Surgical Sutures with Porous Sheaths for the Sustained Release of Growth Factors

Melt-extruded biocompatible surgical sutures loaded with microspheres designed for wound healing

Sutures are commonly used in surgical procedures and have immense potential for direct drug delivery into the wound site. However, incorporating active pharmaceutical ingredients into the sutures has always been challenging as their mechanical strength deteriorates. This study proposes a new method to produce microspheres-embedded surgical sutures that offer adequate mechanical properties for effective wound healing applications. The study used curcumin, a bioactive compound found in turmeric, as a model drug due to its anti-inflammatory, antioxidant, and anti-bacterial properties, which make it an ideal candidate for a surgical suture drug delivery system. Curcumin-loaded microspheres were produced using the emulsion solvent evaporation method with polyvinyl alcohol (PVA) as the aqueous phase. The microspheres' particle sizes, drug loading (DL) capacity, and encapsulation efficiency (EE) were investigated. Microspheres were melt-extruded with polycaprolactone and polyethylene glycol via a 3D bioplotter, followed by a drawing process to optimise the mechanical strength. The sutures' thermal, physiochemical, and mechanical properties were investigated, and the drug delivery and biocompatibility were evaluated. The results showed that increasing the aqueous phase concentration resulted in smaller particle sizes and improved DL capacity and EE. However, if PVA was used at 3% w/v or below, it prevented aggregate formation after lyophilisation, and the average particle size was found to be 34.32 ± 12.82 μm. The sutures produced with the addition of microspheres had a diameter of 0.38 ± 0.02 mm, a smooth surface, minimal tissue drag, and proper tensile strength. Furthermore, due to the encapsulated drug-polymer structure, the sutures exhibited a prolonged and sustained drug release of up to 14 d. Microsphere-loaded sutures demonstrated non-toxicity and accelerated wound healing in thein vitrostudies. We anticipate that the microsphere-loaded sutures will serve as an excellent biomedical device for facilitating wound healing.

Two way workable microchanneled hydrogel suture to diagnose, treat and monitor the infarcted heart

During myocardial infarction, microcirculation disturbance in the ischemic area can cause necrosis and formation of fibrotic tissue, potentially leading to malignant arrhythmia and myocardial remodeling. Here, we report a microchanneled hydrogel suture for two-way signal communication, pumping drugs on demand, and cardiac repair. After myocardial infarction, our hydrogel suture monitors abnormal electrocardiogram through the mobile device and triggers nitric oxide on demand via the hydrogel sutures' microchannels, thereby inhibiting inflammation, promoting microvascular remodeling, and improving the left ventricular ejection fraction in rats and minipigs by more than 60% and 50%, respectively. This work proposes a suture for bidirectional communication that acts as a cardio-patch to repair myocardial infarction, that remotely monitors the heart, and can deliver drugs on demand.

Advances, challenges, and prospects for surgical suture materials

As one of the long-established and necessary medical devices, surgical sutures play an essentially important role in the closing and healing of damaged tissues and organs postoperatively. The recent advances in multiple disciplines, like materials science, engineering technology, and biomedicine, have facilitated the generation of various innovative surgical sutures with humanization and multi-functionalization. For instance, the application of numerous absorbable materials is assuredly a marvelous progression in terms of surgical sutures. Moreover, some fantastic results from recent laboratory research cannot be ignored either, ranging from the fiber generation to the suture structure, as well as the suture modification, functionalization, and even intellectualization. In this review, the suture materials, including natural or synthetic polymers, absorbable or non-absorbable polymers, and metal materials, were first introduced, and then their advantages and disadvantages were summarized. Then we introduced and discussed various fiber fabrication strategies for the production of surgical sutures. Noticeably, advanced nanofiber generation strategies were highlighted. This review further summarized a wide and diverse variety of suture structures and further discussed their different features. After that, we covered the advanced design and development of surgical sutures with multiple functionalizations, which mainly included surface coating technologies and direct drug-loading technologies. Meanwhile, the review highlighted some smart and intelligent sutures that can monitor the wound status in a real-time manner and provide on-demand therapies accordingly. Furthermore, some representative commercial sutures were also introduced and summarized. At the end of this review, we discussed the challenges and future prospects in the field of surgical sutures in depth. This review aims to provide a meaningful reference and guidance for the future design and fabrication of innovative surgical sutures. STATEMENT OF SIGNIFICANCE: This review article introduces the recent advances of surgical sutures, including material selection, fiber morphology, suture structure and construction, as well as suture modification, functionalization, and even intellectualization. Importantly, some innovative strategies for the construction of multifunctional sutures with predetermined biological properties are highlighted. Moreover, some important commercial suture products are systematically summarized and compared. This review also discusses the challenges and future prospects of advanced sutures in a deep manner. In all, this review is expected to arouse great interest from a broad group of readers in the fields of multifunctional biomaterials and regenerative medicine.

The use of connective tissue growth factor mimics for flexor tendon repair

Intrasynovial flexor tendon lacerations of the hand are clinically problematic, typically requiring operative repair and extensive rehabilitation. The small-molecule connective tissue growth factor (CTGF) mimics, oxotremorine M (Oxo-M) and 4-PPBP maleate (4-PPBP), have been shown to improve tendon healing in small animal models by stimulating the expansion and differentiation of perivascular CD146+ cells. To enhance intrasynovial flexor tendon healing, small-molecule CTGF mimics were delivered to repaired canine flexor tendons via porous sutures. In vitro studies demonstrated that Oxo-M and 4-PPBP retained their bioactivity and could be released from porous sutures in a sustained manner. However, in vivo delivery of the CTGF mimics did not improve intrasynovial tendon healing. Histologic analyses and expression of tenogenic, extracellular matrix, inflammation, and remodeling genes showed similar outcomes in treated and untreated repairs across two time points. Although in vitro experiments revealed that CTGF mimics stimulated robust responses in extrasynovial tendon cells, there was no response in intrasynovial tendon cells, explaining the lack of in vivo effects. The results of the current study indicate that therapeutic strategies for tendon repair must carefully consider the environment and cellular makeup of the particular tendon for improving the healing response.

A review of current advancements for wound healing: Biomaterial applications and medical devices

Wound healing is a complex process that is critical in restoring the skin's barrier function. This process can be interrupted by numerous diseases resulting in chronic wounds that represent a major medical burden. Such wounds fail to follow the stages of healing and are often complicated by a pro‐inflammatory milieu attributed to increased proteinases, hypoxia, and bacterial accumulation. The comprehensive treatment of chronic wounds is still regarded as a significant unmet medical need due to the complex symptoms caused by the metabolic disorder of the wound microenvironment. As a result, several advanced medical devices, such as wound dressings, wearable wound monitors, negative pressure wound therapy devices, and surgical sutures, have been developed to correct the chronic wound environment and achieve skin tissue regeneration. Most medical devices encompass a wide range of products containing natural (e.g., chitosan, keratin, casein, collagen, hyaluronic acid, alginate, and silk fibroin) and synthetic (e.g., polyvinyl alcohol, polyethylene glycol, poly[lactic‐co‐glycolic acid], polycaprolactone, polylactic acid) polymers, as well as bioactive molecules (e.g., chemical drugs, silver, growth factors, stem cells, and plant compounds). This review addresses these medical devices with a focus on biomaterials and applications, aiming to deliver a critical theoretical reference for further research on chronic wound healing.

Fabrication of "Spongy Skin" on Diversified Materials Based on Surface Swelling Non-Solvent-Induced Phase Separation

Porous surfaces have attracted tremendous interest for customized incorporation of functional agents on biomedical devices. However, the versatile preparation of porous structures on complicated devices remains challenging. Herein, we proposed a simple and robust method to fabricate "spongy skin" on diversified polymeric substrates based on non-solvent-induced phase separation (NIPS). Through the swelling and the subsequent phase separation process, interconnected porous structures were directly formed onto the polymeric substrates. The thickness and pore size could be regulated in the ranges of 5-200 and 0.3-0.75 μm, respectively. The fast capillary action of the porous structure enabled controllable loading and sustained release of ofloxacin and bovine albumin at a high loading dosage of 79.9 and 24.1 μg/cm², respectively. We verified that this method was applicable to diversified materials including polymethyl methacrylate, polystyrene, thermoplastic polyurethane, polylactide acid, and poly(lactic-co-glycolic acid) and can be realized onto TCPS cell culture plates. This NIPS-based method is promising to generate porous surfaces on medical devices for incorporating therapeutic agents.

Effect of a Porous Suture Containing Transforming Growth Factor Beta 1 on Healing After Rotator Cuff Repair in a Rat Model

BACKGROUND

The healing failure rate after rotator cuff repair is considerably high.

PURPOSE

To evaluate the effect of a porous suture containing transforming growth factor beta 1 (TGF-β1) on the sustained release of TGF-β1 and rotator cuff healing in a rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A porous suture was developed, and its tensile strength was measured. TGF-β1 was delivered using the porous suture, and a TGF-β1 release test and human fibroblast proliferation assay were performed. For the animal experiment, 30 rats were randomly allocated into 3 groups (n = 10 each). A bilateral supraspinatus tendon tear was made in all the rats, and repair was performed. Group 1 received repair only; group 2, repair and a single injection of TGF-β1; and group 3, repair using the porous suture containing TGF-β1. Eight weeks after repair, biomechanical and histological analyses were performed.

RESULTS

The porous suture was successfully developed with mechanical properties compatible with the conventional suture, and the sustained release of TGF-β1 from the porous suture was confirmed. In addition, the cell proliferation assay confirmed the biological safety of the porous suture. In the animal experiment, group 3 biomechanically exhibited the largest cross-sectional area and the highest ultimate failure load and ultimate stress (all P < .05). Histological examination revealed that group 3 showed significantly better collagen fiber density and tendon-to-bone maturation than did groups 1 and 2 (all P < .05).

CONCLUSION

The porous suture containing TGF-β1 could sustainedly and safely release TGF-β1, and its use during rotator cuff repair could improve rotator cuff healing, as assessed on the basis of the biomechanical and histological changes in the rat model in this study. Considering the effectiveness, safety, and convenience of the porous suture without extra effort in surgery, the findings of the present study will have a far-reaching effect on the treatment of rotator cuff tears.

CLINICAL RELEVANCE

The porous suture containing TGF-β1 might improve healing after rotator cuff repair.

Electrospun heparin-loaded nano-fiber sutures for the amelioration of achilles tendon rupture regeneration: in vivo evaluation

Peritendinous blood circulation improvement is a challenge to promote the healing of ruptured tendons in clinical treatment. Although electrospun membranes or scaffolds enable the reduction of complications such as adhesion, however, low efficiency, toxicity issues, the loss of biological activity, and complex electrospinning techniques are all bottlenecks of these systems. Improving the blood supply is crucial for their successful use, which involves promoting the metabolism and nutrient absorption in tendons. Here, a multifunctional, structurally simple strategy involving heparin-loaded sutures (PPH) that are clinically applicable is reported, in the form of electrospun core-shell nanofibers, with the ability to perform sustained release of anticoagulants heparin (verified in our previous publication) for the improvement of the healing of Achilles tendon. The morphology and diameter distribution of the collagen fiber in the PPH group are closely related to the health of the Achilles tendon than those of commercial sutures (CS). The in vivo results of the total collagen content and the expression of collagen type I in the PPH group are more than those of the CS group. After 6 weeks of culture, the tensile strength of the PPH group shows no significant difference compared to the healthy group. The data obtained in this study improves the current understanding on the regeneration of ruptured tendons and presents a promising strategy for clinical treatment.

Bioinspired tough gel sheath for robust and versatile surface functionalization

Sutures pervade surgeries, but their performance is limited by the mechanical mismatch with tissues and the lack of advanced functionality. Existing modification strategies result in either deterioration of suture's bulk properties or a weak coating susceptible to rupture or delamination. Inspired by tendon endotenon sheath, we report a versatile strategy to functionalize fiber-based devices such as sutures. This strategy seamlessly unites surgical sutures, tough gel sheath, and various functional materials. Robust modification is demonstrated with strong interfacial adhesion (>2000 J m-2). The surface stiffness, friction, and drag of the suture when interfacing with tissues can be markedly reduced, without compromising the tensile strength. Versatile functionalization of the suture for infection prevention, wound monitoring, drug delivery, and near-infrared imaging is then presented. This platform technology is applicable to other fiber-based devices and foreseen to affect broad technological areas ranging from wound management to smart textiles.

Phase-Change Materials for Controlled Release and Related Applications

Phase-change materials (PCMs) have emerged as a novel class of thermo-responsive materials for controlled release, where the payloads encapsulated in a solid matrix are released only upon melting the PCM to trigger a solid-to-liquid phase transition. Herein, the advances over the past 10 years in utilizing PCMs as a versatile platform for the encapsulation and release of various types of therapeutic agents and biological effectors are highlighted. A brief introduction to PCMs in the context of desired properties for controlled release and related applications is provided. Among the various types of PCMs, a specific focus is placed on fatty acids and fatty alcohols for their natural availability, low toxicity, biodegradability, diversity, high abundance, and low cost. Then, various methods capable of processing PCMs, and their mixtures with payloads, into stable suspensions of colloidal particles, and the different means for triggering the solid-to-liquid phase transition are discussed. Finally, a range of applications enabled by the controlled release system based on PCMs are presented together with some perspectives on future directions.

Piezoelectric nylon-11 nanoparticles with ultrasound assistance for high-efficiency promotion of stem cell osteogenic differentiation

With the assistance of ultrasound, piezoelectric nylon-11 nanoparticle-mediated electric stimulation can promote the osteogenic differentiation of DPSCs efficiently in a noninvasive way.

The effect of adipose-derived stem cell sheets and CTGF on early flexor tendon healing in a canine model

Intrasynovial tendon injuries are among the most challenging in orthopedics. Despite significant improvements in operative and rehabilitation methods, functional outcomes continue to be limited by adhesions, gap formation, and rupture. Adhesions result from excessive inflammation, whereas tendon gapping and rupture result from inflammation-induced matrix degradation and insufficient regeneration. Therefore, this study used a combined treatment approach to modulate inflammation with adipose-derived mesenchymal stromal cells (ASCs) while stimulating tendon regeneration with connective tissue growth factor (CTGF). ASCs were applied to the repair surface via cell sheets and CTGF was delivered to the repair center via porous sutures. The effect of the combined treatment was assessed fourteen days after repair in a canine flexor tendon injury model. CTGF, either alone or with ASCs, reduced inflammatory (IL1B and IL6) and matrix degrading (MMP3 and MMP13) gene expression, while increasing anti-inflammatory gene (IL4) expression and collagen synthesis compared to control repairs. The combined treatment was more effective than CTGF treatment alone, reducing the inflammatory IFNG and scar-associated COL3A1 gene expression and increasing CD146+ tendon stem/progenitor cells at the tendon surface and interior along the core suture tracks. Therefore, the combined approach is promising in promoting early flexor tendon healing and worthy of further investigation.

Effect of connective tissue growth factor delivered via porous sutures on the proliferative stage of intrasynovial tendon repair

Recent growth factor, cell, and scaffold-based experimental interventions for intrasynovial flexor tendon repair have demonstrated therapeutic potential in rodent models. However, these approaches have not achieved consistent functional improvements in large animal trials due to deleterious inflammatory reactions to delivery materials and insufficient induction of targeted biological healing responses. In this study, we achieved porous suture-based sustained delivery of connective tissue growth factor (CTGF) into flexor tendons in a clinically relevant canine model. Repairs with CTGF-laden sutures were mechanically competent and did not show any evidence of adhesions or other negative inflammatory reactions based on histology, gene expression, or proteomics analyses at 14 days following repair. CTGF-laden sutures induced local cellular infiltration and a significant biological response immediately adjacent to the suture, including histological signs of angiogenesis and collagen deposition. There were no evident widespread biological effects throughout the tendon substance. There were significant differences in gene expression of the macrophage marker CD163 and anti-apoptotic factor BCL2L1; however, these differences were not corroborated by proteomics analysis. In summary, this study provided encouraging evidence of sustained delivery of biologically active CTGF from porous sutures without signs of a negative inflammatory reaction. With the development of a safe and effective method for generating a positive local biological response, future studies can explore additional methods for enhancing intrasynovial tendon repair. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2052-2063, 2018.

Sulfated zwitterionic poly(sulfobetaine methacrylate) hydrogels promote complete skin regeneration

Skin wound healing is a still long-history challenging problem and impeded by the foreign-body reaction including severe inflammation response, poor neovascularization, incomplete re-epithelialization and defective ECM remodeling. Development of biocompatible polymers, in combination with specific drugs or growth factors, has been considered as a promising strategy to treat skin wounds. Significant research efforts have been made to develop poly(ethylene glycol) PEG-based polymers for wound healing, however less efforts has been paid to zwitterionic materials, some of which have demonstrated their super low-fouling property in vitro and anti-inflammatory property in vivo. Here, we synthesized ultra-low-fouling zwitterionic sulfated poly(sulfobetaine methacrylate) (polySBMA) hydrogels and applied them to full-thickness cutaneous wounds in mice. The healing effects of SBMA hydrogels on the wound closure, re-epithelialization ratio, ECM remodeling, angiogenesis, and macrophage responses during wound healing processes were histologically evaluated by in vivo experiments. Collective results indicate that SBMA hydrogels promote full-thickness excisional acute wound regeneration in mice by enhancing angiogenesis, decreasing inflammation response, and modulating macrophage polarization. Consistently, the incorporation of SBMA into PEG hydrogels also improved the overall wound healing efficiency as compared to pure PEG hydrogels. This work demonstrates zwitterionic SBMA hydrogels as promising wound dressings for treating full-thickness excisional skin wounds.

STATEMENT OF SIGNIFICANCE

Development of highly effective wound regeneration system is practically important for biomedical applications. Here, we synthesized ultra-low-fouling zwitterionic sulfated poly(sulfobetaine methacrylate) (polySBMA) hydrogels and applied it to full-thickness cutaneous wounds in mice, in comparison with PEG hydrogels as a control. We are the first to examine and reveal the difference between zwitterionic SBMA hydrogels and PEG hydrogels using a full-thickness excisional mice model. Overall, a series of in vivo systematic tests demonstrated that zwitterionic SBMA hydrogels exhibited superior wound healing property in almost all aspects as compared to PEG hydrogels.

Polymer sutures for simultaneous wound healing and drug delivery - A review

Drug delivery using suitable polymeric devices has gathered momentum in the recent years due to their remarkable properties. The versatility of polymeric materials makes them reliable candidates for site targeted drug release. Among them biodegradable sutures has received considerable attention because they offer great promises in the realm of drug delivery. Sutures have been found to be an effective strategy for the delivery of antibacterial agents or anti-inflammatory drugs to the surgical site. Recent developments yielded sutures with improved mechanical properties, but designing sutures with all the desirable properties is still under investigation. This review is an attempt to analyze the recent developments pertaining to biologically active sutures emphasizing their potential as drug delivery vehicle.

Fabrication of biodegradable textile scaffold based on hydrophobized hyaluronic acid

In this work, we report on the preparation of a novel biodegradable textile scaffold made of palmitoyl-hyaluronan (palHA). Monofilament fibres of palHA with a diameter of 120μm were prepared by wet spinning. The wet-spun fibres were subsequently processed into a warp-knitted textile. To find a compromise between swelling in water and degradability of the final textile scaffold, a series of palHA derivatives with different degrees of substitution of the palmitoyl chain was synthesized. Freeze-drying not only provided shape fixation, but also speeded up scaffold degradation in vitro. Fibronectin, fibrinogen, laminin and collagen IV were physically adsorbed on the textile surface to enhance cell adhesion on the material. The highest amount of adsorbed cell-adhesive proteins was achieved with fibronectin (89%), followed by fibrinogen (81%). Finally, textiles modified with fibronectin or fibrinogen both supported the adhesion and proliferation of normal human fibroblasts in vitro, proving to be a useful cellular scaffold for tissue engineering.