Shape or size matters? Towards standard reporting of tensile testing parameters for human soft tissues: systematic review and finite element analysis.

Material properties of soft-tissue samples are often derived through uniaxial tensile testing. For engineering materials, testing parameters (e.g., sample geometries and clamping conditions) are described by international standards; for biological tissues, such standards do not exist. To investigate what testing parameters have been reported for tensile testing of human soft-tissue samples, a systematic review of the literature was performed using PRISMA guidelines. Soft tissues are described as anisotropic and/or hyperelastic. Thus, we explored how the retrieved parameters compared against standards for engineering materials of similar characteristics. All research articles published in English, with an Abstract, and before 1 January 2023 were retrieved from databases of PubMed, Web of Science, and BASE. After screening of articles based on search terms and exclusion criteria, a total 1,096 articles were assessed for eligibility, from which 361 studies were retrieved and included in this review. We found that a non-tapered shape is most common (209 of 361), followed by a tapered sample shape (92 of 361). However, clamping conditions varied and were underreported (156 of 361). As a preliminary attempt to explore how the retrieved parameters might influence the stress distribution under tensile loading, a pilot study was performed using finite element analysis (FEA) and constitutive modeling for a clamped sample of little or no fiber dispersion. The preliminary FE simulation results might suggest the hypothesis that different sample geometries could have a profound influence on the stress-distribution under tensile loading. However, no conclusions can be drawn from these simulations, and future studies should involve exploring different sample geometries under different computational models and sample parameters (such as fiber dispersion and clamping effects). Taken together, reporting and choice of testing parameters remain as challenges, and as such, recommendations towards standard reporting of uniaxial tensile testing parameters for human soft tissues are proposed.

In vivo ligamentogenesis in embroidered poly(lactic-co-ε-caprolactone) / polylactic acid scaffolds functionalized by fluorination and hexamethylene diisocyanate cross-linked collagen foams.

Although autografts represent the gold standard for anterior cruciate ligament (ACL) reconstruction, tissue-engineered ACLs provide a prospect to minimize donor site morbidity and limited graft availability. This study characterizes the ligamentogenesis in embroidered poly(L-lactide-co-ε-caprolactone) (P(LA-CL)) / polylactic acid (PLA) constructs using a dynamic nude mice xenograft model. (P(LA-CL))/PLA scaffolds remained either untreated (co) or were functionalized by gas fluorination (F), collagen foam cross-linked with hexamethylene diisocyanate (HMDI) (coll), or F combined with the foam (F + coll). Cell-free constructs or those seeded for 1 week with lapine ACL ligamentocytes were implanted into nude mice for 12 weeks. Following explantation, cell vitality and content, histo(patho)logy of scaffolds (including organs: liver, kidney, spleen), sulphated glycosaminoglycan (sGAG) contents and biomechanical properties were assessed.Scaffolds did not affect mice weight development and organs, indicating no organ toxicity. Moreover, scaffolds maintained their size and shape and reflected a high cell viability prior to and following implantation. Coll or F + coll scaffolds seeded with cells yielded superior macroscopic properties compared to the controls. Mild signs of inflammation (foreign-body giant cells and hyperemia) were limited to scaffolds without collagen. Microscopical score values and sGAG content did not differ significantly. Although remaining stable after explantation, elastic modulus, maximum force, tensile strength and strain at Fmax were significantly lower in explanted scaffolds compared to those before implantation, with no significant differences between scaffold subtypes, except for a higher maximum force in F + coll compared with F samples (in vivo). Scaffold functionalization with fluorinated collagen foam provides a promising approach for ACL tissue engineering. a Lapine anterior cruciate ligament (LACL): red arrow, posterior cruciate ligament: yellow arrow. Medial anterior meniscotibial ligament: black arrow. b Explant culture to isolate LACL fibroblasts. c Scaffold variants: co: controls; F: functionalization by gas-phase fluorination; coll: collagen foam cross-linked with hexamethylene diisocyanate (HMDI). c1-2 Embroidery pattern of the scaffolds. d Scaffolds were seeded with LACL fibroblasts using a dynamical culturing approach as depicted. e Scaffolds were implanted subnuchally into nude mice, fixed at the nuchal ligament and sacrospinal muscle tendons. f Two weeks after implantation. g Summary of analyses performed. Scale bars 1 cm (b, d), 0.5 cm (c). (sketches drawn by G.S.-T. using Krita 4.1.7 [Krita foundation, The Netherlands]).