Pore size regulates mesenchymal stem cell response to Bioglass-loaded composite scaffolds

Advances in biomaterials for oral-maxillofacial bone regeneration: spotlight on periodontal and alveolar bone strategies

The intricate nature of oral-maxillofacial structure and function, coupled with the dynamic oral bacterial environment, presents formidable obstacles in addressing the repair and regeneration of oral-maxillofacial bone defects. Numerous characteristics should be noticed in oral-maxillofacial bone repair, such as irregular morphology of bone defects, homeostasis between hosts and microorganisms in the oral cavity and complex periodontal structures that facilitate epithelial ingrowth. Therefore, oral-maxillofacial bone repair necessitates restoration materials that adhere to stringent and specific demands. This review starts with exploring these particular requirements by introducing the particular characteristics of oral-maxillofacial bones and then summarizes the classifications of current bone repair materials in respect of composition and structure. Additionally, we discuss the modifications in current bone repair materials including improving mechanical properties, optimizing surface topography and pore structure and adding bioactive components such as elements, compounds, cells and their derivatives. Ultimately, we organize a range of potential optimization strategies and future perspectives for enhancing oral-maxillofacial bone repair materials, including physical environment manipulation, oral microbial homeostasis modulation, osteo-immune regulation, smart stimuli-responsive strategies and multifaceted approach for poly-pathic treatment, in the hope of providing some insights for researchers in this field. In summary, this review analyzes the complex demands of oral-maxillofacial bone repair, especially for periodontal and alveolar bone, concludes multifaceted strategies for corresponding biomaterials and aims to inspire future research in the pursuit of more effective treatment outcomes.

Three-dimensional (3D) polylactic acid gradient scaffold to study the behavior of osteosarcoma cells under dynamic conditions

This study adopts an in vitro method to recapitulate the behavior of Saos-2 cells, using a system composed of a perfusion bioreactor and poly-L-lactic acid (PLLA) scaffold fabricated using the low-cost thermally-induced phase separation (TIPS) technique. Four distinct scaffold morphologies with different pore sizes were fabricated, characterized by Scanning electron microscopy and micro-CT analysis and tested with osteosarcoma cells under static and dynamic environments to identify the best morphology for cellular growth. In order to accomplish this purpose, cell growth and matrix deposition of the Saos-2 osteosarcoma cell line were assessed using Picogreen and OsteoImage assays. The obtained data allowed us to identify the morphology that better promotes Saos-2 cellular activity in static and dynamic conditions. These findings provided valuable insights into scaffold design and fabrication strategies, emphasizing the importance of the dynamic culture to recreate an appropriate 3D osteosarcoma model. Remarkably, the gradient scaffold exhibits promise for osteosarcoma applications, offering the potential for targeted tissue engineering approaches.

Transcriptomic and cellular decoding of scaffolds-induced suture mesenchyme regeneration

Precise orchestration of cell fate determination underlies the success of scaffold-based skeletal regeneration. Despite extensive studies on mineralized parenchymal tissue rebuilding, regenerating and maintaining undifferentiated mesenchyme within calvarial bone remain very challenging with limited advances yet. Current knowledge has evidenced the indispensability of rebuilding suture mesenchymal stem cell niches to avoid severe brain or even systematic damage. But to date, the absence of promising therapeutic biomaterials/scaffolds remains. The reason lies in the shortage of fundamental knowledge and methodological evidence to understand the cellular fate regulations of scaffolds. To address these issues, in this study, we systematically investigated the cellular fate determinations and transcriptomic mechanisms by distinct types of commonly used calvarial scaffolds. Our data elucidated the natural processes without scaffold transplantation and demonstrated how different scaffolds altered in vivo cellular responses. A feasible scaffold, polylactic acid electrospinning membrane (PLA), was next identified to precisely control mesenchymal ingrowth and self-renewal to rebuild non-osteogenic suture-like tissue at the defect center, meanwhile supporting proper osteointegration with defect bony edges. Especially, transcriptome analysis and cellular mechanisms underlying the well-orchestrated cell fate determination of PLA were deciphered. This study for the first time cellularly decoded the fate regulations of scaffolds in suture-bony composite defect healing, offering clinicians potential choices for regenerating such complicated injuries.

Emerging factors affecting peri-implant bone metabolism

Implant dentistry has evolved to the point that standard implant osseointegration is predictable. This is attributed in part to the advancements in material sciences that have led toward improvements in implant surface technology and characteristics. Nonetheless, there remain several cases where implant therapy fails (specifically at early time points), most commonly attributed to factors affecting bone metabolism. Among these patients, smokers are known to have impaired bone metabolism and thus be subject to higher risks of early implant failure and/or late complications related to the stability of the peri-implant bone and mucosal tissues. Notably, however, emerging data have unveiled other critical factors affecting osseointegration, namely, those related to the metabolism of bone tissues. The aim of this review is to shed light on the effects of implant-related factors, like implant surface or titanium particle release; surgical-related factors, like osseodensification or implanted biomaterials; various drugs, like selective serotonin reuptake inhibitors, proton pump inhibitors, anti-hypertensives, nonsteroidal anti-inflammatory medication, and statins, and host-related factors, like smoking, diet, and metabolic syndrome on bone metabolism, and aseptic peri-implant bone loss. Despite the infectious nature of peri-implant biological complications, these factors must be surveyed for the effective prevention and management of peri-implantitis.

Research progress of vascularization strategies of tissue-engineered bone

The bone defect caused by fracture, bone tumor, infection, and other causes is not only a problematic point in clinical treatment but also one of the hot issues in current research. The development of bone tissue engineering provides a new way to repair bone defects. Many animal experimental and rising clinical application studies have shown their excellent application prospects. The construction of rapid vascularization of tissue-engineered bone is the main bottleneck and critical factor in repairing bone defects. The rapid establishment of vascular networks early after biomaterial implantation can provide sufficient nutrients and transport metabolites. If the slow formation of the local vascular network results in a lack of blood supply, the osteogenesis process will be delayed or even unable to form new bone. The researchers modified the scaffold material by changing the physical and chemical properties of the scaffold material, loading the growth factor sustained release system, and combining it with trace elements so that it can promote early angiogenesis in the process of induced bone regeneration, which is beneficial to the whole process of bone regeneration. This article reviews the local vascular microenvironment in the process of bone defect repair and the current methods of improving scaffold materials and promoting vascularization.

Development of hybrid 3D printing approach for fabrication of high-strength hydroxyapatite bioscaffold using FDM and DLP techniques

This study develops a hybrid 3D printing approach that combines fused deposition modeling (FDM) and digital light processing (DLP) techniques for fabricating bioscaffolds, enabling rapid mass production. The FDM technique fabricates outer molds, while DLP prints struts for creating penetrating channels. By combining these components, hydroxyapatite (HA) bioscaffolds with different channel sizes (600, 800, and 1000μm) and designed porosities (10%, 12.5%, and 15%) are fabricated using the slurry casting method with centrifugal vacuum defoaming for significant densification. This innovative method produces high-strength bioscaffolds with an overall porosity of 32%-37%, featuring tightly bound HA grains and a layered surface structure, resulting in remarkable cell viability and adhesion, along with minimal degradation rates and superior calcium phosphate deposition. The HA scaffolds show hardness ranging from 1.43 to 1.87 GPa, with increasing compressive strength as the designed porosity and channel size decrease. Compared to human cancellous bone at a similar porosity range of 30%-40%, exhibiting compressive strengths of 13-70 MPa and moduli of 0.8-8 GPa, the HA scaffolds demonstrate robust strengths ranging from 40 to 73 MPa, paired with lower moduli of 0.7-1.23 GPa. These attributes make them well-suited for cancellous bone repair, effectively mitigating issues like stress shielding and bone atrophy.

Self-oxygenation of engineered living tissues orchestrates osteogenic commitment of mesenchymal stem cells

Oxygenating biomaterials can alleviate anoxic stress, stimulate vascularization, and improve engraftment of cellularized implants. However, the effects of oxygen-generating materials on tissue formation have remained largely unknown. Here, we investigate the impact of calcium peroxide (CPO)-based oxygen-generating microparticles (OMPs) on the osteogenic fate of human mesenchymal stem cells (hMSCs) under a severely oxygen deficient microenvironment. To this end, CPO is microencapsulated in polycaprolactone to generate OMPs with prolonged oxygen release. Gelatin methacryloyl (GelMA) hydrogels containing osteogenesis-inducing silicate nanoparticles (SNP hydrogels), OMPs (OMP hydrogels), or both SNP and OMP (SNP/OMP hydrogels) are engineered to comparatively study their effect on the osteogenic fate of hMSCs. OMP hydrogels associate with improved osteogenic differentiation under both normoxic and anoxic conditions. Bulk mRNAseq analyses suggest that OMP hydrogels under anoxia regulate osteogenic differentiation pathways more strongly than SNP/OMP or SNP hydrogels under either anoxia or normoxia. Subcutaneous implantations reveal a stronger host cell invasion in SNP hydrogels, resulting in increased vasculogenesis. Furthermore, time-dependent expression of different osteogenic factors reveals progressive differentiation of hMSCs in OMP, SNP, and SNP/OMP hydrogels. Our work demonstrates that endowing hydrogels with OMPs can induce, improve, and steer the formation of functional engineered living tissues, which holds potential for numerous biomedical applications, including tissue regeneration and organ replacement therapy.

Formulation and Evaluation of Chitosan-PLGA Biocomposite Scaffolds Incorporated with Quercetin Liposomes Made by QbD Approach for Improved Healing of Oral Lesions

The current research aims to develop and evaluate chitosan-PLGA biocomposite scaffolds in combination with quercetin liposomes to accomplish the desired impact in oral lesions where pharmacotherapeutic agent treatment through circulation could only reach the low content at the target. Optimization of quercetin-loaded liposomes was carried out using 32 factorial design. The preparation of porous scaffolds comprising produced quercetin-loaded liposomes by thin-film method was carried out in the current study using a unique strategy combining solvent casting and gas foaming procedures. The prepared scaffolds were tested for physicochemical properties, in vitro quercetin release study, ex vivo drug permeation and retention research using goat mucosa, antibacterial activity, and cell migration studies on fibroblast L929 cell lines. Improved cell growth and migration were seen in the order control < liposomes < proposed system. The proposed system has been examined for its biological and physicochemical features, and it has the potential to be utilized as an efficient therapy for oral lesions.

A hybrid hydrogel encapsulating human umbilical cord mesenchymal stem cells enhances diabetic wound healing

BACKGROUND

Diabetic wound is a severe complication of diabetes. Stem cell is considered as a promising therapy for diabetic skin wounds. Hydrogel can supply niche for cells adhesion and survival to improve the efficacy of stem cell therapy, but the development of hydrogel with suitable properties remains a great challenge. Thus, our study was conducted to combine an optimized hydrogel with stem cell to improve complex diabetic wound treatment.

METHODS

This study constructed a hydrogel with low toxicity and adjustable mechanical properties from gelatin methacrylate (GelMA) and chitosan-catechol (Chi-C), and encapsulated human umbilical cord-mesenchymal stem cells (hUMSCs) to repair full-thickness diabetic wound.

RESULTS

We explored the relationship between mechanical stiffness and cell proliferation and differentiation potency, and found 10% GelMA hydrogel with an optimal stiffness improved hUMSCs adhesion, proliferation, and differentiation potency maintenance in vitro. Assistant with optimized hydrogel encapsulating hUMSCs, diabetic wound healing process was greatly accelerated, including accelerated wound closure, inhibited secretion of inflammatory factors TNF-α and IL-1β, promoted vascular regeneration and collagen deposition after treatment of hUMSCs.

CONCLUSIONS

The optimized hydrogel encapsulating hUMSCs improved diabetic wound healing, and has a broad implication for the treatment of diabetic complication. Diabetic wound is a severe complication of diabetes. Stem cell is considered as a promising therapy for diabetic skin wounds. Hydrogel can supply niche for cells adhesion and survival to improve the efficacy of stem cell therapy. This study constructed a hydrogel with low toxicity and adjustable mechanical properties from gelatin methacrylate (GelMA) and chitosan-catechol (Chi-C), and encapsulated human umbilical cord-mesenchymal stem cells (hUMSCs) to repair full-thickness diabetic wound. Hydrogel of 10% GelMA with an optimal stiffness improved hUMSCs adhesion, proliferation, and differentiation potency maintenance in vitro. Assistant with optimized hydrogel encapsulating hUMSCs, diabetic wound healing process was greatly accelerated, including accelerated wound closure, inhibited secretion of inflammatory factors TNF-α and IL-1β, promoted vascular regeneration and collagen deposition after treatment of hUMSCs. The study supplies an alternative treatment for diabetic complication. Hydrogel-hUMSCs combined treatment accelerates wound closure in diabetic mice. A. Representative images of wounds during 21-day in vivo experiments. B. Quantification of wound closure rate (%) over 21-day period. C. HE staining of wounds at days 7, 14 and 21. The bar corresponds to 200 μm.

Poly-l-Lactic Acid (PLLA)-Based Biomaterials for Regenerative Medicine: A Review on Processing and Applications

Synthetic biopolymers are effective cues to replace damaged tissue in the tissue engineering (TE) field, both for in vitro and in vivo application. Among them, poly-l-lactic acid (PLLA) has been highlighted as a biomaterial with tunable mechanical properties and biodegradability that allows for the fabrication of porous scaffolds with different micro/nanostructures via various approaches. In this review, we discuss the structure of PLLA, its main properties, and the most recent advances in overcoming its hydrophobic, synthetic nature, which limits biological signaling and protein absorption. With this aim, PLLA-based scaffolds can be exposed to surface modification or combined with other biomaterials, such as natural or synthetic polymers and bioceramics. Further, various fabrication technologies, such as phase separation, electrospinning, and 3D printing, of PLLA-based scaffolds are scrutinized along with the in vitro and in vivo applications employed in various tissue repair strategies. Overall, this review focuses on the properties and applications of PLLA in the TE field, finally affording an insight into future directions and challenges to address an effective improvement of scaffold properties.

Poly(L-co-D,L lactic acid-co-Trimethylene Carbonate) 3D printed scaffold cultivated with mesenchymal stem cells directed to bone reconstruction: In vitro and in vivo studies

A recent and quite promising technique for bone tissue engineering is the 3D printing, peculiarly regarding the production of high-quality scaffolds. The 3D printed scaffold strictly provides suitable characteristics for living cells, in order to induce treatment, reconstruction and substitution of injured tissue. The purpose of this work was to evaluate the behavior of the 3D scaffold based on Poly(L-co-D,L lactic acid-co-Trimethylene Carbonate) (PLDLA-TMC), which was designed in Solidworks™ software, projected in 3D Slicer™, 3D printed in filament extrusion, cultured with mesenchymal stem cells (MSCs) and tested in vitro and in vivo models. For in vitro study, the MSCs were seeded in a PLDLA-TMC 3D scaffold with 600 μm pore size and submitted to proliferation and osteogenic differentiation. The in vivo assays implanted the PLDLA-TMC scaffolds with or without MSCs in the calvaria of Wistar rats submitted to 8 mm cranial bone defect, in periods of 8-12 weeks. The results showed that PLDLA-TMC 3D scaffolds favored adherence and cell growth, and suggests an osteoinductive activity, which means that the material itself augmented cellular differentiation. The implanted PLDLA-TMC containing MSCs, showed better results after 12 weeks prior grafting, due the absence of inflammatory processes, enlarged regeneration of bone tissue and facilitated angiogenesis. Notwithstanding, the 3D PLDLA-TMC itself implanted enriched tissue repair; the addition of cells known to upregulate tissue healing reinforce the perspectives for the PLDLA-TMC applications in the field of bone tissue engineering in clinical trials.

Three-dimensional printing of gyroid-structured composite bioceramic scaffolds with tuneable degradability

Customisation of bioactivity and degradability of porous bioceramic scaffolds is a formidable challenge in the field of regenerative medicine. In this study, we developed gyroid-structured ternary composite scaffolds (biphasic calcium phosphate (BCP) and 45S5 bioglass® (BG)) using digital light processing 3D printing technology based on material and structural design. Additionally, the mechanical strength, bioactivity, degradability, and biocompatibility of the composite ceramic scaffolds were evaluated. The results revealed that BG reacted with BCP to generate major active crystalline phases of CaSiO₃ and Na₃Ca₆(PO₄)₅. These active crystalline phases accelerated the exchange rate of Si⁴⁺, Ca²⁺, and PO₄^3- with HCO^3- in simulated body fluids and resulted in the rapid formation of carbonated hydroxyapatite (CHA), analogous to the formation of natural bone tissue. Interestingly, the precipitated CHA showed petal- and needle-like morphologies, which provided a large surface area to promote cell adhesion and proliferation. Furthermore, an increase in the BG content improved the degradability of ternary composite scaffolds after soaking in Tris-HCl solution. The tuneable degradability increased by three times at 30 wt% BG and sharply increased by 6.8 times at 40 wt% BG. This study provides a promising strategy to design scaffolds with improved bioactivity and tuneable degradability to assist a diverse population suffering from orthopedic conditions.

Biphasic mineralized collagen based composite scaffold for cranial bone regeneration in developing sheep

Appropriate mechanical support and excellent osteogenic capability are two essential prerequisites of customized implants for regenerating large-sized cranial bone defect. Although porous bone scaffolds have been widely proven to promote bone regeneration, their weak mechanical properties limit the clinical applications in cranioplasty. Herein, we applied two previously developed mineralized collagen-based bone scaffolds (MC), porous MC (pMC) and compact MC (cMC) to construct a biphasic MC composite bone scaffold (bMC) to repair the large-sized cranial bone defect in developing sheep. A supporting frame composed of cMC phase in the shape of tic–tac–toe structure was fabricated first and then embedded in pMC phase. The two phases had good interfacial bond, attributing to the formation of an interfacial zone. The in vivo performance of the bMC scaffold was evaluated by using a cranial bone defect model in 1-month-old sheep. The computed tomography imaging, X-ray scanning and histological evaluation showed that the pMC phase in the bMC scaffold, similar to the pMC scaffold, was gradually replaced by the regenerative bone tissues with comprehensively increased bone mineral density and complete connection of bone bridge in the whole region. The cMC frame promoted new bone formation beneath the frame without obvious degradation, thus providing appropriate mechanical protection and ensuring the structural integrity of the implant. In general, the sheep with bMC implantation exhibited the best status of survival, growth and the repair effect. The biphasic structural design may be a prospective strategy for developing new generation of cranioplasty materials to regenerate cranial bone defect in clinic.

Modelling of Stem Cells Microenvironment Using Carbon-Based Scaffold for Tissue Engineering Application-A Review

A scaffold is a crucial biological substitute designed to aid the treatment of damaged tissue caused by trauma and disease. Various scaffolds are developed with different materials, known as biomaterials, and have shown to be a potential tool to facilitate in vitro cell growth, proliferation, and differentiation. Among the materials studied, carbon materials are potential biomaterials that can be used to develop scaffolds for cell growth. Recently, many researchers have attempted to build a scaffold following the origin of the tissue cell by mimicking the pattern of their extracellular matrix (ECM). In addition, extensive studies were performed on the various parameters that could influence cell behaviour. Previous studies have shown that various factors should be considered in scaffold production, including the porosity, pore size, topography, mechanical properties, wettability, and electroconductivity, which are essential in facilitating cellular response on the scaffold. These interferential factors will help determine the appropriate architecture of the carbon-based scaffold, influencing stem cell (SC) response. Hence, this paper reviews the potential of carbon as a biomaterial for scaffold development. This paper also discusses several crucial factors that can influence the feasibility of the carbon-based scaffold architecture in supporting the efficacy and viability of SCs.

Extracellular Matrix Hydrogels Originated from Different Organs Mediate Tissue-Specific Properties and Function

Porcine extracellular matrix (pECM)-derived hydrogels were introduced, in recent years, aiming to benefit the pECM’s microstructure and bioactivity, while controlling the biomaterial’s physical and mechanical properties. The use of pECM from different tissues, however, offers tissue-specific features that can better serve different applications. In this study, pECM hydrogels derived from cardiac, artery, pancreas, and adipose tissues were compared in terms of composition, structure, and mechanical properties. While major similarities were demonstrated between all the pECM hydrogels, their distinctive attributes were also identified, and their substantial effects on cell-ECM interactions were revealed. Furthermore, through comprehensive protein and gene expression analyses, we show, for the first time, that each pECM hydrogel supports the spontaneous differentiation of induced pluripotent stem cells towards the resident cells of its origin tissue. These findings imply that the origin of ECM should be carefully considered when designing a biomedical platform, to achieve a maximal bioactive impact.

Optimizing Decellularization Strategies for the Efficient Production of Whole Rat Kidney Scaffolds

BACKGROUND

Renal dysfunction remains a global issue, with chronic kidney disease being the 18th most leading cause of death, worldwide. The increased demands in kidney transplants, led the scientific society to seek alternative strategies, utilizing mostly the tissue engineering approaches. Unlike to perfusion decellularization of kidneys, we proposed alternative decellularization strategies to obtain acellular kidney scaffolds. The aim of this study was the evaluation of two different decellularization approaches for producing kidney bioscaffolds.

METHODS

Rat kidneys from Wistar rats, were submitted to decellularization, followed two different strategies. The decellularization solutions used in both approaches were the same and involved the use of 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate and sodium dodecyl sulfate buffers for 12 h each, followed by incubation in a serum medium. Both approaches involved 3 decellularization cycles. Histological analysis, biochemical and DNA quantification were performed. Cytotoxicity assay and repopulation of acellular kidneys were also applied.

RESULTS

Histological, biochemical and DNA quantification confirmed that the 2nd approach had the best outcome regarding the kidney composition and cell elimination. Acellular kidneys from both approaches were successfully recellularized.

CONCLUSION

Based on the above data, the production of kidney scaffolds with the proposed cost- effective decellularization approaches, was efficient.

Biomaterial Properties Modulating Bone Regeneration

Biomaterial scaffolds have been gaining momentum in the past several decades for their potential applications in the area of tissue engineering. They function as three-dimensional porous constructs to temporarily support the attachment of cells, subsequently influencing cell behaviors such as proliferation and differentiation to repair or regenerate defective tissues. In addition, scaffolds can also serve as delivery vehicles to achieve sustained release of encapsulated growth factors or therapeutic agents to further modulate the regeneration process. Given the limitations of current bone grafts used clinically in bone repair, alternatives such as biomaterial scaffolds have emerged as potential bone graft substitutes. This review summarizes how physicochemical properties of biomaterial scaffolds can influence cell behavior and its downstream effect, particularly in its application to bone regeneration.

Tissue engineered platforms for studying primary and metastatic neoplasm behavior in bone

Cancer is the second leading cause of death in the United States, claiming more than 560,000 lives each year. Osteosarcoma (OS) is the most common primary malignant tumor of bone in children and young adults, while bone is a common site of metastasis for tumors initiating from other tissues. The heterogeneity, continual evolution, and complexity of this disease at different stages of tumor progression drives a critical need for physiologically relevant models that capture the dynamic cancer microenvironment and advance chemotherapy techniques. Monolayer cultures have been favored for cell-based research for decades due to their simplicity and scalability. However, the nature of these models makes it impossible to fully describe the biomechanical and biochemical cues present in 3-dimensional (3D) microenvironments, such as ECM stiffness, degradability, surface topography, and adhesivity. Biomaterials have emerged as valuable tools to model the behavior of various cancers by creating highly tunable 3D systems for studying neoplasm behavior, screening chemotherapeutic drugs, and developing novel treatment delivery techniques. This review highlights the recent application of biomaterials toward the development of tumor models, details methods for their tunability, and discusses the clinical and therapeutic applications of these systems.

3-D macro/microporous-nanofibrous bacterial cellulose scaffolds seeded with BMP-2 preconditioned mesenchymal stem cells exhibit remarkable potential for bone tissue engineering

Bone repair using BMP-2 is a promising therapeutic approach in clinical practices, however, high dosages required to be effective pose issues of cost and safety. The present study explores the potential of low dose BMP-2 treatment via tissue engineering approach, which amalgamates 3-D macro/microporous-nanofibrous bacterial cellulose (mNBC) scaffolds and low dose BMP-2 primed murine mesenchymal stem cells (C3H10T1/2 cells). Initial studies on cell-scaffold interaction using unprimed C3H10T1/2 cells confirmed that scaffolds provided a propitious environment for cell adhesion, growth, and infiltration, owing to its ECM-mimicking nano-micro-macro architecture. Osteogenic studies were conducted by preconditioning the cells with 50 ng/mL BMP-2 for 15 min, followed by culturing on mNBC scaffolds for up to three weeks. The results showed an early onset and significantly enhanced bone matrix secretion and maturation in the scaffolds seeded with BMP-2 primed cells compared to the unprimed ones. Moreover, mNBC scaffolds alone were able to facilitate the mineralization of cells to some extent. These findings suggest that, with the aid of 'osteoinduction' from low dose BMP-2 priming of stem cells and 'osteoconduction' from nano-macro/micro topography of mNBC scaffolds, a cost-effective bone tissue engineering strategy can be designed for quick and excellent in vivo osseointegration.

Sustained Release of Magnesium Ions Mediated by a Dynamic Mechanical Hydrogel to Enhance BMSC Proliferation and Differentiation

Hydrogel scaffolds are promising and widely applicable platforms for various therapeutic agents to facilitate bone tissue regeneration due to their biocompatibility and low immunogenicity. Nevertheless, the improvement of local administration efficiency and on-demand release of drugs from a hydrogel system is still an obstacle. In this work, we reported that a novel injectable hydrogel system was fabricated based on coordination of multiarm thiolated polyethylene glycol (PEG-SH) and magnesium ions for bone marrow-derived mesenchymal stem cell (BMSC) proliferation and differentiation. The dynamic nature coordination bond of Mg-S and the dynamic disulfide bond of S-S provide hydrogels with good mechanical performance and typical rheological behavior and thus endow the hydrogels with a satisfactory swelling rate and degradation property. Mg²⁺ was incorporated in the system not only to act as an effective cross-linker to enhance the hydrogel network structure but also to mediate the sustained release of Mg²⁺. Due to the controlled release of Mg²⁺, the PEG-SH/Mg²⁺ hydrogel can effectively improve BMSC proliferation and osteoblastic activity via the PI3K/Akt/GSK3β/β-catenin signal pathway in vitro. These findings indicated that the novel hydrogel controlled release of a Mg²⁺ ion is viewed as a promising and flexible platform for bone regeneration clinically.

The response of host blood vessels to graded distribution of macro-pores size in the process of ectopic osteogenesis

Angiogenesis is of great importance to bone regeneration, but it remains a significant challenge to induce sufficient angiogenesis and osteogenesis within bone grafts for large bone defect healing. The aim of this study is to investigate the effects of hydroxyapatite (HA) scaffold via a novel graded pore distribution approach on vascularization and osteoinduction. Two types of graded porous scaffolds were fabricated by sugar templates-leaching techniques: (1) one with large pores of 1100-1250 μm in the center and small pores of 500-650 μm at the periphery (HALS); (2) the other with small pores of 500-650 μm in the center and large pores of 1100-1250 μm at the periphery (HASL). In vivo data showed different pore size distribution had a remarkable impact on blood vessel formation during bone formation, which led to distinct localization of new bone within the defects. After one month of implantation, the diameters of the blood vessels infiltrated on the periphery of HASL were substantially larger than those in the center though the host blood vessels were successful in infiltrating throughout the whole scaffold. In contrast, vascularization within HALS appeared to be poor with very few blood vessels formed in the center, indicating heterogeneous vascularization in the scaffolds. After 3 months of implantation, we found that HASL induced more homogeneous bone formation in the whole bone graft but new bone was only found at the periphery of HALS. This study suggests that the pores size distribution in graded scaffolds cannot only affected early stage vascularization, but also influence late stage bone formation and remodeling. The architecture of larger pores at the periphery of graded scaffold may be capable of enhancing angiogenesis and osteogenesis during large size bone defect healing.

A Synergistic Relationship between Polycaprolactone and Natural Polymers Enhances the Physical Properties and Biological Activity of Scaffolds

Biomaterials for tissue engineering include natural and synthetic polymers, but their clinical application is still limited due to various disadvantages associated with the use of these polymers. This uncertainty of the polymeric approach in tissue engineering launches an opportunity to address a key question: can we eliminate the disadvantages of both natural and synthetic polymers by combining them to form a synergistic relationship? To answer this question, we fabricated scaffolds from elastin, collagen, fibrin, and electrospun polycaprolactone (PCL) with different ratios. The material characterization of these scaffolds investigated degradation, water contact angle, angiogenesis by an ex ovo chorion allantoic membrane (CAM) assay, and mechanical and structural properties. Biological activity and specific differentiation pathways (MSC, adipogenic, osteogenic, myogenic, and chondrogenic) were studied by using human adipose-derived stem cells. Results indicated that all composite polymers degraded at a different rate, thus affecting their mechanical integrity. Cell-based assays demonstrated continual proliferative and viable properties of the cells on all seeded scaffolds with the particular initiation of a differentiation pathway among which the PCL/collagen/fibrin composite was the most angiogenic material with maximum vasculature. We were able to tailor the physical and biological properties of PCL-based composites to form a synergistic relationship for various tissue regeneration applications.

Porous bio-click microgel scaffolds control hMSC interactions and promote their secretory properties

Human mesenchymal stem/stromal cells (hMSCs) are known to secrete numerous cytokines that signal to endogenous cells and aid in tissue regeneration. However, the role that biomaterial scaffolds can play in controlling hMSC secretory properties has been less explored. Here, microgels were co-assembled with hMSCs using three different microgel populations, with large (190 ± 100 μm), medium (110 ± 60 μm), and small (13 ± 6 μm) diameters, to create distinct porous environments that influenced hMSC clustering. Cells embedded in large diameter microgel networks resided in large clusters (~40 cells), compared to small clusters (~6 cells) observed in networks using medium diameter microgels and primarily single cells in small diameter microgel networks. Using a cytokine microarray, an overall increase in secretion was observed in scaffolds that promoted hMSC clustering, with over 60% of the measured cytokines most elevated in the large diameter microgel networks. N-cadherin interactions were identified as partially mediating these differences, so the microgel formulations were modified with an N-cadherin epitope, HAVDI, to mimic cell-cell interactions. Results revealed increased secretory properties for hMSCs in HAVDI functionalized scaffolds, even the non-clustered cells in small diameter microgel networks. Together, these results demonstrate opportunities for microgel-based scaffold systems for hMSC delivery and tailoring of porous materials properties to promote their secretory potential.

Bio-instructive materials for musculoskeletal regeneration

The prevalence and cost of disorders affecting the musculoskeletal system are predicted to rise significantly in the coming years due to the aging global population and the increase of associated risk factors. Despite being the second largest cause of disability, the clinical options for therapeutic intervention remain limited. The clinical translation of cell-based therapies for the treatment of musculoskeletal disorders faces many challenges including maintenance of cell survival in the harsh in vivo environment and the lack of control over regulating cell phenotype upon implantation. In order to address these challenges, the development of bio-instructive materials to modulate cell behavior has taken center stage as a strategy to increase the therapeutic potential of various cell populations. However, the determination of the necessary cues for a specific application and how these signals should be presented from a biomaterial remains elusive. This review highlights recent biochemical and physical strategies used to engineer bio-instructive materials for the repair of musculoskeletal tissues. There is a particular emphasis on emerging efforts such as the engineering of immunomodulatory and antibacterial materials, as well as the incorporation of these strategies into biofabrication and organ-on-a-chip approaches. STATEMENT OF SIGNIFICANCE: Disorders affecting the musculoskeletal system affect individuals across the lifespan and have a profound effect on mobility and quality of life. While small defects in many tissues can heal successfully, larger defects are often unable to heal or instead heal with inferior quality fibrous tissue and require clinical intervention. Cell-based therapies are a promising option for clinical translation, yet challenges related to maintaining cell survival and instructing cell phenotype upon implantation have limited the success of this approach. Bio-instructive materials provide an exciting opportunity to modulate cell behavior and enhance the efficacy of cell-based approaches for musculoskeletal repair. However, the identification of critical instructive cues and how to present these stimuli is a focus of intense investigation. This review highlights recent biochemical and physical strategies used to engineer bio-instructive materials for the repair of musculoskeletal tissues, while also considering exciting progress in the engineering of immunomodulatory and antibacterial materials.

Tuning pore features of mineralized collagen/PCL scaffolds for cranial bone regeneration in a rat model

Porosity is indispensable for a bone tissue-engineered scaffold for facilitating endogenous cell migration and nascent bone ingrowth. In large-sized cranial bone defect repair, porous scaffolds meet great challenges to match cranial bone regeneration and provide sufficient protection with structural integrity. Therefore, the pore features of the scaffolds for cranial bone regeneration should differ from those typical porous scaffolds used in tubular bone repair and be finely tuned. In this study, a series of porous mineralized collagen/PCL scaffolds with different pore features were fabricated via freeze-drying and applied in a Sprague Dawley rat cranial bone calvarial defect model. The pore size for four groups increased from 10-45 μm to 40-130 μm. As scaffold porosity increased, the compressive strength decreased from 2.09 ± 0.12 MPa to 0.51 ± 0.04 MPa. The micro-computed tomography three-dimensional reconstruction images showed that as pore size and porosity increased, the amount of new bone formation had a maximum in group 3 (pore size: 20-100 μm, compressive strength: 1.06 ± 0.03 MPa). In addition, the histological and histomorphometric analyses showed a consistent tendency which confirmed the Micro-CT results. Meanwhile, histological findings including bony bridging, tissue response at the bone-implant interface and fibrous capsule thickness indicated that the dura mater pathway played the most important role in the regenerative process of this calvarial defect model.

Exogenous Lysyl Oxidase-Like 2 and Perfusion Culture Induce Collagen Crosslink Formation in Osteogenic Grafts

Lysyl oxidase (LOX)-mediated collagen crosslinking can regulate osteoblastic phenotype and enhance mechanical properties of tissues, both areas of interest in bone tissue engineering. The objective of this study is to investigate the effect of lysyl oxidase-like 2 (LOXL2) on osteogenic differentiation of mesenchymal stem cells (MSCs) cultured in perfusion bioreactors, enzymatic collagen crosslink formation in the extracellular matrix (ECM), and mechanical properties of engineered bone grafts. Exogenous LOXL2 to MSCs seeded in composite scaffolds under perfusion culture for up to 28 days is administered. Constructs treated with LOXL2 appear brown in color and possess greater DNA content and osteogenic potential measured by a twofold increase in bone sialoprotein gene expression. Collagen expression of LOXL2-treated scaffolds is lower than untreated controls. Functional outputs such as calcium deposition, osteocalcin expression, and compressive modulus are unaffected by LOXL2 supplementation. Excitingly, LOXL2-treated constructs contain 1.8- and 1.4-times more pyridinoline (PYD) crosslinks per mole of collagen and per wet weight, respectively, than untreated constructs. Despite these increases, compressive moduli of LOXL2-treated constructs are similar to untreated constructs over the 28-day culture duration. This is the first report of LOXL2 application to engineered, three-dimensional bony constructs. The results suggest a potentially new strategy for engineering osteogenic grafts with a mature ECM by modulating crosslink formation.

Photo-crosslinkable, bone marrow-derived mesenchymal stem cells-encapsulating hydrogel based on collagen for osteogenic differentiation

Many patients suffer from bone injury and self-regeneration is not effective. Developing new strategies for effective bone injury repair is highly desired. Herein, collagen, an important component of the extracellular matrix, was modified with glycidyl methacrylate. The water solubility and photochemical cross-linking ability of the resulting collagen derivative was then improved. Thereafter, BMSC-laden hydrogel was fabricated using collagen modified with glycidyl methacrylate and hyaluronic acid modified with methacrylic anhydride under UV light in the presence of I 2959. The physicochemical properties were characterized suggesting that the hydrogel had great potential for enhancing cell adhesion and proliferation. Furthermore, without adding the bone morphogenetic protein-2, the collagen also promoted osteogenic differentiation of BMSCs within the hydrogel. Altogether, this hydrogel system provides a general strategy to fabricate cell-encapsulating hydrogel based on collagen and could be used as 3D scaffold for bone injury repair.

Materials-Directed Differentiation of Mesenchymal Stem Cells for Tissue Engineering and Regeneration

Cell-based therapies are a promising alternative to grafts and organ transplantation for treating tissue loss or damage due to trauma, malfunction, or disease. Over the past two decades, mesenchymal stem cells (MSCs) have attracted much attention as a potential cell population for use in regenerative medicine. While the proliferative capacity and multilineage potential of MSCs provide an opportunity to generate clinically relevant numbers of transplantable cells, their use in tissue regenerative applications has met with relatively limited success to date apart from secreting paracrine-acting factors to modulate the defect microenvironment. Presently, there is significant effort to engineer the biophysical properties of biomaterials to direct MSC differentiation and further expand on the potential of MSCs in tissue engineering, regeneration, and repair. Biomaterials can dictate MSC differentiation by modulating features of the substrate including composition, mechanical properties, porosity, and topography. The purpose of this review is to highlight recent approaches for guiding MSC fate using biomaterials and provide a description of the underlying characteristics that promote differentiation toward a desired phenotype.

Engineering principles for guiding spheroid function in the regeneration of bone, cartilage, and skin

There is a critical need for strategies that effectively enhance cell viability and post-implantation performance in order to advance cell-based therapies. Spheroids, which are dense cellular aggregates, overcome many current limitations with transplanting individual cells. Compared to individual cells, the aggregation of cells into spheroids results in increased cell viability, together with enhanced proangiogenic, anti-inflammatory, and tissue-forming potential. Furthermore, the transplantation of cells using engineered materials enables localized delivery to the target site while providing an opportunity to guide cell fate in situ, resulting in improved therapeutic outcomes compared to systemic or localized injection. Despite promising early results achieved by freely injecting spheroids into damaged tissues, growing evidence demonstrates the advantages of entrapping spheroids within a biomaterial prior to implantation. This review will highlight the basic characteristics and qualities of spheroids, describe the underlying principles for how biomaterials influence spheroid behavior, with an emphasis on hydrogels, and provide examples of synergistic approaches using spheroids and biomaterials for tissue engineering applications.

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.

Bioreactor culture duration of engineered constructs influences bone formation by mesenchymal stem cells

Perfusion culture of mesenchymal stem cells (MSCs) seeded in biomaterial scaffolds provides nutrients for cell survival, enhances extracellular matrix deposition, and increases osteogenic cell differentiation. However, there is no consensus on the appropriate perfusion duration of cellular constructs in vitro to boost their bone forming capacity in vivo. We investigated this phenomenon by culturing human MSCs in macroporous composite scaffolds in a direct perfusion bioreactor and compared their response to scaffolds in continuous dynamic culture conditions on an XYZ shaker. Cell seeding in continuous perfusion bioreactors resulted in more uniform MSC distribution than static seeding. We observed similar calcium deposition in all composite scaffolds over 21 days of bioreactor culture, regardless of pore size. Compared to scaffolds in dynamic culture, perfused scaffolds exhibited increased DNA content and expression of osteogenic markers up to 14 days in culture that plateaued thereafter. We then evaluated the effect of perfusion culture duration on bone formation when MSC-seeded scaffolds were implanted in a murine ectopic site. Human MSCs persisted in all scaffolds at 2 weeks in vivo, and we observed increased neovascularization in constructs cultured under perfusion for 7 days relative to those cultured for 1 day within each gender. At 8 weeks post-implantation, we observed greater bone volume fraction, bone mineral density, tissue ingrowth, collagen density, and osteoblastic markers in bioreactor constructs cultured for 14 days compared to those cultured for 1 or 7 days, and acellular constructs. Taken together, these data demonstrate that culturing MSCs under perfusion culture for at least 14 days in vitro improves the quantity and quality of bone formation in vivo. This study highlights the need for optimizing in vitro bioreactor culture duration of engineered constructs to achieve the desired level of bone formation.

Porous stable poly(lactic acid)/ethyl cellulose/hydroxyapatite composite scaffolds prepared by a combined method for bone regeneration

A major challenge in bone tissue engineering is the development of biomimetic scaffolds which should simultaneously meet mechanical strength and pore structure requirements. Herein, we combined technologies of high concentration solvent casting, particulate leaching, and room temperature compression molding to prepare a novel poly(lactic acid)/ethyl cellulose/hydroxyapatite (PLA/EC/HA) scaffold. The functional, structural and mechanical properties of the obtained porous scaffolds were characterized. The results indicated that the PLA/EC/HA scaffolds at the 20wt% HA loading level showed optimal mechanical properties and desired porous structure. Its porosity, contact angle, compressive yield strength and weight loss after 56days were 84.28±7.04%, 45.13±2.40°, 1.57±0.09MPa and 4.77±0.32%, respectively, which could satisfy the physiological demands to guide bone regeneration. Thus, the developed scaffolds have potential to be used as a bone substitute material for bone tissue engineering application.

Detection of Pentosidine Cross-Links in Cell-Secreted Decellularized Matrices Using Time Resolved Fluorescence Spectroscopy

Hyperglycemia-mediated, nonenzymatic collagen cross-links such as pentosidine (PENT) can have deleterious effects on cellular interactions with the extracellular matrix (ECM). Present techniques to quantify PENT are limited, motivating the need for improved methods to study the accumulation and contribution of PENT toward diabetic clinical challenges such as impaired bone healing. Current methods for studying PENT are destructive, laborious, and frequently employ oversimplified collagen films that lack the complexity of the native ECM. The primary goal of this study was to evaluate the capacity of time-resolved fluorescence spectroscopy (TRFS) to detect PENT in cell-secreted ECMs possessing enhanced compositional complexity. To demonstrate an application of this method, we assessed the response of human mesenchymal stem cells (MSCs) to cross-linked substrates to explore the role of detected PENT on osteogenic differentiation. We exposed MSC-secreted decellularized matrices (DMs) to 0.66 M ribose for 2 weeks and used TRFS to detect the accumulation of PENT. Ribose treatment resulted in a 30 nm blue shift in peak fluorescence emission and a significant decrease in average lifetime compared to that of control DMs (4.4 ± 0.3 ns vs 3.5 ± 0.09 ns). Evaluation of samples with high performance liquid chromatography (HPLC) confirmed that changes in observed fluorescence were due to PENT accumulation. A strong correlation was found between TRFS parameters and the HPLC measurement of PENT, validating the use of TRFS as an alternative method of PENT detection. Osteoblastic gene expression was significantly reduced in MSCs seeded on ribose DMs at days 7 and 14. However, no significant differences in calcium deposition were detected between control and ribose DMs. These data demonstrate the efficacy of nondestructive fluorescence spectroscopy to examine the formation of nonenzymatic collagen cross-links within biomimetic culture platforms and showcase one example where an improved biomimetic substrate can be used to probe cell-ECM interactions in the presence of collagen cross-links.

Electrical stimulation of adipose-derived mesenchymal stem cells and endothelial cells co-cultured in a conductive scaffold for potential orthopaedic applications

Electrical stimulation (ES) has emerged as a useful tool to regulate cell behaviour, but the effect of ES on mesenchymal stem cell (MSC)/vasculogenic cell co-culture has not been investigated. Herein, human adipose-derived MSCs (AD-MSCs) and umbilical vein endothelial cells (HUVECs) were co-cultured in an electrically conductive polypyrrole/chitosan scaffold. Compared with AD-MSC monoculture, calcium deposition in the co-culture without and with ES (200 μA for 4 h/day) was 139% and 346% higher, respectively, after 7 days. As the application of ES to AD-MSC monoculture only increased calcium deposition by 56% compared with that without ES after 7 days, these results indicate that ES and co-culture with HUVECs have synergistic effects on AD-MSCs' osteogenic differentiation. ES application also significantly enhanced CD31 expression of HUVECs. In HUVEC monoculture, application of ES increased CD31 expression by 224%, whereas the corresponding increase in AD-MSC/HUVEC co-culture with ES application was 62%. The gene expression results indicate that ES enhanced the cellular functions in AD-MSC and HUVEC monoculture via autocrine bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF), respectively. In co-culture, crosstalk between AD-MSCs and HUVECs due to paracrine BMP-2 and VEGF enhanced the cellular functions compared with the respective monoculture. With application of ES to the AD-MSC/HUVEC co-culture, autocrine signalling was enhanced, resulting in further promotion of cellular functions. These findings illustrate that co-culturing AD-MSC/HUVEC in a conductive scaffold with ES offers potential benefits for bone defect therapy.

SC79-loaded ZSM-5/chitosan porous scaffolds with enhanced stem cell osteogenic differentiation and bone regeneration

For effectively treating bone defects, the design of novel therapeutic scaffolds is an important strategy for enhancing stem cell osteogenic differentiation and new bone formation. Herein, we, for the first time, fabricated SC79-loaded ZSM-5/chitosan (ZSM-5/CS/SC79) porous scaffolds via the freeze-drying synthesis of ZSM-5/CS porous scaffolds followed by loading SC79 drug molecules. The ZSM-5/CS scaffolds possessed a three-dimensional (3D) interconnected porous structure, and the nanostructured ZSM-5 ellipsoids were uniformly dispersed on the CS films. The ZSM-5/CS/SC79 scaffolds had appropriate drug loading-release properties due to the hierarchically porous structures of ZSM-5 zeolites and the hydrogen bonding between the CS and SC97. In vitro cell tests demonstrated that both the ZSM-5/CS and ZSM-5/CS/SC79 scaffolds could promote the adhesion, spreading and proliferation of human bone mesenchymal stem cells (hBMSCs). Interestingly, the SC97 released from the scaffolds not only promoted the proliferation of hBMSCs, but also enhanced the osteogenic differentiation. As compared with the ZSM-5/CS control group, the ZSM-5/CS/SC79 scaffolds promoted the ALP activity of hBMSCs, improved the mRNA relative expression levels of osteocalcin (OCN), bone morphogenetic protein-2 (BMP-2) and alkaline phosphatise (ALP), and increased the protein level of β-catenin. The enhanced proliferation and osteogenic differentiation of hBMSCs contributed to the upregulation of Akt kinase by an activated Wnt/β-catenin signaling pathway. Moreover, in vivo animal tests indicated that SC79 released from the ZSM-5/CS/SC79 scaffolds promoted the new bone regeneration without systemic side effects in cranial defects. Therefore, ZSM-5/CS/SC79 scaffolds as novel and promising therapeutic scaffolds have promising applications in defined local bone regeneration.

In vitro proliferation and differentiation of human bone marrow mesenchymal stem cells into osteoblasts on nanocomposite scaffolds based on bioactive glass (64SiO2-31CaO-5P2O5)-poly-l-lactic acid nanofibers fabricated by electrospinning method

Electrospinning method was employed for fabrication of SiO₂-CaO-P₂O₅ bioactive glass (BG) nanofibers, poly-l-lactic acid (PLLA) nanofibers and nanocomposite scaffolds fabricated from as-prepared nanofibers. Characterization of the prepared nanofibers and scaffolds by XRD, FTIR, and SEM techniques revealed the formation of nanofibers with mean diameter of about 500nm and fully fibrous scaffolds with porous structure and interconnected pores. The growth, viability and proliferation of cultured human bone marrow mesenchymal stem cells in the fabricated nanofibers and bioactive glass-poly-l-lactic acid (BG-PLLA) nanocomposite scaffolds were studied using various biological assays including MTT, ALP activity, calcium deposit content, Alizarin red staining, and RT-PCR test. Based on the obtained results, incorporation of BG nanofibers in the nanocomposite scaffolds causes the better biological behavior of the scaffolds. In addition, three-dimensional and fibrous-porous structure of the scaffolds further contributes to their improved cell behavior compared to the components.

Core–shell-structured nonstoichiometric bioceramic spheres for improving osteogenic capability

Precisely controlling the composition distribution and pore-network evolution in the foreign ion doped, core–shell Ca-silicate bioceramic microspheres is favorable for tailoring osteogenicity in critical size bone defects.

Extracellular Matrix-Coated Composite Scaffolds Promote Mesenchymal Stem Cell Persistence and Osteogenesis

Composite scaffolds of bioactive glass and poly(lactide-co-glycolide) provide advantages over homogeneous scaffolds, yet their therapeutic potential can be improved by strategies that promote adhesion and present instructive cues to associated cells. Mesenchymal stem cell (MSC)-secreted extracellular matrix (ECM) enhances survival and function of associated cells. To synergize the benefits of an instructive ECM with composite scaffolds, we tested the capacity of ECM-coated composite scaffolds to promote cell persistence and resultant osteogenesis. Human MSCs cultured on ECM-coated scaffolds exhibited increased metabolic activity and decreased apoptosis compared to uncoated scaffolds. Additionally, MSCs on ECM-coated substrates in short-term culture secreted more proangiogenic factors while maintaining markers of osteogenic differentiation. Upon implantation, we detected improved survival of MSCs on ECM-coated scaffolds over 3 weeks. Histological evaluation revealed enhanced cellularization and osteogenic differentiation in ECM-coated scaffolds compared to controls. These findings demonstrate the promise of blending synthetic and natural ECMs and their potential in tissue regeneration.

Bone Morphogenetic Protein-2 Promotes Human Mesenchymal Stem Cell Survival and Resultant Bone Formation When Entrapped in Photocrosslinked Alginate Hydrogels

There is a substantial need to prolong cell persistence and enhance functionality in situ to enhance cell-based tissue repair. Bone morphogenetic protein-2 (BMP-2) is often used at high concentrations for osteogenic differentiation of mesenchymal stem cells (MSCs) but can induce apoptosis. Biomaterials facilitate the delivery of lower doses of BMP-2, reducing side effects and localizing materials at target sites. Photocrosslinked alginate hydrogels (PAHs) can deliver osteogenic materials to irregular-sized bone defects, providing improved control over material degradation compared to ionically cross-linked hydrogels. It is hypothesized that the delivery of MSCs and BMP-2 from a PAH increases cell persistence by reducing apoptosis, while promoting osteogenic differentiation and enhancing bone formation compared to MSCs in PAHs without BMP-2. BMP-2 significantly decreases apoptosis and enhances survival of photoencapsulated MSCs, while simultaneously promoting osteogenic differentiation in vitro. Bioluminescence imaging reveals increased MSC survival when implanted in BMP-2 PAHs. Bone defects treated with MSCs in BMP-2 PAHs demonstrate 100% union as early as 8 weeks and significantly higher bone volumes at 12 weeks, while defects with MSC-entrapped PAHs alone do not fully bridge. This study demonstrates that transplantation of MSCs with BMP-2 in PAHs achieves robust bone healing, providing a promising platform for bone repair.

Engineering Porous Poly(lactic acid) Scaffolds with High Mechanical Performance via a Solid State Extrusion/Porogen Leaching Approach

A knotty issue concerning the poor mechanical properties exists in the porogen leaching approach to porous scaffolds, despite its advantage in tuning pore structure. To address this hurdle, solid state extrusion (SSE) combined with porogen leaching was utilized to engineer porous scaffolds of poly(lactic acid) (PLA). Advances introduced by poly(ethylene glycol) (PEG) caused the PLA ductile to be processed and, on the other hand, enabled the formation of interconnected pores. Thus, a well-interconnected porous architecture with high connectivity exceeding 97% and elevated porosity over 60% was obtained in the as-prepared PLA scaffolds with the composition of NaCl higher than 75.00 wt % and PEG beyond 1.25 wt %. More strikingly, the pore walls of macropores encompassed countless micropores and rough surface topography, in favor of transporting nutrients and metabolites as well as cell attachment. The prominent compressive modulus of the PLA scaffolds was in the range of 85.7⁻207.4 MPa, matching the normal modulus of human trabecular bone (50⁻250 MPa). By means of alkaline modification to improve hydrophilicity, biocompatible porous PLA scaffolds exhibited good cell attachment. These results suggest that the SSE/porogen leaching approach provides an eligible clue for fabricating porous scaffolds with high mechanical performance for use as artificial extracellular matrices.