Multilayered Scaffolds for Osteochondral Tissue Engineering Based on Bioactive Glass and Biodegradable Polymers

Injuries of the articular cartilage may penetrate to the underlying subchondral bone, forming osteochondral defects which have a limited capacity of self-regeneration. Accompanied with limited surgical treatments and the fact that the causes are not understood well, an approach based in tissue engineering becomes a promising strategy for osteochondral repair. Such tissue engineering approaches are based on the combination of synthetic scaffolds, suitable cell sources and active molecules or growth factors. The suitable osteochondral scaffold should be developed considering appropriate biomaterials and processing techniques in order to fabricate engineered scaffolds as suitable 3D microenvironment with sufficient mechanical integrity for cells growth and tissue regeneration. The combination of biodegradable polymers and bioactive glasses in the form of bi- or multilayered composite scaffolds is a promising approach in osteochondral regeneration, whereby the development of robust fabrication methods is crucial for the success of this strategy. In this investigation, two different structural architectures of scaffolds are comparatively studied for the cartilage phase, including (I) porous foams and (II) electrospun fibers fabricated by using freeze drying and electrospinning techniques, respectively. A biocompatible polysaccharide, namely sodium alginate, processed on the upper surface of 3D highly porous interconnected Bioglass®-based foams by freeze-drying followed by ionically crosslinking to produce a cartilage-engineered substrate. Sodium alginate coated Bioglass®-based scaffolds (fabricated by foam replication technique followed by polymer coating), were manufactured as scaffold for subchondral bone. Both phases were integrated by different methods; including using a sodium alginate adhesive layer to from Alg/Na-Alg coated Bioglass® bilayered scaffolds and formation of a monolithic biphasic scaffold. In the second approach, sodium alginate is fabricated into submicron fibers by electrospinning, and deposited on the alginate coated Bioglass®-based scaffold, forming electrospun Alg/Alg-coated Bioglass® bilayered scaffold. In addition, synthetic biodegradable polymer (PDLLA) was used to fabricate the same structural architectures (by using the same techniques) in order to compare between different scaffold materials. The scaffold architecture, constitutive microstructural features, and mechanical properties were investigated with respect to their requirements for regeneration of both cartilage and subchondral bone. Alginate freeze-dried foams provide pore sizes in the range of 125 to 225 µm, whereas alginate coated Bioglass®-based scaffolds for bone regeneration show larger pore sizes (100-600 µm), required for bone regeneration. Both scaffolds exhibit high porosity and pore interconnectivity and they were confirmed to be suitable pore sizes for chondrocyte seeding, for synthesis of cartilaginous ECM, and for bone in-growth and vascularization, respectively. The mechanical properties of Alg-foams and Alg-c-BG scaffolds were confirmed to be closer to those of native tissues. In addition, antibiotic drug, i.e. tetracycline, was incorporated into polymer coated Bioglass-based scaffolds in order to enhance functionality of the scaffolds for use as a drug or biomolecule carrier in bone regeneration. The in vitro studies of Alg-foams and Alg-c-BG scaffolds are carried out separately by seeding chondrocytes and MSCs, and osteoblasts-like cells, respectively. MG-63 osteoblast-like cells were seeded on RGD-Alg-c-BG and Alg-c-BG scaffolds to evaluate the biocompatibility, cell viability, proliferation and differentiation in comparison with BG scaffolds. It was found that BG scaffolds promote high cell proliferation and bone mineralization upon 21 days culture, followed by RGD-Alg-c-BG and Alg-c-BG scaffolds, respectively. Therefore, alginate coated Bioglass-based composite scaffolds represent promising candidates for the regeneration of subchondral bone in osteochondral tissue engineering. Simutaneously, in vitro cell culture studies of alginate and alginate/chondroitin sulfate-foams for cartilage regeneration were evaluated by seeding with porcine chondrocytes and mesenchymal stem cells. All tests proved the biocompatibility of the materials to cells and chondrocytes maintained their phenotype over the investigated culture times (14 days). In addition, MSCs promoted the differentiation into chondrocyte-like cells and also provided the expression of collagen type II and proteoglycan after 7 days in culture, which are the specific markers of cartilage regeneration. The results thus confirmed that alginate based scaffolds have a great potential for use as cartilaginous scaffolds

Osteochondral tissue engineering: scaffolds, stem cells and applications.

Osteochondral tissue engineering has shown an increasing development to provide suitable strategies for the regeneration of damaged cartilage and underlying subchondral bone tissue. For reasons of the limitation in the capacity of articular cartilage to self-repair, it is essential to develop approaches based on suitable scaffolds made of appropriate engineered biomaterials. The combination of biodegradable polymers and bioactive ceramics in a variety of composite structures is promising in this area, whereby the fabrication methods, associated cells and signalling factors determine the success of the strategies. The objective of this review is to present and discuss approaches being proposed in osteochondral tissue engineering, which are focused on the application of various materials forming bilayered composite scaffolds, including polymers and ceramics, discussing the variety of scaffold designs and fabrication methods being developed. Additionally, cell sources and biological protein incorporation methods are discussed, addressing their interaction with scaffolds and highlighting the potential for creating a new generation of bilayered composite scaffolds that can mimic the native interfacial tissue properties, and are able to adapt to the biological environment

Physico-Chemical and <i>In Vitro</i> Cytotoxic Properties of Alginate/Soy Protein Isolated Scaffolds for Tissue Engineering

Three-dimensional (3D) porous alginate/soy protein isolated (Alg/SPI) tissue engineering scaffolds were achieved by freeze-drying. The physico-chemical attributes of the scaffolds including morphology, chemical structure, mechanical properties and in vitro cytotoxicity were investigated for different SPI blends. Results indicated that increasing SPI content to 40 wt% in the blends resulted in the partial existence of closed pores and reduced pore size. The mechanical values of the scaffolds under compression also reduced with increasing SPI in the blends. The addition of SPI did not significantly enhance the cell viability of the scaffolds investigated for in vitro culture with human fibroblasts, which remained in the high (90 – 100%) range. Results demonstrated that Alg/SPI scaffolds have potential for use as tissue engineering scaffolds.</jats:p

Polylactide-based materials science strategies to improve tissue-material interface without the use of growth factors or other biological molecules

In a large number of medical devices, a key feature of a biomaterial is the ability to successfully bond to living tissues by means of engineered mechanisms such as the enhancement of biomineralization on a bone tissue engineering scaffold or the mimicking of the natural structure of the extracellular matrix (ECM). This ability is commonly referred to as “bioactivity”. Materials sciences started to grow interest in it since the development of bioactive glasses by Larry Hench five decades ago. As the main goal in applications of biomedical devices and tissue scaffolds is to obtain a seamless tissue-material interface, achieving optimal bioactivity is essential for the success of most biomaterial-based tissue replacement and regenerative approaches. Polymers derived from lactic acid are largely adopted in the biomedical field, they are versatile, FDA approved and relatively cost-effective. However, as for many other widespread biomedical polymers, they are hydrophobic and lack the intrinsic ability of positively interacting with surrounding tissues. In the last decades scientists have studied many solutions to exploit the positive characteristics of polylactide-based materials overcoming this bottleneck at the same time. The efforts of this research fruitfully produced many effective tissue engineering technologies based on PLA and related biopolymers. This review aims to give an overview on the latest and most promising strategies to improve the bioactivity of lactic acid-based materials, especially focusing on biomolecule-free bulk approaches such as blending, copolymerization or composite fabrication. Avenues for future research to tackle current needs in the field are identified and discussed

Turmeric Herb Extract-Incorporated Biopolymer Dressings with Beneficial Antibacterial, Antioxidant and Anti-Inflammatory Properties for Wound Healing

Bacterial infection and inflammation caused by excess oxidative stress are serious challenges in chronic wound healing. The aim of this work is to investigate a wound dressing based on natural- and biowaste-derived biopolymers loaded with an herb extract that demonstrates antibacterial, antioxidant, and anti-inflammatory activities without using additional synthetic drugs. Turmeric extract-loaded carboxymethyl cellulose/silk sericin dressings were produced by esterification crosslinking with citric acid followed by freeze-drying to achieve an interconnected porous structure, sufficient mechanical properties, and hydrogel formation in situ in contact with an aqueous solution. The dressings exhibited inhibitory effects on the growth of bacterial strains that were related to the controlled release of the turmeric extract. The dressings provided antioxidant activity as a result of the radical scavenging effect on DPPH, ABTS, and FRAP radicals. To confirm their anti-inflammatory effects, the inhibition of nitric oxide production in activated RAW 264.7 macrophages was investigated. The findings suggested that the dressings could be a potential candidate for wound healing.</jats:p