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Inverted pyramids showing opportunities and needs by the National Institutes of Health and the private sector. Slide originates from Dr. Zerhouni's presentation, ''NIH at the crossroads: Strategies for the future.''
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Over the past 20 years, tissue engineering (TE) has evolved into a thriving research and commercial development field. However, applying TE strategies to musculoskeletal (MSK) and craniofacial tissues has been particularly challenging since these tissues must also transmit loads during activities of daily living. To address this need, organizers in...
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Context 1
... It was noted that ''NIH supports high quality basic, applied and clinical research that has the potential to improve the Nation's health'' and ''NIH feeds a pipeline for R&D work … and recognizes the translational nature of TE science.'' Representatives also shared the fact that NIH's ''portfolio'' differs from that of the private sector ( Fig. 1) and that various funding options exist (through special emphasis panels and study sections) to pursue TE research. These include the Bioengineering Research Partnerships and Bioengineering Research ...
Context 2
... It was noted that ''NIH supports high quality basic, applied and clinical research that has the potential to improve the Nation's health'' and ''NIH feeds a pipeline for R&D work … and recognizes the translational nature of TE science.'' Representatives also shared the fact that NIH's ''portfolio'' differs from that of the private sector ( Fig. 1) and that various funding options exist (through special emphasis panels and study sections) to pursue TE research. These include the Bioengineering Research Partnerships and Bioengineering Research ...
Citations
... Specifications are based on insertion requirements for large animal reconstruction models [40]. ...
... The potential complex and possibly opposing roles of canonical and non-canonical Wnt family members only reinforces the need for robust invariant experimental methods. Variability in graft production, whether in the materials used or bioreactor functionality, only compounds the variation inherent in animal models [40]. A high degree of system control is required to establish causal relationships between process factors and ultimate tissue function. ...
Functional tissue-engineered tendons and ligaments remain to be prepared in a reproducible and scalable manner. This study evaluates an acellular 3D extracellular matrix (ECM) scaffold for tendon/ligament tissue engineering and their ability to support strain-induced gene regulation associated with the tenogenesis of cultured mesenchymal stromal cells. Preliminary data demonstrate unique gene regulation patterns compared to other scaffold forms, in particular in Wnt signaling. However, the need for a robust bioreactor system that minimizes process variation was also evident. A design control process was used to design and verify the functionality of a novel bioreactor. The system accommodates 3D scaffolds with clinically-relevant sizes, is capable of long-term culture with customizable mechanical strain regimens, incorporates in-line load measurement for continuous monitoring and feedback control, and allows a variety of scaffold configurations through a unique modular grip system. All critical functional specifications were met, including verification of physiological strain levels from 1–10%, frequency levels from 0.2–0.5 Hz, and accurate load measurement up to 50 N, which can be expanded on the basis of load cell capability. The design process serves as a model for establishing statistical functionality and reliability of investigative systems. This work sets the stage for detailed analyses of ECM scaffolds to identify critical differentiation signaling responses and essential matrix composition and cell–matrix interactions.
... These bioreactors, with or without mechanical, chemical, electrical, or shear stress stimulation, have been able to induce cells cultured in geometrically defined constructs (eg, linear, circular, off-axis), to compact a scaffold and align, increase collagen gene expression, and even cross-link newly formed ECM. 47,74,76,78,79,88,90,[132][133][134][135][136][137] However, the sheer numbers of cellular, scaffold, mechanical, and chemical combinations is overwhelming, especially since the result depends on the specific wound site conditions in vivo. Consequently, human in vivo studies have still not been permitted using TECs to treat tendon and ligament injuries. ...
... One attractive strategy for achieving some of these goals has been the use of FTE and design parameters. 97,137,[141][142][143][144][145][146] Beginning with "the end in mind," investigators used in vivo force transducers 29,147 to first measure or model maximum in vivo forces acting on specific ligaments and tendons in several animal models for different ADLs. [24][25][26][27][28][29]75,105,106,143,[148][149][150] Ligaments were found to normally transmit only 7% to 10% of the tissue's maximum force ...
Bioreactors are powerful tools with the potential to model tissue development and disease in vitro . For nearly four decades, bioreactors have been used to create tendon and ligament tissue‐engineered constructs in order to define basic mechanisms of cell function, extracellular matrix deposition, tissue organization, injury, and tissue remodeling. This review provides a historical perspective of tendon and ligament bioreactors and their contributions to this advancing field. First, we demonstrate the need for bioreactors to improve understanding of tendon and ligament function and dysfunction. Next, we detail the history and evolution of bioreactor development and design from simple stretching of explants to fabrication and stimulation of 2‐ and 3‐dimensional constructs. Then, we demonstrate how research using tendon and ligament bioreactors has led to pivotal basic science and tissue engineering discoveries. Finally, we provide guidance for new basic, applied, and clinical research utilizing these valuable systems, recognizing that fundamental knowledge of cell‐cell and cell‐matrix interactions combined with appropriate mechanical and chemical stimulation of constructs could ultimately lead to functional tendon and ligament repairs in the coming decades.
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... The evaluation should be multimodal and multiscale, in real time, and (although this is not yet always possible) should not compromise the prospects for implantation. 22,96,166 Comprehensively assessing TE cartilage, and indeed any engineered tissue, is an interdisciplinary undertaking, which requires expertise in subject areas such as molecular and cell biology, biomedical, chemical, mechanical, and electrical engineering, advanced imaging and computer modeling. 22,96 Methods for evaluating engineered cartilage are described below. ...
... 22,96,166 Comprehensively assessing TE cartilage, and indeed any engineered tissue, is an interdisciplinary undertaking, which requires expertise in subject areas such as molecular and cell biology, biomedical, chemical, mechanical, and electrical engineering, advanced imaging and computer modeling. 22,96 Methods for evaluating engineered cartilage are described below. They span multiple size scales, from the whole tissue to the molecular level ( Figure 1). ...
In this review, methods for evaluating the properties of tissue engineered (TE) cartilage are described. Many of these have been developed for evaluating properties of native and osteoarthritic articular cartilage. However, with the increasing interest in engineering cartilage, specialized methods are needed for nondestructive evaluation of tissue while it is developing and after it is implanted. Such methods are needed, in part, due to the large inter- and intra-donor variability in the performance of the cellular component of the tissue, which remains a barrier to delivering reliable TE cartilage for implantation. Using conventional destructive tests, such variability makes it near-impossible to predict the timing and outcome of the tissue engineering process at the level of a specific piece of engineered tissue and also makes it difficult to assess the impact of changing tissue engineering regimens. While it is clear that the true test of engineered cartilage is its performance after it is implanted, correlation of pre and post implantation properties determined non-destructively in vitro and/or in vivo with performance should lead to predictive methods to improve quality-control and to minimize the chances of implanting inferior tissue.
... 28,31,40 The linear stiffness results are encouraging as this is the parameter that tissue engineers attempt to replicate as ligaments and tendons routinely operate in the range that is less than 10% of the failure load when patients perform activities of daily living. 6 In addition, we were not able to detect any fluorescent cells in the bio-enhanced ACL repair groups treated with ADSCs or PBSCs. While the MSCs maintained in parallel in vitro cultures could be visualized, suggesting the cells are able to continue to express the flourescent protein for 15 weeks, no flourescent cells were detected in the ACL tissue. ...
Coculture of mesenchymal stem cells (MSCs) from the retropatellar fat pad and peripheral blood has been shown to stimulate anterior cruciate ligament (ACL) fibroblast proliferation and collagen production in vitro. Current techniques of bioenhanced ACL repair in animal studies involve adding a biologic scaffold, in this case an extracellular matrix-based scaffold saturated with autologous whole blood, to a simple suture repair of the ligament. Whether the enrichment of whole blood with MSCs would further improve the in vivo results of bioenhanced ACL repair was investigated.
The addition of MSCs derived from adipose tissue or peripheral blood to the blood-extracellular matrix composite, which is used in bioenhanced ACL repair to stimulate healing, would improve the biomechanical properties of a bioenhanced ACL repair after 15 weeks of healing.
Controlled laboratory study.
Twenty-four adolescent Yucatan mini-pigs underwent ACL transection followed by (1) bioenhanced ACL repair, (2) bioenhanced ACL repair with the addition of autologous adipose-derived MSCs, and (3) bioenhanced ACL repair with the addition of autologous peripheral blood derived MSCs. After 15 weeks of healing, the structural properties of the ACL (yield load, failure load, and linear stiffness) were measured. Cell and vascular density were measured in the repaired ACL via histology, and its tissue structure was qualitatively evaluated using the advanced Ligament Maturity Index.
After 15 weeks of healing, there were no significant improvements in the biomechanical or histological properties with the addition of adipose-derived MSCs. The only significant change with the addition of peripheral blood MSCs was an increase in knee anteroposterior laxity when measured at 30° of flexion.
These findings suggest that the addition of adipose or peripheral blood MSCs to whole blood before saturation of an extracellular matrix carrier with the blood did not improve the functional results of bioenhanced ACL repair after 15 weeks of healing in the pig model.
Whole blood represents a practical biologic additive to ligament repair, and any other additive (including stem cells) should be demonstrated to be superior to this baseline before clinical use is considered.
© 2014 The Author(s).
... 6 Journal of Laboratory Automation activated, to proliferate as myoblasts and self-renew as to replenish the quiescent satellite cell population. 63,64 Scaffolds employed in skeletal muscle engineering can be natural, such as collagen, 65 fibrin, 66 and Matrigel, 67 or synthetic polymers like poly (lactide-co-glycolide) 68 and poly (caprolactone) 69 ; composites of these polymers integrated with various inorganic compounds is also possible. 70 Engineering of ordered uniaxial musculoskeletal tissues is based on the understanding that cells will align parallel to the passive tensions that develop within 3D matrices. ...
Most current drug screening assays used to identify new drug candidates are 2D cell-based systems, even though such in vitro assays do not adequately re-create the in vivo complexity of 3D tissues. Inadequate representation of the human tissue environment during a preclinical test can result in inaccurate predictions of compound effects on overall tissue functionality. Screening for compound efficacy by focusing on a single pathway or protein target, coupled with difficulties in maintaining long-term 2D monolayers, can serve to exacerbate these issues when using such simplistic model systems for physiological drug screening applications. Numerous studies have shown that cell responses to drugs in 3D culture are improved from those in 2D, with respect to modeling in vivo tissue functionality, which highlights the advantages of using 3D-based models for preclinical drug screens. In this review, we discuss the development of microengineered 3D tissue models that accurately mimic the physiological properties of native tissue samples and highlight the advantages of using such 3D microtissue models over conventional cell-based assays for future drug screening applications. We also discuss biomimetic 3D environments, based on engineered tissues as potential preclinical models for the development of more predictive drug screening assays for specific disease models.
... The bio-enhancement did not significantly influence the mean yield and maximum failure loads as none of the ACL reconstructed treatment groups were significantly different from each other (bio-enhanced or traditional). The linear stiffness results are encouraging as this is the parameter that tissue engineers attempt to replicate as ligaments and tendons routinely carry loads that are less than 10% of the failure load when patients perform activities of daily living [3]. ...
The use of an extracellular matrix scaffold (ECM) combined with platelets to enhance healing of an anterior cruciate ligament (ACL) graft ("bio-enhanced ACL reconstruction") has shown promise in animal models. However, the effects of platelet concentration on graft healing remain unknown. The objectives of this study were to determine whether increasing the platelet concentration in the ECM scaffold would (1) improve the graft biomechanical properties and (2) decrease cartilage damage after surgery.
Fifty-five adolescent minipigs were randomized to five treatment groups: untreated ACL transection (n = 10), conventional ACL reconstruction (n = 15) and bio-enhanced ACL reconstruction using 1× (n = 10), 3× (n = 10) or 5× (n = 10) platelet-rich plasma. The graft biomechanical properties, anteroposterior (AP) knee laxity, graft histology and macroscopic cartilage integrity were measured at 15 weeks.
The mean linear stiffness of the bio-enhanced ACL reconstruction procedure using the 1× preparation was significantly greater than traditional reconstruction, while the 3× and 5× preparations were not. The failure loads of all the ACL-reconstructed groups were equivalent but significantly greater than untreated ACL transection. There were no significant differences in the Ligament Maturity Index or AP laxity between reconstructed knees. Macroscopic cartilage damage was relatively minor, though significantly less when the ECM-platelet composite was used.
Only the 1× platelet concentration improved healing over traditional ACL reconstruction. Increasing the platelet concentration from 1× to 5× in the ECM scaffold did not further improve the graft mechanical properties. The use of an ECM-platelet composite decreased the amount of cartilage damage seen after ACL surgery.
... Musculo-skeletal conditions are the most common cause of severe long-term pain and physical disability worldwide [18], with more than 3 million musculoskeletal procedures performed annually in the USA [19]. Degenerative disease, severe infection, trauma and the excision of tumours can result in large non-healing defects in bone and other integrated tissues [20]. Current treatment options for bone have limited effectiveness. ...
The extracellular matrix (ECM) of mammalian tissues has been isolated, decellularized and utilised as a scaffold to facilitate the repair and reconstruction of numerous tissues. Recent studies have suggested that superior function and complex tissue formation occurred when ECM scaffolds were derived from site specific homologous tissues compared to heterologous tissues. The objectives of the present study were to apply a stringent decellularization process to demineralized bone matrix (DBM), prepared from bovine bone, and to characterise the structure and composition of the resulting ECM materials and DBM itself. Additionally, we sought to produce a soluble form of DBM and ECM which could be induced to form a hydrogel. Current clinical delivery of DBM particles for treatment of bone defects requires incorporation of the particles within a carrier liquid. Differences in osteogenic activity, inflammation and nephrotoxicity have been reported with various carrier liquids. The use of hydrogel forms of DBM or ECM may reduce the need for carrier liquids. DBM and ECM hydrogels exhibited sigmoidal gelation kinetics consistent with a nucleation and growth mechanism, with ECM hydrogels characterised by lower storage moduli than the DBM hydrogels. Enhanced proliferation of mouse primary calvarial cells was achieved on ECM hydrogels, compared to collagen type I and DBM hydrogels. These results show that DBM and ECM hydrogels have distinct structural, mechanical and biological properties and have potential for clinical delivery without the need for carrier liquids.
... A small group of bioengineers, biologists, material scientists, and surgeons were recruited from academia, industry, and government. The group used a "reverse tissue engineering strategy" to carefully define two important clinical problems for each tissue type (ligament, articular cartilage, bone, etc.) [70]. Multidisciplinary teams were then assembled to identify design parameters and their minimally acceptable values for each tissue type and clinical problem. ...
... Only then did the group propose in vitro laboratory studies to complement these preclinical and clinical studies. The resulting publication [70] summarized conference findings and was useful as our research team expanded our criteria for tendon tissue-engineered constructs. ...
... Developing a comprehensive treatment strategy will involve clinicians, bioengineers, biologists, and material scientists from industry, academia, and government laboratories [70]. This plan should use reverse tissue engineering that clearly defines the clinical problem before initiating preclinical and then in vitro studies. ...
In this paper, we had four primary objectives. (1) We reviewed a brief history of the Lissner award and the individual for whom it is named, H.R. Lissner. We examined the type (musculoskeletal, cardiovascular, and other) and scale (organism to molecular) of research performed by prior Lissner awardees using a hierarchical paradigm adopted at the 2007 Biomechanics Summit of the US National Committee on Biomechanics. (2) We compared the research conducted by the Lissner award winners working in the musculoskeletal (MS) field with the evolution of our MS research and showed similar trends in scale over the past 35 years. (3) We discussed our evolving mechanobiology strategies for treating musculoskeletal injuries by accounting for clinical, biomechanical, and biological considerations. These strategies included studies to determine the function of the anterior cruciate ligament and its graft replacements as well as novel methods to enhance soft tissue healing using tissue engineering, functional tissue engineering, and, more recently, fundamental tissue engineering approaches. (4) We concluded with thoughts about future directions, suggesting grand challenges still facing bioengineers as well as the immense opportunities for young investigators working in musculoskeletal research. Hopefully, these retrospective and prospective analyses will be useful as the ASME Bioengineering Division charts future research directions.
... There are many advantages for using preclinical models when designing tissueengineered constructs. A detailed consensus statement from experts in the fi eld regarding the best models and outcome measures to consider for tissue engineering development has been published [ 18 ]. When selecting a preclinical model, researchers attempt to recapitulate the relevant biological and biomechanical mechanical with that of the human. ...
... The goal of tissue engineering is to design clinically-relevant implantable materials for the eventual replacement of diseased or damaged tissues. To ensure the viability of devices as potential replacements for musculoskeletal or craniofacial tissue, suitable biomechanical properties of a biomaterial implant or cell-seeded scaffold must be demonstrated prior to clinical investigation (Butler et al., 2008). Tissue engineers use metrics established by the field of biomechanics (Mow and Huiskes, 2005) to contextualize and evaluate the results of testing, analysis, and constitutive modeling of biomaterials. ...
Hydrogels have mechanical properties and structural features that are similar to load-bearing soft tissues including intervertebral disc and articular cartilage, and can be implanted for tissue restoration or for local release of therapeutic factors. To help predict their performance, mechanical characterization and mathematical modeling are the available methods for use in tissue engineering and drug delivery settings. In this study, confined compression creep tests were performed on silk hydrogels, over a range of concentrations, to examine the phenomenological behavior of the gels under a physiological loading scenario. Based on the observed behavior, we show that the time-dependent response can be explained by a consolidation mechanism, and modeled using Biot’s poroelasticity theory. Two observations are in strong support of this modeling framework, namely, the excellent numerical agreement between increasing load step creep data and the linear Terzaghi theory, and the similar values obtained from numerical simulations and direct measurements of the permeability coefficient. The higher concentration gels (8% and 12% w/v) clearly show a strain-stiffening response to creep loading with increasing loads, while the lower concentration gel (4% w/v) does not. A nonlinear elastic constitutive formulation is employed to account for the stiffening. Furthermore, an empirical formulation is used to represent the deformation-dependent permeability.
