PubMed · 2659143
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P R Crawford. 1989. "All implants succeed: all implants fail." Part one.. https://pubmed.ncbi.nlm.nih.gov/2659143/
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To design a mesoscopically ordered structure of the matrices and scaffolds composed of nano- and microscale fiber meshes for artificial and tissue-engineering devices, two new electrospinning techniques are proposed: multilayering electrospinning and mixing electrospinning. First, the following four kinds of component polymers were individually electrospun to determine the conditions for producing stable nano- and microfibers by optimizing the formulation parameters (solvent and polymer concentration) and operation parameters (voltage, air gap, and flow rate) for each polymer: (a) type I collagen, (b) styrenated gelatin (ST-gelatin), (c) segmented polyurethane (SPU), and (d) poly(ethylene oxide). A trilayered electrospun mesh, in which individual fiber meshes (type I collagen, ST-gelatin, and SPU) were deposited layer by layer, was formed by sequential electrospinning; this was clearly visualized by confocal laser scanning microscopy. The mixed electrospun-fiber mesh composed of SPU and PEO was prepared by simultaneous electrospinning on a stainless-steel mandrel with high-speed rotation and traverse movement. A bilayered tubular construct composed of a thick SPU microfiber mesh as an outer layer and a thin type I collagen nanofiber mesh as an inner layer was fabricated as a prototype scaffold of artificial grafts, and visualized by scanning electron microscopy.
To investigate the metal release of each base and alloying elements in vitro, SUS316L stainless steel, Co-Cr-Mo casting alloy, commercially pure Ti grade 2, and Ti-6Al-4V, V-free Ti-6Al-7Nb and Ti-15Zr-4Nb-4Ta alloys were immersed in various solutions, namely, alpha-medium, PBS(-), calf serum, 0.9% NaCl, artificial saliva, 1.2 mass% L-cysteine, 1 mass% lactic acid and 0.01 mass% HCl for 7d. The difference in the quantity of Co released from the Co-Cr-Mo casting alloy was relatively small in all the solutions. The quantities of Ti released into alpha-medium, PBS(-), calf serum, 0.9% NaCl and artificial saliva were much lower than those released into 1.2% L-cysteine, 1% lactic acid and 0.01% HCl. The quantity of Fe released from SUS316L stainless steel decreased linearly with increasing pH. On the other hand, the quantity of Ti released from Ti materials increased with decreasing pH, and it markedly attenuated at pHs of approximately 4 and higher. The quantity of Ni released from stainless steel gradually decreased with increasing pH. The quantities of Al released from the Ti-6Al-4V and Ti-6Al-7Nb alloys gradually decreased with increasing pH. A small V release was observed in calf serum, PBS(-), artificial saliva, 1% lactic acid, 1.2% l-cysteine and 0.01% HCl. The quantity of Ti released from the Ti-15Zr-4Nb-4Ta alloy was smaller than those released from the Ti-6Al-4V and Ti-6Al-7Nb alloys in all the solutions. In particular, it was approximately 30% or smaller in 1% lactic acid, 1.2% L-cysteine and 0.01% HCl. The quantity of (Zr + Nb + Ta) released was also considerably lower than that of (Al + Nb) or (Al + V) released. Therefore, the Ti-15Zr-4Nb-4Ta alloy with its low metal release in vitro is considered advantageous for long-term implants.
This study investigated the effects on polymerisation shrinkage-strain for two unmodified powder and liquid formulations of polymethyl methacrylate (PMMA), methyl methacrylate (MMA) dough-type systems, by varying the powder/liquid (P/L) ratio. Furthermore, the shrinkage-strain effects for the 1.0:1.0 P/L ratio of adding additional amounts of amine and benzoyl peroxide (BPO) were studied. The rationale was the continuing importance of bone cements and the renewed interest in acrylic biomaterials, based on MMA and PMMA co-polymers, as used in new fibre-reinforced systems, where low P/L ratios may be important. Shrinkage-strain is directly related to extent of monomer conversion and has intrinsic importance related to interfacial disruption. Shrinkage-strain kinetics were determined using the "bonded disk" method. The first series of experiments studied two unmodified self-curing materials (MEA and PAL), where specimens with different P/L ratios by volume (3.0, 2.5, 2.0, 1.5 and 1.0 to 1.0) were mixed for 60s. In these formulations, final shrinkage-strain values correlated positively with P/L ratios, rather than negatively, as would be expected from fully polymerised material. This highlights a problem of under-polymerisation through deviation from an optimum or recommended P/L ratio. When an additional 1.0% BPO was added in the powder, final shrinkage-strain values correlated negatively rather than positively, with P/L ratio for both products, except at ratio 1.0:1.0. Specimens mixed at 1.0:1.0 P/L ratio, with increasing amounts of BPO and amine resulted in higher final shrinkage-strain values, indicative of more complete polymerisation. Shrinkage-strain and optimum polymerisation are related, but clinically rather antagonist properties with respect to effective biomaterial utilisation and performance. In both design and surgical application of these polymethacrylate formulations, possible adverse effects of changing P/L ratio, producing either excessive shrinkage-strain or under-polymerisation, must be understood and where possible controlled.