Biomedical subjects

Julie M Hasenwinkel

Publications and source records attributed to Julie M Hasenwinkel.

5 recordsLinked to original sources

PubMed2006

Mechanical and morphological characterization of homogeneous and bilayered poly(2-hydroxyethyl methacrylate) scaffolds for use in CNS nerve regeneration.

Homogeneous and bilayered macroporous poly(2-hydroxyethyl methacrylate), p(HEMA), hydrogel scaffolds were examined as possible matrices for nerve regeneration in the CNS. An important issue to consider for a CNS scaffold is that it must be able to closely mimic the natural tissue it is replacing, while remaining intact, and mechanically stable enough to allow for regenerating axons to elongate through it. Phase-separated homogeneous and bilayered p(HEMA) scaffolds were fabricated, by varying water, crosslinking, and initiating agents; all of which directly affected the mechanical properties of the polymer. An increase in water concentration resulted in a decrease in the modulus for a given crosslinking and initiating concentration for all homogenous scaffolds, but the same result was not evident in the bilayered scaffolds. The distinct regions within the bilayered scaffolds generate a matrix, containing both a highly porous region with modulus values representative of spinal cord tissue, as well as a nonporous region that provides overall mechanical stability to the entire implant. The overall result is a composite matrix for possible use in CNS nerve regeneration, which mimics the mechanical properties of spinal tissue, but can withstand the forces that it will be subjected to in the injury site.

Biocompatible Materials↗

PubMed2006

Tissue response to in situ polymerization of a new two-solution bone cement: evaluation in a sheep model.

A two-solution bone cement (2-SC) was evaluated in a non-load bearing sheep model that simulated insertion of a cemented total joint replacement. A commercial powder-liquid bone cement formulation (Palacos R) was used as the control. The systemic response to the two cements was determined by monitoring changes in arterial blood pressure (ABP) and serum concentrations of methyl methacrylate monomer at intervals after insertion of the cement. The short-term tissue response to the two cements was assessed by quantifying histomorphometric parameters of new bone formation at 2, 4, and 12 weeks postsurgery. Intraoperatively, injection and pressurization of bone cement were well tolerated, with no significant changes in ABP in either group and no detectable circulating monomer in any animal. Several interesting trends were identified in the histomorphometry data. In the trabecular specimens, new bone formation immediately adjacent to the cement mantle was apparently suppressed in the first 2 weeks postsurgery, increased dramatically at 4 weeks, and then returned to baseline values by 12 weeks. This pattern was seen with both Palacos and 2-SC. In the cortical specimens, new bone formation was reduced on the endosteal surface when compared with the periosteal surface, with this effect being more noticeable at 2 and 4 weeks than at 12 weeks. There were no significant histopathological findings in either the bone or the draining lymph nodes. These data indicate that the biological response to 2-SC is substantially equivalent to that of Palacos R. Additional testing in a functional, load-bearing animal model is now recommended to more fully characterize the long-term biological response to 2-SC and to determine the mechanical performance of this new cement in vivo.

Animals↗

PubMed2005

Quantitative analysis of monomer vapor release from two-solution bone cement by using a novel FTIR technique.

Methyl methacrylate monomer can evaporate from bone cement to reach cytotoxic levels of concentrations in the implant bed of total joint prosthesis. Therefore, this study was performed by using a novel Fourier transform infrared spectroscopy method to quantify the release of monomer vapor from experimental two-solution bone cement in vitro during polymerization, to examine the effect of surface area versus cement mass, and to explore the effect of initiation chemistry. The results revealed that monomer vapor release is a surface phenomenon. In addition, initiation chemistry plays a major role in controlling the reaction time, and therefore heat concentration and dissipation, which resulted in a higher absorbance peak as initiation chemicals concentration increased. It was concluded that using the FTIR to monitor MMA vapors is an effective technique to obtain quantitative information about monomer vapor release from bone cements during polymerization and provides insight on the polymerization kinetics of two-solution acrylic bone cement.

Biocompatible Materials↗

PubMed2004

Gentamicin release from two-solution and powder-liquid poly(methyl methacrylate)-based bone cements by using novel pH method.

The release of gentamicin as a function of time was measured for Palacos and two-solution bone cements by using a novel pH technique. The pH of an aqueous solution of gentamicin is a function of the gentamicin concentration and it decreases linearly over concentrations of 0.0-0.1 wt %. Therefore, a new, direct, and inexpensive in vitro technique was developed based on continuous readings of the pH in phosphate-buffered saline (PBS) at 37 degrees C to determine the release kinetics of gentamicin from poly(methyl methacrylate) (PMMA)-based bone cement. In addition, this method was used to compare the release profiles of Palacos R-40 bone cement with a two-solution bone cement developed in our laboratory and loaded with two different concentrations of gentamicin sulfate. Finally, the pH-based method was used to track the elution of gentamicin in both mixed and static conditions to determine the effect of mixing on the diffusion of gentamicin out of the cement. It was found that Palacos R-40 released 4.95 +/- 0.22 wt % of its gentamicin after 24 h in PBS solution. This data compares favorably with previously reported values of gentamicin elution from Palacos R-40, which ranged from 3 to 8 wt % of the total amount of incorporated gentamicin, depending on the size and the surface area of the samples. The results show that Palacos samples released 4.84 +/- 0.27 mg after 24 h, a two-solution cement loaded with an equivalent concentration of gentamicin sulfate released 3.81 +/- 0.52 mg, and two-solution cement loaded with twice the concentration of Palacos released 5.53 +/- 0.26 mg of gentamicin. A higher percentage of release was recorded from Palacos than from the two-solution bone cement, and the effect of PBS mixing conditions on the release kinetics was only significant in the early stages of release and not at 24 h. It was concluded that monitoring the pH is an effective technique to measure gentamicin release from PMMA-based bone cements in PBS solution.

Anti-Bacterial Agents↗

PubMed2002

Effect of initiation chemistry on the fracture toughness, fatigue strength, and residual monomer content of a novel high-viscosity, two-solution acrylic bone cement.

Porous-free, two-solution bone cements have been developed in our laboratory as an alternative to commercial powder/liquid formulations. Each pair of solutions consist of poly(methyl methacrylate) (PMMA) powder dissolved in methyl methacrylate (MMA) monomer, with benzoyl peroxide (BPO) added to one solution as the initiator and N,N-dimethyl-p-toluidine (DMPT) added to the other as the activator. When mixed, the solutions polymerize via a free radical reaction, which is governed by the concentrations of initiator and activator and their molar stoichiometry. Previous work by the authors has demonstrated that these two-solution cement compositions are comparable to Simplex P bone cement in polymerization exotherm, setting time, and flexural mechanical properties. This study was designed to evaluate the effect of BPO and DMPT concentrations, along with their molar ratio, on the fracture toughness, fatigue strength, and residual monomer content of the experimental compositions. The results showed that fracture toughness and fatigue strength for the solution cements were comparable to Simplex P and were not significantly affected by the BPO concentration or the BPO:DMPT molar ratio; however, the highest DMPT concentration yielded significantly lower values for both variables. Residual monomer content was significantly affected by both the individual concentrations of BPO and DMPT and their molar ratios. The two-solution cements had significantly higher residual monomer contents versus Simplex P; however, this can be attributed to their higher initial monomer concentration rather than a lower degree of conversion.

Benzoyl Peroxide↗