Experimental and theoretical investigation of the influence of post-curing on mixed mode fracture properties of 3d-printed polymer samples.

This study explores the mechanical properties and fracture characteristics of additively manufactured acrylonitrile butadiene styrene specimens, focusing on the impact of raster angle and post-process heat treatment. To this end, a large number of tensile and semi-circular bending samples with three distinct raster angles of 0/90°, 22/ - 68°, and 45/ - 45° were prepared and exposed to four types of heat treatments with different temperature and pressure conditions. Simultaneously, theoretical models of maximum tangential stress (MTS) and generalized MTS (GMTS) were developed to estimate the onset of specimen fracture under mixed-mode in-plane loading conditions. Recognizing the non-linear behavior within the stress-strain curve of tensile test samples, particularly in the annealed samples, an effort was undertaken to transform the original ductile material into a virtual brittle material through the application of the equivalent material concept (EMC). This approach serves the dual purpose of bypassing intricate and tedious elastoplastic analysis, while concurrently enhancing the precision of the GMTS criterion. The experimental findings have revealed that while the annealing process has a minimal effect on the yield strength, it considerably enhances energy absorption capacity, increases fracture toughness, and reduces the anisotropy. Additionally, the combined EMC-GMTS criterion has demonstrated its capability to predict the failure of the additively manufactured parts with an acceptable level of accuracy.

Assessment of Nano-Indentation Method in Mechanical Characterization of Heterogeneous Nanocomposite Materials Using Experimental and Computational Approaches.

This study investigates the capacity of the nano-indentation method in the mechanical characterization of a heterogeneous dental restorative nanocomposite using experimental and computational approaches. In this respect, Filtek Z350 XT was selected as a nano-particle reinforced polymer nanocomposite with a specific range of the particle size (50 nm to 4 µm), within the range of indenter contact area of the nano-indentation experiment. A Sufficient number of nano-indentation tests were performed in various locations of the nanocomposite to extract the hardness and elastic modulus properties. A hybrid computational-experimental approach was developed to examine the extracted properties by linking the internal behaviour and the global response of the nanocomposite. In the computational part, several representative models of the nanocomposite were created in a finite element environment to simulate the mechanism of elastic-plastic deformation of the nanocomposite under Berkovich indenter. Dispersed values of hardness and elastic modulus were obtained through the experiment with 26.8 and 48.5 percent average errors, respectively, in comparison to the nanocomposite properties, respectively. A disordered shape was predicted for plastic deformation of the equilateral indentation mark, representing the interaction of the particles and matrix, which caused the experiment results reflect the local behaviour of the nanocomposite instead of the real material properties.

To reduce the maximum stress and the stress shielding effect around a dental implant-bone interface using radial functionally graded biomaterials.

In a dental implant system, the value of stress and its distribution plays a pivotal role on the strength, durability and life of the implant-bone system. A typical implant consists of a Titanium core and a thin layer of biocompatible material such as the hydroxyapatite. This coating has a wide range of clinical applications in orthopedics and dentistry due to its biocompatibility and bioactivity characteristics. Low bonding strength and sudden variation of mechanical properties between the coating and the metallic layers are the main disadvantages of such common implants. To overcome these problems, a radial distributed functionally graded biomaterial (FGBM) was proposed in this paper and the effect of material property on the stress distribution around the dental implant-bone interface was studied. A three-dimensional finite element simulation was used to illustrate how the use of radial FGBM dental implant can reduce the maximum von Mises stress and, also the stress shielding effect in both the cortical and cancellous bones. The results, of course, give anybody an idea about optimized behaviors that can be achieved using such materials. The finite element solver was validated by familiar methods and the results were compared to previous works in the literature.

Formation of porous HPCL/LPCL/HA scaffolds with supercritical CO2 gas foaming method.

Scaffold is a 3D porous structure that is made of different materials, such as synthetic and natural polymers. It plays the role of a synthetic extracellular matrix and permits adhesion, proliferation and differentiation of the cells. Porosity and pore size are the important factors for any 3D scaffold used in bone tissue engineering. In this study, porous scaffolds were prepared by adding hydroxyapatite (HA) nanoparticles as filler to the polymeric matrix of polycaprolactone (PCL) blends with two different molecular weight by using supercritical CO2 (ScCO2) foaming method. The effect of different parameters such as CO2 pressure, ratios of the polymers and amount of the filler on the scaffold properties was investigated. The results showed that porosity increased with increment of pressure and decreased with increasing the ratio of the high molecular weight PCL to the low molecular weight PCL in the scaffolds and also HA content. Optimum condition for obtaining adequate porous scaffold of HPCL/LPCL/HA occurred at 140bar and 45°C. The physical and mechanical properties of the prepared scaffolds were characterized using DSC, XRD, FTIR, SEM, contact angle and compression test. By analyzing the results of these tests, optimum sample for cell culture was selected. The biocompatibility of the selected HPCL/LPCL/HA scaffold (HPCL/LPCL 60/40 containing 2.5% HA) was assessed in vitro by using human mesenchymal stem cells (hMSCs).

A new model for the artificial aorta blood vessels using double-sided radial functionally graded biomaterials.

Based on radial functionally graded biomaterials and inspired by the geometry of a real aorta blood vessel, a new model was proposed to fabricate the artificial blood vessels. A finite element analyzer is employed to reach the optimal and proper material properties while earlier, it was validated by two famous theories, i.e., the first shear deformation and the plane elasticity. First, the geometry of a real ascending aorta part was simulated and then solved under the axially varying blood pressure and other real and actual conditions. Since the construction of artificial blood vessels just similar to the natural one is impossible, it was tried to find the best substitutes for other materials. Due to the significant properties of functionally graded biomaterials in the reduction in sudden changes of stress and deformation, these types of materials were selected and studied. Two types of conventional single-sided and an efficient double-sided radial functionally graded vessel were proposed and simulated. The elastic behaviors of proposed vessels were obtained and compared to ones previously attained from the real vessel. The results show that all the desired behaviors cannot be achieved by using a conventional single-sided radial FG vessel. Instead and as a conjecture, a smart double-sided radial FG biomaterial is suggested. Fortunately, the proposed material can meet all the desired goals and satisfy all of the indices simultaneously.

Tissue engineering strategy using mesenchymal stem cell-based chitosan scafolds in growth plate surgery: a preliminary study in rabbits.

BACKGROUND: Growth plate injury in children could produce limb length discrepancy and angular deformity. Removal of damaged physis or bony bar and insertion of spacers produced variable results and for large defects in young children, the treatment is challenging. In this study, we used tissue-engineered mesenchymal stem cells (MSC-based chitosan scaffold) for restoration of the damaged physis. The usage of chitosan as a spacer was also investigated. MATERIALS AND METHODS: An experimental model of growth arrest was created by removing lateral 50% of distal femoral physis of fourteen 4-week-olds albino rabbits. The left side growth plate defects were filled with MSC-based chitosan scaffold in 10 and scaffold alone in 4 rabbits. For all the rabbits, right-side defects were left alone as the control limb. After 3 months, femoral bones were harvested and gross inspection and radiology for measurement of angulations were done; histological study for evaluation of regeneration of physis was also done. RESULTS: The hemiphyseal resection procedures were successful and all of the operated limbs showed angular deformities. There was a trend toward less angular deformity in cases in which more concentration of MSCs with chitosan scaffold was used. In cases of transfer of MSCs with concentration of less than 1.5 millions, mixed results were observed and angular deformities were not reduced. Transfer of chitosan alone yielded poor results. CONCLUSION: In this study, we have developed an in vitro construction of a transplantable tissue-engineered disk, using natural chitosan scaffold and MSCs. We investigated the efficacy of these disks for repairing the defect of growth plate cartilage at distal femoral physis. Our results showed that the beneficial effect of these cells on scaffold appeared in more concentration of cells. LEVEL OF EVIDENCE: Level III. Low power comparative study.

Effects of temperature change and beverage on mechanical and tribological properties of dental restorative composites.

The aim of this study was to investigate the effects of temperature change and immersion in two common beverages on the mechanical and tribological properties for three different types of dental restorative materials. Thermocycling procedure was performed for simulating temperature changes in oral conditions. Black tea and soft drink were considered for beverages. Universal composite, universal nanohybrid composite and universal nanofilled composite, were used as dental materials. The nanoindentation and nanoscratch experiments were utilized to determine the elastic modulus, hardness, plasticity index and wear resistance of the test specimens. The results showed that thermocycling and immersion in each beverage had different effects on the tested dental materials. The mechanical and tribological properties of nanohybrid composite and nanocomposite were less sensitive to temperature change and to immersion in beverages in comparison with those of the conventional dental composite.

Antioxidant Effects of Bone Marrow Mesenchymal Stem Cell against Carbon Tetrachloride-Induced Oxidative Damage in Rat Livers.

BACKGROUND: Liver fibrosis results from excessive accumulation of extracellular matrix, which affects liver function over time and leads to its failure. In the past, liver transplant was thought to be the only treatment for end-stage liver disease, but due to the shortage of proper donors other medical treatments have been taken into consideration. OBJECTIVE: To evaluate the therapeutic effects of bone marrow derived mesenchymal stem cells (BM-MSC) in CCl4 damaged rats. METHODS: Liver damage in adult male Wistar rats was induced with carbon tetrachloride (CCl4). The rats were divided into normal control group, receiving CCl4, and those receiving CCl4 + marrow derived-MSC. Human BM-MSC was isolated, cultured, and characterized. The rats were injected with xenograft MSCs into the hepatic lobes of the liver. In the eighth week, blood samples were taken from all groups. Histological examination and biochemical analyses were used to compare the morphological and functional liver regeneration among different groups. Measurement of lipid peroxidation and glutathione transferase activity was also performed. RESULTS: Histopathology and biochemical analyses indicated that local injection of human BM-MSCs was effective in treating liver failure in the rat model. Furthermore, oxidative stress was attenuated by increased level of GSH content after MSC transplantation. CONCLUSION: Evidence of this animal model approach showed that bone marrow-derived MSCs promote an antioxidant response and support the potential of using MSCs transplantation as an effective treatment modality for liver disease.

Differential Expression of Insulin-Like Growth Factor-I Receptor on Human Bone Marrow-Derived Mesenchymal Stem Cells Induced by Tumor Necrosis Factor-α.

BACKGROUND: Cell-based therapy has been implicated in the treatment of liver diseases. Mesenchymal stem cells from various sources such as bone marrow are available. These cells are one of the major candidates in cell therapy. The production of insulin-like growth factor-I increases in the regenerating organ. The insulin-like growth factor-I in liver regeneration is effective after binding to insulin-like growth factor-I receptor. OBJECTIVE: To test our hypothesis that tumor necrosis factor-α can stimulate mesenchymal stem cells to express insulin-like growth factor-I receptor. METHODS: Bone marrow was aspirated from normal human donor after taking informed consent. Cells were isolated and cultured. Identification of cells was done by flowcytometry and functional tests. The fourth passage cells were treated with tumor necrosis factor-α at two doses of 1 and 10 ng/mL, and incubated for 2, 10, 24, and 48 hours. Insulin-like growth factor-I receptor gene expression was studied using real-time polymerase chain reaction. RESULTS: Flowcytometry showed that the human bone marrow mesenchymal stem cells were positive for CD90 and negative for CD45 and CD80. The insulin-like growth factor-I receptor gene expression was increased in tumor necrosis factor-α treated in comparison with untreated cells. CONCLUSION: Treatment of human bone marrow-derived mesenchymal stem cells with tumor necrosis factor-α increases gene expression of insulin-like growth factor-I receptor. This finding may be used for increasing the effectiveness of stem cell therapy in those with acute hepatic failure.

Isolation and Characterization of Human Mesenchymal Stem Cells Derived from Human Umbilical Cord Wharton's Jelly and Amniotic Membrane.

BACKGROUND: Mesenchymal stem cells (MSCs) have a capacity for self-renewal and multi-potential differentiations. These cells are considered powerful sources for cell therapy in regenerative medicine and tissue engineering. The cells can be isolated from various tissues; however, harvesting from human umbilical cord and amniotic membrane is easy and accessible source. OBJECTIVE: To isolate and characterize the MSCs derived from human umbilical cord Wharton's jelly (WJ-MSC) and amniotic membrane (AM-MSC) with regard to their morphology, immunophenotype and mesodermal differentiation potential in order to obtain an alternative source of MSC for therapeutic clinical applications. METHODS: Fetal membranes and umbilical cords (n=3) were retrieved from healthy full-term women by elective cesarean delivery. Amniotic membrane and umbilical cord were separately minced and cultured in DMEM supplemented with 10% FBS. After reaching 80% of confluency, the umbilical cord WJ-MSC and AM-MSC were characterized by expression of cell surface markers with flowcytometry, stem cell gene expression with adipogenic/osteogenic potential. RESULTS: Both WJ-MSC and AM-MSC were spindle-shaped cells, expressed MSC surface markers in flowcytometry and stem cell transcriptional factors (OCT4 and NANOG). After induction, the cells differentiated into adipogenic and osteogenic lineages. CONCLUSION: MSC were successfully generated from umbilical cord WJ-MSC and AM-MSC with similar mesenchymal markers and properties.

Human Bone Marrow-derived Mesenchymal Stem Cell: A Source for Cell-Based Therapy.

BACKGROUND: The ability of mesenchymal stem cells (MSCs) to differentiate into many cell types, and modulate immune responses, makes them an attractive therapeutic tool for cell transplantation and tissue engineering. OBJECTIVE: This project was designed for isolation, culture, and characterization of human marrow-derived MSCs based on the immunophenotypic markers and the differentiation potential. METHODS: Bone marrow of healthy donors was aspirated from the iliac crest. Mononuclear cells were layered over the Ficoll-Paque density-gradient and plated in tissue cultures dish. The adherent cells expanded rapidly and maintained with periodic passages until a relatively homogeneous population was established. The identification of adherent cells and the immune-surface markers was performed by flow cytometric analysis at the third passage. The in vitro differentiation of MSCs into osteoblast and adipocytes was also achieved. RESULTS: The MSCs were CD11b (CR3), CD45, CD34, CD31 (PCAM-1), CD40, CD80 (B7-1), and HLA-class II negative because antigen expression was less than 5%, while they showed a high expression of CD90, and CD73. The differentiation of osteoblasts, is determined by deposition of a mineralized extracellular matrix in the culture plates that can be detected with Alizarin Red. Adipocytes were easily identified by their morphology and staining with Oil Red. CONCLUSION: MSCs can be isolated and expanded from most healthy donors, providing for a source of cell-based therapy.

Hematologic and biochemical indices and viral hepatitis in liver transplant patients.

BACKGROUND AND PURPOSE OF STUDY: The pathogenic role of important hepatotropic viral agents to induce hepatic dysfunction and failure may lead to the need for liver transplantation. We focused on the use of hematologic and biochemical laboratory diagnostic indexes to follow the clinical impact of hepatitis B virus (HBV); hepatitis C virus (HCV); and hepatitis G virus-related liver complications in transplant patients. MATERIALS AND METHODS: We collected 141 EDTA-treated blood samples pre- and post-liver transplantation for 2 years among 67 transplant patients. We evaluated the statistical relationships between hematologic and biochemical indices with HBV, HCV, and HGV infections among transplant recipient samples using version 15 of SPSS software. RESULTS: HBV polymerase chain reaction (PCR) positivity significantly correlated with partial thromboplastin (P=.011) pretransplant, with creatinine (P=.026) and Na (P=.034) levels at 1-week posttransplant, and also with alkaline phosphatase (P=.027) and mean corpuscular hemoglobin concentration (P=.050) at 2 weeks posttransplantation. Significant correlations were detected between HCV-reverse transcriptase (RT)-PCR-positive results and blood urea nitrogen (P=.008) and Na (P=.021) levels in the first aspartate aminotransferase and with (P=.025) in the second week after liver transplantation. Also, significant relationships were noted between HGV-RT-PCR-positive results and alkaline phosphatase (P=.05) and creatinine (P=.002) levels in the first and second weeks after liver transplant, respectively. CONCLUSION: Detection of significant correlations between HBV, HCV, and HGV infections with laboratory indices suggested that monitoring hematologic and biochemical liver function-related criteria aid the management of clinical complications of viral hepatitis in liver transplant patients.

Antiphospholipid antibodies and hepatitis C virus infection in Iranian thalassemia major patients.

Although the precise nature of Antiphospholipid antibodies is still not clearly defined, they are known to have association with thromboembolic events and have been found in hepatitis C virus (HCV) infection. Moreover, high prevalence of HCV infection and thrombotic risk is described in thalassemia. We aimed at investigating the prevalence of anticardiolipin antibodies (aCLAbs), lupus anticoagulant (LA), and their relation with HCV infection in Iranian thalassemic patients. Presence of anti-HCV antibody, serum HCV-RNA, aCLAbs, and LA activity was determined in 131 patients with thalassemia major (male/female: 63/68 aged 3-29 years) registered at thalassemia unit, Dastgheib Hospital, Shiraz, Iran. Sixty-one healthy controls were also included. Anti-HCV antibody was positive in 24 (18.3%), IgG aCLAbs in 56 (42.7%), and LA activity in 9 (6.9%) patients. 87.5% of patients positive for aCLAbs had a low titer of aCLAbs. Although none of the participants had a previous history of thrombosis, higher prevalence of aCLAbs was detected in thalassemic patients compared with controls. No significant difference in the prevalence of aCLAbs was found between HCV-infected and noninfected patients. A high prevalence of aCLAbs, the majority in low titers, was detected in Iranian thalassemic patients irrespective of previous history of thrombosis and presence of HCV infection.

Effect of the immunoregulatory cytokines on successful pregnancy depends upon the control of graft rejection mechanisms.

Successful outcomes in allopregnant women depend upon control of graft rejection mechanisms. An understanding of how the fetus escapes the maternal immune system may be relevant for the prevention of transplant rejection. It has been suggested that the same immunosuppressive cytokines contribute to successful pregnancy and transplantation. Recent reports suggest a role for transforming growth factor beta (TGF-beta) in the generation of T-regulatory lymphocytes. In contrast, production of proinflammatory cytokines accompanying intrauterine infection has been associated with fetal rejection or preterm labor. Interleukin-12 (IL-12) is the unique stimulator for differentiation of T-helper lymphocytes (Th) to Th1 cells. It rapidly induces transcription of Th1 cytokines such as interferon-gamma. This study was performed in 70 pregnant women at 21 to 36 weeks gestation, and in 32 healthy nonpregnant controls. An indirect enzyme-linked immunosorbent assay was used to estimate TGF-beta1, and IL-12 in serum. The results showed that TGF-beta1 levels were higher in all pregnant women compared with the nonpregnant controls. No significant changes in serum levels of IL-12 were observed in pregnant compared with the normal control women. The results suggested that the cytokine milieu of the placenta appeared to play a critical role in the maternal acceptance of the fetus, and that TGF-beta1 may function as a regulatory factor in fetal allograft survival during pregnancy.

Urine cytology as a useful screening method for polyoma virus nephropathy in renal transplant patients: a single-center experience.

Polyoma virus nephropathy occurs in 3% to 4% of renal transplant recipients, causing graft loss in 50% of cases. In this study we sought to identify the incidence of polyoma virus infection among our transplanted patients on the basis of age, sex, creatinine level, and postoperative period. During this study the 1086 urine samples collected from 362 patients were centrifuged and stained with the Papaniclaou method. All slides were classified as negative or positive (>1 decoy cell/sample). Among 1086 urine cytologies from 241 men and 121 women, decoy cells were identified in 26.6% (96) of patients, including 29.9% (n = 72) men and 20% (n = 24) women. The incidence of decoy cells (26.6%) was increased among men and associated with a longer transplantation period (P < .05). A significant relation was detected between older age and positive urine cytology. The patients with positive urine cytology for decoy cells showed a greater incidence of abnormal plasma creatinine values (26%) compared with patients showing a negative urine cytology (13.5%). In conclusion, identification of cells with viral inclusions (decoy cells) may help with the diagnosis of viral replication or active infection, therefore, routine urine cytology may be used as screening method for the detection of polyoma virus infection.

Cytokine gene polymorphisms in renal transplant recipients.

OBJECTIVE: Acute rejection remains an important cause of graft loss after renal transplantation, and cytokines are key mediators in the induction and effector phases of all immune and inflammatory responses. However, the influence of gene polymorphisms on the functional immune response of transplant recipient outcomes remains controversial. MATERIALS AND METHODS: The amplification refractory mutation system polymerase chain reaction was used to detect the interleukin-10 (IL-10) (-1082 G/A), tumor necrosis factor-alpha (TNF-alpha) (-308 G/A), and interferon-gamma (IFN-gamma) (+874 T/A) single nucleotide polymorphisms in 100 of the first adult kidney recipients at our institution who were receiving cyclosporine-based immunosuppressive therapy. The diagnosis of acute rejection was based on clinical and histologic findings according to the Banff criteria. RESULTS: The results of multivariate analyses showed no significant association between episodes of acute rejection and single nucleotide polymorphisms in IL- 10, TNF-alpha genes, or dinucleotide repeat polymorphisms in the IFN-gamma gene. CONCLUSIONS: Our results demonstrate that cytokine gene polymorphisms did not influence the early outcome of kidney transplantation.

Transforming growth factor beta-1 influence on fetal allografts during pregnancy.

An understanding of how the fetus escapes the maternal immune system may be relevant for the prevention of transplant rejection. There is evidence that the same immunosuppressive cytokines contribute to a successful pregnancy and transplant success. Transforming growth factor beta (TGF-beta) is a multifunctional cytokine that exhibits potent immunoregulatory and anti-inflammatory properties and may prolong graft survival. Recent reports suggest a role for TGF-beta in the generation of T-regulatory lymphocytes. Also, the role of TGF-beta in trophoblast differentiation and hypertension prompted us to evaluate maternal serum TGF-beta1 levels in normal allopregnant women and in pregnancies complicated by preeclampsia (PE), a disorder characterized by increased blood pressure, proteinuria, and end organ damage. Sixty-one pregnant preeclamptic women (32 cases with severe and 29 with mild PE), 22 normotensive healthy pregnant, and 20 nonpregnant controls formed the study groups. The active form of serum TGF-beta1 was investigated by an indirect ELISA technique. The results showed that TGF-beta1 was highly expressed in all three pregnant groups compared with the nonpregnant controls. No changes in TGF-beta1 serum levels was found in PE compared with a normal pregnancy. The results suggest that: (1) TGF-beta1 may function as a regulatory factor in fetal allograft survival during pregnancy and (2) TGF-beta1 does not have a pathophysiological role in PE.