Acceleration of ligamentization and osseointegration processes after anterior cruciate ligament reconstruction with autologous tissue-engineered polyethylene terephthalate graft

Background

Despite the advantages of excellent mechanical properties for rapid return to sports and early rehabilitation after anterior cruciate ligament (ACL) reconstruction with polyethylene terephthalate (PET) artificial ligament, the graft failure rate during long-term follow-up is relatively high due to poor graft-host incorporation. The purpose of the present study was to investigate the effect of autologous tissue-engineered PET (ATE-PET) grafts on osseointegration and ligamentization after ACL reconstruction.

Methods

Forty-eight New Zealand white rabbits were randomly divided into PET group (n=24) and ATE-PET group (n=24). In the ATE-PET group, the rabbits initially underwent subcutaneous implantation of the PET ligament. Two weeks later, unilateral ipsilateral ACL reconstruction was performed using an ATE-PET graft. In the PET group, the rabbits underwent ACL reconstruction using PET grafts as controls. Macroscopic observation, micro-computed tomography, histological and immunofluorescent staining, and biomechanical tests were conducted to evaluate the effects at 4 and 12 weeks postoperatively.

Results

The ATE-PET graft was highly pre-vascularized with myofibroblast aggregation after two weeks of subcutaneous implantation. With regard to the intraosseous part of the graft, the ATE-PET group had significantly higher bone mineral density and bone volume/total volume ratio at 12 weeks. Histologically, the width of the interface between the graft and bone was smaller. Regarding the intra-articular part, thicker tissue coverage with a glossy appearance was observed in the ATE-PET group at 12 weeks on macroscopic observation. Histological staining also showed more collagen fibers grew in the grafts with fewer inflammatory reactions of the ATE-PET group at both 4 and 12 weeks. Immunofluorescently, both α-SMA-positive vessels and α-SMA-positive myofibroblasts were found to be significantly greater around the graft in the ATE-PET group at 4 weeks and markedly declined at 12 weeks. Moreover, the ATE-PET group presented significantly greater failure load and stiffness than the PET group at 12 weeks (53.7±5.4 vs. 42.5±4.5 N, P<0.01; 12.9±3.0 vs. 9.8±1.3 N/mm, P=0.04).

Conclusions

The ATE-PET artificial ligament with pre-vascularization and myofibroblast aggregation could effectively accelerate intra-articular graft ligamentization and intraosseous graft osseointegration, thus enhancing the biomechanical properties after ACL reconstruction in a rabbit model.

Preparation of multilayer electrospun nanofibrous scaffolds containing soluble eggshell membrane as potential dermal substitute

Electrospinning of natural and synthetic polymers has shown to be a great candidate for the fabrication of tissue engineering scaffolds due to their similarity to the nanofibrous structure of natural extracellular matrix (ECM). Moreover, the addition of ECM-like proteins could enhance the biocompatibility of these scaffolds. In this study, soluble eggshell protein (SEP) was first extracted and synthesized from the raw eggshell membrane. The characteristics and biocompatibility of the extracted SEP were evaluated using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) analysis and 3-(4,5- dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide) (MTT) assay. For scaffolds fabrication, a three-layer nanofibrous composite structure was produced using the electrospinning technique. The outer layers composed of polyvinyl alcohol, chitosan, and extracted SEP while the middle layer composed of polyethylene oxide, gelatin, and zinc oxide nanoparticles (ZnO-NPs). For each layer, the electrospinning parameters were adjusted to form bead-free fibers. To improve fibers' stability against body fluids, the produced fibers were crosslinked using glutaraldehyde vapor. Several techniques such as scanning electron microscopy (SEM), energy dispersive X-ray, ATR-FTIR, swelling, tensile test, in vitro biodegradation, and MTT assay were implemented to evaluate the physical, chemical, and biological characterization of the fabricated fibers. The results showed that crosslinked fibers have adequate stability in water, suitable mechanical properties, and promising water uptake capacity. The MTT results also revealed that SEP and ZnO-NPs could increase scaffolds biocompatibility. Moreover, SEM photographs of cultured fibroblasts cells on the scaffolds showed that cells were well attached on the scaffolds and preserve their natural spindle shapes. Altogether, our findings demonstrated that the produced three-layer composite scaffolds are potential candidates for skin tissue engineering.

Bioengineered Skin Substitutes: Advances and Future Trends

As the largest organ in the human body, the skin has the function of maintaining balance and protecting from external factors such as bacteria, chemicals, and temperature. If the wound does not heal in time after skin damage, it may cause infection or life-threatening complications. In particular, medical treatment of large skin defects caused by burns or trauma remains challenging. Therefore, human bioengineered skin substitutes represent an alternative approach to treat such injuries. Based on the chemical composition and scaffold material, skin substitutes can be classified into acellular or cellular grafts, as well as natural-based or synthetic skin substitutes. Further, they can be categorized as epidermal, dermal, and composite grafts, based on the skin component they contain. This review presents the common commercially available skin substitutes and their clinical use. Moreover, the choice of an appropriate hydrogel type to prepare cell-laden skin substitutes is discussed. Additionally, we present recent advances in the field of bioengineered human skin substitutes using three-dimensional (3D) bioprinting techniques. Finally, we discuss different skin substitute developments to meet different criteria for optimal wound healing.

Harnessing biomaterials for therapeutic strategies against COVID-19

With the emergence of the coronavirus disease 2019 (COVID-19), the world is experiencing a profound human health crisis. The number of infections and deaths due to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to increase every minute, pinpointing major shortcomings in our ability to prevent viral outbreaks. Although several COVID-19 vaccines have been recently approved for emergency use, therapeutic options remain limited, and their long-term potency has yet to be validated. Biomaterials science has a pivotal role to play in pushing the boundaries of emerging technologies for antiviral research and treatment. In this perspective, we discuss how biomaterials can be harnessed to develop accurate COVID-19 infection models, enhance antiviral drug delivery, foster new antiviral strategies, and boost vaccine efficacy. These efforts will not only contribute to stop or mitigate the current pandemic but will also provide unorthodox platforms to understand, prevent, and protect us from future viral outbreaks.

Needle-injectable microcomposite cryogel scaffolds with antimicrobial properties

Porous three-dimensional hydrogel scaffolds have an exquisite ability to promote tissue repair. However, because of their high water content and invasive nature during surgical implantation, hydrogels are at an increased risk of bacterial infection. Recently, we have developed elastic biomimetic cryogels, an advanced type of polymeric hydrogel, that are syringe-deliverable through hypodermic needles. These needle-injectable cryogels have unique properties, including large and interconnected pores, mechanical robustness, and shape-memory. Like hydrogels, cryogels are also susceptible to colonization by microbial pathogens. To that end, our minimally invasive cryogels have been engineered to address this challenge. Specifically, we hybridized the cryogels with calcium peroxide microparticles to controllably produce bactericidal hydrogen peroxide. Our novel microcomposite cryogels exhibit antimicrobial properties and inhibit antibiotic-resistant bacteria (MRSA and Pseudomonas aeruginosa), the most common cause of biomaterial implant failure in modern medicine. Moreover, the cryogels showed negligible cytotoxicity toward murine fibroblasts and prevented activation of primary bone marrow-derived dendritic cells ex vivo. Finally, in vivo data suggested tissue integration, biodegradation, and minimal host inflammatory responses when the antimicrobial cryogels, even when purposely contaminated with bacteria, were subcutaneously injected in mice. Collectively, these needle-injectable microcomposite cryogels show great promise for biomedical applications, especially in tissue engineering and regenerative medicine.