Melt Electrospinning Writing of Mesh Implants for Pelvic Organ Prolapse Repair

Abstract

Over the past decade, melt electrospinning writing has attracted renewed attention. When combined with three-dimensional (3D) printing capabilities, complex 3D structures can be produced, from ultrafine fibers in the absence of toxic solvents, making it particularly attractive to fabricate customized scaffolds and implants for medical applications. This research aimed to develop novel less stiff vaginal mesh implants for pelvic organ prolapse (POP) repair, matching the physiological biomechanics of vaginal tissues. The main objectives, to attain that goal, were: development of a melt electrospinning writing prototype, with additive manufacturing capability, to produce complex structures from micrometer scale fibers, in a direct 3D printing mode; and design and validate new concepts of biodegradable meshes/scaffolds with new geometries, for POP repair. The melt electrospinning writing prototype was built based on different modules. Biodegradable polycaprolactone was used to produce novel implants: three geometries and two fiber configurations were employed. The commercially available Restorelle^® (Coloplast) mesh was used as a benchmark. Printed implants were analyzed via scanning electron microscopy (SEM) and uniaxial tensile testing. The SEM images showed that the geometry is generally well produced; however, some minor deviations are visible due to charge interactions. The tensile test results indicated that, regardless of the geometry, the samples showed an elastic behavior for smaller displacements; aplastic behavior dominates later stages. In the physiological range of deformation, the novel meshes (80 μm fiber diameter) matched the tissue properties (p > 0.05). The Restorelle mesh was significantly stiffer than vaginal tissue (p < 0.05) and novel meshes. The precision of the various geometrical patterns and fiber diameters produced highlights the success of the designed and built prototype equipment. Results showed that the biodegradable meshes produced are biomechanically more compatible with native tissue than commercial implants.

Introduction

The number of publications on melt electrospinning writing (MEW) processes has been rising, increasing attention both on process industrialization and on medical applications, in a particular tissue engineering scaffolds.¹ The latest developments demonstrate that it is possible to produce fibers with diameters at micron and submicron level, thus overcoming one of this technology's main limitations.² Electrowriting technology (three-dimensional [3D] printing) enables employment of biocompatible materials and manufacturing of high reproducibility customized solutions.³ The possibility to mimic the features of biological tissues, with complex hierarchical structures, in a reproducible way, without compromising cellular proliferation and growth, is essential in tissue engineering applications.⁴ MEW-produced scaffolds have the additional advantage of being nontoxic, biodegradable, and with sufficient mechanical strength.

The focus of the research was on developing solutions to solve women pelvic floor disorders, particularly pelvic organ prolapse (POP), that can significantly negatively impact a woman's daily activities and quality of life. POP is the abnormal herniation of pelvic organs through the vagina. It affects 41% of women older than 60 years; one in four is symptomatic.⁵ The overall lifetime risk for primary surgery for POP and stress urinary incontinence is 20% by 80 years.⁶ POPs estimated prevalence is between 2.9% and 8% of the female population, and recent estimates suggest that women have a 12.6% lifetime risk of undergoing surgery for prolapse.⁵ In 2005, the number (rate) of admissions for POP surgery in Germany, France, and England was 102.492 (1.05 per 1000 women), with a substantial cost €308.335.289.⁷ To provide additional support, when repairing weakened or damaged tissue, surgeons have turned to mesh-augmented repairs.⁸ However, the vaginal insertion of mesh has been associated with a high rate of graft-related complications (GRCs),⁸ which may be due to insufficient biocompatibility and inappropriate biomechanical properties of the implants, and/or to patient and surgeon factors.⁹ Most textile implants used today are based on polymer polypropylene (PP). Because of the Food and Drug Administration (FDA) ban to use synthetic meshes for transvaginal prolapse repair, the need for novel materials, devices, and surgical techniques is expected to grow significantly.¹⁰ A completely different approach, to solve this problem, may be the use of non-textile biodegradable implants, which could mimic the host tissue's biomechanical properties, made by 3D melt electrospinning additive manufacturing (AM).

The research results on melt electrospinning optimization and the direct writing process of biodegradable polycaprolactone (PCL) will be reported, and in particular, its application to produce novel implants/meshes for urogynecology applications with a focus on POP repair.

Materials and Methods

Development of the melt electrospinning writing prototype

A melt electrospinning writing prototype was built using a modular architecture, based on different modules and functions, including structure, control, movement, material supply, heating, material collection, and a high-voltage generator as illustrated (Fig. 1). The equipment's main components are stepper motors, the heating and supplying components, and the controller board, which controls the machine's behavior, reading the inputs and generating the outputs via electric signals. The controller unit used in this prototype was the Duet 3D 2.0 Ethernet. The choice was based on this board's versatility that allows the use of several extruders, taking advantage of a high-performing 32-bit processor. A graphic touch screen makes the experience more user-friendly and monitors the equipment's parameters from a safe distance, through a computer and heating chamber.

FIG. 1.

Melt electrospinning writing prototype: 1, structure of the device; 2, linear actuators; 3, Bondtech QR extruder; 4, collector plate with PLA 3D printed platform; 5, LCD touch screen (user interface); 6, high-voltage generator by Linari Engineering. 3D, three-dimensional; LCD, liquid crystal display; PLA, polylactic acid.

The movements in the MEW prototype are guaranteed by linear actuators that are driven by stepper motors. The movement's configuration is Cartesian with the collector's movement, in the X and Y direction, independent of the spinneret head's movement, in the Z direction (a maximum 70 mm in height), with linear actuators driving the three independent motions. The precision of the movement, in this case, is more critical than in solution electrospinning.

The built MEW apparatus material feeding system is different from the traditional electrospinning systems where fibers are deposited in a flat or cylindrical collector. In this case, the polymers are fed with a syringe pump or a screw extruder that allows continuous feeding with controlled rates.^11–14 These systems allow not only stability but also a precise feeding rate of small volumes of polymers. The filament diameter compatible with the prototype equipment is the standard 1.75 mm, which is fed through a direct extruder. The extruder selected was the Bondtech QR, which demonstrated high reliability due to the use of a dual-gear drive system that reduces the possibility of material slipping. Since the material rate directly influences the amount of material in the Taylor cone, there must be a meticulous control of the material volume extruded.

The filament heating system consists of a standard Hotend set used in fused filament fabrication (FFF) equipment with a heater block heated by a ceramic cartridge. The equipment uses an E3D V6 Hotend and includes all components typically employed in domestic 3D printing equipment: heat sink, cooling fan, heat block, heat break, ceramic cartridge, and thermistor.

A conventional nozzle was used as a spinneret, as in conventional FFF devices, instead of the usual needles employed in solution electrospinning. The use of a nozzle allows the formation of the Taylor cone, at the tip, with the nozzle orifice's dimension, controlling the amount of material at the cone. A nozzle with an orifice diameter of 400 μm was used, corresponding to the maximum fiber diameter.

The high-voltage source was purchased from a biomedical equipment supplier (Linari Engineering, Italy), and it is a 60 kV—150 W positive high-voltage generator. The generator has a minimum output current of 0.01 mA, and the interface with the user is a touch screen LCD or a Web interface.

The collection surface consists of a square-shaped aluminum plate with 3 mm thickness and an area of 270 × 270 mm². The collector acts as an electrode, so it is important to guarantee electrical field uniformity over the entire collection area. A highly electrically conductive metal (aluminum with electrical conductivity ranging from 10 to 37 × 10⁵ S/m) was selected. The high-voltage source was applied to the collector. The connection between the moving plate and the intermediate component was a 3D-printed platform, coated with isolating material, and screwed to the plate. The grounding cables were connected to several points on the machine structure to ensure no risk of high-voltage discharges to electrical equipment components and the user.

Calibration

Pattern and commands

Before initializing the fiber placement, according to a predefined pattern, it was necessary to calibrate the melt electrospinning device's parameters to achieve the optimal extrusion conditions. Thus, two different G-Code routes were developed: a static route and a dynamic route.

For temperature calibration, a static route was enough to assess the fiber behavior, whereas for the other parameters, the dynamic route was necessary. The device extrudes polymer in a rectangular shape around the pattern's borders in two loops to stabilize the jet. Once these loops are finished, then the program starts the calibration pattern. For jet calibration, through the static route, the printing head is placed at the center of the printing collector, and a given amount of polymer is extruded at a constant rate. The goal of this program was to assess jet behavior without considering the kinematic parameters. After the static parameters were calibrated, it was necessary to test the collecting plate's movement and associated dynamic parameters. For the parameter optimization, a dynamic pattern with property changes over the route was used.

Temperature

The temperatures tested for PCL were 160°C, 180°C, 200°C, and 220°C. The predefined parameters used in this optimization were as follows: voltage = 5 kV, height = 15 mm, translational speed = 3000 mm/min, and extrusion = 0.2 mm/100 mm.

A variation of the deflection angle with a straighter jet appears as the temperature rises (Fig. 2A). To properly evaluate the spectrum of temperatures that can be employed, it was necessary to measure the diameter of the fibers produced for each condition. At a temperature of 180°C, the error between the predefined and measured fiber diameter was the lowest (Table 1). For higher temperatures, the fiber diameter was smaller due to the reduction of viscosity.

FIG. 2.

(A) Evolution of the PCL jet path with increasing temperature from 160°C to 220°C, with increments of 20°C; PCL jet deflection with different extrusion rates (B), with different linear translation speed (C), with different voltage applied (D) at 200°C and 215°C temperatures (selected images with minor error-above and major error-below).

Table 1.

Polycaprolactone Fiber Diameter Measurements and Error Values for Different Temperature Levels

Temperature (°C)	Predefined fiber diameter (μm)	Measured fiber diameter (μm)	Error (%)
160	63.90	59.53	6.84
180	63.90	60.66	5.07
200	63.90	58.39	8.62
220	63.90	55.79	12.68

Extrusion rate

Two different values of temperature were employed to measure the effective impact of the extrusion rate on the diameter. The conditions employed were as follows: voltage = 5 kV; height = 15 mm; translational speed = 3000 mm/min; extrusion = 0.75, 1.00, 1.50, and 2.00 mm/100 mm; temperature = 200°C and 215°C.

The jet was nearly vertical for both temperature levels, decreasing with increasing extrusion rates (Fig. 2B). The higher the volume of material extruded per time unit, the better the relative placement precision (Table 2). The predefinition of the values was made based on a mass conservation law, with a certain volume of material passing through the extruder being placed on the 100 mm patterned line. The higher flow rates decrease the fibers' mechanical drawing, so there is no effect of fiber stretching. When accelerating and decelerating the printing head, fibers tend to coil or become thicker, depositing a more significant amount of material per displacement unit, causing a variation on the fiber diameter. Overheating the polymer to 215°C resulted in a reduction of the error in all levels, due to a more vertical jet, with reduced mechanical drawing.

Table 2.

Polycaprolactone Fiber Diameter Measurements and Error Values for Different Extrusion Rates, Translational Speeds, and Voltages at 200°C and 215°C Temperature

	Temperature: 200°C			Temperature: 215°C
	Predefined fiber diameter (μm)	Measured fiber diameter (μm)	Error (%)	Predefined fiber diameter (μm)	Measured fiber diameter (μm)	Error (%)
Extrusion (mm/100 mm)
0.75	123.75	101.61	17.89	123.75	104.03	15.92
1.0	142.89	119.34	16.48	142.89	121.69	14.83
1.5	175	147.55	15.69	175	165.04	5.69
2.0	202.07	173.81	13.99	202.07	187.69	7.12

Translational speed (mm/min)
2750	20.21	14.78	26.87	20.21	20.21	0
3500	20.21	6.28	66.91	20.21	21.91	8.41
4250	20.21	4.79	76.31	20.21	15.76	22.01
5000	20.21	2.51	87.56	20.21	10.11	49.97

Voltage (kV)
4	20.21	34.52	14.31	20.21	48.16	38
6.5	20.21	21.03	0.83	20.21	19.83	1.87
9	20.21	18.28	1.93	20.21	15.15	25.01
11.5	20.21	10.14	10.07	20.21	14.39	28.77

Linear printing head speed

The use of different speeds was evaluated maintaining all other conditions constant. The parameters used were as follows: voltage = 5 kV; height = 15 mm; extrusion = 0.02 mm/100 mm; translational speed: 2750, 3500, 4250, and 5000 mm/min; temperature = 200°C and 215°C.

There were no noticeable differences for both temperatures (Fig. 2C); higher jet deflection was observed in both cases. The increase of speed from 2750 to 5000 mm/min induced mechanical drawing causing a fiber diameter reduction (Table 2). When the fibers' extrusion temperature varied from 200°C to 215°C, the degree of error was greatly reduced.

Voltage

The values considered for the parameters were as follows: height = 15 mm; extrusion = 0.02 mm/100 mm; translational speed = 3000 mm/min; voltage = 4, 6.5, 9, and 11.5 kV; temperature = 200°C and 215°C. The jet profiles obtained are illustrated (Fig. 2D), and fiber diameters for different temperatures and translational speeds are indicated (Table 2). As voltage increases, the fibers tend to approximate to the predefined value, and no coiling occurs.

Materials

The meshes produced were benchmarked with a commercially available mesh: Restorelle^® (lightweight PP mesh) (Coloplast). The Restorelle is knitted monofilament (80 μm) PP mesh, with a pore dimension of 2 mm and a density of 19 g/m². Biodegradable PCL, used in this research, has been approved for use in humans by the FDA¹⁵ and has an expected degradation time of 2–3 years.¹⁶ PCL is a material widely used in electrospinning processes. The filament used is a commercially available (non-medical grade) variant sold by 3D4Makers, named Facilan™ PCL 100. It has density of 1.1 g/cm (ISO 1183), filament diameter of 1.75 mm, glass transition temperature of 60°C, melting point of 58–60°C, decomposition temperature of 200°C, and melt flow index of 11.3–5.2 g/10 min.

Mesh printing

The meshes were printed in three geometric patterns illustrated (Fig. 3A). The prototype meshes produced mimicked the geometrical pattern and pore size of Restorelle (Fig. 4C). The mesh patterns were printed in two configurations: three layers of 80 μm filaments and one layer of 240 μm. An analytical balance, with an inherent error of ±0.001 g for each reading, was used to weight the produced implants and calculate the density.

FIG. 3.

(A) The design of novel meshes. (B) Melt electrospun printed meshes (square-shaped [Q], triangular-shaped [T] and cross-shaped [X]).

FIG. 4.

SEM images of the printed meshes; view from above (A), side view (B). SEM image of Restorelle^® mesh (C). SEM, scanning electron microscopy.

Uniaxial testing and sample preparation

Novel printed meshes were cut out into 60 × 10 mm strips, respecting the pore pattern (10 mm from each size for specimen fixation). These sample dimensions were chosen to allow a constant length-to-width aspect ratio of 4 to minimize the nonlinear effects of clamping on the uniaxial mechanical properties. A total of three specimens were obtained for each mesh.

An electronic testing machine “INSTRON^® Electro Plus E1000” was used to conduct the tensile tests on the produced meshes with a 1 kN load cell attached. A preload of 0.1 N was applied to remove all slack from the mesh. This point was defined as elongation zero. A constant elongation rate of 10 mm/min was then used to load the specimen until failure.

The printed meshes were analyzed through force–elongation curves and stress–strain curves. Young's modulus in the comfort zone was defined as the modulus for 10–20% of total elongation. The curve's comfort zone is usually considered to be within the physiological range of deformation.¹⁷

Scanning electron microscopy

The scanning electron microscopy (SEM) analysis was performed using a high-resolution (Schottky) Environmental SEM with X-ray microanalysis and electron backscatter diffraction analysis: FEI Quanta 400 FEG ESEM/EDAX Genesis X4M. All the samples were coated with an Au/Pd thin film, by sputtering, for 80 s.

Statistics

Statistics were performed using GraphPad Prism 5 (GraphPad Software, Inc., La Jolla, CA). Normality of the data was verified using the Kolmogorov–Smirnov test. Quantitative data are reported as mean ± standard error of the mean. For comparison between mesh configurations, disruption force and strain were analyzed using one-way analysis of variance. Dunnett's post-test correction was used to determine whether the differences between multiple pairs were statistically significant. For intra-material comparisons (geometries, filament diameter), an unpaired Student's t-test was used (confidence level of 95%). The level of significance was set at p < 0.05.

Results

Calibration

The temperature that generated the fibers with greater precision was 180°C, with an error of 5.07% and an estimated value of 63.90 μm. The extrusion rate that generated more accurate fibers was 2 mm of filament per 100 mm of printed distance, at 200°C temperature, with an error of 13.99%. The linear speed of 2750 mm/min resulted in more accurate fibers with the minimum error of 28.87% at the temperature of 200°C. The voltage of 6.5 kV resulted in a fiber accuracy, with an error of 0.83% at 200°C and of 1.87% at 215°C.

Printed meshes

The first geometry evaluated was a simple square-shaped pattern (further denoted as Q; Fig. 3B). The pattern consisted of 2 mm/side squares, over an area of 84 × 84 mm.² The second mesh had triangular-shaped geometry (further denoted as T), based on the first geometry; it was reinforced with a pair of opposed vertices connected through the fiber, reducing the vertical fiber's reinforcement (Fig. 3B). The third mesh had cross-shaped geometry (further denoted as X) based on the first geometry, reinforced with fibers crossing the squares' diagonals (Fig. 3B). Each condition was evaluated according to the density, following the classification¹⁷ (Table 3).

Table 3.

Various Shaped Printed Meshes Mass, Density, and Classification

Meshes	Abbreviation	Filament configuration	Mass (g)	Density (g/m²)	Classification
Square-shaped	Q1	80 μm (3 layers)	0.195	27.636	Ultra-lightweight
Square-shaped	Q2	240 μm (1 layer)	0.38	53.855	Lightweight
Triangular-shaped	T1	80 μm (3 layers)	0.23	32.596	Ultra-lightweight
Triangular-shaped	T2	240 μm (1 layer)	0.66	93.537	Mid-weight
Cross-shaped	X1	80 μm (3 layers)	0.31	43.934	Lightweight
Cross-shaped	X2	240 μm (1 layer)	0.91	128.968	Mid-weight

Ozog et al.¹⁷

SEM analysis

When analyzing the pattern (Fig. 4A), it was possible to notice the fiber positioning. Some central areas of the horizontal fibers were flat (Fig. 4B). It has to do with the fibers' sagging since the vertical fibers have been deposited previously and the fiber weight causes them to sag.

The fibers' intersection was uniform and consistent, and fiber sagging was present all over the sample. The T-shaped structure represented an intermediate level when compared with the complexity of the previous structures. It was noticeable an increase of precision, and the small defects were due to the perpendicular grid lines' positioning. Variant X was the mesh configuration with the highest number of crossing fibers on a single point, and the vertical sagging might turn problematic in the long run.

Uniaxial testing

Tensile testing results showed an initial elastic deformation, followed by plastic deformation (Fig. 5A). Once the elastic deformation stage was completed, the plastic deformation dominated the specimen's deformation, and a horizontal path of the graphic appeared. The graphic data were represented until a displacement of 10 mm occurred since only plastic deformation would occur for higher values.

FIG. 5.

(A) Uniaxial tensile test results for the two variants of the square-shaped (Q1, Q2), triangular-shaped (T1, T2), and cross-shaped geometry (X1, X2). (B) Comparison of the produced mesh prototypes with vaginal tissue of the sheep and a commercially available mesh implant. (C) Vertical scatter plot, mean ± standard error of the mean of stiffness (N/mm) and Young's modulus at comfort zone. Significant differences between groups and vaginal tissue (*) and PP mesh Restorelle (R) are displayed above the bars. Significant difference noted when p < 0.05.

A significant difference was observed between the meshes with the same shape but different printing parameters (p < 0.05) (Table 4). The mesh X2, the strongest, with the higher load capacity (6N), but with lower stiffness at the comfort zone (1.42 N/mm), is comparable to the meshes with 240 μm fiber diameter. Q1 mesh was the strongest and had higher stiffness at the comfort zone, among the meshes with the same filament type (80 μm per three layers).

Table 4.

Load (N) and Stiffness (N/mm) at Comfort Zone (Mean ± Standard Error of the Mean) of Printed Mesh Specimens (n = 3) During Uniaxial Loading Test

Variable	Q1	Q2	T1	T2	X1	X2
Load (N)	1.57 ± 0.02	3.79 ± 0.044	1.26 ± 0.05^a	4.69 ± 0.03^b	1.46 ± 0.07	5.99 ± 0.06^b,c
Load (N)	p < 0.0001		p < 0.0001		p < 0.0001
Stiffness at comfort zone (N/mm)	0.56 ± 0.04	2.03 ± 0.02	0.38 ± 0.02^a	1.59 ± 0.18	0.41 ± 0.01^a	1.42 ± 0.01^b
Stiffness at comfort zone (N/mm)	p < 0.0001		p < 0.005		p < 0.0001

Statistical intra-material comparisons of mesh, significant difference was set up when p < 0.05.

Differs from Q1.

Differs from Q2.

Differs from T2.

Comparison with benchmark

The printed meshes were compared with vaginal tissue mechanical behavior from a healthy sheep¹⁹ and PP Restorelle mesh (Fig. 5B). The mesh prototype's behavior was distinct from the behavior of both the commercial product and the vaginal tissue. However, considering the comfort zone (physiological range of deformation), the meshes with a fiber diameter of 80 μm matched the tissue properties (p > 0.05) (Fig. 5C). Restorelle mesh was significantly stiffer compared with vaginal tissue (p < 0.05). Printed meshes with 240 μm diameter were also stiffer than vaginal tissues and Restorelle mesh (p < 0.05).

Discussion

Over the past decade, both electrospinning and AM technologies have greatly improved, with the proliferation of low-cost FFF devices and the increased knowledge of the electrospinning electrohydrodynamic processes. The development of electrowriting technologies, combining both AM and electrospinning, followed this trend.

Most of the MEW types of equipment are still custom-built in the laboratory to fulfill a specific need or application. However, ready-to-use MEW equipment, in a desktop configuration, are presently available in the market such as regenHU,¹¹ Spraybase,¹² Axolotl,¹³ and NovaSpider.¹⁴ Even though the equipment designs vary, the same basic principles apply. Some of the apparatus offers both pressure driven and mechanically driven polymer supply,^11–13 with syringe pumps, mechanical extruders, and screw-driven melt feeders as alternatives. The materials employed can be fed as pellets, powder, or filament. In terms of accuracy, XY directions movement varies from 5 to 20 μm, both at the printing head or the collector. Some devices range from 0 to 20 kV in terms of high-voltage range while others support only up to 6 kV. The majority of the devices is custom-built or adapted for different purposes, taking into account the possibility to industrialize the process,²⁰ the reproducibility,^21–23 the mechanical behavior of deposited fibers,²⁴ and the use of different materials and cost. The works developed at the Mechanical Engineering Department of Sungkyunkwan University²⁵ are examples of both principles' successful application, employing a conventional extruder and heating system while feeding filament in a standardized dimension controlled by a stepper motor. Other works focused specifically on the extrusion parameters while using a filament extruder.²⁶

Melt electrospinning writing is an emerging fiber-based manufacturing technique that can be used to design and build scaffolds suitable for many tissue engineering applications.²⁷ The main benefit and advantage of the melt electrospinning writing technology is the possibility of fabrication of ultrafine polymer fibers in the absence of solvents. This research aimed to contribute to developing novel vaginal meshes for POP correction, less stiff, that match the physiological biomechanics of vaginal support structures. Thus, the main specific objective to attain that goal was developing melt electrospinning writing equipment, with AM capability, to produce complex 3D structures from micrometer scale fibers, in a direct 3D printing mode (Fig. 1). The prototype enables the fabrication of ultrafine polymer fibers in the absence of solvents, avoiding toxicity issues. At the same time, it is more cost-effective (100% of the melt electrospun polymer is collected compared with 2–10% of the total volume processed in solution electrospinning).²⁸ Apart from the above advantages, the approach used in melt electrospinning technology has other benefits: no spool refilling over a long time is needed, thereby avoiding pressure differences and recalibration, which happens in solution electrospinning. Unnecessary material touching will improve good manufacturing practices and hygiene standards.²⁹

The prototype assembly consists of an XY moving collector plate with a Z-moving printing head on an aluminum box structure. The high-voltage supply is separated from the equipment and has an electrode connected to the collection plate and the other connected to the nozzle. The equipment design meets all electrostatic discharge precautions, and all parts, separated from the charged electrode, are earthed to prevent electronic interference and device malfunction. This prototype's innovative aspects are the use of a hot-end extruder as the only heat supply, standard 1.75 mm filament feeding system, and the electronic board of a conventional domestic 3D printer. In the literature, most of the devices use syringe pumps for controlled polymer deposition with heating chambers for pre-heating the material before extrusion, increasing both the devices' complexity and cost.³ After analyzing the results, it is possible to conclude the equipment could write with an assignable precision the predefined routes with minor deviations due to the charge interactions.

Empirical data indicate that meshes with lower weight meshes with pore dimensions over 1 mm are more effective upon implantation, reducing GRCs.³⁰ According to the meshes classification, the printed meshes meet these characteristics, ranging from ultra-lightweight to mid-weight, depending on the configuration (Table 3). The SEM images indicate that the geometry is generally well produced; however, some minor deviations due to charge interactions are visible, requiring further process optimization (Fig. 4A, B). One of the major problems identified was variation in fiber distances. The deficiency in positioning has to do with the electrical interaction of the previously deposited fibers attracted to the jet due to charge effects. This effect causes fibers to be inaccurately placed all over the mesh. In the literature, the bridged fibers' sagging due to the weight has been identified, which may limit the cellular growth.³⁰

The use of PP surgical meshes is associated with GRCs due to lack of biocompatibility, inadequate mechanical properties, or material design.¹⁹ The tensile test results of the printed mesh indicate that, regardless of the geometry, the samples show an elastic behavior for smaller displacements and plastic behavior dominate later stages (Fig. 5A). The elastic behavior is essential as the implant is not permanently deformed, namely for the initial stages when the implants are not colonized by cells.²⁴ The results showed that printed implants had similar mechanical behavior, despite differences in fiber diameter. It was noted that the printed meshes follow more closely the biomechanical properties of native tissues, unlike PP Restorelle implant, in particular in the comfort zone (Fig. 5B).

Regarding the degradation of implants, research in progress will focus on in vitro degradation experiments to create a prediction degradation model of bioabsorbable polymers to optimize its duration and enhance tissue growth. For future experiments on animal models, medical-grade PCL polymers will be used, and the strategy of using implants produced by melt electrospinning relative to textile implants will be studied in greater detail. The plan is to use sinusoidal lines to mimic collagen fibers; this will change the proper geometry and reduce the pore size of the mesh. Other biodegradable polymers, with a slower degradation rate or bioactive properties, could be used to fasten tissue remodeling.

Conclusions

The approach behind the development of melt electrospinning prototype produced and tested was based on the FFF concept design and principles to assess the possibility of producing microfibers, with little modifications to a typical 3D printer with a high-voltage source, due to the following reasons: simplicity—while using a conventional FFF machine as a base for the project, the structure, kinematics, and user-interface are promptly available and ready to be customized; low cost—the rise in the AM industry allowed equipment's and parts' costs to drop significantly, so the built device can have its costs controlled in comparison with available commercial solutions; versatility—there are numerous materials and construction solutions available for FFF devices, so, when using this as a base, the possibility for changing materials and components is almost limitless.

The fact that the geometrical pattern and the fiber diameter were efficiently reproduced in the three different geometries highlights the built prototype's success. The research outcomes will also contribute to developing new methodologies to get more rigorous clinical data for premarket approval of the devices for prolapse repair, as currently required by the FDA, before being marketed as Class III devices (generally high-risk devices).

Footnotes

Acknowledgments

The authors would like to thank Eng. João Paulo Pereira and Dr. Luís Oliveira Costa for technical support in this research.

Author Disclosure Statement

The authors declare that there is no financial, professional, or other personal interest of any nature or kind in any product, service, and/or company that could be constructed as influencing the position.

Funding Information

This study was funded by Ministério da Ciência Tecnologia, e Ensino Superior, FCT, Portugal, and Programa Operacional Competitividade e Internacionalização—POCI the project SPINMESH—Melt electrospinning of polymeric bioabsorbable meshes for pelvic organ prolapse repair—POCI-01-0145-FEDER-029232.

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