Platelet-derived growth factor-BB-immobilized asymmetrically porous membrane for enhanced rotator cuff tendon healing

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.

Cell-Free Book-Shaped Decellularized Tendon Matrix Graft Capable of Controlled Release of BMP-12 to Improve Tendon Healing in a Rat Model

BACKGROUND

Achilles tendon (AT) defects often occur in traumatic and chronic injuries. Currently, no graft can satisfactorily regenerate parallel tendinous tissue at the defect site to completely restore AT function.

PURPOSE

To develop a cell-free functional graft by tethering bone morphogenetic protein 12 (BMP-12) on a book-shaped decellularized tendon matrix (BDTM) and to determine whether this graft is more beneficial for AT defect healing than an autograft.

STUDY DESIGN

Controlled laboratory study.

METHODS

Canine patellar tendon was sectioned into a book shape and decellularized to fabricate a BDTM. The collagen-binding domain (CBD) was fused into the N-terminus of BMP-12 to synthesize a recombinant BMP-12 (CBD-BMP-12), which was tethered to the BDTM to prepare a cell-free functional graft (CBD-BMP-12/BDTM). After its tensile resistance, tenogenic inducibility, and BMP-12 release dynamics were evaluated, the efficacy of the graft for tendon regeneration was determined in a rat model. A total of 140 mature male Sprague-Dawley rats underwent AT tenotomy. The defect was reconstructed with reversed AT (autograft group), native BMP-12 tethered to an intact decellularized tendon matrix (IDTM; NAT-BMP-12/IDTM group), native BMP-12 tethered to a BDTM (NAT-BMP-12/BDTM group), CBD-BMP-12 tethered on an IDTM (CBD-BMP-12/IDTM group), and CBD-BMP-12 tethered on a BDTM (CBD-BMP-12/BDTM group). The rats were sacrificed 4 or 8 weeks after surgery to harvest AT specimens. Six specimens from each group at each time point were used for histological evaluation; the remaining 8 specimens were used for biomechanical testing.

RESULTS

In vitro CBD-BMP-12/BDTM was noncytotoxic, showed high biomimetics with native tendons, was suitable for cell adhesion and growth, and had superior tenogenic inducibility. In vivo the defective AT in the CBD-BMP-12/BDTM group regenerated more naturally than in the other groups, as indicated by more spindle-shaped fibroblasts embedded in a matrix of parallel fibers. The biomechanical properties of the regenerated AT in the CBD-BMP-12/BDTM group also increased more significantly than in the other groups.

CONCLUSION

CBD-BMP-12/BDTM is more beneficial than autograft for healing AT defects in a rat model.

CLINICAL RELEVANCE

The findings of this study demonstrate that CBD-BMP-12/BDTM can serve as a practical graft for reconstructing AT defects.

Biomimetic strategies for tendon/ligament-to-bone interface regeneration

Tendon/ligament-to-bone healing poses a formidable clinical challenge due to the complex structure, composition, cell population and mechanics of the interface. With rapid advances in tissue engineering, a variety of strategies including advanced biomaterials, bioactive growth factors and multiple stem cell lineages have been developed to facilitate the healing of this tissue interface. Given the important role of structure-function relationship, the review begins with a brief description of enthesis structure and composition. Next, the biomimetic biomaterials including decellularized extracellular matrix scaffolds and synthetic-/natural-origin scaffolds are critically examined. Then, the key roles of the combination, concentration and location of various growth factors in biomimetic application are emphasized. After that, the various stem cell sources and culture systems are described. At last, we discuss unmet needs and existing challenges in the ideal strategies for tendon/ligament-to-bone regeneration and highlight emerging strategies in the field.

Tendon-Inspired Nanotopographic Scaffold for Tissue Regeneration in Rotator Cuff Injuries

Acute and chronic rotator cuff (RC) tears are common etiologies of shoulder disabilities. Despite the advanced surgical techniques and graft materials available for tendon repair, the high re-tear rate remains a critical challenge in RC healing. Inspired by the highly organized nanotopography of the extracellular matrix (ECM) in tendon tissue of the shoulder, nanotopographic scaffolds are developed using polycaprolactone for the repair and regeneration of RC tendons. The scaffolds show appropriate flexibility and mechanical properties for application in tendon tissue regeneration. It is found that the highly aligned nanotopographic cues of scaffolds could sensitively control and improve the morphology, attachment, proliferation, and differentiation of tendon-derived cells as well as promote their wound healing capacity in vitro. In particular, this study showed that the scaffolds could promote tendon regeneration along the direction of the nanotopography in the rabbit models of acute and chronic RC tears. Nanotopographic scaffold-augmented rotator cuff repair showed a more appropriate healing pattern compared to the control groups in a rabbit RC tear model. We demonstrated that the tendon ECM-like nanoscale structural cues of the tendon-inspired patch may induce the more aligned tissue regeneration of the underlying tissues including tendon-to-bone interface.

Augmenting endogenous repair of soft tissues with nanofibre scaffolds

As our ability to engineer nanoscale materials has developed we can now influence endogenous cellular processes with increasing precision. Consequently, the use of biomaterials to induce and guide the repair and regeneration of tissues is a rapidly developing area. This review focuses on soft tissue engineering, it will discuss the types of biomaterial scaffolds available before exploring physical, chemical and biological modifications to synthetic scaffolds. We will consider how these properties, in combination, can provide a precise design process, with the potential to meet the requirements of the injured and diseased soft tissue niche. Finally, we frame our discussions within clinical trial design and the regulatory framework, the consideration of which is fundamental to the successful translation of new biomaterials.

Soybean-modified polyamide-6 mats as a long-term cutaneous wound covering

Engineered skin coverings have been adopted clinically to support extensive and deep wounds that result in fewer healthy skin remaining and therefore take longer to heal. Nonetheless, these biomaterials demand intensive labor and an expensive final cost. In comparison to conventional bandages, which do not meet all the requirements of wound care, electrospun fiber mats could potentially provide an excellent environment for healing. In this work, we developed two nanostructured scaffolds based on polyamide-6 (PA-6) to be tested as a wound covering in a rat model of full-thickness incisional wound healing. The central idea was to create a bioconstruct that is simple to implement and biologically safe, with a high survival rate, which provides physical support and biological recognition for new functional tissues. An unmodified PA-6 and a soybean-modified PA-6 were employed as nanofibrillar matrices in this study. The biomaterials showed a dimensional homology to natural extracellular matrix components and neither in vitro toxicity nor in vivo side effects. Both polymeric scaffolds were resistant to the sterilization process and could promote the attachment of 3T3 fibroblast cells, besides successfully incorporating the growth factor PDGF-BB, which had its bioactivity extended for up to 12 h under simulated conditions. The modification of PA-6 chains with a fatty acid derivative increased the scaffold's surface free energy, favoring cell proliferation, collagen formation, and ECM secretion. These results confirm the potential of these materials as a topical dermal covering for skin regeneration.

Harnessing biochemical and structural cues for tenogenic differentiation of adipose derived stem cells (ADSCs) and development of an in vitro tissue interface mimicking tendon-bone insertion graft

Tendon-bone interface tissue is extremely challenging to engineer because it exhibits complex gradients of structure, composition, biologics, and cellular phenotypes. As a step toward engineering these transitional zones, we initially analyzed how different (topographical or biological) cues affect tenogenic differentiation of adipose-derived stem cells (ADSCs). We immobilized platelet-derived growth factor - BB (PDGF-BB) using polydopamine (PD) chemistry on random and aligned nanofibers and investigated ADSC proliferation and tenogenic differentiation. Immobilized PDGF greatly enhanced the proliferation and tenogenic differentiation of ADSCs; however, nanofiber alignment had no effect. Interestingly, the PDGF immobilized aligned nanofiber group showed a synergistic effect with maximum expression of tenogenic markers for 14 days. We also generated a nanofiber surface with spatially controlled presentation of immobilized PDGF on an aligned architecture, mimicking native tendon tissue. A gradient of immobilized PDGF was able to control the phenotypic differentiation of ADSCs into tenocytes in a spatially controlled manner, as confirmed by analysis of the expression of tenogenic markers and immunofluorescence staining. We further explored the gradient formation strategy by generation of a symmetrical gradient on the nanofiber surface for the generation of a structure mimicking bone-patellar-tendon-bone with provision for gradient immobilization of PDGF and controlled mineralization. Our study reveals that, together with biochemical cues, favorable topographical cues are important for tenogenic differentiation of ADSCs, and gradient presentation of PDGF can be used as a tool for engineering stem cell-based bone-tendon interface tissues.

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.

Growth factor delivery strategies for rotator cuff repair and regeneration

The high incidence of degenerative tears and prevalence of retears (20-95%) after surgical repair makes rotator cuff injuries a significant health problem. This high retear rate is attributed to the failure of the repaired tissue to regenerate the native tendon-to-bone insertion (enthesis). Biological augmentation of surgical repair such as autografts, allografts, and xenografts are confounded by donor site morbidity, immunogenicity, and disease transmission, respectively. In contrast, these risks may be alleviated via growth factor therapy, which can actively influence the healing environment to promote functional repair. Several challenges have to be overcome before growth factor delivery can translate into clinical practice such as the selection of optimal growth factor(s) or combination, identification of the most efficient stage and duration of delivery, and the design considerations for the delivery device. Emerging insight into the injury-repair microenvironment and our understanding of growth factor mechanisms in healing are informing the design of advanced delivery scaffolds to effectively treat rotator cuff tears. Here, we review potential growth factor candidates, design parameters and material selection for growth factor delivery, innovative and dynamic delivery scaffolds, and novel therapeutic targets from tendon and developmental biology for the structural and functional healing of rotator cuff repair.