Overlay repair with a synthetic collagen scaffold improves the quality of healing in a rat rotator cuff repair model

Interposition of acellular amniotic membrane at the tendon to bone interface would be better for healing than overlaying above the tendon to bone junction in the repair of rotator cuff injury

PURPOSE

The retear rate of rotator cuff (RC) after surgery is high, and the rapid and functional enthesis regeneration remains a challenge. Whether acellular amniotic membrane (AAM) helps to promote the healing of tendon to bone and which treatment is better are both unclear. The study aims to investigate the effect of AAM on the healing of RC and the best treatment for RC repair.

METHODS

Thirty-three Sprague Dawley rats underwent RC transection and repair using microsurgical techniques and were randomly divided into the suturing repair only (SRO) group (n = 11), the AAM overlaying (AOL) group (n = 11), and the AAM interposition (AIP) group (n = 11), respectively. Rats were sacrificed at 4 weeks, then examined by subsequent micro-CT, and evaluated by histologic and biomechanical tests. The statistical analyses of one-way ANOVA or Kruskal-Wallis test were performed using with SPSS 23.0. A p < 0.05 was considered a significant difference.

RESULTS

AAM being intervened between tendon and bone (AIP group) or overlaid over tendon to bone junction (AOL group) in a rat model, promoted enthesis regeneration, increased new bone and cartilage generation, and improved collagen arrangement and biomechanical properties in comparison with suturing repair only (SRO group) (AOL vs. SRO, p < 0.001, p = 0.004, p = 0.003; AIP vs. SRO, p < 0.001, p < 0.001, p < 0.001). Compared with the AOL group, the AIP group had better results in micro-CT evaluation, histological score, and biomechanical testing (p = 0 0.039, p = 0.011, p = 0.003, respectively).

CONCLUSION

In the RC repair model, AAM enhanced regeneration of the tendon to bone junction. This regeneration was more effective when the AAM was intervened at the tendon to bone interface than overlaid above the tendon to bone junction.

Translational Research on Orthobiologics in the Treatment of Rotator Cuff Disease: From the Laboratory to the Operating Room

Rotator cuff disease is one of the most common human tendinopathies and can lead to significant shoulder dysfunction. Despite efforts to improve symptoms in patients with rotator cuff tears and healing rates after rotator cuff repair, high rates of failed healing and persistent shoulder morbidity exist. Increasing interest has been placed on the utilization of orthobiologics-scaffolds, cell-based augmentation, platelet right plasma (platelet-rich plasma), and small molecule-based strategies-in the management of rotator cuff disease and the augmentation of rotator cuff repairs. This is a complex topic that involves novel treatment strategies, including patches/scaffolds, small molecule-based, cellular-based, and tissue-derived augmentation techniques. Ultimately, translational research, with a particular focus on preclinical models, has allowed us to gain some insights into the utility of orthobiologics in the treatment of rotator cuff disease and will continue to be critical to our further understanding of the underlying cellular mechanisms moving forward.

Scaffold- and graft-based biological augmentation of rotator cuff repair: an updated systematic review and meta-analysis of preclinical and clinical studies for 2010-2022

BACKGROUND

Despite advancements in the surgical techniques of rotator cuff repair (RCR), there remains a high retear rate. Biological augmentation of repairs with overlaying grafts and scaffolds may enhance healing and strengthen the repair construct. This study aimed to investigate the efficacy and safety of scaffold-based (nonstructural) and overlay graft-based (structural) biological augmentation in RCR (excluding superior capsule reconstruction and bridging techniques) in both preclinical and clinical studies.

METHODS

This systematic review was performed in adherence to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines, as well as guidelines outlined by The Cochrane Collaboration. A search of the PubMed, Embase, and Cochrane Library databases from 2010 until 2022 was conducted to identify studies reporting the clinical, functional, and/or patient-reported outcomes of ≥1 biological augmentation method in either animal models or humans. The methodologic quality of included primary studies was appraised using the Checklist to Evaluate a Report of a Non-pharmacological Trial (CLEAR-NPT) for randomized controlled trials and using the Methodological Index for Non-randomized Studies (MINORS) for nonrandomized studies.

RESULTS

A total of 62 studies (Level I-IV evidence) were included, comprising 47 studies reporting outcomes in animal models and 15 clinical studies. Of the 47 animal-model studies, 41 (87.2%) demonstrated biomechanical and histologic enhancement with improved RCR load to failure, stiffness, and strength. Of the 15 clinical studies, 10 (66.7%) illustrated improvement in postoperative clinical, functional, and patient-reported outcomes (eg, retear rate, radiographic thickness and footprint, and patient functional scores). No study reported a significant detriment to repair with augmentation, and all studies endorsed low complication rates. A meta-analysis of pooled retear rates demonstrated significantly lower odds of retear after treatment with biological augmentation of RCR compared with treatment with non-augmented RCR (odds ratio, 0.28; P < .00001), with low heterogeneity (I2 = 0.11).

CONCLUSIONS

Graft and scaffold augmentations have shown favorable results in both preclinical and clinical studies. Of the investigated clinical grafts and scaffolds, acellular human dermal allograft and bovine collagen demonstrate the most promising preliminary evidence in the graft and scaffold categories, respectively. With a low risk of bias, meta-analysis revealed that biological augmentation significantly lowered the odds of retear. Although further investigation is warranted, these findings suggest graft and scaffold biological augmentation of RCR to be safe.

Combined Growth Factor Hydrogel Enhances Rotator Cuff Enthesis Healing in Rat But Not Sheep Model

We hypothesized that a combined growth factor hydrogel would improve chronic rotator cuff tear healing in a rat and sheep model. Insulin-like growth factor 1, transforming growth factor β1, and parathyroid hormone were combined into a tyraminated poly-vinyl-alcohol (PVA-Tyr) hydrogel and applied directly at the enthesis. In total, 30 Sprague-Dawley rats and 16 Romney ewes underwent unilateral rotator cuff tenotomy and then delayed repairs were performed after 3-4 weeks. The animals were divided into a control group (repair alone) and treatment group. The rotator cuffs were harvested at 12 weeks after surgery for biomechanical and histological analyses of the repair site. In the rat model, the stress at failure and Young's modulus were higher in the treatment group in comparison with the control group (73% improvement, p = 0.010 and 56% improvement, p = 0.028, respectively). Histologically, the repaired entheses in the treatment group demonstrated improved healing with higher semi-quantitative scores (10.1 vs. 6.55 of 15, p = 0.032). In the large animal model, there was no observable treatment effect. This PVA-Tyr bound growth factor system holds promise for improving rotator cuff healing. However, our approach was not scalable from a small to a large animal model. Further tailoring of this growth factor delivery system is still required. Level of Evidence: Basic Science Study; Biomechanics and Histology; Animal Model Impact Statement Previous studies using single-growth factor treatment to improve enthesis healing after rotator cuff repair have reported promising, but inconsistent results. A novel approach is to combine multiple growth factors using controlled-release hydrogels that mimic the normal healing process. In this study, we report that a combined growth factor hydrogel can improve the histological quality and strength of rotator cuff repair in a rat chronic tear model. This novel hydrogel growth factor treatment has the potential to be used in human clinical applications to improve healing after rotator cuff repair.

Improved suture pullout through genipin-coated sutures in human biceps tendons with spatially confined changes in cell viability

BACKGROUND

The suture-tendon interface often constitutes the point of failure in tendon suture repair. In the present study, we investigated the mechanical benefit of coating the suture with a cross-linking agent to strengthen the nearby tissue after suture placement in human tendons and we assessed the biological implications regarding tendon cell survival in-vitro.

METHODS

Freshly harvested human biceps long head tendons were randomly allocated to control (n = 17) or intervention (n = 19) group. According to the assigned group, either an untreated or a genipin-coated suture was inserted into the tendon. 24 h after suturing, mechanical testing composed of cyclic and ramp-to-failure loading was performed. Additionally, 11 freshly harvested tendons were used for short-term in vitro cell viability assessment in response to genipin-loaded suture placement. These specimens were analyzed in a paired-sample setting as stained histological sections using combined fluorescent/light microscopy.

FINDINGS

Tendons stitched with a genipin-coated suture sustained higher forces to failure. Cyclic and ultimate displacement of the tendon-suture construct remained unaltered by the local tissue crosslinking. Tissue crosslinking resulted in significant cytotoxicity in the direct vicinity of the suture (<3 mm). At larger distances from the suture, however, no difference in cell viability between the test and the control group was discernable.

INTERPRETATION

The repair strength of a tendon-suture construct can be augmented by loading the suture with genipin. At this mechanically relevant dosage, crosslinking-induced cell death is confined to a radius of <3 mm from the suture in the short-term in-vitro setting. These promising results warrant further examination in-vivo.

Advanced strategies for constructing interfacial tissues of bone and tendon/ligament

Enthesis, the interfacial tissue between a tendon/ligament and bone, exhibits a complex histological transition from soft to hard tissue, which significantly complicates its repair and regeneration after injury. Because traditional surgical treatments for enthesis injury are not satisfactory, tissue engineering has emerged as a strategy for improving treatment success. Rapid advances in enthesis tissue engineering have led to the development of several strategies for promoting enthesis tissue regeneration, including biological scaffolds, cells, growth factors, and biophysical modulation. In this review, we discuss recent advances in enthesis tissue engineering, particularly the use of biological scaffolds, as well as perspectives on the future directions in enthesis tissue engineering.

Decellularized Bovine Pericardial Patch Loaded With Mesenchymal Stromal Cells Enhance the Mechanical Strength and Biological Healing of Large-to-Massive Rotator Cuff Tear in a Rat Model

PURPOSE

The purpose of this study was to determine whether the addition of decellularized bovine pericardial patch loaded with mesenchymal stromal cells enhanced bone-to-tendon healing and improved the biomechanical strength of large-to-massive rotator cuff tears in a small animal model.

METHODS

Adipose-derived mesenchymal stromal cells (MSCs) from rat inguinal fat were isolated, cultured, and loaded onto decellularized bovine pericardium patches. To simulate large-to-massive tears, rats were managed with free cage activity for 6 weeks after tear creation. A total of 18 rats were randomly allocated to repair-only (control), repair with pericardial patch augmentation (patch), or repair with MSC loaded pericardial patch augmentation (patch-MSC). Each group had 6 rats (one shoulder of each rat was used for histological evaluation and another for biomechanical evaluation). MSCs seeded on the pericardial patches were traced on four shoulders from 2 other rats at 4 weeks after surgery. Histological evaluation for bone-to-tendon healing and biomechanical testing was carried out at 8 weeks after repair.

RESULTS

MSCs tagged with a green fluorescent protein were observed in the repair site 4 weeks after the repair. One shoulder each in the control and patch groups showed complete discontinuity between the bone and tendon. One shoulder in the control group showed attenuation with only a tenuous connection. Fibrocartilage and tidemark formation at the bone-to-tendon interface (P = .002) and collagen fiber density (P = .040) and orientation (P = .003) were better in the patch-MSC group than in the control or patch group. Load-to-failure in the patch-MSC and patch groups was higher than that in the control group (P = .001 and .009, respectively).

CONCLUSION

Decellularized bovine pericardial patches loaded with adipose-derived and cultured mesenchymal stromal cells enhanced healing in terms of both histology and mechanical strength at 8 weeks following rotator cuff repair in a rat model.

CLINICAL RELEVANCE

Large-to-massive rotator tears need a strategy to prevent retear and enhance healing. The addition of decellularized bovine pericardial patch loaded with MSCs can enhance bone-to-tendon healing and improve biomechanical healing of large-to-massive rotator cuff tears following repair.

Evaluation of patches for rotator cuff repair: A systematic review and meta-analysis based on animal studies

Based on the published animal studies, we systematically evaluated the outcomes of various materials for rotator cuff repair in animal models and the potentials of their clinical translation. 74 animal studies were finally included, of which naturally derived biomaterials were applied the most widely (50.0%), rats were the most commonly used animal model (47.0%), and autologous tissue demonstrated the best outcomes in all animal models. The biomechanical properties of naturally derived biomaterials (maximum failure load: WMD 18.68 [95%CI 7.71-29.66]; P = 0.001, and stiffness: WMD 1.30 [95%CI 0.01-2.60]; P = 0.048) was statistically significant in the rabbit model. The rabbit model showed better outcomes even though the injury was severer compared with the rat model.

Stem cell sheet interpositioned between the tendon and bone would be better for healing than stem cell sheet overlaid above the tendon-to-bone junction in rotator cuff repair of rats

BACKGROUND

Although stem cells might enhance natural enthesis healing in surgical rotator cuff repair, not much attention has been given to the delivery and location of delivering stem cells. The purpose of this study to know where to locate those stem cells during repair.

METHODS

Animal model of chronic rotator cuff tear was created in 24 rats. Adipose-derived stem cells were engineered as a sheet and transplanted 1) between a torn tendon and humerus (interposition group) or 2) over a repaired tendon-to-bone junction (overlay group) at the time of surgical repair. Tracking of stem cells with overexpression of green fluorescent protein (GFP) were carried out at the time of sacrifice in additional 4 shoulders in each group. Histological and Biomechanical evaluation was performed to compare the differences in tendon-to-bone healing.

RESULTS

Histology showed increased fibrocartilage, a clear boundary at the mineralized fibrocartilage, abundant collagen type III, and higher total scores, especially in the interposition group. GFP-overexpression was observed at the transplanted site at 2 weeks after repair. Although two groups where stem cell sheets applied showed higher load to failure than the repair-only group, the load to failure was not different between the interposition and overlay group.

CONCLUSION

In the chronic rotator cuff repair model, stem cell sheets enhanced regeneration of the tendon-to-bone junction. This regeneration was effective when the stem cell sheet was interpositioned at the tendon-to-bone interface.

LEVEL OF EVIDENCE

Basic Science Study; In Vivo Animal Model; Histology and Biomechanics.

Augmentation of Rotator Cuff Healing With Orthobiologics

The limited regenerative capacity of the tendon-bone enthesis after surgical repair poses a significant challenge to achieving desired clinical outcomes. Biologic augmentation of the repair site has the potential to enhance the biomechanical and histological integrity of the enthesis, leading to lower retear rates and greater patient satisfaction. Platelet-rich plasma, stem cells and bone marrow aspirate concentrate, growth factors, biodegradable or biomimetic scaffolds, and amniotic products have been investigated in preclinical and, in some cases, clinical studies aimed at augmenting tendon-bone healing. Although many of these therapies have achieved some degree of success in improving structural, histological, and clinical outcomes after surgical tendon-bone enthesis repair, none have reliably and consistently lead to clinical improvement. High-quality randomized controlled clinical studies are needed to definitively evaluate the efficacy of these biologic therapies and ultimately determine which, if any, are capable of achieving a tendon-bone repair that is structurally noninferior to the native enthesis before injury.

Novel Growth Factor Combination for Improving Rotator Cuff Repair: A Rat In Vivo Study

BACKGROUND

The lack of healing at the repaired tendon-bone interface is an important cause of failure after rotator cuff repair. While augmentation with growth factors (GFs) has demonstrated promise, the ideal combination must target all 3 tissue types at the tendon-bone interface.

HYPOTHESIS

The GF combination of transforming growth factor beta 1, Insulin-like growth factor 1, and parathyroid hormone will promote tenocyte proliferation and differentiation and improve the biomechanical and histological quality of the repaired tendon-bone interface.

STUDY DESIGN

Controlled laboratory study.

METHODS

In vitro, human tenocytes were cultured in the presence of the GF combination for 72 hours, and cell growth assays and the expression of genes specific to tendon, cartilage, and bone were analyzed. In vivo, adult rats (N = 46) underwent detachment and repair of the left supraspinatus tendon. A PVA-tyramine gel was used to deliver the GF combination to the tendon-bone interface. Histological, biomechanical, and RNA microarray analysis was performed at 6 and 12 weeks after surgery. Immunohistochemistry for type II and X collagen was performed at 12 weeks.

RESULTS

When treated with the GF combination in vitro, human tenocytes proliferated 1.5 times more than control (P = .04). The expression of scleraxis increased 65-fold (P = .013). The expression of Sox-9 (P = .011), type I collagen (P = .021), fibromodulin (P = .0075), and biglycan (P = .010) was also significantly increased, while the expression of PPARγ was decreased (P = .007). At 6 and 12 weeks postoperatively, the quality of healing on histology was significantly higher in the GF group, with the formation of a more mature tendon-bone interface, as confirmed by immunohistochemistry for type II and X collagen. The GF group achieved a load at failure and Young modulus >1.5 times higher at both time points. Microarrays at 6 weeks demonstrated upregulation of genes involved in leukocyte aggregation (S100A8, S100A9) and tissue mineralization (Bglap, serglycin, Fam20c).

CONCLUSION

The GF combination promoted protendon and cartilage responses in human tenocytes in vitro; it also improved the histological appearance and mechanical properties of the repair in vivo. Microarrays of the tendon-bone interface identified inflammatory and mineralization pathways affected by the GF combination, providing novel therapeutic targets for further research.

CLINICAL RELEVANCE

The use of this GF combination is translatable to patients and may improve healing after rotator cuff repair.

Obesity Impairs Enthesis Healing After Rotator Cuff Repair in a Rat Model

BACKGROUND

Being overweight or obese is associated with poor outcomes and an increased risk of failure after rotator cuff (RC) surgery. However, the effect of obesity on enthesis healing has not been well characterized.

HYPOTHESES

Diet-induced obesity (DIO) would result in inferior enthesis healing in a rat model of RC repair, and a dietary intervention in the perioperative period would improve enthesis healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Male Sprague-Dawley rats were divided into 3 weight-matched groups (n = 26 per group): control diet (CD), high-fat diet (HFD), or HFD until surgery and then CD thereafter (HF-CD). After 12 weeks, the left supraspinatus tendon was detached, followed by immediate repair. Animals were sacrificed, and RCs were harvested at 2 and 12 weeks after surgery for biomechanical and histological evaluations. Metabolic end points were assessed using dual-energy X-ray absorptiometry and plasma analyses.

RESULTS

DIO was established in the HFD and HF-CD groups before surgery and subsequently reversed in the HF-CD group after surgery. At 12 weeks after surgery, the body fat percentage (P = .0021) and plasma leptin concentration (P = .0025) were higher in the HFD group compared with the CD group. Histologically, the appearance of the repaired entheses was poorer in both the HFD and HF-CD groups compared with the CD group at 12 weeks after surgery, with semiquantitative scores of 6.20 (P = .0078), 4.98 (P = .0003), and 8.68 of 15, respectively. The repaired entheses in the HF-CD group had a significantly lower load to failure (P = .0278) at 12 weeks after surgery compared with the CD group, while the load to failure in the HFD group was low but not significantly different (P = .0960). There were no differences in the biomechanical and histological results between the groups at 2 weeks after surgery. Body mass at the time of surgery, plasma leptin concentration, and body fat percentage were negatively correlated with histology scores and plasma leptin concentration was correlated with load to failure at 12 weeks after surgery.

CONCLUSION

DIO impaired enthesis healing in this rat RC repair model, with inferior biomechanical and histological outcomes. Restoring a normal weight with dietary changes after surgery did not improve healing outcomes.

CLINICAL RELEVANCE

Obesity is a potentially modifiable factor that impairs RC healing and increases the risk of failure after surgery. Exploring interventions that improve the metabolic state of obese patients and counseling patients appropriately about their modest expectations after repair should be considered.

Nontendinous healing after repairing of retracted rotator cuff tear: an imaging study

BACKGROUND

Follow-up magnetic resonance imaging (MRI) after rotator cuff repair can sometimes demonstrate healing with nontendinous tissue that extends from the footprint to the retracted tendon end, which is inferred as fibrous tissue formation. The aim was to investigate this particular finding and its significance.

METHODS

There were 494 eligible cases of healed supero-posterior medium-sized to massive rotator cuff repairs, after the exclusion of retears. A retrospective review was performed for the 3 groups that were divided according to their MRI appearances of healing: type I described the direct healing of the tendon to the footprint, whereas type II demonstrated the distinctive continuity of nontendinous tissue from the footprint to the retracted tendinous portion, and type III also showed a similar appearance but with obvious thinning of the tissue, without any evidence of defect confirmed on the routine outpatient ultrasonograph.

RESULTS

Only 108 of 494 patients (21.9%) demonstrated type I healing, whereas the signs of nontendinous healing were evident for the rest, with the 116 patients (23.5%) being classified as type III with attenuation. Comparing the preoperative tendon retraction, 34.8% and 37.2% of the Patte stages 2 and 3, respectively, resulted in type III healing, which were significantly higher compared with that of stage 1 (15.3%, P < .001). Type III healing had the highest average preoperative Goutallier grades. The average postoperative visual analog scale and the American Shoulder and Elbow Surgeons (ASES) scores have improved significantly for all 3 groups (P < .05), with the ASES score being 86.1±15.9 for type I, 93.7±36.1 for type II, and 87.8±15.1 for type III without significant differences between the groups (P = .3).

CONCLUSIONS

Only a fifth of the rotator cuff repairs led to a direct healing to the footprint, and the rest healed with MRI appearance of nontendinous tissue formation bridging the retracted tendinous portion and the footprint. These MRI appearances did not represent the true tendinous tissue formation between the torn end of the tendon and the bone after healing. Such appearances did not seem to affect the clinical outcomes.

A Maternal High Fat Diet Leads to Sex-Specific Programming of Mechanical Properties in Supraspinatus Tendons of Adult Rat Offspring

Background: Over half of women of reproductive age are now overweight or obese. The impact of maternal high-fat diet (HFD) is emerging as an important factor in the development and health of musculoskeletal tissues in offspring, however there is a paucity of evidence examining its effects on tendon. Alterations in the early life environment during critical periods of tendon growth therefore have the potential to influence tendon health that cross the lifespan. We hypothesised that a maternal HFD would alter biomechanical, morphological and gene expression profiles of adult offspring rotator cuff tendon. Materials and Methods: Female Sprague-Dawley rats were randomly assigned to either: control diet (CD; 10% kcal or 43 mg/g from fat) or HFD (45% kcal or 235 mg/g from fat) 14 days prior to mating and throughout pregnancy and lactation. Eight female and male offspring from each maternal diet group were weaned onto a standard chow diet and then culled at postnatal day 100 for tissue collection. Supraspinatus tendons were used for mechanical testing and histological assessment (cellularity, fibre organisation, nuclei shape) and tail tendons were collected for gene expression analysis. Results: A maternal HFD increased the elasticity (Young's Modulus) in the supraspinatus tendon of male offspring. Female offspring tendon biomechanical properties were not affected by maternal HFD. Gene expression of SCX and COL1A1 were reduced in male and female offspring of maternal HFD, respectively. Despite this, tendon histological organisation were similar between maternal diet groups in both sexes. Conclusion: An obesogenic diet during pregnancy increased tendon elasticity in male, but not female, offspring. This is the first study to demonstrate that maternal diet can modulate the biomechanical properties of offspring tendon. A maternal HFD may be an important factor in regulating adult offspring tendon homeostasis that may predispose offspring to developing tendinopathies and adverse tendon outcomes in later life.

A Systematic Review of Tissue Engineering Scaffold in Tendon Bone Healing in vivo

Background: Tendon-bone healing is an important factor in determining the success of ligament reconstruction. With the development of biomaterials science, the tissue engineering scaffold plays an extremely important role in tendon-bone healing and bone tissue engineering. Materials and Methods: Electronic databases (PubMed, Embase, and the Web of Science) were systematically searched for relevant and qualitative studies published from 1 January 1990 to 31 December 2019. Only original articles that met eligibility criteria and evaluated the use of issue engineering scaffold especially biomaterials in tendon bone healing in vivo were selected for analysis. Results: The search strategy identified 506 articles, and 27 studies were included for full review including two human trials and 25 animal studies. Fifteen studies only used biomaterials like PLGA, collage, PCL, PLA, and PET as scaffolds to repair the tendon-bone defect, on this basis, the rest of the 11 studies using biological interventions like cells or cell factors to enhance the healing. The adverse events hardly ever occurred, and the tendon bone healing with tissue engineering scaffold was effective and superior, which could be enhanced by biological interventions. Conclusion: Although a number of tissue engineering scaffolds have been developed and applied in tendon bone healing, the researches are mainly focused on animal models which are with limitations in clinical application. Since the efficacy and safety of tissue engineering scaffold has been proved, and can be enhanced by biological interventions, substantial clinical trials remain to be done, continued progress in overcoming current tissue engineering challenges should allow for successful clinical practice.

3D cell-printing of tendon-bone interface using tissue-derived extracellular matrix bioinks for chronic rotator cuff repair

The tendon-bone interface (TBI) in rotator cuffs exhibits a structural and compositional gradient integrated through the fibrocartilaginous transition. Owing to restricted healing capacity, functional regeneration of the TBI is considered a great clinical challenge. Here, we establish a novel therapeutic platform based on 3D cell-printing and tissue-specific bioinks to achieve spatially-graded physiology for functional TBI regeneration. The 3D cell-printed TBI patch constructs are created via a spatial arrangement of cell-laden tendon and bone-specific bioinks in a graded manner, approximating a multi-tissue fibrocartilaginous interface. This TBI patch offers a cell favorable microenvironment, including high cell viability, proliferative capacity, and zonal-specific differentiation of encapsulated stem cells for TBI formation in vitro. Furthermore, in vivo application of spatially-graded TBI patches with stem cells demonstrates their regenerative potential, indicating that repair with 3D cell-printed TBI patch significantly accelerates and promotes TBI healing in a rat chronic tear model. Therefore, our findings propose a new therapeutic strategy for functional TBI regeneration using 3D cell-printing and tissue-specific decellularized extracellular matrix (dECM) bioink-based approach.

A Combination Treatment of Raloxifene and Vitamin D Enhances Bone-to-Tendon Healing of the Rotator Cuff in a Rat Model

BACKGROUND

Tearing and degeneration of the rotator cuff at the tendon-to-bone junction are common in adults aged ≥50 years. Few studies have reported on the relationship between estrogen and the rotator cuff enthesis. In addition to preventing bone loss, selective estrogen receptor modulators have been shown to improve tendon and muscle quality.

PURPOSE

To evaluate the effects of raloxifene (RLX) and vitamin D on rotator cuff tendon-to-bone healing in a rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 29 female rats (58 shoulders) were assigned to 4 groups: (1) control group, (2) ovariectomy (OVX)-only group, (3) no RLX group (OVX and rotator cuff repair [RCR]), and (4) RLX group (OVX, RCR, and RLX). Rats that did not undergo rotator cuff tear (RCT) surgery were divided into the control and OVX-only groups according to OVX surgery. Rats that underwent RCT surgery and RCR were divided into the no RLX and RLX groups according to RLX and vitamin D administration. An estrogen-deficient state was induced by OVX at 12 weeks of age. Bone mineral density (BMD) and trabecular bone characteristics were measured by micro-computed tomography, and healing of the tendon-to-bone junction was evaluated by biomechanical testing, histomorphometry, and micro-magnetic resonance imaging (MRI).

RESULTS

The mean final body weight (BW; 461.6 ± 47.3 g) of the OVX-only group was significantly higher and BMD (0.25 ± 0.07 g/cm³) was significantly lower (P < .001) than the mean final BW (338.5 ± 35.1 g) and BMD (0.48 ± 0.05 g/cm³) of the control group. In contrast, the RLX group showed that the BW (369.6 ± 35.8 g) and BMD (0.41 ± 0.08 g/cm³) were not significantly different from the control group. The RLX group had a significantly higher histomorphometric total score (8.50 ± 1.05) than the no RLX group (4.83 ± 2.48). On biomechanical testing, the RLX group (29.7 ± 9.1 N) showed a significantly higher load to failure than the no RLX group (19.4 ± 8.8 N). On micro-MRI, the RLX group had a more homogeneous low signal and tendon continuity than the no RLX group.

CONCLUSION

The combination treatment of RLX and vitamin D prevented a decrease in local BMD (greater tuberosity of the proximal humerus) and enhanced tendon-to-bone healing of the rotator cuff in a rat model.

CLINICAL RELEVANCE

This study induced an estrogen-deficient state similar to the human postmenopausal state and used drugs that are actually being prescribed in a clinical situation.

Development of a novel bio-inspired "cotton-like" collagen aggregate/chitin based biomaterial with a biomimetic 3D microstructure for efficient hemostasis and tissue repair

Hemostatic materials based on collagen and chitin are commonly assessed with regard to their topical absorbability and bioactivity. However, their clinical application faces challenges such as relatively long hemostatic and wound healing times, single function, as well as wound bleeding in patients with blood diseases. Herein, a novel bio-inspired "cotton-like" collagen aggregate/chitin based biomaterial for rapid hemostatic and tissue repair (V-3D-Ag-col) was fabricated by a specific gradient-removal solvent approach. Significantly, for the first time, an advanced collagen aggregate (Ag-col) composed of typical D-periodic cross-striated collagen fibrils and thick collagen fiber bundles was used instead of traditional collagen molecules (Col) to construct a hemostatic material. The target material showed a biomimetic 3D microstructure and "cotton-like" appearance, as expected, which were conducive to platelet adhesion and aggregation. The fabricated V-3D-Ag-col exhibited superior thermo-stability, hemostatic activity and biodegradability. More importantly, V-3D-Ag-col could significantly promote cell growth and proliferation. Further, V-3D-Ag-col could accelerate the wound healing process better than the same material based on conventional collagen (V-3D-Col). In consequence, V-3D-Ag-col has the potential to become a new generation of collagen-absorbable functional hemostatic materials. Furthermore, Ag-col can replace the currently available conventional collagen materials as raw materials for the new generation of collagen-based biomedical materials.

Nanofiber-based matrices for rotator cuff regenerative engineering

The rotator cuff consists of a cuff of soft tissue responsible for rotating the shoulder. Rotator cuff tendon tears are responsible for a significant source of disability and pain in the adult population. Most rotator cuff tendon tears occur at the bone-tendon interface. Tear size, patient age, fatty infiltration of muscle, have a major influence on the rate of retear after surgical repair. The high incidence of retears (up to 94% in some studies) after surgery makes rotator cuff injuries a critical musculoskeletal problem to address. The limitations of current treatments motivate regenerative engineering approaches for rotator cuff regeneration. Various fiber-based matrices are currently being investigated due to their structural similarity with native tendons and their ability to promote regeneration. This review will discuss the current approaches for rotator cuff regeneration, recent advances in fabrication and enhancement of nanofiber-based matrices and the development and use of complex nano/microstructures for rotator cuff regeneration. STATEMENT OF SIGNIFICANCE: Regeneration paradigms for musculoskeletal tissues involving the rotator cuff of the shoulder have received great interest. Novel technologies based on nanomaterials have emerged as possible robust solutions for rotator cuff injury and treatment due to structure/property relationships. The aim of the review submitted is to comprehensively describe and evaluate the development and use of nano-based material technologies for applications to rotator cuff tendon healing and regeneration.