Advances in Science and Technology Vol. 76

Abstract: The main objective of this project is the study of the addition of chitosan in the polymeric blend of PVP/PVAL to get a biocompatible hydrogel that can be used as a system of controlled release of drugs. The polymeric blend usage is a recent development that expanded the applications of the polymers, due to the improvement of the properties of a single polymer even if they appear to be conflicting. PVP and PVAL were chosen because they present the main required characteristics to the formation of a hydrogel, such as water absorption and crosslinked formation. The flexibility of the PVP was added with the mechanical resistance of the PVAL. The chitosan, biological active polymer molecules, addition is to increment the interaction between the hydrogel and the organism. With the concentrations of PVP and PVAL defined, solutions with different levels of chitosan were made to check which presented better properties.

Abstract: Fracture repair continues to be widely investigated, both within the clinical realm and at the fundamental research level. Clinical application of low intensity pulsed ultrasound (LIPUS) has shown great promise as an effective, minimally invasive treatment for accelerating fracture repair and has warranted further investigation into the cellular manifestation of applied ultrasound. Toward this end much has been learned about the response of osteoblasts to LIPUS stimulation. In vitro and in vivo evaluation of cellular response to LIPUS have revealed an increase in proliferation, protein synthesis, collagen synthesis, membrane permeability, integrin expression, and increased cytosolic calcium, to name a few, further clarifying its utility and overall impact on cellular behavior. Considerable effects of LIPUS on the cells of musculoskeletal soft tissue have been reported as well. The growing body of research in this area suggests that LIPUS may be a powerful tool in the development of novel approaches to musculoskeletal repair and regeneration. Regenerative engineering-based approaches to musculoskeletal healing and regeneration that incorporate polymeric scaffolds and stem cells may be combined with LIPUS to move beyond bone repair to large scale multicomponent tissue repair.

Abstract: Cardiovascular implants including bypass grafts, heart valves and stents are prone to thrombogenicity and mechanical incompatibility thus leading to limited graft patencies. Thus to overcome these issues, a nanocomposite polymer based on polyhedral oligomeric silsesquioxane (POSS) nanoparticles and poly(carbonate urea)urethane (PCU) has been developed and patented. A solvent exchange coagulation technique has been used in the fabrication of a compliant, POSS PCU graft. In addition, we present details of bonding of bioactive peptides to attract progenitor stem cells from peripheral circulating blood onto the implants and the endothelialisation potential on the lumen. Peptides are designed to enhance interactions with cell receptor integrins whilst and in-vitro and in-vivo tests are performed to determine both endothelial and platelet as well as whole blood interactions. In conclusion these results, together with its ease of manufacture and low cost, suggest that POSS-PCU nanocomposite could be an attractive material of choice for the development of cardiovascular implants.

Abstract: Although autogenous bone grafts are currently the standard of care for bone reconstruction in implant dentistry, bone substitute materials are extensively studied in order to avoid harvesting autogenous bone. Recently, the use of tricalcium phosphate (TCP) and bioactive glass 45S5 particles as alloplastic bone graft materials for alveolar ridge augmentation and sinus floor elevation procedures has received increasing attention in implant dentistry. However, given the clinical findings with these current bone substitute materials there continues to be interest in bone substitute materials which degrade more rapidly, but still stimulate osteogenesis at the same time. As a result considerable efforts have been undertaken to produce rapidly resorbable bone substitute materials, which exhibit good bone bonding behaviour by stimulating enhanced bone formation at the interface in combination with a high degradation rate. This has led to the synthesis of a new series of bioactive, rapidly resorbable calcium alkali phosphate materials. These are glassy crystalline calcium alkali orthophosphates, which exhibit stable crystalline Ca₂KNa(PO₄)₂ phases. These materials have a higher solubility than TCP and therefore they are designed to exhibit a higher degree of biodegradability than TCP. On this basis, they are considered as excellent alloplastic materials for alveolar ridge augmentation. In order to evaluate the osteogenic potential in vitro, we first examined the effect of various rapidly resorbable calcium alkali orthophosphate bone grafting materials on the expression of osteogenic markers characteristic of the osteoblastic phenotype in vitro and compared this behaviour to that of the currently clinically used materials β-tricalcium phosphate (TCP) and bioactive glass 45S5. These studies showed that several calcium alkali orthophosphate materials supported osteoblast differentiation to a greater extent than TCP.

Abstract: In view of the imminent release on the Japanese market of hip prostheses made of an advanced alumina/zirconia, we performed morphologic and spectroscopic assessments of their surfaces with high spatial resolution. Femoral heads were characterized to a degree of statistical accuracy in the as-received state and after long-term exposures in vapor-moist environment. Surface and sub-surface screening was made by atomic force microscopy (AFM) and by confocal Raman spectroscopy, respectively. AFM scanning was systematically repeated with nanometer resolution on portions of surface as large as several tens of micrometers, randomly selected on the head surface, while in-depth scanning by the Raman probe allowed non-destructive analysis of phase structure in the sub-surface slab of material. Polymorphic transformation in zirconia was confined to the first few micrometers below the surface and involved no significant increase in surface roughness even after long-term environmental exposure. Surface roughness lied in a range <10 nm after environmental exposures up to 100 h, corresponding to an exposure time in vivo of several human lifetimes (i.e., according to experimentally derived thermal activation energy).

Abstract: I review some recent results obtained by my group at INFN, in collaboration with Collegues at CNR-IREA, Napoli, Italy about the cytotoxicity of buckypaper in human lymphocytes, as well as with Collegues at “La Sapienza” Rome University about the effect of buckypaper on cancer and primary cell lines in vitro and in vivo on laboratory rats

Abstract: Raman microprobe spectroscopy and atomic force microscopy (AFM) were systematically used to characterize the surface of an advanced alumina/zirconia composite (henceforth also referred to as zirconia toughened alumina, ZTA), in comparison with a commercially available femoral head made of monolithic zirconia. Experiments were conducted before and after in vitro exposure in water moist environment up to 100 h. Both materials contained zirconia partly stabilized with yttria. Tetragonal-to-monoclinic phase transformation, which was quantitatively characterized by confocal Raman spectroscopy as a function of grain size, showed significant difference between the investigated samples. Such difference was similarly found with respect to both roughness level and time needed for such topologic changes to occur. Variation of phase fractions and of topologic surface parameters were plotted as a function of in vitro exposure time and compared.

Abstract: A spatially resolved cathodoluminescence (CL) analysis is used as a means for chemical and mechanical analyses of the composite surface after environmental exposure. CL emission proves extremely efficient in concurrently monitoring the concentration of point defects (e.g., oxygen vacancies) on the material surface. Using CL, averaging effects from sub-surface parts of the material can be minimized, and the actual chemical state of the material surface is revealed. As a result, information about the stoichiometry of the material surface can be obtained directly from the lattices of the constituent phases, this enabling one to pattern relevant connections to the environmental resistance of oxide-based bioceramics. A highly fracture resistant alumina/zirconia composite represents the latest trend in ceramics for arthroplastic applications in alternative to monolithic alumina or zirconia ceramics. This composite material is designed from both chemical and microstructural viewpoints in order to prevent environmental degradation and fracture events in vivo, an important step forward in the full exploitation of ceramic materials in the field of arthroplasty. Systematically monitoring the optical activity of oxygen vacancies in both alumina and zirconia phase reveals the distinct role on the kinetics of polymorphic transformation. From the presented data an explicit role is evinced for oxygen vacancy formation in the alumina matrix in the complex cascade of mechanochemical events determining the environmental resistance of the composite.

Abstract: Metal Injection Molding (MIM) is a cost-effective technique for producing small, complex, precision parts in high volumes. MIM consists of four main processing steps: mixing, injection molding, debinding and sintering. In the mixing step, the powder titanium alloy (Ti6Al4V) medical grade is mixed with a binder system based on palm stearin to form a homogeneous feedstock. The rheological studies of the feedstock have been determined properly in order to success during injection into injection molding machine. After molding, the binder holds the particles in place. The binder systems then have to be removed completely through debinding step. Any contamination of the binder systems will affect the final properties of the parts. During debinding step, solvent extraction debinding has been used to remove partly of the binder systems. The debound part is then sintered at high temperature under control atmosphere furnace. The properties of the sintered craniofacial implants then was measured and compared. The sintered craniofacial implants also then were determined in term of in-vitro cytotoxicity study using mouse fibroblast lines L-929. The results show that the sintered craniofacial implants of titanium alloy produced by MIM fullfill the in-vitro cytotoxicity test.

Abstract: The technique of aorta-coronary shunting offered by Dr. M. Soutorine by means of the original stapler developed by "Endogene" allows suturing blood vessels by superelastic Тi-Ni staples on «working heart» (without heart switching-off). The material for staples is a 0.30 and 0.315 mm diam. wire which was studied by DSC, shape recovery and mechanical tests. Thermomechanical treatment (TMT) comprised warm drawing, low- temperature (LTMT) by cold drawing with 25-30% strain in the last pass and following post-deformation annealing (PDA). LTMT leads to increasing of yield stress in comparison with warm drawing. Treatment of wire under LTMT+PDA allows obtaining the highest characteristics of functional properties of the wire. The difference between “dislocation” and “transformation” yield stresses  Δ=900 MPa. Critical stress of superelastic recovery after TMT on the average is 1.5-2 times higher in comparison with warm drawing. The maximum completely recoverable strain r,1max=6.5%. The maximum obtained force value of staples is РrSE=6.5 Н. The shape recovery rate of staples was 85-97 % that provided its functionality. Storage in the stapler in straightened condition within 1 month does not worse the staples.