Methacrylate-based materials are often used in bone cement and dental resins. However, they have high failure rates, as they suffer damage within ten years, affecting the patient’s quality of life and increasing healthcare costs.
Study: Biocompatible nanocapsules for self-healing dental resins and bone cements. Image credit: Alex Mit/Shutterstock.com
Although replacing methacrylate-based materials with self-healing resins and bone cement could increase lifespan, reduce costs, and improve patient outcomes, the practical applicability of these materials is limited due to their low efficacy and toxicity. A paper published in the journal ACS Omega addressed this problem by developing a self-healing system based on dual nanocapsules.
Two polyurethane (PU) shell-based nanocapsules were synthesized: an initiator capsule containing benzoyl peroxide and butylated hydroxytoluene and a monomer capsule containing triethylene glycol dimethacrylate.
Resins with these nanocapsules were tested under tension to failure, followed by bonding of the fractured surfaces. 33% of the samples showed self-healing behavior and could be reloaded for stress testing. The capsules and their components were biocompatible with Caco-2 cell lines, suggesting an in vivo tolerance of the prepared nanocapsules.
Nanocapsules as self-healing materials
Self-healing materials, when damaged by thermal, mechanical and ballistic effects, can heal and restore the materials to their original properties. Few materials inherently have this self-healing capability, which is a valuable feature in system design as it effectively extends use over the product’s lifetime and has desirable economic and human safety attributes.
These self-healing materials could be useful in methacrylate-based systems, including dental resins and bone cement. Aseptic loosening of bone cement through fissure formation can lead to inflammation and bone resorption, requiring expensive surgical intervention. Although modern dental resins avoid any environmental and health effects with mercury, their poor durability causing damage to implants within ten years, has increased the cost of dental care.
Nanocapsules are hollow sphere structures with submicrometer dimensions. These nanocapsules can accommodate large amounts of guest molecules within their hollow central domain. These materials could be useful in applications in the fields of biological chemistry, synthesis and catalysis.
Polymeric nanocapsules have already been proposed with a multitude of applications, such as confined reaction vessels, drug carriers, protective shells for cells or enzymes, transfection vectors in gene therapy, carrier systems in heterogeneous catalysis, dye dispersants or as materials for the removal of pollutants. waste.
Methacrylate-based nanocapsules are easy to implement for self-healing properties in both dental resins and bone cement due to their filler particles that improve the mechanical properties of the material. Initially, the nanocapsules simply act as additional filler. However, when a crack propagates through the material, it ruptures and releases components into the crack through capillary action that later polymerize to cure the matrix.
Biocompatible nanocapsules with self-healing capacity
Nanocapsules were hypothesized to undergo a robust self-healing process with less impact on mechanical properties than larger particles. Thus, the present work aimed to investigate single and double nanocapsule systems based on PU and non-toxic components.
The impact of the prepared single and double nanocapsules on the self-healing process of methacrylate resins was determined by the synthesis of PU nanocapsules, which encapsulate the initiator or the monomer. In addition, mechanical testing and biocompatibility analysis determined the viability of the system as a self-healing additive for bone cement and dental resins.
The monomer used here was TEGDMA, with a long shelf life and rapid polymerization ability. The healing liquid was expected to have a low viscosity to flow through resin cracks and fill it. Therefore, TEGDMA was previously used as a dental monomer.
Here, the use of butylated hydroxytoluene (BHT) together with benzyl peroxide (BPO) prevented the formation of free radicals before their release from the capsule. Thus, the initiator component based on BPO and BHT increased the stability of the self-healing system based on dual capsules.
The fracture of nanocapsules was an important finding of the present work, as their rupture was the basis of the self-healing process. While too thick a shell did not allow the capsule to break, too thin a shell resulted in fragile nanocapsules.
Conclusion
In general, the TEGDMA monomer encapsulating the PU nanocapsule was embedded in an epoxy resin. These embedded resins were compared to their blank counterparts to determine the effects of monomer nanocapsules on the mechanical properties of the resin.
Comparison of the elastic modulus, yield stress, ultimate tensile stress, and stress at fracture indicated that the resin without monomer capsules was stronger than the resin with monomer capsules. The monomer nanocapsules cracked during resin fracture, demonstrating the self-healing effect of the resin nanocapsules.
Furthermore, the premature breakdown of the resins in the gastrointestinal tract did not cause any harmful effect on the patient, suggesting the biocompatibility of the developed self-healing system. In addition, a small degree of self-healing ability was observed in the resins with monomer nanocapsules, unencapsulated BPO, and the resins with monomer nanocapsules and initiator capsules.
reference
Menikheim, S et al. (2022). Biocompatible nanocapsules for self-healing dental resins and bone cements. ACS Omega https://pubs.acs.org/doi/10.1021/acsomega.2c02080
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