Integration Of Scaffolds Research Articles

In vivo response to decellularized mesothelium scaffolds.

Biological surgical scaffolds are used in plastic and reconstructive surgery to support structural reinforcement and regeneration of soft tissue defects. Macrophage and fibroblast cell populations heavily regulate scaffold integration into host tissue following implantation. In the present study, the biological host response to a commercially available surgical scaffold (Meso BioMatrix Surgical Mesh (MBM)) was investigated for up to 9 weeks after subcutaneous implantation; this scaffold promoted superior cell migration and infiltration previously in in vitro studies relative to other commercially available scaffolds. Infiltrating macrophages and fibroblasts phenotypes were assessed for evidence of inflammation and remodeling. At week 1, macrophages were the dominant cell population, but fibroblasts were most abundant at subsequent time points. At week 4, the scaffold supported inflammation modulation as indicated by M1 to M2 macrophage polarization; the foreign body giant cell response resolved by week 9. Unexpectedly, a fibroblast subpopulation expressed macrophage phenotypic markers, following a similar trend in transitioning from a proinflammatory to anti-inflammatory phenotype. Also, α-smooth muscle actin-expressing myofibroblasts were abundant at weeks 4 and 9, mirroring collagen expression and remodeling activity. MBM supported physiologic responses observed during normal wound healing, including cellular infiltration, host tissue ingrowth, remodeling of matrix proteins, and immune modulation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 716-725, 2018.

Our panel of experts highlight the most important research articles across the spectrum of topics relevant to the field of regenerative medicine.

Enzymatically crosslinked microporous hydrogel scaffolds that form in situ promote dermal healing Evaluation of: Griffin DR, Weaver WM, Scumpia PO, DiCarlo D, Segura T. Accelerated wound healing by injectable microporous gel scaffolds assembled from annealed building blocks. Nat. Mater. 14, 737–744 (2015). Tunable scaffolds that respond to environmental factors could enable enhanced tissue integration and wound healing. To achieve this goal, scaffold designs have incorporated biomimetic functionality, including thrombin-activated factor XIII (FXIIIa) crosslinking [1], matrix metalloproteinase responsiveness [2] and mechanical matching [3]. Scaffolds that can alter their properties in situ in response to environmental stimuli are desired to achieve changes in stiffness, shape, release and degradation that can lead to improved tissue regeneration. In this study, Griffin et al. describe a bottom-up strategy to fabricating scaffolds that accelerate wound healing [4]. They use a microfluidic approach to form hydrogel microparticle (microgel) building blocks that can establish interconnected network structures upon FXIIIa-mediated crosslinking. These microporous annealed particles (MAPs) incorporate reactive multiarmed poly(ethylene)glycol-vinyl sulfone, the commonly used RGD cell adhesion peptide and the K and Q noncanonical transglutaminase peptide substrates with cysteine-terminated matrix metalloproteinase-sensitive peptides that allow for cell-controlled material degradation. Scaffolds are annealed by FXIIIa addition and can be injected into wound sites for in situ solidification and shape-conformation. These MAPs are mechanically robust and can be tuned to achieve storage moduli from 10 to 1000 Pa, which fall within the stiffness range of soft tissues. In vitro studies demonstrate that MAP scaffolds enable 3D cellular network formation and cell proliferation and survival after 6 days. In vivo studies in SKH1-HR and Balb/c epidermal wound healing models demonstrate integration of MAP scaffolds after 24 h, significant wound closure as compared with nonporous chemically matched controls after 5 days or physically matched control scaffolds up to 7 days. 5 days following injection of MAP scaffolds, keratin-5, keratin-14 and CD49f staining revealed re-epithelialization, and PECAM-1, NG2 and PDGFR-β staining indicated that the scaffolds promoted complex vascular development. MAP scaffolds were also able to sustain normal hair follicle formation when compared with normal tissue. The scaffolds promoted less CD11b cell infiltration as compared with nonporous controls after 5 days, which suggests that MAP scaffolds cause a lower immune response. Taken together, MAP scaffolds promote accelerated wound healing by utilizing natural enzymatic mechanisms and mimicking favorable mechanical and degradation properties to facilitate cell infiltration and proliferation. The study may have benefited from evaluating wound closure, dermal regeneration and Our panel of experts highlight the most important research articles across the spectrum of topics relevant to the field of regenerative medicine

Phosphonate-chitosan functionalization of a multi-channel hydroxyapatite scaffold for interfacial implant-bone tissue integration.

Nonunion associated with long bone defects continues to be highly researched both experimentally and clinically. A porous hydroxyapatite (HAp) scaffold has been recognized as a bone repair and substitute material clinically, but its use in segmental bone defects has been limited by poor integration and stability, as a consequence of scaffold strength unmatched with the native bone. Herein, we designed a multi-channel HAp-based scaffold for application in segmental bone defects, with a specific geometry and design. It possesses the required porosity for bone tissue regeneration with sufficient mechanical properties. We also developed a surface functionalization/modification method with the goal of early scaffold integration and stability. Initial functionalization with poly(vinyl phosphonic acid), PVPA, allowed simple attachment of a chitosan polymeric layer. The modification improved the biocompatibility of the scaffold and attachment of rat bone marrow-derived mesenchymal stem cells (rBMSC) in vitro. The modification also served as a buffer between the implant scaffold and bone tissue. Significant improvement in the integration behavior with better interlocking of the scaffold to bone tissue was observed for the modified scaffolds implanted in rabbit tibiae. The modified HAp scaffolds exhibited early interfacial implant-bone tissue integration with enhanced new bone formation and high potential for use in segmental bone defects.

A refined Panax ginseng karyotype based on an ultra-high copy 167-bp tandem repeat and ribosomal DNAs

BackgroundPanax ginseng Meyer (Asian ginseng) has a large nuclear genome size of > 3.5 Gbp in haploid genome equivalent of 24 chromosomes. Tandem repeats (TRs) occupy significant portions of the genome in many plants and are often found in specific genomic loci, making them a valuable molecular cytogenetic tool in discriminating chromosomes. In an effort to understand the P. ginseng genome structure, we characterized an ultrahigh copy 167-bp TR (Pg167TR) and explored its chromosomal distribution as well as its utility for chromosome identification. MethodsPolymerase chain reaction amplicons of Pg167TR were labeled, along with 5S and 45S rDNA amplicons, using a direct nick-translation method. Direct fluorescence in situ hybridization (FISH) was used to analyze the chromosomal distribution of Pg167TR. ResultsRecently, we reported a method of karyotyping the 24 chromosome pairs of P. ginseng using rDNA and DAPI (4′,6-diamidino-2-phenylindole) bands. Here, a unique distribution of Pg167TR in all 24 P. ginseng chromosomes was observed, allowing easy identification of individual homologous chromosomes. Additionally, direct labeling of 5S and 45S rDNA probes allowed the identification of two additional 5S rDNA loci not previously reported, enabling the refinement of the P. ginseng karyotype. ConclusionIdentification of individual P. ginseng chromosomes was achieved using Pg167TR-FISH. Chromosome identification is important in understanding the P. ginseng genome structure, and our method will be useful for future integration of genetic linkage maps and genome scaffold anchoring. Additionally, it is a good tool for comparative studies with related species in efforts to understand the evolution of P. ginseng.

Local biological effects of adipose stromal vascular fraction delivery systems after subcutaneous implantation in a murine model

The aim of this study was to test alginate beads and silk fibroin non-woven mats as stromal vascular fraction delivery systems to support cell implantation for tissue repair and regeneration, through trophic and immunomodulant paracrine signaling. Furthermore, in vivo scaffold biocompatibility was histologically analyzed in a murine model at different time endpoints, with particular focus on construct-induced vascularization and neoangiogenesis. The fibroin mat induced a typical foreign body reaction, recruiting macrophages and giant cells and concurrently promoted neovascularization of the implanted construct. Conversely, alginate beads triggered a more circumscribed, chronic inflammatory reaction, which decreased over time. The combined in vivo implantation of alginate beads and fibroin mat with stromal vascular fraction promoted vascularization and integration of scaffolds into the surrounding subcutaneous environment. The new blood vessel ingrowth should, hopefully, support engineered cell viability and functionality, as well as the transport of soluble bioactive molecules. Due to their neovascularization properties, stromal vascular fraction administration, using alginate or fibroin scaffolds, is a new, promising, cost-effective tissue engineering approach.

Expandable Scaffold Improves Integration of Tissue-Engineered Cartilage: An In Vivo Study in a Rabbit Model.

One of the major limitations of tissue-engineered cartilage is poor integration of chondrocytes and scaffold structures with recipient tissue. To overcome this limitation, an expandable scaffold with a honeycomb-like structure has been developed using microfluidic technology. In this study, we evaluated the performance of this expandable gelatin scaffold seeded with rabbit chondrocytes in vivo. The chondrocyte/scaffold constructs were implanted into regions of surgically introduced cylindrical osteochondral defects in rabbit femoral condyles. At 2, 4, and 6 months postsurgery, the implanted constructs were evaluated by gross and histological examinations. As expected, the osteochondral defects, which were untreated or transplanted with blank scaffolds, showed no signs of repair, whereas the defects transplanted with chondrocyte/scaffold constructs showed significant cartilage regeneration. Furthermore, the expandable scaffolds seeded with chondrocytes had more regenerated cartilage tissue and better integration with the recipient tissue than autologous chondrocyte implantation. Biomechanical tests revealed that the chondrocyte/scaffold group had the highest compressive strength among all groups at all three time points and endured a similar compressive force to normal cartilage after 6 months of implantation. Histological examinations revealed that the chondrocytes were distributed uniformly within the scaffolds, maintained a normal phenotype, and secreted functional components of the extracellular matrix. Histomorphometric assessment showed a remarkable total interface of up to 87% integration of the expandable scaffolds with the host tissue at 6 months postoperation. In conclusion, the expandable scaffolds improved chondrocyte/scaffold construct integration with the host tissue and were beneficial for cartilage repair.

3D printed PEGDA microstructures for gelatin scaffold integration and neuron differentiation

Three dimensional (3D) printing techniques can be used for scaffold fabrication but the most of them are limited by resolution and material choice. To bypass these limitations, we developed an approach by combining conventional 3D printing and freeze-drying techniques to produce lattice-type backbone and embedding microporous structures. Polyethylene glycol diacrylate (PEGDA), a biocompatible and photosensitive pre-polymer, was chosen for 3D printing of the backbone, while gelatin was used for the formation of microporous structures. The fabricated PEGDA/gelatin scaffolds were used for culture and differentiation of neural progenitor cells (NPCs), showing infiltration of the cells and outgrowth of differentiated neurites. This strategy of combined use of 3D printing and freeze-drying techniques might be useful for scaffold fabrication in terms of easy design and easy material processing.

In vivo characterization of the integration and vascularization of a silk-derived surgical scaffold

The application of acellular matrices, biomaterials, and polymeric scaffolds in reconstructive surgery facilitates postsurgical tissue remodeling and is increasingly used clinically in order to improve tissue healing and implant coverage. This study presents an invivo investigation of the integration of the knitted, silk-derived surgical scaffold, SERI(®) with regard to angiogenesis and wound healing. SERI(®) Surgical Scaffold was implanted into a full-thickness skin defect in male C57BL/6J mice (n=45) via the dorsal skinfold chamber (DSC). Skin tissue samples were collected for histology on days 2, 5, 7, 10, 14, and 21 (n=5 per time point) post implantation. Immunohistochemistry was performed for various angiogenic and inflammatory markers, as well as collagen deposition (CD31, VEGF, CD3, CD45, Desmin, and Sirius red). Vascular corrosion casting was used to assess the neovasculature within the silk and was visualized with scanning electron microscopy. We observed both early and late stages of inflammation during the healing process characterized by the infiltration of regenerating tissue by different subsets of leukocytes. Histological analysis displayed capillary-containing granulation tissue with full scaffold integration. In addition, collagen deposition within the scaffold and full skin defect was significantly increased over time. Qualitative analysis of the regenerated vasculature through corrosion casting and scanning electron microscopy revealed a complex, angiogenic network of capillaries originating from the wound bed. Based on these findings, SERI(®) displays the potential to be a promising resorbable bioengineered material for use in reconstructive surgery.

Surface modification of a POSS-nanocomposite material to enhance cellular integration of a synthetic bioscaffold

Polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU) is a versatile nanocomposite biomaterial with growing applications as a bioscaffold for tissue engineering. Integration of synthetic implants with host tissue can be problematic but could be improved by topographical modifications. We describe optimization of POSS-PCU by dispersion of porogens (sodium bicarbonate (NaHCO3), sodium chloride (NaCl) and sucrose) onto the material surface, with the principle aim of increasing surface porosity, thus providing additional opportunities for improved cellular and vascular ingrowth. We assess the effect of the porogens on the material's mechanical strength, surface chemistry, wettability and cytocompatibilty. Surface porosity was characterized by scanning electron microscopy (SEM). There was no alteration in surface chemistry and wettability and only modest changes in mechanical properties were detected. The size of porogens correlated well with the porosity of the construct produced and larger porogens improved interconnectivity of spaces within constructs. Using primary human bronchial epithelial cells (HBECs) we demonstrate moderate in vitro cytocompatibility for all surface modifications; however, larger pores resulted in cellular aggregation. These cells were able to differentiate on POSS-PCU scaffolds. Implantation of the scaffold in vivo demonstrated that larger pore sizes favor cellular integration and vascular ingrowth. These experiments demonstrate that surface modification with large porogens can improve POSS-PCU nanocomposite scaffold integration and suggest the need to strike a balance between the non-porous surfaces required for epithelial coverage and the porous structure required for integration and vascularization of synthetic scaffolds in future construct design.

Fabrication and Characterization of Three-Dimensional Electrospun Scaffolds for Bone Tissue Engineering

There are 600,000 bone-grafting procedures performed annually as a result of significant skeletal loss and bone deficiencies. This is an increasing worldwide medical issue as the average life expectancy increases 2–3 % annually. The current standards for bone treatment are autografts and allografts; both of which have drawbacks. Therefore, there is a need for alternative bone graft substitutes such as tissue-engineered grafts. Tissue engineering has emerged as a promising option for bone treatments by using biological or synthetic scaffolds to promote tissue regeneration. The advantages of this treatment include abundant supply and customizable features. The majority of scaffold fabrication techniques used in research focuses on mimicking the porous trabecular bone structure. A major characteristic of optimal scaffold integration and viability is vascularization, which is housed within the osteon canal of the cortical bone. Namely, there is a lack of tissue-engineered scaffolds for bone regeneration that mimic both trabecular and cortical bone structures. In this study, we combined two previously fabricated structures, sintered electrospun sheets and individual osteon-like scaffolds, to create scaffolds that mimic dual structural organization of the native bone with cortical and trabecular regions. Scaffolds were successfully mineralized in 10× simulated body fluid (SBF) up to 48 h with enhanced mineral distribution throughout the scaffolds. Mineralization for 24 h significantly increased mechanical properties of the scaffolds. In vitro studies performed over 28 days with mouse-pre-osteoblastic cells, MC3T3-E1s, proved that the mineralized scaffolds promoted cellular attachment, proliferation, and early stages of osteoblastic differentiation in comparison to the non-mineralized scaffolds. The implications of this study lead to the advancement of tissue-engineered mineralized trabecular and cortical bone scaffolds. The use of tissue-engineered scaffolds to harness a patients' own bone regenerative properties following traumatic bone loss has emerged as an alternative to current bone-grafting procedures. In this manuscript, the development and characterization process of a synthetic scaffold which mimics both the porous trabecular bone structure and dense cortical bone structure is discussed. Qualitative analysis confirmed the biomimetic porous structure necessary for nutrient transport and cellular infiltration and the cortical canal structure to house vascularization. Various mineralization techniques were investigated to determine the optimal mechanical properties. The scaffold also exhibited the ability to promote osteoblastic cellular attachment and proliferation. The mineral content deposited onto the scaffold led to an increase in osteoblastic behavior of the attached cells; suggesting early stages of osteogenesis. The results of this manuscript indicate the potential of utilizing a tissue-engineering scaffold as a promising treatment for bone tissue regeneration applications.

A Rodent Model to Evaluate the Tissue Response to a Biological Scaffold When Adjacent to a Synthetic Material.

The use of biologic scaffold materials adjacent to synthetic meshes is commonplace. A prevalent clinical example is two-staged breast reconstruction, where biologic scaffolds are used to provide support and coverage for the inferior aspect of the synthetic expander. However, limited data exist regarding either the kinetics of biologic scaffold integration or the host tissue response to the biologic scaffold materials used for this application or other applications in which such scaffold materials are used. The present study evaluated the temporal host response to a biological scaffold when placed adjacent to a synthetic material. Evaluation criteria included quantification of material contracture and characterization of the host cell response and tissue remodeling events. Results show a decreased thickness of the collagenous tissue layer at biologic scaffold/silicone interface compared to the abdominal wall/silicone interface during the 12-week experimental time course. All test materials were readily incorporated into surrounding host tissue.

Vascularization of Porous PolyHEMA Scaffolds

Objective The purpose of this study was to quantify the mass transport capabilities of implanted scaffolds for in vivo diagnostics, therapeutics, and cell delivery. We utilized matrix morphology to encourage long-term tissue integration. Methods: We implanted ribbon-shaped solid and porous poly-hydroxyethylmethacrylate (pHEMA) with 80 and 100µm nominal diameter interconnected pore size into rat subcutis. Distance from the nearest microvessel to any point within the polymer scaffold was histologically quantified from CD31 immunostained micrographs. Results: One week post-implantation, the microvessel diffusion distance to any point within the scaffold was 96.6±48.3μm (median±SD) for 80μm pHEMA, 123.8±51.3μm for 100μm pHEMA, and 140.1±45.8μm for solid pHEMA. One month post-implantation, the diffusion distance was 35.6±16.3μm for 80μm pHEMA, 31.3±18.5μm for 100μm pHEMA, and 131.9±57.2μm for solid pHEMA. After 1 month, the porous pHEMA scaffolds demonstrated lower median diffusion distances as compared to solid pHEMA (p<0.05). Conclusion Mass transport is key to successful tissue-engineered platforms. Robust tissue integration of porous pHEMA scaffolds, particularly at the critical implant-tissue interface, minimizes the diffusion distance from the interior of the polymer matrix to the nearest capillary. Supported in part by DARPA grants W911NF-11-1-0119 and HR0011-13-2-0003. The content of the information does not necessarily reflect the position or the policy of the Government, and no official endorsement should be inferred.

Becoming interculturally competent: Theory to practice in international education

Education abroad students are generally expected to return home with enhanced intercultural competence; however, recent research reveals that many do not fully benefit from their stay in the host environment and experience little or no gains in intercultural sensitivity. What steps can be taken to help achieve the intercultural aims of international educational experience? This article centres on an elective, credit-bearing course that was inspired by my education abroad research. Intercultural Transitions: Making Sense of International Experience has been designed to enrich and extend the intercultural learning of undergraduates with recent or current international experience. This credit-bearing course draws on multiple theories: the Intercultural Development Continuum/the Developmental Model of Intercultural Sensitivity, Kolb's experiential learning model, poststructuralist notions of identity change, transformative adult education theory, and the intergroup contact hypothesis. This article describes the course and the lessons learned from multiple offerings. Content analyses of the qualitative data (e.g., reflective essays, Forum chats, open-ended surveys, interview transcripts) generally mirrored the results of the pre- and post-administrations of the Intercultural Development Inventor (IDI), a psychometric instrument that measures intercultural competence, suggesting that this form of intervention helps propel students to higher levels of intercultural competence. The results underscore the benefits of designing a research-driven, learner-centred curriculum to enhance interaction between local and international students, and scaffold deeper intellectual consolidation and integration of intercultural learning. While developed and offered in an Asian setting, similar courses could be implemented in other settings to enhance the intercultural competence of both local and international students.

Simple surface coating of electrospun poly-L-lactic acid scaffolds to induce angiogenesis.

Tissue-engineered constructs often fail due to poor integration with the patient's tissues. Specifically, they fail to be neovascularised, leading to the death and loss of the implanted tissues. Thus, there is a need to produce angiogenic materials to improve tissue integration. We describe the development of a layer-by-layer approach to coat electrospun scaffolds to help promote angiogenesis into these biomaterials once implanted. Electrospun poly-L-lactic acid was coated comparing two different techniques - one using alternative layers of polyethyleneImine (PEI) and polyacrylic Acid (PAC) and one with alternative layers of PEI and heparin for a total of seven layers in both cases. Both scaffolds were then coated with heparin as the final layer. The scaffold coated with alternate PEI and PAC showed a clear ability to bind the most heparin. This scaffold was then studied further for its ability to bind vascular endothelial growth factor, which was confirmed using an ELISA. The scaffold coated with seven alternate layers of PEI and PAC and heparin was then implanted in a chick chorionic allantoic membrane (CAM) assay. After a period of 7 days in the CAM, the coated scaffold showed strong angiogenic activity. In contrast, the uncoated scaffolds did not promote angiogenesis. We conclude that this approach to functionalising scaffolds is effective within a clinically relevant time period (7 days in an in-vivo angiogenic model) and suggest this will be useful for improving integration of scaffolds once implanted.

Thermogelling bioadhesive scaffolds for intervertebral disk tissue engineering: Preliminary in vitro comparison of aldehyde-based versus alginate microparticle-mediated adhesion

Tissue engineering of certain load-bearing parts of the body can be dependent on scaffold adhesion or integration with the surrounding tissue to prevent dislocation. One such area is the regeneration of the intervertebral disc (IVD). In this work, poly(N-isopropylacrylamide) (PNIPAAm) was grafted with chondroitin sulfate (CS) (PNIPAAm-g-CS) and blended with aldehyde-modified CS to generate an injectable polymer that can form covalent bonds with tissue upon contact. However, the presence of the reactive aldehyde groups can compromise the viability of encapsulated cells. Thus, liposomes were encapsulated in the blend, designed to deliver the ECM derivative, gelatin, after the polymer has adhered to tissue and reached physiological temperature. This work is based on the hypothesis that the discharge of gelatin will enhance the biocompatibility of the material by covalently reacting with, or “end-capping”, the aldehyde functionalities within the gel that did not participate in bonding with tissue upon contact. As a comparison, formulations were also created without CS aldehyde and with an alternative adhesion mediator, mucoadhesive calcium alginate particles. Gels formed from blends of PNIPAAm-g-CS and CS aldehyde exhibited increased adhesive strength compared to PNIPAAm-g-CS alone (p<0.05). However, the addition of gelatin-loaded liposomes to the blend significantly decreased the adhesive strength (p<0.05). The encapsulation of alginate microparticles within PNIPAAm-g-CS gels caused the tensile strength to increase twofold over that of PNIPAAm-g-CS blends with CS aldehyde (p<0.05). Cytocompatibility studies indicate that formulations containing alginate particles exhibit reduced cytotoxicity over those containing CS aldehyde. Overall, the results indicated that the adhesives composed of alginate microparticles encapsulated in PNIPAAm-g-CS have the potential to serve as a scaffold for IVD regeneration.

Mesenchymal Stem Cells and Biomaterials Systems – Perspectives for Skeletal Muscle Tissue Repair and Regeneration

Skeletal muscle is essential in voluntary movement and other major vital functions. Muscle injuries are important in clinical practice and, despite skeletal muscle's good regenerative ability, severe tissue loss impairs complete myofibre regeneration, limiting structural and functional recovery of the affected muscle, eventually leading to the development of non-contractile fibrous scar. The intrinsic healing mechanisms rely in great extent on the residing progenitor population but significant drawbacks to their practical application in regenerative strategies boosted the search for alternative cell sources, such as extra-fetal mesenchymal stem cells (MSCs). MSCs have demonstrated to positively influence the regeneration of different disease models. When severe volumetric muscle tissue loss occurs, the body is seldom capable of replacing the lost portions with fully functional tissue. A rational strategy to aid the healing of such situations is the application of biomaterial implants that provide a structural matrix for the ingrowth of regenerating muscle fibres. Both synthetic and natural biomaterials have been hypothesized for this purpose and some have reached as far clinical cases applications. Obvious improvements are observed in most cases, but reaction to some biomaterials and functional recovery are still a challenge. The addition of MSCs to the biomaterials seems to improve the systems’ performance in the overall regenerative milieu. This strategies promote scaffold's vascularization and integration, as well as accelerated tissue ingrowth and reduces scar formation, resulting in improved recovery rates at both structural and functional levels.

Engineering Pre-vascularized Scaffolds for Bone Regeneration.

Survival of functional tissue constructs of clinically relevant size depends on the formation of an organized and uniformly distributed network of blood vessels and capillaries. The lack of such vasculature leads to spatio-temporal gradients in oxygen, nutrients and accumulation of waste products inside engineered tissue constructs resulting in negative biological events at the core of the scaffold. Unavailability of a well-defined vasculature also results in ineffective integration of scaffolds to the host vasculature upon implantation. Arguably, one of the greatest challenges in engineering clinically relevant bone substitutes, therefore, has been the development of vascularized bone scaffolds. Various approaches ranging from peptide and growth factor functionalized biomaterials to hyper-porous scaffolds have been proposed to address this problem with reasonable success. An emerging alternative to address this challenge has been the fabrication of pre-vascularized scaffolds by taking advantage of biomanufacturing techniques, such as soft- and photo-lithography or 3D bioprinting, and cell-based approaches, where functional capillaries are engineered in cell-laden scaffolds prior to implantation. These strategies seek to engineer pre-vascularized tissues in vitro, allowing for improved anastomosis with the host vasculature upon implantation, while also improving cell viability and tissue development in vitro. This book chapter provides an overview of recent methods to engineer pre-vascularized scaffolds for bone regeneration. We first review the development of functional blood capillaries in bony structures and discuss controlled delivery of growth factors, co-culture systems, and on-chip studies to engineer vascularized cell-laden biomaterials. Lastly, we review recent studies using microfabrication techniques and 3D printing to engineer pre-vascularized scaffolds for bone tissue engineering.

Silk microfiber-reinforced silk hydrogel composites for functional cartilage tissue repair

Cartilage tissue lacks an intrinsic capacity for self-regeneration due to slow matrix turnover, a limited supply of mature chondrocytes and insufficient vasculature. Although cartilage tissue engineering has achieved some success using agarose as a scaffolding material, major challenges of agarose-based cartilage repair, including non-degradability, poor tissue–scaffold integration and limited processing capability, have prompted the search for an alternative biomaterial. In this study, silk fiber–hydrogel composites (SF–silk hydrogels) made from silk microfibers and silk hydrogels were investigated for their potential use as a support material for engineered cartilage. We demonstrated the use of 100% silk-based fiber–hydrogel composite scaffolds for the development of cartilage constructs with properties comparable to those made with agarose. Cartilage constructs with an equilibrium modulus in the native tissue range were fabricated by mimicking the collagen fiber and proteoglycan composite architecture of native cartilage using biocompatible, biodegradable silk fibroin from Bombyx mori. Excellent chondrocyte response was observed on SF–silk hydrogels, and fiber reinforcement resulted in the development of more mechanically robust constructs after 42days in culture compared to silk hydrogels alone. Thus, we demonstrate the versatility of silk fibroin as a composite scaffolding material for use in cartilage tissue repair to create functional cartilage constructs that overcome the limitations of agarose biomaterials, and provide a much-needed alternative to the agarose standard.

Engineering Angiogenesis for Myocardial Infarction Repair: Recent Developments, Challenges, and Future Directions

Myocardial infarction is a cardiovascular disorder that remains a critical health issue worldwide. Because of its intrinsic inability to regenerate, cardiac tissue fails to repair itself after myocardial infarction. Cardiovascular engineering is a promising approach to regenerating myocardium for myocardial infarction repair. Despite explosive growth in research and interest in this field, cardiovascular regenerative medicine faces many challenges, with the need for rapid vascularization being the most pressing. Due to the high metabolic demand of cardiac cells, myocytes transplanted or implanted via cardiac scaffolds in the infarcted region do not survive without the timely formation of a microvascular network in the infarcted area or within the scaffolds. To address this issue, various strategies have been developed based on angiogenesis stimulation, prevascularization, and inosculation to promote microvascular network formation within the cardiac scaffolds. This paper describes cardiac tissue engineering strategies, key challenges in cardiovascular regenerative medicine, and various vascularization strategies, with an aim to review recent advances and developments in engineering vascularization and inosculation approaches towards the rapid integration of cardiac scaffolds, once implanted, with the host tissue. Challenges in engineering angiogenesis and future directions to address the issue of rapid inosculation are also discussed.

A compressible scaffold for minimally invasive delivery of large intact neuronal networks.

Millimeter to centimeter-sized injectable neural scaffolds based on macroporous cryogels are presented. The polymer-scaffolds are made from alginate and carboxymethyl-cellulose by a novel simple one-pot cryosynthesis. They allow surgical sterility by means of autoclaving, and present native laminin as an attachment motive for neural adhesion and neurite development. They are designed to protect an extended, living neuronal network during compression to a small fraction of the original volume in order to enable minimally invasive delivery. The scaffolds behave as a mechanical meta-material: they are soft at the macroscopic scale, enabling injection through narrow-bore tubing and potentially good cellular scaffold integration in soft target tissues such as the brain. At the same time, the scaffold material has a high local Young modulus, allowing protection of the neuronal network during injection. Based on macroscopic and nanomechanical characterization, the generic geometrical and mechanical design rules are presented, enabling macroporous cellular scaffold injectability.