PMMA-based nanocomposites for odontology applications: a state-of-the-art

Polymethyl methacrylate (PMMA), a well-known polymer of the methacrylate family, is extensively used in biomedicine, particularly in odontological applications including artificial teeth, dentures and denture bases, obturators, provisional or permanent crowns, and so forth. The exceptional PMMA properties, including aesthetics, inexpensiveness, simple manipulation, low density, and adjustable mechanical properties, make it a perfect candidate in the field of dentistry. However, it presents some deficiencies, including weakness regarding hydrolytic degradation, poor fracture toughness, and a lack of antibacterial activity. To further enhance its properties and solve these drawbacks, different approaches can be performed, including the incorporation of nanofillers. In this regard, different types of metallic nanoparticles, metal oxide nanofillers, and carbon-based nanomaterials have been recently integrated into PMMA matrices with the aim to reduce water absorption and improve their performance, namely their thermal and flexural properties. In this review, recent studies regarding the development of PMMA-based nanocomposites for odontology applications are summarized and future perspectives are highlighted

Bone-Mimicking Injectable Gelatine/Hydroxyapatite Hydrogels

[EN] Bioactive synthetic hydrogels have emerged as promising materials because they can provide molecularly tailored biofunctions and adjustable mechanical properties. To mimic the mineralogical and organic components of the natural bone, hydroxyapatite and a tyramine conjugate of gelatine were combined in this study. The effect of various amounts of in situ synthesized hydroxyapatite in gelatine-tyramine on the morphology and physical properties of injectable hydrogels was investigated. Mineralogical identification confirmed successful precipitation of in situ formed hydrox yapatite. Better distribution of hydroxyapatite crystal agglomerates within modified gelatine was found at 5 % of hydroxyapatite, which could be responsible for increased storage modulus with respect to pure gelatine hydrogel. Prepared composite hydrogels are non-toxic and support the proliferation of Hek293 cells.The authors are grateful for the financial support of the Spanish Ministry of Economy and Competitiveness through the MAT2016-76039-C4-1-R project (including Feder funds) and the Croatian Science Foundation under the project IP-2014-09-3752.Rogina, A.; Sandrk, N.; Teruel Biosca, L.; Antunovic, M.; Ivankovic, M.; Gallego Ferrer, G. (2019). Bone-Mimicking Injectable Gelatine/Hydroxyapatite Hydrogels. Chemical and Biochemical Engineering Quarterly Journal. 33(3):325-335. https://doi.org/10.15255/CABEQ.2019.1663S32533533

Perylene polyphenylmethylsiloxanes for optoelectronic applications

The incorporation of fluorescent organic dyes in an encapsulating matrix represents a route to generate stable and processable materials for optoelectronic devices. Here, we present a method to embed perylene dyes into a high refractive index (HRI) polysiloxane matrix applying an allyl functionalized perylene dye and hydrosilylation chemistry. In a first approach, the dye molecules were covalently integrated into the backbone of linear polyphenylmethylsiloxane chains. The fluorescent and liquid polymers were synthesized with molecular weights from 5660 up to 8400 g mol−1. In a second approach, the dye itself was used as a cross‐linking agent between linear polyphenylmethylsiloxane chains. These preformed fluorescent batch polymers are liquids with dye concentrations between 0.025 and 8 wt %. The applied synthetic methods incorporated the dye covalently into the polymer structure and avoided the crystallization of the dye molecules and thus the formation of excimers, which would reduce the optical emission. The resulting products can be easily incorporated into curable commercially available HRI polyphenylmethylsiloxane resins. The formed materials are ideal LED encapsulants with a solid and flexible consistency, a uniform dispersion of the dyes, and adjustable mechanical properties, realized by changing the amount of perylene polymers. Further properties of the obtained materials are thermal stabilities up to 478 °C, quantum yields larger than 0.97, and high photostabilities. Thus, the covalent integration of dyes into polyphenylsiloxane structures represents a possible route for the stabilization of the organic dyes against the extreme irradiance and thermal conditions in LED applications

Podoplanin immunopositive lymphatic vessels at the implant interface in a rat model of osteoporotic fractures

Insertion of bone substitution materials accelerates healing of osteoporotic fractures. Biodegradable materials are preferred for application in osteoporotic patients to avoid a second surgery for implant replacement. Degraded implant fragments are often absorbed by macrophages that are removed from the fracture side via passage through veins or lymphatic vessels. We investigated if lymphatic vessels occur in osteoporotic bone defects and whether they are regulated by the use of different materials. To address this issue osteoporosis was induced in rats using the classical method of bilateral ovariectomy and additional calcium and vitamin deficient diet. In addition, wedge-shaped defects of 3, 4, or 5 mm were generated in the distal metaphyseal area of femur via osteotomy. The 4 mm defects were subsequently used for implantation studies where bone substitution materials of calcium phosphate cement, composites of collagen and silica, and iron foams with interconnecting pores were inserted. Different materials were partly additionally functionalized by strontium or bisphosphonate whose positive effects in osteoporosis treatment are well known. The lymphatic vessels were identified by immunohistochemistry using an antibody against podoplanin. Podoplanin immunopositive lymphatic vessels were detected in the granulation tissue filling the fracture gap, surrounding the implant and growing into the iron foam through its interconnected pores. Significant more lymphatic capillaries were counted at the implant interface of composite, strontium and bisphosphonate functionalized iron foam. A significant increase was also observed in the number of lymphatics situated in the pores of strontium coated iron foam. In conclusion, our results indicate the occurrence of lymphatic vessels in osteoporotic bone. Our results show that lymphatic vessels are localized at the implant interface and in the fracture gap where they might be involved in the removal of lymphocytes, macrophages, debris and the implants degradation products. Therefore the lymphatic vessels are involved in implant integration and fracture healing

Synthesis and characterization of novel scaffold for bone tissue engineering based on Whartons´s jelly

A composite is a material made of more than one component, and the bond between the components is on a scale larger than the atomic scale. The objective of the present study was to synthesize and perform the structural characterization and biological evaluation of a new biocomposite (BCO) based on a novel combination of an organic and an inorganic phase, for bone tissue engineering applications. The organic phase consisted of Wharton´s Jelly (WJ), which was obtained from embryonic tissue following a protocol developed by our laboratory. The inorganic phase consisted of bioceramic particles (BC), produced by sintering hydroxyapatite (HA) with β- tricalcium phosphate (β-TCP), and bioactive glass particles (BG). Each phase of the BCO was fully characterized by SEM, EDS, XRD and FTIR. Biocompatibility was evaluated in vivo in the tibiae of Wistar rats (n=40). Histological evaluation was performed at 0, 1, 7, 14, 30 and 60 days. XRD showed the phases corresponding to HA and β-TCP, whereas diffractogram of BG showed it to have an amorphous structure. EDS showed mainly Si and Na, Ca, P in BG, and Ca and P in HA and β-TCP. FTIR identified bonds between the organic and inorganic phases. From a mechanical viewpoint, the composite showed high flexural strength of 40.3±0.8MPa. The synthesized BCO exhibited adequate biocompatibility as shown by formation of lamellar type bone linked by BG and BC particles. The biomaterial presented here showed excellent mechanical and biocompatibility properties for its potential clinical use.Fil: Martinez, Cristian. Universidad de Buenos Aires. Facultad de Ingenieria. Instituto de Ingeniería Biomédica; Argentina. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Anatomía Patológica; Argentina. Universidad Nacional de Cuyo. Facultad de Odontologia; ArgentinaFil: Fernández, Carlos. Universidad de Buenos Aires. Facultad de Ingenieria. Instituto de Ingeniería Biomédica; ArgentinaFil: Prado, Miguel Oscar. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ozols, Andres. Universidad de Buenos Aires. Facultad de Ingenieria. Instituto de Ingeniería Biomédica; ArgentinaFil: Olmedo, Daniel Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Anatomía Patológica; Argentin

Lactide and Ethylene Brassylate-Based Thermoplastic Elastomers and Their Nanocomposites with Carbon Nanotubes: Synthesis, Mechanical Properties and Interaction with Astrocytes

Polylactide (PLA) is among the most commonly used polymers for biomedical applications thanks to its biodegradability and cytocompatibility. However, its inherent stiffness and brittleness are clearly inappropriate for the regeneration of soft tissues (e.g., neural tissue), which demands biomaterials with soft and elastomeric behavior capable of resembling the mechanical properties of the native tissue. In this work, both L- and D,L-lactide were copolymerized with ethylene brassylate, a macrolactone that represents a promising alternative to previously studied comonomers (e.g., caprolactone) due to its natural origin. The resulting copolymers showed an elastomeric behavior characterized by relatively low Young’s modulus, high elongation at break and high strain recovery capacity. The thermoplastic nature of the resulting copolymers allows the incorporation of nanofillers (i.e., carbon nanotubes) that further enable the modulation of their mechanical properties. Additionally, nanostructured scaffolds were easily fabricated through a thermo-pressing process with the aid of a commercially available silicon stamp, providing geometrical cues for the adhesion and elongation of cells representative of the nervous system (i.e., astrocytes). Accordingly, the lactide and ethylene brassylate-based copolymers synthesized herein represent an interesting formulation for the development of polymeric scaffolds intended to be used in the regeneration of soft tissues, thanks to their adjustable mechanical properties, thermoplastic nature and observed cytocompatibility.Grant PID2019-106236GB-I00 funded by MCIN/AEI/10.13039/501100011033. The authors are also thankful for funds from the Basque Government, Department of Education (IT-1766-22). C.B.-Á.: acknowledges the predoctoral grant funded by the UPV/EHU. Polimerbio and Y.P. have a Bikaintek Ph.D. grant (20-AF-W2-2018-00001)

Living Bacterial Sacrificial Porogens to Engineer Decellularized Porous Scaffolds

Decellularization and cellularization of organs have emerged as disruptive methods in tissue engineering and regenerative medicine. Porous hydrogel scaffolds have widespread applications in tissue engineering, regenerative medicine and drug discovery as viable tissue mimics. However, the existing hydrogel fabrication techniques suffer from limited control over pore interconnectivity, density and size, which leads to inefficient nutrient and oxygen transport to cells embedded in the scaffolds. Here, we demonstrated an innovative approach to develop a new platform for tissue engineered constructs using live bacteria as sacrificial porogens. E.coli were patterned and cultured in an interconnected three-dimensional (3D) hydrogel network. The growing bacteria created interconnected micropores and microchannels. Then, the scafold was decellularized, and bacteria were eliminated from the scaffold through lysing and washing steps. This 3D porous network method combined with bioprinting has the potential to be broadly applicable and compatible with tissue specific applications allowing seeding of stem cells and other cell types

Design and fabrication considerations for three dimensional scaffold structures

Porous three dimensional structures have seen extensive investigation among design engineers for a wide range of novel applications. The fabrication of such designs would not be possible using traditional manufacturing approaches owing to the dimensional intricacy of such structures, but have now become a distinct possibility owing to the maturity of 3D printing technologies. In this study, we have examined the creation of novel unit cells from mathematic surface renderings as a basis for creating tailored porous structures, before realising the final designs through Fuse Deposition Modelling (FDM) 3D printing. We examined the use of Gyroid and Schwarz primitive (P) surfaces to create novel unit cells not typically found in design software libraries. We then transpose these structures into several test geometries comprising a cylinder, cuboid and tetrahedron, which will adequately test limits of design and fabrication in regular and irregularly shaped structures. It was found that the porosities of the resulting models could be adjusted through discrete dimensional changes in the unit cell and digital wrapping procedures. It was also found that models could be fabricated using FDM printing to a minimum pore diameter of approximately 1mm with a high degree of accuracy and repeatability. Ultimately this work will provide guidance to engineering's when creating porous structures and could find usefulness in applications where optimal material usage versus porosity are required, such as in high throughput 3D fluidic applications, such as heat exchangers and tissue engineered structures