Biomimetic natural biomaterials for tissue engineering and regenerative medicine:new biosynthesis methods,recent advances,and emerging applications

Biomimetic materials have emerged as attractive and competitive alternatives for tissue engineering(TE)and regenerative medicine.In contrast to conventional biomaterials or synthetic materials,biomimetic scaffolds based on natural biomaterial can offer cells a broad spectrum of biochemical and biophysical cues that mimic the in vivo extracellular matrix(ECM).Additionally,such materials have mechanical adaptability,micro-structure interconnectivity,and inherent bioactivity,making them ideal for the design of living implants for specific applications in TE and regenerative medicine.This paper provides an overview for recent progress of biomimetic natural biomaterials(BNBMs),including advances in their preparation,functionality,potential applications and future challenges.We highlight recent advances in the fabrication of BNBMs and outline general strategies for functionalizing and tailoring the BNBMs with various biological and physicochemical characteristics of native ECM.Moreover,we offer an overview of recent key advances in the functionalization and applications of versatile BNBMs for TE applications.Finally,we conclude by offering our perspective on open challenges and future developments in this rapidly-evolving field.

Biomaterials and tissue engineering in traumatic brain injury:novel perspectives on promoting neural regeneration

Traumatic brain injury is a serious medical condition that can be attributed to falls, motor vehicle accidents, sports injuries and acts of violence, causing a series of neural injuries and neuropsychiatric symptoms. However, limited accessibility to the injury sites, complicated histological and anatomical structure, intricate cellular and extracellular milieu, lack of regenerative capacity in the native cells, vast variety of damage routes, and the insufficient time available for treatment have restricted the widespread application of several therapeutic methods in cases of central nervous system injury. Tissue engineering and regenerative medicine have emerged as innovative approaches in the field of nerve regeneration. By combining biomaterials, stem cells, and growth factors, these approaches have provided a platform for developing effective treatments for neural injuries, which can offer the potential to restore neural function, improve patient outcomes, and reduce the need for drugs and invasive surgical procedures. Biomaterials have shown advantages in promoting neural development, inhibiting glial scar formation, and providing a suitable biomimetic neural microenvironment, which makes their application promising in the field of neural regeneration. For instance, bioactive scaffolds loaded with stem cells can provide a biocompatible and biodegradable milieu. Furthermore, stem cells-derived exosomes combine the advantages of stem cells, avoid the risk of immune rejection, cooperate with biomaterials to enhance their biological functions, and exert stable functions, thereby inducing angiogenesis and neural regeneration in patients with traumatic brain injury and promoting the recovery of brain function. Unfortunately, biomaterials have shown positive effects in the laboratory, but when similar materials are used in clinical studies of human central nervous system regeneration, their efficacy is unsatisfactory. Here, we review the characteristics and properties of various bioactive materials, followed by the introduction of applications based on biochemistry and cell molecules, and discuss the emerging role of biomaterials in promoting neural regeneration. Further, we summarize the adaptive biomaterials infused with exosomes produced from stem cells and stem cells themselves for the treatment of traumatic brain injury. Finally, we present the main limitations of biomaterials for the treatment of traumatic brain injury and offer insights into their future potential.

Constructing a biofunctionalized 3D-printed gelatin/sodium alginate/chitosan tri-polymer complex scaffold with improvised biological andmechanical properties for bone-tissue engineering

Sodium alginate(SA)/chitosan(CH)polyelectrolyte scaffold is a suitable substrate for tissue-engineering application.The present study deals with further improvement in the tensile strength and biological properties of this type of scaffold to make it a potential template for bone-tissue regeneration.We experimented with adding 0%–15%(volume fraction)gelatin(GE),a protein-based biopolymer known to promote cell adhesion,proliferation,and differentiation.The resulting tri-polymer complex was used as bioink to fabricate SA/CH/GEmatrices by three-dimensional(3D)printing.Morphological studies using scanning electron microscopy revealed the microfibrous porous architecture of all the structures,which had a pore size range of 383–419μm.X-ray diffraction and Fourier-transform infrared spectroscopy analyses revealed the amorphous nature of the scaffold and the strong electrostatic interactions among the functional groups of the polymers,thereby forming polyelectrolyte complexes which were found to improve mechanical properties and structural stability.The scaffolds exhibited a desirable degradation rate,controlled swelling,and hydrophilic characteristics which are favorable for bone-tissue engineering.The tensile strength improved from(386±15)to(693±15)kPa due to the increased stiffness of SA/CH scaffolds upon addition of gelatin.The enhanced protein adsorption and in vitro bioactivity(forming an apatite layer)confirmed the ability of the SA/CH/GE scaffold to offer higher cellular adhesion and a bone-like environment to cells during the process of tissue regeneration.In vitro biological evaluation including the MTT assay,confocal microscopy analysis,and alizarin red S assay showed a significant increase in cell attachment,cell viability,and cell proliferation,which further improved biomineralization over the scaffold surface.In addition,SA/CH containing 15%gelatin designated as SA/CH/GE15 showed superior performance to the other fabricated 3D structures,demonstrating its potential for use in bone-tissue engineering.

In vitro investigations on the effects of graphene and graphene oxide on polycaprolactone bone tissue engineering scaffolds

Polycaprolactone(PCL)scaffolds that are produced through additive manufacturing are one of the most researched bone tissue engineering structures in the field.Due to the intrinsic limitations of PCL,carbon nanomaterials are often investigated to reinforce the PCL scaffolds.Despite several studies that have been conducted on carbon nanomaterials,such as graphene(G)and graphene oxide(GO),certain challenges remain in terms of the precise design of the biological and nonbiological properties of the scaffolds.This paper addresses this limitation by investigating both the nonbiological(element composition,surface,degradation,and thermal and mechanical properties)and biological characteristics of carbon nanomaterial-reinforced PCL scaffolds for bone tissue engineering applications.Results showed that the incorporation of G and GO increased surface properties(reduced modulus and wettability),material crystallinity,crystallization temperature,and degradation rate.However,the variations in compressive modulus,strength,surface hardness,and cell metabolic activity strongly depended on the type of reinforcement.Finally,a series of phenomenological models were developed based on experimental results to describe the variations of scaffold’s weight,fiber diameter,porosity,and mechanical properties as functions of degradation time and carbon nanomaterial concentrations.The results presented in this paper enable the design of three-dimensional(3D)bone scaffolds with tuned properties by adjusting the type and concentration of different functional fillers.

The marriage of immunomodulatory,angiogenic,and osteogenic capabilities in a piezoelectric hydrogel tissue engineering scafold for military medicine

Background:Most bone-related injuries to grassroots troops are caused by training or accidental injuries.To establish preventive measures to reduce all kinds of trauma and improve the combat effectiveness of grassroots troops,it is imperative to develop new strategies and scafolds to promote bone regeneration.Methods:In this study,a porous piezoelectric hydrogel bone scafold was fabricated by incorporating polydopamine(PDA)-modified ceramic hydroxyapatite(PDA-hydroxyapatite,PHA)and PDA-modified barium titanate(PDABaTiO_(3),PBT)nanoparticles into a chitosan/gelatin(Cs/Gel)matrix.The physical and chemical properties of the Cs/Gel/PHA scafold with 0–10 wt%PBT were analyzed.Cell and animal experiments were performed to characterize the immunomodulatory,angiogenic,and osteogenic capabilities of the piezoelectric hydrogel scafold in vitro and in vivo.Results:The incorporation of BaTiO_(3) into the scafold improved its mechanical properties and increased self-generated electricity.Due to their endogenous piezoelectric stimulation and bioactive constituents,the prepared Cs/Gel/PHA/PBT hydrogels exhibited cytocompatibility as well as immunomodulatory,angiogenic,and osteogenic capabilities;they not only effectively induced macrophage polarization to M2 phenotype but also promoted the migration,tube formation,and angiogenic differentiation of human umbilical vein endothelial cells(HUVECs)and facilitated the migration,osteodifferentiation,and extracellular matrix(ECM)mineralization of MC3T3-E1 cells.The in vivo evaluations showed that these piezoelectric hydrogels with versatile capabilities significantly facilitated new bone formation in a rat large-sized cranial injury model.The underlying molecular mechanism can be partly attributed to the immunomodulation of the Cs/Gel/PHA/PBT hydrogels as shown via transcriptome sequencing analysis,and the PI3K/Akt signaling axis plays an important role in regulating macrophage M2 polarization.Conclusion:The piezoelectric Cs/Gel/PHA/PBT hydrogels developed here with favorable immunomodulation,angiogenesis,and osteogenesis functions may be used as a substitute in periosteum injuries,thereby offering the novel strategy of applying piezoelectric stimulation in bone tissue engineering for the enhancement of combat efectiveness in grassroots troops.

Magnesium-incorporated biocomposite scaffolds:A novel frontier in bone tissue engineering

Nonunion represents a crucial challenge in orthopedic medicine,demanding innovative solutions beyond the scope of traditional bone grafting methods.Among the various strategies available,magnesium(Mg)implants have been recognized for their biocompatibility and biodegradability.However,their susceptibility to rapid corrosion and degradation has garnered notable research interest in bone tissue engineering(BTE),particularly in the development of Mg-incorporated biocomposite scaffolds.These scaffolds gradually release Mg2+,which enhances immunomodulation,osteogenesis,and angiogenesis,thus facilitating effective bone regeneration.This review presents myriad fabrication techniques used to create Mg-incorporated biocomposite scaffolds,including electrospinning,three-dimensional printing,and sol-gel synthesis.Despite these advancements,the application of Mg-incorporated biocomposite scaffolds faces challenges such as controlling the degradation rate of Mg and ensuring mechanical stability.These limitations highlight the necessity for ongoing research aimed at refining fabrication techniques to better regulate the physicochemical and osteogenic properties of scaffolds.This review provides insights into the potential of Mg-incorporated biocomposite scaffolds for BTE and the challenges that need to be addressed for their successful translation into clinical applications.

Engineering vascularized organotypic tissues via module assembly

Adequate vascularization is a critical determinant for the successful construction and clinical implementation of complex organotypic tissue models. Currently, low cell and vessel density and insufficient vascular maturation make vascularized organotypic tissue construction difficult,greatly limiting its use in tissue engineering and regenerative medicine. To address these limitations, recent studies have adopted pre-vascularized microtissue assembly for the rapid generation of functional tissue analogs with dense vascular networks and high cell density. In this article, we summarize the development of module assembly-based vascularized organotypic tissue construction and its application in tissue repair and regeneration, organ-scale tissue biomanufacturing, as well as advanced tissue modeling.

Engineering of ovarian tissue for ovarian dysfunctions:A review

This review explores tissue engineering as a potential solution for reproductive health issues in women caused by genetic or acquired diseases,such as premature ovarian failure or oophorectomy.The loss of ovarian function can lead to infertility,osteoporosis,and cardiovascular disease.Hormone replacement therapy is a common treatment,but it has limitations and risks.The review focuses on two main approaches in tissue engineering:scaffold-based(3D printing,electrospinning,decellularization)and scaffold-free(stem cell transplantation,organoid cultivation).Both approaches show promise in preclinical studies for creating functional ovarian tissue.Challenges include vascularization,innervation,long-term function,and safety.Despite these challenges,tissue engineering offers a potential avenue for restoring fertility and hormone balance in women with ovarian dysfunction.

Research on the Development of Fibroin and Nano-Fiber from Silk Cocoons for Regenerated Tissue Engineering Applications by Electro-Spinning

In this paper, the main goal is to prepare silk fibroin nano-fiber, which is used for regenerated tissue applications. Silk scaffold nano-fibers made by electro-spinning technology can be used in regenerated tissue applications. The purpose of the research is to prepare a silk-fibroin nano-fiber solution for potential applications in tissue engineering. Using a degumming process, pure silk fibroin protein is extracted from silk cocoons. The protein solution for fibroin is purified, and the protein content is determined. The precise chemical composition, exact temperature, time, voltage, distance, ratio, and humidity all have a huge impact on degumming, solubility, and electro-spinning nano-fibers. The SEM investigates the morphology of silk fibroin nano-fibres at different magnifications. It also reveals the surface condition, fiber orientation, and fiber thickness of the silk fibroin nano-fiber. The results show that regenerated silk fibroin and nano-fiber can be used in silk fibroin scaffolds for various tissue engineering applications.

A Review on Silk Fibroin as a Biomaterial in Tissue Engineering

Regenerative medicine progress is based on the development of cell and tissue bioengineering. One of the aims of tissue engineering is the development of scaffolds, which should substitute the functions of the replaced organ after their implantation into the body. The tissue engineering material must meet a range of requirements, including biocompatibility, mechanical strength, and elasticity. Furthermore, the materials have to be attractive for cell growth: stimulate cell adhesion, migration, proliferation and differentiation. One of the natural biomaterials is silk and its component (silk fibroin). An increasing number of scientists in the world are studying silk and silk fibroin. The purpose of this review article is to provide information about the properties of natural silk (silk fibroin), as well as its manufacture and clinical application of each configuration of silk fibroin in medicine. Materials and research methods. Actual publications of foreign authors on resources PubMed, Medline, E-library have been analyzed. The selection criteria were materials containing information about the structure and components of silk, methods of its production in nature. This article placed strong emphasis on silk fibroin, the ways of artificial modification of it for use in various sphere of medicine.

Trilayer anisotropic structure versus randomly oriented structure in heart valve leaflet tissue engineering

It has been hypothesized that leaflet substrates with a trilayer structure and anisotropicmechanical properties could be useful for the production of functional and long-lasting tissue-engineered leaflets.To investigate the influence of the anisotropic structural and mechanical characteristics of a substrate on cells,in this study,we electrospun trilayer anisotropic fibrous substrates and randomly oriented isotropic fibrous substrates(used as controls)from polycaprolactone polymers.Consequently,the random substrates had higher radial and lower circumferential tensile properties than the trilayer substrates;however,they had similar flexural properties.Porcine valvular interstitial cells cultured on both substrates produced random and trilayer cell-cultured constructs,respectively.The trilayer cell-cultured constructs had more anisotropic mechanical properties,17%higher cellular proliferation,14%more extracellular matrix(i.e.,collagen and glycosaminoglycan)production,and superior gene and protein expression,suggesting that more cells were in a growth state in the trilayer constructs than in the random constructs.Furthermore,the random and radial layers of the trilayer constructs had more vimentin,collagen,transforming growth factor-beta 1(TGF-ß1),transforming growth factor-beta 3(TGF-ß3)gene expression than in the circumferential layer of the constructs.This study verifies that the differences in structural,tensile,and anisotropic properties of the trilayer and random substrates influence the characteristics of the cells and ECM in the constructs.

Robotic in situ bioprinting for cartilage tissue engineering

Articular cartilage damage caused by trauma or degenerative pathologies such as osteoarthritis can result in significant pain,mobility issues,and disability.Current surgical treatments have a limited capacity for efficacious cartilage repair,and long-term patient outcomes are not satisfying.Three-dimensional bioprinting has been used to fabricate biochemical and biophysical environments that aim to recapitulate the native microenvironment and promote tissue regeneration.However,conventional in vitro bioprinting has limitations due to the challenges associated with the fabrication and implantation of bioprinted constructs and their integration with the native cartilage tissue.In situ bioprinting is a novel strategy to directly deliver bioinks to the desired anatomical site and has the potential to overcome major shortcomings associated with conventional bioprinting.In this review,we focus on the new frontier of robotic-assisted in situ bioprinting surgical systems for cartilage regeneration.We outline existing clinical approaches and the utilization of robotic-assisted surgical systems.Handheld and robotic-assisted in situ bioprinting techniques including minimally invasive and non-invasive approaches are defined and presented.Finally,we discuss the challenges and potential future perspectives of in situ bioprinting for cartilage applications.

The fabrication of hydroxyapatite mineralized hydrogels for bone tissue engineering

Bone is a complex but orderly mineralized tissue with hydroxyapatite(HA)as the inorganic phase and collagen as the organic phase.Inspired by natural bone tissues,HA-mineralized hydrogels have been widely designed and used in bone tissue engineering.HA is majorly utilized for the treatment of bone defects because of its excellent osteoconduction and bone inductivity.Hydrogel is a three-dimensional hydrophilic network structure with similar properties to the extracellular matrix(ECM).The combination of HA and hydrogels produces a new hybrid material that could effectively promote osteointegration and accelerate the healing of bone defects.In this review,the structure and growth of bone and the common strategies used to prepare HA were briefly introduced.Importantly,we discussed the fabrication of HA mineralized hydrogels from simple blending to in situ mineralization.We hope this review can provide a reference for the development of bone repair hydrogels.

Novel frontiers for bone regeneration:application progress of mesenchymal stem cell-derived exosomes in bone tissue engineering

Identifying an effective way to promote bone regeneration for patients who suffer from bone defects is urgently demanded.In recent years,mesenchymal stem cells(MSCs)have drawed wide attention in bone regeneration.Besides,several studies have indicated the secretions of MSCs,especially exosomes,play a vital role in bone regeneration process.Exosomes can transfer“cargos”of proteins,RNA,DNA,lipids,to regulate fate of recipient cells by affecting their proliferation,differentiation,migration and gene expression.In this paper,the application of MSCs-derived exosomes in bone tissue engineering is reviewed,and the potential therapeutic role of exosome microRNA in bone regeneration is emphasized.

Bone Regeneration Based on Tissue Engineering Conceptions – A 21st Century Perspective

The role of Bone Tissue Engineering in the field of Regenerative Medicine has been the topic of substantial research over the past two decades. Technological advances have improved orthopaedic implants and surgical techniques for bone reconstruction. However, improvements in surgical techniques to reconstruct bone have been limited by the paucity of autologous materials available and donor site morbidity. Recent advances in the development of biomaterials have provided attractive alternatives to bone grafting expanding the surgical options for restoring the form and function of injured bone. Specifically, novel bioactive （second generation） biomaterials have been developed that are characterised by controlled action and reaction to the host tissue environment, whilst exhibiting controlled chemical breakdown and resorption with an ultimate replacement by regenerating tissue. Future generations of biomaterials （third generation） are designed to be not only osteo- conductive but also osteoinductive, i.e. to stimulate regeneration of host tissues by combining tissue engineer- ing and in situ tissue regeneration methods with a focus on novel applications. These techniques will lead to novel possibilities for tissue regeneration and repair. At present, tissue engineered constructs that may find future use as bone grafts for complex skeletal defects, whether from post-traumatic, degenerative, neoplastic or congenital/developmental ＂origin＂ require osseous reconstruction to ensure structural and functional integrity. Engineering functional bone using combinations of cells, scaffolds and bioactive factors is a promising strategy and a particular feature for future development in the area of hybrid materials which are able to exhibit suitable biomimetic and mechanical properties. This review will discuss the state of the art in this field and what we can expect from future generations of bone regeneration concepts.

Application of platelet-rich plasma with stem cells in bone and periodontal tissue engineering

Presently, there is a high paucity of bone grafts in the United States and worldwide. Regenerating bone is of prime concern due to the current demand of bone grafts and the increasing number of diseases causing bone loss. Autogenous bone is the present gold standard of bone regeneration. However, disadvantages like donor site morbidity and its decreased availability limit its use. Even allografts and synthetic grafting materials have their own limitations. As certain specific stem cells can be directed to differentiate into an osteoblastic lineage in the presence of growth factors(GFs), it makes stem cells the ideal agents for bone regeneration.Furthermore, platelet-rich plasma(PRP), which can be easily isolated from whole blood, is often used for bone regeneration, wound healing and bone defect repair. When stem cells are combined with PRP in the presence of GFs, they are able to promote osteogenesis. This review provides in-depth knowledge regarding the use of stem cells and PRP in vitro, in vivo and their application in clinical studies in the future.

Tissue engineering of blood vessels with endothelial cells differentiated from mouse embryonic stem cells

Endothelial cells (TEC_3 cells) derived from mouse embryonic stem (ES) cells were used as seed cells to construct blood vessels. Tissue engineered blood vessels were made by seeding 8 × 10~6 smooth muscle cells (SMCs) obtained from rabbit arteries onto a sheet of nonwoven polyglycolic acid (PGA) fibers, which was used as a biodegradable polymer scaffold. After being cultured in DMEM medium for 7 days in vitro, SMCs grew well on the PGA fibers, and the cell-PGA sheet was then wrapped around a silicon tube, and implanted subcutaneously into nude mice. After 6～8 weeks, the silicon tube was replaced with another silicon tube in smaller diameter, and then the TEC_3 cells (endothelial cells differentiated from mouse ES cells) were injected inside the engineered vessel tube as the test group. In the control group only culture medium was injected. Five days later, the engineered vessels were harvested for gross observation, histological and immunohistochemical analysis. The preliminary results demonstrated that the SMC-PGA construct could form a tubular structure in 6～8 weeks and PGA fibers were completely degraded. Histological and immunohistochemical analysis of the newly formed tissue revealed a typical blood vessel structure, including a lining of endothelial cells (ECs) on the lumimal surface and the presence of SMC and collagen in the wall. No EC lining was found in the tubes of control group. Therefore, the ECs differentiated from mouse ES cells can serve as seed cells for endothelium lining in tissue engineered blood vessels.

Tissue engineering for the repair of peripheral nerve injury

Peripheral nerve injury is a common clinical problem and affects the quality of life of patients. Traditional restoration methods are not satisfactory. Researchers increasingly focus on the field of tissue engineering. The three key points in establishing a tissue engineering material are the biological scaffold material, the seed cells and various growth factors. Understanding the type of nerve injury, the construction of scaffold and the process of repair are necessary to solve peripheral nerve injury and promote its regeneration. This review describes the categories of peripheral nerve injury, fundamental research of peripheral nervous tissue engineering and clinical research on peripheral nerve scaffold material, and paves a way for related research and the use of conduits in clinical practice.

Evaluation of novel decellularizing corneal stroma for cornea tissue engineering applications

AIM:To develop a new decellularization method depended upon the natural corneal structure and to harvest an ideal scaffold with good biocompatibilities for corneal reconstruction.METHODS:The acellular cornea matrix (ACM) were prepared from de-epithelium fresh porcine corneas (DFPCs) by incubation with 100% fresh human sera and additional electrophoresis at 4℃. Human corneal epithelial cells (HCEs) were used for the cytotoxicity tests of ACM. ACM were implanted into the Enhanced Green Fluorecence Protein (eGFP) transgenic mouse anterior chamber for evaluation of histocompatibility.RESULTS:HE and GSIB4 results showed fresh porcine cornea matrix with 100% human sera and electrophoresis could entirely decellularize stromal cell without reducing its transparency. ACM has no cytotoxic effect ex vivo. Animal test showed there was no rejection for one month after surgery.CONCLUSION:These results provide a decellularizing approach for the study of corneal tissue engineering and had the broader implications for the field of biological tissue engineering in other engineered organ or tissue matrix.

Study on β-TCP Coated Porous Mg as a Bone Tissue Engineering Scaffold Material

Three-dimensional honeycomb-structured magnesium （Mg） scaffolds with interconnected pores of accurately controlled pore size and porosity were fabricated by laser perforation technique. Biodegradable and bioactiveβ- tricalcium phosphate （β-TCP） coatings were prepared on and the biodegradation mechanism was simply evaluated the porous Mg to further improve its biocompatibility, in vitro. It was found that the mechanical properties of this type of porous Mg significantly depended on its porosity. Elastic modulus and compressive strength similar to human bones could be obtained for the porous Mg with porosity of 42.6%-51%. It was observed that the human osteosarcoma cells （UMR106） were well adhered and proliferated on the surface of the β- TCP coated porous Mg, which indicates that theβ-TCP coated porous Mg is promising to be a bone tissue engineering scaffold material.