Auto-crosslinked hyaluronic acid gel accelerates healing of rabbit flexor tendons in vivo

Non-collagenous proteins, rather than the collagens, are key biochemical factors that mediate tenogenic bioactivity of tendon extracellular matrix

Despite the growing clinical use of extracellular matrix (ECM)-based biomaterials for tendon repair, undesired healing outcomes or complications have frequently been reported. A major scientific challenge has been the limited understanding of their functional compositions and mechanisms of action due to the complex nature of tendon ECM. Previously, we have reported a soluble ECM fraction from bovine tendons (tECM) by urea extraction, which exhibited strong, pro-tenogenic bioactivity on human adipose-derived stem cells (hASCs). In this study, to advance our previous findings and gain insights into the biochemical nature of its pro-tenogenesis activity, tECM was fractionated using (i) an enzymatic digestion approach (pepsin, hyaluronidase, and chondroitinase) to yield various enzyme-digested tECM fractions; and (ii) a gelation-based approach to yield collagen matrix-enriched (CM) and non-collagenous matrix-enriched (NCM) fractions. Their tenogenic bioactivity on hASCs was assessed. Our results collectively indicated that non-collagenous tECM proteins, rather than collagens, are likely the important biochemical factors responsible for tECM pro-tenogenesis bioactivity. Mechanistically, RNA-seq analysis revealed that tECM and its non-collagenous portion induced similar transcriptional profiles of hASCs, particularly genes associated with cell proliferation, collagen synthesis, and tenogenic differentiation, which were distinct from transcriptome induced by its collagenous portion. From an application perspective, the enhanced solubility of the non-collagenous tECM, compared to tECM, should facilitate its combination with various water-soluble biomaterials for tissue engineering protocols. Our work provides insight into the molecular characterization of native tendon ECM, which will help to effectively translate their functional components into the design of well-defined, ECM biomaterials for tendon regeneration. STATEMENT OF SIGNIFICANCE: Significant progress has been made in extracellular matrix (ECM)-based biomaterials for tendon repair. However, their effectiveness remains debated, with conflicting research and clinical findings. Understanding the functional composition and mechanisms of action of ECM is crucial for developing safe and effective bioengineered scaffolds. Expanding on our previous work with bovine tendon ECM extracts (tECM) exhibiting strong pro-tenogenesis activity, we fractionated tECM to evaluate its bioactive moieties. Our findings indicate that the non-collagenous matrix within tECM, rather than the collagenous portions, plays a major role in the pro-tenogenesis bioactivity on human adipose-derived stem cells. These insights will drive further optimization of ECM-based biomaterials, including our advanced method for preparing highly soluble, non-collagenous matrix-enriched tendon ECM for effective tendon repair.

Polydopamine Nanoparticles-Based Photothermal Effect Against Adhesion Formation in a Rat Model of Achilles Tendon Laceration Repair

Background

Adhesion formation after tendon surgery is a major obstacle to repair of tendon ruptures, and there is still no effective clinical anti-adhesion method. Myofibroblasts expressing α-smooth muscle actin (α-SMA) play a crucial role in adhered fibrous tissue. Heat shock protein (Hsp) 72 can selectively prevent the activation of c-Jun N-terminal kinase (JNK), which mediates the conversion from fibroblasts to myofibroblasts. The purpose of this study was to investigate for the first time whether polydopamine nanoparticles (PDA NPs)-based photothermal effect would attenuate adhesion formation in a rat model of Achilles tendon laceration repair.

Materials and Methods

Forty-five adult male Sprague-Dawley rats were randomly assigned to the photothermal group, the control group and the PDA NPs group (n = 15 per group). The primary outcome measure was the adhesion scores at two weeks after surgery according to the grading of Tang et al. The secondary outcomes included the expressions of Hsp 72, JNK, phosphorylated JNK and α-SMA, which were measured by immunohistochemistry or Western blot.

Results

The average adhesion score was significantly lower in the photothermal group (4.25 ± 0.21) than that in the control group (5.29 ± 0.12) (p = 0.005) and the PDA NPs group (5.29 ± 0.20) (p = 0.005). Relative to the control group and PDA NPs group, Hsp 72 in the photothermal group was significantly increased whereas α-SMA and p-JNK was significantly decreased, but JNK was not found to be different across the three groups.

Conclusion

The photothermal effect produced by PDA NPs could reduce tendon adhesion formation in rats by inhibiting myocyte fibrosis, which may have potential in developing endogenous heating for postsurgical tissue adhesions.

Combined Verapamil-Polydopamine Nanoformulation Inhibits Adhesion Formation in Achilles Tendon Injury Using Rat Model

Introduction

Topical verapamil has been demonstrated to reduce the fibroproliferative scar. Therefore, it was hypothesized that topical verapamil could reduce adhesion formation after tendon repair. The current study aimed to examine the effects of verapamil-loaded polydopamine nanoparticles (VP-PDA NPs) on the adhesion formation of Achilles tendon laceration and repair in a rat model.

Methods

We randomly assigned 72 male Sprague-Dawley rats to the control, the PDA NPs, and the VP-PDA NPs groups (n = 24 per group). The quality of tendon healing was evaluated by the maximal tensile strength four and six weeks after surgery. The degree of tendon adhesion was scored on days 4, 15, 29, and 43 after surgery. The expressions of transforming growth factor-beta 1 (TGF-β1), vimentin, α-smooth muscle actin (α-SMA), and collagens type I and III were detected through Western blotting or immunohistochemistry at four weeks after surgery.

Results

In vitro release tests revealed that 61.3% of verapamil was released from VP-PDA NPs in four weeks. There was a significant increase in average failure to load in the VP-PDA NPs group (89.27 ± 5.09 N) compared with the PDA NPs group (65.52 ± 2.04 N) (p = 0.003) and the control group (74.52 ± 4.24 N) (p = 0.029). Adhesion scores were significantly reduced in the VP-PDA NPs group at six weeks (3.175 ± 0.08) and four weeks (3.35 ± 0.25) compared with the other groups. Moreover, VP-PDA NPs significantly reduced the expression of vimentin, α-SMA, TGF-β1, and collagens type I and III.

Conclusion

These data suggest that VP-PDA NPs reduced adhesion formation and enhanced tendon healing during rat tendon injury. Since topical verapamil has been used in clinics without side effects, VP-PDA NPs would have direct translation implications. However, its anti-adhesive effects on intrasynovial tendon injury must be examined.

A New Animal Model for Pathological Subcutaneous Fibrosis: Surgical Technique and in vitro Analysis

Fibrosis is a condition that affects the connective tissue in an organ or tissue in the restorative or responsive phase as a result of injury. The consequences of excessive fibrotic tissue growth may lead to various physiological complications of deformity and impairment due to hypertrophic scars, keloids, and tendon adhesion without understating the psychological impact on the patient. However, no method accurately quantifies the rate and pattern of subcutaneous induced hypertrophic fibrosis. We, therefore, devised a rodent excisional model to evaluate the extent of fibrosis with talc. Tissue specimens were set on formalin, and paraffin sections for histological, immunohistochemical, and molecular analysis talc was used to induce the fibroproliferative mechanism typical of hypertrophic scars. This pathway is relevant to the activation of inflammatory and fibrotic agents to stimulate human hypertrophic scarring. This model reproduces morpho-functional features of human hypertrophic scars to investigate scar formation and assess potential anti-scarring therapies.

Cross-linked hyaluronan gel to improve pregnancy rate of women patients with moderate to severe intrauterine adhesion treated with IVF: a randomized controlled trial

PURPOSE

To evaluate whether the cross-linked hyaluronan (cHA) gel can improve the clinical pregnancy rate of patients with moderate to severe intrauterine adhesion (IUA) who underwent operative hysteroscopy followed by embryo transfer.

METHODS

Women with moderate to severe IUA desiring to undergo embryo transfer were recruited in this randomized controlled trial. The patients were randomized on the day of receiving hysteroscopy. The control group received standard hysteroscopy, while cHA gel was applied to the treatment group at the end of hysteroscopy and 5-7 days after operation. All patients were expected to undergo in vitro fertilization (IVF)/intracytoplasmic sperm injection and frozen-thawed embryo transfer (FET).

RESULTS

A total of 306 patients were enrolled in this study, of which 202 were assigned to the treatment group and 104 to the control group. Both the clinical pregnancy rate (26.3% [49/186] vs. 15.3% [13/85], P = 0.045), the implantation rate (17.7% [57/322] vs. 9.8% [15/153], P = 0.025), and the endometrial thickness on the day of embryo transfer (7.97 ± 1.37 vs. 7.50 ± 0.60 mm, P < 0.001) were significantly higher in the treatment group compared to the control group. In addition, histological assessment of the paired endometrial tissues collected before and after operation revealed a relatively higher number of tubular glands after operation (15.1 ± 13.2 vs. 28.8 ± 30.4, P = 0.166).

CONCLUSIONS

To conclude, the application of cHA gel in patients with moderate to severe IUA during hysteroscopy can improve the quality of endometrium and uterine receptivity and consequently enhance the clinical pregnancy rate after IVF/CSI and FET.

Managing Pathologic Scars by Injecting Auto-Cross-linked Hyaluronic Acid: A Preliminary Prospective Clinical Study

BACKGROUND

Pathological scars are unattractive and may significantly impair the patient's quality of life. Current treatments provide inconsistent results, and none may be regarded as definitive. Recently, an auto-cross-linked hyaluronic acid (HA) formulation, IAL-SYSTEM ACP, featuring a long residence time and an enhanced safety profile, has been successfully used to prevent surgical adhesions, treat tendon lesions and rejuvenate the face and the décolletage. This study aims to preliminarily investigate whether IAL-SYSTEM ACP may also be effective in treating pathological scars resulting from burns, trauma or iatrogenic causes.

METHODS

Patients presenting one pathological scar were prospectively recruited and treated with two IAL-SYSTEM ACP injections carried out two weeks apart. Scar improvement was measured comparing the patient and observer scar assessment scale (POSAS) scores collected before treatment (T0) and 90 days after the second injection (T90) using nonparametric tests. The effect of age and scar type over score variation was investigated through quantile regression analysis.

RESULTS

Forty-one patients, 10 women and 31 men (median age, 34 years) were recruited. No patient dropped out, and no significant adverse event was observed. At T90, the median observer total score decreased by 11 units (- 77.5%) and the median patient total score decreased by 15 units (- 73.7%). The difference was significant (p < 0.001) in both cases. Traumatic injuries and young patient's age were the most significant predictors of a positive treatment outcome.

CONCLUSIONS

Treatment of pathological scars by two IAL-SYSTEM ACP injections, carried out two weeks apart, may provide significant clinical benefits. These findings should be the subject of further investigations.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Prevention of Peritendinous Adhesion Formation After the Flexor Tendon Surgery in Rabbits: A Comparative Study Between Use of Local Interferon-α, Interferon-β, and 5-Fluorouracil

BACKGROUND

Peritendinous adhesion is the most common complication after tendon surgery, particularly in zone II of the hand. Prevention of inflammation around the tendon, which develops after trauma and surgery, can decrease the tendon adhesion formation. This study compares the effect of some anti-inflammatory cytokines with 5-fluorouracil (5-FU) on the tensile strength and in prevention of peritendinous adhesion formation.

METHODS

Sixteen rabbits were allocated equally into 4 groups. Tendons of the index and ring fingers in zone II of the right hind paw were cut in all animals and then repaired. Interferon (IFN)-α in group 1, 5-FU in group 2, normal saline in group 3, and IFN-β in group 4 were locally applied to the repaired sites. Three weeks later, tensometric and histopathologic evaluations were performed.

RESULTS

The force required for removing the tendon from the sheath was not different between the groups (P = 0.130), but the time required for removal was significantly shorter in 5-FU group (P = 0.049). The strength of repair was not different between the groups in terms of force and time needed for rupture (P = 0.11 and 0.67, respectively). In histopathologic examination, normal architecture of the tendon and peritendon environment was less disturbed in the IFN groups, especially in IFN-β specimens.

CONCLUSIONS

Local application of 5-FU significantly reduced peritendinous adhesion. Local IFN-α and IFN-β had no significant effect on the prevention of peritendinous adhesion formation. The strength of the repair was not affected by these cytokines and 5-FU.

EFFECTS OF HIGH-DOSE VITAMIN C AND HYALURONIC ACID ON TENDON HEALING

OBJECTIVE

To assess the histopathologic and biomechanical effects of hyaluronic acid (HA) and high-dose vitamin C (VC) on rat Achilles tendon healing.

METHODS

Forty-eight Sprague-Dawley rats were randomized to HA and VC and control groups with equal numbers. Each group was further divided into two subgroups to be sacrificed on Day 15 (n=8) and Day 30 (n=8). The Achilles tendons were cut and repaired. While the control rats remained untreated, HA and VC were administered after repair. The repaired tendons were removed for biomechanical and histopathologic analyses. In the biomechanical tests, the tendons were stretched to failure and maximum forces were measured. For histopathologic examination, the specimens were interpreted semiquantitatively using Movin's grading scale and Bonar scores.

RESULTS

The highest mean forces were obtained in the HA group on Day 15 and in the VC group on Day 30, with a significant difference between HA and VC on Day 15 between control and VC on Day 30 (p<0.05). Histological examination showed both Movin and Bonar scores decreased in all groups on Day 30, with significant improvements in the HA and VC groups (p<0.05).

CONCLUSION

Our results demonstrated that both VC and HA had therapeutic effects on tendon healing, especially in the late phase. Level of Evidence I; High quality randomized trial with statistically significant difference.

Regenerative Engineering of the Rotator Cuff of the Shoulder

Rotator cuff tears often heal poorly, leading to re-tears after repair. This is in part attributed to the low proliferative ability of the resident cells (tendon fibroblasts and tendon-stem cells) upon injury to the rotator cuff tissue and the low vascularity of the tendon insertion. In addition, surgical outcomes of current techniques used in clinical settings are often suboptimal, leading to the formation of neo-tissue with poor biomechanics and structural characteristics, which results in re-tears. This has prompted interest in a new approach, which we term as "Regenerative Engineering", for regenerating rotator cuff tendons. In the Regenerative Engineering paradigm, roles played by stem cells, scaffolds, growth factors/small molecules, the use of local physical forces, and morphogenesis interplayed with clinical surgery techniques may synchronously act, leading to synergistic effects and resulting in successful tissue regeneration. In this regard, various cell sources such as tendon fibroblasts and adult tissue-derived stem cells have been isolated, characterized, and investigated for regenerating rotator cuff tendons. Likewise, numerous scaffolds with varying architecture, geometry, and mechanical characteristics of biologic and synthetic origin have been developed. Furthermore, these scaffolds have been also fabricated with biochemical cues (growth factors and small molecules), facilitating tissue regeneration. In this Review, various strategies to regenerate rotator cuff tendons using stem cells, advanced materials, and factors in the setting of physical forces under the Regenerative Engineering paradigm are described.

The past, present and future in scaffold-based tendon treatments

Tendon injuries represent a significant clinical burden on healthcare systems worldwide. As the human population ages and the life expectancy increases, tendon injuries will become more prevalent, especially among young individuals with long life ahead of them. Advancements in engineering, chemistry and biology have made available an array of three-dimensional scaffold-based intervention strategies, natural or synthetic in origin. Further, functionalisation strategies, based on biophysical, biochemical and biological cues, offer control over cellular functions; localisation and sustained release of therapeutics/biologics; and the ability to positively interact with the host to promote repair and regeneration. Herein, we critically discuss current therapies and emerging technologies that aim to transform tendon treatments in the years to come.

The Effect of Phospholipids (Surfactant) on Adhesion and Biomechanical Properties of Tendon: A Rat Achilles Tendon Repair Model

Adhesion of the tendon is a major challenge for the orthopedic surgeon during tendon repair. Manipulation of biological environment is one of the concepts to prevent adhesion. Lots of biochemicals have been studied for this purpose. We aimed to determine the effect of phospholipids on adhesion and biomechanical properties of tendon in an animal tendon repair model. Seventy-two Wistar rats were divided into 4 groups. Achilles tendons of rats were cut and repaired. Phospholipids were applied at two different dosages. Tendon adhesion was determined histopathologically and biomechanical test was performed. At macroscopic evaluation of adhesion, there are statistically significant differences between multiple-dose phospholipid injection group and Control group and also hyaluronic acid group and Control group (p < 0.008). At microscopic evaluation of adhesion, there was no statistically significant difference (p > 0.008). Ultimate strength was highest at hyaluronic acid injection group and lowest at multiple-dose phospholipid injection group. Single-dose phospholipids (surfactant) application may have a beneficial effect on the tendon adhesion. Although multiple applications of phospholipids seem the most effective regime to reduce the tendon adhesion among groups, it deteriorated the biomechanical properties of tendon.

Prevention of peritendinous adhesions using an electrospun DegraPol polymer tube: a histological, ultrasonographic, and biomechanical study in rabbits

Purpose. One of the great challenges in surgical tendon rupture repair is to minimize peritendinous adhesions. In order to reduce adhesion formation, a physical barrier was applied to a sutured rabbit Achilles tendon, with two different immobilization protocols used postoperatively. Methods. Thirty New Zealand white rabbits received a laceration on the Achilles tendon, sutured with a 4-strand Becker suture, and half of the rabbits got a DegraPol tube at the repair site. While fifteen rabbits had their treated hind leg in a 180° stretched position during 6 weeks (adhesion provoking immobilization), the other fifteen rabbits were recasted with a 150° position after 3 weeks (adhesion inhibiting immobilization). Adhesion extent was analysed macroscopically, via ultrasound and histology. Inflammation was determined histologically. Biomechanical properties were analysed. Results. Application of a DegraPol tube reduced adhesion formation by approximately 20%—independently of the immobilization protocol. Biomechanical properties of extracted specimen were not affected by the tube application. There was no serious inflammatory reaction towards the implant material. Conclusions. Implantation of a DegraPol tube tightly set around a sutured tendon acts as a beneficial physical barrier and prevents adhesion formation significantly—without affecting the tendon healing process.

History and performance of implant materials applied as peritendinous antiadhesives

Peritendinous fibrotic adhesions after tendon surgery are still a problem up-to-date. Approaches to overcome or at least minimize adhesion formation include implantation of barrier materials, application of lubricants or combinations of materials and functionalized drugs that are controllably released and support the healing tendon to glide and achieve the full range of motion after regeneration. Although a huge amount of different materials have been experimentally tested, the optimal strategy with respect to material and method has not yet been determined. In this review, we present a historical overview of physical barriers as well as liquid agents that have been used in order to prevent peritendinous adhesion formation. The materials are divided according to their first publication into two time frames; before and after 1980. There is no claim to include all materials tested neither will the "best" material be chosen; however, we present several materials that were experimentally tested in different animal trials as well as in clinical trials in contrast to other materials that were only tested once and disappeared from the assortment of anti-adhesives; which as such is a valuable information about its applicability for this purpose.

2D motion analysis of rabbits after Achilles tendon rupture repair and histological analysis of extracted tendons: can the number of animals be reduced by operating both hind legs simultaneously?

BACKGROUND

Considering the 3Rs principle in animal experiments, there is a demand to perform research experiments with the fewest number of animals possible while warranting the welfare of the animals. Orthopaedic experimental studies involving operations on the hind legs of rabbits are either performed on one hind leg with the second hind leg serving as control or on both hind legs simultaneously (control: rabbits with no operations at all).

METHODS

The Achilles tendon of rabbits was transected and sutured, and the two-dimensional motion pattern of animals having only one leg operated was compared to rabbits having both hind legs operated (control: non-treated animals). Step length, maximum ankle angle, minimum ankle angle and the resulting range of motion of both hind legs were determined weekly over a time span from 3 weeks to 12 weeks post-operation. The results were fitted by a linear mixed effects model including time dependency. Moreover, all tendon specimen were analysed histologically. Tenocyte and tenoblast density, tenocyte and tenoblast nuclei width, inflammation level and collagen fibre alignment were determined.

RESULTS

Statistically significant differences in the motion pattern were found when one-leg treated and two-leg treated animals were compared. However, the absolute differences were on average less than 20%. Histologically, 1-leg treated animals had tendon tissue with higher cell density, but lower inflammation and less ondulated collagen fibres compared to 2-leg treated animals; the nuclei width was the same for both groups. With regard to welfare, all animals were fine during the experiments.

CONCLUSIONS

While comparative studies should be performed with one-leg treated animals due to interaction effects, for proof-of-principle studies, operating two legs per animal may be justified as the welfare of the animals is warranted. This is a great benefit in the sense of the 3Rs because up to 50% of animals can be spared.

Effects on bone union and prevention of tendon adhesion by new porous anti-adhesive poly L-lactide-co-ε-caprolactone membrane in a rabbit model

To prevent adhesion between the tendon and the plate in hand surgery, a porous poly L-lactide-co-ε-caprolactone (P(LA/CL)) membrane was developed as a biologically absorbable anti-adhesion material. Our study aims to confirm the efficacy of this new P(LA/CL) membrane and its influences on the osteotomy site by performing a fundamental experiment assessing the possibility of clinical application. We prepared a rabbit model of tendon-plate adhesion, and evaluated the efficacy of the P(LA/CL) membrane to pullout tendon strength, to be scored in terms of macroscopic, pathological results. Another rabbit model of osteotomy was prepared to confirm the P(LA/CL) membrane influences on bone union by radiological, mechanical and pathological evaluation. The result showed to be significantly lower adhesion in the P(LA/CL) membrane group than in the control group. Also there were no differences between the P(LA/CL) membrane group and control group in the results for bone union.

Preliminary clinical experience with hyaluronan anti-adhesion gel in arthroscopic arthrolysis for posttraumatic elbow stiffness

Background

Loss of motion of the elbow joint is a common finding after elbow trauma. It has been shown that arthroscopic treatment leads to excellent restoration of elbow motion, although it is still a demanding procedure. The aim of our cohort study was to assess clinical outcomes following treatment of posttraumatic elbow stiffness using arthroscopic arthrolysis with or without the associated use of a hyaluronan anti-adhesion gel.

Materials and methods

A cohort of 36 consecutive patients undergoing elbow arthroscopic arthrolysis were enrolled: 17 patients in the hyaluronan gel group and 19 in the control group. The patients underwent prospective control visits 30 and 75 days after surgery. Functional outcome was measured by the range of motion and the Liverpool elbow score (LES), whereas pain and quality of life were evaluated using the visual analogue scale and the SF-36 questionnaire, respectively.

Results

The range of motion and the overall LES score increased over time in both groups. The mean increase over time was statistically significant (p < 0.001) in both groups and there was no difference between the groups. There was also no interaction between time and treatment. The percentage of patients who reported pain decreased significantly over time (p = 0.0419) in the hyaluronan-treated group (suggesting limited contractions and better comfort during rehabilitation), but not in the control group. The intensity of pain decreased significantly over time in both groups (p < 0.0001) without any significant difference between the groups. All the changes in patient quality of life as measured by the SF-36 questionnaire were similar for the two groups of patients. No adverse event or complication related to the application of hyaluronan gel occurred.

Conclusions

Our preliminary clinical experience showed promising results upon the use of hyaluronan gel, considering that it significantly reduced pain in the short term, facilitating a more comfortable rehabilitation. These findings should be confirmed by larger studies.

Effect of lactoferrin peptide (PXL01) on rabbit digit mobility after flexor tendon repair

PURPOSE

Restoration of digital function after flexor tendon injuries remains a clinical challenge. Complications such as adhesion formation and tendon rupture can lead to limited hand function. The aim of this study was to compare the effects of the lactoferrin-derived peptide, PXL01, formulated in sodium hyaluronate (SH), with SH alone on joint mobility as an indirect measure of postsurgical adhesion prevention and healing strength of the tendon and to elucidate the most optimal concentration of PXL01.

METHODS

Using a rabbit flexor tendon repair model, in which the deep flexor tendon was fully transected and repaired, PXL01 in SH or SH alone was administered between the repaired tendon and the tendon sheath before closure of the surgical wound. Three concentrations of PXL01 in SH (5, 20, or 40 mg/mL) were compared to determine the lowest effective concentration. The repaired tendons were evaluated 7 weeks after surgery by measuring the proximal interphalangeal joint mobility by full range of flexion assessment and the tendon repair strength.

RESULTS

Treatment with PXL01 formulated in SH resulted in improved mobility of the proximal interphalangeal joint with an average of 10°, corresponding to improvement of approximately 25% to 60% of the flexion of nonoperated toes at the different measuring points compared with SH alone. The difference was statistically significant in 5 out of 6 measuring points (0.5, 1, 2, 3, and 4 N; P < .05). The dose-response study indicated that the lowest effective concentration of PXL01 was 20 mg/mL. There was no difference in healing strength of the tendon between the groups as assessed by load-to-failure breaking strength.

CONCLUSIONS

PXL01 in SH significantly improved the mobility compared with the carrier SH alone, without any negative effect on healing strength, and PXL01 at 20 mg/mL was the lowest effective concentration.

CLINICAL RELEVANCE

The result provides a valuable basis for a clinical trial to assess efficacy and safety of PXL01 in clinical hand surgery.

Cationised gelatin and hyaluronic acid coating enhances polyethylene terephthalate artificial ligament graft osseointegration in porcine bone tunnels

PURPOSE

The aim of this study was to investigate whether cationised gelatin and hyaluronic acid (CH) coating could induce polyethylene terephthalate (PET) artificial ligament graft osseointegration in the bone tunnel.

METHODS

Surface modification of PET artificial ligament graft was performed by layer-by-layer (LBL) self-assembly CH coating. Six pigs underwent anterior cruciate ligament (ACL) reconstruction on the right knees, with three pigs receiving the CH-coated PET grafts and the other three pigs non-CH-coated PET grafts as controls. They were sacrificed at three months after surgery and the graft-bone complexes were acquired for computed tomography (CT) scan and histological examination.

RESULTS

CT scans showed a significant difference at the distal femoral site (p = 0.031) or at the distal tibial site (p = 0.0078), but no significant difference in the bone tunnel areas' enlargement at other sites (p > 0.05) between the CH group and the control group. Histologically, application of CH coating induced new bone formation between graft and bone at three months compared with the controls at the distal site. The interface width of the CH group was significantly lower than that of the control group at the distal femoral site (p = 0.0327) and at the distal tibial site (p = 0.0047).

CONCLUSIONS

The study has shown that CH coating on the PET artificial ligament surface has a positive biological effect in the induction of artificial ligament osseointegration within the bone tunnel at the distal site of the bone tunnel.

The use of layer by layer self-assembled coatings of hyaluronic acid and cationized gelatin to improve the biocompatibility of poly(ethylene terephthalate) artificial ligaments for reconstruction of the anterior cruciate ligament

In this study layer by layer (LBL) self-assembled coatings of hyaluronic acid (HA) and cationized gelatin (CG) were used to modify polyethylene terephthalate (PET) artificial ligament grafts. Changes in the surface properties were characterized by scanning electron microscopy, attenuated total reflection Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and contact angle and biomechanical measurements. The cell compatibility of this HA-CG coating was investigated in vitro on PET films seeded with human foreskin dermal fibroblasts over 7days. The results of our in vitro studies demonstrated that the HA-CG coating significantly enhanced cell adhesion, facilitated cell growth, and suppressed the expression of inflammation-related genes relative to a pure PET graft. Furthermore, rabbit and porcine anterior cruciate ligament reconstruction models were used to evaluate the effect of this LBL coating in vivo. The animal experiment results proved that this LBL coating significantly inhibited inflammatory cell infiltration and promoted new ligament tissue regeneration among the graft fibers. In addition, the formation of type I collagen in the HA-CG coating group was much higher than in the control group. Based on these results we conclude that PET grafts coated with HA-CG have considerable potential as substitutes for ligament reconstruction.

Repeated administration of exogenous Sodium-hyaluronate improved tendon healing in an in vivo transection model

GOALS AND OBJECTIVES

This study was designed to evaluate the effects of exogenous Sodium-Hyaluronate (NaH) on full thickness Superficial Digital Flexor Tendon (SDFT) rupture in the early phase of healing in rabbits.

METHODS

Forty White New Zealand mature male rabbits were randomly divided into two equal groups of injured treated and injured untreated. After full thickness tendon transection and surgical repair, using modified Kessler technique and running suture, the injured legs were casted for 14 days. Sodium-Hyaluronate was injected subcutaneously over the lesion on days 3, 7 and 10 post-injury (DPI). The control animals received normal saline injection following the same protocol. Weight of the animals, tendon diameter, ultrasonographic evaluations was conducted at weekly intervals. The rabbits were euthanized on 28 DPI and the tendons were assessed for macroscopic, histopathologic, ultrastructural, and percentage dry weight analysis.

RESULTS

Although there was no significant difference in the radiographs of the treated and untreated lesions, treatment significantly reduced tendon diameter, ultimate and yield strain and increased echogenicity and dry weight content of the injured tendons compared to those of the untreated ones. Treatment also significantly enhanced the maturation rate of the tenoblasts, diameter and density of the collagen fibrils.

CONCLUSION

Treatment of NaH has been shown to be effective in restoring the morphological and biomechanical properties of lacerated SDFT of rabbits and may be valuable in the clinical trial studies.

Effect of platelet-rich plasma with fibrin matrix on healing of intrasynovial flexor tendons

PURPOSE

To investigate the effects of platelet-rich plasma (PRP) with fibrin matrix on the healing of intrasynovial flexor tendons in a rabbit model in vivo.

METHODS

We transected and repaired 156 toe flexors of 73 rabbits using the technique of Tsuge et al and a simple running epitendinous suture. We randomly assigned Repaired tendons to groups that recieved no additional treatment (control) or to which we applied PRP, fibrin (F), or PRP with fibrin matrix (PRP-F) at the repair site. We scored edema and adhesion at 2, 3, and 6 weeks after surgery, and linearly tested repaired tendons for load to failure. We also histologically evaluated tendons at 2 and 3 weeks.

RESULTS

Edema scores and adhesion scores did not significantly differ among the 4 groups at any time point. Mean load to failure in the PRP-F group (14.7 N) was the highest among the 4 groups at 2 weeks after surgery, and was significantly higher than in the control group (10.0 N). Median histological scores in the PRP-F group (3.3 points) were significantly higher than in the control group (1.0 point). Mean load to failure in the PRP-F group (16.1 N) was highest, and median histological scores in the PRP-F group (3.5 points) were higher than in the control group (2.4 points) at 3 weeks, although there were no significant differences at 3 or 6 weeks.

CONCLUSIONS

In a rabbit model of cut flexor tendons, PRP with fibrin matrix significantly increased healing strength within 2 weeks after surgery. Side effects such as increases in toe edema or adhesions around the tendons did not arise.

CLINICAL RELEVANCE

Platelet-rich plasma with fibrin matrix might help reduce the risk of repeated rupture after flexor tendon surgery, and lead to early rehabilitation.

The mechanics of flexor tendon adhesions

The mechanics of adhesions at a local tissue level have not been extensively studied. This study compared microstrains and macrostrains in adhesions of immobilized and mobilized partially lacerated flexor digitorum profundus tendons in a New Zealand White rabbit model. At 2 weeks, 50 digits were randomized to either gross tensile testing or micromechanical assessment, in which the movement of fluorescently labelled cell nuclei, acting as dynamic markers, was visualized using real-time confocal microscopy. The structural stiffness and load at failure of immobilized adhesions were 140% and 160% of that of mobilized adhesions, respectively, and both differences were statistically significant. Micromechanically, different patterns of loading and failure were observed. Mobilized adhesions exhibited over a three-fold higher local strain, which was less uniformly distributed. Confocal microscopy provided an accurate measure of local strain. For the first time, it has been possible to visualize, define, and quantify local adhesion tissue mechanics. Mobilization appears to favour the formation of sites expressing increased local strain responses or those predisposed to heterogeneity and localized failure.

The bio-tribological properties of anti-adhesive agents commonly used during tendon repair

Frictional resistance to tendon gliding is minimized by surrounding loose areolar tissue. During periods of prolonged immobilization, for example, post-tendon-repair, adhesions can form between these two adjacent tissues, thereby limiting tendon function. Anti-adhesive agents can be applied during surgery to prevent adhesion formation, whilst reportedly providing some reduction in friction during in vitro tendon-bony pulley investigations. This bio-tribological study evaluates whether application of these agents can improve the lubrication between the tendon and surrounding tissue, thus potentially reducing the risk of re-rupturing the tendon at the repair site. The use of bovine synovial fluid (BSF) enabled an approximation of the in vivo lubrication regime, and subsequent comparison of the performance of three synthetic agents (50 mg/ml 5-fluorouracil; 5 mg/ml hyaluronic acid; ADCON-T/N). Coefficient of friction data was recorded and then compared with the Stribeck curve. BSF generated a fluid film that separated the two surfaces, giving rise to optimal lubrication conditions. This efficient regime was also generated following application of each anti-adhesion agent. The use of phosphate-buffered saline solution in generating only a boundary lubrication regime highlighted the effectiveness of the agents in reducing friction. Hyaluronic acid (5 mg/ml) was marginally deemed the most effective anti-adhesive agent at lubricating the tendon. Subsequently, it is concluded that the application of anti-adhesive agents post-surgery has secondary, tribological benefits that serve to reduce friction, and thus potentially the risk of failure, at the tendon repair site.

Scaffolds in tendon tissue engineering

Tissue engineering techniques using novel scaffold materials offer potential alternatives for managing tendon disorders. Tissue engineering strategies to improve tendon repair healing include the use of scaffolds, growth factors, cell seeding, or a combination of these approaches. Scaffolds have been the most common strategy investigated to date. Available scaffolds for tendon repair include both biological scaffolds, obtained from mammalian tissues, and synthetic scaffolds, manufactured from chemical compounds. Preliminary studies support the idea that scaffolds can provide an alternative for tendon augmentation with an enormous therapeutic potential. However, available data are lacking to allow definitive conclusion on the use of scaffolds for tendon augmentation. We review the current basic science and clinical understanding in the field of scaffolds and tissue engineering for tendon repair.

A lactoferrin-derived peptide (PXL01) for the reduction of adhesion formation in flexor tendon surgery: an experimental study in rabbits

Injuries to flexor tendons can lead to loss of finger function after healing due to adhesion formation. The aim of this study was to assess the efficacy and safety of the new peptide, PXL01, in the prevention of peritendinous adhesions. The effect of a single intraoperative administration of PXL01 in sodium hyaluronate on mobility of the affected digit after surgery was assessed in a rabbit model by measuring total active motion, metatarsophalangeal-claw distance and resistance to bending the digits. Load-to-failure testing was done in the same specimens to assess tendon healing. The results demonstrated that a single application of PXL01 in sodium hyaluronate significantly improved mobility of the treated digits compared with the digits in which the same surgery was carried out but no treatment was provided. No negative effects on tendon healing were observed in connection with the treatment.

Growth factor and protease expression during different phases of healing after rabbit deep flexor tendon repair

The purpose of the study was to contribute to the mapping of molecular events during flexor tendon healing, in particular the growth factors insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF) and nerve growth factor (NGF), matrix metalloproteinases (MMP-3 and MMP-13) and their inhibitors (tissue inhibitors of metalloproteinases, TIMP-1 and TIMP-3, and the protease cathepsin K. In a rabbit model of flexor tendon injury, the mRNA expression for the growth factors, MMPs and TIMPs were measured in tendon and tendon sheath tissue at several time points (3, 6, 21, and 42 days) representing different phases of the healing process. We found that MMP-13 remained increased during the study period, whereas MMP-3 returned to normal levels within the first week after injury. TIMP-3 was down-regulated in the tendon sheaths. Cathepsin K was up-regulated in tendons and sheaths after injury. NGF was present in both tendons and sheaths, but unaltered. IGF-1 exhibited a late increase in the tendons, while VEGF was down-regulated at the later time points. In conclusion, we have demonstrated the presence of NGF in flexor tendons. MMP-13 expression appears to play a more protracted role in flexor tendon healing than MMP-3. The relatively low levels of endogenous IGF-1 and VEGF mRNA following injury support their potential beneficial role as exogenous modulators to optimize tendon healing and strength without increasing adhesion formation.

Effectiveness of subacromial anti-adhesive agent injection after arthroscopic rotator cuff repair: prospective randomized comparison study

BACKGROUND

Arthroscopic rotator cuff repair generally has a good clinical outcome but shoulder stiffness after surgery due to subacromial adhesion is one of the most common and clinically important complications. Sodium hyaluronate (HA) has been reported to be an anti-adhesive agent in a range of surgical procedures. However, there are few reports of the outcomes of arthroscopic rotator cuff repair of the shoulder. This study examined whether a subacromial injection of HA/carboxymethylated cellulose (CMC) affected the postoperative shoulder stiffness and healing of rotator cuff repair, as well as the safety of an injection.

METHODS

Between January 2008 and May 2008, 80 consecutive patients with arthroscopic rotator cuff repair were enrolled. The patients were assigned randomly to the HA/CMC injection group (n = 40) or control group (n = 40). All patients were evaluated using the visual analog scale (VAS) for pain, passive range of motion at 2, 6 weeks, 3, 6, 12 months after surgery, and the functional scores at 6, 12 months postoperatively. Cuff healing was also evaluated using CT arthrography or ultrasonography at 6 or 12 months after surgery.

RESULTS

The HA/CMC injection group showed faster recovery of forward flexion at 2 weeks postoperatively than the control group but the difference was not statistically significant (p = 0.09). There were no significant difference in pain VAS, internal rotation, external rotation and functional scores between two groups at each follow-up period. The functional scores improved 6 months after surgery in both groups but there were no differences between the two groups. The incidence of unhealed rotator cuff was similar in the two groups. There were no complications related to an injection of anti-adhesive agents including wound problems or infections.

CONCLUSIONS

A subacromial injection of an anti-adhesive agent after arthroscopic rotator cuff repair tended to produce faster recovery in forward flexion with no adverse effects on cuff healing. However, its anti-adhesive effects after rotator cuff repair should be considered carefully with further studies.

Tissue engineered biological augmentation for tendon healing: a systematic review

INTRODUCTION

Tendon injuries give rise to significant morbidity. In the last few decades, several techniques have been increasingly used to optimize tendon healing.

SOURCES OF DATA

We performed a comprehensive search of PubMed, Medline, Cochrane, CINAHL and Embase databases using various combinations of the commercial names of each scaffold and the keywords 'tendon', 'rotator cuff', 'supraspinatus tendon', 'Achilles tendon', 'growth factors', 'cytokines', 'gene therapy', 'tissue engineering', 'mesenchymal' and 'stem cells' over the years 1966-2009. All articles relevant to the subject were retrieved, and their bibliographies were hand searched for further references in the context to tissue-engineered biological augmentation for tendon healing.

AREAS OF AGREEMENT

Several new techniques are available for tissue-engineered biological augmentation for tendon healing, growth factors, gene therapy and mesenchimal stem cells.

AREAS OF CONTROVERSY

Data are lacking to allow definitive conclusions on the use of these techniques for routine management of tendon ailments.

GROWING POINTS

The emerging field of tissue engineering holds the promise to use new techniques for tendon augmentation and repair. Preliminary studies support the idea that these techniques can provide an alternative for tendon augmentation with great therapeutic potential.

AREAS TIMELY FOR DEVELOPING RESEARCH

The optimization strategies discussed in this article are currently at an early stage of development. Although these emerging technologies may develop into substantial clinical treatment options, their full impact needs to be critically evaluated in a scientific fashion.

Regional differences in biochemical, biomechanical and histomorphological characteristics of the equine suspensory ligament

REASONS FOR PERFORMING STUDY

Desmopathies of the suspensory ligament are relatively frequent and vary in prevalence over different anatomical regions. This variation may be because of regional differences in tissue characteristics.

OBJECTIVE

To characterise different regions of healthy forelimb suspensory ligaments (SLs) by means of biochemical, biomechanical and histomorphological techniques.

HYPOTHESIS

There is substantial topographical heterogeneity in the SL with respect to structural, compositional and functional characteristics.

METHODS

SLs were harvested from 38 limbs and used for biochemical (n = 20), biomechanical (n = 14) and histomorphological (n = 4) evaluation. Sulphated glycosaminoglycan (S-GAG), DNA and collagen content, degree of lysyl hydroxylation and numbers of enzymatic and nonenzymatic cross-links were determined in 7 regions of the SL: lateral and medial part of the origin (OM, OL), mid-body (MB), axial and abaxial parts of the lateral and medial branches (ILAX, ILAB, IMAX and IMAB, respectively). Passive resistance to tensile loading was measured in 5 regions of the SL (all except OL and OM).

RESULTS

DNA content was lower in OL and OM than in all other parts. GAG content was also lower in OL and OM and highest in ILAB and IMAB. Collagen content was lower in OL/OM and highest in ILAX/IMAX. Pentosidine levels were highest in OL and significantly lower in the lateral insertion (ILAX/ILAB). There were no differences in hydroxylysylpyridinoline (HP) cross-links or lysyl hydroxylation. Stiffness (P<0.01) and modulus of elasticity (P<0.01) were substantially higher in the MB region than in all other regions except for IMAB. Strain at failure was lower in the MB region (P<0.0001), resulting in a comparable force at rupture as in the other regions.

CONCLUSIONS

Matrix composition differs to a relatively limited extent between different regions of the SL. The mid-body of the ligament is stiffer than the branches, which have similar properties and relevance and mechanical differences between mid-body and branches/origin may explain some use-related differences in the prevalence of lesions.

Neuropeptide, mast cell, and myofibroblast expression after rabbit deep flexor tendon repair

PURPOSE

Increased numbers of myofibroblasts, mast cells, and neuropeptide-containing nerve fibers have been found in a number of fibrotic processes in connective tissues. The purpose of the present study was to investigate the occurrence of factors implicated in a hypothesized profibrotic neuropeptide-mast cell-myofibroblast pathway in deep flexor tendon healing.

METHODS

In a rabbit model of flexor tendon injury, with repair of the sharply transected deep flexor tendon using a modified Kessler and a running circumferential peripheral suture, segments of flexor tendons and sheaths were analyzed. The time points chosen-3, 6, 21, and 42 days after tendon repair-represent different stages in tendon healing. The messenger RNA levels of transforming growth factor-β1 and α-smooth muscle actin were measured with conventional reverse transcription-polymerase chain reaction, and the numbers of myofibroblasts, mast cells, and neuropeptide-containing nerve fibers were determined with immunohistochemistry.

RESULTS

The messenger RNA levels for transforming growth factor-β1 and the myofibroblast marker α-smooth muscle actin were significantly increased in deep flexor tendons after injury and repair, at all studied time points, but remained unchanged or even down-regulated in the sheaths. Myofibroblasts, mast cells, and neuropeptide-containing nerve fibers all increased significantly in the healing tendons, exhibiting similar patterns of change in percentages of total cell number over time, reaching levels resembling that of the tendon sheaths with 33% to 50% of the total cell population.

CONCLUSIONS

After injury to the deep flexor tendon in a rabbit model, the proportion of myofibroblasts, mast cells, and neuropeptide-containing nerve fibers increases significantly. These findings support the hypothesis that the profibrotic neuropeptide-mast cell-myofibroblast pathway is activated in deep flexor tendon healing.

Hyaluronan modulates proliferation and migration of rabbit fibroblasts derived from flexor tendon epitenon and endotenon

PURPOSE

There is a growing body of evidence supporting the use of hyaluronan (HA) for treatment of injured tendons, although the mechanism of the healing effect has not yet been clarified. We therefore investigated the effects of HA on the proliferation and migration of tendon fibroblasts derived from rabbit flexor tendon epitenon and endotenon.

METHODS

From explanted rabbit intrasynovial flexor tendons (n = 5), we cultured tendon fibroblasts derived from the epitenon and endotenon. CD44 expression on the tendon fibroblasts was detected by flow cytometric analysis. Various concentrations of HA (0.1-5.0 mg/mL) were added to monolayer-cultured tendon fibroblasts. We evaluated cell proliferation by recording changes in cell number, and measured cell migration by wound-healing assay.

RESULTS

Flow cytometric analysis detected CD44 expression on the tendon fibroblasts. Treatment with HA at various concentrations notably and dose dependently inhibited cell proliferation and promoted cell migration.

CONCLUSIONS

Hyaluronan modulates the proliferation and migration of rabbit fibroblasts derived from the flexor tendon epitenon and endotenon.