Vascularization in tissue engineering: The architecture cues of pores in scaffolds

Architecture of β-lactoglobulin coating modulates bioinspired alginate dialdehyde-gelatine/polydopamine scaffolds for subchondral bone regeneration

In this study, we developed polydopamine (PDA)-functionalized alginate dialdehyde-gelatine (ADA-GEL) scaffolds for subchondral bone regeneration. These polymeric scaffolds were then coated with β-Lactoglobulin (β-LG) at concentrations of 1 mg/ml and 2 mg/ml. Morphological analysis indicated a homogeneous coating of the β-LG layer on the surface of network-like scaffolds. The β-LG-coated scaffolds exhibited improved swelling capacity as a function of the β-LG concentration. Compared to ADA-GEL/PDA scaffolds, the β-LG-coated scaffolds demonstrated delayed degradation and enhanced biomineralization. Here, a lower concentration of β-LG showed long-lasting stability and superior biomimetic hydroxyapatite mineralization. According to the theoretical findings, the single-state, representing the low concentration of β-LG, exhibited a homogeneous distribution on the surface of the PDA, while the dimer-state (high concentration) displayed a high likelihood of uncontrolled interactions. β-LG-coated ADA-GEL/PDA scaffolds with a lower concentration of β-LG provided a biocompatible substrate that supported adhesion, proliferation, and alkaline phosphatase (ALP) secretion of sheep bone marrow mesenchymal stem cells, as well as increased expression of osteopontin (SPP1) and collagen type 1 (COL1A1) in human osteoblasts. These findings indicate the potential of protein-coated scaffolds for subchondral bone tissue regeneration. STATEMENT OF SIGNIFICANCE: This study addresses a crucial aspect of osteochondral defect repair, emphasizing the pivotal role of subchondral bone regeneration. The development of polydopamine-functionalized alginate dialdehyde-gelatine (ADA-GEL) scaffolds, coated with β-Lactoglobulin (β-LG), represents a novel approach to potentially enhance subchondral bone repair. β-LG, a milk protein rich in essential amino acids and bioactive peptides, is investigated for its potential to promote subchondral bone regeneration. This research explores computationally and experimentally the influence of protein concentration on the ordered or irregular deposition, unravelling the interplay between coating structure, scaffold properties, and in-vitro performance. This work contributes to advancing ordered protein coating strategies for subchondral bone regeneration, providing a biocompatible solution with potential implications for supporting subsequent cartilage repair.

Recent trends in bone tissue engineering: a review of materials, methods, and structures

Bone tissue engineering (BTE) provides the treatment possibility for segmental long bone defects that are currently an orthopedic dilemma. This review explains different strategies, from biological, material, and preparation points of view, such as using different stem cells, ceramics, and metals, and their corresponding properties for BTE applications. In addition, factors such as porosity, surface chemistry, hydrophilicity and degradation behavior that affect scaffold success are introduced. Besides, the most widely used production methods that result in porous materials are discussed. Gene delivery and secretome-based therapies are also introduced as a new generation of therapies. This review outlines the positive results and important limitations remaining in the clinical application of novel BTE materials and methods for segmental defects.

Design, In Vitro Evaluation and In Vivo Biocompatibility of Additive Manufacturing Three-Dimensional Printing of β beta-Tricalcium Phosphate Scaffolds for Bone Regeneration

The reconstruction of bone deficiencies remains a challenge due to the limitations of autologous bone grafting. The objective of this study is to evaluate the bone regeneration efficacy of additive manufacturing of tricalcium phosphate (TCP) implants using lithography-based ceramic manufacturing (LCM). LCM uses LithaBone TCP 300 slurry for 3D printing, producing cylindrical scaffolds. Four models of internal scaffold geometry were developed and compared. The in vitro studies included cell culture, differentiation, seeding, morphological studies and detection of early osteogenesis. The in vivo studies involved 42 Wistar rats divided into four groups (control, membrane, scaffold (TCP) and membrane with TCP). In each animal, unilateral right mandibular defects with a total thickness of 5 mm were surgically performed. The animals were sacrificed 3 and 6 months after surgery. Bone neoformation was evaluated by conventional histology, radiology, and micro-CT. Model A (spheres with intersecting and aligned arrays) showed higher penetration and interconnection. Histological and radiological analysis by micro-CT revealed increased bone formation in the grafted groups, especially when combined with a membrane. Our innovative 3D printing technology, combined with precise scaffold design and efficient cleaning, shows potential for bone regeneration. However, further refinement of the technique and long-term clinical studies are crucial to establish the safety and efficacy of these advanced 3D printed scaffolds in human patients.

Advances in natural and synthetic macromolecules with stem cells and extracellular vesicles for orthopedic disease treatment

Serious orthopedic disorders resulting from myriad diseases and impairments continue to pose a considerable challenge to contemporary clinical care. Owing to its limited regenerative capacity, achieving complete bone tissue regeneration and complete functional restoration has proven challenging with existing treatments. By virtue of cellular regenerative and paracrine pathways, stem cells are extensively utilized in the restoration and regeneration of bone tissue; however, low survival and retention after transplantation severely limit their therapeutic effect. Meanwhile, biomolecule materials provide a delivery platform that improves stem cell survival, increases retention, and enhances therapeutic efficacy. In this review, we present the basic concepts of stem cells and extracellular vesicles from different sources, emphasizing the importance of using appropriate expansion methods and modification strategies. We then review different types of biomolecule materials, focusing on their design strategies. Moreover, we summarize several forms of biomaterial preparation and application strategies as well as current research on biomacromolecule materials loaded with stem cells and extracellular vesicles. Finally, we present the challenges currently impeding their clinical application for the treatment of orthopedic diseases. The article aims to provide researchers with new insights for subsequent investigations.

Biomaterial design for regenerating aged bone: materiobiological advances and paradigmatic shifts

China's aging demographic poses a challenge for treating prevalent bone diseases impacting life quality. As bone regeneration capacity diminishes with age due to cellular dysfunction and inflammation, advanced biomaterials-based approaches offer hope for aged bone regeneration. This review synthesizes materiobiology principles, focusing on biomaterials that target specific biological functions to restore tissue integrity. It covers strategies for stem cell manipulation, regulation of the inflammatory microenvironment, blood vessel regeneration, intervention in bone anabolism and catabolism, and nerve regulation. The review also explores molecular and cellular mechanisms underlying aged bone regeneration and proposes a database-driven design process for future biomaterial development. These insights may also guide therapies for other age-related conditions, contributing to the pursuit of 'healthy aging'.

Magnetic biocomposite scaffold based on decellularized tendon ECM and MNP-deposited halloysite nanotubes: physicochemical, thermal, rheological, mechanical andin vitrobiological evaluations

The development of new three-dimensional biomaterials with advanced versatile properties is critical to the success of tissue engineering (TE) applications. Here, (a) bioactive decellularized tendon extracellular matrix (dECM) with a sol-gel transition feature at physiological temperature, (b) halloysite nanotubes (HNT) with known mechanical properties and bioactivity, and (c) magnetic nanoparticles (MNP) with superparamagnetic and osteogenic properties were combined to develop a new scaffold that could be used in prospective bone TE applications. Deposition of MNPs on HNTs resulted in magnetic nanostructures without agglomeration of MNPs. A completely cell-free, collagen- and glycosaminoglycan- rich dECM was obtained and characterized. dECM-based scaffolds incorporated with 1%, 2% and 4% MNP-HNT were analysed for their physical, chemical, andin vitrobiological properties. Fourier-transform infrared spectroscopy, x-ray powder diffractometry and vibrating sample magnetometry analyses confirmed the presence of dECM, HNT and MNP in all scaffold types. The capacity to form apatite layer upon incubation in simulated body fluid revealed that dECM-MNP-HNT is a bioactive material. Combining dECM with MNP-HNT improved the thermal stability and compressive strength of the macroporous scaffolds upto 2% MNP-HNT.In vitrocytotoxicity and hemolysis experiments showed that the scaffolds were essentially biocompatible. Human bone marrow mesenchymal stem cells adhered and proliferated well on the macroporous constructs containing 1% and 2% MNP-HNT; and remained metabolically active for at least 21 din vitro. Collectively, the findings support the idea that magnetic nanocomposite dECM scaffolds containing MNP-HNT could be a potential template for TE applications.

Decellularized Bone Matrix/45S5 Bioactive Glass Biocomposite Hydrogel-Based Constructs with Angiogenic and Osteogenic Properties: Ex Ovo and Ex Vivo Evaluations

Decellularized extracellular matrix is often used to create an in vivo-like environment that supports cell growth and proliferation, as it reflects the micro/macrostructure and molecular composition of tissues. On the other hand, bioactive glasses (BG) are surface-reactive glass-ceramics that can convert to hydroxyapatite in vivo and promote new bone formation. This study is designed to evaluate the key properties of a novel angiogenic and osteogenic biocomposite graft made of bovine decellularized bone matrix (DBM) hydrogel and 45S5 BG microparticles (10 and 20 wt%) to combine the existing superior properties of both biomaterial classes. Morphological, physicochemical, mechanical, and thermal characterizations of DBM and DBM/BG composite hydrogels are performed. Their in vitro biocompatibility is confirmed by cytotoxicity and hemocompatibility analyses. Ex vivo chick embryo aortic arch and ex ovo chick chorioallantoic membrane (CAM) assays reveal that the present pro-angiogenic property of DBM hydrogels is enhanced by the incorporation of BG. Histochemical stainings (Alcian blue and Alizarin red) and digital image analysis of ossification on hind limbs of embryos used in the CAM model reveal the osteogenic potential of biomaterials. The findings support the notion that the developed DBM/BG composite hydrogel constructs have the potential to be a suitable graft for bone repair.

Bone ingrowth into a porous structure is achieved by preceding fibrogenesis and vascularization

Porous structures are frequently used in surgical implants to strengthen the interlocking power produced by bone ingrowth. Therefore, we aimed to elucidate the mechanism underlying bone ingrowth into a porous structure accompanied by vascularization. A nonbioactive polyetheretherketone implant with a 3D-printed porous structure was prepared and implanted in a bone hole created in the tibias of rabbits. We observed bone ingrowth in the same individual specimens immediately and at 2, 4, 8, and 12 weeks post-implantation using in-vivo computed tomography (CT). Furthermore, a detailed evaluation with blood vessels of each specimen at 2, 4, and 12 weeks was performed with ex-vivo CT and histological specimen. Additional histological evaluation was performed using thin sections of an implant made with thermoplastic polyurethane having the same structure. As a result, the bone invasion began after four weeks, when the construction of fibrous tissue and the spread of new blood vessels within the voids matured. As the bone matured in the load-bearing area, new blood vessels outside the bone matrix regressed. This longitudinal evaluation study suggests that preceding fibrogenesis and vascularization may be key in developing bone ingrowth. STATEMENT OF SIGNIFICANCE: A porous structure is an essential structure for dental and orthopedic implants because it provides strong fixation through bone invasion. Although it was known that vascularization was involved in this, the details were not known. This in vivo study revealed that in order for bone ingrowth to begin, a preparatory period of approximately 4 weeks was required to establish blood flow inside and outside the implant. Furthermore, it was confirmed that by spreading the fibrous structure in advance, it has an advantageous effect on the migration of cells involved in the formation of bones and blood vessels. We pointed out that it is necessary to consider fibrogenesis and vascularization when creating future implants.

Accelerating Patterned Vascularization Using Granular Hydrogel Scaffolds and Surgical Micropuncture

Bulk hydrogel scaffolds are common in reconstructive surgery. They allow for the staged repair of soft tissue loss by providing a base for revascularization. Unfortunately, they are limited by both slow and random vascularization, which may manifest as treatment failure or suboptimal repair. Rapidly inducing patterned vascularization within biomaterials has profound translational implications for current clinical treatment paradigms and the scaleup of regenerative engineering platforms. To address this long-standing challenge, a novel microsurgical approach and granular hydrogel scaffold (GHS) technology are co-developed to hasten and pattern microvascular network formation. In surgical micropuncture (MP), targeted recipient blood vessels are perforated using a microneedle to accelerate cell extravasation and angiogenic outgrowth. By combining MP with an adjacent GHS with precisely tailored void space architecture, microvascular pattern formation as assessed by density, diameter, length, and intercapillary distance is rapidly guided. This work opens new translational opportunities for microvascular engineering, advancing reconstructive surgery, and regenerative medicine.

New Insights and Advanced Strategies for In Vitro Construction of Vascularized Tissue Engineering

Inadequate vascularization is a significant barrier to clinical application of large-volume tissue engineered grafts. In contrast to in vivo vascularization, in vitro prevascularization shortens the time required for host vessels to grow into the graft core and minimizes necrosis in the core region of the graft. However, the challenge of prevascularization is to construct hierarchical perfusable vascular networks, increase graft volume, and form a vascular tip that can anastomose with host vessels. Understanding advances in in vitro prevascularization techniques and new insights into angiogenesis could overcome these obstacles. In the present review, we discuss new perspectives on angiogenesis, the differences between in vivo and in vitro tissue vascularization, the four elements of prevascularized constructs, recent advances in perfusion-based in vitro prevascularized tissue fabrication, and prospects for large-volume prevascularized tissue engineering.

Recent advancement in vascularized tissue-engineered bone based on materials design and modification

Bone is one of the most vascular network-rich tissues in the body and the vascular system is essential for the development, homeostasis, and regeneration of bone. When segmental irreversible damage occurs to the bone, restoring its vascular system by means other than autogenous bone grafts with vascular pedicles is a therapeutic challenge. By pre-generating the vascular network of the scaffold in vivo or in vitro, the pre-vascularization technique enables an abundant blood supply in the scaffold after implantation. However, pre-vascularization techniques are time-consuming, and in vivo pre-vascularization techniques can be damaging to the body. Critical bone deficiencies may be filled quickly with immediate implantation of a supporting bone tissue engineered scaffold. However, bone tissue engineered scaffolds generally lack vascularization, which requires modification of the scaffold to aid in enhancing internal vascularization. In this review, we summarize the relationship between the vascular system and osteogenesis and use it as a basis to further discuss surgical and cytotechnology-based pre-vascularization strategies and to describe the preparation of vascularized bone tissue engineered scaffolds that can be implanted immediately. We anticipate that this study will serve as inspiration for future vascularized bone tissue engineered scaffold construction and will aid in the achievement of clinical vascularized bone.

3D printed elastomeric biomaterial mitigates compaction during in vitro vasculogenesis

A key parameter for the success of most cellular implants is the formation of a complete and comprehensive intra-implant vessel network. Pre-vascularization, the generation of vessel structures in vitro prior to transplantation, provides accelerated implant perfusion via anastomosis, but scalability and ease of integration hinder clinical translation. For fibrin-based vasculogenesis approaches, the remodeling and degradation of the fragile, hydrogel matrix during the formation of vessel-like structures results in rapid, cell-mediated construct compaction leading to dense, capillary-like structures with ineffective network coverage. To resolve these challenges, vasculogenic hydrogels were embedded within a highly porous, biostable three-dimensional (3D) polydimethylsiloxane (PDMS) scaffold. Using reverse-casting of 3D-printed molds, scaffolds exhibited highly interconnected and reproducible pore structures. Pore size was optimized via in vivo screening of intra-device angiogenesis. The inclusion of the PDMS frame with vasculogenic hydrogels significantly reduced fibrin compaction in vitro, resulting in easily manipulated constructs with predictable dimensionality and increased surface area compared to fibrin hydrogel alone. Globally, vascular morphogenesis was altered by the PDMS frame, with significantly larger and less dense network structures. Vasculogenic proteomic evaluation showed a temporal impact of the addition of the PDMS frame, indicating altered cellular proliferation and migration signaling. This work establishes a platform for improving the generation of translational pre-vascularized networks for greater flexibility to meet the needs of clinically scaled, engineered tissues. STATEMENT OF SIGNIFICANCE: Competent intra-implant vascularization is a significant issue hindering the success of engineered tissues. Pre-vascularization approaches, whereby a vascular network is formed in vitro and subsequently implanted into the host to anastomose, is a promising approach but it is limited by the compacted, dense, and poorly functional microcapillary structures typically formed using soft hydrogels. Herein, we have uniquely addressed this challenge by adding a 3D printed PDMS-based open framework structure that serves to prevent hydrogel compaction. Globally, we observed distinct differences in overall construct geometry, vascular network density, compaction, and morphogenesis, indicating that this PDMS framework lead to elevated maturity of this in vitro network while retaining its global dimensions. Overall, this novel approach elevates the translational potential of pre-vascularized constructs.

Influence of Macrophages on Vascular Invasion of Inflammatory Breast Cancer Emboli Measured Using an In Vitro Microfluidic Multi-Cellular Platform

Inflammatory breast cancer (IBC) is an aggressive disease with a poor prognosis and a lack of effective treatments. It is widely established that understanding the interactions between tumor-associated macrophages (TAMs) and the tumor microenvironment is essential for identifying distinct targeting markers that help with prognosis and subsequent development of effective treatments. In this study, we present a 3D in vitro microfluidic IBC platform consisting of THP1 M0, M1, or M2 macrophages, IBC cells, and endothelial cells. The platform comprises a collagen matrix that includes an endothelialized vessel, creating a physiologically relevant environment for cellular interactions. Through the utilization of this platform, it was discovered that the inclusion of tumor-associated macrophages (TAMs) led to an increase in the formation of new blood vessel sprouts and enhanced permeability of the endothelium, regardless of the macrophage phenotype. Interestingly, the platforms containing THP-1 M1 or M2 macrophages exhibited significantly greater porosity in the collagen extracellular matrix (ECM) compared to the platforms containing THP-1 M0 and the MDA-IBC3 cells alone. Cytokine analysis revealed that IL-8 and MMP9 showed selective increases when macrophages were cultured in the platforms. Notably, intravasation of tumor cells into the vessels was observed exclusively in the platform containing MDA-IBC3 and M0 macrophages.

Triply Periodic Minimal Surface-Based Scaffolds for Bone Tissue Engineering: A Mechanical, In Vitro and In Vivo Study

Triply periodic minimal surfaces (TPMSs) are found to be promising microarchitectures for bone substitutes owing to their low weight and superior mechanical characteristics. However, existing studies on their application are incomplete because they focus solely on biomechanical or in vitro aspects. Hardly any in vivo studies where different TPMS microarchitectures are compared have been reported. Therefore, we produced hydroxyapatite-based scaffolds with three types of TPMS microarchitectures, namely Diamond, Gyroid, and Primitive, and compared them with an established Lattice microarchitecture by mechanical testing, 3D-cell culture, and in vivo implantation. Common to all four microarchitectures was the minimal constriction of a sphere of 0.8 mm in diameter, which earlier was found superior in Lattice microarchitectures. Scanning by μCT revealed the precision and reproducibility of our printing method. The mechanical analysis showed significantly higher compression strength for Gyroid and Diamond samples compared with Primitive and Lattice. After in vitro culture with human bone marrow stromal cells in control or osteogenic medium, no differences between these microarchitectures were observed. However, from the TPMS microarchitectures, Diamond- and Gyroid-based scaffolds showed the highest bone ingrowth and bone-to-implant contact in vivo. Therefore, Diamond and Gyroid designs appear to be the most promising TPMS-type microarchitectures for scaffolds produced for bone tissue engineering and regenerative medicine. Impact Statement Extensive bone defects require the application of bone grafts. To match the existing requirements, scaffolds based on triply periodic minimal surface (TPMS)-based microarchitectures could be used as bone substitutes. This work is dedicated to the investigation of mechanical and osteoconductive properties of TPMS-based scaffolds to determine the influencing factors on differences in their behavior and choose the most promising design to be used in bone tissue engineering.

Fabrication of ACP-CCS-PVA composite membrane for a potential application in guided bone regeneration

The barrier membranes of guided bone regeneration (GBR) have been widely used in clinical medicine to repair bone defects. However, the unmatched mechanical strength, unsuitable degradation rates, and insufficient regeneration potential limit the application of the current barrier membranes. Here, amorphous calcium phosphate-carboxylated chitosan-polyvinyl alcohol (ACP-CCS-PVA) composite membranes are fabricated by freeze-thaw cycles, in which the ATP-stabilized ACP nanoparticles are uniformly distributed throughout the membranes. The mechanical performance and osteogenic properties are significantly improved by the ACP incorporated into the CCS-PVA system, but excess ACP would suppress cell proliferation and osteogenic differentiation. Our work highlights the pivotal role of ACP in GBR and provides insight into the need for biomaterial fabrication to balance mechanical strength and mineral content.

Hollow channels scaffold in bone regenerative: a review

Bone substitute materials have been extensively used for bone regeneration over the past 50 years. The development of novel materials, fabrication technologies and the incorporation and release of regenerative cytokines, growth factors, cells and antimicrobials has been driven by the rapid development in the field of additive manufacturing technology. There are still however, significant challenges that need addressing, including ways to better mediate the rapid vascularization of bone scaffolds to enhance subsequent regeneration and osteogenesis. Increasing construct porosity can accelerate the development of blood vessels in the scaffold, but doing so also weakens the constructs mechanical properties. A novel design for promoting rapid vascularization is to fabricate custom-made hollow channels as bone scaffolds. Summarized here are the current developments in hollow channels scaffold, including their biological attributes, physio-chemical properties, and effects on regeneration. An overview of recent developments in scaffold fabrication as they relate to hollow channel constructs and their structural features will be introduced with an emphasis on attributes that enhance new bone and vessel formation. Furthermore, the potential to enhance angiogenesis and osteogenesis by replicating the structure of real bone will be highlighted.

Dual-Functional Drug Delivery System for Bisphosphonate-Related Osteonecrosis Prevention and Its Bioinspired Releasing Model and In Vitro Assessment

Clindamycin (CDM)/geranylgeraniol (GGOH)-loaded plasma-treated mesoporous silica nanoparticles/carboxymethyl chitosan composite hydrogels (CHG60 and CHG120) were developed for the prevention of medication-related osteonecrosis of the jaw associated with bisphosphonates (MRONJ-B). The pore structure and performances of CHGs, e.g., drug release profiles and kinetics, antibacterial activity, zoledronic acid (ZA)-induced cytotoxicity reversal activity, and acute cytotoxicity, were evaluated. The bioinspired platform mimicking in vivo fibrin matrices was also proposed for the in vitro/in vivo correlation. CHG120 was further encapsulated in the human-derived fibrin, generating FCHG120. The SEM and μCT images revealed the interconnected porous structures of CHG120 in both pure and fibrin-surrounding hydrogels with %porosity of 75 and 36%, respectively, indicating the presence of fibrin inside the hydrogel pores, besides its peripheral region, which was evidenced by confocal microscopy. The co-presence of GGOH moderately decelerated the overall releases of CDM from CHGs in the studied releasing fluids, i.e., phosphate buffer saline-based fluid (PBB) and simulated interstitial fluid (SIF). The whole-lifetime release patterns of CDM, fitted by the Ritger-Peppas equation, appeared nondifferentiable, divided into two releasing stages, i.e., rapid and steady releasing stages, whereas the biphasic drug release patterns of GGOH were observed with Phase I and II releases fitted by the Higuchi and Ritger-Peppas equations, respectively. Notably, the burst releases of both drugs were subsided with lengthier durations (up to 10-12 days) in SIF, compared with those in PBB, enabling CHGs to elicit satisfactory antibacterial and ZA cytotoxicity reversal activities for MRONJ-B prevention. The fibrin network in FCHG120 further reduced and sustained the drug releases for at least 14 days, lengthening bactericidal and ZA cytotoxicity reversal activities of FCHG and decreasing in vitro and in ovo acute drug toxicity. This highlighted the significance of fibrin matrices as appropriate in vivo-like platforms to evaluate the performance of an implant.

Highly Porous Gas-Blown Hydrogels for Direct Cell Encapsulation with High Cell Viability

Cell transplant therapies show potential as treatments for a large number of diseases. The encapsulation of cells within hydrogels is often used to mimic the extracellular matrix and protect cells from the body's immune response. However, cell encapsulation can be limited in terms of both scaffold size and cell viability due to poor nutrient and waste transport throughout the bulk of larger volume hydrogels. Strategies to address this issue include creating prevascularized or porous structured materials. For example, cell-laden hydrogels can be formed by porogen leaching or three-dimensional printing, but these techniques involve the use of multiple materials, long preparation times, and/or specialized equipment. Postfabrication cell seeding in porous scaffolds can result in inconsistent cell density throughout scaffold volumes and typically requires a bioreactor to ensure even cell distribution. In this study, we developed a highly cytocompatible direct cell encapsulation method during the rapid fabrication of porous hydrogels. Using sodium bicarbonate and citric acid as blowing agents, we employed photocurable polymers to produce highly porous materials within a matter of minutes. Cells were directly encapsulated within methacrylated poly(vinyl alcohol), poly(ethylene glycol), and gelatin hydrogels at viabilities as high as 93% by controlling solution variables, such as citric acid content, viscosity, pH, and curing time. Cell viability within the resulting porous constructs was high (>80%) over 14 days of analysis with multiple cell types. This work provides a simple, versatile, and tunable method for cell encapsulation within highly porous constructs that can be built upon in future work for the delivery of cell-based therapies. Impact Statement This simple method to obtain cell-laden hydrogel foams allows direct cell encapsulation within biomaterials without the need for porogens or microcarriers, while maintaining high cell viability. The successful encapsulation of multiple cell types into gas-blown hydrogels with varied chemistries shows the versatility of this method. While this work focuses on photocrosslinkable polymers, any quick gelling material could be used for foam fabrication in expansion of this work. The potential future impact of this work on the treatment of diseases and injuries that utilize cell therapies is wide-ranging.

Enzymatically Crosslinked Collagen as a Versatile Matrix for In Vitro and In Vivo Co-Engineering of Blood and Lymphatic Vasculature

Adequate vascularization is required for the successful translation of many in vitro engineered tissues. This study presents a novel collagen derivative that harbors multiple recognition peptides for orthogonal enzymatic crosslinking based on sortase A (SrtA) and Factor XIII (FXIII). SrtA-mediated crosslinking enables the rapid co-engineering of human blood and lymphatic microcapillaries and mesoscale capillaries in bulk hydrogels. Whereas tuning of gel stiffness determines the extent of neovascularization, the relative number of blood and lymphatic capillaries recapitulates the ratio of blood and lymphatic endothelial cells originally seeded into the hydrogel. Bioengineered capillaries readily form luminal structures and exhibit typical maturation markers both in vitro and in vivo. The secondary crosslinking enzyme Factor XIII is used for in situ tethering of the VEGF mimetic QK peptide to collagen. This approach supports the formation of blood and lymphatic capillaries in the absence of exogenous VEGF. Orthogonal enzymatic crosslinking is further used to bioengineer hydrogels with spatially defined polymer compositions with pro- and anti-angiogenic properties. Finally, macroporous scaffolds based on secondary crosslinking of microgels enable vascularization independent from supporting fibroblasts. Overall, this work demonstrates for the first time the co-engineering of mature micro- and meso-sized blood and lymphatic capillaries using a highly versatile collagen derivative.

Rapid fabrication and screening of tailored functional 3D biomaterials: Validation in bone tissue repair - Part II

Regenerative medicine strategies place increasingly sophisticated demands on 3D biomaterials to promote tissue formation at sites where tissue would otherwise not form. Ideally, the discovery/fabrication of the 3D scaffolds needs to be high-throughput and uniform to ensure quick and in-depth analysis in order to pinpoint appropriate chemical and mechanical properties of a biomaterial. Herein we present a versatile technique to screen new potential biocompatible acrylate-based 3D scaffolds with the ultimate aim of application in tissue repair. As part of this process, we identified an acrylate-based 3D porous scaffold that promoted cell proliferation followed by accelerated tissue formation, pre-requisites for tissue repair. Scaffolds were fabricated by a facile freeze-casting and an in-situ photo-polymerization route, embracing a high-throughput synthesis, screening and characterization protocol. The current studies demonstrate the dependence of cellular growth and vascularization on the porosity and intrinsic chemical nature of the scaffolds, with tuneable 3D scaffolds generated with large, interconnected pores suitable for cellular growth applied to skeletal reparation. Our studies showed increased cell proliferation, collagen and ALP expression, while chorioallantoic membrane assays indicated biocompatibility and demonstrated the angiogenic nature of the scaffolds. VEGRF2 expression in vivo observed throughout the 3D scaffolds in the absence of growth factor supplementation demonstrates a potential for angiogenesis. This novel platform provides an innovative approach to 3D scanning of synthetic biomaterials for tissue regeneration.

Tailored Biocompatible Polyurethane-Poly(ethylene glycol) Hydrogels as a Versatile Nonfouling Biomaterial

Polyurethane-based hydrogels are relatively inexpensive and mechanically robust biomaterials with ideal properties for various applications, including drug delivery, prosthetics, implant coatings, soft robotics, and tissue engineering. In this report, a simple method is presented for synthesizing and casting biocompatible polyurethane-poly(ethylene glycol) (PU-PEG) hydrogels with tunable mechanical properties, nonfouling characteristics, and sustained tolerability as an implantable material or coating. The hydrogels are synthesized via a simple one-pot method using commercially available precursors and low toxicity solvents and reagents, yielding a consistent and biocompatible gel platform primed for long-term biomaterial applications. The mechanical and physical properties of the gels are easily controlled by varying the curing concentration, producing networks with complex shear moduli of 0.82-190 kPa, similar to a range of human soft tissues. When evaluated against a mechanically matched poly(dimethylsiloxane) (PDMS) formulation, the PU-PEG hydrogels demonstrated favorable nonfouling characteristics, including comparable adsorption of plasma proteins (albumin and fibrinogen) and significantly reduced cellular adhesion. Moreover, preliminary murine implant studies reveal a mild foreign body response after 41 days. Due to the tunable mechanical properties, excellent biocompatibility, and sustained in vivo tolerability of these hydrogels, it is proposed that this method offers a simplified platform for fabricating soft PU-based biomaterials for a variety of applications.

Scalable macroporous hydrogels enhance stem cell treatment of volumetric muscle loss

Volumetric muscle loss (VML), characterized by an irreversible loss of skeletal muscle due to trauma or surgery, is accompanied by severe functional impairment and long-term disability. Tissue engineering strategies combining stem cells and biomaterials hold great promise for skeletal muscle regeneration. However, scaffolds, including decellularized extracellular matrix (dECM), hydrogels, and electrospun fibers, used for VML applications generally lack macroporosity. As a result, the scaffolds used typically delay host cell infiltration, transplanted cell proliferation, and new tissue formation. To overcome these limitations, we engineered a macroporous dECM-methacrylate (dECM-MA) hydrogel, which we will refer to as a dECM-MA sponge, and investigated its therapeutic potential in vivo. Our results demonstrate that dECM-MA sponges promoted early cellularization, endothelialization, and establishment of a pro-regenerative immune microenvironment in a mouse VML model. In addition, dECM-MA sponges enhanced the proliferation of transplanted primary muscle stem cells, muscle tissue regeneration, and functional recovery four weeks after implantation. Finally, we investigated the scale-up potential of our scaffolds using a rat VML model and found that dECM-MA sponges significantly improved transplanted cell proliferation and muscle regeneration compared to conventional dECM scaffolds. Together, these results validate macroporous hydrogels as novel scaffolds for VML treatment and skeletal muscle regeneration.