diameter of 0.40 mm, covered by an external layer of 16 yarns with a diameter of 0.50 mm); T3/A8B40/E8B50 (internal layer with a braid of 8 yarns with a diameter of 0.40 mm, covered by an external layer of 8 yarns with a diameter of 0.50 mm).

2.2 Braiding

In the context of this research, we focused on the production of 2D braided structures. These structures are formed in continuous turns in concentric circles (clockwise and counterclockwise directions) (Figure 9a and b), thereby encountering other yarns simultaneously and intertwining them mutually around each other. In this manner, we can understand the structure as biaxial, composed of a minimum of two or three yarns in the same plane, intersecting at specific angles [56,57,58]. Regarding the braiding mechanism, beside the cams are the spindle slots, and each slot can accommodate a spindle that moves when the cams begin their motion. On the underside of the cams, there is a group of “spaces” individually filled by the spindles, defining the trajectory in the formation of the braid (Figure 9b). It is along this trajectory that the spindle’s “base” is guided during movement (Figure 9c and d) [56,59,60].

Figure 9 (a) Description of the braiding mechanism in a top view of the cams and their groups of spindles (first spindle group (a) and second spindle group (b)). (b) Description of the movement/trajectory of the spindles and bobbins. (c) Braided structures, yarns, bobbins, and trajectories of the cams, along with a demonstration of operation. (d) Detailed depiction of the spindles and their respective components. Extracted and adapted from [61].
Figure 9

(a) Description of the braiding mechanism in a top view of the cams and their groups of spindles (first spindle group (a) and second spindle group (b)). (b) Description of the movement/trajectory of the spindles and bobbins. (c) Braided structures, yarns, bobbins, and trajectories of the cams, along with a demonstration of operation. (d) Detailed depiction of the spindles and their respective components. Extracted and adapted from [61].

The spindle is a crucial component in the braiding process of the structures. The machine used, Trenz-Export 16/100, features a model of vertical spindles that, when equipped with bobbins, enables the construction of various types of braids. The spindles of the machine used consist of a metal rod with a lateral eyelet where the first passage of the yarn is carried out; subsequently, the yarn is passed through the second eyelet of the spindle, which has a compression spring that, upon receiving a pull, releases the bobbin and allows the yarn to unwind. The yarn is then passed through a third eyelet positioned diametrically opposite to the eyelet of the compression spring, namely at the top of the spindle (Figure 10a) [56]. The yarning of the yarn through the spindle eyelets is crucial for lightly tensioning the yarn and enabling the introduction of a new yarn segment into the system when the compression spring is raised, in accordance with the spindle movement [62]. The bobbin also plays an important role, as there is a group of different bobbins according to the machine – and what may vary in this case is the base of the bobbin where the mechanism that attaches it to the spindle can be observed (Figure 10b).

Figure 10 (a) Operational mechanism of the spindles of the Trenz-Export model 16/100 machine. (b and c) Detail of the bobbin and its respective mechanism for adhering to the spindle (bobbin used in the Trenz-Export model 16/100 machine).
Figure 10

(a) Operational mechanism of the spindles of the Trenz-Export model 16/100 machine. (b and c) Detail of the bobbin and its respective mechanism for adhering to the spindle (bobbin used in the Trenz-Export model 16/100 machine).

The braiding construction process must first consider a set of relevant characteristics, such as the diameter of the structure, braiding angle, yarn diameter, and the number of yarns (according to the machine and its number of spindles). Other parameters to be considered include braiding angle, yarn orientation, and, most importantly, the speed of the pulling system. The latter deserves significant attention because pulling directly influences the braiding angle and the compacting of the yarns in the braid; thus, a high speed of the system results in an open braid and acute braiding angle, while the opposite results in a compacted structure and obtuse angles [63].

2.3 Thermosetting process

Thermosetting was performed sequentially at 160°C for 15 min to maintain the same structures. The selected temperature was determined based on a literature review and the procedure of finishing materials [22,63]. This process enables the exposure of the structures to temperatures close to the glass transition point previously set by thermogravimetric analysis, allowing for their fixation. The procedure consisted of the following steps:

  1. The structure forms are put in the stenter machine.

  2. The stenter machine is heated to a temperature of 160°C.

  3. The samples are left for 15 min.

  4. After 15 min, the samples are removed and left to cool at room temperature for 1 h.

2.4 Characterization methods

2.4.1 Morphological characterization

It is noteworthy that there is a correlation between the braid angles and the mass per unit area (g/m2). Thus, the mass per unit area will increase with the reduction of the angle size, and conversely, an increase in the angle represents a reduction in the mass per unit area. The mass per unit area was calculated as follows.

2.4.2 Area of the structure

The calculation considers the logic of the cylinder’s area; initially, the area of the lateral surface base is calculated in a process of flattening the side of the cylindrical structure. When we open the cylinder, we have a rectangular structure, and the circumference’s perimeter is equal to 2·π·d/2 [22].

(1) A = ( d / 2 ) × 2 × π × h ,

where d is the diameter of the braid (mm), h is the height of the braid (mm), formula for mass per unit area:

(2) M ( g / m 2 ) = ( P × 10 6 ) / A ,

where M is the mass per unit area in g/m2, P is the mass of the braid in grams, and A is the area of the stent in mm2.

2.4.3 Coverage factor and porosity

Porosity is an important factor in the formulation of scaffold structures, and its evaluation requires observing the number of fibrous materials deposited on the mandrel surface. The coverage factor consists precisely of the proportion of the mandrel area that is covered by individual filaments. Additionally, the coverage factor is an indication of the uniformity of the weave. The coverage factor is defined with the following equations [22,23]:

Definition of coverage factor:

(3) Cover factor = 1 − 1 − W y × N c 4 π R cos α 2 ,

where W y is the diameter of the monofilament (mm), N c is the number of bobbins, R is the radius of the mandrel (mm), and α is the braiding angle (rad).

Definition of porosity:

(4) Porosity = 1 − Cover factor .

2.4.4 Optical microscopy

To verify the developed structure, the Optical Microscopy – Olympus, model BH – 50×, was used.

2.4.5 Characterization of the produced structure angle

The structure images were analysed using the open-source software ImageJ (version 1.8.0) to identify and measure the braiding angle of the produced structures. For the analysis in ImageJ, the images were captured and imported into the program. Ten measurements were taken on specimens, and the average angle of ten samples was obtained.

2.4.6 Mechanical properties of the scaffold structure

2.4.6.1 Evaluation of cyclic compression resistance

The resistance to radial cyclic loads tests is important due to in vivo environmental, since the implant is continuously subjected to severe loads [64,65]. Mechanical tests were conducted on the three produced structures, with each having three specimens. The specimens were subjected to ten cycles of compressive deformation to half of the diameter (50% of the diameter) of the structure for each specimen. The equipment used was the Hounsfield HTE Dynamometer, applying compression mode at a test speed of 1 mm/min with a load cell of 2,500 N. Additionally, radial compression measurement was performed using ASTM D3410 [66] standard as a reference (Figure 11).

Figure 11 (a) Hounsfield HTE machine with a load cell of 2,500 N, (b) compression test of the structure.
Figure 11

(a) Hounsfield HTE machine with a load cell of 2,500 N, (b) compression test of the structure.

The primary objective of this test is to understand the elastic recovery or resilience of the structure, for which the following equations are used:

(5) RE ( % ) = ( L 1 − L 0 − L 2 ) / ( L 1 − L 0 ) ,

where RE is the elastic recovery (%), L1 is the distance in (mm) between the sensor at t = 0 and half of the structure diameter, L0 is the distance in (mm) between the sensor at t = 0 and the surface of the structure in its initial shape, L2 is the distance in (mm) between the sensor and the surface of the structure at the end of the test, after the compression process.

Resilience also needs to be calculated, and for this purpose, the following formulas were used:

(6) U R = U r − U D ,

(7) U r = ∫ a b f ( x ) d s − ∫ a b f 1 ( x ) d s ,

where U R is the resilience energy, U r is the total energy, and U D is the dissipated energy. In this context, the first term ( ∫ a b f ( x ) d s ) represents the total energy supplied to the material during loading. The second term ( ∫ a b f 1 ( x ) d s ) represents the energy recovered during unloading. The difference between these terms (U r) corresponds to the unrecovered energy. Together, these formulas are used to calculate resilience (U R), which reflects a material's ability to absorb energy elastically (without permanent deformation).

2.4.6.2 Evaluation of the tensile strength of the braided structures

The tensile strength test was conducted on five specimens for each of the three produced samples. The equipment used was the Hounsfield H100KS Dynamometer, with a test speed of 100 mm/min, a load cell of 10,000 N, and a distance of 20 cm between the jaws. The test was based on the ISO 2062 [67] standard.

The experiment was conducted, and the force values (N) applied in relation to the elongation (mm) were automatically recorded in the control units of the device. The elongation was analysed using the following equation:

(8) Elongation ( % ) = L f − L 0 L 0 × 100 ,

where Lf is the final length (cm) between the jaws of the dynamometer after rupture, and L0 is the initial length (cm) between the jaws of the dynamometer before the test.

The tensile stress (σ) was also calculated:

(9) σ = F / ( π r 2 ) ,

where F is the maximum force in Newton, and r is the radius of the circular section (mm). Elongation at maximum force (ε):

(10) ε = ( 100 × A l ) / L 0 ,

where Al is the elongation at maximum force measured on the force/elongation curve (mm); L0 is the Reference length of the extensometer (mm).

3 Results and discussion

3.1 Analysis of the structural morphology

The produced braids were characterized concerning their construction and structure, the type of structure used (Regular – 2/2), density or number of ligaments per centimetres (cm), and mass per unit surface area (g/m2) (Table 1).

Table 1

Characterization of constructed scaffold structures

Samples T1/A8B30/E16B50 T2/A8B40/E16B50 T3/A8B40/E8B50
Internal layer yarn diameter (mm) 0.30 0.40 0.40
External layer yarn diameter (mm) 0.50 0.50 0.50
Average external diameter of internal layer (mm) 1.42 1.75 1.75
Average external diameter of external layer (mm) 4.26 4.43 3.23
Internal layer crossing density (cm) 7 6 6
External layer crossing density (cm) 8 8 4
Bobbins used in the internal layer 8 8 8
Bobbins used in the external layer 16 16 8
Structure Regular Regular Regular

The produced samples exhibit significant characteristics, such as structural porosity and three-dimensionality. Regarding porosity, it was observed that the prototyped internal layer with 0.30 mm yarns showed greater porosity (48.5%) compared to the internal layer with 0.40 mm yarns, which presented porosity of 34.5%. This variation in porosity is primarily attributed to the yarn diameter, as larger yarn diameters cover a greater area (coverage factor), meaning the deposited area will be larger, as seen in previous studies on braided structures [56,63,68]. In the external layer, the coverage factor was higher in the T1/A8B30/E16B50 and T2/A8B40/E16B50 samples, resulting in lower porosity compared to the third structure. However, the porosity values of the structures are relatively similar (Table 2).

Table 2

Characterization of constructed scaffold structures concerning structure area, mass, coverage factor, porosity, and angle

Samples T1/A8B30/E16B50 T2/A8B40/E16B50 T3/A8B40/E8B50
Average internal layer diameter (mm) ±1.42 ±1.75 ±1.75
Lateral surface area of the scaffold (mm2) ±445.88 ±549.5 ±549.5
Mass per Unit Surface Area (g/m2) ±657.58 ±547.04 ±547.04
Coverage factor (%) 51% 65% 65%
Porosity (%) 48.5% 34.5% 34.5%
Average angle of internal layer (°) ±28.00 ±24.46 ±24.46
Average external layer diameter (mm) ±4.26 ±4.43 ±3.23
Lateral surface area of the scaffold (mm2) ±1337.64 ±1391.02 ±1014.22
Mass per Unit Surface Area (g/m2) ±1481.49 ±1325.72 ±819.84
Coverage factor (%) 51.0% 49.3% 35.56%
Porosity (%) 49.0% 50.7% 64.4%
Average angle of external layer (°) ±31.68 ±31.59 ±31.90

Figures 12–14 display two types of images: in “A,” the designs generated by an algorithm using Rhinoceros 3D software, and in “B,” the images of the structures produced by the Trenz-Export (16:100) braiding machine. In Figure 12a, small pores are identifiable, and in comparison, Figure 12b shows no significant differences between the algorithm-generated image and the structure produced by the braiding machine. Figure 12 represents the internal layer of the structure, while Figures 13 and 14 correspond to the external layer.

Figure 12 (a) Internal structure featuring small pores, designed using Grasshopper and Rhinoceros 3D software. (b) Interlaced structure observed under an optical microscope, showing porosity in the internal scaffold structure prototyped with PA 6 with 8 yarns, each with a diameter of 0.40 mm.
Figure 12

(a) Internal structure featuring small pores, designed using Grasshopper and Rhinoceros 3D software. (b) Interlaced structure observed under an optical microscope, showing porosity in the internal scaffold structure prototyped with PA 6 with 8 yarns, each with a diameter of 0.40 mm.

Figure 13 (a) External layer with small pores, designed using 16 yarns with a diameter of 0.50 mm in Grasshopper and Rhinoceros 3D software; (b) external layer of the prototyped braided structure, consisting of 16 PA 6 yarns with a diameter of 0.50 mm, observed under an optical microscope.
Figure 13

(a) External layer with small pores, designed using 16 yarns with a diameter of 0.50 mm in Grasshopper and Rhinoceros 3D software; (b) external layer of the prototyped braided structure, consisting of 16 PA 6 yarns with a diameter of 0.50 mm, observed under an optical microscope.

Figure 14 (a) External layer with small pores, designed using 8 yarns with a diameter of 0.50 mm in Grasshopper and Rhinoceros 3D software; (b) external layer of the prototyped braided structure, consisting of 8 PA 6 yarns with a diameter of 0.50 mm, observed using an optical microscope.
Figure 14

(a) External layer with small pores, designed using 8 yarns with a diameter of 0.50 mm in Grasshopper and Rhinoceros 3D software; (b) external layer of the prototyped braided structure, consisting of 8 PA 6 yarns with a diameter of 0.50 mm, observed using an optical microscope.

Figure 12 shows that the material has retained small pores in both the internal and external layers of the structure, which facilitate liquid permeability, nutrient exchange, and cell adhesion. Figures 13 and 14 highlight the variation in coverage (coverage factor) of the external layer and demonstrate the influence of the number of yarns on the structure’s geometry and, consequently, on pore size. In Figure 13, the higher coverage factor results in smaller pores, whereas in Figure 14, the lower coverage factor leads to larger pores.

The angles generated by the program showed minor deviations when compared to the actual structure. In the internal layer, the designed angle was ±21.36° using 0.40 mm yarns, while the measured angle in the real structure was ±24.46°. For the external layer, the program projected angles of ±31.41°, whereas the real structure exhibited an average angle of ±31.59° using 0.50 mm yarns. It is important to note that prototyping conditions and the machinery used can influence the final structures, as they do not allow for precise control of all variables, potentially impacting production outcomes.

3.2 Tensile strength of the braided structures

The tensile tests of the structures were conducted to understand the mechanical resistance behaviour of the structure, as these results are important to ensure scaffold stability and post-implant efficiency. Although not the only aspect, crystalline and aligned fibrous structures exhibit a good capacity to mimic nervous tissue; however, this is not relevant regarding the improvement of mechanical capacity and perceived rigidity by cells. In this sense, other structural arrangements are more efficient since the effective rigidity of fibres and structures in the longitudinal direction compared to the transverse, for example, promotes greater cell adhesion and migration in the direction of the fibre axis. Structures with stiffer fibres accelerate cell migration speed [69].

Braided structures themselves exhibit good tensile strength in the longitudinal direction due to stability, although the same is not evident when subjected to axial compression in the direction of the fibres [57]. In Figure 15, the three groups of braided structures produced subjected to tension in T1/A8B30/E16B50 are observed; the structure has an internal layer composed of 5 braided structures with 8 yarns of 0.30 mm and coated with an external layer of 16 yarns of 0.50 mm with Tex 1298.867. The structure T2/A8B40/E16B50 differs from the previous structure by the presence of internal structures with 0.40 mm yarns, maintaining an external layer of 16 yarns of 0.50 mm with Tex 1080.733; T3/A8B40/E8B50 has cores of 0.40 mm and an external layer of 8 yarns with 0.50 mm with Tex 1058.033.

Figure 15 Average curves of the test specimens T1/A8B30/E16B50; T2/A8B40/E16B50; T3/A8B40/E8B50 regarding tensile strength properties.
Figure 15

Average curves of the test specimens T1/A8B30/E16B50; T2/A8B40/E16B50; T3/A8B40/E8B50 regarding tensile strength properties.

In view of this, the structure T2/A8B40/E16B50 demonstrates better properties regarding tensile strength in the longitudinal direction, reaching a maximum force of 1,674 N, followed by T1/A8B30/E16B50 (1,504 N) and T3/A8B40/E8B50 (1,295 N). Given the data, it is possible to infer that samples with external layers of 16 yarns showed better results when subjected to the test, whereas structures with 8 yarns of the external layer showed inferior results. The importance of the external layer becomes even more evident when comparing structure T1/A8B30/E16B50 with T3/A8B40/E8B50, as the former has internal yarns with a smaller diameter and shows better results when subjected to tension. And, as already evidenced by Vila (2009), yarns with a larger diameter show better tensile strength test results.

3.3 Radial compression

Upon conducting radial compression tests, it was observed that the samples exhibited distinct outcomes: T1/A8B30/E16B50 showed better performance regarding compression in the first and tenth cycles of radial compression, followed by sample T2/A8B40/E16B50. Conversely, sample T3/A8B40/E8B50 yielded the worst outcome in all ten cycles. It is conjectured that the result is related to the external layer, given that only the structure with the worst result has eight yarns in this layer (Figure 16).

Figure 16 Average compression and recovery curves of the test specimens T1/A8B30/E16B50; T2/A8B40/E16B50; T3/A8B40/E8B50 regarding radial compression resistance properties after ten cycles. The figure presents the average curve of each sample and their respective first and last compression curves.
Figure 16

Average compression and recovery curves of the test specimens T1/A8B30/E16B50; T2/A8B40/E16B50; T3/A8B40/E8B50 regarding radial compression resistance properties after ten cycles. The figure presents the average curve of each sample and their respective first and last compression curves.

Given the results depicted in Figure 16 regarding the resilience of the designed structures and the possibility that structures with higher coverage factor may exhibit better compression results, it can be compared the results with the elastic recovery data. The procedure was conducted immediately following the compression test. The results presented in Table 3 indicate that the T1/A8B30/E16B50 structure exhibited the best performance under cyclic compression (66.6 N). However, immediate elastic recovery was the lowest among the samples, averaging 83.82%. A possible explanation for this behaviour may be associated with the internal layer yarns, which have larger interstitial spacing, leading to reduced structural recovery.

Table 3

Analysis chart of cyclic recovery of structures after ten cycles of cyclic compression

Samples Initial diameter Final diameter Average recovery after ten cycles (%)
T1/A8B30/E16B50 5.72 4.72 83.82
5 4.38
5.09 4.14
T2/A8B40/E16B50 5.82 5.68 96.47
5.7 5.6
5.77 5.4
T3/A8B40/E8B50 5.41 5.22 97.43
5.3 5.25
5.35 5.24

In comparison, the T2/A8B40/E16B50 structure, which is very similar to T1/A8B30/E16B50, differs only in the larger diameter of its internal yarns (0.40 mm). This minor structural modification resulted in superior elastic recovery at the end of the compression test, with an average of 96.47%. The enhanced performance of T2/A8B40/E16B50 is directly related to the use of monofilaments with an internal diameter of 0.40 mm and an external diameter of 0.50 mm. In contrast, the T1/A8B30/E16B50 structure had an internal layer with larger interstitial spacing and smaller diameter yarns, leading to greater deformation under compression, as the reduction in monofilament diameter decreases compressive strength and the capacity to withstand.

Figure 16 shows a greater displacement in the T2/A8B40/E16B50 and T3/A8B40/E8B50 structures. This displacement reflects the resilience of the samples; both structures, despite supporting a lower load, have greater return capacity, as shown in Table 3: T2/A8B40/E16B50 (96.47%) and T3/A8B40/E8B50 (97.43%).

Recovery is directly linked to the structural design and choice of yarns. The results demonstrate that structures with an external layer of 16 yarns, each 0.50 mm in diameter, performed better in tensile and compression tests in terms of resistance to force (N), as seen with the T1/A8B30/E16B50 and T2/A8B40/E16B50 structures. However, the internal layer, composed of thinner diameter yarns (0.30 mm), reduces recovery capacity, resulting in lower resilience and increased structural damage, as observed in the T1/A8B30/E16B50 structure. When the external layer is reduced to eight yarns, a decrease in tensile and compressive strength is observed. Although the displacement is greater, indicating improved adjustment and recovery capacity, the external structure with eight yarns is structurally more unstable, as evidenced by T3/A8B40/E8B50.

It is important to note that none of the samples exhibited poor recovery after ten cycles, and the difference between the sample with the best and worst results was only 13.61%. After ten cycles, the maximum observed elongation was 16.18%. This selected structure is highlighted in Figure 17 – T2/A8B40/E16B50.

Figure 17 Structure T2/A8B40/E16B50: (a) structure prototyped on Trenz-Export braider; (b) structure rendered in Rhinoceros 3D®.
Figure 17

Structure T2/A8B40/E16B50: (a) structure prototyped on Trenz-Export braider; (b) structure rendered in Rhinoceros 3D®.

4 Conclusions

The objective of this study was to develop a potential fibrous structure for application in the treatment of SCIs. The scaffold structure project encompasses structural characteristics aimed at promoting cell growth and proliferation, as well as guiding the growth of neuron extensions. The structures produced are characterized by porosity, mechanical strength, dimensional stability (compression), and a three-dimensional configuration. Notably, the T2/A8B40/E16B50 structure demonstrated the best performance in terms of tensile strength, withstanding a maximum force of 1,674 N, surpassing the other two samples. The external layer, composed of 16 yarns with a diameter of 0.50 mm, and the internal layer, consisting of yarns with a diameter of 0.40 mm, contribute to greater rigidity and an enhanced capacity to support higher loads. In comparison, the T3/A8B40/E8B50 structure, with only eight yarns in the external layer, exhibited lower strength, underscoring the importance of a higher number of yarns in the external layer for structural robustness.

In cyclic compression and recovery testing, the T2/A8B40/E16B50 structure also displayed high elastic recovery after ten cycles, with an average of 96.47%, second only to T3/A8B40/E8B50, which achieved 97.43%. This result indicates that, although the structure supports high loads, it retains excellent recovery capacity. Conversely, the T1/A8B30/E16B50 structure, with smaller diameter yarns in the internal layer (0.30 mm), exhibited the poorest elastic recovery, at 83.82%, likely due to the lower compressive strength of the internal layer.

The T2/A8B40/E16B50 structure had a coverage factor of 49.3% and a porosity of 50.7%, striking a balance between good permeability and nutrient exchange capacity, alongside mechanical strength. This suggests that the choice of yarn diameters and the number of yarns directly affects porosity and, consequently, the functionality of the structure for biomedical applications, such as scaffolds for tissue regeneration. In this context, the T2/A8B40/E16B50 structure is considered the most suitable for implant testing.

Acknowledgments

This research was funded by the European Regional Development Fund through the Operational Competitiveness Program and the National Foundation for Science and Technology of Portugal (FCT) under the projects UID/CTM/00264/2020 of the Centre for Textile Science and Technology (2C2T) on its components base (https://doi.org/10.54499/UIDB/00264/2020, accessed on 10 January 2025) and program (https://doi.org/10.54499/UIDP/00264/2020). Diana P. Ferreira is thankful to CEECIND/02803/2017, funded by National Funds through FCT/MCTES (https://doi.org/10.54499/CEECIND/02803/2017/CP1458/CT0003).

  1. Funding information: Authors state no funding involved.

  2. Author contributions: All authors contributed to the study's conception and design: Ivis de Aguiar Souza, Lais Kohan, Maurício José da Silva Filho, Raul Fangueiro, and Diana Sara Pereira Ferreira. Data collection was performed by Ivis de Aguiar Souza, Lais Kohan, and Joaquim Jorge Peixoto. The algorithm and simulation presented were developed by Ivis de Aguiar Souza and Maurício José da Silva Filho. Material preparation and analysis were performed by Ivis de Aguiar Souza, Lais Kohan, and Joaquim Jorge Peixoto. The first draft of the manuscript was written by Ivis de Aguiar Souza, Lais Kohan, Joana M. Rocha, and Diana Sara Pereira Ferreira, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

  3. Conflict of interest: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

  4. Ethical approval: The conducted research is not related to either human or animals use.

  5. Data availability statement: The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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Received: 2024-04-23
Revised: 2024-10-30
Accepted: 2024-11-07
Published Online: 2025-06-11

© 2025 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/aut-2024-0019
Keywords for this article
Braided; fibrous structures; grasshopper; parametric design; Rhinoceros 3D®; scaffold; spinal cord injury
Creative Commons
BY 4.0

Articles in the same Issue

  2. Study and restoration of the costume of the HuoLang (Peddler) in the Ming Dynasty of China
  3. Texture mapping of warp knitted shoe upper based on ARAP parameterization method
  4. Extraction and characterization of natural fibre from Ethiopian Typha latifolia leaf plant
  5. The effect of the difference in female body shapes on clothing fitting
  6. Structure and physical properties of BioPBS melt-blown nonwovens
  7. Optimized model formulation through product mix scheduling for profit maximization in the apparel industry
  8. Fabric pattern recognition using image processing and AHP method
  9. Optimal dimension design of high-temperature superconducting levitation weft insertion guideway
  10. Color analysis and performance optimization of 3D virtual simulation knitted fabrics
  11. Analyzing the effects of Covid-19 pandemic on Turkish women workers in clothing sector
  12. Closed-loop supply chain for recycling of waste clothing: A comparison of two different modes
  13. Personalized design of clothing pattern based on KE and IPSO-BP neural network
  14. 3D modeling of transport properties on the surface of a textronic structure produced using a physical vapor deposition process
  15. Optimization of particle swarm for force uniformity of personalized 3D printed insoles
  16. Development of auxetic shoulder straps for sport backpacks with improved thermal comfort
  17. Image recognition method of cashmere and wool based on SVM-RFE selection with three types of features
  18. Construction and analysis of yarn tension model in the process of electromagnetic weft insertion
  19. Influence of spacer fabric on functionality of laminates
  20. Design and development of a fibrous structure for the potential treatment of spinal cord injury using parametric modelling in Rhinoceros 3D®
  21. The effect of the process conditions and lubricant application on the quality of yarns produced by mechanical recycling of denim-like fabrics
  22. Textile fabrics abrasion resistance – The instrumental method for end point assessment
  23. CFD modeling of heat transfer through composites for protective gloves containing aerogel and Parylene C coatings supported by micro-CT and thermography
  24. Comparative study on the compressive performance of honeycomb structures fabricated by stereo lithography apparatus
  25. Effect of cyclic fastening–unfastening and interruption of current flowing through a snap fastener electrical connector on its resistance
  26. NIRS identification of cashmere and wool fibers based on spare representation and improved AdaBoost algorithm
  27. Biο-based surfactants derived frοm Mesembryanthemum crystallinum and Salsοla vermiculata: Pοtential applicatiοns in textile prοductiοn
  28. Predicted sewing thread consumption using neural network method based on the physical and structural parameters of knitted fabrics
  29. Research on user behavior of traditional Chinese medicine therapeutic smart clothing
  30. Effect of construction parameters on faux fur knitted fabric properties
  31. The use of innovative sewing machines to produce two prototypes of women’s skirts
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