Assessment of the Defatting Efficacy of Mechanical and Chemical Treatment for Allograft Cancellous Bone and Its Effects on Biomechanics Properties of Bone

Effect of gamma and Ultraviolet-C sterilization on BMP-7 level of indigenously prepared demineralized freeze-dried bone allograft

The presence of bone morphogenetic proteins in demineralized freeze-dried bone allograft (DFDBA) are responsible for developing hard tissues in intraosseous defects. The most common mode of sterilization of bone allografts, i.e., Gamma rays, have dramatic effects on the structural and biological properties of DFDBA, leading to loss of BMPs. Ultraviolet-C radiation is a newer approach to sterilize biodegradable scaffolds, which is simple to use and ensures efficient sterilization. However, UV-C radiation has not yet been effectively studied to sterilize bone allografts. This study aimed to compare and evaluate the effectiveness of Gamma and Ultraviolet-C rays in sterilizing indigenously prepared DFDBA and assess their effect on the quantity of BMP-7 present in the allograft. DFDBA samples from non-irradiated, gamma irradiated, and UV-C irradiated groups were tested for BMP-7 level and samples sterilized with gamma and UV-C rays were analysed for sterility testing. The estimated mean BMP-7 level was highest in non-irradiated DFDBA samples, followed by UV-C irradiated, and the lowest in gamma irradiated samples. Our study concluded that UV-C rays effectively sterilized DFDBA as indicated by negative sterility test and comprised lesser degradation of BMP-7 than gamma irradiation.

High-Speed Centrifugation Efficiently Removes Immunogenic Elements in Osteochondral Allografts

OBJECTIVES

The current clinical pulse lavage technique for flushing fresh osteochondral allografts (OCAs) to remove immunogenic elements from the subchondral bone is ineffective. This study aimed to identify the optimal method for removing immunogenic elements from OCAs.

METHODS

We examined five methods for the physical removal of immunogenic elements from OCAs from the femoral condyle of porcine knees. We distributed the OCAs randomly into the following seven groups: (1) control, (2) saline, (3) ultrasound, (4) vortex vibration (VV), (5) low-pulse lavage (LPL), (6) high-pulse lavage (HPL), and (7) high-speed centrifugation (HSC). OCAs were evaluated using weight measurement, micro-computed tomography (micro-CT), macroscopic and histological evaluation, DNA quantification, and chondrocyte activity testing. Additionally, the subchondral bone was zoned to assess the bone marrow and nucleated cell contents. One-way ANOVA and paired two-tailed Student's t-test are used for statistical analysis.

RESULTS

Histological evaluation and DNA quantification showed no significant reduction in marrow elements compared to the control group after the OCAs were treated with saline, ultrasound, or VV treatments; however, there was a significant reduction in marrow elements after LPL, HPL, and HSC treatments. Furthermore, HSC more effectively reduced the marrow elements of OCAs in the middle and deep zones compared with LPL (p < 0.0001) and HPL (p < 0.0001). Macroscopic evaluation revealed a significant reduction in blood, lipid, and marrow elements in the subchondral bone after HSC. Micro-CT, histological analyses, and chondrocyte viability results showed that HSC did not damage the subchondral bone and cartilage; however, LPL and HPL may damage the subchondral bone.

CONCLUSION

HSC may play an important role in decreasing immunogenicity and therefore potentially increasing the success of OCA transplantation.

Bone Allograft Acid Lysates Change the Genetic Signature of Gingival Fibroblasts

Bone allografts are widely used as osteoconductive support to guide bone regrowth. Bone allografts are more than a scaffold for the immigrating cells as they maintain some bioactivity of the original bone matrix. Yet, it remains unclear how immigrating cells respond to bone allografts. To this end, we have evaluated the response of mesenchymal cells exposed to acid lysates of bone allografts (ALBA). RNAseq revealed that ALBA has a strong impact on the genetic signature of gingival fibroblasts, indicated by the increased expression of IL11, AREG, C11orf96, STC1, and GK-as confirmed by RT-PCR, and for IL11 and STC1 by immunoassays. Considering that transforming growth factor-β (TGF-β) is stored in the bone matrix and may have caused the expression changes, we performed a proteomics analysis, TGF-β immunoassay, and smad2/3 nuclear translocation. ALBA neither showed detectable TGF-β nor was the lysate able to induce smad2/3 translocation. Nevertheless, the TGF-β receptor type I kinase inhibitor SB431542 significantly decreased the expression of IL11, AREG, and C11orf96, suggesting that other agonists than TGF-β are responsible for the robust cell response. The findings suggest that IL11, AREG, and C11orf96 expression in mesenchymal cells can serve as a bioassay reflecting the bioactivity of the bone allografts.

Effects of demineralization mode and particle size of allogeneic bone powder on its physical and chemical properties

At present, the commonly used allogeneic bone powder in the clinic can be divided into nondemineralized bone matrix and demineralized bone matrix (DBM). Commonly used demineralizers include acids and ethylene diamine tetraacetic acid (EDTA). There may be some diversities between them. Also, the size of the bone particle can affects its cell compatibility and osteogenic ability. We produced different particle sizes i.e., < 75, 75-100, 100-315, 315-450, 450-650, and 650-1000 μm, and treated in three ways (nondemineralized, demineralized by EDTA, and demineralized by HCl). Scanning electron microscopy showed that the surface of the samples in each group was relatively smooth without obvious differences. The results of specific surface area and porosity analysis showed that they were significantly higher in demineralized bone powder than in nondemineralized bone powder, however, there was no significant difference between the two decalcification methods. The content of hydroxyproline in nondemineralized bone powder and EDTA-demineralized bone powder had no statistical difference, while HCl-demineralization had statistical significance compared with the former two, and the content increased with the decrease of particle size. The protein and BMP-2 extracted from HCl demineralized bone powder were significantly higher than that from nondemineralized bone powder and EDTA demineralized bone powder, and there were differences among different particle sizes. These results suggested the importance of demineralization mode and particle size of the allogenic bone powder and provided guidance for the choice of the most appropriate particle size and demineralization mode to be used in tissue bioengineering.

Open-source perfusion system for medium-scale fabrication of demineralized bone matrix chip grafts

Demineralized bone matrix (DBM) is considered one of the most reliable bone tissue grafts for regular surgical use, as it provides a scaffold that is structurally like native bone, and that enhances bone regeneration. However, commercially available DBM products are not suited for surgical restitutions of large bones. Therefore, each Tissue Bank is urged to implement their own demineralization protocol, which usually does not meet the high demand for bone grafting. In this project, we developed an open source system for medium-scale manufacturing of DBM grafts from human cadaveric donors to automate the demineralization protocol and improve its reproducibility. The device consists in (1) unidirectional flow reaction chamber, where the demineralization protocol takes place; (2) automated syringe pump, which controls the reagent́s inlet and vacuum; and (3) reagent dispenser, for the management of the reagents need for the demineralization protocol. Validation of the device included histological analysis, DNA quantification temperature regulation, electrochemiluminescence and colorimetric protocols, followed by the optimization of physicochemical parameters based on Response Surface Methodology. The results showed values of residual lipids and calcium within standardized ranges, and the maintenance of the structural integrity of the DBM, demonstrating the capacity of the system to support the proposed demineralization protocol.

Effects of Allogeneic Bone Substitute Configurations on Cell Adhesion Process In Vitro

OBJECTIVE

To explore the potential effect of three allogenic bone substitute configurations on the viability, adhesion, and spreading of osteoblasts in vitro.

METHODS

Freeze-dried cortical bone were ground and fractions were divided into three groups with different sizes and shapes, defined as bone fiber (0.1 mm × 0.1 mm × 3 mm), bone powder (0.45-0.9 mm), and bone granule group (3-6 mm). MC3T3-E1 cells were divided and co-cultured within groups to induce cell adhesion. The configuration of allogenic bone was captured by scanning electron microscopy and confocal laser scanning microscopy, and substrate roughness values were quantified. Cell adhesion rate was assessed using the hemocyte counting method, cell viability was determined by CCK-8 assay and live/dead staining, and cell morphology was visualized by Phalloidin and DAPI, and the mRNA expression of adhesion-related gene (vinculin) of different substitutes were determined with quantitative real-time polymerase chain reaction.

RESULTS

The roughness values of bone fiber, bone powder, and bone granule group were 1.878 μm (1.578-2.415 μm), 5.066 μm (3.891-6.162 μm), and 0.860 μm (0.801-1.452 μm), respectively (bone powder group compared with bone granule group, H = 18.015, P < 0.001). Similar OD values of all groups in CCK-8 assay indicated good biocompatibility of these substitutes (bone fiber, 0.201 ± 0.004; bone powder, 0.206 ± 0.008; bone granule group, 0.197 ± 0.006; and the control group, 0.202 ± 0.016, F = 0.7152, P > 0.05). In addition, representative cell adhesion rates at 24 h showed significantly lower cell adhesion rate in bone fiber group (20.3 ± 1.6%) compared to bone powder (29.3 ± 4.4%) and bone granule group (27.3 ± 3.2%) (F = 10.51，P = 0.009 and P = 0.034, respectively), but there was no significant difference between the latter two groups (P > 0.05). Interestingly, the expression of vinculin mRNA steadily decreased in a time-dependent manner. The vinculin expression reached its peak at 6 h in each group, and the vinculin levels in bone fiber, bone powder, and bone granule group were 2.119 ± 0.052, 3.842 ± 0.108, and 3.585 ± 0.068 times higher than those in the control group, respectively (F = 733.643, all P < 0.001). Meanwhile, there was a significant difference in the expression of target gene between bone powder and bone granule group (P = 0.006).

CONCLUSION

All allogenic bone substitutes presented an excellent cell viability. Moreover, bone powder and bone granule group were more likely to promote cell adhesion and spreading compared to bone fiber group.

Selected mechanical properties of human cancellous bone subjected to different treatments: short-term immersion in physiological saline and acetone treatment with subsequent immersion in physiological saline

Background

Physiological saline (0.9% NaCl) and acetone are extensively used for storage (as well as hydration) and removal of bone marrow, respectively, of cancellous bone during preparation and mechanical testing. Our study aimed to investigate the mechanical properties of cancellous bone subjected to short-term immersion in saline and acetone treatment with subsequent immersion in saline.

Methods

Cylindrical samples (Ø6 × 12 mm) were harvested from three positions (left, middle, and right) of 1 thoracic vertebral body, 19 lumbar vertebral bodies, and 5 sacral bones, as well as from 9 femoral heads. All samples were divided into two groups according to the different treatments, (i) samples from the left and middle sides were immersed in saline at 4℃ for 43 h (saline-immersed group, n = 48); (ii) samples from the respective right side were treated with a combination of acetone and ultrasonic bath (4 h), air-dried at room temperature (21℃, 15 h), and then immersed in saline at room temperature (21℃, 24 h) (acetone and saline-treated group, n = 38). All samples were subjected, both before and after treatment, to a non-destructive compression test with a strain of 0.45%, and finally destructive tests with a strain of 50%. Actual density (ρ_act), initial modulus (E₀), maximum stress (σ_max), energy absorption (W), and plateau stress (σ_p) were calculated as evaluation indicators.

Results

Based on visual observation, a combination of acetone and ultrasonic bath for 4 h failed to completely remove bone marrow from cancellous bone samples. The mean values of ρ_act, σ_max, W, and σ_p were significantly higher in the femoral head than in the spine. There was no significant difference in E₀ between non-treated and saline-immersed samples (non-treated 63.98 ± 20.23 vs. saline-immersed 66.29 ± 20.61, p = 0.132). The average E₀ of acetone and saline-treated samples was significantly higher than that of non-treated ones (non-treated 62.17 ± 21.08 vs. acetone and saline-treated 74.97 ± 23.98, p = 0.043).

Conclusion

Short-term storage in physiological saline is an appropriate choice and has no effect on the E₀ of cancellous bone. Treatment of cancellous bone with acetone resulted in changes in mechanical properties that could not be reversed by subsequent immersion in physiological saline.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-022-03265-4.

Paeonol Disrupts the Integrity of Aspergillus flavus Cell Walls via Releasing Surface Proteins, Inhibiting the Biosynthesis of β-1,3-Glucan and Promoting the Degradation of Chitin, and an Identification of Cell Surface Proteins

Paeonol can effectively inhibit Aspergillus flavus (A. flavus) via damaging cell walls. In this work, paeonol treatment remarkably destroyed both the outer amorphous layer and the inner fibrous layer of cell walls. Furthermore, FT-IR and XPS characterization showed that OH functional groups were altered and proteins in the outer layer were released. According to proteomic analysis, 605 proteins have been identified and annotated. The activities of β-1,3-glucan synthase and chitinase were prohibited and promoted, respectively, by paeonol treatment, however, the activities of β-1,3-glucanase and chitin synthase were not influenced. QRT-PCR results suggested that FKSP, CHIIII, and CHIV genes might be the antifungal targets of paeonol. In addition, paeonol can effectively restrain the pathogenicity of A. flavus on peanut butter. This study provided a new elucidation on the mode of action of paeonol against cell walls of A. flavus, facilitating the application of paeonol in the preservation of agricultural products.

Assessment of the efficiency of different chemical treatments and ultrasonic cleaning for defatting of cancellous bone samples

Our study aimed to asses the defatting efficiency of different methods, which are commonly used and easily available in the laboratory in order to find a method that is effective, convenient, safe, and economical. Cylindrical cancellous bone specimens were obtained from fresh-frozen human cadaver femoral condyles, cut into multiple small specimens (Ø8 × 2 mm), and assigned to two groups that were treated with either chemical solvent soaking (Solvent group) or ultrasonic cleaning (Ultrasound group). Each group was divided into several subgroups based on different treatments. Digital photographs were taken of each specimen. The difference of material density (Δρ_b), apparent density (Δρ_app), and porosity (ΔP) before and after treatment were used as evaluation indicators. For the solvent group, in Δρ_b, only the combination of 99% ethanol and detergent solution showed a significant difference before and after treatment (P = 0.00). There was no significant difference in ΔP among acetone, the mixture of 99% ethanol and acetone, and the combination of 99% ethanol and detergent solution (P = 0.93). For the ultrasound group, the median of all subgroups in Δρ_app and ΔP were all lower than the solvent group. The combination of 99% ethanol and detergent solution (v/v = 1:20), as well as the mixture of 99% ethanol and acetone (v/v = 1:1), seem to be the optimal defatting methods for 2 mm thick cancellous bone slices due to their effectiveness, availability, low-cost and safety. Chemical soaking for 24 h is more effective than ultrasonic cleaning with 99% ethanol or acetone for 20 or 40 min.

o-Vanillin, a promising antifungal agent, inhibits Aspergillus flavus by disrupting the integrity of cell walls and cell membranes

o-Vanillin is a natural product that has been widely applied in the food and pharmaceutical industries. In this study, we determined that o-vanillin can strongly inhibit the growth of Aspergillus flavus mycelia. However, the inhibition mechanism of o-vanillin is still elusive. The ultrastructural morphology of mycelia was injured, and the cell walls were destroyed. The OH functional groups on cell walls were altered, and the content of protein in mycelial cell walls was reduced by o-vanillin. The content of β-1,3-glucan in cell walls was significantly (P < 0.05) reduced by o-vanillin in a dose-dependent manner, while chitin was not markedly affected. Moreover, o-vanillin led to an increase in the permeability of cell membranes. o-Vanillin also exhibited a promising antifungal effect on contaminated corn kernels. Therefore, o-vanillin inhibited the growth of mycelia by disrupting the integrity of cell walls and cell membranes. This study not only sheds light on the antifungal mechanism of o-vanillin but also indicates that it is a promising agent for the control of A. flavus infection. KEY POINTS: • o-Vanillin has strong inhibitory effects on A. flavus. • o-Vanillin destroyed the integrity of cell walls and cell membranes. • o-Vanillin could effectively inhibit the growth of A. flavus on corn kernels.