Injectable and thermosensitive TGF-β1-loaded PCEC hydrogel system for in vivo cartilage repair

Tissue engineering strategies hold promise for the repair of articular cartilage injury

Articular cartilage damage and wear can result in cartilage degeneration, ultimately culminating in osteoarthritis. Current surgical interventions offer limited capacity for cartilage tissue regeneration and offer only temporary alleviation of symptoms. Tissue engineering strategies are increasingly recognized as promising modalities for cartilage restoration. Currently, various biological scaffolds utilizing tissue engineering materials are extensively employed in both fundamental and clinical investigations of cartilage repair. In order to optimize the cartilage repair ability of tissue engineering scaffolds, researchers not only optimize the structure and properties of scaffolds from the perspective of materials science and manufacturing technology to enhance their histocompatibility, but also adopt strategies such as loading cells, cytokines, and drugs to promote cartilage formation. This review provides an overview of contemporary tissue engineering strategies employed in cartilage repair, as well as a synthesis of existing preclinical and clinical research. Furthermore, the obstacles faced in the translation of tissue engineering strategies to clinical practice are discussed, offering valuable guidance for researchers seeking to address these challenges.

Hydrogel-Based Growth Factor Delivery Platforms: Strategies and Recent Advances

Growth factors play a crucial role in regulating a broad variety of biological processes and are regarded as powerful therapeutic agents in tissue engineering and regenerative medicine in the past decades. However, their application is limited by their short half-lives and potential side effects in physiological environments. Hydrogels are identified as having the promising potential to prolong the half-lives of growth factors and mitigate their adverse effects by restricting them within the matrix to reduce their rapid proteolysis, burst release, and unwanted diffusion. This review discusses recent progress in the development of growth factor-containing hydrogels for various biomedical applications, including wound healing, brain tissue repair, cartilage and bone regeneration, and spinal cord injury repair. In addition, the review introduces strategies for optimizing growth factor release including affinity-based delivery, carrier-assisted delivery, stimuli-responsive delivery, spatial structure-based delivery, and cellular system-based delivery. Finally, the review presents current limitations and future research directions for growth factor-delivering hydrogels.

Fabricating the cartilage: recent achievements

This review aims to describe the most recent achievements and provide an insight into cartilage engineering and strategies to restore the cartilage defects. Here, we discuss cell types, biomaterials, and biochemical factors applied to form cartilage tissue equivalents and update the status of fabrication techniques, which are used at all stages of engineering the cartilage. The actualized concept to improve the cartilage tissue restoration is based on applying personalized products fabricated using a full cycle platform: a bioprinter, a bioink consisted of ECM-embedded autologous cell aggregates, and a bioreactor. Moreover, in situ platforms can help to skip some steps and enable adjusting the newly formed tissue in the place during the operation. Only some achievements described have passed first stages of clinical translation; nevertheless, the number of their preclinical and clinical trials is expected to grow in the nearest future.

Stimuli-responsive hydrogels: smart state of-the-art platforms for cardiac tissue engineering

Biomedicine and tissue regeneration have made significant advancements recently, positively affecting the whole healthcare spectrum. This opened the way for them to develop their applications for revitalizing damaged tissues. Thus, their functionality will be restored. Cardiac tissue engineering (CTE) using curative procedures that combine biomolecules, biomimetic scaffolds, and cells plays a critical part in this path. Stimuli-responsive hydrogels (SRHs) are excellent three-dimensional (3D) biomaterials for tissue engineering (TE) and various biomedical applications. They can mimic the intrinsic tissues' physicochemical, mechanical, and biological characteristics in a variety of ways. They also provide for 3D setup, adequate aqueous conditions, and the mechanical consistency required for cell development. Furthermore, they function as competent delivery platforms for various biomolecules. Many natural and synthetic polymers were used to fabricate these intelligent platforms with innovative enhanced features and specialized capabilities that are appropriate for CTE applications. In the present review, different strategies employed for CTE were outlined. The light was shed on the limitations of the use of conventional hydrogels in CTE. Moreover, diverse types of SRHs, their characteristics, assembly and exploitation for CTE were discussed. To summarize, recent development in the construction of SRHs increases their potential to operate as intelligent, sophisticated systems in the reconstruction of degenerated cardiac tissues.

Nanomedicines Reprogram Synovial Macrophages by Scavenging Nitric Oxide and Silencing CA9 in Progressive Osteoarthritis

Osteoarthritis (OA) is a progressive joint disease characterized by inflammation and cartilage destruction, and its progression is closely related to imbalances in the M1/M2 synovial macrophages. A two-pronged strategy for the regulation of intracellular/extracellular nitric oxide (NO) and hydrogen protons for reprogramming M1/M2 synovial macrophages is proposed. The combination of carbonic anhydrase IX (CA9) siRNA and NO scavenger in "two-in-one" nanocarriers (NAHA-CaP/siRNA nanoparticles) is developed for progressive OA therapy by scavenging NO and inhibiting CA9 expression in synovial macrophages. In vitro experiments demonstrate that these NPs can significantly scavenge intracellular NO similar to the levels as those in the normal group and downregulate the expression levels of CA9 mRNA (≈90%), thereby repolarizing the M1 macrophages into the M2 phenotype and increasing the expression levels of pro-chondrogenic TGF-β1 mRNA (≈1.3-fold), and inhibiting chondrocyte apoptosis. Furthermore, in vivo experiments show that the NPs have great anti-inflammation, cartilage protection and repair effects, thereby effectively alleviating OA progression in both monoiodoacetic acid-induced early and late OA mouse models and a surgical destabilization of medial meniscus-induced OA rat model. Therefore, the siCA9 and NO scavenger "two-in-one" delivery system is a potential and efficient strategy for progressive OA treatment.

Prevention and Repair of Ultraviolet B-Induced Skin Damage in Hairless Mice via Transdermal Delivery of Growth Factors Immobilized in a Gel-in-Oil Nanoemulsion

Ultraviolet (UV) radiation from the sun or artificial sources is one of the primary causes of skin damage, including sunburns, tanning, erythema, and skin cancer. Among the three different types of UV rays, UVB rays have a medium wavelength that can penetrate the epidermal layer of the skin, resulting in sunburn, suntan, blistering, and melanoma in case of chronic exposure. This study aimed to evaluate the preventive and therapeutic effects of a gel-in-oil nanogel dispersion (G/O-NGD) as a transdermal delivery biomolecular carrier for skin damage caused by UVB light. The efficacy of this carrier against UVB-induced skin damage was investigated in vivo by delivering different growth factors (GFs) encapsulated in a G/O-NGD. Artificial UVB light was used to induce skin damage in nude mice, followed by the transdermal application of five GF [vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), transforming growth factor (TGF)-1, and insulin-like growth factor (IGF)-α]-immobilized G/O-NGD. Among these GFs, VEGF and bFGF promoted angiogenesis, while EGF, TGF-1, and IGF-α promoted the repair and regeneration of damaged cells. The results showed that G/O-NGD was superior to heparin-immobilized G/O-NGD in reducing UVB-induced skin damage, such as erythema, epidermal water reduction, inflammation, and dermis thickening. In addition, G/O-NGD could prevent and treat abnormal follicle proliferation caused by UVB rays and exhibited potential to repair lipid glands. Overall, our results demonstrate the potential of G/O-NGDs for the treatment of UVB-induced skin damage.

Adhesive hydrogels in osteoarthritis: from design to application

Osteoarthritis (OA) is the most common type of degenerative joint disease which affects 7% of the global population and more than 500 million people worldwide. One research frontier is the development of hydrogels for OA treatment, which operate either as functional scaffolds of tissue engineering or as delivery vehicles of functional additives. Both approaches address the big challenge: establishing stable integration of such delivery systems or implants. Adhesive hydrogels provide possible solutions to this challenge. However, few studies have described the current advances in using adhesive hydrogel for OA treatment. This review summarizes the commonly used hydrogels with their adhesion mechanisms and components. Additionally, recognizing that OA is a complex disease involving different biological mechanisms, the bioactive therapeutic strategies are also presented. By presenting the adhesive hydrogels in an interdisciplinary way, including both the fields of chemistry and biology, this review will attempt to provide a comprehensive insight for designing novel bioadhesive systems for OA therapy.

Management of bone diseases: looking at scaffold-based strategies for drug delivery

The bone tissue can regenerate itself completely and continuously; however, large-scale bone defects may overpower this self-regenerative process. Furthermore, the aging population, the increment in obesity incidence, and the sedentary lifestyles are serious risk factors for bone diseases' development which are associated with the self-regenerative process's failure, high morbidity, and mortality rates. Thus, there is an ever-growing need for strategic approaches targeting bone replacement, its remodelling, and its regeneration. Bone scaffolds have successfully been used as synthetic bone grafts for many years, yet recent bone tissue engineering strategies attempt to explore their multifunctionality by investigating them as drug delivery systems. Bone diseases' treatments can be substantially difficult due to the avascular nature of the surrounding cartilage; thus, targeted drug delivery to the bone can be advantageous: it provides local high drug concentrations and minimizes adverse effects while securing a space for new, healthy tissue growth. Despite the promising scientific progress, studies underlining bone scaffolds' use as local drug delivery systems are not abundant. Hence, this work reviews bone scaffolds' therapeutic interest for local drug delivery in five distinct bone disorders-osteomyelitis, osteoporosis, osteoarthritis, osteosarcoma, and cancer bone metastasis. Additionally, it presents the challenges of this possible therapeutic approach and its future perspectives. Albeit bone scaffolds present therapeutic benefits by acting as drug delivery systems, further pre-clinical and clinical assessments are needed to strengthen their understanding and enable research evidence translation into clinical practice. The mismatch between scientific evolution and regulatory frameworks remains one of the major future challenges.

Targeting Inflammation and Regeneration: Scaffolds, Extracellular Vesicles, and Nanotechnologies as Cell-Free Dual-Target Therapeutic Strategies

Osteoarthritis (OA) affects over 250 million people worldwide and despite various existing treatment strategies still has no cure. It is a multifactorial disease characterized by cartilage loss and low-grade synovial inflammation. Focusing on these two targets together could be the key to developing currently missing disease-modifying OA drugs (DMOADs). This review aims to discuss the latest cell-free techniques applied in cartilage tissue regeneration, since they can provide a more controllable approach to inflammation management than the cell-based ones. Scaffolds, extracellular vesicles, and nanocarriers can be used to suppress inflammation, but they can also act as immunomodulatory agents. This is consistent with the latest tissue engineering paradigm, postulating a moderate, controllable inflammatory reaction to be beneficial for tissue remodeling and successful regeneration.

In situ regeneration of nasal septal defects using acellular cartilage enhanced with platelet-derived growth factor

Nasal septum defects can currently only be reconstructed using autologous cartilage grafts. In this study, we examine the reconstruction of septal cartilage defects in a rabbit model using porcine decellularized nasal septal cartilage (DNSC) functionalized with recombinant platelet-derived growth factor-BB (PDFG-BB). The supportive function of the transplanted DNSC was estimated by the degree of septum deviation and shrinkage using magnetic resonance imaging (MRI). The biocompatibility of the transplanted scaffolds was evaluated by histology according to international standards. A study group with an autologous septal transplant was used as a reference. In situ regeneration of cartilage defects was assessed by histological evaluation 4 and 16 weeks following DNSC transplantation. A study group with non-functionalized DNSC was introduced for estimation of the effects of PDFG-BB functionalization. DNSC scaffolds provided sufficient structural support to the nasal septum, with no significant shrinkage or septal deviations as evaluated by the MRI. Biocompatibility analysis after 4 weeks revealed an increased inflammatory reaction of the surrounding tissue in response to DNSC as compared to the autologous transplants. The inflammatory reaction was, however, significantly attenuated after 16 weeks in the PDGF-BB group whereas only a slight improvement of the biocompatibility score was observed in the untreated group. In situ regeneration of septal cartilage, as evidenced by the degradation of the DNSC matrix and production of neocartilage, was observed in both experimental groups after 16 weeks but was more pronounced in the PDFG-BB group. Overall, DNSC provided structural support to the nasal septum and stimulated in situ regeneration of the cartilage tissue. Furthermore, PDFG-BB augmented the regenerative potential of DNSC and enhanced the healing process, as demonstrated by reduced inflammation after 16 weeks.

PCL-PEG copolymer based injectable thermosensitive hydrogels

A number of stimuli-responsive-based hydrogels has been widely explored in biomedical applications in the last few decades because of their excellent biodegradability and biocompatibility. The development of synthetic chemistry and materials science leads to the emergence of in situ stimuli-responsive hydrogels. In this regard, several synthetic and natural polymers have been synthesized and utilized to prepare temperature-sensitive in situ forming hydrogels. This could be best used via injections as temperature stimulus could trigger in situ hydrogels gelation and swelling behaviors. There are many smart polymers available for the formulation of the in situ based thermoresponsive injectable hydrogel. Among these, poly (ε-caprolactone) (PCL) polymer has been recognized and approved by the FDA for numerous biomedical applications. More specifically, the PCL is coupled with polyethylene glycol (PEG) to obtain amphiphilic thermosensitive "smart" copolymers (PCL-PEG), to form rapid and reversible physical gelation behavior. However, the chemical structure of the copolymer is a critical aspect in determining water solubility, thermo-gelation behavior, drug release rate, degradation rate, and the possibility to deliver a diverse range of drugs. In this review, we have highlighted the typical PCL-PEG-based thermosensitive injectable hydrogels progress in the last decade for tissue engineering and localized drug delivery applications to treat various diseases. Additionally, the impact of molecular weight of PCL-PEG upon gelling behavior has also been critically highlighted for optimum hydrogels properties for potential pharmaceutical and biomedical applications.

Smart/stimuli-responsive hydrogels: Cutting-edge platforms for tissue engineering and other biomedical applications

Recently, biomedicine and tissue regeneration have emerged as great advances that impacted the spectrum of healthcare. This left the door open for further improvement of their applications to revitalize the impaired tissues. Hence, restoring their functions. The implementation of therapeutic protocols that merge biomimetic scaffolds, bioactive molecules, and cells plays a pivotal role in this track. Smart/stimuli-responsive hydrogels are remarkable three-dimensional (3D) bioscaffolds intended for tissue engineering and other biomedical purposes. They can simulate the physicochemical, mechanical, and biological characters of the innate tissues. Also, they provide the aqueous conditions for cell growth, support 3D conformation, provide mechanical stability for the cells, and serve as potent delivery matrices for bioactive molecules. Many natural and artificial polymers were broadly utilized to design these intelligent platforms with novel advanced characteristics and tailored functionalities that fit such applications. In the present review, we highlighted the different types of smart/stimuli-responsive hydrogels with emphasis on their synthesis scheme. Besides, the mechanisms of their responsiveness to different stimuli were elaborated. Their potential for tissue engineering applications was discussed. Furthermore, their exploitation in other biomedical applications as targeted drug delivery, smart biosensors, actuators, 3D and 4D printing, and 3D cell culture were outlined. In addition, we threw light on smart self-healing hydrogels and their applications in biomedicine. Eventually, we presented their future perceptions in biomedical and tissue regeneration applications. Conclusively, current progress in the design of smart/stimuli-responsive hydrogels enhances their prospective to function as intelligent, and sophisticated systems in different biomedical applications.

Recombinant Human Bone Morphogenic Protein-2 Immobilized Fabrication of Magnesium Functionalized Injectable Hydrogels for Controlled-Delivery and Osteogenic Differentiation of Rat Bone Marrow-Derived Mesenchymal Stem Cells in Femoral Head Necrosis Repair

Femoral head necrosis (FHN) is a clinically progressive disease that leads to overwhelming complications without an effective therapeutic approach. In recent decades, transplantation of mesenchymal stem cells (MSCs) has played a promising role in the treatment of FHN in the initial stage; however, the success rate is still low because of unsuitable cell carriers and abridged osteogenic differentiation of the transplanted MSCs. Biopolymeric-derived hydrogels have been extensively applied as effective cell carriers and drug vesicles; they provide the most promising contributions in the fields of tissue engineering and regenerative medicine. However, the clinical potential of hydrogels may be limited because of inappropriate gelation, swelling, mechanical characteristics, toxicity in the cross-linking process, and self-healing ability. Naturally, gelated commercial hydrogels are not suitable for cell injection and infiltration because of their static network structure. In this study, we designed a novel thermogelling injectable hydrogel using natural silk fibroin-blended chitosan (CS) incorporated with magnesium (Mg) substitutes to improve physical cross-linking, stability, and cell osteogenic compatibility. The presented observations demonstrate that the developed injectable hydrogels can facilitate the controlled delivery of immobilized recombinant human bone morphogenic protein-2 (rhBMP-2) and rat bone marrow-derived MSCs (rBMSCs) with greater cell encapsulation efficiency, compatibility, and osteogenic differentiation. In addition, outcomes of in vivo animal studies established promising osteoinductive, bone mineral density, and bone formation rate after implantation of the injectable hydrogel scaffolds. Therefore, the developed hydrogels have great potential for clinical applications of FHN therapy.

Therapeutic application of 3B-PEG injectable hydrogel/Nell-1 composite system to temporomandibular joint osteoarthritis

This study aims to construct a composite system of the tri-block polyethylene glycol injectable hydrogel (3B-PEG IH) and neural epithelial growth factor-like protein 1 (Nell-1), and to analyze its therapeutic effect on temporomandibular joint osteoarthritis (TMJOA). Sol-gel transition temperature was measured via inverting test. The viscoelastic modulus curves was measured by rheometer. Degradation and controlled release profiles of 3B-PEG IH were drawnin vitro.In vivogel retention and biocompatibility were completed subcutaneously on the back of rats. After primary chondrocytes were extracted and identified, the cell viability in 3B-PEG IH was measured. Evaluation of gene expression in hydrogel was performed by real-time polymerase chain reaction. TMJOA rabbits were established by intra-articular injection of type II collagenase. Six weeks after composite systems being injected, gross morphological score, micro-CT, histological staining and grading were evaluated. The rusults showed that different types of 3B-PEG IH all reached a stable gel state at 37 °C and could support the three-dimensional growth of chondrocytes, but poly(lactide-co-caprolactone)-block-poly(ethyleneglycol)-block-poly(lactide-co-caprolactone) (PLCL-PEG-PLCL) hydrogel had a wider gelation temperature range and better hydrolytic stability for about 4 weeks. Its controlled release curve is closest to the zero-order release kinetics.In vitro, PLCL-PEG-PLCL/Nell-1 could promote the chondrogenic expression and reduce the inflammatory expression.In vivo, TMJOA rabbits were mainly characterized by the disorder of cartilage structure and the destruction of subchondral bone. However, PLCL-PEG-PLCL/Nell-1 could reverse the destruction of the subchondral trabecula, restore the fibrous and proliferative layers of the surface, and reduce the irregular hyperplasia of fibrocartilage layer. In conclusion, by comparing the properties of different 3B-PEG IH, 20 wt% PLCL-PEG-PLCL hydrogel was selected as the most appropriate material. PLCL-PEG-PLCL/Nell-1 composite could reverse osteochondral damage caused by TMJOA, Nfatc1-Runx3 signaling pathway may play a role in it. This study may provide a novel, minimally-invasive therapeutic strategy for the clinical treatment of TMJOA.

Enhanced efficacy of transforming growth factor-β1 loaded an injectable cross-linked thiolated chitosan and carboxymethyl cellulose-based hydrogels for cartilage tissue engineering

Growth factors (GFs) are soluble proteins extracellular that control a wide range of cellular processes as well as tissue regeneration. While transforming growth factor beta-1 (TGF-β1) promotes chondrogenesis, its medical use is restricted by its potential protein instability, which necessitates high doses of the protein, which can result in adverse side effects such as inefficient cartilage formation. In this work, we have developed a novel hydrogel composite based on the polymer, cross-linked thiolated chitosan; TCS and carboxymethyl cellulose; CMC (TCS/CMC) hydrogel system was utilized as injectable TGF-β1 carriers for cartilage tissue engineering applications. Rheological measurements showed that the elastic modulus of TCS/CMC hydrogels with an optimized CMC concentration could reach around 2.5 kPa or higher than their respective viscous modulus, indicating that they behaved like strong hydrogels. Crosslinking significantly alters the overall network distribution, surface morphology, pore size, porosity, gelation time, swelling ratio, water content, and in vitro degradation of the TCS/CMC hydrogels. TCS/CMC hydrogels maintain more than 90% of their weight and retain their original form after 21 days. TGF-β1 released marginally from TCS/CMC hydrogels as incubation time increased, up to 21 days, with around 18.6 ± 0.9% of the drug stored inside the TCS/CMC hydrogels. On day 21, BMSC treated with TGF-β1 in medium or TGF-β1-loaded TCS/CMC hydrogels grew faster than the other groups. For in vivo cartilage repair, full-thickness cartilage defects were induced on rat knees for 8 weeks. The optimal ability of this novel TGF-β1-loaded TCS/CMC hydrogel system was further demonstrated by histological analysis, resulting in a novel therapeutic strategy for repairing articular cartilage defects.Research HighlightsAn in situ forming and injectable thiolated chitosan and carboxymethyl cellulose hydrogel was fabricated for cartilage tissue engineering.TCS/CMC displays suitable gelation time with high swelling ratio, tunable mechanical properties and highly porous.TGF-β1-loaded-TCS/CMC hydrogels showed maximum drug release activity.TGF-β1-loaded-TCS/CMC hydrogels had good biocompatibility to articular chondrocytes.An injectable TCS/CMC/TGF-β1 hydrogel is a promising material system for cartilage tissue engineering.

Synthesis and Characterization of New Biodegradable Injectable Thermosensitive Smart Hydrogels for 5-Fluorouracil Delivery

In this paper, injectable, thermosensitive smart hydrogel local drug delivery systems (LDDSs) releasing the model antitumour drug 5-fluorouracil (5-FU) were developed. The systems were based on biodegradable triblock copolymers synthesized via ring opening polymerization (ROP) of ε-caprolactone (CL) in the presence of poly(ethylene glycol) (PEG) and zirconium(IV) acetylacetonate (Zr(acac)₄), as co-initiator and catalyst, respectively. The structure, molecular weight (M_n) and molecular weight distribution (Đ) of the synthesized materials was studied in detail using nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) techniques; the optimal synthesis conditions were determined. The structure corresponded well to the theoretical assumptions. The produced hydrogels demonstrated a sharp sol–gel transition at temperature close to physiological value, forming a stable gel with good mechanical properties at 37 °C. The kinetics and mechanism of in vitro 5-FU release were characterized by zero order, first order, Higuchi and Korsmeyer–Peppas mathematical models. The obtained results indicate good release control; the kinetics were generally defined as first order according to the predominant diffusion mechanism; and the total drug release time was approximately 12 h. The copolymers were considered to be biodegradable and non-toxic; the resulting hydrogels appear to be promising as short-term LDDSs, potentially useful in antitumor therapy.

A novel intramural TGF β 1 hydrogel delivery method to decrease murine abdominal aortic aneurysm and rat aortic pseudoaneurysm formation and progression

OBJECTIVES

Aneurysms are generally the result of dilation of all 3 layers of the vessel wall, and pseudoaneurysms are the result of localized extravasation of blood that is contained by surrounding tissue. Since there is still no recommended protocol to decrease aneurysm formation and progression, we hypothesised that intramural delivery of TGF β1 hydrogel can decrease aneurysm and pseudoaneurysm formation and progression.

MATERIALS

Male C57BL/6 J mice (12-14 wk), SD rats (200 g) and pig abdominal aortas were used, and hydrogels were fabricated by the interaction of sodium alginate (SA), hyaluronic acid (HA) and CaCO3.

METHODS

A CaCl2 adventitial incubation model in mice and a decellularized human great saphenous vein patch angioplasty model in rats were used. TGF β1 hydrogel was intramurally delivered after CaCl2 incubation in mice; at day 7, the abdomen in some mice was reopened, and TGF β1 hydrogel was injected intramurally into the aorta. In rats, TGF β1 hydrogel was delivered intramurally after patch angioplasty completion. Tissues were harvested at day 14 and analysed by histology and immunohistochemistry staining. The pig aorta was also intramurally injected with hydrogel.

RESULTS

In mice, rhodamine hydrogel was still found between the medium and adventitia at day 14. In the mouse aneurysm model, there was a thicker wall and smaller amount of elastin breaks in the TGF β1 hydrogel-delivered groups both at day 0 and day 7 after CaCl2 incubation, and there were larger numbers of p-smad2- and TAK1-positive cells in the TGF β1 hydrogel-injected groups. In the rat decellularized human saphenous vein patch pseudoaneurysm model, there was a higher incidence of pseudoaneurysm formation when the patch was decellularized using 3% SDS, and delivery of TGF β1 hydrogel could effectively decrease the formation of pseudoaneurysm formation and increase p-smad2 and TAK1 expression. In pig aortas, hydrogels can be delivered between the medium and adventitia easily and successfully.

CONCLUSIONS

Intramural delivery of TGF β1 hydrogel can effectively decease aneurysm and pseudoaneurysm formation and progression in both mice and rats, and pig aortas can also be successfully intramurally injected with hydrogel. This technique may be a promising drug delivery method and therapeutic choice to decrease aneurysm and pseudoaneurysm formation and progression in the clinic.

Research progress on tissue engineering in repairing tempomandibular joint

Temporomandibular joint osteoarthritis (TMJOA) is mainly manifested as perforation of temporomandibular joint disc (TMJD) and destruction of condylar osteochondral complex (COCC). In recent years, tissue engineering technology has become one of the effective strategies in repairing this damage. With the development of scaffold material technology, composite scaffolds have become an important means to optimize the performance of scaffolds with the combined advantages of natural materials and synthetic materials. The gelling method with the minimally invasive concept can greatly solve the problems of surgical trauma and material anastomosis, which is beneficial to the clinical transformation of temporomandibular joint tissue engineering. Extracellular matrix scaffolds technology can solve the problem of scaffold source and maximize the simulation of the extracellular environment, which provides an important means for the transformation of temporo joint tissue engineering to animal level. Due to the limitation of the source and amplification of costal chondrocytes, the use of mesenchymal stem cells from different sources has been widely used for temporomandibular joint tissue engineering. The fibrochondral stem cells isolated from surface layer of articular cartilage may provide one more suitable cell source. Transforming growth factor β superfamily, due to its osteochondrogenesis activity has been widely used in tissue engineering, and platelet-rich derivative as a convenient preparation of compound biological factor, gradually get used in temporomandibular joint tissue engineering. With the deepening of research on extracellular microenvironment and mechanical stimulation, mesenchymal stem cells, exosomes and stress stimulation are increasingly being used to regulate the extracellular microenvironment. In the future, the combination of complex bioactive factors and certain stress stimulation may become a trend in the temporomandibular joint tissue engineering research. In this article, the progress on tissue engineering in repairing COCC and TMJD, especially in scaffold materials, seed cells and bioactive factors, are reviewed, so as to provide information for future research design and clinical intervention.

3D composite engineered using supercritical CO2 decellularized porcine cartilage scaffold, chondrocytes, and PRP: Role in articular cartilage regeneration

At present, no definitive treatment for articular cartilage defects has been perfected. Most of the previous treatments involved multiple drilling and microfracture over defect sites with repair-related substances, which poses a limited therapeutic effect. End-stage therapy includes artificial knee joint replacement. In this study, we prepared a novel decellularized natural cartilage scaffold from porcine articular cartilage by supercritical CO₂ extraction technology and three-dimensional (3D) composites made using decellularized porcine cartilage graft (dPCG) as scaffolds, platelet-rich plasma (PRP), thrombin as signals and chondrocytes as cells for the treatment of articular cartilage defects. In this study, in vitro and in vivo cartilage regeneration and the expression of chondrogenic markers were examined. Decellularized cartilage graft (dPCG) was evaluated for the extent of cell and DNA removal. Residual cartilage ECM structure was confirmed to be type II collagen by SDS PAGE and immunostaining. The new 3D composite with dPCG (100 mg and 2 × 10⁶ chondrocytes) scaffold promotes chondrogenic marker expression in vitro. We found that the in vivo 3D composite implanted cartilage defect showed significant regeneration relative to the blank and control implant. Immunohistochemical staining showed increase of expression including Collagen type II and aggrecan in 3D composite both in vitro and in vivo studies. In this study, the bioengineered 3D composite by combining dPCG scaffold, chondrocytes, and PRP facilitated the chondrogenic marker expression in both in vitro and in vivo models with accelerated cartilage regeneration. This might serve the purpose of clinical treatment of large focal articular cartilage defects in humans in the near future.

Innovative Tissue-Engineered Strategies for Osteochondral Defect Repair and Regeneration: Current Progress and Challenges

Clinical treatments for the repair of osteochondral defects (OCD) are merely palliative, not completely curative, and thus enormously unfulfilled challenges. With the in-depth studies of biology, medicine, materials, and engineering technology, the conception of OCD repair and regeneration should be renewed. During the past decades, many innovative tissue-engineered approaches for repairing and regenerating damaged osteochondral units have been widely explored. Various scaffold-free and scaffold-based strategies, such as monophasic, biphasic, and currently fabricated multiphasic and gradient architectures have been proposed and evaluated. Meanwhile, progenitor cells and tissue-specific cells have also been intensively investigated in vivo as well as ex vivo. Concerning bioactive factors and drugs, they have been combined with scaffolds and/or living cells, and even released in a spatiotemporally controlled manner. Although tremendous progress has been achieved, further research and development (R&D) is needed to convert preclinical outcomes into clinical applications. Here, the osteochondral unit structure, its defect classifications, and diagnosis are summarized. Commonly used clinical reparative techniques, tissue-engineered strategies, emerging 3D-bioprinting technologies, and the status of their clinical applications are discussed. Existing challenges to translation are also discussed and potential solutions for future R&D directions are proposed.

Crystallization enhanced thermal-sensitive hydrogels of PCL-PEG-PCL triblock copolymer for 3D printing

Temperature-sensitive hydrogels with mild gel-forming process, good biocompatibility and biodegradability have been widely studied as bioinks and biomaterial inks for 3D bioprinting. However, the hydrogels synthesized via copolymerization of aliphatic polyesters and polyethylene glycols have low mechanical strength and cannot meet the needs of 3D printing. In this paper, we propose a strategy of enhancing the strength of hydrogels by introducing crystallization between blocks to meet the requirements of 3D bioprinting inks. A series of polycaprolactone-polyethylene glycol-polycaprolactone (PCL-PEG-PCL) triblock polymers were prepared by ring-opening polymerization, of which the strong crystallinity of polycaprolactone blocks improved the printability and enhanced the mechanical properties of the ink. It was found that the resulted hydrogels were temperature-responsive, and the PCL blocks could form a crystalline phase in the state of the hydrogel, thereby significantly increasing the modulus of the hydrogel. Moreover, the mechanical strength of the hydrogel could be adjusted by changing the composition ratio of each block of the copolymer. The 3D printing results showed that the PCL-PEG-PCL hydrogel with crystallinity can not only be extruded and printed via temperature adjustment, but also the three-dimensional structure can be effectively maintained after 3D printing. The gels demonstrated good cell compatibility, and the cell survival rate was maintained at a high level.

Biphasic Double-Network Hydrogel With Compartmentalized Loading of Bioactive Glass for Osteochondral Defect Repair

Periarticular injury usually causes the defects of superficial cartilage and the underlying subchondral bone. Although some efficacious outcomes have been achieved by the existing therapeutic methods both in clinics and research, like symptomatic treatment, microfracture surgery, and tissue engineering technology, they still present specific disadvantages and complications. To improve this situation, we designed a biphasic (bi-) scaffold aiming to repair the structure of cartilage and subchondral bone synchronously. The scaffold consisted of a superior double-network (DN) hydrogel layer and a lower bioactive glass (BG) reinforced hydrogel layer, and the DN hydrogel included glycol chitosan (GC) and dibenzaldhyde functionalized poly(ethylene oxide) network, and sodium alginate (Alg) and calcium chloride (CaCl₂) network. To investigate its effectiveness, we applied this biphasic scaffold to repair osteochondral full-thickness defects in rabbit models. We set up six observation groups in total, including Untreated group, Microfracture group, BG only group, DN gel group, bi-DN gel group, and bi-DN/TGF-β gel group. With a follow-up period of 24 weeks, we evaluated the treatment effects by gross observation, micro-CT scan and histological staining. Besides, we further fulfilled the quantitative analysis of the data from ICRS score, O’Driscoll score and micro-CT parameters. The results revealed that neat GC/Alg DN hydrogel scaffold was only conductive to promoting cartilage regeneration and neat BG scaffold merely showed the excellent ability to reconstruct subchondral bone. While the biphasic scaffold performed better in repairing osteochondral defect synchronously, exhibiting more well-integrated cartilage-like tissue with positive staining of toluidine blue and col II immunohistochemistry, and more dense trabecular bone connecting closely with the surrounding host bone. Therefore, this method possessed the clinical application potential in treating articular injury, osteochondral degeneration, osteochondral necrosis, and sclerosis.

A moldable thermosensitive hydroxypropyl chitin hydrogel for 3D cartilage regeneration in vitro and in vivo

Because of poor self-repair capacity, the repair of cartilage defect is always a great challenge in clinical treatment. In vitro cartilage regeneration provides a potential strategy for functional reconstruction of cartilage defect. Hydrogel has been known as an ideal cartilage regeneration scaffold. However, to date, in vitro cartilage regeneration based on hydrogel has not achieved satisfactory results. The current study explored the feasibility of in vitro 3D cartilage regeneration based on a moldable thermosensitive hydroxypropyl chitin (HPCH) hydrogel and its in vivo fate. The thermosensitive HPCH hydrogel was prepared and characterized. Goat auricular chondrocytes were encapsulated into the HPCH hydrogel to form a chondrocyte-hydrogel construct. The constructs were injected subcutaneously into nude mice or molded into different shapes for in vitro chondrogenic culture followed by in vivo implantation. The results demonstrated that the HPCH hydrogel possessed satisfactory gelation properties (gelation time < 18 s at 37 °C), biocompatibility (cell amount almost doubled within one week), and the ability to be applied as an injectable hydrogel for cartilage regeneration. All the constructs of in vitro culture basically maintained their original shapes (in vitro to initial: 110.8%) and displayed typical cartilaginous features with abundant lacunae and cartilage specific matrix deposition. These in vitro samples became more mature with prolonged in vivo implantation and largely maintained the original shape (in vivo to in vitro: 103.5%). These results suggested that the moldable thermosensitive HPCH hydrogel can serve as a promising scaffold for cartilage regeneration with defined shapes in vitro and in vivo. STATEMENT OF SIGNIFICANCE: Because of avascular and non-nervous characteristic of cartilage, in vitro regeneration plays an important role in reconstructing cartilage function. Hydrogel has been known as an ideal cartilage regeneration scaffold. However, to date, in vitro cartilage regeneration based on hydrogel has not achieved satisfactory results. The current study demonstrated that the chondrocyte-hydrogel construct generated by high density of chondrocytes encapsulated into a thermosensitive HPCH hydrogel could successfully regenerate in vitro typical cartilage-like tissue with defined shapes and further mature to form homogeneous cartilage with their original shapes after in vivo implantation. The current study indicated that the moldable thermosensitive HPCH hydrogel could serve as a promising scaffold for in vitro and in vivo cartilage regeneration with different shapes.

In situ Enabling Approaches for Tissue Regeneration: Current Challenges and New Developments

In situ tissue regeneration can be defined as the implantation of tissue-specific biomaterials (by itself or in combination with cells and/or biomolecules) at the tissue defect, taking advantage of the surrounding microenvironment as a natural bioreactor. Up to now, the structures used were based on particles or gels. However, with the technological progress, the materials' manipulation and processing has become possible, mimicking the damaged tissue directly at the defect site. This paper presents a comprehensive review of current and advanced in situ strategies for tissue regeneration. Recent advances to put in practice the in situ regeneration concept have been mainly focused on bioinks and bioprinting techniques rather than the combination of different technologies to make the real in situ regeneration. The limitation of conventional approaches (e.g., stem cell recruitment) and their poor ability to mimic native tissue are discussed. Moreover, the way of advanced strategies such as 3D/4D bioprinting and hybrid approaches may contribute to overcome the limitations of conventional strategies are highlighted. Finally, the future trends and main research challenges of in situ enabling approaches are discussed considering in vitro and in vivo evidence.

In situ Enabling Approaches for Tissue Regeneration: Current Challenges and New Developments

In situ tissue regeneration can be defined as the implantation of tissue-specific biomaterials (by itself or in combination with cells and/or biomolecules) at the tissue defect, taking advantage of the surrounding microenvironment as a natural bioreactor. Up to now, the structures used were based on particles or gels. However, with the technological progress, the materials' manipulation and processing has become possible, mimicking the damaged tissue directly at the defect site. This paper presents a comprehensive review of current and advanced in situ strategies for tissue regeneration. Recent advances to put in practice the in situ regeneration concept have been mainly focused on bioinks and bioprinting techniques rather than the combination of different technologies to make the real in situ regeneration. The limitation of conventional approaches (e.g., stem cell recruitment) and their poor ability to mimic native tissue are discussed. Moreover, the way of advanced strategies such as 3D/4D bioprinting and hybrid approaches may contribute to overcome the limitations of conventional strategies are highlighted. Finally, the future trends and main research challenges of in situ enabling approaches are discussed considering in vitro and in vivo evidence.

Fabrication of Nanofibrous/Xerogel Layer-by-Layer Biocomposite Scaffolds for Skin Tissue Regeneration: In Vitro Study

Skin burn wounds are a crucial issue that could reduce life quality. Although numerous effective skin products have invaded the biomedical market, most of them still demonstrate some limitations regarding their porosity, swelling and degradation behaviors, antibacterial properties, and cytotoxicity. Thus, the aim of this study is to fabricate novel trilayered asymmetric porous scaffolds that can mimic the natural skin layers. In particular, the fabricated scaffold constitutes an upper electrospun chitosan-poly(vinyl alcohol) layer and a lower xerogel layer, which is made of effective skin extracellular matrix components. Both layers are fixed together using fibrin glue as a middle layer. The results of this study revealed promising scaffold swelling capability suitable for absorbing wound exudates, followed by a constant degradable weight over time, which is appropriate for a burn wound environment. Scanning electron microscopy images revealed an average pore diameter in the range of 138.39-170.18 nm for the cross-linked electrospun mats and an average pore size of 2.29-30.62 μm for the fabricated xerogel layers. This further provided an optimum environment for fibroblast migration and proliferation. The electrospun nanofibrous layer was examined for its antibacterial properties and showed expressive complete bacterial inhibition against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacterial strains (log reduction = 3 and 2.70, respectively). Next, mouse embryonic fibroblast cytotoxicity and migration rate were investigated against the developed asymmetrical composite to assess its biocompatibility. Tissue culture experiments demonstrated significant cell proliferation and migration in the presence of the constructed scaffold (P < 0.0001). A complete wound closure was observed in vitro in the presence of the three scaffold asymmetrical layers against the mouse embryonic fibroblast. The results of this study proved superior biological characteristics of the innovative asymmetrical composite that could further replace the burned or damaged skin layers with promising potential for clinical applications.

[Preparation and evaluation of carboxymethyl chitosan/sodium alginate hydrogel for cartilage tissue engineering]

OBJECTIVE

This study aimed to optimize the preparation of carboxymethyl chitosan/sodium alginate (CMCS/OSA) compound hydrogels. This study also aimed to investigate the applicability of the hydrogels in cartilage tissue engi-neering.

METHODS

Three groups of CMCS/OSA composite hydrogels with amino-to-aldehyde ratios of 2∶1, 1∶1 and 1∶2 were prepared. The microstructure, physical properties, and cell biocompatibility of the three groups of CMCS/OSA com-posite hydrogels were evaluated. Samples were subjected to scanning electron microscopy, rheological test, adhesion tension test, swelling rate test, and cell experiments to identify the CMCS/OSA composite hydrogel with the cross-linking degree that can meet the requirements for scaffolds in cartilage tissue engineering.

RESULTS

The experimental results showed that the CMCS/OSA hydrogel with a amine-to-aldhyde ratio of 1∶1 had good porosity, suitable gelling time, strong adhesive force, stable swelling rate, and good cellular biocompatibility.

CONCLUSIONS

The CMCS/OSA compound hydrogel prepared with a 1∶1 ratio of amino and aldehyde groups has potential applications in cartilage tissue engineering.

Comparison of various reagents for preparing a decellularized porcine cartilage scaffold

Cartilage lesion repair is difficult due to the limited self-repair capability of cartilage and its lack of vascularization. Our previous study established a sandwich model for engineering cartilage with acellular cartilage sheets (ACSs) and chondrocytes. However, there is still debate over which agent achieves the optimal decellularization of cartilage sheets. In addition, changes in the extracellular matrix after decellularization are worth studying. We aimed to determine the optimal decellularization reagents and decellularization time for preparing cartilage sheets. This study compared the effects of 2 extraction chemicals [t-octylphenoxypolyethoxyethanol (Triton X-100) and sodium dodecyl sulfate (SDS)] on cartilage sheets. The sheets were soaked in various concentrations (0.1-2%) of the extraction solutions for various time periods (24-72 h). After the decellularization process with the various treatments, we examined the cell removal and preservation of the matrix components and microstructure to determine which method was the most efficient while inducing minimal damage to the perichondrium. Both protocols achieved decellularization within an acceptable time. DNA analysis showed that the reagent removed nearly all of the DNA from the cartilage sheets. The growth factor contents in the Triton X-100 samples were higher than those in the SDS samples, quantified by enzyme-linked immunosorbent assay (ELISA). Furthermore, Triton X-100 decreased the glycosaminoglycan (GAG) and increased the chondromodulin-I contents compared with SDS. The results of a Cell Counting Kit-8 (CCK-8) assay revealed that the ACSs were not cytotoxic. In conclusion, our results demonstrate that cartilage sheets decellularized by 1% SDS for 24 h or by 2% Triton X-100 for 48 h may be suitable candidate scaffolds for cartilage tissue engineering.

Review of craniofacial regeneration in China

AIM

Tissue engineering has been recognised as one of the most effective means to form a new viable tissue for medical purpose. Tissue engineering involves a combination of scaffolds, cells, suitable biochemical and physicochemical factors, and engineering and materials methods. This review covered some biomedicine, such as biomaterials, bioactive factors, and stem cells, and manufacturing technologies used in tissue engineering in the oral maxillofacial region, especially in China.

MATERIALS AND METHODS

Data for this review were identified by searches of Web of Science and PubMed, and references from relevant articles using the search terms "biomaterials", "oral tissue regeneration", "bioactive factors" and "stem cells". Only articles published in English between 2013 and 2018 were included.

CONCLUSION

The combination of stem cells, bioactive factors and 3D scaffolds could be of far-reaching significance for the future therapies in tissue repair or tissue regeneration. Furthermore, the review also mentions issues that need to be solved in the application of these biomedicines.

Thermo-Sensitive Nanomaterials: Recent Advance in Synthesis and Biomedical Applications

Progress in nanotechnology has enabled us to open many new fronts in biomedical research by exploiting the peculiar properties of materials at the nanoscale. The thermal sensitivity of certain materials is a highly valuable property because it can be exploited in many promising applications, such as thermo-sensitive drug or gene delivery systems, thermotherapy, thermal biosensors, imaging, and diagnosis. This review focuses on recent advances in thermo-sensitive nanomaterials of interest in biomedical applications. We provide an overview of the different kinds of thermoresponsive nanomaterials, discussing their potential and the physical mechanisms behind their thermal response. We thoroughly review their applications in biomedicine and finally discuss the current challenges and future perspectives of thermal therapies.

Study on the Effect of 1-Butanol Soluble Lignin on Temperature-Sensitive Gel

A protocol for the fractionation of lignin with 1-butanol as solvent has been proposed in order to improve the utilization of industry alkali lignin. 1-butanol soluble lignin (BSL) was used as a building block for temperature-sensitive hydrogel with N-isopropylacrylamide (NIPAAm) through graft polymerization. The result shows that 1-butanol fractionation is an effective method to improve the molecular weight homogeneity of lignin (PDI, 2.5 to 1.83) and increase the hydroxyl group content (0.585⁻1.793 mmol/g). The incorporation of BSL into the temperature-sensitive hydrogel can enhance the thermal stability and increase the hydrophobicity of the gel, which leads to a decrease in lower critical solution temperature (LCST). In addition, the compression strength, swelling ratio, and pore size of the gel can be adjusted by the dosage of lignin. This stimuli-responsive gel, with an LCST around 32 °C, is expected to be applied in the agricultural field as a pesticide carrier by stimulating release and absorption properties based on the change in natural environmental temperature.

Bushenhuoxue Formula Facilitates Articular Cartilage Repair and Attenuates Matrix Degradation by Activation of TGF-β Signaling Pathway

Objective

To investigate the effect and underlying mechanism of Bushenhuoxue (BSHX) formula on articular cartilage repair.

Methods

Twenty-four full-thickness cartilage defect rats were divided into two groups: model group and BSHX group (treated with BSHX formula). Macroscopic observation and histopathological study were conducted after 4- and 8-week treatment. Additionally, we also evaluated chondrocyte proliferation, extracellular matrix (ECM) deposition, cartilage degradation, and chondrocyte hypertrophy-related genes expression in chondrogenic ATDC5 cells cultured in BSHX formula-mediated serum. Moreover, we assessed aforementioned genes expression and pSMAD2/3 protein level in Tgfβr2 siRNA transfected chondrogenic ATDC5 cells in order to address whether BSHX formula exerts cartilage repairing effect through TGF-β signaling.

Results

Neocartilage regeneration promotion effect was observed in cartilage defect rats after BSHX formula treatment, with increases in Col2 and pSMAD2 and decreases in Mmp13 and Runx2. Moreover, cell proliferation, the elevated Col2a1, Aggrecan and pSMAD2/3, reduced Mmp13, Adamts5, Col10a1, and Runx2 expression were also observed in chondrogenic ATDC5 cells cultured in BSHX formula-mediated serum. Besides, the expression alteration of ECM deposition, cartilage degradation, chondrocyte hypertrophy-related genes, and pSMAD2/3 protein levels presented in Tgfβr2 downregulated chondrogenic ATDC5 cells couldn't be adjusted by BSHX formula treatment.

Conclusion

By activation of TGF-β signaling, BSHX formula can promote articular cartilage repair by accelerating chondrocyte proliferation and maintaining chondrocyte phenotype, upregulate ECM accumulation, and inhibit matrix degradation.

Increased recruitment of endogenous stem cells and chondrogenic differentiation by a composite scaffold containing bone marrow homing peptide for cartilage regeneration

Even small cartilage defects could finally degenerate to osteoarthritis if left untreated, owing to the poor self-healing ability of articular cartilage. Stem cell transplantation has been well implemented as a common approach in cartilage tissue engineering but has technical complexity and safety concerns. The stem cell homing-based technique emerged as an alternative promising therapy for cartilage repair to overcome traditional limitations. In this study, we constructed a composite hydrogel scaffold by combining an oriented acellular cartilage matrix (ACM) with a bone marrow homing peptide (BMHP)-functionalized self-assembling peptide (SAP). We hypothesized that increased recruitment of endogenous stem cells by the composite scaffold could enhance cartilage regeneration. Methods: To test our hypothesis, in vitro proliferation, attachment and chondrogenic differentiation of rabbit mesenchymal stem cells (MSCs) were tested to confirm the bioactivities of the functionalized peptide hydrogel. The composite scaffold was then implanted into full-thickness cartilage defects on rabbit knee joints for cartilage repair, in comparison with microfracture or other sample groups. Stem cell recruitment was monitored by dual labeling with CD29 and CD90 under confocal microcopy at 1 week after implantation, followed by chondrogenic differentiation examined by qRT-PCR. Repaired tissue of the cartilage defects was evaluated by histological and immunohistochemistry staining, microcomputed tomography (micro-CT) and magnetic resonance imaging (MRI) at 3 and 6 months post-surgery. Macroscopic and histological scoring was done to evaluate the optimal in vivo repair outcomes of this composite scaffold. Results: The functionalized SAP hydrogels could stimulate rabbit MSC proliferation, attachment and chondrogenic differentiation during in vitro culture. At 7 days after implantation, increased recruitment of MSCs based on CD29+ /CD90+ double-positive cells was found in vivo in the composite hydrogel scaffold, as well as upregulation of cartilage-associated genes (aggrecan, Sox9 and type II collagen). After 3 and 6 months post-surgery, the articular cartilage defect in the composite scaffold-treated group was fully covered with cartilage-like tissue with a smooth surface, which was similar to the surrounding native cartilage, according to the results of histological and immunohistochemistry staining, micro-CT and MRI analysis. Macroscopic and histological scoring confirmed that the quality of cartilage repair was significantly improved with implantation of the composite scaffold at each timepoint, in comparison with microfracture or other sample groups. Conclusion: Our findings demonstrated that the composite scaffold could enhance endogenous stem cell homing and chondrogenic differentiation and significantly improve the therapeutic outcome of chondral defects. The present study provides a promising approach for in vivo cartilage repair without cell transplantation. Optimization of this strategy may offer great potential and benefits for clinical application in the future.

Thermoresponsive and Biodegradable Amphiphilic Block Copolymers with Pendant Functional Groups

BACKGROUND

To develop the biodegradability and thermoresponsive hydrogel, in this work we designed a pendant-functionalized, thermoresponsive, amphiphilic block copolymer.

METHODS

Methoxy poly(ethylene glycol) (MPEG)-b-[poly(ε-caprolactone)-ran-poly(ε-caprolactone-3-one)-ran-polylactic acid] (MCL) and (MPEG-b-[PCL-ran-POD-ran-PLA]) [MCL-(CO)] block copolymers were prepared by ring-opening polymerization of ε-caprolactone, OD and lactide monomers. The subsequent derivatization of MCL-(CO) provided MPEG-b-[PCL-ran-poly(ε-caprolactone-3-COOH)-ran-PLA] [MCL-(COOH)] with COOH pendant groups and MPEG-b-[PCL-ran-poly(ε-caprolactone-3-NH2)-ran-PLA] [MCL-(NH2)] with NH2 pendant groups.

RESULTS

The measured segment ratios of MCL-(CO), MCL-(COOH), and MCL-(NH2) agreed well with the target ratios. The abundances of the COOH and NH2 groups in the MCL-(COOH) and MCL-(NH2) copolymers were determined by 1H- and 13C-nuclear magnetic resonance spectroscopy, and agreed well with the target abundances. MCL-(CO), MCL-(COOH), and MCL-(NH2) formed homogeneous, white, opaque emulsions at room temperature. Rheological analysis of the block copolymer suspensions indicated a solution-to-hydrogel phase transition as a function of temperature. The solution-to-hydrogel phase transitions and the biodegradation of MCL-(CO), MCL-(COOH), and MCL-(NH2) were affected by varying the type (ketone, COOH, or NH2) and abundance of the pendant groups.

CONCLUSION

MCL-(CO), MCL-(COOH), and MCL-(NH2) with ketone, COOH, and NH2 pendant groups showed solution-to-hydrogel phase transitions and biodegradation behaviors that depended on both the type and number of pendant groups.