Revolutionizing Healthcare: Recent Advances of Polyamide 12 in Medical Applications

Catheter

PA 12 is very effective in cardiovascular treatments as a percutaneous transluminal coronary angioplasty (PCTA) balloon catheter.^[4] PCTA balloon catheters are needed to restore the blood flow at occluded or stenotic coronary arteries. PA 12 is usually used in the fabrication of distal PCTA balloon catheter shafts as it exhibits a low coefficient of sliding friction, good abrasions, and chemical resistance. The low moisture absorption of PA 12, resulting from its low concentration of amide groups, plays a crucial role in its success as a catheter material. Unlike other polyamides that absorb moisture and may degrade or lose mechanical integrity in humid or aqueous environments, PA 12 maintains its structural stability, flexibility, and performance. This makes it an ideal choice for catheters, which require durability, biocompatibility, and resistance to moisture-related degradation during medical procedures.^[5] According to Amstutz et al.,^[4] necking, a pre-forming process aimed at reducing the thickness of the outer wall, is highly crucial for boosting material strength. They observed that an increase in temperature leads to further softening of the material, highlighting the possibility of small cross-sectioned catheters with higher mechanical strength in the future. On the other hand, Touris et al.^[6] found that PA 12 is susceptible to degradation mechanisms that can cause brittleness and fractures in catheter shafts. Their study focused on the impact of moisture on PA 12, finding that increased hydration makes the polymer more elastic, but this effect is reversible upon drying. They concluded that further research is needed to address and improve the brittleness of PA 12.

Bone tissue engineering (BTE)

BTE is an emerging area of research for treatments of bone defects.^[7] BTE provides an innovative approach to regenerating and repairing bone tissue that was damaged by integrating cell growth with 3D porous scaffolds. Innumerable studies are focused on developing biologically inert and cost-effective biomaterials to be used as or substitute adjuvants for treating lesions in various organs and tissues. Dias et al.^[8] highlighted the usage of PA 12 in BTE. They observed the growth of highly vascularized connective tissues at the PA 12 rod insertion site, along with differentiation into osteoblasts. There are no signs of acute or chronic inflammatory responses that usually occur when an implant is placed inside an organism. This is due to the biocompatibility of PA 12 with bone tissue, which is evident by no inflammatory reaction recorded in the fragments after 90 days. Furthermore, a strong positive immunostaining for vascular endothelial growth factor, an antibody essential for restoring vascular supply during the angiogenesis phase, was observed in both osteoblasts and endothelial cells, indicating consistent nourishment of the lesion for effective local repair. A study by Yao et al.^[9] reported that incorporating hydroxyapatite (HA) in suitable amounts significantly changes the biological activity and mechanical properties of PA 12-based porous scaffolds showing potential for osteochondral regeneration. Furthermore, micro-scale voids within the scaffold, created by incorporating a small amount of HA, promote cell growth and proliferation. Thus, the incorporation of appropriate amounts of HA significantly enhances the biological activity and mechanical properties of porous scaffolds made from PA 12, making them a suitable choice for osteochondral regeneration. The findings from this study highlight the PA 12/HA composite scaffold as a promising candidate for clinical transplantation.^[9] Literature also concludes that PA 12 composites can deliver more reliable BTE scaffolds with excellent mechanical properties.^[7]

Denture base

Polymethyl methacrylate (PMMA) is the commonly used material in removable denture fabrication, which exhibits adequate material properties and simple application. Yet, the visibility of metal clasps compromises the aesthetic appearance of the acrylic removable partial dentures. The increasing rate of intolerance among medical personnel and patients toward the monomers present in PMMA dentures has raised concern as well. Therefore, it is safe to say PA 12 can be an attainable alternative to PMMA-based removable dentures. The color of the gingiva and teeth can be matched as the flexibility of PA 12 enables retentive elements. However, the biggest drawback observed through this research is that PA 12 is more susceptible to discoloration by staining liquids in opposition to PMMA.^[10] Nonetheless, proper oral hygiene practice and professional care should be implemented to substantially minimize the staining problem. In addition, Vojdani and Giti^[11] suggested adding glass fiber filler to polyamides to increase stiffness and other mechanical properties. Figure 2 summarizes the other superior and inferior qualities of polyamide-based dentures over conventional PMMA dentures.

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Figure 2:

Characteristics of polyamide-based denture.

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Biomedical implants

Over the past two decades, PA 12 has been one of the desirable biomaterials that have gained attention in surgical implants. During total hip replacement surgery, a plastic liner is inserted between the femoral head and the femoral ball. This acetabular liner is generally composed of polymer powder like polyamide. PA 2200 (EOS, GmbH, Germany) which is made from PA 12 is the latest biocompatible powder with great stiffness and strength.^[12] Subhedar et al.^[13] investigated the applicability of carbon fiber-reinforced PA 12 (CF/PA 12) as a femoral head which forms the body’s largest joint. This study has discovered the application of PA 12 in the management of hip disability and pain, which is mostly caused by rheumatoid arthritis, osteoarthritis, and traumatic arthritis. The fundamental conclusion that derived from the analysis is that PA 12 is the most economical material, and CF/PA 12 material is cytocompatible on which adhesion, spreading, proliferation, and differentiation of immature osteoblastic cells are observed vividly. Specifically, a CF/PA 12 implant exhibits a lower percentage of bone loss (9%) postoperatively. This is due to the implant promoting a more uniform density distribution in the bone and reducing stress shielding compared to metallic implants. Based on these explanations, CF/PA 12 stands out as one of the most suitable implant materials, surpassing metals and ceramics.

3D printing

Three-dimensional (3D) printing is undeniably transitioning rapidly from manufacturing to medical fields and even into the homes of patients and doctors.^[18] Since the first report of 3D printed parts by Hideo Kodama in 1982,^[30] 3D printing has received a lot of attention and massively helped the medical industry, especially during the unprecedented COVID-19 times.^[15] Addictive manufacturing (AM), also called 3D printing, denotes the various processes for printing a physical 3D model using digital information in which incremental layers of the materials are built up under computer control.^[18,19] The type of 3D printer used is often determined by the materials to be used and how the layers in the end product are bonded.^[20] Various additive manufacturing techniques have been developed through extensive research over time. The different techniques of 3D printing have been summarized in Table 2.

Over time, extensive research has aimed to enhance the properties of PA 12 for 3D printing use. Research has proved that the incorporation of 1.5 and 3 wt% carbon black (CB) into PA 12 can increase the maximum degradation temperature of the entire sintered CB/PA 12 composite. This improvement is due to the exceptional thermal properties of CB particles, which enhance overall thermal stability. This occurs because a carbon layer forms on the PA 12 surface, which inhibits the combustion process.^[14]

Vidakis et al.^[15] pointed out that the antibacterial performance of PA 12 can be enhanced with the silver-doped antibacterial nanopowder (AgDANP) for 3D printing applications. Silver nanoparticles possess strong bactericidal characteristics and have proven not accountable for microbial resistance.^[22] Hence, they evaluated the potential of the PA 12/AgDANP. The addition of 2.0 wt% of AgDANP showed significantly higher antibacterial properties compared to other nanocomposites.^[15] This development presents the potential application of PA 12 membranes, fabricated through selective laser sintering (SLS) and incorporated with AgDANP, for use in wound dressings, which are typically designed to exhibit bactericidal properties.^[22]

PA 12 is currently known to replace materials such as acrylonitrile butadiene styrene, polylactic acid, and polyethylene terephthalate glycol in the AM of orthoses because of the high thermal, mechanical, and fatigue strength using Multi Jet Fusion (MJF) and SLS technologies. PA 12 also quickly absorbs moisture from the environment, is biocompatible according to ISO 10993-1, and does not trigger allergic reactions or any immune response in most individuals.^[17,28] Another highlighted feature is the ability for polishing, dyeing, powder coating, and many more possibilities for finishing parts as aesthetics is a major concern for orthosis. Zakręcki et al.^[17] also revealed the possibility of producing a lightweight and openwork structure for orthosis, which significantly reduces the expenses, production time, and weight. On the other hand, MJF techniques offer a notable benefit over other 3D printing methods, as the geometry components can be created in any orientation without including other materials. However, the absence of resistance to microbial is regarded as a disadvantage and dyeing PA 12 is more challenging due to its chemical composition.^[28]