Primary and Revision Hip Arthroscopy in Borderline Hip Dysplasia Shows Comparable Outcomes at Minimum 5-Year Follow-Up

PURPOSE

To compare patient-reported outcomes (PROs), achievement of clinically significant outcomes (CSOs), and reoperation-free survivorship between primary and revision hip arthroscopy (HA) for femoroacetabular impingement syndrome (FAIS) in propensity-matched borderline hip dysplasia (BHD) patients at minimum 5-year follow-up.

METHODS

Patients with BHD, characterized by a lateral center-edge angle 18°-25°, who underwent HA for FAIS with capsular repair by a single surgeon between 01/2012-06/2018 with minimum 5-year follow-up were identified. Cases of revision HA were propensity-matched 1:2 to cases of primary HA, controlling for age, sex, and body mass index (BMI). A 1:2 ratio was chosen to maximize the number of included patients. Collected PROs included: Hip Outcome Score-Activities of Daily Living and Sport Subscales, International Hip Outcome Score 12, modified Harris Hip Score, and Visual Analog Scale for Pain. Achievement of minimal clinically important difference (MCID), patient acceptable symptom state (PASS), and substantial clinical benefit (SCB) for any measured PRO were compared between groups along with reoperation-free survivorship using Kaplan-Meier analysis.

RESULTS

Thirty-six revision HA hips (34 patients) were propensity-matched to 72 primary HA hips (70 patients). The groups were similar in age (31.5±10.3 years vs. 30.5±11.2,P=0.669), sex (69.4% female vs. 70.8%,P=0.656), and BMI (25.7±4.0 kg/m2 vs. 25.5±3.7,P=0.849). The revision group showed a greater prevalence of prolonged preoperative pain (50.0% vs. 27.8%,P=0.032) compared to the primary group. A significant improvement in all PROs was observed for both groups with comparable PROs preoperatively and at 5-year follow-up between groups (P≥0.086). The revision and primary groups showed comparable MCID (95.0% vs. 95.7%,P=1.000), PASS (80.0% vs. 83.6%,P=0.757), and SCB (62.5% vs. 70.7%,P=0.603) achievement for any PRO. Comparable reoperation-free survivorship was observed (P=0.151).

CONCLUSION

Propensity-matched patients with BHD undergoing primary and revision hip arthroscopy for FAIS achieved similar minimum 5-year PROs, CSOs, and reoperation-free survivorship.

LEVEL OF EVIDENCE

Level III, Retrospective Comparative Case Series.

Outcomes of Flexibility Sport Athletes With Borderline Hip Dysplasia After Hip Arthroscopy for Femoroacetabular Impingement Syndrome: A Propensity-Matched Analysis at Minimum 2-Year Follow-up

BACKGROUND

Hip arthroscopy has proved successful in treating femoroacetabular impingement syndrome (FAIS) in patients with and without borderline hip dysplasia (BHD). Despite a high prevalence of BHD in patients who participate in sports with high flexibility requirements, a paucity of literature evaluates the efficacy of hip arthroscopy in treating FAIS in flexibility sport athletes with BHD.

PURPOSE

To compare minimum 2-year patient-reported outcomes (PROs) and achievement of clinically significant outcomes in flexibility sport athletes with BHD undergoing primary hip arthroscopy for FAIS with capsular plication with results in flexibility sport athletes without dysplasia.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Data were prospectively collected for patients undergoing primary hip arthroscopy for FAIS with BHD, defined as a lateral center-edge angle of 18° to 25°, who reported participation in a sport with a high flexibility requirement, including dance, gymnastics, figure skating, yoga, cheerleading, and martial arts, according to previous literature. These patients were matched 1:2 to flexibility sport athletes without dysplasia, controlling for age, sex, and body mass index. Preoperative and minimum 2-year postoperative PROs were collected and compared between groups. Cohort-specific minimal clinically important difference and patient acceptable symptom state achievement was compared between groups.

RESULTS

In total, 52 flexibility sport athletes with BHD were matched to 104 flexibility sport athletes without BHD. Both groups showed similar sport participation (P = .874) and a similar level of competition (P = .877). Preoperative lateral center-edge angle (22.2°± 1.6° vs 31.5°± 3.9°; P < .001) and Tönnis angle (10.9°± 3.7° vs 5.8°± 4.4°; P < .001) differed between groups. Capsular plication was performed in all cases. Both groups achieved significant improvement in all PROs (P < .001) with no differences in postoperative PROs between groups (P≥ .147). High minimal clinically important difference (BHD group: 95.7%; control group: 94.8%) and patient acceptable symptom state (BHD group: 71.7%; control group: 72.2%) achievement for any PRO was observed with no differences between groups (P≥ .835).

CONCLUSION

Flexibility sport athletes with BHD achieved similar outcomes as those of flexibility sport athletes without BHD after hip arthroscopy for FAIS with capsular plication.

Hip Arthroscopy Patients With Lower Back Pain Show Delayed Clinical Improvement and Inferior Time-Dependent Survivorship: A Propensity Matched Study at Mid-Term Follow-Up

PURPOSE

To evaluate patient-reported outcomes (PROs) and survivorship at mid-term follow-up after hip arthroscopy (HA) for femoroacetabular impingement syndrome (FAIS) in patients with and without preoperative lower back pain (LBP).

METHODS

Patients with self-endorsed preoperative LBP who underwent HA for FAIS with mid-term follow-up were identified and propensity matched 1:1 to patients without back pain by age, sex, and body mass index (BMI). PROs collected preoperatively and at postoperative years 1, 2, and 5 included Hip Outcome Score-Activities of Daily Living (HOS-ADL) and Hip Outcome Score-Sports Subscale (HOS-SS), 12-item International Hip Outcome Tool (iHOT-12), modified Harris Hip Score (mHHS), and Visual Analog Scale (VAS) for Pain. Achievement of minimal clinically important difference (MCID) and patient acceptable symptom state (PASS) were compared. Survivorship was compared with Kaplan-Meier analysis.

RESULTS

In total, 119 patients with LBP were matched to 119 patients without LBP. Group demographic factors were as follows: age (37.4 ± 11.9 vs 37.6 ± 12.6 years, P = .880), sex (64.4% vs 67.7% female, P = .796), and BMI (25.3 ± 5.1 vs 25.3 ± 5.4, P = .930). Average follow-up duration was 6.0 ± 1.9 years. LBP patients showed similar preoperative PROs, yet lower 1-year scores for all PROs (P ≤ .044). At final follow-up, similar PROs were shown between groups (P ≥ .196). LBP and non-LBP patients had similar MCID achievement for HOS-ADL (59.3% vs 63.1%, P = .640), HOS-SS (73.9% vs 70.8%, P = .710), mHHS (66.7% vs 73.4%, P = .544), iHOT-12 (85.1% vs 79.4%, P = .500), and VAS Pain (75.6% vs 69.9%, P = .490). Groups also had similar PASS achievement for HOS-ADL (63.5% vs 61.3%, P = .777), HOS-SS (57.0% vs 62.5%, P = .461), mHHS (81.9% vs 79.1%, P = .692), iHOT-12 (54.6% vs 61.2%, P = .570), and VAS Pain (51.0% vs 55.4%, P = .570). Additionally, achievement of MCID ≥ 1 PRO (P ≥ .490) and PASS ≥ 1 PRO (P ≥ .370) was similar across groups. Conversion to total hip arthroplasty occurred in 3.4% of hips with LBP and 0.8% of hips without LBP (P = .370). Back pain patients demonstrated inferior time-dependent survivorship compared with patients without back pain on Kaplan-Meier survival analysis (P = .023).

CONCLUSIONS

Patients undergoing primary hip arthroscopy for FAIS with LBP achieve comparable PROs and clinically significant outcomes to patients without back pain at mid-term, despite lower 1-year PRO scores. LBP patients show inferior reoperation-free time-dependent survivorship compared with those without LBP.

LEVEL OF EVIDENCE

Level III, retrospective comparative case series.

Six-Month Outcomes Correlate with 10-Year Outcomes Following Hip Arthroscopy for Femoroacetabular Impingement Syndrome

PURPOSE

To identify whether 6-month outcomes following hip arthroscopy for FAIS correlate with outcomes at minimum 10-year follow-up.

METHODS

Patients who underwent primary hip arthroscopy for FAIS from 2012-2013 were reviewed and included if they had 6-month and minimum 10-year follow-up. Patient-reported outcome (PRO) measures included Hip Outcome Score Activities of Daily Living (HOS-ADL) and Sports-Specific (HOS-SS) subscales, modified Harris Hip Score (mHHS), and Visual Analog Scales for Pain (VAS-P) and Satisfaction (VAS-S). Six-month and 10-year outcome scores were compared and the relationships between 6-month and 1-, 2-, 5-, and 10-year outcome scores were analyzed using Pearson correlation coefficients (r). 6-month scores and clinically significant outcome (CSO) achievement were then compared to 10-year CSO achievement and reoperations, including revision hip arthroscopy and total hip arthroplasty (THA) conversion, using logistic regressions and Fisher's exact tests.

RESULTS

Sixty patients (60.0% female, age: 36.0±12.2 years) were included. mHHS, VAS-P, and VAS-S significantly improved from 6-month to 10-year follow-up (p≤0.021), while HOS-ADL and HOS-SS did not (p≥0.072). There were significant correlations between 6-month and 10-year scores for HOS-ADL (r=0.505), HOS-SS (r=0.592), and mHHS (r=0.362, p≤0.022 for all), as well as significant correlations between 6-month and 1-, 2-, and 5-year scores (p<0.014, for all). 6-month HOS-ADL, HOS-SS, and mHHS were all significantly associated with their respective 10-year PASS achievement (p≤0.044). Furthermore, 6-month HOS-ADL and mHHS were significantly associated with THA conversion (p≤0.041). Comparable 6-month and 10-year minimal clinically important difference (96.5% vs. 97.8%, p=1.000) and patient acceptable symptom state (85.2% vs. 87.5%, p=1.000) achievement for any PRO was observed.

CONCLUSION

Following hip arthroscopy for FAIS, patients' 6-month HOS-ADL and mHHS scores were significantly associated with their 10-year PROs, PASS achievement, and THA conversion; although, correlation strengths decreased with increasing time from surgery.

LEVEL OF EVIDENCE

IV, case series.

Gluteus Repair Yields Satisfactory Clinically Significant Outcome Achievement by 1 Year in Mostly Partial-Thickness Tears With Preoperative Hip Abduction Weakness Associated With Delayed Achievement

PURPOSE

To define the time to achievement of clinically significant outcomes (CSOs) after primary gluteus medius and/or minimus (GM) repair and to identify factors associated with delayed CSO achievement.

METHODS

Patients who underwent primary GM repair between January 2012 and June 2021 with complete preoperative, 6-month, 1-year, and 2-year Hip Outcome Score-Activities of Daily Living (HOS-ADL) were retrospectively identified. Cohort-specific minimal clinically important difference (MCID) and patient acceptable symptom state (PASS) were calculated. The time to achievement of MCID and PASS was analyzed using Kaplan-Meier survival analysis. Median time to MCID and PASS achievement was recorded. Multivariate stepwise Cox regressions were used to identify factors associated with delayed CSO achievement.

RESULTS

Fifty GM repairs were identified (age 59.4 ± 9.7 years, body mass index 27.9 ± 6.2, 94% female). Tears were grade 1 in 39 cases, grade 2 in 7 cases, and grade 3 in 4 cases. Endoscopic repair was performed in 35 cases, and open repair was performed in 15 cases. Labral debridement and repair were each performed in 15 cases. Median time to CSO achievement was 5.7 months for MCID and 11.0 months for PASS. The 2-year cumulative probability of MCID and PASS achievement was 92.7% and 66.7%, respectively. Preoperative hip abduction weakness on physical examination was associated with delayed achievement of MCID (hazard ratio 2.27, confidence interval 1.067-7.41, P = .039) and PASS (hazard ratio 3.89, confidence interval 1.341-11.283, P = .012).

CONCLUSIONS

This study demonstrated that in patients undergoing repair of primarily grade 1 GM tears, most achieved MCID by 6 months, and more than one half achieved PASS by 12 months. Preoperative hip abduction weakness on physical examination was associated with delayed CSO achievement.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

The Promising 2-Year Performance of the Patient-Reported Outcomes Measurement Information System in Primary Hip Arthroscopy for Femoroacetabular Impingement Syndrome

BACKGROUND

Minimal clinically important difference (MCID) and patient acceptable symptom state (PASS) thresholds have been previously defined for the Patient-Reported Outcomes Measurement Information System (PROMIS) at 1-year follow-up in patients undergoing hip arthroscopy for femoroacetabular impingement syndrome; however, the MCID and PASS thresholds are yet to be defined for the PROMIS at 2-year follow-up.

PURPOSE

(1) To establish MCID and PASS thresholds for the PROMIS Pain Interference (PROMIS-PI) and PROMIS Physical Function (PROMIS-PF) at 2-year follow-up and (2) to correlate PROMIS scores with hip-specific patient-reported outcome measure (PROM) scores.

STUDY DESIGN

Cohort study (diagnosis); Level of evidence, 3.

METHODS

Patients undergoing primary hip arthroscopy for femoroacetabular impingement syndrome between August and November 2020 with preoperative and minimum 2-year postoperative data were identified. Collected scores included those for the PROMIS-PI, PROMIS-PF, Hip Outcome Score-Activities of Daily Living (HOS-ADL), Hip Outcome Score-Sports Subscale (HOS-SS), International Hip Outcome Tool-12 (iHOT-12), and visual analog scale (VAS) for pain. MCID thresholds were calculated using the distribution-based method and PASS thresholds using the anchor-based method. Pearson correlation coefficients were used to compare scores between PROMs.

RESULTS

A total of 65 patients met the criteria for inclusion (72.3% female; mean age, 36.9 ± 13.5 years; mean body mass index, 26.2 ± 6.0). The mean follow-up was 25.3 ± 3.3 months. Significant preoperative to postoperative improvements were observed for all PROMs (P < .001). MCID thresholds and achievement rates were as follows: HOS-ADL, 10.1 and 75%, respectively; HOS-SS, 13.8 and 79%, respectively; iHOT-12, 14.0 and 67%, respectively; VAS pain, -13.8 and 78%, respectively; PROMIS-PI, -4.7 and 65%, respectively; and PROMIS-PF, 5.8 and 60%, respectively. PASS thresholds and achievement rates were as follows: HOS-ADL, 78.7 and 67%, respectively; HOS-SS, 76.4 and 62%, respectively; iHOT-12, 67.4 and 60%, respectively; VAS pain, 25.5 and 61%, respectively; PROMIS-PI, 57.0 and 65%, respectively; and PROMIS-PF, 45.6 and 58%, respectively. PROMIS-PI scores correlated most strongly with HOS-ADL (r = -0.836), HOS-SS (r = -0.767), and iHOT-12 (r = -0.719) scores and exhibited at least moderate correlations (r≥-0.595) with the other PROM scores. PROMIS-PF demonstrated moderate correlations with all the other PROM scores (r≥-0.586). Strong correlations were seen between the hip-specific PROM scores (r≥-0.745).

CONCLUSION

This study defined 2-year MCID and PASS thresholds for the PROMIS-PI and PROMIS-PF and demonstrated moderate to strong correlations between PROMIS scores and hip-specific PROM scores.

Cartilage Defects Are Negatively Associated With Long-Term Hip Survivorship Following Contemporary Hip Arthroscopy for Femoroacetabular Impingement Syndrome: A Propensity-Matched Analysis at Minimum 10-Year Follow-Up

PURPOSE

To identify the timing and risk factors associated with secondary surgery following primary hip arthroscopy for femoroacetabular impingement syndrome (FAIS) at 10-year minimum follow-up.

METHODS

A prospectively collected clinical repository was evaluated for cases of primary hip arthroscopy for FAIS between January 2012 and February 2013 with minimum 10-year follow-up. Patients who underwent secondary surgery were propensity matched 1:4 to patients who did not undergo secondary surgery, controlling for age, sex, and body mass index (BMI). The groups were compared on demographics, radiographs, intraoperative findings, operative procedures, and patient-reported outcomes. A Kaplan-Meier survivorship curve was generated. Among the reoperation-free survivors, minimal clinically important difference (MCID) and patient acceptable symptom state (PASS) achievement were recorded for Hip Outcome Score-Activities of Daily Living (HOS-ADL), Hip Outcome Score-Sports Specific (HOS-SS) subscales, modified Harris Hip Score (mHHS), 12-item international Hip Outcome Tool (iHOT-12), and Visual Analog Scale for Pain (VAS Pain).

RESULTS

Twenty-four reoperation patients (67% female; age 40.1 ± 14.3 years; BMI 27.2 ± 5.5) were matched to 96 reoperation-free patients (62% female; age 37.0 ± 10.8 years; BMI 25.2 ± 4.7, P ≥ .111). Mean follow-up was 10.3 ± 0.2 years. No preoperative demographic differences were found between groups. The reoperation group showed more high-grade cartilage defects on the acetabulum and femoral head (33% vs 8%, P = .004; 29% vs 7%, P = .007). A bimodal distribution of time to reoperation was evidenced independent of the secondary surgery performed. Among the reoperation-free survivors, MCID and PASS achievement was as follows: HOS-ADL (69.1%, 62.1%), HOS-SS (69.9%, 74.4%), mHHS (73.3%, 58.1%), iHOT-12 (n/a, 63.8%), and VAS-Pain (80.2%, 62.6%).

CONCLUSIONS

Patients requiring reoperation following primary hip arthroscopy for FAIS demonstrated more severe cartilage defects and a bimodal distribution of time to reoperation.

LEVEL OF EVIDENCE

Level III, retrospective comparative case series.

2-Chlorofatty acids are biomarkers of sepsis mortality and mediators of barrier dysfunction in rats

Sepsis is defined as the systemic, dysregulated host immune response to an infection that leads to injury to host organ systems and, often, death. Complex interactions between pathogens and their hosts elicit microcirculatory dysfunction. Neutrophil myeloperoxidase (MPO) is critical for combating pathogens, but MPO-derived hypochlorous acid (HOCl) can react with host molecular species as well. Plasmalogens are targeted by HOCl, leading to the production of 2-chlorofatty acids (2-CLFAs). 2-CLFAs are associated with human sepsis mortality, decrease in vitro endothelial barrier function, and activate human neutrophil extracellular trap formation. Here, we sought to examine 2-CLFAs in an in vivo rat sepsis model. Intraperitoneal cecal slurry sepsis with clinically relevant rescue therapies led to ∼73% mortality and evidence of microcirculatory dysfunction. Plasma concentrations of 2-CLFAs assessed 8 h after sepsis induction were lower in rats that survived sepsis than in nonsurvivors. 2-CLFA levels were elevated in kidney, liver, spleen, lung, colon, and ileum in septic animals. In vivo, exogenous 2-CLFA treatments increased kidney permeability, and in in vitro experiments, 2-CLFA also increased epithelial surface expression of vascular cell adhesion molecule 1 and decreased epithelial barrier function. Collectively, these studies support a role of free 2-CLFAs as biomarkers of sepsis mortality, potentially mediated, in part, by 2-CLFA-elicited endothelial and epithelial barrier dysfunction.

Fraser syndrome without cryptophthalmos: Two cases

Fraser syndrome (MIM#219000) is an autosomal recessive disorder, characterized by the association of cryptophthtalmos, syndactyly of the four extremities, urinary tract abnormalities and laryngo-tracheal anomalies. This condition is due to homozygous or compound heterozygous mutations in the FRAS/FREM complex genes: FRAS1, FREM2 and GRIP1. Here we report two atypical cases of Fraser syndrome due to mutations in the FRAS1 gene without cryptophthalmos. The first proband had syndactyly of three extremities, bilateral nostril coloboma, dysplastic ears with bilateral conductive hearing loss, blepharophimosis and lacrimal duct abnormalities. FRAS1 sequencing identified two pathogenic compound heterozygous variants: a nonsense variant in exon 70 and a missense variant in exon 24. The second proband had membranous syndactyly of the four extremities, left renal agenesis, laryngeal and ano-rectal malformations, dysplastic ears and bilateral conductive hearing loss. FRAS1 sequencing identified a pathogenic homozygous variant in the last exon of the gene. This first description of molecularly confirmed cases with Fraser syndrome without cryptophthalmos could contribute to further delineation of the clinical spectrum of Fraser syndrome, especially for possible phenotypically milder cases. Larger cohorts are required to try to refer the hypothesis of genotype-phenotype correlation.

Optical performance of an oscillating, pinned-contact double droplet liquid lens

Liquid droplets can produce spherical interfaces that are smooth down to the molecular scale due to surface tension. For typical gas/liquid systems, spherical droplets occur on the millimeter and smaller scales. By coupling two droplets, with contact lines pinned at each edge of a cylindrical hole through a plate, a biconvex lens is created. Using a sinusoidal external pressure, this double droplet system (DDS) can be readily forced to oscillate at resonance. The resulting change in the curvatures of the droplets produces a time-varying focal length. Such an oscillating DDS was introduced in 2008 [Nat. Photonics 2, 610 (2008)]. Here we provide a more comprehensive description of the system's optical performance, showing the effects of liquid volume and driving pressure amplitude on the back focal distance, radii of curvature, object distance, and image sharpness.

Electromagnetic liquid pistons for capillarity-based pumping

The small scales associated with lab-on-a-chip technologies lend themselves well to capillarity-dominated phenomena. We demonstrate a new capillarity-dominated system where two adjoining ferrofluid droplets can behave as an electronically-controlled oscillator or switch by an appropriate balance of magnetic, capillary, and inertial forces. Their oscillatory motion can be exploited to displace a surrounding liquid (akin to an axial piston pump), forming electromagnetic "liquid pistons." Such ferrofluid pistons can pump a precise volume of liquid via finely tunable amplitudes (cf. pump stroke) or resonant frequencies (cf. pump speed) with no solid moving parts for long-term operation without wear in a small device. Furthermore, the rapid propagation of electromagnetic fields and the favorable scaling of capillary forces with size permit micron sized devices with very fast operating speeds (∼kHz). The pumping dynamics and performance of these liquid pistons is explored, with experimental measurements showing good agreement with a spherical cap model. While these liquid pistons may find numerous applications in micro- and mesoscale fluidic devices (e.g., remotely activated drug delivery), here we demonstrate the use of these liquid pistons in capillarity-dominated systems for chip-level, fast-acting adaptive liquid lenses with nearly perfect spherical interfaces.

Coarsening of capillary drops coupled by conduit networks

A system of n spherical-cap drops, coupled by a network of conduits, coarsens due to surface tension forces. The total interfacial energy drives the fluid through the conduits such that, with time, the volume becomes increasingly localized into fewer large drops. The coarsening rate is predicted heuristically for drops coupled by orthogonal networks, a porous medium, and fractal networks of various dimensions. The predicted coarsening law as it depends upon the type and dimension of network, total number of drops, and initial drop volume is compared against numerical simulations of large n . Additionally, distributions of large drop volumes are obtained using a Lifshitz-Slyozov-Wagner (LSW) model. The predicted distributions are independent of network topology; in contrast, simulation results depend weakly on the network dimension. The heuristic coarsening rate laws are recovered using the LSW model for all but a square network topology.

Determination of the zeta potential of porous substrates by droplet deflection: II. Generation of electrokinetic flow in a nonpolar liquid

Here we study the nature and extent of free electrical charges in nonpolar liquids, using a recently introduced technique of observing droplet deflection generated by electrokinetic flow in a porous substrate. In the presence of dispersed water, surfactant molecules agglomerate and inverted micelles are generated which may act as charge carriers. In the present work, the conductivities of solutions of a nonpolar liquid with several concentrations of a dissolved surfactant are measured by electrical transients. The induced current densities are proportional to the applied voltage, indicating that the solutions represent an ohmic system. The conductivity does not scale simply with the surfactant concentration, though. It is inferred that different micellization mechanisms exist depending on the surfactant concentration, and a model is sketched. Further experiments reveal that flows of such solutions can be generated within saturated porous substrates when they are subjected to moderate electric fields. An investigation of the phenomena leads to the conclusion that these flows exist due to the presence of an electrical double layer; that is, they are of electrokinetic (electroosmotic) origin. Hence, the measured electrokinetic flow rates can be related to the zeta potential of the porous substrate saturated with the solution. Plotting the zeta potential against the logarithm of the ionic strength reveals a linear relationship.

Determination of the zeta potential of porous substrates by droplet deflection. I. The influence of ionic strength and pH value of an aqueous electrolyte in contact with a borosilicate surface

This paper presents a new method to determine the zeta potential of porous substrates in contact with a liquid. Electroosmosis, arising near the solid/liquid boundaries within a fully saturated porous substrate, pumps against the capillary pressure arising from the surface tension of a droplet placed in series with the pump. The method is based on measuring the liquid/gas interface deflection due to the imposed electric potential difference. The distinguishing features of our technique are accuracy, speed, and reliability, accomplished with a straightforward and cost-effective setup. In this particular setup, a bistable configuration of two opposing droplets is used. The energy barrier between the stable states defines the range of capillary resistance and can be tuned by the total droplet volume. The electroosmotic pump is placed between the droplets. The large surface area-to-volume ratio of the porous substrate enables the pumping strength to exceed the capillary resistance even for droplets small enough that their shapes are negligibly influenced by gravity. Using a relatively simple model for the flow within the porous substrate, the zeta potential resulting from the substrate-liquid combination is determined. Extensive measurements of a borosilicate substrate in contact with different aqueous electrolytes are made. The results of the measurements clarify the influence of the ionic strength and pH value on the zeta potential and yield an empirical relationship important to engineering approaches.

Effects of shearing flow with inertia on monolayer mesoscale structure

In an experimental flow system capable of imparting a well-controlled shear-rate distribution with inertia to a monolayer consisting of coexisting phases, we have studied the resulting phase morphology and domain fragmentation. These evolve on distinct time scales: the viscous time associated with the viscosity in the bulk and the Marangoni stress and the fragmentation/relaxation time associated with the phase morphology. A relationship between the microstructure (line tension) and macroflow (shear rate) determining the meso length scale of the coexisting phase domains has been deduced from dimensional analysis and was found to correlate well with the quantitative experimental observations.

The electroosmotic droplet switch: countering capillarity with electrokinetics

Electroosmosis, originating in the double-layer of a small liquid-filled pore (size R) and driven by a voltage V, is shown to be effective in pumping against the capillary pressure of a larger liquid droplet (size B) provided the dimensionless parameter sigmaR(2)/epsilon|zeta|VB is small enough. Here sigma is surface tension of the droplet liquid/gas interface, epsilon is the liquid dielectric constant, and zeta is the zeta potential of the solid/liquid pair. As droplet size diminishes, the voltage required to pump electroosmotically scales as V approximately R(2)/B. Accordingly, the voltage needed to pump against smaller higher-pressure droplets can actually decrease provided the pump poresize scales down with droplet size appropriately. The technological implication of this favorable scaling is that electromechanical transducers made of moving droplets, so-called "droplet transducers," become feasible. To illustrate, we demonstrate a switch whose bistable energy landscape derives from the surface energy of a droplet-droplet system and whose triggering derives from the electroosmosis effect. The switch is an electromechanical transducer characterized by individual addressability, fast switching time with low voltage, and no moving solid parts. We report experimental results for millimeter-scale droplets to verify key predictions of a mathematical model of the switch. With millimeter-size water droplets and micrometer-size pores, 5 V can yield switching times of 1 s. Switching time scales as B(3)/VR(2). Two possible "grab-and-release" applications of arrays of switches are described. One mimics the controlled adhesion of an insect, the palm beetle; the other uses wettability to move a particle along a trajectory.

Influence of coexisting phases on the surface dilatational viscosity of Langmuir monolayers

Monolayer hydrodynamics are usually described in terms of a Newtonian constitutive relationship. However, this macroscopic view fails to account for small-scale coexisting phase domains, which are generally present in the monolayer and appear to have profound macroscopic effects. Here, we provide direct evidence of these effects, consisting of Brewster angle microscopy images of the monolayer, space- and time-resolved interfacial velocity measurements, and comparisons with predictions based on the Navier-Stokes equations together with the classic model for a Newtonian interface.

Flow-induced patterning of Langmuir monolayers

Insoluble monolayers on water have been patterned at the macroscopic scale (i.e., at the centimeter scale of the flow apparatus) as well as the mesoscopic scale (i.e., down to the micron scale resolvable via optical microscopy). The macroscopic patterning at the air/water interface results from a hydrodynamic instability leading to a steadily precessing flow pattern. The velocity field is measured, and the associated shear stress at the interface is shown to be locally amplified by the flow pattern. The resulting hydrodynamic effects on two different monolayer systems are explored: (1) the pattern in a model monolayer consisting of micron-size, surface-bound particles is visualized to show that the particles are concentrated into isolated regions of converging flow with high shear, and (2) Brewster angle microscopy of a Langmuir monolayer (vitamin K1) shows not only that the monolayer is patterned at the macroscopic scale but also that the localized high-shear flow further patterns the monolayer at the mesoscale.

A molecular basis of cryopreservation failure and its modulation to improve cell survival

The requirement for more effective cryopreservation (CP) methodologies in support of the emerging fields of cell bioprocessing and cell therapy is now critical. Current CP strategies appropriately focus on minimizing the damaging actions of physicochemical stressors and membrane disruption associated with extra- and intracellular ice formation that occurs during the freeze-thaw process. CP protocols derived from this conceptual paradigm, however, yield suboptimal survival rates. We now provide the first report on the identification of delayed-onset cell death following CP and the significance of modulating molecular biological aspects of the cellular responses (apoptosis) to low temperature as an essential component to improve postthaw outcome. In this study we quantitatively examined the molecular basis of cell death associated with CP failure in a canine renal cell model. In addition, we report on the significant improvement in CP outcome through the modulation of these molecular mechanisms by the utilization of an organ preservation solution. HypoThermosol. Further, the utilization of HypoThermosol as the preservation medium and the modulation of molecular-based cell death have led to a paradigm shift in biologic preservation methodologies. The recognition of molecular mechanisms associated with CP-induced cell death offers the promise of improved CP of more complex and/or fragile biological systems such as stem cells, engineered tissues, and human organs.

Second-generation microstimulator

The first-generation injectable microstimulator was glass encased with an external tantalum capacitor electrode. This second-generation device uses a hermetically sealed ceramic case with platinum electrodes. Zener diodes protect the electronics from defibrillation shocks and from electrostatic discharge. The capacitor is sealed inside the case so that it cannot be inadvertently damaged by surgical instruments. This microstimulator, referred to as BION, is the main component of a 255-channel wireless stimulating system. BION devices have been implanted in rats for periods of up to 5 months. Results show benign tissue reactions resulting in identical encapsulation around BION and controls. Stimulation threshold levels did not change significantly over time and ranged between 0.81 to 1.35 mA for all the animals at a 60 micros pulse width. All of the tests performed to date indicate that the BION is safe and effective for long-term human implant. We have elected to develop BION applications by seeking collaboration with the research community through our BION Technology Partnership.

Health care in the distended society: the American hospital in its social contexts

The hospital at every stage in its development has been a product of social, political, cultural, and economic forces as well as a reflection of the kind of medical and scientific knowledge available in a given era. That we have as many hospitals as we do, that they are organized and financed the way are, that they practice the kind of medicine and provide the services they do (and that they now face the crises they do) is a result of past decisions in which health concerns sometimes played only a marginal role. Institutional inertia--the fact that institutions once set in motion cling tenaciously to life--means that a set of historical facts which have little to do with health care has saddled the United States with a hospital system that now distorts our health care expenditures and even affects how we think about disease and health.