Matrix generation within a macroporous non-degradable implant for osteochondral defects is not enhanced with partial enzymatic digestion of the surrounding tissue: evaluation in an in vivo rabbit model.

Articular cartilage defects are a significant source of pain, have limited ability to heal, and can lead to the development of osteoarthritis. However, a surgical solution is not available. To tackle this clinical problem, non-degradable implants capable of carrying mechanical load immediately after implantation and for the duration of implantation, while integrating with the host tissue, may be viable option.

Augmenting the articular cartilage-implant interface: Functionalizing with a collagen adhesion protein.

The lack of integration between implants and articular cartilage is an unsolved problem that negatively impacts the development of treatments for focal cartilage defects. Many approaches attempt to increase the number of matrix-producing cells that can migrate to the interface, which may help to reinforce the boundary over time but does not address the problems associated with an initially unstable interface. The objective of this study was to develop a bioadhesive implant to create an immediate bond with the extracellular matrix components of articular cartilage.

Characterization of a macroporous polyvinyl alcohol scaffold for the repair of focal articular cartilage defects.

Focal cartilage defects reduce the ability of articular cartilage to resist mechanical loading and provide lubrication during joint motion. The limitations in current surgical treatments have motivated the use of biocompatible scaffolds as a future treatment option. Here we describe a second generation macroporous, polyvinyl alcohol (PVA) scaffold with independently tunable morphological and mechanical properties.

A novel macroporous polyvinyl alcohol scaffold promotes chondrocyte migration and interface formation in an in vitro cartilage defect model.

Scaffold-cartilage integration is critical for the clinical success of a scaffold used for the repair of a focal cartilage defect. In this study, a macroporous polyvinyl alcohol (PVA) scaffold was found to facilitate chondrocyte infiltration and interfacial matrix formation in a juvenile bovine in vitro cartilage defect model. These results were found to depend on the press-fit between the scaffold and the cartilage, pretreatment of the cartilage with collagenase prior to scaffold insertion, and chondrocyte preseeding of the scaffold.

Differential cross-linking and radio-protective effects of genipin on mature bovine and human patella tendons.

Gamma irradiation is a proven sterilization method, but is not widely used on allografts for anterior cruciate ligament reconstruction (e.g., patella tendon) due to radiation-induced decreases in mechanical strength.

Transient supplementation of anabolic growth factors rapidly stimulates matrix synthesis in engineered cartilage.

The purpose of the presented work is to examine the response of engineered cartilage to a transient, 2-week application of anabolic growth factors compared to continuous exposure in in vitro culture. Immature bovine chondrocytes were suspended in agarose hydrogel and cultured for 28 days (Study 1) or 42 days (Study 2) in chondrogenic media with TGF-β1, TGF-β3, or IGF-I either added for only the first 14 days in culture or added to the media for the entire study period. In both studies, there were no statistical differences in tissue mechanical or biochemical properties between the growth factors on day 14.

A semi-degradable composite scaffold for articular cartilage defects.

Few options exist to replace or repair damaged articular cartilage. The optimal solution that has been suggested is a scaffold that can carry load and integrate with surrounding tissues; but such a construct has thus far been elusive. The objectives of this study were to manufacture and characterize a nondegradable hydrated scaffold.

Duty Cycle of Deformational Loading Influences the Growth of Engineered Articular Cartilage.

This study examines how variations in the duty cycle (the duration of applied loading) of deformational loading can influence the mechanical properties of tissue engineered cartilage constructs over one month in bioreactor culture. Dynamic loading was carried out with three different duty cycles: 1 h on/1 h off for a total of 3 h loading/day, 3 h continuous loading, or 6 h of continuous loading per day, with all loading performed 5 days/week. All loaded groups showed significant increases in Young's modulus after one month (vs.

Passaged adult chondrocytes can form engineered cartilage with functional mechanical properties: a canine model.

It was hypothesized that previously optimized serum-free culture conditions for juvenile bovine chondrocytes could be adapted to generate engineered cartilage with physiologic mechanical properties in a preclinical, adult canine model. Primary or passaged (using growth factors) adult chondrocytes from three adult dogs were encapsulated in agarose, and cultured in serum-free media with transforming growth factor-beta3. After 28 days in culture, engineered cartilage formed by primary chondrocytes exhibited only small increases in glycosaminoglycan content.

Zonal chondrocytes seeded in a layered agarose hydrogel create engineered cartilage with depth-dependent cellular and mechanical inhomogeneity.

We hypothesized that zonal populations of chondrocytes seeded into a bilayered scaffold with initially prescribed depth-varying, compressive material properties will lead to a biomimetic cartilage tissue construct with depth-dependent cellular and compressive mechanical inhomogeneity similar to that of the native tissue. Superficial zone chondrocytes (SZCs) and middle/deep zone chondrocytes (MDZCs) were isolated and encapsulated with 2% or 3% agarose to form single-layered constructs of 2% SZC, 3% SZC, 2% MDZC; bilayered constructs of 2% SZC/2% MDZC and 3% SZC/2% MDZC; and 2% mixed chondrocyte controls. For SZCs on day 42, increased glycosaminoglycan (GAG) and collagen was found with increased agarose concentration and when layered with MDZCs.

Influence of temporary chondroitinase ABC-induced glycosaminoglycan suppression on maturation of tissue-engineered cartilage.

Objective: A fundamental challenge of cartilage tissue engineering has been the inability to promote collagen synthesis up to native levels. In contrast, recent protocols have demonstrated that glycosaminoglycans (GAG) can be synthesized to native levels in 4-6 weeks of in vitro culture. We hypothesize that rapid GAG synthesis may be an impediment to collagen synthesis, possibly by altering transport pathways of nutrients or synthesis products.

Culture duration modulates collagen hydrolysate-induced tissue remodeling in chondrocyte-seeded agarose hydrogels.

Media supplementation with collagen hydrolysate was hypothesized to increase the collagen content in engineered cartilage. By d28, hydrolysate at 0.5 mg/mL increased type II collagen content and 1 mg/mL increased mechanical properties, total collagen content, and type II collagen content over controls.

Osmotic loading of spherical gels: a biomimetic study of hindered transport in the cell protoplasm.

Osmotic loading of cells has been used to investigate their physicochemical properties as well as their biosynthetic activities. The classical Kedem-Katchalsky framework for analyzing cell response to osmotic loading, which models the cell as a fluid-filled membrane, does not generally account for the possibility of partial volume recovery in response to loading with a permeating osmolyte, as observed in some experiments. The cell may be more accurately represented as a hydrated gel surrounded by a semi-permeable membrane, with the gel and membrane potentially exhibiting different properties.

Dynamic deformational loading results in selective application of mechanical stimulation in a layered, tissue-engineered cartilage construct.

The application of dynamic physiologic loading to a bilayered chondrocyte-seeded agarose construct with a 2% (wt/vol) top layer and 3% (wt/vol) bottom layer was hypothesized to (1) improve overall construct properties and (2) result in a tissue that mimics the mechanical inhomogeneity of native cartilage. Dynamic loading over the 28 day culture period was found to significantly increase bulk mechanical and biochemical properties versus free-swelling culture. The initial depth-distribution of the compressive Young's modulus (EY) reflected the intrinsic properties of the gel in each layer and a similar trend to the native tissue, with a softer 2% gel layer and a much stiffer 3% gel layer.

Evaluation of different scaffolds for BMP-2 genetic orthopedic tissue engineering.

To better understand the effects of scaffold materials for bone morphogenetic protein 2 (BMP-2) genetic tissue engineering in vivo, several gels, including alginate, collagen, agarose, hyaluronate, fibrin, or Pluronic, were mixed with adenovirus-mediated human BMP-2 gene (Adv-hBMP-2) transduced bone marrow stromal cells (BMSCs) and injected into the muscles of athymic mice to evaluate the resulting osteogenesis and chondrogenesis. These gel and gene-transduced BMSC mixtures were also loaded onto beta-TCP/HAP biphasic calcined bone (BCB) and observed under scanning electron microscopy (SEM). In addition, these composite scaffolds were implanted into the subcutaneous site of athymic mice to construct tissue-engineered bone.

Spatial and temporal development of chondrocyte-seeded agarose constructs in free-swelling and dynamically loaded cultures.

Dynamic deformational loading has been shown to significantly increase the development of material properties of chondrocyte-seeded agarose hydrogels, however little is known about the spatial development of the material properties within these constructs. In this study, a technique that combines video microscopy and optimized digital image correlation, was applied to assess the spatial development of material properties in tissue-engineered cartilage constructs cultured in free-swelling and dynamically-loaded conditions (3h/day, 5 days/week, and maintained in free-swelling conditions when not being loaded) over a 6-week period. Although homogeneous at day 0, both free-swelling and dynamically loaded samples progressively developed stiffer outer edges and a softer central region.

A layered agarose approach to fabricate depth-dependent inhomogeneity in chondrocyte-seeded constructs.

Inspired by the depth-dependent inhomogeneity of articular cartilage, it was hypothesized that a novel layered agarose technique, using a 2% (wt/vol) top and a 3% (wt/vol) bottom layer, would create an inhomogenous tissue construct with distinct material properties in conjoined regions. The biochemical and mechanical development of these constructs was observed alongside uniform 2% and 3% constructs. Initially, uniform 3% agarose disks had the highest bulk Young's modulus (E(Y) approximately 28 kPa) of all groups.

Functional tissue engineering of chondral and osteochondral constructs.

Due to the prevalence of osteoarthritis (OA) and damage to articular cartilage, coupled with the poor intrinsic healing capacity of this avascular connective tissue, there is a great demand for an articular cartilage substitute. As the bearing material of diarthrodial joints, articular cartilage has remarkable functional properties that have been difficult to reproduce in tissue-engineered constructs. We have previously demonstrated that by using a functional tissue engineering approach that incorporates mechanical loading into the long-term culture environment, one can enhance the development of mechanical properties in chondrocyte-seeded agarose constructs.