Controlled drug delivery in tissue engineering

Application of PLGA nano/microparticle delivery systems for immunomodulation and prevention of allotransplant rejection

INTRODUCTION

Allograft transplantation is an effective end-point therapy to replace the function of an impaired organ. The main problem associated with allotransplantation is the induction of immune responses that results in acute and chronic graft rejection. To modulate the response of the immune system, transplant recipients generally take high dose immunosuppressant drugs for life. These drugs are associated with serious side effects such as infection with opportunistic pathogens and the development of neoplasia.

AREAS COVERED

We reviewed the obstacles to successful transplantation and PLGA-based strategies to reduce immune-mediated allograft rejection.

EXPERT OPINION

Biomaterial-based approaches using micro- and nanoparticles such as poly (lactic-co-glycolic acid) (PLGA) can be used to achieve controlled release of drugs. This approach decreases the required effective dose of drugs and enables local delivery of these agents to specific tissues and cells, whilst decreasing systemic effects.

Natural Medicinal Compounds in Bone Tissue Engineering

Recent advances in 3D printing have provided unprecedented opportunities in bone tissue engineering applications for producing a variety of complex patient-specific implants for the treatment of critical-sized bone defects. Natural medicinal compounds (NMCs) with osteogenic potential can be incorporated into these 3D-printed parts to improve bone formation and therefore enhance implant performance. Using NMCs to treat bone-related disorders may prove to be a healthy preventive choice as they are considered safe, have lesser or no side effects, and are more suitable for prolonged use than synthetic drugs. In this review paper, the current challenges of bone tissue engineering are addressed briefly, highlighting the immense potential of NMCs integrated within tissue engineering scaffolds for orthopedic and dental applications.

Significant effect of simvastatin and/or ezetimibe-loaded nanofibers on the healing of femoral defect: An experimental study

BACKGROUND

Fracture healing complications are associated with significant healthcare and economic burden. In this study, we aimed to investigate how the combined administration of local simvastatin and ezetimibe into the femoral defect of the animal model affects the bone-healing process in comparison with their monotherapy.

METHODS

A total of 32 four-month-old adult male Wistar rats were randomized into the four study groups: simvastatin + ezetimibe-loaded nanofibers (group 1), simvastatin-loaded nanofibers (group 2), ezetimibe-loaded nanofibers (group 3), and non-loaded nanofibers (group 4). After the generation of femoral defects, the predesigned nanofibers were locally administered into the defect site. The healing measures were serum and bone osteoprotegerin (OPG) expression, pathologic evaluation of union (Allen's fracture healing scores), and radiographic evaluation of bone density (Hounsfield scale) at weeks 2 and 4.

RESULTS

The improvement of all evaluated healing measures was remarkably superior in rats that were treated with loaded nanofibers in comparison with the control group. Also, the improvement of all evaluated healing measures was considerably more in the simvastatin-ezetimibe combination therapy group compared to their monotherapy. All the evaluated measures were superior in the ezetimibe monotherapy group compared to the simvastatin monotherapy group.

CONCLUSION

The cumulative effect of simvastatin and ezetimibe on the induction of bone healing is more significant than the individual effect of these drugs. Therefore, local administration of nanofibers loaded with simvastatin and ezetimibe could be regarded as a promising osteoinductive compound for the acceleration of bone repair.

A 3D porous microsphere with multistage structure and component based on bacterial cellulose and collagen for bone tissue engineering

Collagen (COL) and bacterial cellulose (BC) were chemically recombined by Malaprade and Schiff-base reactions. A three-dimensional (3D) porous microsphere of COL/BC/Bone morphogenetic protein 2 (BMP-2) with multistage structure and components were prepared by the template method combined with reverse-phase suspension regeneration. The microspheres were full of pores and had a rough surface. The particle size ranged from 8 to 12 microns, the specific surface area (S_BET) was 123.4 m²/g, the pore volume (V_Pore) was 0.59 cm³/g, and the average pore diameter (D_BJH) was 198.5 nm. The adsorption isotherm of the microspheres on the N₂ molecule belongs to that of mesoporous materials. The microspheres showed good biocompatibility, and the 3D porous microspheres with multiple structures and components effectively promoted the adhesion, proliferation, and osteogenic differentiation of mice MC3T3-E1 cells. The study can provide a theoretical basis for the application of COL/BC porous microspheres in the field of bone tissue engineering.

Reduced Graphene Oxide Incorporated GelMA Hydrogel Promotes Angiogenesis For Wound Healing Applications

PURPOSE

Non-healing or slow healing chronic wounds are among serious complications of diabetes that eventually result in amputation of limbs and increased morbidities and mortalities. Chronic diabetic wounds show reduced blood vessel formation (lack of angiogenesis), inadequate cell proliferation and poor cell migration near wounds. In this paper, we report the development of a hydrogel-based novel wound dressing material loaded with reduced graphene oxide (rGO) to promote cell proliferation, cell migration and angiogenesis for wound healing applications.

METHODS

Gelatin-methacryloyl (GelMA) based hydrogels loaded with different concentrations of rGO were fabricated by UV crosslinking. Morphological and physical characterizations (porosity, degradation, and swelling) of rGO incorporated GelMA hydrogel was performed. In vitro cell proliferation, cell viability and cell migration potential of the hydrogels were analyzed by MTT assay, live/dead staining, and wound healing scratch assay respectively. Finally, in vivo chicken embryo angiogenesis (CEO) testing was performed to evaluate the angiogenic potential of the prepared hydrogel.

RESULTS

The experimental results showed that the developed hydrogel possessed enough porosity and exudate-absorbing capacity. The biocompatibility of prepared hydrogel on three different cell lines (3T3 fibroblasts, EA.hy926 endothelial cells, and HaCaT keratinocytes) was confirmed by in vitro cell culture studies (live/dead assay). The GelMA hydrogel containing 0.002% w/w rGO considerably increased the proliferation and migration of cells as evident from MTT assay and wound healing scratch assay. Furthermore, rGO impregnated GelMA hydrogel significantly enhanced the angiogenesis in the chick embryo model.

CONCLUSION

The positive effect of 0.002% w/w rGO impregnated GelMA hydrogels on angiogenesis, cell migration and cell proliferation suggests that these formulations could be used as a functional wound healing material for the healing of chronic wounds.

Alveolar bone repair of rhesus monkeys by using BMP-2 gene and mesenchymal stem cells loaded three-dimensional printed bioglass scaffold

Over the past years, the study about bone tissue engineering in the field of regenerative medicine has been a main research topic. Using three-dimensional (3D) porous degradable scaffold complexed with mesenchymal stem cells (MSCs) and growth factor gene to improve bone tissue repair and regeneration has raised much interest. This study mainly evaluated the osteogenesis of alveolar bone defects of animal in the following experimental groups: sham-operated (SO), 3D printed bioglass (3D-BG), 3D-BG with BMP-2 gene loaded CS (3D-BG + BMP/CS) and 3D-BG with rhesus marrow bone MSCs and BMP/CS (3D-BG + BMP/CS + rBMSCs). Simulated human bone defect with critical size of 10 × 10 × 5 mm were established in quadrumana - rhesus monkeys, and in vivo osteogenesis was characterized by X-ray, micro-Computed Tomography (mCT) and history. Our results revealed that 3D-BG + rBMSCs + BMP/CS scaffold could improve bone healing best by showing its promote osteogenic properties in vivo. Considering the great bone repair capacity of 3D-BG + BMP/CS + rBMSCs in humanoid primate rhesus monkeys, it could be a promising therapeutic strategy for surgery trauma or accidents, especially for alveolar bones defects.

Amplified intracellular Ca2+ for synergistic anti-tumor therapy of microwave ablation and chemotherapy

BACKGROUND

Developing new strategies to reduce the output power of microwave (MW) ablation while keeping anti-tumor effect are highly desirable for the simultaneous achievement of effective tumor killing and avoidance of complications. We find that mild MW irradiation can significantly increase intracellular Ca2+ concentration in the presence of doxorubicin hydrochloride (DOX) and thus induce massive tumor cell apoptosis. Herein, we designed a synergistic nanoplatform that not only amplifies the intracellular Ca2+ concentration and induce cell death under mild MW irradiation but also avoids the side effect of thermal ablation and chemotherapy.

RESULTS

The as-made NaCl-DOX@PLGA nanoplatform selectively elevates the temperature of tumor tissue distributed with nanoparticles under low-output MW, which further prompts the release of DOX from the PLGA nanoparticles and tumor cellular uptake of DOX. More importantly, its synergistic effect not only combines thermal ablation and chemotherapy, but also obviously increases the intracellular Ca2+ concentration. Changes of Ca2+ broke the homeostasis of tumor cells, decreased the mitochondrial inner membrane potential and finally induced the cascade of apoptosis under nonlethal temperature. As such, the NaCl-DOX@PLGA efficiently suppressed the tumor cell progression in vivo and in vitro under mild MW irradiation for the triple synergic effect.

CONCLUSIONS

This work provides a biocompatible and biodegradable nanoplatform with triple functions to realize the effective tumor killing in unlethal temperature. Those findings provide reliable solution to solve the bottleneck problem bothering clinics about the balance of thermal efficiency and normal tissue protection.

Heat-curing polylactide for bone implants: Preparation and investigation on properties relevant to degradation

Several processes have been used to produce polylactide for bone replacement. The challenge remains, however, to produce these devices by a simpler and more economical process. In this study, a method of combining powder and liquid parts was introduced. Star-shaped polylactides with molecular weights ranging from 3 to 16 kg/mol were synthesized and blended with a linear polylactide (Mw = 188 kg/mol) using the technique of emulsion solvent evaporation. The blends in a form of spherical powder were characterized by scanning electron microscopy, gel permeation chromatography, and particle size analysis. The heat-curing polylactide was fabricated by mixing the powder with triethylene glycol dimethacrylate, molded, and then heated in a hot water bath to solidify. The effects of powder composition in terms of amount and molecular weight of the star-shaped polylactide on mechanical properties were investigated. The results showed an increase in flexural strength with increase in the amount of star-shaped polylactide. The powder comprised star-shaped polylactide having the molecular weight of 10,770 g/mol, not less than 80wt%, offered the fabricated heat-curing polylactide with high strength ranging from 95 to 100 MPa. This formulation was further incorporated with hydroxyapatite to improve biocompatibility and subjected to degradation at 37°C. Mechanical test and weight loss determination together with biological test were conducted at certain times during degradation of the materials. Both materials with and without hydroxyapatite showed mechanical stability upon degradation for at least 6 months, but the one with hydroxyapatite revealed significantly better bioactivity at the end of 1-year follow-up study, making it the most promising material for bone implants.

Injectable and fast self-healing protein hydrogels

Injectable hydrogels are adapted to irregularities in the desired location by injection as a liquid and gelation in situ. However, traditional slow-gelling injectable hydrogels may result in loss of cargo (cells/drugs) as well as diffusion at the target site, and extremely rapid gelation may lead to undesired premature coagulation. These practical problems can be solved by using self-healing hydrogels. Herein, through the reduction of disulfide bonds in BSA protein by using a reducing agent, the disulfide bonds between the individual BSA protein molecules are re-matched to form a network structure, thereby forming a protein hydrogel. This hydrogel shows an efficient and rapid self-healing property, and the broken protein hydrogel can be fast repaired within 1-2 minutes in response to H₂O₂ stimulation, and the repair efficiency reached up to 100%. The hydrogel can be extruded using only a pinhole syringe, and cytotoxicity experiments have demonstrated excellent biocompatibility of the protein hydrogel. This non-toxic, injectable, fast self-healing protein hydrogel is expected to be widely used in biomedical, tissue engineering, injectable gel, 3D bioprinting, and other applications.

Hydrogel vehicles for sequential delivery of protein drugs to promote vascular regeneration

In recent years, as the mechanisms of vasculogenesis and angiogenesis have been uncovered, the functions of various pro-angiogenic growth factors (GFs) and cytokines have been identified. Therefore, therapeutic angiogenesis, by delivery of GFs, has been sought as a treatment for many vascular diseases. However, direct injection of these protein drugs has proven to have limited clinical success due to their short half-lives and systemic off-target effects. To overcome this, hydrogel carriers have been developed to conjugate single or multiple GFs with controllable, sustained, and localized delivery. However, these attempts have failed to account for the temporal complexity of natural angiogenic pathways, resulting in limited therapeutic effects. Recently, the emerging ideas of optimal sequential delivery of multiple GFs have been suggested to better mimic the biological processes and to enhance therapeutic angiogenesis. Incorporating sequential release into drug delivery platforms will likely promote the formation of neovasculature and generate vast therapeutic potential.

Scaffold-mediated sequential drug/gene delivery to promote nerve regeneration and remyelination following traumatic nerve injuries

Neural tissue regeneration following traumatic injuries is often subpar. As a result, the field of neural tissue engineering has evolved to find therapeutic interventions and has seen promising outcomes. However, robust nerve and myelin regeneration remain elusive. One possible reason may be the fact that tissue regeneration often follows a complex sequence of events in a temporally-controlled manner. Although several other fields of tissue engineering have begun to recognise the importance of delivering two or more biomolecules sequentially for more complete tissue regeneration, such serial delivery of biomolecules in neural tissue engineering remains limited. This review aims to highlight the need for sequential delivery to enhance nerve regeneration and remyelination after traumatic injuries in the central nervous system, using spinal cord injuries as an example. In addition, possible methods to attain temporally-controlled drug/gene delivery are also discussed for effective neural tissue regeneration.

Soft-Nanoparticle Functionalization of Natural Hydrogels for Tissue Engineering Applications

Tissue engineering has emerged as an important research area that provides numerous research tools for the fabrication of biologically functional constructs that can be used in drug discovery, disease modeling, and the treatment of diseased or injured organs. From a materials point of view, scaffolds have become an important part of tissue engineering activities and are usually used to form an environment supporting cellular growth, differentiation, and maturation. Among various materials used as scaffolds, hydrogels based on natural polymers are considered one of the most suitable groups of materials for creating tissue engineering scaffolds. Natural hydrogels, however, do not always provide the physicochemical and biological characteristics and properties required for optimal cell growth. This review discusses the properties and tissue engineering applications of widely used natural hydrogels. In addition, methods of modulation of their physicochemical and biological properties using soft nanoparticles as fillers or reinforcing agents are presented.

Nanotherapeutics Engineered to Cross the Blood-Brain Barrier for Advanced Drug Delivery to the Central Nervous System

Drug delivery to the brain remains challenging mainly due to the blood-brain barrier (BBB) that regulates the entrance of substances to the brain. Advances in nanotechnology have enabled the engineering of nanomedicines for biomedical applications including enhanced drug delivery into the brain. In this review, we describe strategies of nanomedicines engineered to traverse the BBB and deliver therapeutic molecules to target brain sites. We highlight the representative applications with materials including polymers, lipids, and inorganic elements for brain drug delivery. We finalize this review with the current challenges and future perspective of nanotherapeutics for advanced drug delivery to the brain.

Analysing diffusion and flow-driven instability using semidefinite programming

Diffusion and flow-driven instability, or transport-driven instability, is one of the central mechanisms to generate inhomogeneous gradient of concentrations in spatially distributed chemical systems. However, verifying the transport-driven instability of reaction-diffusion-advection systems requires checking the Jacobian eigenvalues of infinitely many Fourier modes, which is computationally intractable. To overcome this limitation, this paper proposes mathematical optimization algorithms that determine the stability/instability of reaction-diffusion-advection systems by finite steps of algebraic calculations. Specifically, the stability/instability analysis of Fourier modes is formulated as a sum-of-squares optimization program, which is a class of convex optimization whose solvers are widely available as software packages. The optimization program is further extended for facile computation of the destabilizing spatial modes. This extension allows for predicting and designing the shape of the concentration gradient without simulating the governing equations. The streamlined analysis process of self-organized pattern formation is demonstrated with a simple illustrative reaction model with diffusion and advection.

Stability of lysozyme incorporated into electrospun fibrous mats for wound healing

In this study, we investigated the feasibility of incorporating protein drugs into electrospun fibrous mats (EFMs) for wound healing using lysozyme as a model drug. Lysozyme nanoparticles (Lyso- NPs) were first obtained by electrospray. Lysozyme solutions were prepared with a binary solvent mixture of ethanol (EtOH)-water (H₂O) at varied volume ratios. Subsequently, Lyso-NPs were suspended in poly(lactic-co-glycolic acid) (PLGA) solutions using trifluoroethanol (TFE) as a solvent. Lyso-NPs loaded EFMs were obtained by electrospinning of the aforementioned suspensions, and the bioactivity of lysozyme in the EFMs was investigated using fluorescence-based assay kit. The electrosprayed Lyso-NPs were spherical with barely altered bioactivity as compared to the untreated raw material when using EtOH- H₂O (30:70, v/v) as the solvent. After the subsequent electrospinning process, more than 90% of the bioactivity of lysozyme was retained compared to the raw material. The cytotoxicity of the produced EFMs was evaluated by thiazolyl blue tetrazolium bromide (MTT) study and the proliferation and distribution of mouse fibroblast cells (L929) growing on EFMs were investigated using 4,6-diamidino-2-phenylindol dihydrochloride (DAPI) for nucleic acid staining. Nearly negligible cytotoxicity of all the EFMs was observed according to the MTT study. Furthermore, it was observed that the L929 cells grew well on the Lyso-EFMs, especially those with the modification of polyethylene glycol (PEG) that was added to improve the hydrophilicity of EFMs. This study demonstrated that the electrospray/electrospinning processes are suitable for loading biomacromolecules to produce functionalized wound dressings to promote wound healing.

Biodegradable and pH Sensitive Peptide Based Hydrogel as Controlled Release System for Antibacterial Wound Dressing Application

The stimuli-sensitive and biodegradable hydrogels are promising biomaterials as controlled drug delivery systems for diverse biomedical applications. In this study, we construct hybrid hydrogels combined with peptide-based bis-acrylate and acrylic acid (AAc). The peptide-based bis-acrylate/AAc hybrid hydrogel displays an interconnected and porous structure by scanning electron microscopy (SEM) observation and exhibits pH-dependent swelling property. The biodegradation of hybrid hydrogels was characterized by SEM and weight loss, and the results showed the hydrogels have a good enzymatic biodegradation property. The mechanical and cytotoxicity properties of the hydrogels were also tested. Besides, triclosan was preloaded during the hydrogel formation for drug release and antibacterial studies. In summary, the peptide-based bis-acrylate/AAc hydrogel with stimuli sensitivity and biodegradable property may be excellent candidates as drug delivery systems for antibacterial wound dressing application.

Hyaluronic Acid and Polyethylene Glycol Hybrid Hydrogel Encapsulating Nanogel with Hemostasis and Sustainable Antibacterial Property for Wound Healing

Immediate hemorrhage control and anti-infection play important roles in the wound management. Besides, a moist environment is also beneficial for wound healing. Hydrogels are promising materials in urgent hemostasis and drug release. However, hydrogels have the disadvantage of rapid release profiles, leading to the exposure to high drug concentrations. In this study, we constructed hybrid hydrogels with rapid hemostasis and sustainable antibacterial property combining aminoethyl methacrylate hyaluronic acid (HA-AEMA) and methacrylated methoxy polyethylene glycol (mPEG-MA) hybrid hydrogels and chlorhexidine diacetate (CHX)-loaded nanogels. The CHX-loaded nanogels (CLNs) were prepared by the enzyme degradation of CHX-loaded lysine-based hydrogels. The HA-AEMA and mPEG-MA hybrid hydrogel loaded with CLNs (labeled as Gel@CLN) displayed a three-dimensional microporous structure and exhibited excellent swelling, mechanical property, and low cytotoxicity. The Gel@CLN hydrogel showed a prolonged release period of CHX over 240 h and the antibacterial property over 10 days. The hemostasis and wound-healing properties were evaluated in vivo using a mouse model. The results showed that hydrogel had the rapid hemostasis capacity and accelerated wound healing. In summary, CLN-loaded hydrogels may be excellent candidates as hemostasis and anti-infection materials for the wound dressing application.

Mesoporous silicate nanoparticles/3D nanofibrous scaffold-mediated dual-drug delivery for bone tissue engineering

Controlled delivery systems play a critical role in the success of bone morphogenetic proteins (i.e., BMP2 and BMP7) for challenged bone repair. Instead of single-drug release that is currently and commonly prevalent, dual-drug delivery strategies are highly desired to achieve effective bone regeneration because natural bone repair process is driven by multiple factors. Particularly, angiogenesis is essential for osteogenesis and requires more than just one factor (e.g., Vascular Endothelial Growth Factor, VEGF). Therefore, we developed a novel mesoporous silicate nanoparticles (MSNs) incorporated-3D nanofibrous gelatin (GF) scaffold for dual-delivery of BMP2 and deferoxamine (DFO). DFO is a hypoxia-mimetic drug that can activate hypoxia-inducible factor-1 alpha (HIF-1α), and trigger subsequent angiogenesis. Sustained BMP2 release system was achieved through encapsulation into large-pored MSNs, while the relative short-term release of DFO was engineered through covalent conjugation with chitosan to reduce its cytotoxicity and elongate its half-life. Both MSNs and DFO were incorporated onto a porous 3D GF scaffold to serve as a biomimetic osteogenic microenvironment. Our data indicated that DFO and BMP2 were released from a scaffold at different release rates (10 vs 28 days) yet maintained their angiogenic and osteogenic ability, respectively. Importantly, our data indicated that the released DFO significantly improved BMP2-induced osteogenic differentiation where the dose/duration was important for its effects in both mouse and human stem cell models. Thus, we developed a novel and tunable MSNs/GF 3D scaffold-mediated dual-drug delivery system and studied the potential application of the both FDA-approved DFO and BMP2 for bone tissue engineering.

Keratin: dissolution, extraction and biomedical application

Keratinous materials such as wool, feathers and hooves are tough unique biological co-products that usually have high sulfur and protein contents. A high cystine content (7-13%) differentiates keratins from other structural proteins, such as collagen and elastin. Dissolution and extraction of keratin is a difficult process compared to other natural polymers, such as chitosan, starch, collagen, and a large-scale use of keratin depends on employing a relatively fast, cost-effective and time efficient extraction method. Keratin has some inherent ability to facilitate cell adhesion, proliferation, and regeneration of the tissue, therefore keratin biomaterials can provide a biocompatible matrix for regrowth and regeneration of the defective tissue. Additionally, due to its amino acid constituents, keratin can be tailored and finely tuned to meet the exact requirement of degradation, drug release or incorporation of different hydrophobic or hydrophilic tails. This review discusses the various methods available for the dissolution and extraction of keratin with emphasis on their advantages and limitations. The impacts of various methods and chemicals used on the structure and the properties of keratin are discussed with the aim of highlighting options available toward commercial keratin production. This review also reports the properties of various keratin-based biomaterials and critically examines how these materials are influenced by the keratin extraction procedure, discussing the features that make them effective as biomedical applications, as well as some of the mechanisms of action and physiological roles of keratin. Particular attention is given to the practical application of keratin biomaterials, namely addressing the advantages and limitations on the use of keratin films, 3D composite scaffolds and keratin hydrogels for tissue engineering, wound healing, hemostatic and controlled drug release.

A comparison study on the behavior of human endometrial stem cell-derived osteoblast cells on PLGA/HA nanocomposite scaffolds fabricated by electrospinning and freeze-drying methods

Background

An engineered tissue structure is an artificial scaffold combined with cells and signaling factors. Among various polymers, the polylactide-co-glycolide/hydroxyapatite (PLGA/HA) has attracted much attention due to their optimal properties. The aim of this study was to study the behavior of human endometrial stem cell (hEnSC)-derived osteoblast cells cultured on PLGA/HA nanocomposite scaffolds.

Methods

hEnSCs were isolated and exposed to osteogenic media for 21 days. Differentiated cells were cultured on PLGA/HA synthetic scaffolds. The PLGA/HA-based nanocomposite scaffolds were fabricated using either electrospinning or freeze-drying methods. Behavior of the cells was evaluated a week after seeding hEnSC-derived osteoblast-like cells on these scaffolds. Osteogenesis was investigated in terms of alkaline phosphatase activity, gene expression, immunocytochemistry (ICC), proliferation, and scanning electron microscopy (SEM). Moreover, scaffold properties, such as pore size and morphology of the cells, onto the scaffolds were evaluated using SEM. Furthermore, biocompatibility of these scaffolds was confirmed by 3-(4,5-dimethylthiazoyl-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

Results

The matrix mineralization was proved by alizarin red staining, and the osteogenic media-treated cultures positively expressed osteocalcin and osteopontin markers. Moreover, qRT-PCR results confirmed the positive gene expression of osteopontin and osteonectin in the differentiated osteoblast-like cells. The results of behavior assessment of the cultured cells on electrospinning and freeze-dried scaffolds showed that the behavior of the cultured cells on the freeze-dried PLGA/HA scaffolds was significantly better than the electrospinning PLGA/HA scaffolds.

Conclusion

It has been shown that the freeze-dried PLGA/HA nanocomposite scaffolds can appropriately support the attachment and proliferation of the differentiated osteoblast cells and are a suitable candidate for bone tissue engineering.

Priming the body to receive the therapeutic agent to redefine treatment benefit/risk profile

Many therapeutic agents offer a low useful dose (dose responsible for efficacy)/useless dose (dose eliminated or responsible for toxicity) ratio, mainly due to the fact that therapeutic agents must ensure in one single object all the functions required to deliver the treatment, which leads to compromises in their physico-chemical design. Here we introduce the concept of priming the body to receive the treatment by uncorrelating these functions into two distinct objects sequentially administered: a nanoprimer occupying transiently the main pathway responsible for therapeutic agent limited benefit/risk ratio followed by the therapeutic agent. The concept was evaluated for different nature of therapeutic agents: For nanomedicines we designed a liposomal nanoprimer presenting preferential hepatic accumulation without sign of acute toxicity. This nanoprimer was able to increase the blood bioavailability of nanomedicine correlated with a lower hepatic accumulation. Finally this nanoprimer markedly enhanced anti-tumor efficacy of irinotecan loaded liposomes in the HT-29 tumor model when compared to the nanomedicine alone. Then, for small molecules we demonstrated the ability of a cytochrome inhibitor loaded nanoprimer to increase efficacy of docetaxel treatment. These results shown that specific nanoprimers could be designed for each family of therapeutic agents to answer to their specific needs.

Advancements and Challenges in Multidomain Multicargo Delivery Vehicles

Reparative and regenerative processes are well-orchestrated temporal and spatial events that are governed by multiple cells, molecules, signaling pathways, and interactions thereof. Yet again, currently available implantable devices fail largely to recapitulate nature's complexity and sophistication in this regard. Herein, success stories and challenges in the field of layer-by-layer, composite, self-assembly, and core-shell technologies are discussed for the development of multidomain/multicargo delivery vehicles.

Breath figures in tissue engineering and drug delivery: State-of-the-art and future perspectives

The breath figure (BF) method is an easy, low-cost method to prepare films with a highly organized honeycomb-like porous surface. The particular surface topography and porous nature of these materials makes them valuable substrates for studying the complex effects of topography on cell fate, and to produce biomimetic materials with high performance in tissue engineering. Numerous researchers over the last two decades have studied the effects of the honeycomb topography on a variety of primary and immortalized cell lines, and drew important conclusions that can be translated to the construction of optimal biomaterials for cell culture. The literature also encouragingly shows the potential of honeycomb films to induce differentiation of stem cells down a specific lineage without the need for biochemical stimuli. Here, we review the main studies where BF honeycomb films are used as substrates for tissue engineering applications. Furthermore, we highlight the numerous advantages of the porous nature of the films, such as the enhanced, spatially controlled adsorption of proteins, the topographical cues influencing cellular behavior, and the enhanced permeability which is essential both in vitro and in vivo. Finally, this review highlights the elegant use of honeycomb films as drug-eluting biomaterials or as reservoirs for distinct drug delivery systems.

STATEMENT OF SIGNIFICANCE

Combining biocompatible surfaces and 3D nano/microscale topographies, such as pores or grooves, is an effective strategy for manufacturing tissue engineering scaffolds. The breath figure (BF) method is an easy technique to prepare cell culture substrates with an organized, honeycomb-like porous surface. These surface features make these scaffolds valuable for studying how the cells interact with the biomaterials. Their unique surface topography can also resemble the natural environment of the tissues in the human body. For that reason, numerous studies, using different cell types, have shown that honeycomb films can constitute high performance substrates for cell culture. Here, we review those studies, we highlight the advantages of honeycomb films in tissue engineering and we discuss their potential as unique drug-eluting systems.

Elastomeric and pH-responsive hydrogels based on direct crosslinking of the poly(glycerol sebacate) pre-polymer and gelatin

The synthesis and biomedical applications of novel elastomeric, pH-responsive, biocompatible and biodegradable copolymer hydrogels based on poly(glycerol sebacate) and gelatin.

An Implantable Micro-Caged Device for Direct Local Delivery of Agents

Local and controlled delivery of therapeutic agents directly into focally afflicted tissues is the ideal for the treatment of diseases that require direct interventions. However, current options are obtrusive, difficult to implement, and limited in their scope of utilization; the optimal solution requires a method that may be optimized for available therapies and is designed for exact delivery. To address these needs, we propose the Biocage, a customizable implantable local drug delivery platform. The device is a needle-sized porous container capable of encasing therapeutic molecules and matrices of interest to be eluted into the region of interest over time. The Biocage was fabricated using the Nanoscribe Photonic Professional GT 3D laser lithography system, a two-photon polymerization (2PP) 3D printer capable of micron-level precision on a millimeter scale. We demonstrate the build consistency and features of the fabricated device; its ability to release molecules; and a method for its accurate, stable delivery in mouse brain tissue. The Biocage provides a powerful tool for customizable and precise delivery of therapeutic agents into target tissues.

Biodegradable Scaffolds for Bone Regeneration Combined with Drug-Delivery Systems in Osteomyelitis Therapy

A great deal of research is ongoing in the area of tissue engineering (TE) for bone regeneration. A possible improvement in restoring damaged tissues involves the loading of drugs such as proteins, genes, growth factors, antibiotics, and anti-inflammatory drugs into scaffolds for tissue regeneration. This mini-review is focused on the combination of the local delivery of antibiotic agents with bone regenerative therapy for the treatment of a severe bone infection such as osteomyelitis. The review includes a brief explanation of scaffolds for bone regeneration including scaffolds characteristics and types, a focus on severe bone infections (especially osteomyelitis and its treatment), and a literature review of local antibiotic delivery by the combination of scaffolds and drug-delivery systems. Some examples related to published studies on gentamicin sulfate-loaded drug-delivery systems combined with scaffolds are discussed, and future perspectives are highlighted.

Administration of signalling molecules dictates stem cell homing for in situ regeneration

Ex vivo-expanded stem cells have long been a cornerstone of biotherapeutics and have attracted increasing attention for treating intractable diseases and improving tissue regeneration. However, using exogenous cellular materials to develop restorative treatments for large numbers of patients has become a major concern for both economic and safety reasons. Advances in cell biological research over the past two decades have expanded the potential for using endogenous stem cells during wound healing processes, and in particular, recent insight into stem cell movement and homing has prompted regenerative research and therapy based on recruiting endogenous cells. Inspired by the natural healing process, artificial administration of specific chemokines as signals systemically or at the injury site, typically using biomaterials as vehicles, is a state-of-the-art strategy that potentiates stem cell homing and recreates an anti-inflammatory and immunomodulatory microenvironment to enhance in situ tissue regeneration. However, pharmacologically coaxing endogenous stem cells to act as therapeutics in the field of biomedicine remains in the early stages; its efficacy is limited by the lack of innovative methodologies for chemokine presentation and release. This review describes how to direct the homing of endogenous stem cells via the administration of specific signals, with a particular emphasis on targeted signalling molecules that regulate this homing process, to enhance in situ tissue regeneration. We also provide an outlook on and critical considerations for future investigations to enhance stem cell recruitment and harness the reparative potential of these recruited cells as a clinically relevant cell therapy.

Strategies to retain properties of bone marrow-derived mesenchymal stem cells ex vivo

Mesenchymal stem cells (MSCs) have been extensively used for cell therapies and tissue engineering. The current MSC strategy requires a large quantity of cells for such applications, which can be achieved through cell expansion in culture. In the body, stem cell fate is largely determined by their microenvironment, known as the niche. The complex and dynamic stem cell niche provides physical, mechanical, and chemical cues to collaboratively regulate cell activities. It remains a great challenge to maintain the properties of MSCs in culture. Constructing a microenvironment as an engineered stem cell niche in culture to maintain MSC phenotypes, properties, and functions is a viable strategy to address the issue. Here, we review the current understanding of MSC behavior in the bone marrow niche, describe different strategies to engineer an in vitro microenvironment for maintaining MSC properties and functions, and discuss previous findings on environmental factors critical to the modulation of MSC activities in engineered microenvironments.

Microfluidic Bioprinting for Engineering Vascularized Tissues and Organoids

Engineering vascularized tissue constructs and organoids has been historically challenging. Here we describe a novel method based on microfluidic bioprinting to generate a scaffold with multilayer interlacing hydrogel microfibers. To achieve smooth bioprinting, a core-sheath microfluidic printhead containing a composite bioink formulation extruded from the core flow and the crosslinking solution carried by the sheath flow, was designed and fitted onto the bioprinter. By blending gelatin methacryloyl (GelMA) with alginate, a polysaccharide that undergoes instantaneous ionic crosslinking in the presence of select divalent ions, followed by a secondary photocrosslinking of the GelMA component to achieve permanent stabilization, a microfibrous scaffold could be obtained using this bioprinting strategy. Importantly, the endothelial cells encapsulated inside the bioprinted microfibers can form the lumen-like structures resembling the vasculature over the course of culture for 16 days. The endothelialized microfibrous scaffold may be further used as a vascular bed to construct a vascularized tissue through subsequent seeding of the secondary cell type into the interstitial space of the microfibers. Microfluidic bioprinting provides a generalized strategy in convenient engineering of vascularized tissues at high fidelity.

Biphasic Calcium Phosphate (BCP)-Immobilized Porous Poly (d,l-Lactic-co-Glycolic Acid) Microspheres Enhance Osteogenic Activities of Osteoblasts

The purpose of this study was to evaluate the potential of porous poly (d,l-lactic-co-glycolic acid) (PLGA) microspheres (PMSs) immobilized on biphasic calcium phosphate nanoparticles (BCP NPs) (BCP-IM-PMSs) to enhance osteogenic activity. PMSs were fabricated using a fluidic device, and their surfaces were modified with l-lysine (aminated-PMSs), whereas the BCP NPs were modified with heparin⁻dopamine (Hep-DOPA) to obtain heparinized⁻BCP (Hep-BCP) NPs. BCP-IM-PMSs were fabricated via electrostatic interactions between the Hep-BCP NPs and aminated-PMSs. The fabricated BCP-IM-PMSs showed an interconnected pore structure. In vitro studies showed that MG-63 cells cultured on BCP-IM-PMSs had increased alkaline phosphatase activity, calcium content, and mRNA expression of osteocalcin (OCN) and osteopontin (OPN) compared with cells cultured on PMSs. These data suggest that BCP NP-immobilized PMSs have the potential to enhance osteogenic activity.

Preparation and properties of a novel carbon nanotubes/poly(vinyl alcohol)/epidermal growth factor composite biological dressing

Wound dressings with drug delivery system have drawn increasing attention in skin damage recombination. Herein, a novel composite biological dressing was prepared and based on poly(vinyl alcohol) (PVA) combined with carbon nanotubes (CNTs) and epidermal growth factor (EGF) by electrospinning on gauze. The properties of the CNTs/PVA/EGF composite dressing were systemically investigated by general observation, and scanning electron microscopy (SEM). In vitro, the cytotoxicity of this dressing was investigated using a methyl thiazolyl tetrazolium (MTT) assay on L929 fibroblasts. In order to study the sustained release of EGF from this dressing, the concentration of EGF at different times was tested by ELISA. Furthermore, the biological activity of the released EGF was also evaluated using the MTT assay. Moreover, an in vivo experiment was conducted to observe whether this dressing was capable of improving healing in the model of wounded skin on rats. It was revealed that this dressing had a well-distributed microstructure by SEM. Additionally, the grade of cytotoxicity was low, and the EGF had a sustained release rate from this dressing. Furthermore, a maximum accumulative release rate of 12.47% was identified at 12 h, and was retained at 9.4% after 48 h. Simultaneously, the relative growth rate of L929 fibroblasts in the 12 h experimental group and 48 h group was 291.24 and 211.3%, respectively. Next, the efficacy of these products was evaluated in vivo using Sprague-Dawley rats with a skin injury model. The healing of wounded skin of rats was sped up by this dressing based on the gross and histological appearances. From 7 to 10 days, the wounds in the experimental group were almost healed. In conclusion, this CNTs/PVA/EGF dressing had a well-distributed structure and an ability to release EGF at a sustained rate with the activity being favorable. On the basis of those results, a positive influence of designed dressing for accelerated wound healing was confirmed.

Poly(Lactic-co-Glycolic Acid): Applications and Future Prospects for Periodontal Tissue Regeneration

Periodontal tissue regeneration is the ultimate goal of the treatment for periodontitis-affected teeth. The success of regenerative modalities relies heavily on the utilization of appropriate biomaterials with specific properties. Poly (lactic-co-glycolic acid) (PLGA), a synthetic aliphatic polyester, has been actively investigated for periodontal therapy due to its favorable mechanical properties, tunable degradation rates, and high biocompatibility. Despite the attractive characteristics, certain constraints associated with PLGA, in terms of its hydrophobicity and limited bioactivity, have led to the introduction of modification strategies that aimed to improve the biological performance of the polymer. Here, we summarize the features of the polymer and update views on progress of its applications as barrier membranes, bone grafts, and drug delivery carriers, which indicate that PLGA can be a good candidate material in the field of periodontal regenerative medicine.

Engineering a Cell Home for Stem Cell Homing and Accommodation

Distilling complexity to advance regenerative medicine from laboratory animals to humans, in situ regeneration will continue to evolve using biomaterial strategies to drive endogenous cells within the human body for therapeutic purposes; this approach avoids the need for delivering ex vivo-expanded cellular materials. Ensuring the recruitment of a significant number of reparative cells from an endogenous source to the site of interest is the first step toward achieving success. Subsequently, making the "cell home" cell-friendly by recapitulating the natural extracellular matrix (ECM) in terms of its chemistry, structure, dynamics, and function, and targeting specific aspects of the native stem cell niche (e.g., cell-ECM and cell-cell interactions) to program and steer the fates of those recruited stem cells play equally crucial roles in yielding a therapeutically regenerative solution. This review addresses the key aspects of material-guided cell homing and the engineering of novel biomaterials with desirable ECM composition, surface topography, biochemistry, and mechanical properties that can present both biochemical and physical cues required for in situ tissue regeneration. This growing body of knowledge will likely become a design basis for the development of regenerative biomaterials for, but not limited to, future in situ tissue engineering and regeneration.

Photocrosslinkable polyaspartamide/polylactide copolymer and its porous scaffolds for chondrocytes

With the aim to produce, by a simple and reproducible technique, porous scaffolds potentially employable for tissue engineering purposes, in this work, we have synthesized a methacrylate (MA) copolymer of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) and polylactic acid (PLA). PHEA-PLA-MA has been dissolved in organic solvent at different concentrations in the presence of NaCl particles with different granulometry, and through UV irradiation and further salt leaching technique, various porous scaffolds have been prepared. Obtained samples have been characterized by scanning electron microscopy and their porosity has been evaluated as well as their degradation profile in aqueous medium in the absence or in the presence of esterase from porcine liver. PHEA-PLA-MA scaffold that has shown homogeneous porosity and the best degradation profile has been further characterized to study its mechanical properties along with its capacity to incorporate and to control the release of dexamethasone. Finally, the ability to allow a three-dimensional culture of bovine articular chondrocytes have been also investigated.

Drug-Loaded Polymeric Nanoparticles for Cancer Stem Cell Targeting

Cancer stem cells (CSCs) have been reported to play critical roles in tumor initiation, propagation, and regeneration of cancer. Nano-size vehicles are employed to deliver drugs to target the CSCs for cancer therapy. Polymeric nanoparticles have been considered as the most efficient vehicles for drug delivery due to their excellent pharmacokinetic properties. The CSCs specific antibodies or ligands can be conjugated onto the surface or interior of nanoparticles to successfully target and finally eliminate CSCs. In this review, we focus on the approaches of polymeric nanoparticles design for loading drug, and their potential application for CSCs targeting in cancer therapy.

[Biodegradable synthetic polymers for the design of implantable medical devices: the ligamentoplasty case]

The sector of implantable medical devices is a growing sector of health products especially dynamic in the field of research. To improve the management of patients and to meet clinical requirements, researchers are developing new types of medical devices. They use different families of biomaterials presenting various chemical and physical characteristics in order for providing clinicians with health products optimized for biomedical applications. In this article, we aim to show how, starting from a family of biomaterials (degradable polymers), it is possible to design an implantable medical device for the therapeutic management of the failure of anterior cruciate ligament. The main steps leading to the design of a total ligament reinforcement are detailed. They range from the synthesis and characterization of degradable polymer to the shaping of the knitted implant, through the assessment of the study of the impact of sterilization on mechanical properties and checking cytocompatibility.