Mild Photothermal-Stimulation Based on Injectable and Photocurable Hydrogels Orchestrates Immunomodulation and Osteogenesis for High-Performance Bone Regeneration

A photoactivated bone scaffold integrated with minimally invasive implantation and mild thermal-stimulation capability shows great promise in the repair and regeneration of irregularly damaged bone tissues. Developing multifunctional photothermal biomaterials that can simultaneously serve as both controllable thermal stimulators and biodegradable engineering scaffolds for integrated immunomodulation, infection therapy, and impaired bone repair remains an enormous challenge. Herein, an injectable and photocurable hydrogel therapeutic platform (AMAD/MP) based on alginate methacrylate, alginate-graft-dopamine, and polydopamine (PDA)-functionalized Ti3C2 MXene (MXene@PDA) nanosheets is rationally designed for near-infrared (NIR)-mediated bone regeneration synergistic immunomodulation, osteogenesis, and bacterial elimination. The optimized AMAD/MP hydrogel exhibits favorable biocompatibility, osteogenic activity, and immunomodulatory functions in vitro. The proper immune microenvironment provided by AMAD/MP could further modulate the balance of M1/M2 phenotypes of macrophages, thereby suppressing reactive oxygen species-induced inflammatory status. Significantly, this multifunctional hydrogel platform with mild thermal stimulation efficiently attenuates local immune reactions and further promotes new bone formation without the addition of exogenous cells, cytokines, or growth factors. This work highlights the potential application of an advanced multifunctional hydrogel providing photoactivated on-demand thermal cues for bone tissue engineering and regenerative medicine.     

Carbon nanotubes with high bone-tissue compatibility and bone-formation acceleration effects

Carbon nanotubes (CNTs) have been used in various fields as composites with other substances or alone to develop highly functional materials. CNTs hold great interest with respect to biomaterials, particularly those to be positioned in contact with bone such as prostheses for arthroplasty, plates or screws for fracture fixation, drug delivery systems, and scaffolding for bone regeneration. Accordingly, bone-tissue compatibility of CNTs and CNT influence on bone formation are important issues, but the effects of CNTs on bone have not been delineated. Here, it is found that multi-walled CNTs adjoining bone induce little local inflammatory reaction, show high bone-tissue compatibility, permit bone repair, become integrated into new bone, and accelerate bone formation stimulated by recombinant human bone morphogenetic protein-2 (rhBMP-2). This study provides an initial investigational basis for CNTs in biomaterials that are used adjacent to bone, including uses to promote bone regeneration. These findings should encourage development of clinical treatment modalities involving CNTs.     

Biomedical materials for new millennium: perspective on the future

Abstract

Millions of orthopaedic prostheses made of bioinert materials have been implanted with an excellent 15 year survivability of 75–85%. Improved metal alloys, special polymers, and medical grade ceramics are the basis for this success, which has enhanced the quality of life for millions of patients. However, an increasing percentage of our aging population require greater than 30 years survivability of the devices. It is proposed that to satisfy this growing need for very long term orthopaedic repair a paradigm shift is needed; a shift in emphasis from the replacement of tissues to the regeneration of tissues. Such a shift from a materials and mechanics approach to tissue repair requires an increase in the understanding and utilisation of biologically approaches. Two new biologically orientated alternatives in biomaterials for orthopaedics in the new millennium are discussed: tissue regeneration, where in situ repair is initiated in the host tissue, and tissue engineering, where repair is initiated in vitro on cellularly seeded scaffolds and then transplanted to the recipient. The concept of the use of class A bioactive materials to stimulate the regeneration of trabecular bone is described along with clinical applications. Eleven reaction stages lead to the enhanced proliferation and differentiation of osteoblasts and the recreation of trabecular bone architecture. Recent results showing the effects of microchemical gradients on the genetic activation of bone cells are related to the molecular design of hierarchical bioactive resorbable scaffolds for the tissue engineering of bone constructs.     

Advanced engineering and biomimetic materials for bone repair and regeneration

Over the past decade, there has been tremendous progress in developing advanced biomaterials for tissue repair and regeneration. This article reviews the frontiers of this field from two closely related areas, new engineering materials for bone substitution and biomimetic mineralization for bone-like nanocomposites. Rather than providing an exhaustive overview of the literature, we focus on several representative directions. We also discuss likely future trends in these areas, including synthetic biology-enabled biomaterials design and multifunctional implant materials for bone repair and regeneration.     

Bioactivation of calcium deficient hydroxyapatite with foamed gelatin gel. A new injectable self-setting bone analogue

An alternative approach to bone repair for less invasive surgical techniques, involves the development of biomaterials directly injectable into the injury sites and able to replicate a spatially organized platform with features of bone tissue. Here, the preparation and characterization of an innovative injectable bone analogue made of calcium deficient hydroxyapatite and foamed gelatin is presented. The biopolymer features and the cement self-setting reaction were investigated by rheological analysis. The porous architecture, the evolution of surface morphology and the grains dimension were analyzed with electron microscopy (SEM/ESEM/TEM). The physico-chemical properties were characterized by X-ray diffraction and FTIR analysis. Moreover, an injection test was carried out to prove the positive effect of gelatin on the flow ensuing that cement is fully injectable. The cement mechanical properties are adequate to function as temporary substrate for bone tissue regeneration. Furthermore, MG63 cells and bone marrow-derived human mesenchymal stem cells (hMSCs) were able to migrate and proliferate inside the pores, and hMSCs differentiated to the osteoblastic phenotype. The results are paving the way for an injectable bone substitute with properties that mimic natural bone tissue allowing the successful use as bone filler for craniofacial and orthopedic reconstructions in regenerative medicine.     

Macrophage interactions with modified material surfaces

An understanding of the biological response at material surfaces is a key biomaterials research area. Inflammation, tissue repair and regeneration are hallmarks of this response. Macrophages are long-lived and versatile cells and have a pivotal role at surfaces of implanted medical devices. The present review provides an update on macrophage behaviour at material surfaces. The interactions between cells and material surfaces are dynamic processes which require additional experimental models with different degrees of environmental complexity. It is concluded that both modifications of material surface properties and cellular signalling pathways will provide strategies for optimising the performance of biomedical devices.     

Hematoma-inspired alginate/platelet releasate/CaPO4 composite: initiation of the inflammatory-mediated response associated with fracture repair in vitro and ex vivo injection delivery

A clinical need continues for consistent bone remodeling within problematic sites such as those of fracture nonunion, avascular necrosis, or irregular bone formations. In attempt to address such needs, a biomaterial system is proposed to induce early inflammatory responses after implantation and to provide later osteoconductive scaffolding for bone regeneration. Biomaterial-induced inflammation would parallel the early stage of hematoma-induced fracture repair and allow scaffold-promoted remodeling of osseous tissue to a healthy state. Initiation of the wound healing cascade by two human concentrated platelet releasate-containing alginate/β-tricalcium phosphate biocomposites has been studied in vitro using the TIB-71? RAW264.7 mouse monocyte cell line. Inflammatory responses inherent to the base material were found and could be modulated through incorporation of platelet releasate. Differences in hydrogel wt% (2 vs. 8 %) and/or calcium phosphate granule vol.% (20 vs. 10 %) allowed for tuning the response associated with platelet releasate-associated growth factor elution. Tunability from completely suppressing the inflammatory response to augmenting the response was observed through varied elution profiles of both releasate-derived bioagents and impurities inherent to alginate. A 2.5-fold upregulation of inducible-nitric oxide synthase gene expression followed by a tenfold increase in nitrite media levels was induced by inclusion of releasate within the 8 wt%/10 vol.% formulation and was comparable to an endotoxin positive control. Whereas, near complete elimination of inflammation was seen when releasate was included within the 2 wt%/20 vol.% formulation. These in vitro results suggested tunable interactions between the multiple platelet releasate-derived bioagents and the biocomposites for enhancing hematoma-like fracture repair. Additionally, minimally invasive delivery for in situ curing of the implant system via injection was demonstrated in rat tail vertebrae using microcomputed tomography.     

A novel photothermally controlled multifunctional scaffold for clinical treatment of osteosarcoma and tissue regeneration

After an osteosarcoma excision, recurrence, large bone defects, and soft tissue injury are significant challenges for clinicians. Conventional treatment by implanting bone replacement materials can induce bone regeneration after surgery, but this does not prevent bleeding, promote soft tissue repair, or help destroy the residual tumor cells. We attempted to develop a new multifunctional scaffold, with the clinical goals of facilitating tumor cell death through thermal ablation and promoting osteogenesis. Accordingly, we first investigated the effect of nano-hydroxyapatite/graphene oxide (nHA/GO) composite particles with different proportions on human osteosarcoma cells (HOS), pre-osteoblastic MC3T3-E1 cells, and human bone marrow mesenchymal stem cells (hBMSC) with or without 808-nm near-infrared (NIR) light irradiation. Next, we fabricated a novel temperature-controlled multifunctional nano-hydroxyapatite/graphene oxide/chitosan (nHA/GO/CS) scaffold, which can effectively kill human osteosarcoma cells under 808-nm NIR irradiation by reaching a temperature of 48 °C and further promote osteogenesis of hBMSC at 42 ± 0.5 °C in coordination with nHA. This scaffold demonstrates the best post-operative bone volume/tissue volume (BV/TV) ratio performance (20.36%) 8 weeks after scaffold implantation in the cranial defects of rats. Further exploration has revealed that NIR irradiation may promote the osteogenesis of hBMSC with the addition of nHA by enhancing the BMP2/Smad signaling pathway. Further, this scaffold has a good hemostatic effect and facilitates soft tissue repair under irradiation. This novel photothermally controlled multifunctional scaffold, which not only kills human osteosarcoma cells but also facilitates tissue regeneration, is a promising clinical tool for treating tissue injuries from an osteosarcoma resection.     

Biomaterials affect cell-cell interactions in vitro in tissue engineering

The facts that most tissues or organs consist of a variety of cells suggest that interactions between different types of cells play critical roles in tissue or organ development.In tissue engineering,the effects of biomaterials on cell-cell interactions have recently attracted increasing attention for better elucidating the mechanisms through which biomaterials promote tissue regeneration.Numerous studies have focused on these effects of biomaterials on cell-cell interactions.In this review,comprehensive information was provided about the existing cell co-culture technologies and the main behavioral modes of cell-cell interactions.The effects of biomaterials on the cell-cell interactions in various types of tissue regeneration have been summarized and discussed.In the end,the existing problems and future perspectives that would help promote the research of biomaterials in tissue engineering have been proposed.This article can help researchers to understand the progress and importance of studying the effects of biomaterials on cell-cell interactions in tissue engineering and to choose the optimal cell-cell co-culture models for designing experiments.     

Bioactive materials to control cell cycle

Many of the present generation biomaterials are still based upon the early concept that implantable materials should be bioinert and therefore designed to evoke minimal tissue response, if none. However, a growing body of clinical data demonstrates that the long survivability of these materials is hampered by high rates of failure, which is primarily attributed to interfacial instability. It has therefore become understood that this approach is not optimal. Modern approaches implicate the use of biomaterials that can actively interact with tissues and induce their intrinsic repair and regenerative potential. This involves control over the cell cycle, the molecular framework that controls cell proliferation and differentiation. Class A bioactive glass-ceramic materials were the first materials shown to endorse these properties and, depending upon the rate of resorption and release of ions, can create chemical gradients with specific biological actions over cells and tissues. Optimising this bioactive regenerative capacity of Bioactive glass-ceramics offers great hope for producing biomaterials that can stimulate growth, repair, and regeneration of any human tissue. Received: 12 April 2000 / Reviewed and accepted: 8 June 2000     

Calcium-phosphate ceramics and polysaccharide-based hydrogel scaffolds combined with mesenchymal stem cell differently support bone repair in rats

Research in bone tissue engineering is focused on the development of alternatives to autologous bone grafts for bone reconstruction. Although multiple stem cell-based products and biomaterials are currently being investigated, comparative studies are rarely achieved to evaluate the most appropriate approach in this context. Here, we aimed to compare different clinically relevant bone tissue engineering methods and evaluated the kinetic repair and the bone healing efficiency supported by mesenchymal stem cells and two different biomaterials, a new hydrogel scaffold and a commercial hydroxyapatite/tricalcium phosphate ceramic, alone or in combination.Syngeneic mesenchymal stem cells (5?×?10⁵) and macroporous biphasic calcium phosphate ceramic granules (Calciresorb C35^®, Ceraver) or porous pullulan/dextran-based hydrogel scaffold were implanted alone or combined in a drilled-hole bone defect in rats. Using quantitative microtomography measurements and qualitative histological examinations, their osteogenic properties were evaluated 7, 30, and 90 days after implantation. Three months after surgery, only minimal repair was evidenced in control rats while newly mineralized bone was massively observed in animals treated with either hydrogels (bone volume/tissue volume?=?20%) or ceramics (bone volume/tissue volume?=?26%). Repair mechanism and resorption kinetics were strikingly different: rapidly-resorbed hydrogels induced a dense bone mineralization from the edges of the defect while ceramics triggered newly woven bone formation in close contact with the ceramic surface that remained unresorbed. Delivery of mesenchymal stem cells in combination with these biomaterials enhanced both bone healing (>20%) and neovascularization after 1 month, mainly in hydrogel.Osteogenic and angiogenic properties combined with rapid resorption make hydrogels a promising alternative to ceramics for bone repair by cell therapy.     

Bioadaptability: An Innovative Concept for Biomaterials

Biocompatibility is the basic requirement of biomaterials for tissue repair. However, the present concept of biocompatibility has a certain limitation in explaining the phenomena involved in biomaterial-based tissue repair. New materials, in particular those for tissue engineering and regeneration, have been developed with common characteristics, i.e. they participate deeply into important chemical and biological processes in the human body and the interaction between the biomaterials and tissues is far more complex.Understanding the interplay between these biomaterials and tissues is vital for their development and functionalization. Herein, we suggest the concept of bioadaptability of biomaterials. This concept describes the three most important aspects that can determine the performance of biomaterials in tissue repair: 1) the adaptability of the micro-environment created by biomaterials to the native microenvironment in situ; 2) the adaptability of the mechanical properties of biomaterials to the native tissue;3) the adaptability of the degradation properties of biomaterials to the new tissue formation. The concept of bioadaptability emphasizes both the material's characteristics and biological aspects within a certain micro-environment and molecular mechanism. It may provide new inspiration to uncover the interaction mechanism of biomaterials and tissues, to foster the new ideas of functionalization of biomaterials and to investigate the fundamental issues during the tissue repair process by biomaterials. Furthermore, designing biomaterials with such bioadaptability would open a new door for repairing and regenerating organs or tissues. In this review, we summarized the works in recent years on the bioadaptability of biomaterials for tissue repair applications.     

Tethering of Gly-Arg-Gly-Asp-Ser-Pro-Lys Peptides on Mg-Doped Hydroxyapatite

Stem cell homing, namely the recruitment of mesenchymal stem cells (MSCs) to injured tissues, is highly effective for bone regeneration in vivo. In order to explore whether the incorporation of mimetic peptide sequences on magnesium-doped (Mg-doped) hydroxyapatite (HA) may regulate the homing of MSCs, and thus induce cell migration to a specific site, we covalently functionalized MgHA disks with two chemotactic/haptotactic factors: either the fibronectin fragment III₁-C human (FF III₁-C), or the peptide sequence Gly-Arg-Gly-Asp-Ser-Pro-Lys, a fibronectin analog that is able to bind to integrin transmembrane receptors. Preliminary biological evaluation of MSC viability, analyzed by 3-(4,5-dimethyl­thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test, suggested that stem cells migrate to the MgHA disks in response to the grafted haptotaxis stimuli.     

Sonopiezoelectric Nanomedicine and Materdicine

Endogenous electric field is ubiquitous in a multitude of important living activities such as bone repair, cell signal transduction, and nerve regeneration, signifying that regulating the electric field in organisms is highly beneficial to maintain organism health. As an emerging and promising research direction, piezoelectric nanomedicine and materdicine precisely activated by ultrasound with synergetic advantages of deep tissue penetration, remote spatiotemporal selectivity, and mechanical-electrical energy interconversion, have been progressively utilized for disease treatment and tissue repair by participating in the modulation of endogenous electric field. This specific nanomedicine utilizing piezoelectric effect activated by ultrasound is typically regarded as “sonopiezoelectric nanomedicine”. This comprehensive review summarizes and discusses the substantially employed sonopiezoelectric nanomaterials and nanotherapies to provide an insight into the internal mechanism of the corresponding biological behavior/effect of sonopiezoelectric biomaterials in versatile disease treatments. This review primarily focuses on the sonopiezoelectric biomaterials for biosensing, drug delivery, tumor therapy, tissue regeneration, antimicrobia, and further illuminates the underlying sonopiezoelectric mechanism. In addition, the challenges and developments/prospects of sonopiezoelectric nanomedicine are analyzed for promoting the further clinical translation. It is earnestly expected that this kind of nanomedicine/biomaterials-enabled sonopiezoelectric technology will provoke the comprehensive investigation and promote the clinical development of the next-generation multifunctional materdicine.     

In vitro and in vivo methods to determine the interactions of osteogenic cells with biomaterials

To assess new biomaterials for possible use as bone graft substitutes, a number of techniques allow interactions with osteoblastic cells to be studied, with respect to effects on proliferation and differentiation of osteoprogenitors. In vitro models include the use of bone explant cultures, fetal rat calvarial-derived osteoblast cells, primary stromal populations, transformed and non-transformed cell lines and immortalized osteoblast cell lines. However, these assessments are limited by the extent of osteogenic differentiation and bone formation that can be observed in vitro, species differences and phenotypic drift of cells cultured in vitro. The use of in vivo experimental systems such as the segmental/calvarial bone defect model, the subcutaneous implant model and the diffusion chamber implantation model circumvent some of these issues and, in the appropriate model, provide data on efficacy, biocompatibility and osteointegration of a biomaterial. The combination of in vitro and in vivo approaches together with the development of new cell labeling techniques, in particular the ability to genetically mark and select specific human bone cell populations provides new avenues for their potential evaluation in combination with appropriate biomaterials for clinical use. These in vitro and in vivo techniques are reviewed and those recently developed for assessment of human osteogenic cells should be applicable to many other cell systems where knowledge of specific human tissue or cell interactions with biomaterials is required. © 1999 Kluwer Academic Publishers     

Personalised bone tissue engineering scaffold with controlled architecture using fractal tool paths in layered manufacturing

The scaffolds for bone tissue engineering should consider the functional requirements such as the external shape of the replacement, porosity for vessel and nutrient conduit, and stiffness in order to avoid stress shielding and to stimulate growth of the new tissue. Layered manufacturing (LM) has shown great promise in fabricating such porous bone scaffold. The present work proposes a biomimetic design and LM of patient- and site-specific controlled porosity scaffolds for optimised mechanical properties for repair and regeneration of bone. Correlation models between porosity and modulus for bone, and known biomaterials processable by LM are used to estimate the site-specific porosity requirements in the scaffold model. A novel method for generating a tool path using space-filling fractal curves eliminates representation difficulties associated with LM of porous objects. A representative study of a hydroxyapatite scaffold for a cortical bone defect site in human femur is presented to illustrate the methodology.     

The chorioallantoic membrane of the chick embryo as a simple model for the study of the angiogenic and inflammatory response to biomaterials

Angiogenesis is essential in wound healing and a common feature in chronic inflammation which is crucially involved in the biological response to biomaterials. A useful system to evaluate the angiogenic activity and the inflammatory potency of various agents is the chorioallantoic membrane (CAM) of the chick embryo. Here we examined its response to different biomaterials. Smooth materials such as PVC or the polyurethane Tecoflex® either unmodified or modified by an OH- or N(CH₃) ₃ ⁺ -end group (HEMA or MAPTAC) inhibited angiogenesis and did not induce the formation of granulation tissue. The anti-angiogenic effects of PVC, Tecoflex® and its HEMA modification, however, were only seen at an early stage of development. In contrast, the MAPTAC modified Tecoflex>® inhibited angiogenesis over the whole time. Rough materials, e.g. filter paper or a collagen/elastin membrane, stimulated angiogenesis and induced the formation of inflammatory tissue. Histological analysis revealed that the filter material was homogeneously populated with cells consisiting mainly of macrophages, fibroblasts and endothelial cells. The collagen/elastin membrane was only partially infiltrated with cells. Among those also clusters of granulocytes were present pointing to an acute inflammatory process. These data show that the angiogenic activity and inflammatory response of biomaterials strongly depend on the chemical composition and the physical structure of the material. The CAM assay appears to be a useful tool for studying biocompatibility. © 2001 Kluwer Academic Publishers     

Interplay of reactive oxygen species (ROS) and tissue engineering: a review on clinical aspects of ROS-responsive biomaterials

Reactive oxygen species (ROS) refers to the reactive molecules and free radicals of oxygen generated as the by-products of aerobic respiration. Historically, ROS are known as stress markers that are linked to the response of immune cell against microbial invasion, but recent discoveries suggest their role as secondary messengers in signal transduction and cell cycle. Tissue engineering (TE) techniques have the capabilities to harness such properties of ROS for the effective regeneration of damaged tissues. TE employs stem cells and biomaterial matrix, to heal and regenerate injured tissue and organ. During regeneration, one of the constraints is the unavailability of oxygen as proper vasculature is absent at the injured site. This creates hypoxic conditions at the site of regeneration. Hence, effective response against the stresses like hypoxia spurs the regeneration process. Contrary, hyperoxic condition may increase the risk of ROS stress at the site. TE tries to overcome these limitations with the new class of biomaterials that can sense such stresses and respond accordingly. This review endeavors to explain the role of ROS in stem cell proliferation and differentiation, which is a key component in regeneration. This compilation also highlights the new class of biomaterials that can overcome the hypoxic conditions during tissue regeneration along with emphasis on the ROS-responsive biomaterials and their clinical applications. Incorporating these biomaterials in scaffolds development holds huge potential in tissue or organ regeneration and even in drug delivery.

Graphical abstract