Machine learning-aided engineering of hydrolases for PET depolymerization.

Plastic waste poses an ecological challenge1-3 and enzymatic degradation offers one, potentially green and scalable, route for polyesters waste recycling4. Poly(ethylene terephthalate) (PET) accounts for 12% of global solid waste5, and a circular carbon economy for PET is theoretically attainable through rapid enzymatic depolymerization followed by repolymerization or conversion/valorization into other products6-10. Application of PET hydrolases, however, has been hampered by their lack of robustness to pH and temperature ranges, slow reaction rates and inability to directly use untreated postconsumer plastics11. Here, we use a structure-based, machine learning algorithm to engineer a robust and active PET hydrolase. Our mutant and scaffold combination (FAST-PETase: functional, active, stable and tolerant PETase) contains five mutations compared to wild-type PETase (N233K/R224Q/S121E from prediction and D186H/R280A from scaffold) and shows superior PET-hydrolytic activity relative to both wild-type and engineered alternatives12 between 30 and 50 °C and a range of pH levels. We demonstrate that untreated, postconsumer-PET from 51 different thermoformed products can all be almost completely degraded by FAST-PETase in 1 week. FAST-PETase can also depolymerize untreated, amorphous portions of a commercial water bottle and an entire thermally pretreated water bottle at 50 ºC. Finally, we demonstrate a closed-loop PET recycling process by using FAST-PETase and resynthesizing PET from the recovered monomers. Collectively, our results demonstrate a viable route for enzymatic plastic recycling at the industrial scale.

Porous TiO2 Nanotube Arrays for Drug Loading and Their Elution Sensing.

Porous TiO2 nanotube arrays have been attracting much attention as optical sensing layers and surface layers of dental implants because they are stable in acid and biocompatible. To use them as the optical sensing layers, TiO2 nanotube arrays with various structures were fabricated and obtained an optimized microstructure at 50 V, 50 min and 0.5 wt% of NH4F, 7.4 vol% deionized water in ethylene glycol. TiO2 nanotube arrays which had diameters of ~73.54 nm and lengths of ~3.39 µm showed the best sensing performance. A Ti implant was also anodized at 60 V for 4 hr in an ethylene glycol electrolyte and TiO2 nanotube arrays showed the pore diameter of 156.01 nm and the thickness of 6.87 µm. Recombinant human bone morphogenetic protein-2 (rhBMP-2), isobutylphenyl propionic acid, and sodium alendronate were loaded into the TiO2 nanotube arrays on the surface of the Ti implant. For elution of these drugs, optical thickness changes of 2.4 nm, 3.5 nm and 3.1 nm were respectively observed for about 2.2 hr, 3.6 hr and 3.1 hr. The TiO2 nanotube arrays were useful for drug loading and their elution interferometric sensing.

Effect of drug-loaded TiO2 nanotube arrays on osseointegration in an orthodontic miniscrew: an in-vivo pilot study.

Osseointegration was evaluated for the surface of miniscrews with TiO2 nanotube arrays containing drugs in this in-vivo study. The diameter and length of the TiO2 nanotube arrays were about 70 nm and 5 µm, respectively. Recombinant human bone morphogenetic protein-2 (rhBMP-2) or ibuprofen was loaded in the TiO2 nanotube arrays with 12 miniscrews. The 12 drug-loaded miniscrews, 6 miniscrews with no drug-loaded TiO2 nanotube arrays and 6 conventional miniscrews, were placed on the tibias of New Zealand white rabbits. Histological osseointegration was assessed 8 weeks after implantation by measuring the bone-to-implant contact (BIC) ratio. Ibuprofen-loaded miniscrews showed a significantly higher BIC of 71.6% over conventional miniscrews of 44.3% on average. The mean BIC ratios of rhBMP-2-loaded miniscrews and no drug-loaded miniscrews was 24.6% and 60.1%, respectively. Our results suggest that TiO2 nanotube arrays on the surface of miniscrews could be used as carriers of drugs, and loading ibuprofen in TiO2 nanotube arrays may improve osseointegration of miniscrews. However, the effect of rhBMP-2 loaded in TiO2 nanotube arrays on osseointegration of miniscrews was questionable in this pilot study.

Effects of Electrospinning Parameters on the Microstructure of PVP/TiO2 Nanofibers.

Titanium dioxide has excellent chemical, electrical, and optical properties, as well as good chemical stability. For that reason, it is widely used in many fields of study and industry, such as photocatalysts, organic solar cells, sensors, dental implants, and other applications. Many nanostructures of TiO2 have been reported, and electrospinning is an efficient practical technique that has a low cost and high efficiency. In various studies on improving performance, the researchers created nanofibers with suitable microstructures by changing various properties and the many process parameters that can be controlled. In this study, PVP/TiO2 nanofibers were fabricated by the electrospinning process. The diameters of the nanofibers were controlled by various parameters. To understand the effects on the diameter of the nanofibers, various process parameters were controlled: the molecular weight and concentration of the polymers, deionized water, applied voltage, fluid velocity, and concentration of titanium precursor. The average diameter of the PVP nanofibers was controlled in a range of 42.3 nm to 633.0 nm. The average diameter of the PVP/TiO2 nanofibers was also controlled in a range of 63.5 nm to 186.0 nm after heat treatment.

Effects of ibuprofen-loaded TiO2 nanotube dental implants in alloxan-induced diabetic rabbits.

PURPOSE: Some systemic conditions, especially diabetes mellitus (DM), adversely affect dental implant success. This study aimed to investigate the effects of ibuprofen-loaded TiO2 nanotube (ILTN) dental implants in alloxan-induced diabetic rabbits. METHODS: Twenty-six New Zealand white rabbits were treated with alloxan monohydrate to induce DM. At 2 weeks following DM induction, 3 types of implants (sandblasted, large-grit, and acid-etched [SLA], ILTN, and machined) were placed into the proximal tibia in the 10 rabbits that survived following DM induction. Each type of implant was fitted randomly in 1 of the holes (round-robin method). The animals were administered alizarin (at 3 weeks) and calcein (at 6 weeks) as fluorescent bone markers, and were sacrificed at 8 weeks for radiographic and histomorphometric analyses. RESULTS: TiO2 nanotube arrays of ~70 nm in diameter and ~17 µm in thickness were obtained, and ibuprofen was loaded into the TiO2 nanotube arrays. A total of 26 rabbits were treated with alloxan monohydrate and only 10 rabbits survived. The 10 surviving rabbits showed a blood glucose level of 300 mg/dL or higher, and the implants were placed in these diabetic rabbits. The implant stability quotient (ISQ) and bone-to-implant contact (BIC) values were significantly higher in the ILTN group (ISQ: 61.8, BIC: 41.3%) and SLA group (ISQ: 62.6, BIC: 46.3%) than in the machined group (ISQ: 53.4, BIC: 20.2%), but the difference in the BIC percentage between the SLA and ILTN groups was not statistically significant (P=0.628). However, the bone area percentage was significantly higher in the ILTN group (78.0%) than in the SLA group (52.1%; P=0.000). CONCLUSIONS: The ILTN dental implants showed better stability (ISQ) and BIC than the machined implants; however, these values were similar to the commercially used SLA implants in the 2-week diabetic rabbit model.