Evaluating the physicochemical effects of conjugating peptides into thermogelling hydrogels for regenerative biomaterials applications

Aspects of a Suspended Bioprinting System Affect Cell Viability and Support Bath Properties

Suspended hydrogel printing is a growing method for fabricating bioprinted hydrogel constructs, largely due to how it enables nonviscous hydrogel inks to be used in extrusion printing. In this work, a previously developed poly(N-isopropylacrylamide)-based thermogelling suspended bioprinting system was examined in the context of chondrocyte-laden printing. Material factors such as ink concentration and cell concentration were found to have a significant effect on printed chondrocyte viability. In addition, the heated poloxamer support bath was able to maintain chondrocyte viability for up to 6 h of residence within the bath. The relationship between the ink and support bath was also assessed by measuring the rheological properties of the bath before and after printing. Bath storage modulus and yield stress decreased during printing as nozzle size was reduced, indicating the likelihood that dilution occurs over time through osmotic exchange with the ink. Altogether this work demonstrates the promise for printing high-resolution cell-encapsulating tissue engineering constructs, while also elucidating complex relationships between the ink and bath, which must be taken into consideration when designing suspended printing systems.

Thermogelling hydrogel charge and lower critical solution temperature influence cellular infiltration and tissue integration in an ex vivo cartilage explant model

Thermogelling hydrogels based on poly(N-isopropyl acrylamide) (p[NiPAAm]) and crosslinked with a peptide-bearing macromer poly(glycolic acid)-poly(ethylene glycol)-poly(glycolic acid)-di(but-2-yne-1,4-dithiol) (PdBT) were fabricated to assess the role of hydrogel charge and lower critical solution temperature (LCST) over time in influencing cellular infiltration and tissue integration in an ex vivo cartilage explant model over 21 days. The p(NiPAAm)-based thermogelling polymer was synthesized to possess 0, 5, and 10 mol% dimethyl-γ-butyrolactone acrylate (DBA) to raise the LCST over time as the lactone rings hydrolyzed. Further, three peptides were designed to impart charge into the hydrogels via conjugation to the PdBT crosslinker. The positively, neutrally, and negatively charged peptides K4 (+), zwitterionic K2E2 (0), and E4 (-), respectively, were conjugated to the modular PdBT crosslinker and the hydrogels were evaluated for their thermogelation behavior in vitro before injection into the cartilage explant models. Samples were collected at days 0 and 21, and tissue integration and cellular infiltration were assessed via mechanical pushout testing and histology. Negatively charged hydrogels whose LCST changed over time (10 mol% DBA) were demonstrated to promote the greatest tissue integration when compared to the positive and neutral gels of the same thermogelling polymer formulation due to increased transport and diffusion across the hydrogel-tissue interface. Indeed, the negatively charged thermogelling polymer groups containing 5 and 10 mol% DBA demonstrated cellular infiltration and cartilage-like matrix deposition via histology. This study demonstrates the important role that material physicochemical properties play in dictating cell and tissue behavior and can inform future cartilage tissue engineering strategies.

Recent advances in regenerative biomaterials

Nowadays, biomaterials have evolved from the inert supports or functional substitutes to the bioactive materials able to trigger or promote the regenerative potential of tissues. The interdisciplinary progress has broadened the definition of 'biomaterials', and a typical new insight is the concept of tissue induction biomaterials. The term 'regenerative biomaterials' and thus the contents of this article are relevant to yet beyond tissue induction biomaterials. This review summarizes the recent progress of medical materials including metals, ceramics, hydrogels, other polymers and bio-derived materials. As the application aspects are concerned, this article introduces regenerative biomaterials for bone and cartilage regeneration, cardiovascular repair, 3D bioprinting, wound healing and medical cosmetology. Cell-biomaterial interactions are highlighted. Since the global pandemic of coronavirus disease 2019, the review particularly mentions biomaterials for public health emergency. In the last section, perspectives are suggested: (i) creation of new materials is the source of innovation; (ii) modification of existing materials is an effective strategy for performance improvement; (iii) biomaterial degradation and tissue regeneration are required to be harmonious with each other; (iv) host responses can significantly influence the clinical outcomes; (v) the long-term outcomes should be paid more attention to; (vi) the noninvasive approaches for monitoring in vivo dynamic evolution are required to be developed; (vii) public health emergencies call for more research and development of biomaterials; and (viii) clinical translation needs to be pushed forward in a full-chain way. In the future, more new insights are expected to be shed into the brilliant field-regenerative biomaterials.

Fabrication and biological evaluation of three-dimensional (3D) Mg substituted bi-phasic calcium phosphate porous scaffolds for hard tissue engineering

This work reports on the fabrication of three-dimensional (3D) magnesium substituted bi-phasic calcium phosphate (Mg-BCP) scaffolds by gel-casting, their structural and physico-chemical characterization, and on the assessment of their in vitro and in vivo performances. The crystalline phase assemblage, chemical functional groups and porous morphology features of the scaffolds were evaluated by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) and field emission scanning electron microscopy (FE-SEM), respectively. The sintered scaffolds revealed an interconnected porosity with pore sizes ranging from 4.3 to 7.28 μm. The scaffolds exhibited good biomineralization activity upon immersion in simulated body fluid (SBF), while an in vitro study using MG-63 cell line cultures confirmed their improved biocompatibility, cell proliferation and bioactivity. Bone grafting of 3D scaffolds was performed in non-load bearing bone defects surgically created in tibia of rabbits, used as animal model. Histological and radiological observations indicated the successful restoration of bone defects. The overall results confirmed the suitability of the scaffolds to be further tested as synthetic bone grafts in bone regeneration surgeries and in bone tissue engineering applications.