Dental follicle stem cells in bone regeneration on titanium implants.

BACKGROUND: We aimed to demonstrate that DF stem cells from impacted molars and canines can be used to improve bone regeneration on titanium implants surfaces. This study highlights the presence of stem cells in DF, their potential to adhere and differentiate into osteoblasts on different types of titanium surfaces. RESULTS: Isolated cells from the harvested DF tissue from impacted canine/molars, expressed stem cells markers. Differentiation into bone cells was induced in presence or absence of BMP-2 and TGFß1. The presence of growth factors until 28 days in medium maintained the cells in an earlier stage of differentiation with a lower level of specific bone proteins and a higher expression of alkaline phosphatase (ALP). Influence of titanium implants with different bioactive coatings, hydroxyapatite (TiHA) and with silicatitanate (TiSiO2), and porous Ti6Al7Nb implants as control (TiCtrl), was studied in terms of cell adhesion and viability. Ti HA implants proved to be more favorable for adhesion and proliferation of DF stem cells in first days of cultivation. The influence of titanium coatings and osteogenic differentiation mediums with or without growth factors were evaluated. Additional BMP-2 in the medium did not allow DF stem cells to develop a more mature phenotype, leaving them in a pre-osteogenic stage. The best sustained mineralization process evaluated by immuno-cytochemical staining, scanning electron microscopy and Ca(2+) quantification was observed for TiHA implants with a higher expression of ALP, collagen and Ca(2+) deposition. Long term culturing (70 days) on titanium surfaces of DF stem cells in standard medium without soluble osteogenic inducers, indicated that HA coating is more favorable, with the acquisition of a more mature osteoblastic phenotype as shown by immunocytochemical staining. These findings demonstrated that even in absence of exogenous osteogenic factors, TiHA implants and in a lesser extent TiCtrl and TiSiO2 implants can induce and sustain osteogenic differentiation of DF stem cells, by their chemical and topographical properties. CONCLUSIONS: Our research demonstrated that DF stem cells have a spontaneous tendency for osteogenic differentiation and can be used for improving bone regeneration on titanium implants surfaces.

Selective Laser Sintering of PA 2200 for Hip Implant Applications: Finite Element Analysis, Process Optimization, Morphological and Mechanical Characterization.

Polyamide 12 (PA 22000) is a well-known material and one of the most biocompatible materials tested and used to manufacture customized medical implants by selective laser sintering technology. To optimize the implants, several research activities were considered, starting with the design and manufacture of test samples made of PA 2200 by selective laser sintering (SLS) technology, with different processing parameters and part orientations. The obtained samples were subjected to compression tests and later to SEM analyses of the fractured zones, in which we determined the microstructural properties of the analyzed samples. Finally, an evaluation of the surface roughness of the material and the possibility of improving the surface roughness of the realized parts using finite element analysis to determine the optimum contact pressure between the component made of PA 2200 by SLS and the component made of TiAl6V4 by SLM was performed.

Correction: Razvan et al. Selective Laser Sintering of PA 2200 for Hip Implant Applications: Finite Element Analysis, Process Optimization, Morphological and Mechanical Characterization. Materials2021, 14, 4240.

The authors wish to make the following correction to their paper [...].

Cast Iron Parts Obtained in Ceramic Molds Produced by Binder Jetting 3D Printing-Morphological and Mechanical Characterization.

Mechanical behavior and characteristics of two different types of materials: cast iron with lamellar graphite EN-GJL-250 and cast iron with spheroidal graphite EN-GJS-400-15 which were cast in ceramic molds using gravitational casting method has considered in this research. The ceramic molds were obtained by 3D printing method. First, a finite element analysis was developed to determine Tresca and von Mises stresses and the deformations of the ceramic molds under an applied pressure of 25 MPa. Samples were produced by gravitational casting using two types of cast iron materials. Mechanical tests were made using samples produced from these two types of materials and microstructure analysis evaluation of fractured zones was realized by scanning electron microscopy. Obtained results were finally used for designing, developing, and producing of one 'hydraulic block' of a railway installation by the Benninger Guss company of Switzerland.

Physical-Mechanical Characteristics and Microstructure of Ti6Al7Nb Lattice Structures Manufactured by Selective Laser Melting.

The demand of lattice structures for medical applications is increasing due to their ability to accelerate the osseointegration process, to reduce the implant weight and the stiffness. Selective laser melting (SLM) process offers the possibility to manufacture directly complex lattice applications, but there are a few studies that have focused on biocompatible Ti6Al7Nb alloy. The purpose of this work was to investigate the physical-mechanical properties and the microstructure of three dissimilar lattice structures that were SLM-manufactured by using Ti6Al7Nb powder. In particular, the strut morphology, the fracture characterization, the metallographic structure, and the X-ray phase identification were analyzed. Additionally, the Gibson-Ashby prediction model was adapted for each lattice topology, indicating the theoretical compressive strength and Young modulus. The resulted porosity of these lattice structures was approximately 56%, and the pore size ranged from 0.40 to 0.91 mm. Under quasi-static compression test, three failure modes were recorded. Compared to fully solid specimens, the actual lattice structures reduce the elastic modulus from 104 to 6-28 GPa. The struts surfaces were covered by a large amount of partial melted grains. Some solidification defects were recorded in struts structure. The fractographs revealed a brittle rupture of struts, and their microstructure was mainly α' martensite with columnar grains. The results demonstrate the suitability of manufacturing lattice structures made of Ti6Al7Nb powder having unique physical-mechanical properties which could meet the medical requirements.

Sterilization protocol for porous dental implants made by Selective Laser Melting.

BACKGROUND AND AIMS: Although dental implants are widely and successfully used, failure rates because of bacterial colonization are still high. Adequate fabrication and sterilization techniques as well as proper management of infectious complications represent a constant field of interest and research. In this study, we focused our attention on implants with controlled porosity produced by Selective Laser Melting (SLM). The difficulty to sterilize porous implantable devices is well known and finding an adequate sterilization protocol represents a challenge worldwide. Before testing the biological and mechanical properties of porous implants, a preliminary study in order to determine a correct sterilization protocol must be conducted.Our aim was to establish a valid sterilization protocol for porous titanium alloy dental implants, as such protocols are not officially available yet. METHODS: Twenty dental implants were fabricated from a titanium alloy by SLM. Ten of them were made using a 150W laser beam (porosity of 1% - group A) and the rest using a 75W laser beam (porosity of 23% - Group B), all of them with a non-defined internal structure. The implants were initially sterilized (5 from group A and 5 from group B, using dry heat - 180°C for 2 hours; the rest using steam sterilization - 121 °C for15 min) and then spent 18 hours in culture media with developing bacteria (Bacillus cereus (ATCC 11778), Staphylococcus aureus (ATCC 49444), Enterococcus faecalis (ATCC 29212), Listeria monocytogenes (ATCC 19114), three Gram negative bacteria: Escherichia coli (ATCC 25922), Salmonella typhimurium (ATCC 14028) and Pseudomonas aeruginosa (ATCC 27853). The first ten implants (5 from group A and 5 from group B) were then sterilized with dry heat and the others with steam. After sterilization, they were all placed in sterile culture media in order to observe if any bacterial growth were present. RESULTS: The culture media was observed 18 hours after the sterilized implants were placed inside. No bacterial growth was observed. CONCLUSIONS: Our tests reached their aims of defining a protocol to sterilize porous implants. Future tests regarding biological and mechanical aspects of these implants may now follow.

Comparative in vitro study regarding the biocompatibility of titanium-base composites infiltrated with hydroxyapatite or silicatitanate.

BACKGROUND: The development of novel biomaterials able to control cell activities and direct their fate is warranted for engineering functional bone tissues. Adding bioactive materials can improve new bone formation and better osseointegration. Three types of titanium (Ti) implants were tested for in vitro biocompatibility in this comparative study: Ti6Al7Nb implants with 25% total porosity used as controls, implants infiltrated using a sol-gel method with hydroxyapatite (Ti HA) and silicatitanate (Ti SiO2). The behavior of human osteoblasts was observed in terms of adhesion, cell growth and differentiation. RESULTS: The two coating methods have provided different morphological and chemical properties (SEM and EDX analysis). Cell attachment in the first hour was slower on the Ti HA scaffolds when compared to Ti SiO2 and porous uncoated Ti implants. The Alamar blue test and the assessment of total protein content uncovered a peak of metabolic activity at day 8-9 with an advantage for Ti SiO2 implants. Osteoblast differentiation and de novo mineralization, evaluated by osteopontin (OP) expression (ELISA and immnocytochemistry), alkaline phosphatase (ALP) activity, calcium deposition (alizarin red), collagen synthesis (SIRCOL test and immnocytochemical staining) and osteocalcin (OC) expression, highlighted the higher osteoconductive ability of Ti HA implants. Higher soluble collagen levels were found for cells cultured in simple osteogenic differentiation medium on control Ti and Ti SiO2 implants. Osteocalcin (OC), a marker of terminal osteoblastic differentiation, was most strongly expressed in osteoblasts cultivated on Ti SiO2 implants. CONCLUSIONS: The behavior of osteoblasts depends on the type of implant and culture conditions. Ti SiO2 scaffolds sustain osteoblast adhesion and promote differentiation with increased collagen and non-collagenic proteins (OP and OC) production. Ti HA implants have a lower ability to induce cell adhesion and proliferation but an increased capacity to induce early mineralization. Addition of growth factors BMP-2 and TGFß1 in differentiation medium did not improve the mineralization process. Both types of infiltrates have their advantages and limitations, which can be exploited depending on local conditions of bone lesions that have to be repaired. These limitations can also be offset through methods of functionalization with biomolecules involved in osteogenesis.