Novel Fabricating Process for Porous Polyglycolic Acid Scaffolds by Melt-Foaming Using Supercritical Carbon Dioxide

Stepwise degradable PGA-SF core-shell electrospinning scaffold with superior tenacity in wetting regime for promoting bone regeneration

Regenerating bone in the oral and maxillofacial region is clinically challenging due to the complicated osteogenic environment and the limitation of existing bone graft materials. Constructing bone graft materials with controlled degradation and stable mechanical properties in a physiological environment is of utmost importance. In this study, we used silk fibroin (SF) and polyglycolic acid (PGA) to fabricate a coaxial PGA-SF fibrous scaffold (PGA-SF-FS) to meet demands for bone grafts. The SF shell exerted excellent osteogenic activity while protecting PGA from rapid degradation and the PGA core equipped scaffold with excellent tenacity. The experiments related to biocompatibility and osteogenesis (e.g., cell attachment, proliferation, differentiation, and mineralization) demonstrated the superior ability of PGA-SF-FS to improve cell growth and osteogenic differentiation. Furthermore, in vivo testing using Sprague-Dawley rat cranial defect model showed that PGA-SF-FS accelerates bone regeneration as the implantation time increases, and its stepwise degradation helps to match the remodeling kinetics of the host bone tissue. Besides, immunohistochemical staining of CD31 and Col-1 confirmed the ability of PGA-SF-FS to enhance revascularization and osteogenesis response. Our results suggest that PGA-SF-FS fully utilizing the advantages of both components, exhibites stepwise degradation and superior tenacity in wetting regime, making it a promising candidate in the treatment of bone defects.

Biomaterials / bioinks and extrusion bioprinting

Bioinks are formulations of biomaterials and living cells, sometimes with growth factors or other biomolecules, while extrusion bioprinting is an emerging technique to apply or deposit these bioinks or biomaterial solutions to create three-dimensional (3D) constructs with architectures and mechanical/biological properties that mimic those of native human tissue or organs. Printed constructs have found wide applications in tissue engineering for repairing or treating tissue/organ injuries, as well as in vitro tissue modelling for testing or validating newly developed therapeutics and vaccines prior to their use in humans. Successful printing of constructs and their subsequent applications rely on the properties of the formulated bioinks, including the rheological, mechanical, and biological properties, as well as the printing process. This article critically reviews the latest developments in bioinks and biomaterial solutions for extrusion bioprinting, focusing on bioink synthesis and characterization, as well as the influence of bioink properties on the printing process. Key issues and challenges are also discussed along with recommendations for future research.

An overview of translational research in bone graft biomaterials

Natural bone healing is often inadequate to treat fractures with critical size bone defects and massive bone loss. Immediate surgical interventions through bone grafts have been found to be essential on such occasions. Naturally harvested bone grafts, although are the preferred choice of the surgeons; they suffer from serious clinical limitations, including disease transmission, donor site morbidity, limited supply of graft etc. Synthetic bone grafts, on the other hand, offer a more clinically appealing approach to decode the pathways of bone repair through use of tissue engineered biomaterials. This article critically retrospects the translational research on various engineered biomaterials towards bringing transformative changes in orthopaedic healthcare. The first section of the article discusses about composition and ultrastructure of bone along with the global perspectives on statistical escalation of bone fracture surgeries requiring use of bone grafts. The next section reviews the types, benefits and challenges of various natural and synthetic bone grafts. An overview of clinically relevant biomaterials from traditionally used metallic, bioceramic, and biopolymeric biomaterials to new generation composites have been summarised. Finally, this narrative review concludes with the discussion on the emerging trends and future perspectives of the promising bone grafts.

Recent advances in bioengineered scaffold for in vitro meat production

In vitro meat production via stem cell technology and tissue engineering provides hypothetically elevated resource efficiency which involves the differentiation of muscle cells from pluripotent stem cells. By applying the tissue engineering technique, muscle cells are cultivated and grown onto a scaffold, resulting in the development of muscle tissue. The studies related to in vitro meat production are advancing with a seamless pace, and scientists are trying to develop various approaches to mimic the natural meat. The formulation and fabrication of biodegradable and cost-effective edible scaffold is the key to the successful development of downstream culture and meat production. Non-mammalian biopolymers such as gelatin and alginate or plant-derived proteins namely soy protein and decellularized leaves have been suggested as potential scaffold materials for in vitro meat production. Thus, this article is aimed to furnish recent updates on bioengineered scaffolds, covering their formulation, fabrication, features, and the mode of utilization.

Polymeric Gel Scaffolds and Biomimetic Environments for Wound Healing

Infected wounds that do not heal are a worldwide problem that is worsening, with more people dying and more money being spent on care. For any disease to be managed effectively, its root cause must be addressed. Effective wound care becomes a bigger problem when various traditional wound healing methods and products may not only fail to promote good healing. Still, it may also hinder the healing process, causing wounds to stay open longer. Progress in tissue regeneration has led to developing three-dimensional scaffolds (3D) or constructs that can be leveraged to facilitate cell growth and regeneration while preventing infection and accelerating wound healing. Tissue regeneration uses natural and fabricated biomaterials that encourage the growth of tissues or organs. Even though the clinical need is urgent, the demand for polymer-based therapeutic techniques for skin tissue abnormalities has grown quickly. Hydrogel scaffolds have become one of the most imperative 3D cross-linked scaffolds for tissue regeneration because they can hold water perfectly and are porous, biocompatible, biodegradable, and biomimetic. For damaged organs or tissues to heal well, the porosity topography of the natural extracellular matrix (ECM) should be imitated. This review details the scaffolds that heal wounds and helps skin tissue to develop. After a brief overview of the bioactive and drug-loaded polymeric hydrogels, the discussion moves on to how the scaffolds are made and what they are made of. It highlights the present uses of in vitro and in-vivo employed biomimetic scaffolds. The prospects of how well bioactiveloaded hydrogels heal wounds and how nanotechnology assists in healing and regeneration have been discussed.

Next-Generation 3D Scaffolds for Nano-Based Chemotherapeutics Delivery and Cancer Treatment

Cancer is the leading cause of death after cardiovascular disease. Despite significant advances in cancer research over the past few decades, it is almost impossible to cure end-stage cancer patients and bring them to remission. Adverse effects of chemotherapy are mainly caused by the accumulation of chemotherapeutic agents in normal tissues, and drug resistance hinders the potential therapeutic effects and curing of this disease. New drug formulations need to be developed to overcome these problems and increase the therapeutic index of chemotherapeutics. As a chemotherapeutic delivery platform, three-dimensional (3D) scaffolds are an up-and-coming option because they can respond to biological factors, modify their properties accordingly, and promote site-specific chemotherapeutic deliveries in a sustainable and controlled release manner. This review paper focuses on the features and applications of the variety of 3D scaffold-based nano-delivery systems that could be used to improve local cancer therapy by selectively delivering chemotherapeutics to the target sites in future.

Novel strategies for designing regenerative skin products for accelerated wound healing

Healthy skin protects from pathogens, water loss, ultraviolet rays, and also maintains homeostasis conditions along with sensory perceptions in normal circumstances. Skin wound healing mechanism is a multi-phased biodynamic process that ultimately triggers intercellular and intracellular mechanisms. Failure to implement the normal and effective healing process may result in chronic injuries and aberrant scarring. Chronic wounds lead to substantial rising healthcare expenditure, and innovative methods to diagnose and control severe consequences are urgently needed. Skin tissue engineering (STE) has achieved several therapeutic accomplishments during the last few decades, demonstrating tremendous development. The engineered skin substitutes provide instant coverage for extensive wounds and facilitate the prevention of microbial infections and fluid loss; furthermore, they help in fighting inflammation and allow rapid neo-tissue formation. The current review primarily focused on the wound recovery and restoration process and the current conditions of STE with various advancements and complexities associated with different strategies such as cell sources, biopolymers, innovative fabrication techniques, and growth factors delivery systems.

Novel Approaches and Biomaterials for Bone Tissue Engineering: A Focus on Silk Fibroin

Bone tissue engineering (BTE) represents a multidisciplinary research field involving many aspects of biology, engineering, material science, clinical medicine and genetics to create biological substitutes to promote bone regeneration. The definition of the most appropriate biomaterials and structures for BTE is still a challenge for researchers, aiming at simultaneously combining different features such as tissue generation properties, biocompatibility, porosity and mechanical strength. In this scenario, among the biomaterials for BTE, silk fibroin represents a valuable option for the development of functional devices because of its unique biological properties and the multiple chances of processing. This review article aims at providing the reader with a general overview of the most recent progresses in bone tissue engineering in terms of approaches and materials with a special focus on silk fibroin and the related mechanisms involved in bone regeneration, and presenting interesting results obtained by different research groups, which assessed the great potential of this protein for bone tissue engineering.

MAGNESIUM BASED ALLOYS FOR BIODEGRADABLE IMPLANTS APPLICATIONS USING ADDITIVE MANUFACTURING TECHNIQUE: A REVIEW

Biodegradable materials have various advantages compared to nonbiodegradable materials. Developing implants using biodegradable materials eliminates the need for secondary surgery, improves mechanical and biological properties, and improves biocompatibility. Magnesium (Mg) and its alloys are frequently used in orthopedic applications nowadays. However, the rapid degradation of Mg poses a substantial challenge. As a result, for the bone to heal properly, a proper balance between implant degeneration rate and bone healing must be obtained. Mg has certain other drawbacks, such as the need for an inert atmosphere when employing powder metallurgy and casting procedures to manufacture it because of its reactive nature. In this paper, Additive manufacturing (AM) techniques for manufacturing orthopedic biodegradable implants made of Mg and its alloys are discussed which helps in obtaining improved biological and mechanical properties of the implants. These orthopedic implants should have a controlled rate of degradation and antibacterial functional surfaces. There is also a description of the use of several AM processes utilized to enhance the mechanical and biological characteristics of implants employing Mg. This paper also seeks to present the concept of integrating established techniques into a production process to obtain the needed biodegradable implant material for orthopedic applications.

Biomimetic PLGA/Strontium-Zinc Nano Hydroxyapatite Composite Scaffolds for Bone Regeneration

Synthetic bone graft substitutes have attracted increasing attention in tissue engineering. This study aimed to fabricate a novel, bioactive, porous scaffold that can be used as a bone substitute. Strontium and zinc doped nano-hydroxyapatite (Sr/Zn n-HAp) were synthesized by a water-based sol-gel technique. Sr/Zn n-HAp and poly (lactide-co-glycolide) (PLGA) were used to fabricate composite scaffolds by supercritical carbon dioxide technique. FTIR, XRD, TEM, SEM, and TGA were used to characterize Sr/Zn n-HAp and the composite scaffolds. The synthesized scaffolds were adequately porous with an average pore size range between 189 to 406 µm. The scaffolds demonstrated bioactive behavior by forming crystals when immersed in the simulated body fluid. The scaffolds after immersing in Tris/HCl buffer increased the pH value of the medium, establishing their favorable biodegradable behavior. ICP-MS study for the scaffolds detected the presence of Sr, Ca, and Zn ions in the SBF within the first week, which would augment osseointegration if implanted in the body. nHAp and their composites (PLGA-nHAp) showed ultimate compressive strength ranging between 0.4–19.8 MPa. A 2.5% Sr/Zn substituted nHAp-PLGA composite showed a compressive behavior resembling that of cancellous bone indicating it as a good candidate for cancellous bone substitute.

Milestones and current achievements in development of multifunctional bioscaffolds for medical application

Tissue engineering (TE) is a rapidly growing interdisciplinary field, which aims to restore or improve lost tissue function. Despite that TE was introduced more than 20 years ago, innovative and more sophisticated trends and technologies point to new challenges and development. Current challenges involve the demand for multifunctional bioscaffolds which can stimulate tissue regrowth by biochemical curves, biomimetic patterns, active agents and proper cell types. For those purposes especially promising are carefully chosen primary cells or stem cells due to its high proliferative and differentiation potential. This review summarized a variety of recently reported advanced bioscaffolds which present new functions by combining polymers, nanomaterials, bioactive agents and cells depending on its desired application. In particular necessity of study biomaterial-cell interactions with in vitro cell culture models, and studies using animals with in vivo systems were discuss to permit the analysis of full material biocompatibility. Although these bioscaffolds have shown a significant therapeutic effect in nervous, cardiovascular and muscle, tissue engineering, there are still many remaining unsolved challenges for scaffolds improvement.

A Comparative Review of Natural and Synthetic Biopolymer Composite Scaffolds

Tissue engineering (TE) and regenerative medicine integrate information and technology from various fields to restore/replace tissues and damaged organs for medical treatments. To achieve this, scaffolds act as delivery vectors or as cellular systems for drugs and cells; thereby, cellular material is able to colonize host cells sufficiently to meet up the requirements of regeneration and repair. This process is multi-stage and requires the development of various components to create the desired neo-tissue or organ. In several current TE strategies, biomaterials are essential components. While several polymers are established for their use as biomaterials, careful consideration of the cellular environment and interactions needed is required in selecting a polymer for a given application. Depending on this, scaffold materials can be of natural or synthetic origin, degradable or nondegradable. In this review, an overview of various natural and synthetic polymers and their possible composite scaffolds with their physicochemical properties including biocompatibility, biodegradability, morphology, mechanical strength, pore size, and porosity are discussed. The scaffolds fabrication techniques and a few commercially available biopolymers are also tabulated.

Advancement of Nanobiomaterials to Deliver Natural Compounds for Tissue Engineering Applications

Recent advancement in nanotechnology has provided a wide range of benefits in the biological sciences, especially in the field of tissue engineering and wound healing. Nanotechnology provides an easy process for designing nanocarrier-based biomaterials for the purpose and specific needs of tissue engineering applications. Naturally available medicinal compounds have unique clinical benefits, which can be incorporated into nanobiomaterials and enhance their applications in tissue engineering. The choice of using natural compounds in tissue engineering improves treatment modalities and can deal with side effects associated with synthetic drugs. In this review article, we focus on advances in the use of nanobiomaterials to deliver naturally available medicinal compounds for tissue engineering application, including the types of biomaterials, the potential role of nanocarriers, and the various effects of naturally available medicinal compounds incorporated scaffolds in tissue engineering.

Fabrication techniques of biomimetic scaffolds in three-dimensional cell culture: A review

In the last four decades, several researchers worldwide have routinely and meticulously exercised cell culture experiments in two-dimensional (2D) platforms. Using traditionally existing 2D models, the therapeutic efficacy of drugs has been inappropriately validated due to the failure in generating the precise therapeutic response. Fortunately, a 3D model addresses the foregoing limitations by recapitulating the in vivo environment. In this context, one has to contemplate the design of an appropriate scaffold for favoring the organization of cell microenvironment. Instituting pertinent model on the platter will pave way for a precise mimicking of in vivo conditions. It is because animal cells in scaffolds oblige spontaneous formation of 3D colonies that molecularly, phenotypically, and histologically resemble the native environment. The 3D culture provides insight into the biochemical aspects of cell-cell communication, plasticity, cell division, cytoskeletal reorganization, signaling mechanisms, differentiation, and cell death. Focusing on these criteria, this paper discusses in detail, the diversification of polymeric scaffolds based on their available resources. The paper also reviews the well-founded and latest techniques of scaffold fabrication, and their applications pertaining to tissue engineering, drug screening, and tumor model development.

Biodegradable Polymers as the Pivotal Player in the Design of Tissue Engineering Scaffolds

Biodegradable polymers play a pivotal role in in situ tissue engineering. Utilizing various technologies, researchers have been able to fabricate 3D tissue engineering scaffolds using biodegradable polymers. They serve as temporary templates, providing physical and biochemical signals to the cells and determining the successful outcome of tissue remodeling. Furthermore, a biodegradable scaffold also presents the fourth dimension for tissue engineering, namely time. The properties of the biodegradable polymer change over time, presenting continuously changing features during the degradation process. These changes become more complicated when different materials are combined together to fabricate a composite or heterogeneous scaffold. This review undertakes a systematic analysis of the basic characteristics of biodegradable polymers and describe recent advances in making composite biodegradable scaffolds for in situ tissue engineering and regenerative medicine. The interaction between implanted biodegradable biomaterials and the in vivo environment are also discussed, including the properties and functional changes of the degradable scaffold, the local effect of degradation on the contiguous tissue and their evaluation using both in vitro and in vivo models.

Foaming of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with Supercritical Carbon Dioxide: Foaming Performance and Crystallization Behavior

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) samples were successfully foamed using supercritical carbon dioxide as a physical foaming agent. PHBV sheets were first saturated at 175 °C followed by a foaming process at different temperatures (145 to 165 °C) and different CO2 pressures (10 to 29 MPa). It was found that microcellular structures with average cell sizes ranging from 6 to 22 μm and cell densities ranging from 108 to 1.2 × 109 cells/cm3 could be controllably prepared by selecting suitable foaming conditions. To investigate crystallization behavior during the foaming process and explore the corresponding foaming mechanism, differential scanning calorimetry, wide angle X-ray diffraction, and small-angle X-ray scattering characterizations were carried out. Stretching behavior during the cell growth stage may increase the crystal nucleation rate, and the generated crystal nucleus accelerates the crystallization rate as well as thickens PHBV crystal lamellae.

Fabrication of fibrillated and interconnected porous poly(ε-caprolactone) vascular tissue engineering scaffolds by microcellular foaming and polymer leaching

This paper provides a method combining eco-friendly supercritical CO₂ microcellular foaming and polymer leaching to fabricate small-diameter vascular tissue engineering scaffolds.

Body temperature polymerization and in situ drug encapsulation in supercritical carbon dioxide

Body-temperature and solvent-free polymerization and in situ fabrication of drug-loaded microparticles are reported for the first time.

Nanofibrous, Emulsion-Templated Syndiotactic Polystyrenes with Superhydrophobicity for Oil Spill Cleanup

A series of syndiotactic polystyrene (sPS) monoliths with controllable shapes, nanofibrous structures, hierarchical pores, superhydrophobicity, high specific surface area, and high strength have been fabricated for the first time by solidifying nonaqueous high internal phase emulsions (HIPEs) through crystallization-induced gelation. The nonaqueous HIPEs were formed by dispersing glycerol in 1,2,4-trichlorobenzene stabilized by sulfonated sPS at a high temperature of 120 °C, and with sPS in the continuous phase, these HIPEs were solidified by cooling at room temperature to obtain sPS monoliths. The shapes of the sPS monoliths were controllable, and excitedly, nanofibrous structures were found at void walls, with fiber diameters ranging from 20 to 100 nm. The sPS monoliths exhibited pores in different scales: emulsion-templated voids at nearly 10 μm with pore throats ranging from 1 to 2 μm and macropores and mesopores between nanofibers, enabling the monoliths to exhibit extremely high specific surface area of up to 420 m²·g^-1. The porous sPS monoliths were robust, and they did not fail even at a compressive strain of 70%, with Young's moduli ranging from 157.7 to 2638.0 kPa. The monoliths were superhydrophobic and oleophilic, with water contact angles over 150° and with oils absorbed rapidly. The superhydrophobicity and oleophilicity enabled the porous sPS monoliths to absorb bulk oils on the water surface, underwater oils, and even oils within oil-in-water emulsions. The monoliths absorbed a large amount of organic solvents, edible oils, and fuel oils with equilibrium liquid uptakes up to 81.3, 44.4, and 41.9 g·g^-1 for chloroform, olive oil, and diesel, respectively. The liquid absorption was rapid, and the monoliths exhibited a relatively high reusability. These porous sPS monoliths were demonstrated to be a candidate for the applications of oil/water separation and/or oil spill cleanup.

Impregnation of Curcumin into a Biodegradable (Poly-lactic-co-glycolic acid, PLGA) Support, to Transfer Its Well Known In Vitro Effect to an In Vivo Prostate Cancer Model

Prostate cancer (PCa) is one of the most common cancers in older men and is associated with high mortality. Despite advances in screening for early detection of PCa, a large proportion of patients continue to be diagnosed with metastatic disease, with ~20% of men showing a high tumor grade and stage. Medicinal plant extracts have a great potential to prevent/treat PCa, as well as to reduce its incidence/prevalence and improve survival rates. One of the most promising extracts is curcumin, which is a major, nontoxic, bioactive compound of Curcuma longa. Curcumin has strong antitumor activity in vitro. However, its potential beneficial in vivo affects are limited by its low intestinal absorption and rapid metabolism. In this study, curcumin was impregnated into a biodegradable poly(lactic-co-glycolic) acid (PLGA) support and characterized by FTIR and DSC, and its release by UV spectrophotometry. PLGA-curcumin was tested in different subcutaneous PCa xenograft models (PC3, 22rv1, and DU145 PCa cell-lines), and its effects evaluated by tumor progression an immuno-histochemical analysis (Trichromic, Ki67 and TUNEL stainings), were compared with those of a commercial curcumin preparation. Our results indicate that curcumin-impregnated PLGA is significantly more active (~2-fold increase) with respect to oral curcumin, which supports its use for subcutaneous administration.

Supercritical CO2 foamed composite scaffolds incorporating bioactive lipids promote vascularized bone regeneration via Hif-1α upregulation and enhanced type H vessel formation

Bone tissue engineering has substantial potential for the treatment of massive bone defects; however, efficient vascularization coupled with bone regeneration still remains a challenge in this field. In the current study, supercritical carbon dioxide (scCO₂) foaming technique was adopted to fabricate mesoporous bioactive glasses (MBGs) particle-poly (lactic-co-glycolic acid) (PLGA) composite scaffolds with appropriate mechanical and degradation properties as well as in vitro bioactivity. The MBG-PLGA scaffolds incorporating the bioactive lipid FTY720 (designated as FTY/MBG-PLGA) exhibited simultaneously sustained release of the bioactive lipid and ions. In addition to providing a favorable microenvironment for cellular adhesion and proliferation, FTY/MBG-PLGA scaffolds significantly facilitated the in vitro osteogenic differentiation of rBMSCs and also markedly stimulated the upregulation of Hif-1α expression via the activation of the Erk1/2 pathway, which mediated the osteogenic and pro-angiogenic effects on rBMSCs. Furthermore, FTY/MBG-PLGA extracts induced superior in vitro angiogenic performance of HUVECs. In vivo evaluation of critical-sized rat calvarial bone defects indicated that FTY/MBG-PLGA scaffolds potently promoted vascularized bone regeneration. Notably, the significantly enhanced formation of type H vessels (CD31^hiEmcn^hi neo-vessels) was observed in newly formed bone tissue in FTY/MBG-PLGA group, strongly suggesting that FTY720 and therapeutic ions released from the scaffolds synergistically induced more type H vessel formation, which indicated the coupling of angiogenesis and osteogenesis to achieve efficiently vascularized bone regeneration. Overall, the results indicated that the foamed porous MBG-PLGA scaffolds incorporating bioactive lipids achieved desirable vascularization-coupled bone formation and could be a promising strategy for bone regenerative medicine. STATEMENT OF SIGNIFICANCE: Efficacious coupling of vascularizationandbone formation is critical for the restoration of large bone defects. Anoveltechnique was used to fabricate composite scaffolds incorporating bioactive lipids which possessedsynergistic cues of bioactive lipids and therapeutic ions to potently promotebone regenerationas well as vascularization. The underlying molecular mechanism for the osteogenic and pro-angiogenic effects of the compositescaffolds was unveiled. Interestingly, the scaffolds were furtherfoundto enhance the formation oftype H capillarieswithin the bone healing microenvironment to couple angiogenesis to osteogenesis to achieve satisfyingvascularizedbone regeneration.These findings provide a novel strategy to develop efficiently vascularized engineering constructs to treat massive bone defects.

Cellulose Nanostructure-Based Biodegradable Nanocomposite Foams: A Brief Overview on the Recent Advancements and Perspectives

The interest in designing new environmentally friendly materials has led to the development of biodegradable foams as a potential substitute to most currently used fossil fuel-derived polymer foams. Despite the possibility of developing biodegradable and environmentally friendly polymer foams, the challenge of foaming biopolymers still persists as they have very low melt strength and viscosity as well as low crystallisation kinetics. Studies have shown that the incorporation of cellulose nanostructure (CN) particles into biopolymers can enhance the foamability of these materials. In addition, the final properties and performance of the foamed products can be improved with the addition of these nanoparticles. They not only aid in foamability but also act as nucleating agents by controlling the morphological properties of the foamed material. Here, we provide a critical and accessible overview of the influence of CN particles on the properties of biodegradable foams; in particular, their rheological, thermal, mechanical, and flammability and thermal insulating properties and biodegradability.