Trends in bioactivity: inducing and detecting mineralization of regenerative polymeric scaffolds

Due to limitations of biological and alloplastic grafts, regenerative engineering has emerged as a promising alternative to treat bone defects. Bioactive polymeric scaffolds are an integral part of such an approach. Bioactivity importantly induces hydroxyapatite mineralization that promotes osteoinductivity and osseointegration with surrounding bone tissue. Strategies to confer bioactivity to polymeric scaffolds utilize bioceramic fillers, coatings and surface treatments, and additives. These approaches can also favorably impact mechanical and degradation properties. A variety of fabrication methods are utilized to prepare scaffolds with requisite morphological features. The bioactivity of scaffolds may be evaluated with a broad set of techniques, including in vitro (acellular and cellular) and in vivo methods. Herein, we highlight contemporary and emerging approaches to prepare and assess scaffold bioactivity, as well as existing challenges.

Bioactive gelatin-sheets as novel biopapers to support prevascularization organized by laser-assisted bioprinting for bone tissue engineering

Despite significant advances in the management of patients with oral cancer, maxillofacial reconstruction after ablative surgery remains a clinical challenge. In bone tissue engineering, biofabrication strategies have been proposed as promising alternatives to solve issues associated with current therapies and to produce bone substitutes that mimic both the structure and function of native bone. Among them, laser-assisted bioprinting (LAB) has emerged as a relevant biofabrication method to print living cells and biomaterials with micrometric resolution onto a receiving substrate, also called 'biopaper'. Recent studies have demonstrated the benefits of prevascularization using LAB to promote vascularization and bone regeneration, but mechanical and biological optimization of the biopaper are needed. The aim of this study was to apply gelatin-sheet fabrication process to the development of a novel biopaper able to support prevascularization organized by LAB for bone tissue engineering applications. Gelatin-based sheets incorporating bioactive glasses (BGs) were produced using various freezing methods and crosslinking (CL) parameters. The different formulations were characterized in terms of microstructural, physical, mechanical, and biological properties in monoculture and coculture. Based on multi-criteria analysis, a rank scoring method was used to identify the most relevant formulations. The selected biopaper underwent additional characterization regarding its ability to support mineralization and vasculogenesis, its bioactivity potential andin vivodegradability. The biopaper 'Gel5wt% BG1wt%-slow freezing-CL160 °C 24 h' was selected as the best candidate, due to its suitable properties including high porosity (91.69 ± 1.55%), swelling ratio (91.61 ± 0.60%), Young modulus (3.97 × 104± 0.97 × 104Pa) but also its great cytocompatibility, osteogenesis and bioactivity properties. The preorganization of human umbilical vein endothelial cell using LAB onto this new biopaper led to the formation of microvascular networks. This biopaper was also shown to be compatible with 3D-molding and 3D-stacking strategies. This work allowed the development of a novel biopaper adapted to LAB with great potential for vascularized bone biofabrication.

Recent Advances in Bioengineering Bone Revascularization Based on Composite Materials Comprising Hydroxyapatite

The natural healing process of bone is impaired in the presence of tumors, trauma, or inflammation, necessitating external assistance for bone regeneration. The limitations of autologous/allogeneic bone grafting are still being discovered as research progresses. Bone tissue engineering (BTE) is now a crucial component of treating bone injuries and actively works to promote vascularization, a crucial stage in bone repair. A biomaterial with hydroxyapatite (HA), which resembles the mineral makeup of invertebrate bones and teeth, has demonstrated high osteoconductivity, bioactivity, and biocompatibility. However, due to its brittleness and porosity, which restrict its application, scientists have been prompted to explore ways to improve its properties by mixing it with other materials, modifying its structural composition, improving fabrication techniques and growth factor loading, and co-cultivating bone regrowth cells to stimulate vascularization. This review scrutinizes the latest five-year research on HA composite studies aimed at amplifying vascularization in bone regeneration.

A bioactive microparticle-loaded osteogenically enhanced bioprinted scaffold that permits sustained release of BMP-2

Extrusion-based bioprinting technology is widely used for tissue regeneration and reconstruction. However, the method that uses only hydrogel as the bioink base material exhibits limited biofunctional properties and needs improvement to achieve the desired tissue regeneration. In this study, we present a three-dimensionally printed bioactive microparticle-loaded scaffold for use in bone regeneration applications. The unique structure of the microparticles provided sustained release of growth factor for > 4 weeks without the use of toxic or harmful substances. Before and after printing, the optimal particle ratio in the bioink for cell viability demonstrated a survival rate of ≥ 85% over 7 days. Notably, osteogenic differentiation and mineralization-mediated by human periosteum-derived cells in scaffolds with bioactive microparticles-increased over a 2-week interval. Here, we present an alternative bioprinting strategy that uses the sustained release of bioactive microparticles to improve biofunctional properties in a manner that is acceptable for clinical bone regeneration applications.

Ascorbic Acid 2-Phosphate-Releasing Supercritical Carbon Dioxide-Foamed Poly(L-Lactide-Co-epsilon-Caprolactone) Scaffolds Support Urothelial Cell Growth and Enhance Human Adipose-Derived Stromal Cell Proliferation and Collagen Production

Tissue engineering can provide a novel approach for the reconstruction of large urethral defects, which currently lacks optimal repair methods. Cell-seeded scaffolds aim to prevent urethral stricture and scarring, as effective urothelium and stromal tissue regeneration is important in urethral repair. In this study, the aim was to evaluate the effect of the novel porous ascorbic acid 2-phosphate (A2P)-releasing supercritical carbon dioxide-foamed poly(L-lactide-co-ε-caprolactone) (PLCL) scaffolds (scPLCLA2P) on the viability, proliferation, phenotype maintenance, and collagen production of human urothelial cell (hUC) and human adipose-derived stromal cell (hASC) mono- and cocultures. The scPLCLA2P scaffold supported hUC growth and phenotype both in monoculture and in coculture. In monocultures, the proliferation and collagen production of hASCs were significantly increased on the scPLCLA2P compared to scPLCL scaffolds without A2P, on which the hASCs formed nonproliferating cell clusters. Our findings suggest the A2P-releasing scPLCLA2P to be a promising material for urethral tissue engineering.

Polysaccharide-Based Composite Scaffolds for Osteochondral and Enthesis Regeneration

The rotator cuff and Achilles tendons along with the anterior cruciate ligament (ACL) are frequently injured with limited healing capacity. At the soft-hard tissue interface, enthesis is prone to get damaged and its regeneration in osteochondral defects is essential for complete healing. The current clinical techniques used in suturing procedures to reattach tendons to bones need much improvement for the generation of the native interface tissue, that is, enthesis, for patients to regain their full functions. Recently, inspired by the composite native tissue, much effort has been made to fabricate composite scaffolds for enthesis tissue regeneration. This review first focuses on the studies that used composite scaffolds for the regeneration of enthesis. Then, the use of polysaccharides for osteochondral tissue engineering is reviewed and their potential for enthesis regeneration is presented based on their supporting effects on osteogenesis and chondrogenesis. Gellan gum (GG) is selected and reviewed as a promising polysaccharide due to its unique osteogenic and chondrogenic activities that help avoid the inherent weakness of dissimilar materials in composite scaffolds. In addition, original preliminary results showed that GG supports collagen type I production and upregulation of osteogenic marker genes. Impact Statement Enthesis regeneration is essential for complete and functional healing of tendon and ligament tissues. Current suturing techniques to reattach the tendon/ligament to bones have high failure rates. This review highlights the studies on biomimetic scaffolds aimed to regenerate enthesis. In addition, the potential of using polysaccharides to regenerate enthesis is discussed based on their ability to regenerate osteochondral tissues. Gellan gum is presented as a promising biopolymer that can be modified to simultaneously support bone and cartilage regeneration by providing structural continuity for the scaffold.

Gellan Gum Is a Suitable Biomaterial for Manual and Bioprinted Setup of Long-Term Stable, Functional 3D-Adipose Tissue Models

Due to its wide-ranging endocrine functions, adipose tissue influences the whole body’s metabolism. Engineering long-term stable and functional human adipose tissue is still challenging due to the limited availability of suitable biomaterials and adequate cell maturation. We used gellan gum (GG) to create manual and bioprinted adipose tissue models because of its similarities to the native extracellular matrix and its easily tunable properties. Gellan gum itself was neither toxic nor monocyte activating. The resulting hydrogels exhibited suitable viscoelastic properties for soft tissues and were stable for 98 days in vitro. Encapsulated human primary adipose-derived stem cells (ASCs) were adipogenically differentiated for 14 days and matured for an additional 84 days. Live-dead staining showed that encapsulated cells stayed viable until day 98, while intracellular lipid staining showed an increase over time and a differentiation rate of 76% between days 28 and 56. After 4 weeks of culture, adipocytes had a univacuolar morphology, expressed perilipin A, and secreted up to 73% more leptin. After bioprinting establishment, we demonstrated that the cells in printed hydrogels had high cell viability and exhibited an adipogenic phenotype and function. In summary, GG-based adipose tissue models show long-term stability and allow ASCs maturation into functional, univacuolar adipocytes.

Polysaccharide-Based Hydrogels for Microencapsulation of Stem Cells in Regenerative Medicine

Stem cell-based therapy appears as a promising strategy to induce regeneration of damaged and diseased tissues. However, low survival, poor engraftment and a lack of site-specificity are major drawbacks. Polysaccharide hydrogels can address these issues and offer several advantages as cell delivery vehicles. They have become very popular due to their unique properties such as high-water content, biocompatibility, biodegradability and flexibility. Polysaccharide polymers can be physically or chemically crosslinked to construct biomimetic hydrogels. Their resemblance to living tissues mimics the native three-dimensional extracellular matrix and supports stem cell survival, proliferation and differentiation. Given the intricate nature of communication between hydrogels and stem cells, understanding their interaction is crucial. Cells are incorporated with polysaccharide hydrogels using various microencapsulation techniques, allowing generation of more relevant models and further enhancement of stem cell therapies. This paper provides a comprehensive review of human stem cells and polysaccharide hydrogels most used in regenerative medicine. The recent and advanced stem cell microencapsulation techniques, which include extrusion, emulsion, lithography, microfluidics, superhydrophobic surfaces and bioprinting, are described. This review also discusses current progress in clinical translation of stem-cell encapsulated polysaccharide hydrogels for cell delivery and disease modeling (drug testing and discovery) with focuses on musculoskeletal, nervous, cardiac and cancerous tissues.

Biological and bioactivity assessment of dextran nanocomposite hydrogel for bone regeneration

Insufficient biological and bioactive properties of dextran hydrogels limit their applications as promising scaffolds for tissue engineering. We developed nanocomposite dextran hydrogels comprised of bioactive glass (nBGC: 64% SiO2, 31% CaO, 5% P₂O₅) nanoparticles with an average particle size of 77 nm using a chemical crosslinking of dextran chains to form 3D hydrogel networks. In the current study; bioactivity of the obtained nanocomposite hydrogels was evaluated through the formation of apatite crystal structures after the incubation in simulated body fluid (SBF) at various submersion periods and nBGC content. The scanning electron microscopy (SEM) micrographs represented an enhanced hydroxyapatite formation on the cross section of nanocomposite comprising of nBGC content from 2 to 8 (% by wt). Biomineralization results of Dex-8 (% by wt) composite during 7, 14 and 28 days immersion indicated the apatite layer formation and the growth of apatite crystal size on the surface and cross section of the nanocomposite. Moreover, MTT assessments indicated that human osteosarcoma cells (SaOS-2) were able to adhere and spread within the dextran hydrogels reinforced with the bioactive glass nanoparticles. With regard to enhanced bioactivity and biocompatibility, the developed dextran-nBGC hydrogel could be considered as a suitable candidate for bone tissue engineering application.

Sustainable aquaculture side-streams derived hybrid biocomposite for bone tissue engineering

Despite being a rich source of bioactive compounds, the current exploitation of aquatic biomass is insufficient. Majority of the aquaculture industry side-streams are currently used for low-value purposes such as animal feed or composting material, with low economical returns. To maximize resource reuse and minimize waste generation, valorization efforts should be augmented with the aim to produce high-value products. Herein, we present a novel aquaculture wastes-derived multi-scale osteoconductive hybrid biocomposite that is composed of chemically crosslinked American bullfrog (Rana catesbeiana) skin-derived type I tropocollagen nanofibrils (~22.3 nm) network and functionalized with micronized (~1.6 μm) single-phase hydroxyapatite (HA) from discarded snakehead (Channa micropeltes) fish scales. The bioengineered construct is biocompatible, highly porous (>90%), and exhibits excellent osteoconductive properties, as indicated by robust adhesion and proliferation of human fetal osteoblastic 1.19 cell line (hFOB 1.19). Furthermore, increased expression level of osteo-related ALPL and BGLAP mRNA transcripts, as well as enhanced osteocalcin immunoreactivity and increasing Alizarin red S staining coverage on the hybrid biocomposite was observed over 21 days of culture. Collectively, the devised "waste-to-resource" platform represents a sustainable waste valorization strategy that is amendable for advanced bone repair and regeneration applications.