1. Introduction
Coronavirus disease (COVID-19) mutations still occur in many countries [
1]. Concerns about the presence of new omicron subvariants take more attention from various parties [
2,
3]. Since the beginning of the COVID-19 pandemic, three-dimensional printing (3DP) has become an important technology in the development of medical device design [
4] and supports enhanced healthcare and emergency response [
5]. 3DP technology, also known as additive manufacturing (AM), creates three-dimensional objects layer-by-layer or point-by-point in a subsequent manner from a digital 3D model [
6,
7]. 3DP technologies have been popularly applied in different applications from medical devices, art, oil and gas industries, and outdoor equipment [
8,
9,
10,
11,
12,
13,
14,
15] due to advances in the development of printable materials [
7] and the ability of 3DP technologies to produce complex structures on a micro-scale [
16]. Furthermore, 3DP technology provides faster, easier, minimum waste, reduced energy, and inexpensive solutions for various applications [
12,
13,
15]. According to ISO/ASTM 52900:2021, AM processes are classified into seven categories based on the basic principle of their operation: binder jetting (BJ), directed energy deposition (DED), material extrusion (ME), material jetting (MJ), powder bed fusion (PBF), sheet lamination (SL), and vat photopolymerization (VP). VP has the best print quality compared to other AM methods in terms of printing resolution [
17], surface roughness [
18], dimensional accuracy [
19], and low porosity of printed parts [
20] for basic shapes, but a limited choice of materials as the photopolymer resin material has to be photopolymerizable [
21]. VP changes the liquid material, in this case, photopolymer resin, into a solid material layer by layer using light in the photopolymerization process [
14]. VP can be categorized into three types based on the mechanism of light exposure to the resin liquid: stereolithography (SLA), digital light processing (DLP), and liquid crystal display (LCD) printing [
22].
Recently, the spread of COVID-19 still concerns scientists because the COVID-19 virus continues to mutate. COVID-19 testing is crucial to control the deployment of COVID-19 because it functions to find patients or individuals affected by COVID-19 to immediately isolate or limit close contact with the people around them [
23]. One way to find out patients infected by the COVID-19 virus is by carrying out a PCR swab test (polymerase chain reaction), where ribonucleic acid (RNA) is detected using nucleic acid with the help of a PCR reaction, which is sampling respiratory was obtained using a nasopharyngeal swab [
24]. A nasopharyngeal swab is inserted through the nostril until it reaches the inferior turbinate and back of the nasopharynx. The Nasopharyngeal swab was then rotated several times and pulled out. After sampling, a nasopharyngeal swab was put into a vial containing several milliliters of liquid solution for further virus check [
25].
At the beginning of the COVID-19 pandemic, many countries faced shortages of nasopharyngeal swabs due to increased demand and decreased supply for COVID-19 testing [
26]. 3DP technology has emerged to solve the shortages as an alternative manufacturing method and design development of nasopharyngeal swabs [
25]. 3DP technologies have several advantages for the rapid development of nasopharyngeal swabs, such as fast prototyping for iteration design, the multiplicity of material, and printing processes available [
22], which means there are many alternatives to create a swab and 3D printers already used in hospitals and clinic so that they can print their swabs to fulfill the demand [
23]. In addition, the ability to transmit the nasopharyngeal swab models using various platforms and the internet and then print them in a particular place means that the manufacture of nasopharyngeal swabs using 3DP technology can overcome the supply chain disruption that will occur and simultaneously reach all user [
27].
Many studies have been conducted on the development of 3D-printed nasopharyngeal swabs. Alghounaim et al. [
28] compared 3D-printed nasopharyngeal swabs to commercially manufactured swabs. Polylactic acid and polyester were chosen as source materials because they were inexpensive and easy to get. Fused deposition modeling (FDM) 3D printer was used to manufacture the prototype of a nasopharyngeal swab. They reported that polylactic acid and polyester 3D-printed nasopharyngeal swabs were effective for COVID-19 sample collection. Williams et al. [
29] developed a 3D-printed nasopharyngeal swab using a selective laser sintering (SLS) printer and medical-grade bio-compatible nylon as source material. Design optimization was developed on the tip geometry swab for maximum sample collection, shaft geometry swab for flexibility, easy to use, and ensured overall design parameters were suitable for patient comfort. Ford et al. [
30] developed and manufactured a 3D-printed nasopharyngeal swab via a stereolithography (SLA) 3D printer since it was easily accessible for biocompatible and inexpensive materials. Tay et al. [
31] designed and clinically validated a 3D-printed nasopharyngeal swab. The swab was printed from medical grade resin and broke at an average load of 40 N, also able to carry fluid of 38 µL. A novel design was developed for realizing patient-specific nasopharyngeal swabs using MATLAB and the patient’s CT data [
32]. Furthermore, a creative design of 3D-printed nasopharyngeal swab for children and infants have been developed by Alazemi et al. [
33]. A total of 160 swab designs from various parties have been evaluated and validated four designs by Callahan et al. [
25]. In addition to mechanical strength considerations, the nasopharyngeal swab designs have been widely developed to obtain sufficient samples for COVID-19 testing [
27,
30].
Based on previous studies, vat photopolymerization 3D printing is broadly used for the fabrication of 3D-printed nasopharyngeal swabs because it can produce a superior quality printed part, easy to get in the market, available in a diverse range of materials and relatively more affordable prices compared to other AM methods. Furthermore, materials used in fabricating 3D-printed nasopharyngeal swab using vat photopolymerization still focuses on surgical-grade resins, which is relatively expensive. There have been many studies regarding 3D-printed nasopharyngeal swab fabrication using vat photopolymerization 3D printing. However, no research yet examines the influence of printing parameters and curing process treatment on the characteristics of the 3D-printed nasopharyngeal swab to ensure that the 3D-printed nasopharyngeal swab is suitable for use before being tested clinically. Therefore, this study aims to design, manufacture, and evaluate 3D-printed nasopharyngeal swabs for COVID-19 sample collection with two sections to reduce medical waste and keep the environment cleaner. The influence of printing parameters and curing time treatment on mechanical properties, dimensional accuracy, and surface roughness of 3D-printed nasopharyngeal swabs will be studied. The characteristics and performance of 3D-printed nasopharyngeal swabs were evaluated. A novel 3D-printed nasopharyngeal swab consisting of a multi-part component was proposed. 3D-printed nasopharyngeal swabs were subjected to mechanical tensile testing, surface roughness testing, dimensional accuracy testing, and sample collection testing for preclinical testing. A digital light processing (DLP) 3D printer machine was used to manufacture 3D-printed nasopharyngeal swabs using PLA PRO photopolymer resin and dental non-castable photopolymer resin as source material. The defectiveness of the 3D-printed nasopharyngeal swab manufacturing process was also presented.
4. Conclusions
The manufacturing process, characteristics, performance, defectiveness, and influence of printing parameters and post-curing process of nasopharyngeal swabs using vat photopolymerization 3D-printing have also been evaluated. A multi-part component 3D-printed nasopharyngeal swab was proposed, in which the swab and handle were manufactured separately; thus, the swab size became shorter. The shorter swab size can reduce the printing time and photopolymer resin material. In addition, the proposed swab design also gives stress concentration or breaking point at a particular position to ensure the patient’s safety. 3D-printed nasopharyngeal swabs show outperforms in tensile testing compared to the commercial flock nasopharyngeal swabs. The flexural test results showed that PLA PRO has greater flexural strength than dental non-castable. However, the swab neck flexibility test showed that both PLA and dental non-castable 3D-printed nasopharyngeal swabs were able to bend 180°. Subsequently, the PLA PRO swab showed a lower surface roughness value than the dental non-castable swab, indicating that the PLA PRO 3D-printed nasopharyngeal swab was smoother than the dental non-castable. Artificial mucus with various viscosity was set to measure the sample collection ability of a 3D-printed nasopharyngeal swab. Both PLA PRO and dental non-castable photopolymer resin have shown engaging material as source material for swab fabrication. It should be noted that 3D-printed nasopharyngeal swab needs to be clinically tested before being widely applied. The selection of printing parameters and post-curing time treatment affected the characteristics of 3D-printed nasopharyngeal swabs. Smaller layer thickness and longer curing time will create a greater performance in tensile testing of a nasopharyngeal swab. In addition, smaller layer thickness provides a better surface quality but lacks dimensional length accuracy. Lastly, rapid prototyping and fabrication via VAT photopolymerization 3D-printing is an adorable option to consider for nasopharyngeal swab production, especially in a critical situation. 3D printing allows multiple designs to be printed, tested, and then quickly redesigned. Moreover, various types of materials and printing processes are available, which means that there are many alternatives for producing nasopharyngeal swabs using 3D printing technology.