Synthetic sutures: Clinical evaluation and future developments

Evaluation of biomechanical properties and biocompatibility: are partially absorbable cords eligible for anterior cruciate ligament reconstruction?

Introduction: Independent augmentation technology based on reinforcing devices has been reported to signifi-cantly reduce the elongation behavior of graft and improve knee stability after anterior cruciate ligament reconstruction (ACLR). Using biodegradable devices could reduce the risk of severe inflammatory reactions due to particle accumulation from foreign bodies. Given the limitations of the mechanical properties of biodegradable materials, partially biodegradable composite devices may offer a compromise strategy. Methods: Three types of partially absorbable core-sheath sutures, including low-absorbable cord (LA-C), medium-absorbable cord (MA-C) and high-absorbable cord (HA-C), were braided using unabsorbable ultra-high molecular weight polyethylene (UHMWPE) yarn and absorbable polydioxanone (PDO) monofil-ament bundle based on the desired configuration. The feasibility of these partially absorbable cords were verified by biomechanical testing, material degradation testing, and cell experiments, all performed in vitro. Results: Reinforcement of an 8 mm graft with the cords decreased dynamic elongation by 24%-76%, was positively related to dynamic stiffness, and increased the failure load by 44%-105%, during which LA-C showed maximum enhancement. Human ligament-derived fibroblasts showed good proliferation and vitality on each cord over 2 weeks and aligned themselves in the direction of the fibers, especially the UHMWPE portion. Discussion: This study supports the potential of partially degradable UHMWPE/PDO cords, particularly LA-C, for graft protection. Nervertheless, a higher proportion of biodegradable material results in lower stiffness, which may impair the protective and lead to mechanical instability during degradation.

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.

Individualized Wound Closure-Mechanical Properties of Suture Materials

Wound closure is a key element of any procedure, especially aesthetic and reconstructive plastic surgery. Therefore, over the last decades, several devices have been developed in order to assist surgeons in achieving better results while saving valuable time. In this work, we give a concise review of the literature and present a biomechanical study of different suturing materials under mechanical load mimicking handling in the operating theatre. Nine different suture products, all of the same USP size (4-0), were subjected to a standardized crushing load by means of a needle holder. All materials were subjected to 0, 1, 3 and 5 crushing load cycles, respectively. The linear tensile strength was measured by means of a universal testing device. Attenuation of tensile strength was evaluated between materials and between crush cycles. In the pooled analysis, the linear tensile strength of the suture materials deteriorated significantly with every cycle (p < 0.0001). The suture materials displayed different initial tensile strengths (in descending order: polyglecaprone, polyglactin, polydioxanone, polyamid, polypropylene). In comparison, materials performed variably in terms of resistance to crush loading. The findings were statistically significant. The reconstructive surgeon has to be flexible and tailor wound closure techniques and materials to the individual patient, procedure and tissue demands; therefore, profound knowledge of the physical properties of the suture strands used is of paramount importance. The crushing load on suture materials during surgery can be detrimental for initial and long-term wound repair strength. As well as the standard wound closure methods (sutures, staples and adhesive strips), there are promising novel devices.

Synthesis of a novel monofilament bioabsorbable suture for biomedical applications

In this research, a novel bioabsorbable suture that is, monofilament and capable of localized drug delivery, was developed from a combination of natural biopolymers that where not previously applied for this purpose. The optimized suture formulation comprised of sodium alginate (6% wt/vol), pectin (0.1% wt/vol), and gelatin (3% wt/vol), in the presence of glycerol (4% vol/vol) which served as a plasticizer. The monofilament bioabsorbable sutures where synthesized via in situ ionic crosslinking in a barium chloride solution (2% wt/vol). The resulting suture was characterized in terms of mechanical properties, morphology, swelling, degradation, drug release, and biocompatibility, in addition to Fourier-transform infrared (FTIR) spectroscopy, Powder X-ray Diffraction (PXRD) and Differential Scanning Calorimetry (DSC) analysis. The drug loaded and non-drug loaded sutures had a maximum breaking strength of 4.18 and 4.08 N, in the straight configuration and 2.44 N and 2.59 N in the knot configuration, respectively. FTIR spectrum of crosslinked sutures depicted Δ9 cm^-1 downward shift for the carboxyl stretching band which was indicative of ionic interactions between barium ions and sodium alginate. In vitro analysis revealed continued drug release for 7 days and gradual degradation by means of surface erosion, which was completed by day 28. Biocompatibility studies revealed excellent hemocompatibility and no cytotoxicity. These results suggest that the newly developed bioabsorbable suture meets the basic requirements of a suture material and provides a viable alternative to the synthetic polymer sutures that are currently on the market.

Suture Materials, Needles, and Methods of Skin Closure: What Every Hand Surgeon Should Know

Sutures are used ubiquitously in surgery and are the most implanted materials in hand surgery. However, surgical training does not routinely include formal education on stitching materials or needles. Rather, suture familiarity is passed down by common use throughout training. We focus on a brief history and evolution of suture materials and suture needles, their material and mechanical properties, hand surgery-specific applications, other methods of skin closure (staples, skin glue, and adhesive strips), a cost analysis, and advances in musculoskeletal suturing, with a look toward the future. Equipped with a fundamental knowledge of suture needles and suture materials, hand surgeons will be better prepared to select the most appropriate, situation-specific tools.

Smart surgical sutures using soft artificial muscles

Wound closure with surgical sutures is a critical challenge for flexible endoscopic surgeries. Substantial efforts have been introduced to develop functional and smart surgical sutures to either monitor wound conditions or ease the complexity of knot tying. Although research interests in smart sutures by soft robotic technologies have emerged for years, it is challenging to develop a soft robotic structure that possesses a similar physical structure as conventional sutures while offering a self-tightening knot or anchor to close the wound. This paper introduces a new concept of smart sutures that can be programmed to achieve desired and uniform tension distribution while offering self-tightening knots or automatically deploying secured anchors. The core technology is a soft hydraulic artificial muscle that can be elongated and contracted under applied fluid pressure. Each suture is equipped with a pressure locking mechanism to hold its temporary elongated state and to induce self-shrinking ability. The puncturing and holding force for the smart sutures with anchors are examined. Ex-vivo experiments on fresh porcine stomach and colon demonstrate the usefulness of the new smart sutures. The new approaches are expected to pave the way for the further development of smart sutures that will benefit research, training, and commercialization in the surgical field.

Early development of a polycaprolactone electrospun augment for anterior cruciate ligament reconstruction

Despite the clinical success of Anterior Cruciate Ligament reconstruction (ACLR) in some patients, unsatisfactory clinical outcomes secondary to graft failure are seen, indicating the need to develop new regeneration strategies. The use of degradable and bioactive textiles has the potential to improve the biological repair of soft tissue. Electrospun (ES) filaments are particularly promising as they have the ability to mimic the structure of natural tissues and influence endogenous cell behaviour. In this study, we produced continuous polycaprolactone (PCL) ES filaments using a previously described electrospinning collection method. These filaments were stretched, twisted, and assembled into woven structures. The morphological, tensile, and biological properties of the woven fabric were then assessed. Scanning electron microscopy (SEM) images highlighted the aligned and ACL-like microfibre structure found in the stretched filaments. The tensile properties indicated that the ES fabric reached suitable strengths for a use as an ACLR augmentation device. Human ACL-derived cell cultured on the fabric showed approximately a 3-fold increase in cell number over 2 weeks and this was equivalent to a collagen coated synthetic suture commonly used in ACLR. Cells generally adopted a more elongated cell morphology on the ES fabric compared to the control suture, aligning themselves in the direction of the microfibres. A NRU assay confirmed that the ES fabric was non-cytotoxic according to regulatory standards. Overall, this study supports the development of ES textiles as augmentation devices for ACLR.

Bioactive nano yarns as surgical sutures for wound healing

Surgical sutures are the most widely used medical device in any surgical procedure worldwide. In this study, modified electrospinning technique has been used as manufacturing technique to produce nanofiber bundles twisted simultaneously to obtain nanofiber yarns. Taking the advantage of nanofiber yarns in terms of biomimetic structure, mechanical strength and handling properties, the material is chosen. Curcumin, a natural compound is incorporated to the nanofiber yarns by blend electrospinning technique for its anti-inflammatory, antibiotic and wound healing properties. The synthesized nanofiber yarns were characterized by various characterization techniques such as XRD, FTIR, SEM, Tensile testing, stem cell interaction, hemocompatibility, bacterial response, drug release profiling and in vivo studies. Curcumin loaded nanofiber yarns demonstrated sustained release with improved antibacterial, antiplatelet, cell migration and stem cell interaction in vitro. The results from skin inflammation animal model revealed that curcumin laden nanofiber yarn suture manifested reduced inflammation and cellularity. The three dimensional structure, adequate mechanical strength and biological properties of the nanofiber yarn provide naive environment for wound healing with the balanced degradation of suture material in rat model.

Rational engineering and applications of functional bioadhesives in biomedical engineering

For the past decades, several bioadhesives have been developed to replace conventional wound closure medical tools such as sutures, staples, and clips. The bioadhesives are easy to use and can minimize tissue damage. They are designed to provide strong adhesion with stable mechanical support on tissue surfaces. However, this monofunctionality of the bioadhesives hinders their practical applications. In particular, a bioadhesive can lose its intended function under harsh tissue environments or delay tissue regeneration during wound healing. Based on several natural and synthetic biomaterials, functional bioadhesives have been developed to overcome the aforementioned limitations. The functional bioadhesives are designed to have specific characteristics such as antimicrobial, cell infiltrative, stimuli-responsive, electrically conductive, and self-healing to ensure stability under harsh tissue conditions, facilitate tissue regeneration, and effectively monitor biosignals. Herein, we thoroughly review the functional bioadhesives from their fundamental background to recent progress with their practical applications for the enhancement of tissue healing and effective biosignal sensing. Furthermore, the future perspectives on the applications of functional bioadhesives and current challenges in their commercialization are also discussed.

Multifaceted Design and Emerging Applications of Tissue Adhesives

Tissue adhesives can form appreciable adhesion with tissues and have found clinical use in a variety of medical settings such as wound closure, surgical sealants, regenerative medicine, and device attachment. The advantages of tissue adhesives include ease of implementation, rapid application, mitigation of tissue damage, and compatibility with minimally invasive procedures. The field of tissue adhesives is rapidly evolving, leading to tissue adhesives with superior mechanical properties and advanced functionality. Such adhesives enable new applications ranging from mobile health to cancer treatment. To provide guidelines for the rational design of tissue adhesives, here, existing strategies for tissue adhesives are synthesized into a multifaceted design, which comprises three design elements: the tissue, the adhesive surface, and the adhesive matrix. The mechanical, chemical, and biological considerations associated with each design element are reviewed. Throughout the report, the limitations of existing tissue adhesives and immediate opportunities for improvement are discussed. The recent progress of tissue adhesives in topical and implantable applications is highlighted, and then future directions toward next-generation tissue adhesives are outlined. The development of tissue adhesives will fuse disciplines and make broad impacts in engineering and medicine.

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.

Cross-section modified and highly elastic sutures reduce tissue incision and show comparable biocompatibility: in-vitro and in-vivo evaluation of novel thermoplastic urethane surgical threads

Surgical sutures are indispensable for a vast majority of operative procedures. An ideal suture is characterized by high tissue compliance without cutting into the mended tissue and optimal biocompatibility. Therefore, we assessed these mechanical and biological properties for novel elastic thermoplastic polyurethane (TPU) and cross-sectional modified "snowflake" sutures. Circular and "snowflake"-shaped TPU threads were manufactured and compared to similar surface modified polyvinylidene fluoride (PVDF) sutures. Regular PVDF sutures were used as the control group. Single-axis tensile test with and without gelatinous tissue surrogates were performed to evaluate the suture incision into the specimens. Biocompatibility was evaluated by subcutaneous implantation (n = 18) in rats for 7 and 21 days. Histology and immunohistology was conducted for assessment of the foreign body reaction. Regular and modified TPU threads showed a significant reduction of incision into the tissue surrogates compared to the control. Both TPU sutures and the modified PVDF sutures achieved comparable biocompatibility versus regular PVDF threads. Detailed histology revealed novel tissue integration into the notches of the surface modified sutures, we termed this newly shaped granuloma "intrafilamentous" granuloma. Elastic TPU threads showed a significant reduction of tissue surrogate incision and suture tension loss. Biocompatibility did not significantly differ from standard PVDF. Histology demonstrated tissue ingrowth following the surface modification of the suture referred to as "intrafilamentous" granuloma. Further in vivo studies are required to illuminate the exact potential of the new sutures to optimize intestinal anastomosis.