3D-printed microgels supplemented with dentin matrix molecules as a novel biomaterial for direct pulp capping.

OBJECTIVES: To develop a 3D-printed, microparticulate hydrogel supplemented with dentin matrix molecules (DMM) as a novel regenerative strategy for dental pulp capping. MATERIALS AND METHODS: Gelatin methacryloyl microgels (7% w/v) mixed with varying concentrations of DMM were printed using a digital light projection 3D printer and lyophilized for 2 days. The release profile of the DMM-loaded microgels was measured using a bicinchoninic acid assay. Next, dental pulp exposure defects were created in maxillary first molars of Wistar rats. The exposures were randomly capped with (1) inert material - negative control, (2) microgels, (3) microgels + DMM 500 µg/ml, (4) microgels + DMM 1000 µg/ml, (5) microgels + platelet-derived growth factor (PDGF 10 ng/ml), or (6) MTA (n = 15/group). After 4 weeks, animals were euthanized, and treated molars were harvested and then processed to evaluate hard tissue deposition, pulp tissue organization, and blood vessel density. RESULTS: All the specimens from groups treated with microgel + 500 µg/ml, microgel + 1000 µg/ml, microgel + PDGF, and MTA showed the formation of organized pulp tissue, tertiary dentin, newly formed tubular and atubular dentin, and new blood vessel formation. Dentin bridge formation was greater and pulp necrosis was less in the microgel + DMM groups compared to MTA. CONCLUSIONS: The 3D-printed photocurable microgels doped with DMM exhibited favorable cellular and inflammatory pulp responses, and significantly more tertiary dentin deposition. CLINICAL RELEVANCE: 3D-printed microgel with DMM is a promising biomaterial for dentin and dental pulp regeneration in pulp capping procedures.

Embedding cells within nanoscale, rapidly mineralizing hydrogels: A new paradigm to engineer cell-laden bone-like tissue.

Bone mineralization is a highly specific and dynamic nanoscale process that has been studied extensively from a structural, chemical, and biological standpoint. Bone tissue, therefore, may be defined by the interplay of its intricately mineralized matrix and the cells that regulate its biological function. However, the far majority of engineered bone model systems and bone replacement materials have been unable to replicate this key characteristic of bone tissue; that is, the ability of cells to be gradually and rapidly embedded in a three-dimensional (3D) heavily calcified matrix material. Here we review the characteristics that define the bone matrix from a nanostructural perspective. We then revisit the benefits and challenges of existing model systems and engineered bone replacement materials, and discuss recent efforts to replicate the biological, cellular, mechanical, and materials characteristics of bone tissue on the nano- to microscale. We pay particular attention to a recently proposed method developed by our group, which seeks to replicate key aspects of the entrapment of bone cells within a mineralized matrix with precisions down to the level of individual nano-crystallites, inclusive of the bone vasculature, and osteogenic differentiation process. In summary, this paper discusses existing and emerging evidence pointing towards future developments bridging the gap between the fields of biomineralization, structural biology, stem cells, and tissue engineering, which we believe will hold the key to engineer truly functional bone-like tissue in the laboratory.

Surface functionalized magnetic nanoparticles shift cell behavior with on/off magnetic fields.

Magnetic nanoparticles (MNPs) are used as contrast agents and targeted drug delivery systems (TDDS) due to their favorable size, surface charge, and magnetic properties. Unfortunately, the toxicity associated with MNPs limits their biological applications. Surface functionalization of MNPs with selective polymers alters the surface chemistry to impart better biocompatibility. We report the preparation of surface functionalized MNPs using iron oxide NPs (MNPs), poly (lactic-co-glycolic acid) (PLGA), and sodium alginate via co-precipitation, emulsification, and electro-spraying, respectively. The NPs are in the nanosize range and negatively charged. Morphological and structural analyses affirm the surface functionalized nanostructure of the NPs. The surface functionalized MNPs are biocompatible, and demonstrate enhanced intracellular delivery under an applied magnetic field (H), which evinces the targeting ability of MNPs. After NP treatment, the physico-mechanical properties of fibroblasts are decided by the selective MNP uptake under "on" or "off" magnetic field conditions. We envision potential use of biocompatible surface functionalized MNP for intracellular-, targeted-DDS, imaging, and for investigating cellular mechanics.

In vitro development and optimization of cell-laden injectable bioprinted gelatin methacryloyl (GelMA) microgels mineralized on the nanoscale.

Bone defects may occur in different sizes and shapes due to trauma, infections, and cancer resection. Autografts are still considered the primary treatment choice for bone regeneration. However, they are hard to source and often create donor-site morbidity. Injectable microgels have attracted much attention in tissue engineering and regenerative medicine due to their ability to replace inert implants with a minimally invasive delivery. Here, we developed novel cell-laden bioprinted gelatin methacrylate (GelMA) injectable microgels, with controllable shapes and sizes that can be controllably mineralized on the nanoscale, while stimulating the response of cells embedded within the matrix. The injectable microgels were mineralized using a calcium and phosphate-rich medium that resulted in nanoscale crystalline hydroxyapatite deposition and increased stiffness within the crosslinked matrix of bioprinted GelMA microparticles. Next, we studied the effect of mineralization in osteocytes, a key bone homeostasis regulator. Viability stains showed that osteocytes were maintained at 98 % viability after mineralization with elevated expression of sclerostin in mineralized compared to non-mineralized microgels, showing that mineralization can effectively enhances osteocyte maturation. Based on our findings, bioprinted mineralized GelMA microgels appear to be an efficient material to approximate the bone microarchitecture and composition with desirable control of sample injectability and polymerization. These bone-like bioprinted mineralized biomaterials are exciting platforms for potential minimally invasive translational methods in bone regenerative therapies.

Dual growth factor delivery using biocompatible core-shell microcapsules for angiogenesis.

An optimized electrodropping system produces homogeneous core-shell microcapsules (C-S MCs) by using poly(L-lactic-co-glycolic acid) (PLGA) and alginate. Fluorescence imaging clearly shows the C-S domain in the MC. For release control, the use of high-molecular-weight PLGA (HMW 270 000) restrains the initial burst release of protein compared to that of low-MW PLGA (LMW 40 000). Layer-by-layer (LBL) assembly of chitosan and alginate on MCs is also useful in controlling the release profile of biomolecules. LBL (7-layer) treatment is effective in suppressing the initial burst release of protein compared to no LBL (0-layer). The difference of cumulative albumin release between HMW (7-layer LBL) and LMW (0-layer LBL) PLGA is determined to be more than 40% on day 5. When dual angiogenic growth factors (GFs), such as platelet-derived GF (PDGF) and vascular endothelial GF (VEGF), are encapsulated separately in the core and shell domains, respectively, the VEGF release rate is much greater than that of PDGF, and the difference of the cumulative release percentage between the two GFs is about 30% on day 7 with LMW core PLGA and more than 45% with HMW core PLGA. As for the angiogenic potential of MC GFs with human umbilical vein endothelial cells (HUVECs), the fluorescence signal of CD31+ suggests that the angiogenic sprout of ECs is more active in MC-mediated GF delivery than conventional GF delivery, and this difference is significant, based on the number of capillary branches in the unit area. This study demonstrates that the fabrication of biocompatible C-S MCs is possible, and that the release control of biomolecules is adjustable. Furthermore, MC-mediated GFs remain in an active form and can upregulate the angiogenic activity of ECs.

Engineering of an Osteoinductive and Growth Factor-Free Injectable Bone-Like Microgel for Bone Regeneration.

Bone autografts remain the gold standard for bone grafting surgeries despite having increased donor site morbidity and limited availability. Bone morphogenetic protein-loaded grafts represent another successful commercial alternative. However, the therapeutic use of recombinant growth factors has been associated with significant adverse clinical outcomes. This highlights the need to develop biomaterials that closely approximate the structure and composition of bone autografts, which are inherently osteoinductive and biologically active with embedded living cells, without the need for added supplements. Here, injectable growth factor-free bone-like tissue constructs are developed, that closely approximate the cellular, structural, and chemical composition of bone autografts. It is demonstrated that these micro-constructs are inherently osteogenic, and demonstrate the ability to stimulate mineralized tissue formation and regenerate bone in critical-sized defects in-vivo. Furthermore, the mechanisms that allow human mesenchymal stem cells (hMSCs) to be highly osteogenic in these constructs, despite the lack of osteoinductive supplements, are assessed, whereby Yes activated protein (YAP) nuclear localization and adenosine signaling appear to regulate osteogenic cell differentiation. The findings represent a step toward a new class of minimally invasive, injectable, and inherently osteoinductive scaffolds, which are regenerative by virtue of their ability to mimic the tissue cellular and extracellular microenvironment, thus showing promise for clinical applications in regenerative engineering.

Effect of Target Power on Microstructure, Tribological Performance and Biocompatibility of Magnetron Sputtered Amorphous Carbon Coatings.

The tribological properties and preosteoblast behavior of an RF magnetron-sputtered amorphous carbon coating on a Si (100) substrate were evaluated. The graphite target power was varied from 200 to 500 W to obtain various coating structures. The amorphous nature of the coatings was confirmed via Raman analysis. The contact angle also increased from 58º to 103º, which confirmed the transformation of the a-C surface from a hydrophilic to hydrophobic nature with an increasing graphite target power. A minimum wear rate of about 4.73 × 10-8 mm3/N*mm was obtained for an a-C coating deposited at a 300 W target power. The 300 W and 400 W target power coatings possessed good tribological properties, and the 500 W coating possessed better cell viability and adhesion on the substrate. The results suggest that the microstructure, wettability, tribological behavior and biocompatibility of the a-C coating were highly dependent on the target power of the graphite. A Finite Element Analysis (FEA) showed a considerable increase in the Von Mises stress as the mesh size decreased. Considering both the cell viability and tribological properties, the 400 W target power coating was identified to have the best tribological property as well as biocompatibility.

High-Throughput Bioprinting of Geometrically-Controlled Pre-Vascularized Injectable Microgels for Accelerated Tissue Regeneration.

Successful integration of cell-laden tissue constructs with host vasculature depends on the presence of functional capillaries to provide oxygen and nutrients to the embedded cells. However, diffusion limitations of cell-laden biomaterials challenge regeneration of large tissue defects that require bulk-delivery of hydrogels and cells. Herein, a strategy to bioprint geometrically controlled, endothelial and stem-cell laden microgels in high-throughput is introduced, allowing these cells to form mature and functional pericyte-supported vascular capillaries in vitro, and then injecting these pre-vascularized constructs minimally invasively in-vivo. It is demonstrated that this approach offers both desired scalability for translational applications as well as unprecedented levels of control over multiple microgel parameters to design spatially-tailored microenvironments for better scaffold functionality and vasculature formation. As a proof-of-concept, the regenerative capacity of the bioprinted pre-vascularized microgels is compared with that of cell-laden monolithic hydrogels of the same cellular and matrix composition in hard-to-heal defects in vivo. The results demonstrate that the bioprinted microgels have faster and higher connective tissue formation, more vessels per area, and widespread presence of functional chimeric (human and murine) vascular capillaries across regenerated sites. The proposed strategy, therefore, addresses a significant issue in regenerative medicine, demonstrating a superior potential to facilitate translational regenerative efforts.

In vitro development and optimization of cell-laden injectable bioprinted gelatin methacryloyl (GelMA) microgels mineralized on the nanoscale.

Bone defects may occur in different sizes and shapes due to trauma, infections, and cancer resection. Autografts are still considered the primary treatment choice for bone regeneration. However, they are hard to source and often create donor-site morbidity. Injectable microgels have attracted much attention in tissue engineering and regenerative medicine due to their ability to replace inert implants with a minimally invasive delivery. Here, we developed novel cell-laden bioprinted gelatin methacrylate (GelMA) injectable microgels, with controllable shapes and sizes that can be controllably mineralized on the nanoscale, while stimulating the response of cells embedded within the matrix. The injectable microgels were mineralized using a calcium and phosphate-rich medium that resulted in nanoscale crystalline hydroxyapatite deposition and increased stiffness within the crosslinked matrix of bioprinted GelMA microparticles. Next, we studied the effect of mineralization in osteocytes, a key bone homeostasis regulator. Viability stains showed that osteocytes were maintained at 98% viability after mineralization with elevated expression of sclerostin in mineralized compared to non-mineralized microgels, indicating that mineralization effectively enhances osteocyte maturation. Based on our findings, bioprinted mineralized GelMA microgels appear to be an efficient material to approximate the bone microarchitecture and composition with desirable control of sample injectability and polymerization. These bone-like bioprinted mineralized biomaterials are exciting platforms for potential minimally invasive translational methods in bone regenerative therapies.

Biogenic synthesis of multidimensional gold nanoparticles assisted by Streptomyces hygroscopicus and its electrochemical and antibacterial properties.

The fabrication of reliable, green chemistry processes for nanomaterial synthesis is an important aspect of nanotechnology. The biosynthesis of single-pot room-temperature reduction of aqueous chloroaurate ions by Streptomyces hygroscopicus cells has been reported to facilitate the development of an industrially viable greener methodology for the synthesis of technologically important gold nanoparticles (AuNPs). Multidimensional AuNPs are generated via the manipulation of key growth parameters, including solution pH and reaction time. The synthesized nanostructures are characterized by UV/Vis and energy dispersive X-ray analysis studies. Particle morphology is characterized by HRTEM, FE-SEM and BioAFM. Additionally, we have demonstrated the electrochemical and antibacterial properties of AuNPs via cyclic voltammetry analysis and a minimal inhibitory concentration assay. Owing to the drawbacks of chemical synthesis, a biological synthesis method has been developed to generate biocompatible, inexpensive and eco-friendly size-controlled nanoparticles.

Vascular inflammation exposes perivascular cells to SARS-CoV-2 infection.

Pericytes stabilize blood vessels and promote vascular barrier function. However, vessels subjected to pro-inflammatory conditions have impaired barrier function, which has been suggested to potentially expose perivascular cells to SARS-CoV-2. To test this hypothesis, we engineered pericyte-supported vascular capillaries on-a-chip, and determined that the extravasation and binding of spike protein (S1) on perivascular cells of inflamed vessels to be significantly higher that in healthy controls, indicating a potential target to understand COVID-19 vascular complications.

Fibroblasts Close a Void in Free Space by a Purse-String Mechanism.

The mechanism by which stromal cells fill voids in injured tissue remains a fundamental question in regenerative medicine. While it is well-established that fibroblasts fill voids by depositing extracellular matrix (ECM) proteins as they migrate toward the wound site, little is known about their ability to adopt an epithelial-like purse-string behavior. To investigate fibroblast behavior during gap closure, we created an artificial wound with a large void space. We discovered that fibroblasts could form a free-standing bridge over deep microvoids, closing the void via purse-string contraction, a mechanism previously thought to be unique to epithelial wound closure. The findings also revealed that myosin II mediated contractility and intercellular adherent junctions were required for the closure of the fibroblast gap in our fabricated three-dimensional artificial wound. To fulfill their repair function under the specific microenvironmental conditions of wounds, fibroblasts appeared to acquire the structural features of epithelial cells, namely, contractile actin bundles that span over multiple cells along the boundary. These findings shed light on a novel mechanism by which stromal cells bridge the 3D gap during physiological processes such as morphogenesis and wound healing.

Copper-glucosamine microcubes: synthesis, characterization, and C-reactive protein detection.

Cubelike microstructures of glucosamine-functionalized copper (GlcN-CuMC's) have been fabricated by the integration of injection pump and ultrasonochemistry. Although bulk microstructures and the nanostructure of metallic copper exhibit distinct applications, the amino sugar surface-functionalized copper is almost biocompatible and exhibits advanced features such as more crystallinity, high thermal stability, and electrochemical feasibility toward biomolecule (C-reactive protein, CRP) detection. An electrochemical test of this GlcN-CuMC's was demonstrated by immobilization on a conventional gold-PCB (Au-PCB) electrode. The combination of a biointerface membrane, from glucosamine functionalization, and electroactive sites of metallic copper provides a very efficient electrochemical response against various concentration of CRP. A perfect scaling of steady-state currents with r(2) values of 0.9862 (I(pa)) and 0.9972 (I(pc)) indicate the promise of this kind of biofunctionalized microstructure electrode for many surface and interface applications.

Structural and biological evaluation of a multifunctional SWCNT-AgNPs-DNA/PVA bio-nanofilm.

A bio-nanofilm consisting of a tetrad nanomaterial (nanotubes, nanoparticles, DNA, polymer) was fabricated utilizing in situ reduction and noncovalent interactions and it displayed effective antibacterial activity and biocompatibility. This bio-nanofilm was composed of homogenous silver nanoparticles (AgNPs) coated on single-walled carbon nanotubes (SWCNTs), which were later hybridized with DNA and stabilized in poly(vinyl alcohol) (PVA) in the presence of a surfactant with the aid of ultrasonication. Electron microscopy and bio-AFM (atomic force microscopy) images were used to assess the morphology of the nanocomposite (NC) structure. Functionalization and fabrication were examined using FT-Raman spectroscopy by analyzing the functional changes in the bio-nanofilm before and after fabrication. UV-visible spectroscopy and X-ray powder diffraction (XRD) confirmed that AgNPs were present in the final NC on the basis of its surface plasmon resonance (370 nm) and crystal planes. Thermal gravimetric analysis was used to measure the percentage weight loss of SWCNT (17.5%) and final SWCNT-AgNPs-DNA/PVA (47.7%). The antimicrobial efficiency of the bio-nanofilm was evaluated against major pathogenic organisms. Bactericidal ratios, zone of inhibition, and minimum inhibitory concentration were examined against gram positive and gram negative bacteria. A preliminary cytotoxicity analysis was conducted using A549 lung cancer cells and IMR-90 fibroblast cells. Confocal laser microscopy, bio-AFM, and field emission scanning electron microscopy (FE-SEM) images demonstrated that the NCs were successfully taken up by the cells. These combined results indicate that this bio-nanofilm was biocompatible and displayed antimicrobial activity. Thus, this novel bio-nanofilm holds great promise for use as a multifunctional tool in burn therapy, tissue engineering, and other biomedical applications.

Prevascularized hydrogels with mature vascular networks promote the regeneration of critical-size calvarial bone defects in vivo.

Adequate vascularization of scaffolds is a prerequisite for successful repair and regeneration of lost and damaged tissues. It has been suggested that the maturity of engineered vascular capillaries, which is largely determined by the presence of functional perivascular mural cells (or pericytes), plays a vital role in maintaining vessel integrity during tissue repair and regeneration. Here, we investigated the role of pericyte-supported-engineered capillaries in regenerating bone in a critical-size rat calvarial defect model. Prior to implantation, human umbilical vein endothelial cells and human bone marrow stromal cells (hBMSCs) were cocultured in a collagen hydrogel to induce endothelial cell morphogenesis into microcapillaries and hBMSC differentiation into pericytes. Upon implantation into the calvarial bone defects (8 mm), the prevascularized hydrogels showed better bone formation than either untreated controls or defects treated with autologous bone grafts (positive control). Bone formation parameters such as bone volume, coverage area, and vascularity were significantly better in the prevascularized hydrogel group than in the autologous bone group. Our results demonstrate that tissue constructs engineered with pericyte-supported vascular capillaries may approximate the regenerative capacity of autologous bone, despite the absence of osteoinductive or vasculogenic growth factors.

Nanoscale mineralization of cell-laden methacrylated gelatin hydrogels using calcium carbonate-calcium citrate core-shell microparticles.

Conventional biomaterials developed for bone regeneration fail to fully recapitulate the nanoscale structural organization and complex composition of the native bone microenvironment. Therefore, despite promoting osteogenic differentiation of stem cells, they fall short of providing the structural, biochemical, and mechanical stimuli necessary to drive osteogenesis for bone regeneration and function. To address this, we have recently developed a novel strategy to engineer bone-like tissue using a biomimetic approach to achieve rapid and controlled nanoscale mineralization of a cell-laden matrix in the presence of osteopontin, a non-collagenous protein, and a supersaturated solution of calcium and phosphate medium. Here, we build on this approach to engineer bone regeneration scaffolds comprising methacrylated gelatin (GelMA) hydrogels incorporated with calcium citrate core-shell microparticles as a sustained and reliable source of calcium ions for in situ mineralization. We demonstrate successful biomineralization of GelMA hydrogels by embedded calcium carbonate-calcium citrate core-shell microparticles with the resultant mineral chemistry, structure, and organization reminiscent of that of native bone. The biomimetic mineralization was further shown to promote osteogenic differentiation of encapsulated human mesenchymal stem cells even in the absence of other exogenous osteogenic induction factors. Ultimately, by combining the superior biological response engendered by biomimetic mineralization with the intrinsic tissue engineering advantages offered by GelMA, such as biocompatibility, biodegradability, and printability, we envision that our system offers great potential for bone regeneration efforts.

Triple growth factor delivery promotes functional bone regeneration following composite musculoskeletal trauma.

Successful bone healing in severe trauma depends on early revascularization to restore oxygen, nutrient, growth factor, and progenitor cell supply to the injury. Therapeutic angiogenesis strategies have therefore been investigated to promote revascularization following severe bone injuries; however, results have been inconsistent. This is the first study investigating the effects of dual angiogenic growth factors (VEGF and PDGF) with low-dose bone morphogenetic protein-2 (BMP-2; 2.5 µg) on bone healing in a clinically challenging composite bone-muscle injury model. Our hydrogel-based delivery systems demonstrated a more than 90% protein entrapment efficiency and a controlled simultaneous release of three growth factors over 28 days. Co-stimulation of microvascular fragment constructs with VEGF and PDGF promoted vascular network formation in vitro compared to VEGF or PDGF alone. In an in vivo model of segmental bone and volumetric muscle loss injury, combined VEGF (5 µg) and PDGF (7.5 µg or 15 µg) delivery with a low dose of BMP-2 significantly enhanced regeneration of vascularized bone compared to BMP-2 treatment alone. Notably, the regenerated bone mechanics reached ~60% of intact bone, a value that was previously only achieved by delivery of high-dose BMP-2 (10 µg) in this injury model. Overall, sustained delivery of VEGF, PDFG, and BMP-2 is a promising strategy to promote functional vascularized bone tissue regeneration following severe composite musculoskeletal injury. Although this study is conducted in a clinically relevant composite injury model in rats using a simultaneous release strategy, future studies are necessary to test the regenerative potential of spatiotemporally controlled delivery of triple growth factors on bone healing using large animal models. STATEMENT OF SIGNIFICANCE: Volumetric muscle loss combined with delayed union or non-union bone defect causes deleterious effects on bone regeneration even with the supplementation of bone morphogenetic protein-2 (BMP-2). In this study, the controlled delivery of dual angiogenic growth factors (vascular endothelial growth factor [VEGF] + Platelet-derived growth factor [PDGF]) increases vascular growth in vitro. Co-delivering VEGF+PDGF significantly increase the bone formation efficacy of low-dose BMP-2 and improves the mechanics of regenerated bone in a challenging composite bone-muscle injury model.

Effects of controlled dual growth factor delivery on bone regeneration following composite bone-muscle injury.

The objective of this study was to investigate the controlled release of two growth factors (BMP-2 and VEGF) as a treatment strategy for bone healing in clinically challenging composite injuries, consisting of a femoral segmental bone defect and volumetric muscle loss. This is the first investigation of dual growth factor delivery in a composite injury model using an injectable delivery system consisting of heparin microparticles and alginate gel. The loading efficiency of growth factors into these biomaterials was found to be >90%, revealing a strong affinity of VEGF and BMP-2 to heparin and alginate. The system could achieve simultaneous or tunable release of VEGF and BMP-2 by varying the loading strategy. Single growth factor delivery (VEGF or BMP-2 alone) significantly enhanced vascular growth in vitro. However, no synergistic effect was observed for dual growth factor (BMP-2 + VEGF) delivery in vitro. Effective bone healing was achieved in all treatment groups (BMP-2, simultaneous or tunable delivery of BMP-2 and VEGF) in the composite injury model. The mechanics of the regenerated bone reached a maximum strength of ~52% of intact bone with tunable delivery of VEGF and BMP-2. Overall, simultaneous or tunable co-delivery of low-dose BMP-2 and VEGF failed to fully restore the mechanics of bone in this injury model. Given the severity of the composite injury, VEGF alone may not be sufficient to establish mature and stable blood vessels when compared with previous studies co-delivering BMP-2+VEGF enhanced bone tissue regeneration. Hence, future studies are warranted to develop an alternative treatment strategy focusing on better control over growth factor dose, spatiotemporal delivery, and additional growth factors to regenerate fully functional bone tissue. STATEMENT OF SIGNIFICANCE: We have developed an injectable delivery system consisting of heparin microparticles and an alginate hydrogel that is capable of delivering multiple growth factors in a tunable manner. We used this delivery system to deliver BMP-2 and VEGF in a rodent model of composite bone-muscle injury that mimics clinical type III open fractures. An advanced treatment strategy is necessary for these injuries in order to avoid the negative side effects of high doses of growth factors and because it has been shown that the addition of a muscle injury in this model attenuates the bone regenerative effect of BMP-2. This is the first study to test the effects of dual growth factor delivery (BMP-2/VEGF) on bone healing in a composite bone-muscle injury model and is expected to open up new directions in protein delivery for regenerative medicine.

3D Printing of Microgel-Loaded Modular Microcages as Instructive Scaffolds for Tissue Engineering.

Biomaterial scaffolds have served as the foundation of tissue engineering and regenerative medicine. However, scaffold systems are often difficult to scale in size or shape in order to fit defect-specific dimensions, and thus provide only limited spatiotemporal control of therapeutic delivery and host tissue responses. Here, a lithography-based 3D printing strategy is used to fabricate a novel miniaturized modular microcage scaffold system, which can be assembled and scaled manually with ease. Scalability is based on an intuitive concept of stacking modules, like conventional toy interlocking plastic blocks, allowing for literally thousands of potential geometric configurations, and without the need for specialized equipment. Moreover, the modular hollow-microcage design allows each unit to be loaded with biologic cargo of different compositions, thus enabling controllable and easy patterning of therapeutics within the material in 3D. In summary, the concept of miniaturized microcage designs with such straight-forward assembly and scalability, as well as controllable loading properties, is a flexible platform that can be extended to a wide range of materials for improved biological performance.