The effect of selected growth factors on human anterior cruciate ligament cell interactions with a three-dimensional collagen-GAG scaffold

Commitment of human mesenchymal stromal cells towards ACL fibroblast differentiation upon rAAV-mediated FGF-2 and TGF-β overexpression using pNaSS-grafted PCL films

Despite various clinical options, human anterior cruciate ligament (ACL) lesions do not fully heal. Biomaterial-guided gene therapy using recombinant adeno-associated virus (rAAV) vectors may improve the intrinsic mechanisms of ACL repair. Here, we examined whether poly(sodium styrene sulfonate)-grafted poly(ε-caprolactone) (pNaSS-grafted PCL) films can deliver rAAV vectors coding for the reparative basic fibroblast growth factor (FGF-2) and transforming growth factor beta (TGF-β) in human mesenchymal stromal cells (hMSCs) as a source of implantable cells in ACL lesions. Efficient and sustained rAAV-mediated reporter (red fluorescent protein) and therapeutic (FGF-2 and TGF-β) gene overexpression was achieved in the cells for at least 21 days in particular with pNaSS-grafted PCL films relative to all other conditions (up to 5.2-fold difference). Expression of FGF-2 and TGF-β mediated by rAAV using PCL films increased the levels of cell proliferation, the DNA contents, and the deposition of proteoglycans and of type-I and -III collagen (up to 2.9-fold difference) over time in the cells with higher levels of transcription factor expression (Mohawk, Scleraxis) (up to 1.9-fold difference), without activation of inflammatory tumor necrosis alpha especially when using pNaSS-grafted PCL films compared with the controls. Overall, the effects mediated by TGF-β were higher than those promoted by FGF-2, possibly due to higher levels of gene expression achieved upon rAAV gene transfer. This study shows the potential of using functionalized PCL films to apply rAAV vectors for ACL repair.

rAAV TGF-β and FGF-2 Overexpression via pNaSS-Grafted PCL Films Stimulates the Reparative Activities of Human ACL Fibroblasts

Lesions in the human anterior cruciate ligament (ACL) are frequent, unsolved clinical issues due to the limited self-healing ability of the ACL and lack of treatments supporting full, durable ACL repair. Gene therapy guided through the use of biomaterials may steadily activate the processes of repair in sites of ACL injury. The goal of the present study was to test the hypothesis that functionalized poly(sodium styrene sulfonate)-grafted poly(ε-caprolactone) (pNaSS-grafted PCL) films can effectively deliver recombinant adeno-associated virus (rAAV) vectors as a means of overexpressing two reparative factors (transforming growth factor beta-TGF-β and basic fibroblast growth factor-FGF-2) in primary human ACL fibroblasts. Effective, durable rAAV reporter red fluorescent protein and candidate TGF-β and FGF-2 gene overexpression was achieved in the cells for at least 21 days, especially when pNaSS-grafted PCL films were used versus control conditions, such as ungrafted films and systems lacking vectors or films (between 1.8- and 5.2-fold differences), showing interactive regulation of growth factor production. The expression of TGF-β and FGF-2 from rAAV via PCL films safely enhanced extracellular matrix depositions of type-I/-III collagen, proteoglycans/decorin, and tenascin-C (between 1.4- and 4.5-fold differences) in the cells over time with increased levels of expression of the specific transcription factors Mohawk and scleraxis (between 1.7- and 3.7-fold differences) and without the activation of the inflammatory mediators IL-1β and TNF-α, most particularly with pNaSS-grafted PCL films relative to the controls. This work shows the value of combining rAAV gene therapy with functionalized PCL films to enhance ACL repair.

Development of three-layer collagen scaffolds to spatially direct tissue-specific cell differentiation for enthesis repair

Enthesis repair remains a challenging clinical indication. Herein, a three-layer scaffold composed of a tendon-like layer of collagen type I, a fibrocartilage-like layer of collagen type II and a bone-like layer of collagen type I and hydroxyapatite, was designed to recapitulate the matrix composition of the enthesis. To aid tenogenic and fibrochondrogenic differentiation, bioactive molecules were loaded in the tendon-like layer or the fibrocartilage-like layer and their effect was assessed in in vitro setting using human bone marrow derived mesenchymal stromal cells and in an ex vivo model. Seeded human bone marrow mesenchymal stromal cells infiltrated and homogeneously spread throughout the scaffold. As a response to the composition of the scaffold, cells differentiated in a localised manner towards the osteogenic lineage and, in combination with differentiation medium, towards the fibrocartilage lineage. Whilst functionalisation of the tendon-like layer did not improve tenogenic cell commitment within the time frame of this work, relevant fibrochondrogenic markers were detected in the fibrocartilage-like layer when scaffolds were functionalised with bone morphogenetic protein 2 or non-functionalised at all, in vitro and ex vivo, respectively. Altogether, our data advocate the use of compartmentalised scaffolds for the repair and regeneration of interfacial tissues, such as enthesis.

Advanced Gene Therapy Strategies for the Repair of ACL Injuries

The anterior cruciate ligament (ACL), the principal ligament for stabilization of the knee, is highly predisposed to injury in the human population. As a result of its poor intrinsic healing capacities, surgical intervention is generally necessary to repair ACL lesions, yet the outcomes are never fully satisfactory in terms of long-lasting, complete, and safe repair. Gene therapy, based on the transfer of therapeutic genetic sequences via a gene vector, is a potent tool to durably and adeptly enhance the processes of ACL repair and has been reported for its workability in various experimental models relevant to ACL injuries in vitro, in situ, and in vivo. As critical hurdles to the effective and safe translation of gene therapy for clinical applications still remain, including physiological barriers and host immune responses, biomaterial-guided gene therapy inspired by drug delivery systems has been further developed to protect and improve the classical procedures of gene transfer in the future treatment of ACL injuries in patients, as critically presented here.

Arthroscopic foveal repair with suture anchors for traumatic tears of the triangular fibrocartilage complex

Background

Foveal tears of the traumatic triangular fibrocartilage complex (TFCC) are the most commonly neglected high-energy injuries of the wrist joint, and the patients with such tears often experience unrecovered ulnar-sided wrist pain and poor wrist function. This study investigated the functional outcomes of patients who underwent arthroscopic repair of foveal TFCC tears with suture anchors and adjuvant platelet-rich plasma (PRP) injections after the surgery.

Methods

From September 2014 to August 2018, 156 men and 45 women with diagnoses of foveal TFCC tears without wrist fractures underwent arthroscopic repair by using the outside-in method with 1.3-mm suture anchors and subsequent PRP injection. After surgery, splinting was applied for 6 weeks, and the patients underwent rehabilitation, re-examination, and follow-up at our clinic. The patients’ wrist functional scores and grip strength data were retrospectively collected.

Results

The mean follow-up period was 32.6 months, and the mean age was 26.7 years. The mean modified Mayo wrist score improved from 48.5 ± 2.6 to 82.4 ± 2.5, whereas the mean Disabilities of the Arm, Shoulder and Hand (DASH) score decreased from 39.2 ± 6.7 to 10.6 ± 7.5. Overall, the wrist functions of 186 (92.5%) of the patients were satisfactory according to their modified Mayo wrist scores, and the patients with satisfactory scores returned to sports or work activities. These patients retained normal ranges of motion, and their average grip strength in the affected hand was restored to at least 85% of that of the other hand.

Conclusions

According to the postoperative 25–36 months surgical results of our study, arthroscopic repair with adjuvant PRP injections is a satisfactory method of repairing early foveal tears of the TFCC and can enhance wrist function by relieving pain and increasing tolerance for work or sports.

The healing potential of an acutely repaired ACL: a sequential MRI study

Background

Recently, there has been renewed interest in primary anterior cruciate ligament (ACL) repair. The aim of this study is to report early clinical and radiological results of a consecutive series of acute ACL tears treated with arthroscopic primary ACL repair within 14 days from injury.

Patients and methods

A consecutive series of patients with acute ACL tears were prospectively included in the study. Based on MRI appearance, ACL tears were classified into five types, and tissue quality was graded as good, fair, and poor. Patients with type I, II, and III tears and at least 50% of ACL tibial remnant intact with good tissue quality were ultimately included. Clinical outcomes were measured using the Tegner Lysholm Knee Scoring Scale (TLKSS), the Knee Injury and Osteoarthritis Outcome Score (KOOS), subjective and objective International Knee Documentation Committee (IKDC) scores, and KT-1000. Patients were also followed up with MRI evaluations at 1, 3, and 6 months postoperatively. ACL appearance was graded based on morphology (normal or abnormal) and signal intensity (isointense, intermediate, and hyperintense).

Results

The mean TLKSS was 98.1, the mean subjective IKDC was 97.6, and the mean KOOS was 98.2. The objective IKDC score was A in eight of ten patients and B in two patients. KT-1000 measurements showed a maximum manual side-to-side difference of less than 2 mm in eight of ten patients, whereas two patients showed a difference of 3 mm. The morphology of the repaired ACL was normal (grade 1) at 1 month follow-up in ten of ten cases, and this appearance persisted at 3 and 6 months postoperatively. The signal intensity at 1 month postoperatively was graded as isointense (grade 1) in four of ten patients, intermediate (grade 2) in five of ten patients, and hyperintense (grade 3) in one of ten patients. At both 3 and 6 months postoperatively, the signal intensity was graded as isointense (grade 1) in nine of ten patients and intermediate (grade 2) in one of ten patients.

Conclusions

Arthroscopic primary ACL repair performed acutely in a carefully selected group of patients with proximal ACL tears and good tissue quality showed good early clinical and radiological results.

Level of evidence

Level 4.

Effect of platelet-rich plasma and platelet-rich fibrin matrix on healing of vertical meniscal tears in a rabbit model

OBJECTIVE

This study aimed to investigate the effect of platelet-rich plasma (PRP) and platelet-rich fibrin matrix (PRFM) on the healing of vertical medial meniscal tears in a rabbit model.

METHODS

The study was conducted on 72 New Zealand mature rabbits aged more than 6 months. Rabbits were randomly assigned to six groups: control (C) group, meniscal repair (MR) group, PRP group, PRFM group, MR+PRP group, and MR+PRFM group, with 12 rabbits in each group. A 5-mm full-thickness vertical tear was created in the avascular zone of the medial meniscus corpus in the right knee of all rabbits. The respective treatment for each group was given to the meniscal tear in each rabbit. Histological evaluation of healing was performed 6 and 12 weeks after surgery.

RESULTS

Defect filling and collagen formation remained low in the C group. However, in all other groups, there was no significant difference in the 6th week. In the 12th week, similar results as those obtained in the 6th week were obtained. In the C group, there was a difference in defect filling and cell type. This difference was that the defect filling and collagen formation remained low in the 12th week. No significant difference was observed between MR, MR + PRP and MR + PRFM groups. The MR group significantly differed from the other groups in the defect-filling rate and cell type; however, the use of PRP and PRFM did not provide an obvious benefit.

CONCLUSION

The contradictory results obtained in previous studies emphasize the need for further research on the use of PRP in meniscal recovery and repair. We believe that if surgery is indicated, repair is absolutely necessary to improve the healing of the tissue in meniscal tears. Studies using human meniscal tissue for meniscal injury and those that evaluate clinical applications of PRP are warranted.

Nonoperative Choice of Anterior Cruciate Ligament Partial Tear: Ultrasound-Guided Platelet-Rich Plasma Injection

Anterior cruciate ligament (ACL) injury is one of the common musculoskeletal injuries. The most serious condition shall be managed by surgery, while the partial tear prefers conservative treatment, rehabilitation, exercise training, or platelet-rich plasma (PRP) injection. We describe the case of a 25-year-old female started to have right knee pain for a long time and the ACL partial tear was diagnosed through the magnetic resonance imaging (MRI). After three times of PRP injection through ultrasound guidance, the pain, instability, and enhancements of ACL tear in the postintervention MRI were decreased. This case confirms the effect of PRP combined with conservative treatment under the accuracy procedure and may provide another choice for the treatment of the ACL tear.

Anterior Cruciate Ligament Reconstruction Using a Bone-Patellar Tendon-Bone Graft With and Without a Ligament Augmentation Device: A 25-Year Follow-up of a Prospective Randomized Controlled Trial

Background

Various grafts and ligament augmentation devices (LADs) have been used in the search for optimal reconstruction of the anterior cruciate ligament (ACL).

Purpose

To compare 25-year follow-up results after ACL reconstruction using a bone-patellar tendon-bone (BPTB) graft with or without the Kennedy LAD.

Study Design

Randomized controlled trial; Level of evidence, 1.

Methods

One hundred patients undergoing ACL reconstruction between 1991 and 1993 were randomized into 2 groups: reconstruction using a BPTB graft alone (BPTB group, 51 patients) or a BPTB graft with the Kennedy LAD (LAD group, 49 patients). The 25-year follow-up evaluation included a clinical knee examination, patient-reported outcome measures, and an assessment of radiological osteoarthritis (OA) according to the Ahlbäck classification. Additional outcomes were reruptures and knee arthroplasty.

Results

Ninety-three patients (93%) were available for the follow-up evaluation: 48 patients in the BPTB group and 45 in the LAD group. Through telephone calls, 26 patients were excluded from further investigation because of reruptures and arthroplasty in the knee of interest; 67 patients were further investigated. A total of 43 of 44 (98%) and 42 of 44 (95%) patients had negative or 1+ Lachman and pivot-shift test results, respectively. The mean Lysholm score was 85 for the BPTB group and 83 for the LAD group. All mean Knee injury and Osteoarthritis Outcome Score (KOOS) subscale values were ≥73. There were no statistically significant differences between groups in any of these outcomes or regarding the Tegner score, radiological classification of OA, or number of ACL reruptures. Signs of radiological OA were detected in all patients, and severe radiological OA (Ahlbäck grade III, IV, or V) was detected in 32% of patients in the BPTB group and 21% of patients in the LAD group (P = .37). There were 12 patients in the BPTB group and 7 in the LAD group who had documented reruptures (P = .40). One patient in the BPTB group and 6 in the LAD group underwent knee arthroplasty (P = .054).

Conclusion

In the present study, there were no statistically significant differences between groups in any of the outcomes. After 25 years, 19% of patients had reruptures, 27% had severe radiological OA, and 7% underwent knee arthroplasty.

Presence of meniscus tear alters gene expression profile of anterior cruciate ligament tears

Anterior cruciate ligament (ACL) tears occur in isolation or in tandem with other intra-articular injuries such as meniscus tears. The impact of injury pattern on the molecular biology of the injured ACL is unknown. Here, we tested the hypothesis that the biological response of the ACL to injury varies based on the presence or absence of concomitant meniscus tear. We performed RNA-seq on 28 ACL tears remnants (12 isolated, 16 combined). In total, 16,654 transcripts were differentially expressed between isolated and combined injury groups at false discovery rate of 0.05. Due to the large number of differentially expressed transcripts, we undertook an Ensembl approach to discover features that acted as hub genes that did not necessarily have large fold changes or high statistical significance, but instead had high biological significance. Our data revealed a negatively correlated module containing 5,960 transcripts (down-regulated in combined injury) and a positively correlated module containing 2,260 transcripts (up-regulated in combined injury). TNS1, MEF2D, NOTCH3, SOGA1, and MLXIP were highly-connected hub genes in the negatively correlated module and SCN2A, CSMD3, LRC44, USH2A, and LRP1B were critical hub genes in the positively correlated module. Transcripts in the negatively correlated module were associated with biological adhesion, actin-filament organization, cell junction assembly, and cell matrix adhesion. The positively correlated module transcripts were enriched for neuron migration and exocytosis regulation. These findings indicate genes and pathways reflective of healing deficiency and gain of neurogenic signaling in combined ACL and meniscus tears, suggesting their diminished repair potential. The biological response of ACL to injury could have implications for healing potential of the ligament and the long term health of the knee. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2612-2621, 2018.

Use of a platelet-rich plasma-collagen scaffold as a bioenhanced repair treatment for management of partial cruciate ligament rupture in dogs

Dogs are commonly affected with cruciate ligament rupture (CR) and associated osteoarthritis (OA), and frequently develop a second contralateral CR. Platelet rich plasma (PRP) is a component of whole blood that contains numerous growth factors, which in combination with a collagen scaffold may act to promote bioenhanced primary repair of ligament. This study tested the hypothesis that treatment of partial stable CR stifles with an intra-articular collagen scaffold and PRP would decrease the disease progression, synovitis and risk of complete CR over a 12-month study period. We conducted a prospective cohort study of 29 client-owned dogs with an unstable stifle due to complete CR and stable contralateral stifle with partial CR. All dogs were treated with tibial plateau leveling osteotomy (TPLO) on the unstable stifle and a single intra-articular application of PRP-collagen in the stable partial CR stifle. Dogs were evaluated at the time of diagnosis, and at 10-weeks and 12-months after treatment. We evaluated correlation between both development of complete CR and time to complete CR with diagnostic tests including bilateral stifle radiographs, 3.0 Tesla magnetic resonance (MR) imaging, and bilateral stifle arthroscopy. Additionally, histologic evaluation of synovial biopsies, C-reactive protein (CRP) concentrations in serum and synovial fluid, and synovial total nucleated cell count, were determined. Results indicated that a single application of PRP-collagen in partial CR stifles of client owned dogs is not an effective disease-modifying therapy for the prevention of progression to complete CR. Radiographic effusion, arthroscopic evaluation of cranial cruciate ligament (CrCL) damage, and MR assessment of ligament fiber tearing in partial CR stifles correlated with progression to complete CR over the 12-month follow-up period. We determined that the best predictive model for development of complete CR in PRP-collagen treated partial CR stifles included variables from multiple diagnostic modalities.

Bench-to-bedside: Bridge-enhanced anterior cruciate ligament repair

Anterior cruciate ligament (ACL) injuries are one of the most well-known orthopaedic injuries and are treated with one of the most common orthopaedic procedures performed in the United States. This surgical procedure, ACL reconstruction, is successful at restoring the gross stability of the knee. However, the outcomes of ACL reconstruction can be limited by short and long-term complications, including muscle weakness, graft rupture, and premature osteoarthritis. Thus, new methods of treating this injury are being explored. This review details the pathway of how a tissue engineering strategy can be used to improve the healing of the ACL in preclinical studies and then translated to patients in an FDA-approved clinical study. This review paper will outline the clinical importance of ACL injuries, history of primary repair, the pathology behind failure of the ACL to heal, pre-clinical studies, the FDA approval process for a high risk medical device, and the preliminary results from a first-in-human study. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2606-2612, 2017.

Modulating microfibrillar alignment and growth factor stimulation to regulate mesenchymal stem cell differentiation

The ideal tissue engineering (TE) strategy for ligament regeneration should recapitulate the bone - calcified cartilage - fibrocartilage - soft tissue interface. Aligned electrospun-fibers have been shown to guide the deposition of a highly organized extracellular matrix (ECM) necessary for ligament TE. However, recapitulating the different tissues observed in the bone-ligament interface using such constructs remains a challenge. This study aimed to explore how fiber alignment and growth factor stimulation interact to regulate the chondrogenic and ligamentous differentiation of mesenchymal stem cells (MSCs). To this end aligned and randomly-aligned electrospun microfibrillar scaffolds were seeded with bone marrow derived MSCs and stimulated with transforming growth factor β3 (TGFβ3) or connective tissue growth factor (CTGF), either individually or sequentially. Without growth factor stimulation, MSCs on aligned-microfibers showed higher levels of tenomodulin (TNMD) and aggrecan gene expression compared to MSCs on randomly-oriented fibers. MSCs on aligned-microfibers stimulated with TGFβ3 formed cellular aggregates and underwent robust chondrogenesis, evidenced by increased type II collagen expression and sulphated glycosaminoglycans (sGAG) synthesis compared to MSCs on randomly-oriented scaffolds. Bone morphogenetic protein 2 (BMP2) and type I collagen gene expression were higher on randomly-oriented scaffolds stimulated with TGFβ3, suggesting this substrate was more supportive of an endochondral phenotype. In the presence of CTGF, MSCs underwent ligamentous differentiation, with increased TNMD expression on aligned compared to randomly aligned scaffolds. Upon sequential growth factor stimulation, MSCs expressed types I and II collagen and deposited higher overall levels of collagen compared to scaffolds stimulated with either growth factor in isolation. These findings demonstrate that modulating the alignment of microfibrillar scaffolds can be used to promote either an endochondral, chondrogenic, fibrochondrogenic or ligamentous MSC phenotype upon presentation of appropriate biochemical cues.

STATEMENT OF SIGNIFICANCE

Polymeric electrospun fibers can be tuned to match the fibrillar size and anisotropy of collagen fibers in ligaments, and can be mechanically competent. Therefore, their use is attractive when attempting to tissue engineer the bone-ligament interface. A central challenge in this field is recapitulating the cellular phenotypes observed across the bone-ligament interface. Here we demonstrated that it is possible to direct MSCs seeded onto aligned electrospun fibres towards either a ligamentogenic, chondrogenic or fibrochondrogenic phenotype upon presentation of appropriate biochemical cues. This opens the possibility of using aligned microfibrillar scaffolds that are spatially functionalized with specific growth factors to direct MSC differentiation for engineering the bone-ligament interface.

Anterior Cruciate Ligament: Structure, Injuries and Regenerative Treatments

Anterior cruciate ligament (ACL) is one of the most vulnerable ligaments of the knee. ACL impairment results in episodic instability, chondral and meniscal injury and early osteoarthritis. The poor self-healing capacity of ACL makes surgical treatment inevitable. Current ACL reconstructions include a substitution of torn ACL via biological grafts such as autograft, allograft. This review provides an insight of ACL structure, orientation and properties followed by comparing the performance of various constructs that have been used for ACL replacement. New approaches, undertaken to induce ACL regeneration and fabricate biomimetic scaffolds, are also discussed.

An ex vivo model using human osteoarthritic cartilage demonstrates the release of bioactive insulin-like growth factor-1 from a collagen-glycosaminoglycan scaffold

Biomimetic scaffolds hold great promise for therapeutic repair of cartilage, but although most scaffolds are tested with cells in vitro, there are very few ex vivo models (EVMs) where adult cartilage and scaffolds are co-cultured to optimize their interaction prior to in vivo studies. This study describes a simple, non-compressive method that is applicable to mammalian or human cartilage and provides a reasonable throughput of samples. Rings of full-depth articular cartilage slices were derived from human donors undergoing knee replacement for osteoarthritis and a 3 mm core of a collagen/glycosaminoglycan biomimetic scaffold (Tigenix, UK) inserted to create the EVM. Adult osteoarthritis chondrocytes were seeded into the scaffold and cultures maintained for up to 30 days. Ex vivo models were stable throughout experiments, and cells remained viable. Chondrocytes seeded into the EVM attached throughout the scaffold and in contact with the cartilage explants. Cell migration and deposition of extracellular matrix proteins in the scaffold was enhanced by growth factors particularly if the scaffold was preloaded with growth factors. This study demonstrates that the EVM represents a suitable model that has potential for testing a range of therapeutic parameters such as numbers/types of cell, growth factors or therapeutic drugs before progressing to costly pre-clinical trials. © 2015 The Authors. Cell Biochemistry and Function Published by John Wiley & Sons Ltd.

Bridge-enhanced ACL repair: A review of the science and the pathway through FDA investigational device approval

Injuries to the anterior cruciate ligament (ACL) are currently treated with replacement of the torn ligament with a graft of tendon harvested from elsewhere in the knee. This procedure, called "ACL reconstruction," is excellent for restoring gross stability to the knee; however, there are relatively high graft failure rates in adolescent patients (Barber et al. in Arthroscopy 30(4):483-491, (2014); Engelman et al. in Am J Sports Med, (2014); Webster et al. in Am J Sports Med 42(3):641-647, (2014)), and the ACL reconstruction procedure does not prevent the premature osteoarthritis seen in patients after an ACL injury (Ajuied et al. in Am J Sports Med, (2013); Song et al. in J Sports Med 41(10):2340-2346, (2013); Tourville et al. Am J Sports Med 41(4):769-778, (2013)) .Thus, new solutions are needed for ACL injuries. Researchers have been investigating the use of scaffolds, growth factors and cells to supplement a suture repair of the ACL (bridge-enhanced repair; also called bio-enhanced repair in prior publications). In this paper, we will review the varied approaches which have been investigated for stimulating ACL healing and repair in preclinical models and how one of these technologies was able to move from promising preclinical results to FDA acceptance of an investigational device exemption application for a first-in-human study.

Bioactive IGF-1 release from collagen-GAG scaffold to enhance cartilage repair in vitro

Tissue engineering is a promising technique for cartilage repair. Toward this goal, a porous collagen-glycosaminoglycan (CG) scaffold was loaded with different concentrations of insulin-like growth factor-1 (IGF-1) and evaluated as a growth factor delivery device. The biological response was assessed by monitoring the amount of type II collagen and proteoglycan synthesised by the chondrocytes seeded within the scaffolds. IGF-1 release was dependent on the IGF-1 loading concentration used to adsorb IGF-1 onto the CG scaffolds and the amount of IGF-1 released into the media was highest at day 4. This initial IGF-1 release could be modelled using linear regression analysis. Osteoarthritic (OA) chondrocytes seeded within scaffolds containing adsorbed IGF-1 deposited decorin and type II collagen in a dose dependent manner and the highest type II collagen deposition was achieved via loading the scaffold with 50 μg/ml IGF-1. Cells seeded within the IGF-1 loaded scaffolds also deposited more extracellular matrix than the no growth factor control group thus the IGF-1 released from the scaffold remained bioactive and exerted an anabolic effect on OA chondrocytes. The effectiveness of adsorbing IGF-1 onto the scaffold may be due to protection of the molecule from proteolytic digestion allowing a more sustained release of IGF-1 over time compared to adding multiple doses of exogenous growth factor. Incorporating IGF-1 into the CG scaffold provided an initial therapeutic burst release of IGF-1 which is beneficial in initiating ECM deposition and repair in this in vitro model and shows potential for developing this delivery device in vivo.

The market trend analysis and prospects of scaffolds for stem cells

Background

Scaffolds are one of the three most important elements constituting the basic concept of regenerative medicine, and are included in the core technology of regenerative medicine along with stem cells and tissue engineering. Stem cells are very important technology because they are directly responsible for the regenerative treatment of the disease and the damaged tissue, but with regards to the technology and the products that use stem cells exclusively, there is a technical limitation of limited survival rate and the engraftment rate of the transplanted cell, and rather than recovering the damaged tissue fundamentally, there is a limit that the concept is more of just another medicine treatment using cells.

A scaffold is a natural or synthetic biocompatible material transplanted into a human body to be used as the exclusive treatment or as an assisted method of another treatment of a disease and for the recovery of damaged tissue. Therefore, according to the characteristics of the tissue to be applied, scaffolds must have the characteristics such as the excellent biocompatibility, biodegradability, minimum immunity and inflammation, proper mechanical strength and interaction between the material and the cells.

Results

The world stem cell market was approximately 2.715 billion dollars in 2010, and with a growth rate of 16.8% annually, a market of 6.877 billion dollars will be formed in 2016. From 2017, the expected annual growth rate is 10.6%, which would expand the market to 11.38 billion dollars by 2021. Meanwhile, the world scaffold element technology market was approximately 4.57 million dollars in 2013, and by increasing 13.4% annually, it is estimated to expand to 10.63 million dollars by 2020. The Korean scaffold element technology market was about 22 million dollars in 2013, and with a steady growth of approximately 13.4% every year, it is prospected to be about 52 million dollars by 2020.

Conclusions

In comparison to the medical material and medicine sales growth rate, the future scaffold element technology market is judged to be higher in growth possibility.

The use of PRP in ligament and meniscal healing

Platelet-rich plasma (PRP) has become a popular treatment for acute and chronic soft tissue injuries. Although the majority of research has focused on its use in tendinopathy, PRP may have potential in meniscus and ligament healing. Some level II studies support a possible benefit for anterior cruciate ligament (ACL) allograft maturation, and preliminary animal studies point to a potential role for PRP in primary ACL repair. However, randomized controlled trials have not demonstrated a benefit of PRP for ACL tendon allograft-tunnel integration. To date, 2 studies document the use of PRP for meniscal applications, but this field is largely unexplored. With respect to ligament and meniscal applications, the current literature suggests PRP may be promising for primary ACL repair in skeletally immature patients, ACL graft maturation, and repair of meniscal tears in the avascular zone.

Basic science of anterior cruciate ligament injury and repair

Injury to the anterior cruciate ligament (ACL) is one of the most devastating and frequent injuries of the knee. Surgical reconstruction is the current standard of care for treatment of ACL injuries in active patients. The widespread adoption of ACL reconstruction over primary repair was based on early perception of the limited healing capacity of the ACL. Although the majority of ACL reconstruction surgeries successfully restore gross joint stability, post-traumatic osteoarthritis is commonplace following these injuries, even with ACL reconstruction. The development of new techniques to limit the long-term clinical sequelae associated with ACL reconstruction has been the main focus of research over the past decades. The improved knowledge of healing, along with recent advances in tissue engineering and regenerative medicine, has resulted in the discovery of novel biologically augmented ACL-repair techniques that have satisfactory outcomes in preclinical studies. This instructional review provides a summary of the latest advances made in ACL repair. Cite this article: Bone Joint Res 2014;3:20-31.

Mechanoregulation of valvular interstitial cell phenotype in the third dimension

A quantitative understanding of the complex interactions between cells, soluble factors, and the biological and mechanical properties of biomaterials is required to guide cell remodeling toward regeneration of healthy tissue rather than fibrocontractive tissue. In the present study, we characterized the combined effects of boundary stiffness and transforming growth factor-β1 (TGF-β1) on cell-generated forces and collagen accumulation. We first generated a quantitative map of cell-generated tension in response to these factors by culturing valvular interstitial cells (VICs) within micro-scale fibrin gels between compliant posts (0.15-1.05 nN/nm) in chemically-defined media with TGF-β1 (0-5 ng/mL). The VICs generated 100-3000 nN/cell after one week of culture, and multiple regression modeling demonstrated, for the first time, quantitative interaction (synergy) between these factors in a three-dimensional culture system. We then isolated passive and active components of tension within the micro-tissues and found that cells cultured with high levels of stiffness and TGF-β1 expressed myofibroblast markers and generated substantial residual tension in the matrix yet, surprisingly, were not able to generate additional tension in response to membrane depolarization signifying a state of continual maximal contraction. In contrast, negligible residual tension was stored in the low stiffness and TGF-β1 groups indicating a lower potential for shrinkage upon release. We then studied if ECM could be generated under the low tension environment and found that TGF-β1, but not EGF, increased de novo collagen accumulation in both low and high tension environments roughly equally. Combined, these findings suggest that isometric cell force, passive retraction, and collagen production can be tuned by independently altering boundary stiffness and TGF-β1 concentration. The ability to stimulate matrix production without inducing high active tension will aid in the development of robust tissue engineered heart valves and other connective tissue replacements where minimizing tissue shrinkage upon implantation is critical.

Biology of anterior cruciate ligament injury and repair: Kappa delta ann doner vaughn award paper 2013

Anterior cruciate ligament (ACL) injuries are currently treated by removing the injured ligament and replacing it with a tendon graft. Recent studies have examined alternative treatment methods, including repair and regeneration of the injured ligament. In order to make such an approach feasible, a basic understanding of ACL biology and its response to injury is needed. Identification of obstacles to native ACL healing can then be identified and potentially resolved using tissue engineering strategies-first, with in vitro screening assays, and then with in vivo models of efficacy and safety. This Perspectives paper outlines this path of discovery for optimizing ACL healing using a bio-enhanced repair technique. This journey required constructing indices of the functional tissue response, pioneering physiologically based methods of biomechanical testing, developing, and validating clinically relevant animal models, and creating and optimizing translationally feasible scaffolds, surgical techniques, and biologic additives. Using this systematic translational approach, "bio-enhanced" ACL repair has been advanced to the point where it may become an option for future treatment of acute ACL injuries and the prevention of subsequent post-traumatic osteoarthritis associated with this injury.

Preservation of remnant attachment improves graft healing in a rabbit model of anterior cruciate ligament reconstruction

PURPOSE

To determine the effect of remnant preservation on the healing of anterior cruciate ligament (ACL) tendon graft after reconstruction in an animal model.

METHODS

Fifty-two New Zealand rabbits were divided into 6 groups. Revascularization and graft healing were studied in groups 1 through 4 (n = 8 each). The biomechanical properties of the graft complex were evaluated in group 5 (n = 12). The blood flow and biomechanical characteristics of the intact ACL were evaluated in group 6 (n = 8). Both knees of each rabbit were subjected to ACL reconstruction with 2-mm grafts of Achilles tendon splits. The right knees were reconstructed with remnant preservation, whereas the remnants in the left knees were debrided. The revascularization and remodeling of grafts were evaluated at 6, 12, 18, and 24 weeks after reconstruction. Tendon-to-bone integration was investigated histomorphologically. The tensile load strengths of graft complexes were also tested.

RESULTS

The blood flow in the graft was significantly higher in the remnant-preserved group than in the remnant-debrided group (P < .01). Specifically, the blood flow of the graft with remnant preservation was markedly enhanced at 6 weeks and 12 weeks after reconstruction (P < .05). The number of CD34-positive vessels in the graft was higher in the remnant-preservation group (P < .05). The ligamentization and remodeling of the graft were improved and the collagen type III content in the graft was higher in the remnant-preserved group (P < .05). Tendon-to-bone integration was improved by remnant preservation. At 24 weeks after reconstruction, the failure load of the graft complex was significantly higher in the remnant-preserved group (23.46 ± 7.40 N) than in the remnant-debrided group (18.63 ± 4.26 N) (P < .05).

CONCLUSIONS

The preservation of the remnant attachment in ACL reconstruction improved the revascularization and remodeling of the graft and enhanced the biomechanical properties of the integrated graft.

CLINICAL RELEVANCE

Preservation of the remnant attachment may benefit healing of the tendon graft in ACL reconstruction.

Marine collagen scaffolds for nasal cartilage repair: prevention of nasal septal perforations in a new orthotopic rat model using tissue engineering techniques

Autologous grafts are frequently needed for nasal septum reconstruction. Because they are only available in limited amounts, there is a need for new cartilage replacement strategies. Tissue engineering based on the use of autologous chondrocytes and resorbable matrices might be a suitable option. So far, an optimal material for nasal septum reconstruction has not been identified. The aim of our study was to provide the first evaluation of marine collagen for use in nasal cartilage repair. First, we studied the suitability of marine collagen as a cartilage replacement matrix in the context of in vitro three dimensional cultures by analyzing cell migration, cytotoxicity, and extracellular matrix formation using human and rat nasal septal chondrocytes. Second, we worked toward developing a suitable orthotopic animal model for nasal septum repair, while simultaneously evaluating the biocompatibility of marine collagen. Seeded and unseeded scaffolds were transplanted into nasal septum defects in an orthotopic rat model for 1, 4, and 12 weeks. Explanted scaffolds were histologically and immunohistochemically evaluated. Scaffolds did not induce any cytotoxic reactions in vitro. Chondrocytes were able to adhere to marine collagen and produce cartilaginous matrix proteins, such as collagen type II. Treating septal cartilage defects in vivo with seeded and unseeded scaffolds led to a significant reduction in the number of nasal septum perforations compared to no replacement. In summary, we demonstrated that marine collagen matrices provide excellent properties for cartilage tissue engineering. Marine collagen scaffolds are able to prevent septal perforations in an autologous, orthotopic rat model. This newly described experimental surgical procedure is a suitable way to evaluate new scaffold materials for their applicability in the context of nasal cartilage repair.

Direct FGF-2 gene transfer via recombinant adeno-associated virus vectors stimulates cell proliferation, collagen production, and the repair of experimental lesions in the human ACL

BACKGROUND

Basic fibroblast growth factor (FGF-2) is a powerful stimulator of fibroblast proliferation and type I/III collagen production.

HYPOTHESIS

Overexpression of FGF-2 via direct recombinant adeno-associated virus (rAAV) vector-mediated gene transfer enhances the healing of experimental lesions to the human anterior cruciate ligament (ACL).

STUDY DESIGN

Controlled laboratory study.

METHODS

rAAV vectors carrying a human FGF-2 sequence or the lacZ marker gene were applied to primary human ACL fibroblasts in vitro and to intact or experimentally injured human ACL explants in situ to evaluate the efficacy and duration of transgene expression and the potential effects of FGF-2 treatment upon the proliferative, metabolic, and regenerative activities in these systems.

RESULTS

Sustained, effective dose-dependent lacZ expression was achieved in all systems tested (up to 96% ± 2% in vitro and 80%-85% in situ for at least 30 days). rAAV allowed for continuous FGF-2 production both in vitro and in the intact ACL in situ (32.7 ± 1.4 and 33.1 ± 0.8 pg/mL/24 h, respectively, ie, up to 41-fold more than in the controls at day 30; always P ≤ .001), leading to significantly and durably enhanced levels of proliferation and type I/III collagen production vis-à-vis lacZ (at least 3- and 4-fold increases at day 30, respectively; always P ≤ .001). Most notably, rAAV FGF-2 promoted a significant, long-term production of the factor in experimental ACL lesions (92.7 ± 3.9 pg/mL/24 h, ie, about 5-fold more than in the controls; P ≤ .001) associated with enhanced levels of proliferation and type I/III collagen synthesis (at least 2- and 4-fold increases at day 30, respectively; always P ≤ .001). Remarkably, the FGF-2 treatment allowed for a decrease in the amplitude of such lesions possibly because of the increased expression in contractile α-smooth muscle actin, ligament-specific transcription factor scleraxis, and nuclear factor-κB for proliferation and collagen deposition, which are all markers commonly induced in response to injury.

CONCLUSION

Efficient, stable FGF-2 expression via rAAV enhances the healing of experimental human ACL lesions by activating key cellular and metabolic processes.

CLINICAL RELEVANCE

This approach has potential value for the development of novel, effective treatments for ligament reconstruction.

Regenerative tendon and ligament healing: opportunities with recombinant human platelet-derived growth factor BB-homodimer

Intrinsic tendon healing in response to injury is a reparative process that often results in formation of scar tissue with functional and mechanical properties inferior to those of the native tendon. Development of therapies that can promote regenerative, rather than reparative, healing hold the promise of improving patient recovery from tendon and ligament injuries by producing tissue that is morphologically and functionally equivalent to the native tissue. One therapeutic approach that has been a frequent topic of investigation in the preclinical literature is the use of recombinant human platelet-derived growth factor-BB (rhPDGF-BB) to augment tendon and ligament repair. The chemotactic, mitogenic, and pro-angiogenic properties of rhPDGF-BB have been shown to result in recruitment and proliferation of tenogenic cells and a commensurate boost in extracellular matrix deposition and organization, improving the morphological and biomechanical properties of healing tendons and ligaments. The outcomes of the preclinical studies reviewed here strongly suggest that rhPDGF-BB will provide a new therapeutic opportunity to improve the treatment of injured tendons and ligaments.

Effects of age and platelet-rich plasma on ACL cell viability and collagen gene expression

Platelet-rich plasma (PRP) has shown in vivo potential to stimulate anterior cruciate ligament (ACL) healing at early time points in large animal models. However, in animal models, the healing potential of the ACL is dependent on animal age. In this study, we hypothesized that there are age-dependent differences in ACL cell metabolism, collagen gene expression, and the ability of the cells to respond to growth factors in PRP. To test this hypothesis, ACL cells were obtained from skeletally immature, adolescent and adult pigs, and cultured in a collagen type I hydrogel with or without PRP for 14 days. When cultured in collagen-only hydrogel, ACL cells from adult pigs had a 19% lower apoptotic rate as compared to immature pigs (p = 0.001) and a 25% higher cellular metabolic activity as compared to adolescent pigs (p = 0.006). The addition of PRP to the collagen hydrogel resulted in a significantly increased cellular metabolic activity, reduced apoptotic rate, and stimulation of collagen production in the cells from the immature and adolescent animals (p < 0.05 for all comparisons) but had less effect on adult cells. These findings suggest that skeletal maturity may influence ACL cells' metabolic activity, apoptosis, collagen production, and response to PRP.

The suitability of human adipose-derived stem cells for the engineering of ligament tissue

Rupture of the anterior cruciate ligament (ACL) is the one of the most common sports-related injuries. With its poor healing capacity, surgical reconstruction using either autografts or allografts is currently required to restore function. However, serious complications are associated with graft reconstructions and the number of such reconstructions has steadily risen over the years, necessitating the search for an alternative approach to ACL repair. Such an approach may likely be tissue engineering. Recent engineering approaches using ligament-derived fibroblasts have been promising, but the slow growth rate of such fibroblasts in vitro may limit their practical application. More promising results are being achieved using bone marrow mesenchymal stem cells (MSCs). The adipose-derived stem cell (ASC) is often proposed as an alternative choice to the MSC and, as such, may be a suitable stem cell for ligament engineering. However, the use of ASCs in ligament engineering still remains relatively unexplored. Therefore, in this study, the potential use of human ASCs in ligament tissue engineering was initially explored by examining their ability to express several ligament markers under growth factor treatment. ASC populations treated for up to 4 weeks with TGFβ1 or IGF1 did not show any significant and consistent upregulation in the expression of collagen types 1 and 3, tenascin C and scleraxis. While treatment with EGF or bFGF resulted in increased tenascin C expression, increased expression of collagens 1 and 3 were never observed. Therefore, simple in vitro treatment of human ASC populations with growth factors may not stimulate their ligament differentiative potential.

Up-regulation expressions of lysyl oxidase family in Anterior Cruciate Ligament and Medial Collateral Ligament fibroblasts induced by Transforming Growth Factor-Beta 1

PURPOSE

The lysyl oxidase (LOX) family plays a crucial role in the formation and stabilisation of extracellular matrix (ECM) by catalysing the cross-linking of collagen and elastin, implicating its important fundamental roles in injury healing. A high level of transforming growth factor-β(1) (TGF-β(1)) accompanies the inflammatory phase of an injury of the knee joint. Our purpose was to detect the expressions of the LOX family in anterior cruciate ligament (ACL) and medial collateral ligament (MCL) response to TGF-β(1).

METHODS

This study used reversed transcript PCR, real time quantitative PCR and Western blot for analyses.

RESULTS

The results showed significant increases in mRNA levels of LOX family members. At 5 ng/ml concentration of TGF-β(1,) the gene profiles of LOXs showed most active, and LOX and LOXL-3 showed increasing peaks at 12 hours after TGF-β(1) treatment (LOX: 7.2, 8.8-fold and LOXL-3: 3.8, 5.4-fold compared with normal controls in ACL and MCL, respectively); LOXL-1, LOXL-2 and LOXL-4 reached their highest amounts at six hours (LOXL-1: 1.9, 2.4-fold; LOXL-2: 14.8, 16.2-fold; LOXL-4: 2.5, 4.4-fold in ACL and MCL, respectively). Protein assays revealed that LOXs in ACL cells had relatively lower response to TGF-β(1) compared with those in MCL cells.

CONCLUSIONS

The differential expression and activities of LOXs might help to explain the intrinsic difference between ACL and MCL, and LOXs could imply a potential capability for ACL healing.

TGF-β1 promoted MMP-2 mediated wound healing of anterior cruciate ligament fibroblasts through NF-κB

The adult human anterior cruciate ligament (ACL) has poor functional healing response. Transforming growth factor (TGF)-β1 enhances the wound repair by stimulating matrix proteins deposition as well as the proliferation and migration of cells. However, the function of the TGF-β1-induced matrix metalloproteinases' (MMPs) activities in the wound healing process is poorly understood. In this study, exogenous MMP-2 is added to mimic the TGF-β1-induced MMP-2 expression. Role of NF-κB pathway is further examined. Our results show that TGF-β1 induces dramatic elevation of MMP-2 activities and the MMP-2/tissue inhibitors of metalloproteinases ratio. Furthermore, the exogenous MMP-2 significantly promoted in vitro wound healing abilities of ACL fibroblasts that are significantly blocked with the addition of its inhibitors. TGF-β1 also increases the proliferation of ACL fibroblasts whereas MMP-2 alone does not, indicating that MMP-2 activities are not involved in the proliferation. TGF-β1-induced MMP-2 activity is inhibited by Bay11-7082 and Bay11-7085 (NF-κB inhibitors). Our results demonstrate that increased TGF-β1 facilitates the ACL healing process by promoting the fibroblasts migration and proliferation. The migration process is mediated by MMP-2 and NF-κB pathway is involved in TGF-β1-mediated MMP-2 release.

Effects of autologous platelet-rich plasma on cell viability and collagen synthesis in injured human anterior cruciate ligament

BACKGROUND

Platelet-rich plasma is a fraction of plasma in which platelets are concentrated. It is reported to represent a source of multiple growth factors that promote tissue repair. In anticipation of the eventual testing of platelet-rich plasma in anterior cruciate ligament (ACL)-deficient patients, we examined the effect of autologous platelet-rich plasma on human ACL cell function in vitro.

METHODS

Fresh blood and ACL remnants were obtained from four patients who underwent ACL reconstruction surgery. Platelet-poor plasma and platelet-rich plasma were prepared from the blood samples. The concentrations of various growth factors in each preparation were tested with use of enzyme-linked immunosorbent assays. Isolated ACL cells were cultured in the presence of 5% fetal bovine serum, 5% platelet-poor clot releasate, 5% platelet-rich clot releasate, or 10% platelet-rich clot releasate. Platelet-rich plasma and platelet-poor plasma releasates were applied to the ACL cells from the same patient autologously. Cell viability and collagen synthesis in each group were analyzed, and semiquantitative gene-expression assays for type-I and III collagen were also performed.

RESULTS

The concentrations of the main growth factors (transforming growth factor-beta, platelet-derived growth factor, epidermal growth factor, and vascular endothelial growth factor) were much higher in platelet-rich clot releasate than in platelet-poor clot releasate. In vitro treatment of ACL cells with platelet-rich clot releasate resulted in a significant increase in cell number compared with platelet-poor clot releasate. Total collagen production by the platelet-rich clot releasate-treated cells was significantly higher than that of the platelet-poor clot releasate-treated cells only because of enhanced cell proliferation. There was no significant effect of platelet-rich clot releasate treatment on gene expression for type-I collagen, but expression of type-III collagen was significantly enhanced by the treatment with platelet-rich clot releasate.

CONCLUSIONS

These results suggest that autologous platelet-rich plasma can enhance ACL cell viability and function in vitro.

Potential applications of natural origin polymer-based systems in soft tissue regeneration

Despite the many advances in tissue engineering approaches, scientists still face significant challenges in trying to repair and replace soft tissues. Nature-inspired routes involving the creation of polymer-based systems of natural origins constitute an interesting alternative route to produce novel materials. The interest in these materials comes from the possibility of constructing multi-component systems that can be manipulated by composition allowing one to mimic the tissue environment required for the cellular regeneration of soft tissues. For this purpose, factors such as the design, choice, and compatibility of the polymers are considered to be key factors for successful strategies in soft tissue regeneration. More recently, polysaccharide-protein based systems have being increasingly studied and proposed for the treatment of soft tissues. The characteristics, properties, and compatibility of the resulting materials investigated in the last 10 years, as well as commercially available matrices or those currently under investigation are the subject matter of this review.

Delay of 2 or 6 weeks adversely affects the functional outcome of augmented primary repair of the porcine anterior cruciate ligament

BACKGROUND

Enhanced primary anterior cruciate ligament repair, in which suture repair is performed in conjunction with a collagen-platelet composite to stimulate healing, is a potential new treatment option for anterior cruciate ligament injuries. Previous studies have evaluated this approach at the time of anterior cruciate ligament disruption.

HYPOTHESIS

Delaying surgery by 2 or 6 weeks would have a significant effect on the functional outcome of the repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixteen female Yorkshire pigs underwent staged, bilateral surgical anterior cruciate ligament transections. Anterior cruciate ligament transection was initially performed on 1 knee and the knee closed. Two or 6 weeks later, enhanced primary repair was performed in that knee while the contralateral knee had an anterior cruciate ligament transection and immediate repair. Biomechanical parameters were measured after 15 weeks in vivo to determine the effect of delay time relative to immediate repair on the healing response.

RESULTS

Yield load of the repairs at 15 weeks was decreased by 40% and 60% in the groups where repair was delayed for 2 and 6 weeks, respectively (P = .01). Maximum load showed similar results (55% and 60% decrease in the 2- and 6-week delay groups, respectively; P = .011). Linear stiffness also was adversely affected by delay (50% decrease compared with immediate repair after either a 2- or 6-week delay, P = .011). Anterior-posterior laxity after 15 weeks of healing was 40% higher in knees repaired after a 2-week delay and 10% higher in those repaired after a 6-week delay (P = .012) when tested at 30° of flexion, but was not significantly affected by delay when tested at 60° or 90° (P = .21).

CONCLUSION

A delay between anterior cruciate ligament injury and enhanced primary repair has a significant negative effect on the functional performance of the repair.

CLINICAL RELEVANCE

As future investigations assess new techniques of anterior cruciate ligament repair, the timing of the repair should be considered in the design and the interpretation of experimental studies.

Periodic Nanomechanical Stimulation in a Biokinetics Model Identifying Anabolic and Catabolic Pathways Associated With Cartilage Matrix Homeostasis

Enhancing the available nanotechnology to describe physicochemical interactions during biokinetic regulation will strongly support cellular and molecular engineering efforts. In a recent mathematical model developed to extend the applicability of a statically loaded, single-cell biomechanical analysis, a biokinetic regulatory threshold was presented (Saha and Kohles, 2010, "A Distinct Catabolic to Anabolic Threshold Due to Single-Cell Static Nanomechanical Stimulation in a Cartilage Biokinetics Model," J. Nanotechnol. Eng. Med., 1(3), p. 031005). Results described multiscale mechanobiology in terms of catabolic to anabolic pathways. In the present study, we expand the mathematical model to continue exploring the nanoscale biomolecular response within a controlled microenvironment. Here, we introduce a dynamic mechanical stimulus for regulating cartilage molecule synthesis. Model iterations indicate the identification of a biomathematical mechanism balancing the harmony between catabolic and anabolic states. Relative load limits were defined to distinguish between "healthy" and "injurious" biomolecule accumulations. The presented mathematical framework provides a specific algorithm from which to explore biokinetic regulation.

Ligament-derived matrix stimulates a ligamentous phenotype in human adipose-derived stem cells

Human adipose stem cells (hASCs) can differentiate into a variety of phenotypes. Native extracellular matrix (e.g., demineralized bone matrix or small intestinal submucosa) can influence the growth and differentiation of stem cells. The hypothesis of this study was that a novel ligament-derived matrix (LDM) would enhance expression of a ligamentous phenotype in hASCs compared to collagen gel alone. LDM prepared using phosphate-buffered saline or 0.1% peracetic acid was mixed with collagen gel (COL) and was evaluated for its ability to induce proliferation, differentiation, and extracellular matrix synthesis in hASCs over 28 days in culture at different seeding densities (0, 0.25 x 10(6), 1 x 10(6), or 2 x 10(6) hASC/mL). Biochemical and gene expression data were analyzed using analysis of variance. Fisher's least significant difference test was used to determine differences between treatments following analysis of variance. hASCs in either LDM or COL demonstrated changes in gene expression consistent with ligament development. hASCs cultured with LDM demonstrated more dsDNA content, sulfated-glycosaminoglycan accumulation, and type I and III collagen synthesis, and released more sulfated-glycosaminoglycan and collagen into the medium compared to hASCs in COL (p <or= 0.05). Increased seeding density increased DNA content incrementally over 28 days in culture for LDM but not COL constructs (p <or= 0.05). These findings suggest that LDM can stimulate a ligament phenotype by hASCs, and may provide a novel scaffold material for ligament engineering applications.

Engineering orthopedic tissue interfaces

While a wide variety of approaches to engineering orthopedic tissues have been proposed, less attention has been paid to the interfaces, the specialized areas that connect two tissues of different biochemical and mechanical properties. The interface tissue plays an important role in transitioning mechanical load between disparate tissues. Thus, the relatively new field of interfacial tissue engineering presents new challenges--to not only consider the regeneration of individual orthopedic tissues, but also to design the biochemical and cellular composition of the linking tissue. Approaches to interfacial tissue engineering may be distinguished based on if the goal is to recreate the interface itself, or generate an entire integrated tissue unit (such as an osteochondral plug). As background for future efforts in engineering orthopedic interfaces, a brief review of the biology and mechanics of each interface (cartilage-bone, ligament-bone, meniscus-bone, and muscle-tendon) is presented, followed by an overview of the state-of-the-art in engineering each tissue, including advances and challenges specific to regenerating the interfaces.

Age dependence of expression of growth factor receptors in porcine ACL fibroblasts

Tissue engineering approaches that harness the stimulatory power of platelet-rich plasma have produced encouraging results in anterior cruciate ligament (ACL) repair. However, a number of recent studies have demonstrated age-dependent differences in cellular responses to such an approach. Identifying the reasons for these differences would allow counteracting them and consequently improve outcomes. In this study we hypothesized that these age-related effects are caused by differences in the expression of the receptors for growth factors released from platelet-rich plasma (PRP). Porcine ACL fibroblasts from a predetermined number of animals of different ages were obtained, and mRNA levels of the receptors of platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-beta), fibroblast growth factor (FGF), and vascular endothelial growth factor (VEGF) were determined. Expression levels were compared across age groups (young and adolescent) and regressed on age in days. While no significant difference was seen across groups, the regression analysis showed decreases in receptor expression with increasing age. These differences were statistically significant for TGF-beta receptor 1, FGF receptor, and VEGF receptor 2; and borderline significant for TGF-beta receptor 3 and PDGF receptor. The only receptor that was not associated with age was VEGF receptor 1, a regulator of VEGF receptor 2. These findings suggest that the decrease in growth factor receptor expression as a likely reason for reduced PRP action with increasing age.

Platelets and plasma proteins are both required to stimulate collagen gene expression by anterior cruciate ligament cells in three-dimensional culture

Collagen-platelet (PL)-rich plasma composites have shown in vivo potential to stimulate anterior cruciate ligament (ACL) healing at early time points in large animal models. However, little is known about the cellular mechanisms by which the plasma component of these composites may stimulate healing. We hypothesized that the components of PL-rich plasma (PRP), namely the PLs and PL-poor plasma (PPP), would independently significantly influence ACL cell viability and metabolic activity, including collagen gene expression. To test this hypothesis, ACL cells were cultured in a collagen type I hydrogel with PLs, PPP, or the combination of the two (PRP) for 14 days. The inclusion of PLs, PPP, and PRP all significantly reduced the rate of cell apoptosis and enhanced the metabolic activity of fibroblasts in the collagen hydrogel. PLs promoted fibroblast-mediated collagen scaffold contraction, whereas PPP inhibited this contraction. PPP and PRP both promoted cell elongation and the formation of wavy fibrous structure in the scaffolds. The addition of only PLs or only plasma proteins did not significantly enhance gene expression of collagen types I and III but the combination, as PRP, did. Our findings suggest that the addition of both PLs and plasma proteins to collagen hydrogel may be useful in stimulating ACL healing by enhancing ACL cell viability, metabolic activity, and collagen synthesis.

ACL prosthesis: any promise for the future?

Biological tissue autograft reconstruction using the patellar tendon or quadrupled semitendinosus/gracilis tendons has become the most popular procedure in surgical treatment of a ruptured anterior cruciate ligament (ACL). This article provides a review of the history of the use of prosthetics with respect to ACL reconstruction grafts including Carbon Fibre, Gore-Tex and Dacron prosthetics, as well as the Leeds-Keio Artificial Ligament and the Kennedy Ligament Augmentation Device (LAD). Emphasis is placed on the ligament advanced reinforcement system (LARS) as preliminary investigations of its use have been encouraging. Significant progress has been made recently with respect to the understanding of ACL anatomy, composition, biomechanics, and healing processes, leading to innovative techniques using approaches based in tissue engineering principles. Most of grafts that have been developed to date have failed due to unsatisfactory long-term physiological and functional performance. Most permanent ACL prostheses are prone to creep, fatigue, and mechanical failure within several years after implantation. In view of these factors, prosthetics are not widely used today in ACL reconstruction, and autogenous tissue grafts remain the gold standard used by the majority of surgeons. Perhaps development of resorbable, tissue inducing and cell-seeded biomaterials will improve the long-term biomechanical performance of the reconstructed ACL. Tissue ingrowth scaffolds and ligament augmentation devices require further refinement to provide effective mechanical support while avoiding stress shielding of the host tissue. While research into improved ACL treatment options continues, the synthesis of recent advancements provides some new optimism towards the regeneration of an ACL mirroring its original stability, function, and longevity.

Functional tissue engineering of ligament healing

Ligaments and tendons are dense connective tissues that are important in transmitting forces and facilitate joint articulation in the musculoskeletal system. Their injury frequency is high especially for those that are functional important, like the anterior cruciate ligament (ACL) and medial collateral ligament (MCL) of the knee as well as the glenohumeral ligaments and the rotator cuff tendons of the shoulder. Because the healing responses are different in these ligaments and tendons after injury, the consequences and treatments are tissue- and site-specific. In this review, we will elaborate on the injuries of the knee ligaments as well as using functional tissue engineering (FTE) approaches to improve their healing. Specifically, the ACL of knee has limited capability to heal, and results of non-surgical management of its midsubstance rupture have been poor. Consequently, surgical reconstruction of the ACL is regularly performed to gain knee stability. However, the long-term results are not satisfactory besides the numerous complications accompanied with the surgeries. With the rapid development of FTE, there is a renewed interest in revisiting ACL healing. Approaches such as using growth factors, stem cells and scaffolds have been widely investigated. In this article, the biology of normal and healing ligaments is first reviewed, followed by a discussion on the issues related to the treatment of ACL injuries. Afterwards, current promising FTE methods are presented for the treatment of ligament injuries, including the use of growth factors, gene delivery, and cell therapy with a particular emphasis on the use of ECM bioscaffolds. The challenging areas are listed in the future direction that suggests where collection of energy could be placed in order to restore the injured ligaments and tendons structurally and functionally.

Collagen density significantly affects the functional properties of an engineered provisional scaffold

The formation of a provisional scaffold is essential in wound healing. However, for tissues inside of joints, this process is impeded by the synovial fluid environment and wound healing is significantly impaired as a result. Therefore, development of substitute provisional scaffolds which are effective in the intra-articular environment is of great interest. Collagen-platelet hydrogels have recently been found useful as substitute provisional scaffolding materials. In this study, our hypothesis was that increasing the collagen density in the hydrogel would result in physiologic changes that would be likely to affect their function as provisional scaffold substitutes. The primary functional outcome measures were modulus of the hydrogel, platelet activation, fibroblast proliferation, and scaffold retraction. Increased collagen density resulted in collagen-platelet hydrogels with a higher storage modulus. Platelet activation was not found to be dependent on the collagen density within the range tested. Increasing the collagen density had a suppressive effect on both fibroblast proliferation and scaffold retraction. These studies suggest that the collagen density may be able to significantly influence the function of collagen-platelet hydrogels used as substitute provisional scaffolds.

Translational studies in anterior cruciate ligament repair

Translational research, which can be explained as the principle of combining advances in both basic research and clinical understanding in a bedside-to-bench-to-bedside approach, has become one of the central themes of present-day medical research. One orthopedic problem that has strongly benefited from such an approach is tissue-engineering-enhanced primary repair of the anterior cruciate ligament. Recent years have shown a clearer definition of the clinical problem and established an underlying mechanistic cause of the incapacity of the anterior cruciate ligament to heal-the premature loss of provisional scaffold in the wound site. These clinical findings were then translated into a research objective, namely, to replace the missing scaffold with a biomaterial with appropriate structural and bio-stimulatory characteristics. Subsequently, a tissue-engineering-based treatment using a collagen-platelet composite was developed and tested in vitro. After proofing the efficacy of this new treatment in the laboratory, it was translated into a potential clinical application, which showed highly successful results in structural integrity and biomechanical capacity in large animal testing. This approach of defining the scientific mechanism underlying a clinical observation and then using that information to design new therapies is but one example of how translational research in tissue engineering can help define and develop new treatments for challenging problems faced by patients.