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A common phenomenon in tissue engineering is rapid tissue formation on the outer edge of the scaffold which restricts cell penetration and nutrient exchange to the scaffold centre, resulting in a necrotic core. To address this problem, we generated scaffolds with both random and anisotropic open porous architectures to enhance cell and subsequent tissue infiltration throughout the scaffold for applications in bone and cartilage engineering. Hydroxyapatite (HA) and poly(D,L-lactic acid) (P(DL)LA) scaffolds with random open porosity were manufactured, using modified slip-casting and by supercritical fluid processing respectively, and subsequently characterised. An array of porous aligned channels (400 microm) was incorporated into both scaffold types and cell (human osteoblast sarcoma, for HA scaffolds; ovine meniscal fibrochondrocytes, for P(DL)LA scaffolds) and tissue infiltration into these modified scaffolds was assessed in vitro (cell penetration) and in vivo (tissue infiltration; HA scaffolds only). Scaffolds were shown to have an extensive random, open porous structure with an average porosity of 85%. Enhanced cell and tissue penetration was observed both in vitro and in vivo demonstrating that scaffold design alone can influence cell and tissue infiltration into the centre of tissue engineering scaffolds.

The present retrospective analysis of 117 surgically excised anterior cruciate ligament (ACL) prostheses was designed to elucidate the etiology and mechanisms of failure of synthetic ligamentous prostheses. They were harvested from young and active patients (26 +/- 7 yrs) at various orthopaedic centers in France between 1983 and 1993. The average duration of implantation of augmentation and replacement prostheses were 21.5 +/- 12.6 and 33.2 +/- 25.3 months, respectively. The principal causes for their excision were ruptures and synovitis. Each ACL prosthesis was examined macroscopically, histologically, and, after tissue removal, by scanning electron microscopy (SEM) to determine the model, manufacturer, surgical technique used at implantation, the extent of healing, the site of rupture, and the morphology of the damaged fibers. Fourteen types of ACL prostheses were analysed, each fabricated using a different combination of polymers, fibers and textile constructions. Consequently, they generated a variety of healing characteristics and mechanical responses in vivo. SEM observations revealed that abrasion of the textile fibers as a result of yarn-on-yarn and/or yarn-on-bone contact was a common phenomenon to almost all models, and was the primary cause of prosthetic failure. Healing inside the synthetic ACL was poorly organized, incomplete and unpredictable as the extent of collagenous infiltration into the textile structure did not increase with the duration of implantation. In fact, the collagenous infiltration into certain models appeared to be more detrimental than beneficial since it caused deterioration and fraying of the textile structure rather than serving as a reinforcing matrix around the prosthesis. In conclusion, the present study shows that three mechanisms may be involved in the failure of ACL prostheses: (1) inadequate fiber abrasion resistance against osseous surfaces; (2) flexural and rotational fatigue of the fibers, and (3) loss of integrity of the textile structure due to unpredictable tissue infiltration during healing.