Bladder wall biomechanics: A comprehensive study on fresh porcine urinary bladder.

Regenerative medicine for reconstructive urogenital surgery has been widely studied during the last two decades. One of the key factors affecting the quality of bladder regeneration is the mechanical properties of the bladder scaffold. Insight into the biomechanics of this organ is expected to assist researchers with functional regeneration of the bladder wall. Due to extensive similarities between human bladder and porcine bladder, and with regard to lack of comprehensive biomechanical data from the porcine bladder wall (BW), our main goal here was to provide a thorough evaluation on viscoelastic properties of fresh porcine urinary BW. Three testing modes including Uniaxial tensile, ball-burst (BB) and Dynamic Mechanical Analysis (DMA) were applied in parallel. Uniaxial tests were applied to study how different circumferential and longitudinal cut-outs of lateral region of BW behave under load. DMA was used to measure the viscoelastic properties of the bladder tissue (storage and loss modulus) in a frequency range of 0.1-3Hz. BB was selected as a different technique, replicating normal physiological conditions where the BW is studied in whole. According to uniaxial tests, the anisotropic behavior of bladder is evident at strain loads higher than 200%. According to DMA, storage modulus is consistently higher than loss modulus in both directions, revealing the elasticity of the BW. The stress-strain curves of both uniaxial and BB tests showed similar trends. However, the ultimate stress measured from BB was found to be around 5 times of the relevant stress from uniaxial loading. The ultimate strain in BB (389.9 ± 59.8) was interestingly an approximate average of rupture strains in longitudinal (358 ± 21) and circumferential (435 ± 69) directions. Considering that each testing mode applied here reveals distinct information, outcomes from the combination of the three can be considered as a helpful data-base to refer to for researchers aiming to regenerate the bladder.

Clinically relevant mechanical testing of hernia graft constructs.

BACKGROUND: To understand the mechanical behavior of grafts in the context of hernia repair, there is a need to develop and adopt methods for mechanical testing of grafts in a clinically-relevant manner with clinically-relevant outcomes. MATERIALS AND METHODS: Ball-burst and planar-biaxial methods were used to test three commercially-available hernia grafts (DermaMatrix, Biodesign, VitaMesh Blue). Both load-to-failure and cyclic fatigue tests were performed (n=6-11/group/test). Grafts were tested as sutured constructs in patch geometry. Dilatational strain analysis was performed considering the construct (both test methods) or the graft (planar-biaxial only) as the area of interest. RESULTS: DermaMatrix, Biodesign, and VitaMesh grafts showed differences in mechanical properties at the point of construct failure (load, in-plane load-per-suture and membrane tension) in ball-burst tests and differences in sub-failure properties (stiffness, dilatational strain at 16N/cm and cyclic mechanical properties) in planar-biaxial tests. In both load-to-failure and cyclic fatigue tests, each graft construct tended to be stiffer in planar-biaxial than ball-burst testing. In biaxial testing, the strain analysis method influenced the mechanical properties with the construct being more compliant than the graft. CONCLUSIONS: This study demonstrates that graft-fixation method, test mode and analysis method are important considerations for mechanical characterization of hernia grafts. Ball-burst tests can only estimate construct or material properties, whereas planar-biaxial tests capture anisotropy and can estimate construct, graft and material properties of the same test specimen. When the clinical performance of a graft in the context of hernia repair is of interest, testing a sutured construct and performing construct strain analysis arguably provides the most clinically-relevant assessment method.

Fiber-reinforced dermis graft for ventral hernia repair.

Ventral hernia repair (VHR) continues to be a challenge for surgeons. Poor long-term durability of the commonly-used human acellular dermal matrix (HADM) grafts often results in VHR failure and reherniation. We hypothesized that fiber-reinforcement will improve the mechanical properties of HADM grafts and maintain these properties after enzymatic degradation. We designed a reinforced HADM (r-HADM) graft comprised of HADM and a small amount (~10wt% or 56g/m(2)) of 2-0 monofilament polypropylene. We evaluated the failure and fatigue biomechanics of r-HADM grafts and HADM controls, before and after 8h of in vitro enzymatic degradation, in ball-burst and planar biaxial testing modes (n=6-11/group/test). Fiber-reinforcement improved time-zero failure properties of HADM. While enzymatic degradation resulted in a significant reduction in nearly all mechanical properties and frequent premature failure of HADM, key sub-failure parameters and cyclic dilatational strain were maintained in r-HADM, with no sample having premature failure. These data show that fiber-reinforcement improves biomechanical properties and imparts mechanical durability to r-HADM during enzymatic degradation. Our findings suggest that fiber-reinforcement may be a strategy to mitigate the loss of HADM graft mechanical properties after in vivo implantation, and thereby limit VHR bulging and improve outcomes.