The Photoinitiator Lithium Phenyl (2,4,6-Trimethylbenzoyl) Phosphinate with Exposure to 405 nm Light Is Cytotoxic to Mammalian Cells but Not Mutagenic in Bacterial Reverse Mutation Assays.

Lithium phenyl (2,4,6-trimethylbenzoyl) phosphinate (LAP) is a free radical photo-initiator used to initiate free radical chain polymerization upon light exposure, and is combined with gelatin methacryloyl (GelMA) to produce a photopolymer used in bioprinting. The free radicals produced under bioprinting conditions are potentially cytotoxic and mutagenic. Since these photo-generated free radicals are highly-reactive but short-lived, toxicity assessments should be conducted with light exposure. In this study, photorheology determined that 10 min exposure to 9.6 mW/cm2 405 nm light from an LED light source fully crosslinked 10 wt % GelMA with >3.4 mmol/L LAP, conditions that were used for subsequent cytotoxicity and mutagenicity assessments. These conditions were cytotoxic to M-1 mouse kidney collecting duct cells, a cell type susceptible to lithium toxicity. Exposure to ≤17 mmol/L (0.5 wt %) LAP without light was not cytotoxic; however, concurrent exposure to ≥3.4 mmol/L LAP and light was cytotoxic. No condition of LAP and/or light exposure evaluated was mutagenic in bacterial reverse mutation assays using S. typhimurium strains TA98, TA100 and E. coli WP2 uvrA. These data indicate that the combination of LAP and free radicals generated from photo-excited LAP is cytotoxic, but mutagenicity was not observed in bacteria under typical bioprinting conditions.

Age-associated impairments in tissue strength and immune response in a rat vaginal injury model.

INTRODUCTION AND HYPOTHESIS: Surgical repair of pelvic organ prolapse often includes native tissue repair during which the patient's own vaginal connective tissue is used to achieve pelvic support. This method, based on plication and suspension often yields suboptimal anatomical outcomes, possibly due to inadequate healing of the vaginal connective tissue. We hypothesized that age might have a negative effect on the time course and tissue biomechanics of vaginal wound healing in a rat model. METHODS: Fifty young (12 weeks) and old (12 months) female 344BN Fischer rats were subjected to a posterior midline vaginal incision. The time course of repair was determined by measuring the size of the wound on days 1, 3, 7, and 14 post-injury. These findings correlated with the immune response to injury using a marker of impaired wound healing, the inflammatory cytokine macrophage migration inhibitory factor in the vaginal muscularis. Biomechanical properties of the healed vaginal tissue were tested 30 days post-injury. RESULTS: Wound healing was assessed on days 1, 3, 7, and 14 post-injury. On day 3 post-injury, the wounds in the young animals had all closed whereas the wounds in the old animals remained open. Furthermore, on day 7, the wound gap was still filled with granulation tissue in the old rats, whereas for the young rats, the wound area was almost indistinguishable from the non-injured area. Macrophage migration inhibitory factor was highly expressed in the vaginal epithelium and in the vaginal muscularis after injury. When compared with young animals, macrophage migration inhibitory factor levels of old rats began to rise more than 2 days later and the increased tissue expression persisted for 7 days longer. The breakpoint force of the healed vagina of old rats was almost 4-fold weaker than in young rats. At 30 days post-injury, the healed vagina in old rats regained less of the original (healthy) force at breakpoint than the young rats. CONCLUSIONS: In this rat model, age impaired vaginal wound healing, which was reflected in the altered inflammatory response to injury and reduced tissue strength.

Controlled initial surge despite high drug fraction and high solubility.

Potential connections between release profiles and solvent evaporation rates alongside polymer chemistry were elucidated for the release of tetracycline hydrochloride from two different poly (d, l-lactide-co-glycolide) (PLGA) film matrices containing high drug fractions (50%, 30%, and 15%), and prepared at two distinct solvent evaporation rates. At highest tetracycline concentrations (50%), (i) the early release rates were ≤0.5 µg/min in all cases; (ii) release was linear from systems fabricated with lower lactic content and slower solvent evaporation rate and bimodal from systems fabricated with higher lactic content and faster evaporation rate; (iii) surface fractions covered by the drug were similar at both evaporation rates for 85:15 PLGA but very different for 50:50 PLGA, leading to unexpectedly reduced early release from 50:50 PLGA than from 85:15 PLGA when both the matrices were fabricated using a slower evaporation rate. These features remained unaffected in case of low drug concentration. Results suggested that during the formation of the drug-polymer microstructure, the combined effect of polymer chemistry and solvent evaporation rate sets apart the surface characteristics and the initial release profiles of systems containing high drug fraction, and an appropriate combination of these parameters may be utilized to control the early stage of drug release.

Bacterial endotoxin detection in hyaluronic acid-based medical devices.

A simple and rapid method has been developed for testing bacterial endotoxin in hyaluronic acid (HA)-based medical devices. High-molecular-weight HA (HMW HA) in solution or HA-based medical devices was digested by the enzyme hyaluronidase to reduce solution viscosity by truncating the long chains of HA and to test for bacterial endotoxin. The bacterial endotoxin level was detected and measured by kinetic chromogenic Limulus Amebocyte Lysate (LAL) assay. The method was applied to two different ophthalmic viscosurgical devices (OVDs) and one dermal filler, and may easily be adapted to use with up to 3% HA solutions and other HA-based medical devices. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. J Biomed Mater Res Part B: Appl Biomater, 2016. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1210-1215, 2017.

Exposure of natural rubber to personal lubricants--swelling and stress relaxation as potential indicators of reduced seal integrity of non-lubricated male condoms.

BACKGROUND: Male condoms act as mechanical barriers to prevent passage of body fluids. For effective use of condoms the mechanical seal is also expected to remain intact under reasonable use conditions, including with personal lubricants. Absorption of low molecular weight lubricant components into the material of male condoms may initiate material changes leading to swelling and stress relaxation of the polymer network chains that could affect performance of the sealing function of the device. Swelling indicates both a rubber-solvent interaction and stress relaxation, the latter of which may indicate and/or result in a reduced seal pressure in the current context. METHODS: Swelling and stress relaxation of natural rubber latex condoms were assessed in a laboratory model in the presence of silicone-, glycol-, and water-based lubricants. RESULTS: Within 15 minutes, significant swelling (≥6 %) and stress reduction (≥12 %) of condoms were observed with 2 out of 4 silicone-based lubricants tested, but neither was observed with glycol- or water-based lubricants tested. Under a given strain, reduction in stress was prominent during the swelling processes, but not after the process was complete. CONCLUSIONS: Lubricant induced swelling and stress relaxation may loosen the circumferential stress responsible for the mechanical seal. Swelling and stress relaxation behavior of latex condoms in the presence of personal lubricants may be useful tests to identify lubricant-rooted changes in condom-materials. IMPLICATION: For non-lubricated latex condoms, material characteristics--which are relevant to failure--may change in the presence of a few silicone-based personal lubricants. These changes may in turn induce a loss of condom seal during use, specifically at low strain conditions.

Limitations of using synthetic blood clots for measuring in vitro clot capture efficiency of inferior vena cava filters.

The purpose of this study was first to evaluate the clot capture efficiency and capture location of six currently-marketed vena cava filters in a physiological venous flow loop, using synthetic polyacrylamide hydrogel clots, which were intended to simulate actual blood clots. After observing a measured anomaly for one of the test filters, we redirected the focus of the study to identify the cause of poor clot capture performance for large synthetic hydrogel clots. We hypothesized that the uncharacteristic low clot capture efficiency observed when testing the outlying filter can be attributed to the inadvertent use of dense, stiff synthetic hydrogel clots, and not as a result of the filter design or filter orientation. To study this issue, sheep blood clots and polyacrylamide (PA) synthetic clots were injected into a mock venous flow loop containing a clinical inferior vena cava (IVC) filter, and their captures were observed. Testing was performed with clots of various diameters (3.2, 4.8, and 6.4 mm), length-to-diameter ratios (1:1, 3:1, 10:1), and stiffness. By adjusting the chemical formulation, PA clots were fabricated to be soft, moderately stiff, or stiff with elastic moduli of 805 ± 2, 1696 ± 10 and 3295 ± 37 Pa, respectively. In comparison, the elastic moduli for freshly prepared sheep blood clots were 1690 ± 360 Pa. The outlying filter had a design that was characterized by peripheral gaps (up to 14 mm) between its wire struts. While a low clot capture rate was observed using large, stiff synthetic clots, the filter effectively captured similarly sized sheep blood clots and soft PA clots. Because the stiffer synthetic clots remained straight when approaching the filter in the IVC model flow loop, they were more likely to pass between the peripheral filter struts, while the softer, physiological clots tended to fold and were captured by the filter. These experiments demonstrated that if synthetic clots are used as a surrogate for animal or human blood clots for in vitro evaluation of vena cava filters, the material properties (eg, elastic modulus) and dynamic behavior of the surrogate should first be assessed to ensure that they accurately mimic an actual blood clot within the body.

pH effect on the synthesis, shear properties, and homogeneity of iron-crosslinked hyaluronic acid-based gel/adhesion barrier.

Iron-crosslinked hyaluronic acid hydrogel (FeHA) has been used to reduce postsurgical adhesions in patients undergoing open, gynecological surgery. The performance of FeHA gel as an adhesion barrier device is influenced by many factors, including the physicochemical gel properties, which, in turn, depend on the chemistry and conditions of the device manufacturing. In this work, we demonstrate the effect of reaction pH on rheology and homogeneity of FeHA gels formulated in house and also compare the viscoelastic properties of FeHA gels with that of uncrosslinked HA solution of similar HA concentration and ionic strength. Dynamic mechanical analyses provide evidence that the reaction of HA with Fe(III) ions leads to the formation of "weak" gels. The viscoelastic properties and homogeneity of FeHA gels vary depending on the pH at which crosslinking was initiated. When solution pH, at the start of crosslinking, varied between 1.5 and 3, the low-shear rate viscosity of FeHA varied between 10,000 and 40,000 cPoise (10-40 Pa s). The highest steady-state shear viscosity and viscoelasticity were measured when pH was around 2.6, which is similar to the pH-dependent viscoelasticity of pure HA solution. Initiating HA crosslinking at pH ≤ 3 led to relatively homogenous solutions, while crosslinking higher pH > 3 caused instantaneous gel precipitation and inhomogeneities. Sensitivity of FeHA gel properties to small variations in reaction pH clearly supports the need for a tight manufacturing control during medical device fabrication.