A biomimetic 3D microtubule-orientated poly(lactide-co-glycolide) scaffold with interconnected pores for tissue engineering

Hierarchically Biomimetic Scaffolds with Anisotropic Micropores and Nanotopological Patterns to Promote Bone Regeneration via Geometric Modulation

Structural engineering is an appealing means to modulate osteogenesis without the intervention of exogenous cells or therapeutic agents. In this work, a novel 3D scaffold with anisotropic micropores and nanotopographical patterns is developed. Scaffolds with oriented pores are fabricated via the selective extraction of water-soluble polyethylene oxide from its poly(ε-caprolactone) co-continuous mixture and uniaxial stretching. The plate apatite-like lamellae are subsequently hatched on the pore walls through surface-induced epitaxial crystallization. Such a unique geometric architecture yields a synergistic effect on the osteogenic capability. The prepared scaffold leads to a 19.2% and 128.0% increase in the alkaline phosphatase activity of rat bone mesenchymal stem cells compared to that of the scaffolds with only oriented pores and only nanotopographical patterns, respectively. It also induces the greatest upregulation of osteogenic-related gene expression in vitro. The cranial defect repair results demonstrate that the prepared scaffold effectively promotes new bone regeneration, as indicated by a 350% increase in collagen I expression in vivo compared to the isotropic porous scaffold without surface nanotopology after implantation for 14 weeks. Overall, this work provides geometric motifs for the transduction of biophysical cues in 3D porous scaffolds, which is a promising option for tissue engineering applications.

Fabrication of bio-inspired anisotropic structures from biopolymers for biomedical applications: A review

The anisotropic features play indispensable roles in regulating various life activities in different organisms. Increasing efforts have been made to learn and mimic various tissues' intrinsic anisotropic structure or functionality for broad applications in different areas, especially in biomedicine and pharmacy. This paper discusses the strategies for fabricating biomaterials using biopolymers for biomedical applications with the case study analysis. Biopolymers, including different polysaccharides, proteins, and their derivates, that have been confirmed with sound biocompatibility for different biomedical applications are summarized, with a special focus on nanocellulose. Advanced analytical techniques for understanding and characterizing the biopolymer-based anisotropic structures for various biomedical applications are also summarized. Challenges still exist in precisely constructing biopolymers-based biomaterials with anisotropic structures from molecular to macroscopic levels and fitting the dynamic processes in native tissue. It is foreseeable that with the advancement of biopolymers' molecular functionalization, biopolymer building block orientation manipulation strategies, and structural characterization techniques, developing anisotropic biopolymer-based biomaterials for different biomedical applications would significantly contribute to a friendly disease-curing and healthcare experience.

Silk fibroin-based biomaterials for cartilage/osteochondral repair

Osteoarthritis (OA) is a common joint disease with a high disability rate. In addition, OA not only causes great physiological and psychological harm to patients, but also puts great pressure on the social healthcare system. Pathologically, the disintegration of cartilage and the lesions of subchondral bone are related to OA. Currently, tissue engineering, which is expected to overcome the defects of existing treatment methods, had a lot of research in the field of cartilage/osteochondral repair. Silk fibroin (SF), as a natural macromolecular material with good biocompatibility, unique mechanical properties, excellent processability and degradability, holds great potential in the field of tissue engineering. Nowadays, SF had been prepared into various materials to adapt to the demands of cartilage/osteochondral repair. SF-based biomaterials can also be functionally modified to enhance repair performance further. In this review, the preparation methods, types, structures, mechanical properties, and functional modifications of SF-based biomaterials used for cartilage/osteochondral repair are summarized and discussed. We hope that this review will provide a reference for the design and development of SF-based biomaterials in cartilage/osteochondral repair field.

A review of biomimetic scaffolds for bone regeneration: Toward a cell-free strategy

In clinical terms, bone grafting currently involves the application of autogenous, allogeneic, or xenogeneic bone grafts, as well as natural or artificially synthesized materials, such as polymers, bioceramics, and other composites. Many of these are associated with limitations. The ideal scaffold for bone tissue engineering should provide mechanical support while promoting osteogenesis, osteoconduction, and even osteoinduction. There are various structural complications and engineering difficulties to be considered. Here, we describe the biomimetic possibilities of the modification of natural or synthetic materials through physical and chemical design to facilitate bone tissue repair. This review summarizes recent progresses in the strategies for constructing biomimetic scaffolds, including ion-functionalized scaffolds, decellularized extracellular matrix scaffolds, and micro- and nano-scale biomimetic scaffold structures, as well as reactive scaffolds induced by physical factors, and other acellular scaffolds. The fabrication techniques for these scaffolds, along with current strategies in clinical bone repair, are described. The developments in each category are discussed in terms of the connection between the scaffold materials and tissue repair, as well as the interactions with endogenous cells. As the advances in bone tissue engineering move toward application in the clinical setting, the demonstration of the therapeutic efficacy of these novel scaffold designs is critical.

Recent Progress on Biodegradable Tissue Engineering Scaffolds Prepared by Thermally-Induced Phase Separation (TIPS)

Porous biodegradable scaffolds provide a physical substrate for cells allowing them to attach, proliferate and guide the formation of new tissues. A variety of techniques have been developed to fabricate tissue engineering (TE) scaffolds, among them the most relevant is the thermally-induced phase separation (TIPS). This technique has been widely used in recent years to fabricate three-dimensional (3D) TE scaffolds. Low production cost, simple experimental procedure and easy processability together with the capability to produce highly porous scaffolds with controllable architecture justify the popularity of TIPS. This paper provides a general overview of the TIPS methodology applied for the preparation of 3D porous TE scaffolds. The recent advances in the fabrication of porous scaffolds through this technique, in terms of technology and material selection, have been reviewed. In addition, how properties can be effectively modified to serve as ideal substrates for specific target cells has been specifically addressed. Additionally, examples are offered with respect to changes of TIPS procedure parameters, the combination of TIPS with other techniques and innovations in polymer or filler selection.

Growth factor loading on aliphatic polyester scaffolds

Cells, scaffolds and growth factors are three elements of tissue engineering. The success of tissue engineering methods relies on precise and dynamic interactions between cells, scaffolds and growth factors. Aliphatic polyester scaffolds are promising tissue engineering scaffolds that possess good mechanical properties, low immunogenicity, non-toxicity, and adjustable degradation rates. How growth factors can be loaded onto/into aliphatic polyester scaffolds and be constantly released with the required bioactivity to regulate cell growth and promote defect tissue repair and regeneration has become the main concern of tissue engineering researchers. In this review, the existing main methods of loading growth factors on aliphatic polyester scaffolds, the release behavior of loaded growth factors and their positive effects on cell, tissue repair and regeneration are introduced. Advantages and shortcomings of each method also are mentioned. It is still a great challenge to control the release of loaded growth factors at a certain time and at a concentration simulating the biological environment of native tissue.

Preparation of Doxorubicin-Loaded Amphiphilic Poly(D,L-Lactide-Co-Glycolide)-b-Poly(N-Acryloylmorpholine) AB2 Miktoarm Star Block Copolymers for Anticancer Drug Delivery

Owing to their unique topology and physical properties, micelles based on miktoarm amphiphilic star block copolymers play an important role in the biomedical field for drug delivery. Herein, we developed a series of AB2-type poly(D,L-lactide-co-glycolide)-b-poly(N-acryloyl morpholine) (PLGA-b-PNAM2) miktoarm star block copolymers by reversible addition-fragmentation chain-transfer polymerization and ring-opening copolymerization. The resulting miktoarm star polymers were investigated by 1H NMR spectroscopy and gel permeation chromatography. The critical micellar concentration value of the micelles increases with an increase in PNAM block length. As revealed by transmission electron microscopy and dynamic light scattering, the amphiphilic miktoarm star block copolymers can self-assemble to form spherical micellar aggregates in water. The anticancer drug doxorubicin (DOX) was encapsulated by polymeric micelles; the drug-loading efficiency and drug-loading content of the DOX-loaded micelles were 81.7% and 9.1%, respectively. Acidic environments triggered the dissociation of the polymeric micelles, which led to the more release of DOX in pH 6.4 than pH 7.4. The amphiphilic PLGA-b-PNAM2 miktoarm star block copolymers may have broad application as nanocarriers for controlled drug delivery.

Fabrication of a biomimetic spinal cord tissue construct with heterogenous mechanical properties using intrascaffold cell assembly

In tissue engineering studies, scaffolds play a very important role in offering both physical and chemical cues for cell growth and tissue regeneration. However, in some cases, tissue regeneration requires scaffolds with high mechanical properties (e.g., bone and cartilage), while cells need a soft mechanical microenvironment. In this study, to mimic the heterogenous mechanical properties of a spinal cord tissue, a biomimetic rat tissue construct is fabricated. A collagen-coated poly(lactic-co-glycolic acid) scaffold is manufactured using thermally induced phase separation casting. Primary rat neural cells (P01 Wistar rat cortex) with soft hydrogels are later printed within the scaffold using an image-guided intrascaffold cell assembly technique. The scaffolds have unidirectional microporous structure with parallel axial macrochannels (260 ± 4 µm in diameter). Scaffolds showed mechanical properties similar to rat spine (ultimate tensile strength: 0.085 MPa, Young's modulus [stretch]: 0.31 MPa). The bioink composed of gelatin/alginate/fibrinogen is precisely printed into the macrochannels and showed mechanical properties suitable for neural cells (Young's modulus [compressive]: 3.814 kPa). Scaffold interface, cell viability, and immunostaining analyses show uniform distribution of stable, healthy, and elongated neural cells and neurites over 14 culture days in vitro. The results demonstrated that this method can serve as a valuable tool to aid manufacturing of tissue constructs requiring heterogenous mechanical properties for complex cell and/or biomolecule assembly.

Facile Fabrication of Composite Scaffolds for Long-Term Controlled Dual Drug Release

Bone tuberculosis (TB) caused by mycobacterium tuberculosis continues to present a formidable challenge to humans. To effectively cure serious bone TB, a novel kind of composite scaffolds with long-term dual drug release behaviours were prepared to satisfy the needs of both bone regeneration and antituberculosis drug therapy. In virtue of an improved O/W emulsion technique, water-soluble isoniazid (INH)-loaded gelatin microparticles were obtained by tailoring the content of β-tricalcium phosphate (β-TCP), which played significant roles in INH entrapment efficiency and drug release behaviours. By mixing with the poly(ε-caprolactone)-block-poly (lactic-co-glycolic acid) (b-PLGC) solution containing oil-soluble rifampicin (RFP) via the particle leaching combined with phase separation technique, the dual drugs-loaded composite scaffolds were fabricated, which possessed interconnected porous structures and achieved the steady release of INH and RFP drugs for three months. Moreover, this dual drugs-loaded system could basically achieve their expectant roles of respective drugs without obvious influences with each other. This strategy on preparation of intelligent composite scaffolds with the multi-drugs loading capacity and controlled long-term release behaviour will be potential and promising substrates in clinical treatment of bone tuberculosis.

Influence of pore architectures of silk fibroin/collagen composite scaffolds on the regeneration of osteochondral defects in vivo

The aligned scaffolds facilitate migration of endogenous reparative cells, leading to better regeneration of osteochondral defects.

Chemically Treated 3D Printed Polymer Scaffolds for Biomineral Formation

We present the synthesis of nylon-12 scaffolds by 3D printing and demonstrate their versatility as matrices for cell growth, differentiation, and biomineral formation. We demonstrate that the porous nature of the printed parts makes them ideal for the direct incorporation of preformed nanomaterials or material precursors, leading to nanocomposites with very different properties and environments for cell growth. Additives such as those derived from sources such as tetraethyl orthosilicate applied at a low temperature promote successful cell growth, due partly to the high surface area of the porous matrix. The incorporation of presynthesized iron oxide nanoparticles led to a material that showed rapid heating in response to an applied ac magnetic field, an excellent property for use in gene expression and, with further improvement, chemical-free sterilization. These methods also avoid changing polymer feedstocks and contaminating or even damaging commonly used selective laser sintering printers. The chemically treated 3D printed matrices presented herein have great potential for use in addressing current issues surrounding bone grafting, implants, and skeletal repair, and a wide variety of possible incorporated material combinations could impact many other areas.

The influence of bubble size on chondrogenic differentiation of adipose-derived stem cells in gelatin microbubble scaffolds

In human bodies, cartilage tissue lacks the ability to heal when it encounters trauma or lesions.

Surface modification of porous PLGA scaffolds with plasma for preventing dimensional shrinkage and promoting scaffold–cell/tissue interactions

An effective strategy for simultaneously tackling the dimensional shrinkage of a highly porous PLGA scaffold and improving the scaffold–tissue integration.

Plasma surface modification of polymers for sensor applications

Polymeric sensors play an increasingly important role in monitoring the environment we live in, providing relevant information for a host of applications.

Regeneration of osteochondral defects in vivo by a cell-free cylindrical poly(lactide-co-glycolide) scaffold with a radially oriented microstructure

A scaffold with an oriented porous architecture to facilitate cell infiltration and bioactive interflow between neo-host tissues is of great importance for in situ inductive osteochondral regeneration. In this study, a poly(lactide-co-glycolide) (PLGA) scaffold with oriented pores in its radial direction was fabricated via unidirectional cooling of the PLGA solution in the radial direction, following with lyophilization. Micro-computed tomography evaluation and scanning electron microscopy observation confirmed the radially oriented microtubular pores in the scaffold. The scaffold had porosity larger than 90% and a compressive modulus of 4 MPa in a dry state. Culture of bone marrow stem cells in vitro revealed faster migration and regular distribution of cells in the poly(lactide-co-glycolide) scaffold with oriented pores compared with the random PLGA scaffold. The cell-free oriented macroporous PLGA scaffold was implanted into rabbit articular osteochondral defect in vivo for 12 weeks to evaluate its inductive tissue regeneration function. Histological analysis confirmed obvious tide mark formation and abundant chondrocytes distributed regularly with obvious lacunae in the cartilage layer. Safranin O-fast green staining showed an obvious boundary between the two layers with distinct staining results, indicating the simultaneous regeneration of the cartilage and subchondral bone layers, which is not the case for the random poly(lactide-co-glycolide) scaffold after the same implantation in vivo. The oriented macroporous PLGA scaffold is a promising material for the in situ inductive osteochondral regeneration without the necessity of preseeding cells.

Biodegradable polymer scaffolds

Tissue engineering aims to repair the damaged tissue by transplantation of cells or introducing bioactive factors in a biocompatible scaffold. In recent years, biodegradable polymer scaffolds mimicking the extracellular matrix have been developed to promote the cell proliferation and extracellular matrix deposition. The biodegradable polymer scaffolds thus act as templates for tissue repair and regeneration. This article reviews the updated information regarding various types of natural and synthetic biodegradable polymers as well as their functions, physico-chemical properties, and degradation mechanisms in the development of biodegradable scaffolds for tissue engineering applications, including their combination with 3D printing.

Cell-Free HA-MA/PLGA Scaffolds with Radially Oriented Pores for In Situ Inductive Regeneration of Full Thickness Cartilage Defects

A bioactive scaffold with desired microstructure is of great importance to induce infiltration of somatic and stem cells, and thereby to achieve the in situ inductive tissue regeneration. In this study, a scaffold with oriented pores in the radial direction is prepared by using methacrylated hyaluronic acid (HA-MA) via controlled directional cooling of a HA-MA solution, and followed with photo-crosslinking to stabilize the structure. Poly(lactide-co-glycolide) (PLGA) is further infiltrated to enhance the mechanical strength, resulting in a compressive modulus of 120 kPa. In vitro culture of bone marrow stem cells (BMSCs) reveals spontaneous cell aggregation inside this type of scaffold with a spherical morphology. In vivo transplantation of the cell-free scaffold in rabbit knees for 12 w regenerates simultaneously both cartilage and subchondral bone with a Wakitani score of 2.8. Moreover, the expression of inflammatory factor interleukin-1β (IL-1β) is down regulated, although tumor necrosis factor-α (TNF-α) is remarkably up regulated. With the anti-inflammatory, bioactive properties and good restoration of full thickness cartilage defect in vivo, the oriented macroporous HA-MA/PLGA hybrid scaffold has a great potential for the practical application in the in situ cartilage regeneration.

Biodegradability of poly(lactic-co-glycolic acid) after femtosecond laser irradiation

Biodegradation is a key property for biodegradable polymer-based tissue scaffolds because it can provide suitable space for cell growth as well as tailored sustainability depending on their role. Ultrashort pulsed lasers have been widely used for the precise processing of optically transparent materials, including biodegradable polymers. Here, we demonstrated the change in the biodegradation of a poly(lactic-co-glycolic acid) (PLGA) following irradiation with femtosecond laser pulses at different wavelengths. Microscopic observation as well as water absorption and mass change measurement revealed that the biodegradation of the PLGA varied significantly depending on the laser wavelength. There was a significant acceleration of the degradation rate upon 400 nm-laser irradiation, whereas 800 nm-laser irradiation did not induce a comparable degree of change. The X-ray photoelectron spectroscopy analysis indicated that laser pulses at the shorter wavelength dissociated the chemical bonds effectively, resulting in a higher degradation rate at an early stage of degradation.

Three-Dimensional Graphene: A Biocompatible and Biodegradable Scaffold with Enhanced Oxygenation

Owing to its high porosity, specific surface area and three-dimensional structure, three-dimensional graphene (3D-C) is a promising scaffold material for tissue engineering, regenerative medicine as well as providing a more biologically relevant platform for living organisms in vivo studies. Recently, its differentiation effects on cells growth and anti-inflammation properties have also been demonstrated. Here, we report a complete study of 3D-C as a fully adequate scaffold for tissue engineering and systematically analyze its biocompatibility and biodegradation mechanism. The metabolic activities of liver cells (HepG2 hepatocarcinoma cells) on 3D-C are studied and our findings show that cell growth on 3D-C has high cell viability (> 90%), low lactate production (reduced by 300%) and its porous structure also provides an excellent oxygenation platform. 3D-C is also biodegradable via a 2-step oxidative biodegradation process by first, disruption of domains and lift off of smaller graphitic particles from the surface of the 3D-C and subsequently, the decomposition of these graphitic flakes. In addition, the speed of the biodegradation can be tuned with pretreatment of O2 plasma.

Fabrication and effect on regulating vSMC phenotype of a biomimetic tunica media scaffold

We constructed a bFGF@TGF-β1 loaded porous film-like PLGA scaffold with dual surface topography of nanofiber and micro-orientation structures for regulating the phenotype of vascular smooth muscle cell (vSMC).

An injectable scaffold based on crosslinked hyaluronic acid gel for tissue regeneration

An injectable scaffold of crosslinked hyaluronic acid gel for tissue regeneration.

Uniform PEGylated PLGA Microcapsules with Embedded Fe3O4 Nanoparticles for US/MR Dual-Modality Imaging

Well-designed agents for enhanced multimodal imaging have attracted great interests in recent years. In this work, we adopted a premix membrane emulsification (PME) method to prepare uniform PEGylated poly(lactic-co-glycolic acid) (PLGA) microcapsules (MCs) with superparamagnetic Fe3O4 nanoparticles (NPs) embedded in the shell (Fe3O4@PEG-PLGA MCs) for ultrasound (US)/magnetic resonance (MR) bimodal imaging. Compared to Fe3O4@PLGA MCs without PEGylation, Fe3O4@PEG-PLGA MCs could more stably and homogeneously disperse in physiological solutions. In vitro and in vivo trials demonstrated that Fe3O4@PEG-PLGA MCs (∼3.7 μm) with very narrow size distribution (PDI=0.03) could function as efficient dual-modality contrast agents to simultaneously enhance US and MR imaging performance greatly. In vitro cell toxicity and careful histological examinations illustrated no appreciable cytotoxicity and embolism of Fe3O4@PEG-PLGA MCs to mice even at high dose. The uniform composite MCs developed here can act as clinical bimodal contrast agents to improve hybrid US/MR imaging contrast, which is promising for accurate diagnosis and real-time monitoring of difficult and complicated diseases.

In vitro and in vivo drug release behavior and osteogenic potential of a composite scaffold based on poly(ε-caprolactone)-block-poly(lactic-co-glycolic acid) and β-tricalcium phosphate

To cure serious bone tuberculosis, a novel long-term drug delivery system was designed and prepared to satisfy the needs of both bone regeneration and antituberculous drug therapy.