The aging behavior of degradable plastic polylactic acid under the interaction of environmental factors.

Microplastics leaching from aging biodegradable plastics pose potential environmental threats. This study used response surface methodology (RSM) to investigate the impact of temperature, light, and humidity on the aging characteristics of polylactic acid (PLA). Key evaluation metrics included the C/O ratio, functional groups, crystallinity, surface topography, and mechanical properties. Humidity was discovered to have the greatest effect on the ageing of PLA, followed by light and temperature. The interactions between temperature and light, as well as humidity and sunlight, significantly impact the aging of PLA. XPS analysis revealed PLA underwent aging due to the cleavage of the ester bond (O-C=O), resulting in the addition of C=O and C-O. The aging process of PLA was characterized by alterations in surface morphology and augmentation in crystallinity, resulting in a decline in both tensile strength and elongation. These findings might offer insights into the aging behavior of degradable plastics under diverse environmental conditions.

Characteristics of dissolved organic matter composition in biochar: Effects of feedstocks and pyrolysis temperatures.

Biochar has widely used in soil pollution remediation due to its advantages of high efficiency and environmental sustainability. Dissolved organic matter (DOM) released by biochar plays a non-negligible role in the migration and transformation of pollutants in environment, and its composition was regarded as main impact factor. In this study, 28 biochar were investigated to detect the effect of pyrolysis temperature and feedstock on DOM content and components. Results showed that the content of DOM released from biochar at low pyrolysis temperatures (300-400 ℃) was higher than that from high pyrolysis temperatures (500-600 ℃). In addition, the specific UV-Visible absorbance at 254 nm (SUVA254) results expressed that DOM from peanut shell biochar (PSBC), rice husk biochar (RHBC) and bamboo biochar (BBC) had higher humification at high temperatures. Moreover, one fulvic acid-like (C2) and two humic acid-like (C1, C3) substances were main fluorescent components of biochar-derived DOM identified by parallel factor analysis based on excitation emission matrices fluorescence spectroscopies (EEM-PARAFAC). With the increase of pyrolysis temperature, humic acid substances content gradually decreased. The correlation analysis results revealed that pyrolysis temperatures and O/C, H/C, DOM content, the biological index (BIX), humification index (HIX), C1% and C3% was negatively correlated (p < 0.001). Thus, the pyrolysis temperatures take important roles in composition of DOM released from biochar, and this research would provide a reference for the application of biochar in the environment.

Studies on competitive adsorption characteristics of bisphenol A and 17α-ethinylestradiol on thermoplastic polyurethane by site energy distribution theory.

Compound pollution of microplastics and estrogens is a growing ecotoxicological problem in aquatic environments. The adsorption isothermal properties of bisphenol A (BPA) and 17α-ethinyl estradiol (EE2) on polyamide (TPU) in monosolute and bisolute systems were studied. Under the same adsorption concentration (1-4 mg L-1), EE2 had a greater adsorption capacity than BPA in the monsolute system. Compared to the energy distribution features of the adsorption sites of EE2 and BPA, the BPA adsorption sites were located in the higher energy area and were more evenly distributed than those of EE2, while the quantity of BPA adsorption sites was less than that of EE2. In the bisolute system, the average site energy, site energy inhomogeneity, and adsorption site numbers of BPA increased by 1.674, -17.166, and 16.793%, respectively. In comparison, the average site energy, site energy inhomogeneity, and adsorption sites numbers of EE2 increased by 2.267, 4.416, and 8.585%, respectively. The results showed that BPA and EE2 had a cooperative effect on the competitive adsorption of TPU. XPS analysis showed that BPA and EE2 had electron transfer on TPU, although the chemisorption effects and hydrogen bonds between BPA and TPU were more significant. Comparing the changes in the relative functional group content of TPU in monosolute and bisolute systems, BPA and EE2 were synergistically absorbed on TPU. This study can provide a theoretical reference for the study of competitive adsorption between coexisting organic pollutants.

The surface degradation and release of microplastics from plastic films studied by UV radiation and mechanical abrasion.

During service or on discarding in the environment, solar ultraviolet radiation (UVR) and mechanical abrasion (MA) often act on plastic surface in combination, which cause the surface of plastics deterioration and micro- and nano- plastics release. Here, we examined how the set conditions (UVR, MA and UVR+MA (i.e., UVR combined with MA)) and polymer composition affected plastic degradation and microplastics (MPs) release. The surface degradation process and release of MPs of two types of plastic films (polyethylene (PE) and thermoplastic polyurethane (TPU)) under the action of UVR, MA and UVR+MA were analyzed and compared. The main results are as follow: First, the surface change of PE and TPU films by UVR+MA was observed more prominently than by UVR and MA. UVR+MA resulted in the accelerated surface degradation compared to UVR and MA. A large number of MPs were released from both PE and TPU films and significant differences were observed between UVR, MA and UVR+MA conditions. The UVR+MA treatment led to the generation of the largest amount of MPs with a smallest particle size, followed by MA and UVR. Second, plastics with different compositions exhibited different levels of resistance to UVR and MA. PE films released more MPs than TPU under the three set conditions. Finally, optical microscopy provided a direct and non-invasive method to assess the plastics degradation and the observed change in relative transmittance as a function of exposure time could be fitted linearly in some circumstances, which can be used to quantify the release of MPs. This study provided a basis for better understanding the degradation mechanisms of plastics surface and the relationship with MPs release during use and into the environment.

Effect of humic acid on Se and Fe transformations in soil during waterlogged incubation.

Humic acid (HA) serves as electron donor and acceptor in the biogeochemical cycle of Fe and Se in soil. In anoxic condition, a series of redox reactions occur, including reductive dissolution of Fe oxides, decomposition of organic matters, and transformation of trace elements. Thus, this study demonstrates the effect of HA on Se and Fe transformations in soil during waterlogged incubation. Soils were incubated under anoxic condition for 56 days, and pH, redox potential (Eh), and Fe and Se concentrations were measured at specific reaction times (days 2, 4, 8, 15, 28, and 56 of incubation). Moreover, sequential extraction and X-ray photoelectron spectroscopy (XPS) were used to obtain Se and Fe transformations, respectively. High resolution transmission electron microscopy (HR-TEM) was used to observe the morphology properties of soil. Results indicated that 4% HA addition decreased the pH and inhibited Eh decline continuously, and HA addition inhibited the Fe and Se release from soil. The Se concentration in soil solution without and with 4% HA addition at the day 15 of incubation were 1.05 mg L-1 and 0.30 mg L-1, respectively. Moreover, the residual Se fraction in soil with HA addition was evidently more than that in soil without HA addition. XPS of Se3d and Fe2p revealed that the binding energy of the main peak shifted to low values and the peak shape varied with the increase in HA addition. XPS2p3/2 and HR-TEM data indicated that the surface structure of Fe oxides in soil varied with the variations in anoxic incubation time and HA addition amount. HA addition would negatively influence Se and Fe release in soil solution and then reduce their bioavailability. This study aids in understanding the environmental behavior changes of Se and Fe when high HA concentrations enter the soils, especially wetland or paddy soil.

In vitro cytocompatibility evaluation of MGF-Ct24E chemically grafted and physically blended with maleic anhydride modified poly(D, L-lactic acid).

As a growth repair factor, mechano-growth factor (MGF) and its 24 amino acid peptide analogs corresponding to the unique C-terminal E-domain (MGF-Ct24E) positively regulate bone regeneration. MGF-Ct24E was introduced into the poly(D, L-lactic acid) (PDLLA) to improve bone regeneration in our previous study. MGF-Ct24E-grafted PDLLA was chemically characterized and showed potential as a biofunctional polymer. In this study, we evaluated the cytocompatibility of MGF-Ct24E chemically grafted and physically blended with maleic anhydride modified PDLLA, relative to maleic anhydride modified PDLLA (MPLA) as the control. The surface properties of these three polymer films were characterized with scanning electron microscopy and X-ray photoelectron spectroscopy. Rat calvarial osteoblasts were seeded on the three polymer films, and cell adhesion, spreading, and proliferation were assessed with an inverted microscope, laser scanning confocal microscope, and a cell counting kit-8, respectively. The alkaline phosphatase activity and extracellular calcium production were exploited to characterize the differentiation and mineralization of rat calvarial osteoblasts on various polymer films. The results revealed that compared with MPLA, MGF-Ct24E-MPLA, and MGF-Ct24E/MPLA blends promoted adhesion, spreading, proliferation, and the later differentiation and mineralization process of rat calvarial osteoblasts. In addition, the positive effect of MGF-Ct24E-MPLA on rat calvarial osteoblasts was maintained longer than the MGF-Ct24E/MPLA blends. In conclusion, MGF-Ct24E-MPLA synthesized chemically might be a promising biomaterial for bone tissue engineering.

Synthesis, characterization, and biocompatibility of a novel biomimetic material based on MGF-Ct24E modified poly(D, L-lactic acid).

Mechano-growth factor (MGF) is an alternative splicing variant of Insulin-like growth factor I. MGF and its 24 amino acid peptide analog corresponding to the unique C-terminal E-domain (MGF-Ct24E) are the positive regulator for tissue regenesis in bone. A novel biomimetic poly(D, L-lactic acid) (PDLLA) modification was designed and synthesized based on MGF-Ct24E grafted maleic anhydride modified PDLLA (MPLA). MGF-Ct24Es were grafted into the side chain of MPLA via a stable covalent amide bond using 1-ethyl-3-(3-dimethyllaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide as the condensing agent to produce biomimetic MPLA materials (MGF-Ct24E-MPLA). Fourier transform infrared spectrometry, amino acid analyzer, and elementary analysis were used to characterize the MGF-Ct24E-MPLA. The hydrophilicity of MGF-Ct24E-MPLA was evaluated by means of the water-uptake ratios and static water contact angle. Data revealed that the grafting efficiency of MGF-Ct24E was about 29.9%. MGF-Ct24E-MPLA had better hydrophilicity than PDLLA and MPLA. The osteoblasts behavior of proliferation, differentiation, and mineralization on PDLLA, MPLA, and MGF-Ct24E-MPLA films was investigated and the results indicated that the introduction of MGF-Ct24E could improve osteoblasts proliferation, mineralization, and delay differentiation. The MGF-Ct24E modified MPLA with higher bioactivity may have potential application for bone tissue engineering.

The nuclear localization of MGF receptor in osteoblasts under mechanical stimulation.

Mechano-growth factor (MGF) has emerged as an important mechanosensitive player in bone repair, but understanding of MGF function is hampered by the fact that MGF receptor and the underlying pathways remain unknown. In this study, fluorescein isothiocyanate (FITC)-labeled MGF-Ct24E (FITC-MGF) was used to determine the subcellular localization of MGF receptor in osteoblasts. After the primary osteoblasts were exposed to stretch with the strain at 10 %, and/or loaded with 50 ng/ml exogenous MGF-Ct24E, cells were incubated with the different concentrations of FITC-MGF (0.01, 0.1, and 1 mg/ml) followed by flow cytometry and laser scanning confocal microscope analysis. Our results showed that the fluorescence intensity and cell population internalizing FITC-MGF increased with the concentration of FITC-MGF. And all the cells were labeled with fluorescence at 1 mg/ml. Notably, FITC-MGF had nuclear localization when osteoblasts were exposed to stretch and/or 50 ng/ml MGF-Ct24E added, compared to the evident cytoplasmic localization in the static culture group. The nuclear localization of FITC-MGF in response to mechanical loading was found to associate with high expression of proliferating cell nuclear antigen, suggesting MGF and its receptor could serve as potential messengers that replay information in nuclei to control cell proliferation.

An approach to architecture 3D scaffold with interconnective microchannel networks inducing angiogenesis for tissue engineering.

The angiogenesis of 3D scaffold is one of the major current limitations in clinical practice tissue engineering. The new strategy of construction 3D scaffold with microchannel circulation network may improve angiogenesis. In this study, 3D poly(D: ,L: -lactic acid) scaffolds with controllable microchannel structures were fabricated using sacrificial sugar structures. Melt drawing sugar-fiber network produced by a modified filament spiral winding method was used to form the microchannel with adjustable diameters and porosity. This fabrication process was rapid, inexpensive, and highly scalable. The porosity, microchannel diameter, interconnectivity and surface topographies of the scaffold were characterized by scanning electron microscopy. Mechanical properties were evaluated by compression tests. The mean porosity values of the scaffolds were in the 65-78% and the scaffold exhibited microchannel structure with diameter in the 100-200 µm range. The results showed that the scaffolds exhibited an adequate porosity, interconnective microchannel network, and mechanical properties. The cell culture studies with endothelial cells (ECs) demonstrated that the scaffold allowed cells to proliferate and penetrate into the volume of the entire scaffold. Overall, these findings suggest that the fabrication process offers significant advantages and flexibility in generating a variety of non-cytotoxic tissue engineering scaffolds with controllable distributions of porosity and physical properties that could provide the necessary physical cues for ECs and further improve angiogenesis for tissue engineering.

A novel mechanical loading model for studying the distributions of strain and mechano-growth factor expression.

Mechano-growth factor (MGF), an insulin-like growth factor-I (IGF-I) splice variant, often serves as an important local tissue repair factor in response to the mechanical environment. However, there is no model for exhibiting the MGF expression in a series of strain distribution up to now. In this study, a novel mechanical loading model containing different stresses and strains simultaneously was developed to examine the MGF expression. The strain distributions were predicted by finite element modeling. The MC3T3-E1 cells on a silicone membrane with a central circular hole were exposed to a variable strain environment through stretching. The finite element analysis showed that, when the strain reached the magnitude of 10%, the strain concentration near the circular hole displayed along with the vertical stretch direction, while the minimum strain appeared in the parallel stretch direction. Furthermore, the results showed that MGF expression decreased gradually from high to low strain regions by immunocytochemistry. Meanwhile, the proliferation of osteoblasts increased significantly in the high strain region. In conclusion, this mechanical loading model can present the different distributions of the strain of osteoblasts in vitro. MGF expression and osteoblast proliferation have a high correlation with the levels of strain.