Jinjin Ma

Prostatic Fibrosis is Associated with Lower Urinary Tract Symptoms

PURPOSE Current therapies for male lower urinary tract symptoms secondary to prostate enlargement prevent hormonal effects on prostate growth and inhibit smooth muscle contraction to ease bladder neck and urethral pressure. However, lower urinary tract symptoms can be refractory to these therapies, suggesting that additional biological processes not addressed by them may also contribute to lower urinary tract symptoms. Aging associated fibrotic changes in tissue architecture contribute to dysfunction in multiple organ systems. Thus, we tested whether such changes potentially have a role in impaired urethral function and perhaps in male lower urinary tract symptoms. MATERIALS AND METHODS Periurethral tissues were obtained from a whole prostate ex vivo and from 28 consecutive men treated with radical prostatectomy. Lower urinary tract symptoms were assessed using the American Urological Association symptom index. Prostate tissues were subjected to mechanical testing to assess rigidity and stiffness. Fixed sections of these tissues were evaluated for collagen and elastin content, and glandularity to assess fibrosis. Statistical analysis included the Student t test and calculation of Pearson correlation coefficients to compare groups. RESULTS Periurethral prostate tissues demonstrated nonlinear viscoelastic mechanical behavior. Tissue from men with lower urinary tract symptoms was significantly stiffer (p = 0.0016) with significantly higher collagen content (p = 0.0038) and lower glandularity than that from men without lower urinary tract symptoms (American Urological Association symptom index 8 or greater vs 7 or less). CONCLUSIONS Findings show that extracellular matrix deposition and fibrosis characterize the periurethral prostate tissue of some men with lower urinary tract symptoms. They point to fibrosis as a factor contributing to lower urinary tract symptom etiology.

Morphological and Functional Characteristics of Three- Dimensional Engineered Bone-Ligament-Bone Constructs Following Implantation

The incidence of ligament injury has recently been estimated at 400,000/year. The preferred treatment is reconstruction using an allograft, but outcomes are limited by donor availability, biomechanical incompatibility, and immune rejection. The creation of an engineered ligament in vitro solely from patient bone marrow stromal cells (has the potential to greatly enhance outcomes in knee reconstructions. Our laboratory has developed a scaffoldless method to engineer three-dimensional (3D) ligament and bone constructs from rat bone marrow stem cells in vitro. Coculture of these two engineered constructs results in a 3D bone-ligament-bone (BLB) construct with viable entheses, which was successfully used for medial collateral ligament (MCL) replacement in a rat model. 1 month and 2 month implantations were applied to the engineered BLBs. Implantation of 3D BLBs in a MCL replacement application demonstrated that our in vitro engineered tissues grew and remodeled quickly in vivo to an advanced phenotype and partially restored function of the knee. The explanted 3D BLB ligament region stained positively for type I collagen and elastin and was well vascularized after 1 and 2 months in vivo. Tangent moduli of the ligament portion of the 3D BLB 1 month explants increased by a factor of 2.4 over in vitro controls, to a value equivalent to those observed in 14-day-old neonatal rat MCLs. The 3D BLB 1 month explants also exhibited a functionally graded response that closely matched native MCL inhomogeneity, indicating the constructs functionally adapted in vivo.

Experimental and Computational Investigation of Viscoelasticity of Native and Engineered Ligament and Tendon

The important mechanisms by which soft collagenous tissues such as ligament and tendon respond to mechanical deformation include non-linear elasticity, viscoelasticity and poroelasticity. These contributions to the mechanical response are modulated by the content and morphology of structural proteins such as type I collagen and elastin, other molecules such as glycosaminoglycans, and fluid. Our ligament and tendon constructs, engineered from either primary cells or bone marrow stromal cells and their autogenous matricies, exhibit histological and mechanical characteristics of native tissues of different levels of maturity. In order to establish whether the constructs have optimal mechanical function for implantation and utility for regenerative medicine, constitutive relationships for the constructs and native tissues at different developmental levels must be established. A micromechanical model incorporating viscoelastic collagen and non-linear elastic elastin is used to describe the non-linear viscoelastic response of our homogeneous engineered constructs in vitro. This model is incorporated within a finite element framework to examine the heterogeneity of the mechanical responses of native ligament and tendon.

A Micromechanical Viscoelastic Constitutive Model for Native and Engineered Anterior Cruciate Ligaments

Ligaments and tendons are soft tissues that are largely composed of aligned collagen and elastin. Due to this microstructure, they have nonlinear viscoelastic responses. We have developed a micromechanical constitutive model to capture the inhomogeneous, nonlinear viscoelastic properties of native ACL and of a tissue engineered ligament graft upon explantation. This constitutive model incorporates a viscoelastic collagen network and a nonlinear elastic elastin network. The model captures the nonlinear viscoelastic responses of these tissues using a limited number of parameters that can be interpreted in terms of physical properties of the collagen fibers and elastin. The parameters used to model the tissue engineered ligament response are similar to those found for the native ACL, indicating that the microstructure of the tissue engineered ligament graft has developed in vivo to match that of the native ACL.

Non-Linear Viscoelastic Mechanics of Native and Engineered Ligaments and Tendons

Patellar tendon (PT) autografts and allografts are the most common methods currently used to replace a torn anterior cruciate ligament (ACL). The PT is not only much stiffer than the ACL it replaces it also exhibits qualitatively and quantitatively different non-linear viscoelastic behavior from those of the ACL. These mis-matched biomechanics may be contributing to the high incidence of early onset osteoarthritis suffered by patients who have had ACL surgeries. Thus there is a need for an ACL graft that can reproduce normal ligament biomechanics and knee function. This talk examines the inhomogeneous, non-linear viscoelastic response of native ACL and of a tissue engineered ACL graft designed to rapidly grow and remodel in vivo to restore the proper biomechanical properties of native ligament. The results using this graft as an ACL replacement are compared against those using a PT autograft for the ACL replacement. Uniaxial loading reveals that after nine months as an ACL replacement, the tissue-engineered graft develops a strain contour pattern closely resembling that of native ACL whereas the PT graft fails to similarly remodel in vivo.Copyright

Nonlinear viscoelasticity of native and engineered ligament and tendon

Ligaments and tendons are non-linear viscoelastic materials and their response functions are typically assessed using creep and stress relaxation tests. Non-linear viscoelastic models such as multiple Maxwell elements in parallel and the quasilinear viscoelastic model (QLV) used to capture the non-linear viscoelastic response of ligaments and tendons frequently employ multiple relaxation time constants determined from curve-fitting the entire available data set and generally lack a clear physiological relevance. Uniaxial load-unload tension tests on ligament and tendon also manifests the viscoelastic response and such experiments suggest that the bulk of the non-linearity in the response of these soft tissues is in the elasticity. We propose physiologically relevant nonlinear viscoelastic models in which the response of the main structural proteins in ligament and tendon (e.g. collagen and elastin) are described using non-linear elasticity. Our approach using a three-element, non-linear solid micromechanical model captures this viscoelastic response in load-unload, stress relaxation and creep with a limited number of physically meaningful parameters. Previous research also shows different viscoelastic responses between native tendon and ligaments. In our model, by varying the properties of the non-linear springs, we are able to capture the differences in the viscoelastic responses of ligaments verses tendon. We will demonstrate the capabilities of our model by comparing to the experimental results from testing native and engineered ligament and tendon.

Mechanical Characteristics of Tissue Engineered Bone-Ligament-Bone Constructs Following ACL Replacement in Sheep

With approximately 400,000 reported each year, anterior crucial ligament (ACL) injuries are the most common injury in the US. Unfortunately current ACL replacement strategies, which involve using either allografts from cadavers or autografts from patients’ own patellar tendons (PT) or hamstring tendons as a replacement, have several limitations including graft availability, risk of rejection, increased morbidity and, more importantly, unmatched intra-articular biomechanical properties of grafts and ACL. The objective of this study is to use self-assembling, scaffold-less bone-ligament-bone (BLB) engineered tissue constructs as grafts in a sheep ACL repair model to characterize the biomechanical behaviors of native ACL, PT, and tissue engineered ligament and subsequently present a viable option of using tissue engineered ligament graft for ACL repair.Copyright

Erratum to: The effect of implantation on scaffoldless three-dimensional engineered bone constructs

E. M. ArrudaMechanical Engineering, University of Michigan,2250 GG Brown, 2350 Hayward,Ann Arbor, MI 48109, USAE. M. ArrudaProgram in Macromolecular Science and Engineering,University of Michigan,2250 GG Brown, 2350 Hayward,Ann Arbor, MI 48109, USAT. KostrominovaDepartment of Anatomy and Cell Biology,Indiana University School of Medicine-Northwest,Gary, IN 46409-1008, USAIn Vitro Cell.Dev.Biol.—Animal (2010) 46:82DOI 10.1007/s11626-009-9251-0

Experimental and Computational Investigation of the Poroviscoelastic Response of Engineered and Native Ligament

Experiments on explanted soft tissue and collagen gels [1], and the theory of soft tissue mechanics [2], indicate that the important mechanisms by which soft collagenous tissues deform and develop stress include elasticity, viscoelasticity and poroelasticity. These contributions to the mechanical response are directly modulated by the content and morphology of collagen, elastin, other molecules such as proteoglycans and glycosaminoglycans, and fluid, which is water. Our engineered collagenous constructs demonstrate histological and mechanical characteristics of native tendon and ligament of different levels of maturity. In order to evaluate whether the constructs have optimal mechanical function for implantation and utility for regenerative medicine, the relation must be established between the content and morphology of collagen and elastin, and the elastic, viscoelastic and poroelastic response of the engineered collagenous constructs at these different developmental levels.Copyright