Tailoring lactide/caprolactone co-oligomers as tissue adhesives

Biodegradable, Tissue Adhesive Polyester Blends for Safe, Complete Wound Healing

Pressure-sensitive adhesives typically used for bandages are nonbiodegradable, inhibiting healing, and may cause an allergic reaction. Here, we investigated the effect of biodegradable copolymers with promising thermomechanical properties on wound healing for their eventual use as biodegradable, biocompatible adhesives. Blends of low molecular weight (LMW) and high molecular weight (HMW) poly(lactide-co-caprolactone) (PLCL) are investigated as tissue adhesives in comparison to a clinical control. Wounds treated with PLCL blend adhesives heal completely with similar vascularization, scarring, and inflammation indicators, yet require fewer dressing changes due to integration of the PLCL adhesive into the wound. A blend of LMW and HMW PLCL produces an adhesive material with significantly higher adhesive strength than either neat polymer. Wound adhesion is comparable to a polyurethane bandage, utilizing conventional nonbiodegradable adhesives designed for extremely strong adhesion.

In Situ Generated Medical Devices

Medical devices play a major role in all areas of modern medicine, largely contributing to the success of clinical procedures and to the health of patients worldwide. They span from simple commodity products such as gauzes and catheters, to highly advanced implants, e.g., heart valves and vascular grafts. In situ generated devices are an important family of devices that are formed at their site of clinical function that have distinct advantages. Among them, since they are formed within the body, they only require minimally invasive procedures, avoiding the pain and risks associated with open surgery. These devices also display enhanced conformability to local tissues and can reach sites that otherwise are inaccessible. This review aims at shedding light on the unique features of in situ generated devices and to underscore leading trends in the field, as they are reflected by key developments recently in the field over the last several years. Since the uniqueness of these devices stems from their in situ generation, the way they are formed is crucial. It is because of this fact that in this review, the medical devices are classified depending on whether their in situ generation entails chemical or physical phenomena.

Recent advances in degradable lactide-based shape-memory polymers

Biodegradable polymers are versatile polymeric materials that have a high potential in biomedical applications avoiding subsequent surgeries to remove, for example, an implanted device. In the past decade, significant advances have been achieved with poly(lactide acid) (PLA)-based materials, as they can be equipped with an additional functionality, that is, a shape-memory effect (SME). Shape-memory polymers (SMPs) can switch their shape in a predefined manner upon application of a specific external stimulus. Accordingly, SMPs have a high potential for applications ranging from electronic engineering, textiles, aerospace, and energy to biomedical and drug delivery fields based on the perspectives of new capabilities arising with such materials in biomedicine. This study summarizes the progress in SMPs with a particular focus on PLA, illustrates the design of suitable homo- and copolymer structures as well as the link between the (co)polymer structure and switching functionality, and describes recent advantages in the implementation of novel switching phenomena into SMP technology.

Tissue adhesives for meniscus tear repair: an overview of current advances and prospects for future clinical solutions

Menisci are crucial structures in the knee joint as they play important functions in load transfer, maintaining joint stability and in homeostasis of articular cartilage. Unfortunately, ones of the most frequently occurring knee injuries are meniscal tears. Particularly tears in the avascular zone of the meniscus usually do not heal spontaneously and lead to pain, swelling and locking of the knee joint. Eventually, after a (partial) meniscectomy, they will lead to osteoarthritis. Current treatment modalities to repair tears and by that restore the integrity of the native meniscus still carry their drawbacks and a new robust solution is desired. A strong tissue adhesive could provide such a solution and could potentially improve on sutures, which are the current gold standard. Moreover, a glue could serve as a carrier for biological compounds known to enhance tissue healing. Only few tissue adhesives, e.g., Dermabond(®) and fibrin glue, are already successfully used in clinical practice for other applications, but are not considered suitable for gluing meniscus tissue due to their sub-optimal mechanical properties or toxicity. There is a growing interest and research field focusing on the development of novel polymer-based tissue adhesives, but up to now, there is no material specially designed for the repair of meniscal tears. In this review, we discuss the current clinical gold standard treatment of meniscal tears and present an overview of new developments in this field. Moreover, we discuss the properties of different tissue adhesives for their potential use in meniscal tear repair. Finally, we formulate recommendations regarding the design criteria of material properties and adhesive strength for clinically applicable glues for meniscal tears.

Study on the shape memory effects of poly(L-lactide-co-epsilon-caprolactone) biodegradable polymers

The thermal properties, crystalline structure and shape memory effects of poly(L-lactide) (PLLA) and poly(L-lactide-co-epsilon-caprolactone) (PCLA) copolymers are systematically investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and tensile tests. The effects of the deformation strain on the shape recovery rate and recovery stress are also revealed. The polymers have the PLLA crystal and the amorphous phase, which are served as the fixed phase and reversible phase, respectively. The shape recovery rate and the recovery stress are significantly affected by the compositions and the deformation strain. With the increase of the deformation strain, the shape recovery rate decrease and higher shape recovery rate can be obtained in the polymers which have higher epsilon-CL content. However, the variation of recovery stress with the deformation strain is quite different and the maximum recovery stress of all polymers exceeds 3 MPa.

Influence of Peripheral Hydrogen Bonding on the Mechanical Properties of Photo-Cross-Linked Star-Shaped Poly(d,l-lactide) Networks

Four-arm, star-shaped poly(D,L-lactide) (PDLLA) oligomers of controlled molar mass and narrow molar mass distribution were successfully synthesized by use of an ethoxylated pentaerythritol initiator. Derivatization of the terminal hydroxyl groups with either methacrylic anhydride (MAAH) or 2-isocyanatoethyl methacrylate (IEM) to yield PDLLA-M (M = methacrylate end group) and PDLLA-UM (UM = urethane methacrylate end group), respectively, was monitored by in situ Fourier transform infrared (FTIR) spectroscopy. Photo-cross-linking of the functional oligomers yielded networks with high gel contents (>95%). The glass transition temperature (T(g)) of these networks was strongly dependent on prepolymer molar mass, and networks based on low molar mass precursors were more rigid than the networks obtained from higher molar mass oligomers. The tensile strength (TS) and Young's modulus of the PDLLA-M samples, approximately 7 and 17 MPa, respectively, were significantly lower than the values of 19 MPa (TS) and 113-354 MPa (Young's modulus) for the PDLLA-UM samples. The introduction of terminal hydrogen-bonding sites that were adjacent to the photo-cross-linking site resulted in higher performance poly(lactide)-based bioadhesives.