Enhanced histologic repair in a central wound in the anterior cruciate ligament with a collagen–platelet-rich plasma scaffold
ABSTRACT The anterior cruciate ligament (ACL) of the knee is an intra-articular ligament that fails to heal after primary repair. The medial collateral ligament (MCL) of the knee is an extra-articular ligament that heals uneventfully in the majority of cases. Why these two ligaments have such different responses to injury remains unclear. In this article, we address two hypotheses: first, that the histologic response to injury is different in intra-articular and extra-articular ligaments, and second, that the response of the intra-articular ligaments can be altered by placing a collagen-platelet-rich plasma (collagen-PRP) hydrogel in the wound site. Wounds were created in extra-articular ligaments (MCL and/or patellar ligament) and an intra-articular ligament (ACL) in canine knees, and the histologic response to injury evaluated at 3 days (n = 3), 7 days (n = 4), 3 weeks (n = 5), and 6 weeks (n = 5). In the 3-week (n = 5) and 6-week (n = 5) animals, bilateral central wounds were made in the ACLs and the wounds in one knee of each animal treated with a collagen-PRP hydrogel while the contralateral side was untreated. Extra-articular ligament wounds had greater filling of the wound site and increased presence in the wound site of fibrinogen, fibronectin, PDGF-A, TGF-beta1, FGF-2, and von Willebrand's factor when compared to intra-articular ligament wounds. Treatment of the intra-articular wound with a collagen-PRP hydrogel resulted in increased filling of the wound site with repair tissue that had similar profiles of growth factor and protein expression to the extra-articular ligament wounds. The use of a collagen-PRP scaffold can ameliorate histologic differences noted between healing extra-articular ligamentous wounds and nonhealing intra-articular ligamentous wounds. This study supports the hypothesis that premature scaffold failure may play a key role in the normally expected failure of the ACL to heal after injury.
- SourceAvailable from: gatech.edu[Show abstract] [Hide abstract]
ABSTRACT: Knee injuries are a major cause of orthopedic disabilities in the United States. Current reconstruction techniques for torn anterior cruciate ligaments (ACL) require extensive surgery and long physical rehabilitation times since the tissue does not heal upon injury. A common ACL injury occurs where the gap at the rupture site remains open after injury and fails to heal, which can lead to premature osteoarthritis and disability. Hydrogels are a popular material used for tissue engineering applications due to their ability to retain water and good biocompatibility. Previous work has shown that hydrogels can be made through the mixed-mode reaction of radically crosslinked thiol groups and acrylate end groups. This project explores mixed-mode oligo[poly(ethylene glycol) fumarate] (OPF)-based hydrogels as alternate carriers for regeneration of partial tear ligament defects. The main purpose of this project was to determine the degradative properties of and cell response to thiol-PEG-thiol (PEG-diSH), a novel hydrogel material. The swelling and degradative properties of hydrogels containing three components OPF, PEG-diacrylate (PEG-DA), and PEG-diSH were characterized by their fold swelling. In addition, cell viability, morphology changes, proliferation and collagen production were analyzed in tri-ratio hydrogels with and without the presence of RGD over three weeks. Results showed that the hydrogels containing PEG-diSH demonstrated significantly larger fold swelling and promoted cell clustering (as shown by increased area of clusters), probably due to the larger mesh size and possibly due to the presence of free thiol functional groups present in the network from the mixed-mode reaction. However, an increase in cell number was not found in these gels up to eight days, suggesting that cell migration may play a role in the appearance of clusters. Additionally, increased cell spreading in response to RGD was observed inside gels containing PEG-diSH; no spreading was seen in the non PEG-diSH gels (± RGD), possibly because the mesh size was too small to allow for clustering or spreading within the matrix. Results from this work suggest that the presence of PEG-diSH could promote cell-cell contact within the clusters which could be useful in systems where direct contact promotes tissue formation or cell differentiation. M.S. Committee Chair: Johnna Temenoff; Committee Member: Andres Garcia; Committee Member: Marc Levenston; Committee Member: Ravi Bellamkonda
- [Show abstract] [Hide abstract]
ABSTRACT: Anterior cruciate ligament rupture (ACL) is a major source of morbidity in the dog, leading to severe osteoarthritis of the knee joint and marked lameness. Following rupture, the ACL will not heal and in the dog, ACL rupture is thought to be the end stage of degenerative ligament disease (non-contact ACL injury). The extracellular matrix (ECM) of CLs has been extensively studied but little is known of the role of elastic fibres in the physiology of the ECM, the mechanics of CL function and in CL degeneration. Elastic fibres include polymers of fibrillins (microfibrils), bundles of microfibrils (oxytalan fibres) and elastin fibres (bundles of microfibrils with an elastin core). The hypothesis of this thesis is that elastin has a mechanical and a biological role in the canine cruciate ligament complex. It is further hypothesised that the distribution and function of elastic fibres will vary between three breeds of dog with differing risk of ACL rupture are: the greyhound with a low risk, the beagle with a low-to-moderate risk and the Labrador retriever with a high risk. The distribution of elastic fibres, fibrillins and cells was investigated throughout the CL complex using a combination of histochemical staining and immunofluorescence. CL microanatomy was studied using Nomarski differential interference microscopy. Elastin was measured biochemically and compared to histologic assessment of tissue architecture, elastic fibre staining and other biochemical parameters. The biological effect of elastin degradation products (EDPs) was assessed in an in vitro ACL cell culture model. A low risk dog breed to ACL rupture (greyhound) was used in all investigations and comparisons were made with other breeds with regard to cellular and elastic fibre anatomy. Differences in cell morphology between breeds with differing risk of ACL rupture may reflect fundamental differences in CL physiology possibly through altered cell-to-cell communication. Cellular and matrix changes, considered degenerative, were seen throughout the CL complex and may reflect adaptation rather than degeneration in certain dog breeds such as the greyhound. Elastin content ranged from 5.9 to 19.4% of ligament dry weight. This was a far greater proportion of canine CLs than previously. Elastin fibres may have a mechanical role in bundle reorganization following ligament deformation. The distribution of fibrillins 1 and 2 was different from the pattern previously reported in tendon and may represent a fundamental difference between ligament and tendon. In the greyhound CL there was a significant proportional increase in oxytalan fibre staining with advancing CL degeneration. This response was seen also in the Labrador retriever and the beagle but the increase in oxytalan fibre staining was less marked with advancing degeneration. Therefore production of oxytalan fibres may reflect a healing response in damaged CL tissue in breeds at a low risk of ligament rupture. Fragments of elastin containing the VGVAPG motif affect canine ACL cells in vitro resulting in increased transcription of fibrillin 2 mRNA. Additionally, there was synergism with TGF-β1 resulting in upregulation of the elastin laminin receptor 1, through which EDPs are transduced. EDPs may thus have a role in response to injury in the CL.
- [Show abstract] [Hide abstract]
ABSTRACT: Combat games are formulated as zero-sum differential games with unilateral event constraints. An interior penalty function approach is employed to approximate optimal strategies for the players. The method is very attractive computationally and possesses suitable approximation and convergence properties.Computers & Mathematics with Applications 01/1985; 18(1-3-18):127-131. DOI:10.1016/0898-1221(89)90130-2 · 2.00 Impact Factor