Exploring biomechanical methods to study the human vaginal wall.

AIMS: To critically review studies of the biomechanical properties of connective tissue in the normal and prolapsed human vaginal wall and to identify criteria that are suitable for in vivo measurements which could improve patient management. METHODS: This review covers past and current ex vivo and in vivo instrumentation and analytical methods related to the elastic and viscoelastic properties of vaginal wall connective tissues. RESULTS: Classical methods, including digital evaluation of the vagina, histological and biomechanical studies of fresh and frozen-thawed extracts, and biomechanical cadaveric tissue studies have important limitations and have yielded inconsistent results. Newer biomechanical methods may resolve these inconsistencies. One of the more promising is transient, vacuum-induced tissue expansion and relaxation, via cutometer-like devices. The technique permits noninvasive observation, applicable to longitudinal studies of patients. In vivo and ex vivo biomechanical methods may better match vaginal wall tissue properties to help with the design of surgical mesh materials, thus improving surgical support and healing. CONCLUSION: Methods have been identified to characterize the in vivo biomechanical behavior of the prolapsing vagina which may serve to advance the care of affected women. Neurourol. Urodynam. 36:499-506, 2017. © 2016 Wiley Periodicals, Inc.

Current status of direct pulp-capping materials for permanent teeth.

Direct pulp-capping is a method for treating exposed vital pulp with dental material to facilitate the formation of reparative dentin and to maintain vital pulp. Two types of pulp-capping materials, calcium hydroxide and mineral trioxide aggregate, have been most commonly used in clinics, and an adhesive resin has been considered a promising capping material. However, until now, there has been no comprehensive review of these materials. Therefore, in this paper, the composition, working mechanisms and clinical outcome of these types of pulp-capping materials are reviewed.

Mechanical Interaction of an Expanding Coiled Stent with a Plaque-Containing Arterial Wall: A Finite Element Analysis.

Wall injury is observed during stent expansion within atherosclerotic arteries, related in part to stimulation of the inflammatory process. Wall stress and strain induced by stent expansion can be closely examined by finite element analysis (FEA), thus shedding light on procedure-induced sources of inflammation. The purpose of this work was to use FEA to examine the interaction of a coiled polymer stent with a plaque-containing arterial wall during stent expansion. An asymmetric fibrotic plaque-containing arterial wall model was created from intravascular ultrasound (IVUS) images of a diseased artery. A 3D model for a coil stent at unexpanded state was generated in SolidWorks. They were imported into ANSYS for FEA of combined stent expansion and fibrotic plaque-distortion. We simulated the stent expansion in the plaqued lumen by increasing balloon pressure from 0 to 12 atm in 1 atm step. At increasing pressure, we examined how the expanding stent exerts forces on the fibrotic plaque and vascular wall components, and how the latter collectively resist and balance the expansive forces from the stent. Results show the expanding coiled stent creates high stresses within the plaque and the surrounding fibrotic capsule. Lower stresses were observed in adjacent medial and adventitial layers. High principal strains were observed in plaque and fibrotic capsule. The results suggest fibrotic capsule rupture might occur at localized regions. The FEA/IVUS method can be adapted for routine examination of the effects of the expansion of selected furled stents against IVUS-reconstructed diseased vessels, to improve stent deployment practices.

Influence of body mass index on the biomechanical properties of the human prolapsed anterior vaginal wall.

INTRODUCTION AND HYPOTHESIS: We report the influence of body mass index (BMI) on the biomechanical properties of human prolapsed anterior vaginal wall (AVW) tissue samples. We hypothesize that women with AVW prolapse would have the same vaginal wall biomechanical properties regardless of their weight. METHODS: Following Institutional Review Board approval, age-comparable postmenopausal women with symptomatic stage II-III AVW prolapse underwent excision of a short vaginal wall sample during transvaginal prolapse repair. Excised samples were subjected to uniaxial tensile testing using an Instron 5655 (Instron, Norwood, MA, USA) within 2 h of harvest to measure intrinsic biomechanical properties. Patients were divided into two groups (A: BMI <25 and B: BMI >25) to compare tissue biomechanical properties after controlling for age and parity. RESULTS: From 2011 to 2013, 28 consecutive women were studied, 13 in group A and 15 in group B. Patients with BMI >25 developed higher tissue stresses, including higher tangent moduli, at selected strain levels than patients with BMI <25. CONCLUSIONS: Contrary to our hypothesis, this study observed a relationship between BMI and human AVW biomechanical properties, with more obese women having stiffer tissue properties.

Influence of powder composition and morphology on penetration of Gray and White ProRoot mineral trioxide aggregate and calcium hydroxide into dentin tubules.

This study examined the influence of powder composition and morphology on the penetration of Gray and White ProRoot mineral trioxide aggregate (GMTA, WMTA) and calcium hydroxide (CH) into open dentin tubules. GMTA, WMTA, and CH particle dimensions were analyzed by flow particle image analysis (FPIA). Penetration of open dentin tubules into dentin discs was studied by scanning electron microscopy. Five samples of each material were randomly selected and prepared for this study. The GMTA averages for length (µm), width (µm), perimeter (µm), and aspect ratio were 1.94 ± 1.65, 1.43 ± 1.19, 5.61 ± 4.27, and 0.76 ± 0.14, respectively. Corresponding averages for WMTA were 2.04 ± 1.87, 1.49 ± 1.33, 5.88 ± 4.81, and 0.76 ± 0.14, and for CH were 2.26 ± 1.99, 1.62 ± 1.46, 6.70 ± 5.60, and 0.74 ± 0.15, respectively. The rank order of the averages for particle length, width and perimeter from the largest to the smallest material was CH > WMTA > GMTA. The rank order of the averaged aspect ratios was GMTA > WMTA > CH. SEM showed that all three materials, when deposited and agitated on dentin discs, penetrated the open dentin tubules. Tubule occlusion occurred as particle surface concentrations increased. Significant differences in particle length, width, perimeter, and aspect ratio were observed for GMTA, WMTA, and CH (P < 0.0001 in all cases). All particle types penetrated into open tubules when agitated on dentin discs; all tubules were eventually occluded as particle concentrations grew. (J Oral Sci 56, 287-293, 2014).

Viscoelastic properties measurement of the prolapsed anterior vaginal wall: a patient-directed methodology.

OBJECTIVE: In-vivo measurement of the viscoelastic properties of the prolapsed anterior vaginal wall (AVW) in post-menopausal women undergoing cystocele repair. STUDY DESIGN: A BTC-2000 cutometer-like instrument was introduced during vaginal repair of symptomatic stage 2-3 AVW prolapse. Under anesthesia, 10-mm orifice probe was applied to the AVW at the level of the bladder neck. A suction pressure ramp (0 to -147 mmHg in 6s) was delivered causing tissue uplift, followed by immediate release to 0 mmHg, measuring tissue relaxation for 20s. Similar measurements were performed over the suprapubic region (SP) for comparison purpose. The rate of tissue recovery was obtained by fitting a Voigt model to the data and expressing results as the ratio E/η [(spring modulus E)/(dashpot viscosity η)]. The effective strain energy (SE) was calculated from the pressure-uplift data and evaluated from initiation to: (1) maximum storage in tissue at peak vacuum; (2) tissue recovery after vacuum release; (3) net SE loss over the entire loading-unloading cycle. RESULTS: In 22 women, higher AVW peak and residual tissue uplift values, and lower E/η ratios were found compared with SP results. The AVW stored less elastic strain energy at peak vacuum than did the SP, and AVW net energy loss over the uplift-recovery cycle was greater than for SP controls. Not only was the AVW more compliant than the SP, with higher viscous damping, but the tissue was also less able to store recoverable energy upon distension. CONCLUSION: Such in-vivo measurements quantify the biomechanical properties of the prolapsed AVW and may assist in its management.

Thymosin ß4 sustained release from poly(lactide-co-glycolide) microspheres: synthesis and implications for treatment of myocardial ischemia.

A sustained release formulation for the therapeutic peptide thymosin ß4 (Tß4) that can be localized to the heart and reduce the concentration and frequency of dose is being explored as a means to improve its delivery in humans. This review contains concepts involved in the delivery of peptides to the heart and the synthesis of polymer microspheres for the sustained release of peptides, including Tß4. Initial results of poly(lactic-co-glycolic acid) microspheres synthesized with specific tolerances for intramyocardial injection that demonstrate the encapsulation and release of Tß4 from double-emulsion microspheres are also presented.

Do biomechanical properties of anterior vaginal wall prolapse tissue predict outcome of surgical repair?

PURPOSE: We determined the relevance of the biomechanical properties of freshly harvested vaginal tissue during large cystocele repair on clinical outcome at a minimum 1-year followup. MATERIALS AND METHODS: With institutional review board approval we prospectively studied the biomechanical properties of full thickness vaginal wall tissue from postmenopausal women with symptomatic Baden-Walker prolapse undergoing anterior vaginal wall suspension with cystocele repair from 2002 to 2005. A standardized biomechanical protocol was applied with stress-strain curves for Young's modulus obtained by blinded investigators. Failed repair was defined as recurrence on examination or reoperation for recurrent anterior prolapse. RESULTS: A total of 32 patients (median age 72 years) had a median followup of 34 months (range 12 to 62). Median Young's modulus was statistically different in tissue samples transported in immersed vs moistened media (median 3.8 vs 7.6, p = 0.008). Associations between Young's modulus and clinical variables were described. On followup 7 patients experienced failure of the repair. After controlling for tissue transport protocol no association was seen between Young's modulus and failures (HR 1.1, p = 0.34). CONCLUSIONS: This study found no association between Young's modulus and clinical results at long-term followup. This finding suggests that retropubic scarring and pelvic floor muscle properties may be more important for a successful reparative outcome than the intrinsic properties of the vaginal wall.

Formulation and characterization of a covalently coated magnetic nanogel.

The aim of this study was to develop a novel method to encapsulate magnetic nanoparticles (MNPs) with polymer via covalent bonding, in order to increase the magnetic nanoparticle stability and ease the synthesis process. In this technique, silane coated MNPs act as a template for polymerization of the monomer N-isopropylacrylamide, (NIPA) via radical polymerization. Transmission and scanning electron microscopy indicated the size of the original MNP was approximately 10 nm, the silane-coated MNP was 40 nm and the NIPA silane-coated MNP was 100 +/- 10 nm. Chemical composition and chemical state analysis of NIPA MNPs by FTIR and XPS showed that the MNPs were actually encapsulated by silane and NIPA. Furthermore, the magnetic properties of different layers on the MNP, analyzed by SQUID, indicated a decrease in saturation magnetization for each layer. The results demonstrate the feasibility of encapsulation of the MNP with NIPA by means of silane covalent bonding. Future work will investigate the phase transition and biocompatibility properties of the NIPA-coated MNP for drug delivery and tissue engineering applications.

Methodology for biomechanical testing of fresh anterior wall vaginal samples from postmenopausal women undergoing cystocele repair.

GOAL: To explore the methodological challenges of biomechanical testing of freshly harvested human anterior vaginal wall (HAVW) samples. METHOD: Longitudinal full-thickness samples of HAVW were excised during cystocele repair in postmenopausal women and age-matched controls. Two methods of tissue storage during transport were compared. All samples were prepared for uniaxial testing within 2 hr of harvest and loaded at a rate of 0.5 mm/sec, until irreversible deformation was observed. Young's modulus and other parameters were extracted from the tensile stress-strain curves. RESULTS: Samples were obtained over 2 years from 42 patients. Significant differences in biomechanical parameters were noted based on the degree of hydration of the tissue, suggesting that the wetter samples were mechanically weaker. CONCLUSIONS: This study reports on a new method for testing the biomechanical properties of freshly harvested HAVW tissues and the impact of tissue hydration during transport between the operating room and the testing lab.

The influence of thermal treatment on the mechanical characteristics of a PLLA coiled stent.

We studied the effects of thermal treatment on the expansive characteristics of a coil-within-coil Poly(L-lactic acid) (PLLA) fiber stent developed at our institution to improve its mechanical performance and reproducibility. Following fabrication, furled stents were thermally treated at 62 degrees C for 25 min. The mechanical characteristics were measured compared with those of untreated stents when both were expanded via sequential balloon catheter pressure loading up to 12 atm. Treated stents reached full diameter at 3 atm and maintained that diameter despite further pressure increases. Using measurements of pressure, diameter, and axial length, we calculated the sequential mechanical work required to unfurl the stent. The mechanical work for complete unfurling of treated stents was significantly less than that required for untreated controls. Little axial dimensional change was observed for treated stents. Treated stents exhibited higher stiffness than controls at all pressure levels and also demonstrated higher resistance to external pressure-induced collapse, as measured in a special apparatus developed in our laboratory. Differential scanning calorimetry measurements indicated higher crystallinity values for fibers used in treated stents compared with controls. SEM examination of striations revealed that treated stents underwent less twist than controls following balloon-induced unfurling. The results indicate that, thermal treatment improves the reorientation and realignment of fiber crystalline structure, and favorably influences on the fiber stress-strain behavior and the expansive mechanical characteristics of the PLLA fiber stents.

Monocyte activation in on-pump versus off-pump coronary artery bypass surgery.

OBJECTIVE: Monocyte activation plays a key role in amplifying both inflammatory and coagulopathic sequelae in patients undergoing on-pump coronary artery bypass graft (CABG) surgery. Off-pump CABG diminishes, but does not eliminate, the systemic inflammatory response and its influence on monocyte activation remains unclear. This study was performed to determine if off-pump CABG suppresses all features of monocyte activation. DESIGN: Prospective, controlled, clinical study. SETTING: University-affiliated veterans affairs hospital and laboratory. PARTICIPANTS: Twenty-two patients scheduled to undergo primary CABG surgery (11 on-pump and 11 off-pump). INTERVENTIONS: On-pump and off-pump CABG surgery was performed via median sternotomy. Anticoagulation and heparin reversal were identical. Moderate hypothermia (28 degrees-30 degrees C) was used for on-pump CABG surgery, whereas temperature was maintained above 35.5 degrees C for off-pump CABG. No antifibrinolytic agents were used. MEASUREMENTS AND MAIN RESULTS: Perioperative monocyte changes were assessed by using cellular (CD11b, monocyte-platelet conjugates) and secreted markers (plasma IL-6, IL-8, and IL-10) measured at 6 time points before, during, and after CABG surgery. Off-pump CABG surgery completely blocked the increases in monocyte CD11b expression (p < 0.001) and monocyte-platelet conjugate formation (p < 0.001) observed in the on-pump group. In contrast, plasma interleukin levels were significantly elevated in both groups, although off-pump CABG surgery resulted in lower levels (p < 0.001) and a delayed time course. CONCLUSIONS: Off-pump CABG surgery attenuates monocyte secreted cytokines and completely suppresses activation-dependent monocyte cell-surface changes (CD11b, monocyte-platelet conjugate formation). Whether these pathophysiologic differences in monocyte activation translate into a reduction in adverse events after CABG surgery warrants a larger, randomized, outcomes study.

Characterizing the expansive deformation of a bioresorbable polymer fiber stent.

Polymeric vascular stents must employ other strategies than malleable deformation, as generally practiced with metal stents, to expand and withstand compressive stresses in situ. The stent expansion strategy must further consider induced flow perturbations and wall stresses that may injure the vessel wall and promote thrombogenesis. Analyzing the stresses furled stents undergo during balloon-assisted expansion is an important first step in achieving a better understanding of stent-wall mechanical interactions, thereby to improve stent function. To this end, we performed finite element (FE) analysis of the balloon-induced unfurling of an internally coiled, bioresorbable polymeric stent employing a 3D FE solid model of a 120 degrees symmetric stent segment and a large deformation finite strain formulation. Uni-axial tensile testing of stent fiber elastic to plastic yielding provided the mechanical property information, and the von Mises criterion was employed to establish the elastic-plastic transition in the FE model. The model was validated with pressure and deformation measurements obtained during stent expansion tests. The internal coils of this inner coil-outer coil design twisted as the stent expanded, leading to plastic yielding at the point of tangency of the inner and outer coils. The remaining stent fiber portions underwent elastic bending. Cross-sections revealed only the outside surface layer of the coiled fiber underwent plastic yielding. The interior elastic fiber was supported by this plastic shell. The analysis suggests that during balloon-induced expansion, local plastic yielding in torsion "sets" the stent fibers, imparting high radial collapse resistance. The results further suggest that the stent exerts non-uniform mechanical forces on the vessel wall during expansion.

Single trocar laparoscopic nephrectomy using magnetic anchoring and guidance system in the porcine model.

PURPOSE: We assessed the feasibility of single keyhole laparoscopic surgery using a novel transabdominal magnetic anchoring and guidance system platform in the porcine model. MATERIALS AND METHODS: A collaborative research group was formed to build a prototype system of magnetically anchored instruments for trocar-free laparoscopy. The design mandate was that the developed technology should be able to deploy into the insufflated abdomen through an existing 12 mm diameter trocar and then be moved into position in the peritoneum by manipulating external magnets. The magnetic anchoring and guidance system concept was advanced to a working prototype with a system of external magnetic anchors, an internal camera system and a hook cautery supported by an intra-abdominal robotic arm. This prototype system was then evaluated in vivo in a porcine laparoscopic nephrectomy model. RESULTS: Two nonsurvival porcine laparoscopic nephrectomies were successfully completed without complications via a single 15 mm transumbilical trocar using the prototype magnetic anchoring and guidance system camera and the magnetically anchored robotic arm cauterizer. A conventional laparoscopic grasper was used for retraction through the 15 mm trocar after magnetic anchoring and guidance system deployment. The renal artery and vein were transected with a conventional Endo-GIA stapler introduced through the 15 mm trocar. Procedure time was not recorded and blood loss was minimal. CONCLUSIONS: Single trocar laparoscopic nephrectomy using magnetically anchored instrumentation is technically feasible, demonstrating that intracorporeal instrument manipulation may overcome the limitations of current laparoscopic and robotic surgery by allowing unhindered intra-abdominal movement. This single access technique may be used with natural orifice surgery approaches and it has the potential to realize incision-free intra-abdominal surgery.

Trocar-less instrumentation for laparoscopy: magnetic positioning of intra-abdominal camera and retractor.

OBJECTIVE: To develop a novel laparoscopic system of moveable instruments that are positioned intra-abdominally and "locked" into place by external permanent magnets placed on the abdomen. SUMMARY BACKGROUND DATA: In conventional laparoscopy, multiple trocars are required because of the limited degrees of freedom of conventional instrumentation, and the limited working envelope (an inverted cone) created by the fulcrum motion around each port. While robotic systems can improve the number of degrees of freedom, they are restricted by even smaller working envelopes. METHODS: A collaborative research group from the Department of Urology and the Automation & Robotics Research Institute of the University of Texas, Arlington built a prototype system of magnetically anchored instruments for trocar-less laparoscopy. The only design mandate was that the developed technology be able to pass into the abdomen through one existing 12-mm diameter trocar. RESULTS: A transabdominal "magnetic anchoring and guidance system" (MAGS) platform was developed to incorporate instruments, retractors, and a controllable intra-abdominal camera. In vitro, the platform was able to anchor 375 and 147 g across porcine tissue 1.8 and 2.5 cm thick, respectively. The permanent magnet platforms were sufficiently strong to retract the porcine liver and securely anchor the camera. Its versatility was demonstrated by moving the camera to virtually any location in the peritoneum with no working envelope restrictions and the subsequent completion of porcine laparoscopic procedures with 2 trocars only. CONCLUSIONS: Trocar-less laparoscopy using magnetically anchored instruments is feasible and may expand intracorporeal instrument manipulation substantially beyond current-day capability. The ability to reduce the number of trocars necessary for laparoscopic surgery has the potential to revolutionize surgical practice.

Phagocyte responses to degradable polymers.

Although many biodegradable polymers, such as poly-L-lactic acid and poly-L-glycolic acid, are preferentially composed of biological residues normally present in the human body, implants made of these materials often trigger inflammatory and fibrotic responses. Unfortunately, the mechanisms involved in degradable material-mediated tissue responses remain largely unknown. Using animal implantation and cell culture system models, we found a strong correlation between the rate of material degradation and the degree of inflammatory response to material implants. Furthermore, we have identified that both water-soluble and water-insoluble degradation products are potent triggers of phagocyte activation, including at the least, superoxide production. These results support a new concept that slow degradation may improve the biocompatibility of degradable drug-releasing particles and tissue engineering scaffolds.

Drug-eluting bioresorbable stents for various applications.

A stent is a medical device designed to serve as a temporary or permanent internal scaffold to maintain or increase the lumen of a body conduit. Metallic coronary stents were first introduced to prevent arterial dissections and to eliminate vessel recoil and intimal hyperplasia associated with percutaneous transluminal coronary angioplasty. The stent application range has expanded as more experience was gained, and encouraging results have been obtained in the treatment of vascular diseases. Stents are currently used for support of additional body conduits, including the urethra, trachea, and esophagus. The rationale for bioresorbable stents is the support of a body conduit only during its healing process. The stent mass and strength decrease with time, and the mechanical load is gradually transferred to the surrounding tissue. Bioresorbable stents also enable longer term delivery of drugs to the conduit wall from an internal reservoir and abolish the need for a second surgery to remove the device. The present review describes recent advances in bioresorbable stents, focusing on drug-eluting bioresorbable stents for various applications. Controlled release of an active agent from a stent can be used to enhance healing of the surrounding tissues, to increase the implant's biocompatibility, as well as to help cure certain diseases. Because a lot of research in this field has been done by us, examples for these functions are described based mainly on developments in our laboratories.

Selective tessellation algorithm for modeling interactions between surgical instruments and tissues.

We present a selective spatial tessellation algorithm that is specifically optimized for instrument-to-tissue and instrument-to-instrument collision detection cases, which are the essential part of interaction modeling in surgery simulation with haptic feedback. Virtual surgeries demand haptic rate collision solutions only when instruments are involved in collisions. Other collision cases can be processed at slower rates. The proposed selective tessellation algorithm is capable of differentiating among various collision cases and assigning different priorities to their processing. Without making assumptions about any object movement, the algorithm derives clipping volume as collision detection regions which tightly enclose the objects of interest. Results of implementation of the algorithm in a surgical simulation are provided.

A novel laparoscopic mesh placement part task trainer.

BACKGROUND: We present a surgical simulator, developed for the training of a laparoscopic surgery and in particular for mesh placement during an inguinal herniorrhaphy. METHODS: Major technical issues related to virtual surgery training systems include virtual patient modelling, collision detection and collision response, haptic and graphic rendering, 3-D motion tracking and some special effects, such as bleeding, cauterizing and so on. Among these problems, real-time deformation modelling and collision detection are the most challenging research topics. RESULTS: In this paper, we describe novel approaches addressing the above issues, which have been successfully adopted in our bimanual hernia repair simulator. CONCLUSION: The implementations of our new collision detection and deformation appear to work well, even at haptic rates for the limited scope of mesh placement training. More sophisticated techniques are needed for full organ deformation especially for blunt dissection simulation.