PubMed · 5228319
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A Massassati. 1966. [Denture relining with self-curing resins].. https://pubmed.ncbi.nlm.nih.gov/5228319/
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Investigators that require the chronic implantation of hardware on the non-human primate skull are often challenged with the possible failure of head implants. To improve the success rate of our head implants, titanium anchor screws, referred to as titanium endosseous implants, were implanted in the skulls of six macaques. Techniques adapted from the processing of dentures were utilized to pre-fabricate an acrylic "skull cap", which provided the mechanical support structure for our study-specific hardware. A two-stage procedure adapted from dentistry (Brånemark et al., 1977) was employed for the placement of titanium endosseous implants in the skull. This two-stage technique incorporates the principles of osseointegration and a healing period. Of the six skull-anchored implants prepared implementing the methods described in this paper, we have not experienced any failures. Additionally, all of the titanium endosseous implants examined post mortem were functionally successful (n=30). Histology results confirmed that there was healthy bone in direct contact with the titanium endosseous implants. The dense cortical bone of the macaque skull is ideal for the implantation of titanium endosseous implants. Titanium endosseous implants have provided secure, functional anchor points for the attachment of hardware to the macaque skull and have resulted in healthy, stable head implants that can remain on the skull for extended periods of time.
The dynamics of the deswelling and swelling processes in thermoresponsive poly-N-isopropylacrylamide (pNIPAm) hydrogel nanoparticles have been studied by using time-resolved transmittance measurements, in combination with a nanosecond laser-induced temperature-jump (T-jump) technique. A decrease in the solution transmittance associated with deswelling of the particles has been observed as the solution temperature traverses the volume phase transition temperature of the particles. Upon inducing the T-jump, the deswelling transition only occurs in a small percentage (<10%) of the particle volume, which was found to be a thin periphery layer of the particles. The particle deswelling occurs on the microsecond time scale, and as shown previously, the collapse time can be tuned via adding small amounts of hydrophobic component to the particle shell. In contrast, the reswelling of the particles was thermodynamically controlled by bath equilibration, and only small differences in particle reswelling kinetics were found due to sluggish heat dissipation (millisecond time scale) from the sample cell.
This paper analyzes the effects of Tween 80, Pluronic F-127, sodium dodecylsulfate (SDS), and benzalkonium chloride on the macro and microviscosity of Carbopol 934NF (0.25-0.50 g/dl) pharmaceutical gels. Carbopol/surfactant interactions, which were reflected in changes in the intrinsic viscosity of the polymer and in shifts of IR spectra bands of films, considerably modified the rheological properties of the gel (flow and oscillatory rheometry) and the diffusion coefficients of polystyrene particles (dynamic light scattering, DLS). At pH 4, any surfactant at a concentration of 0.01 g/dl promoted interpolymer connections producing an open three-dimensional network with maximum viscous and elastic moduli, which does not disturb the diffusive movement of polystyrene particles. An increase in non-ionic surfactant (0.05-0.50 g/dl) gradually decreased viscosity and elasticity since there were more surfactant molecules to surround each carbopol particle, forming intrapolymeric micelles and breaking the interpolymer connections. This macroscopic effect is, however, not reflected in a decrease but in an increase in microviscosity (estimated by DLS) owing to the formation of larger carbopol/surfactant aggregates and free micelles that contribute significantly to the obstruction of the diffusional path. Both ionic surfactants decreased macroviscosity owing to ionic aggregation (benzalkonium chloride) or increase in ionic strength (mainly SDS), while the repercussion on the diffusion of polystyrene particles was dramatically different, and was hindered (due to the carbopol/surfactant aggregates) or enhanced (due to the shrinking of carbopol microgels), respectively. At pH 7.4, the ionization of the carboxylic groups produced an expansion of the polymer chains accompanied by a huge increase in viscosity and elasticity and a decrease in diffusion coefficients in comparison with those obtained at pH 4. The effects of the surfactants were similar to those observed at pH 4 but less intense. Chloramphenicol release studies (Franz-Chien cells) revealed that 0.01 g/dl surfactant did not affect the diffusion while a change in pH dramatically altered the process. The results show that by choosing the appropriate proportion of the most suitable surfactant, it is possible to modulate the flow behavior, elastic properties, and diffusional microenvironment of carbopol gels, without losing the pH-dependent gelling ability, which could improve the suitability of carbopol gels for drug delivery through different routes.