Mechanical Behavior of a Porous, Sub-total Meniscus Implant Based on Poly(trimethylene carbonate)

Meniscus tears often occur in the avascular inner part of the meniscus and therefore do not heal spontaneously. Current treatments such as meniscectomy and the implantation of allografts are insufficient. In this study we prepared a designed, sub-total, porous meniscus implant from functionalized poly(trimethylene carbonate) by stereolithography, and investigated its mechanical behavior in a human cadaveric knee. The sub-total meniscus implant was sutured to the peripheral rim of the meniscus and placed in the medial compartment of the knee. To determine the peak- and mean pressures and the contact area pressure distribution, measurements were made and compared to those of the native meniscus-, meniscectomy- and allograft implant situations. Compared to the native meniscus, meniscectomy results in considerably higher peak- and mean pressures. Compared to meniscectomy, the allograft and PTMC implants show a limited decrease in peak pressures and a much lower mean pressure. The mean pressures are close to those of the native meniscus. Both the allograft and the PTMC implant show improved mechanical behavior compared to meniscectomy. It can be expected that the mechanical function of the PTMC implant will improve upon the formation of tissue in the pores of the implant after implantation in patients

Changes in articular cartilage after meniscectomy and meniscus replacement using a biodegradable porous polymer implant

Purpose: To evaluate the long-term effects of implantation of a biodegradable polymer meniscus implant on articular cartilage degeneration and compare this to articular cartilage degeneration after meniscectomy. Methods: Porous polymer polycaprolacton-based polyurethane meniscus implants were implanted for 6 or 24 months in the lateral compartment of Beagle dog knees. Contralateral knees were meniscectomized, or left intact and served as controls. Articular cartilage degeneration was evaluated in detail using India ink staining, routine histology, immunochemistry for denatured (Col2-¾M) and cleaved (Col2-¾Cshort) type II collagen, Mankin’s grading system, and cartilage thickness measurements. Results: Histologically, fibrillation and substantial immunohistochemical staining for both denatured and cleaved type II collagen were found in all three treatment groups. The cartilage of the three groups showed identical degradation patterns. In the 24 months implant group, degradation appeared to be more severe when compared to the 6 months implant group and meniscectomy group. Significantly more cartilage damage (India ink staining, Mankin’s grading system, and cartilage thickness measurements) was found in the 24 months implant group compared to the 6 months implant group and meniscectomy group. Conclusion: Degradation of the cartilage matrix was the result of both mechanical overloading as well as localized cell-mediated degradation. The degeneration patterns were highly variable between animals. Clinical application of a porous polymer implant for total meniscus replacement is not supported by this study.

In Vivo Performance of a Novel, Anatomically Shaped, Total Meniscal Prosthesis Made of Polycarbonate Urethane: A 12-Month Evaluation in Goats

Background: Injury or loss of the meniscus generally leads to degenerative osteoarthritic changes in the knee joint. However, the treatment options for symptomatic patients with total meniscectomy are limited. Therefore, we developed a novel, anatomically shaped, total meniscal implant made of polycarbonate urethane. Purpose: To evaluate the in vivo performance of this novel total meniscal implant. The assessment particularly focused on the implant's response to long-term physiological loading in a goat model and its chondroprotective capacity in comparison to clinically relevant controls. Study Design: Controlled laboratory study. Methods: Surgery was performed to the stifle joint of 26 female Saanen goats, subdivided into 4 groups: implant, allograft, total meniscectomy, and sham surgery. The sham group's contralateral joints served as nonoperated controls. After 12 months of follow-up, investigators evaluated implant wear, deformation, and the histopathological condition of the synovium and cartilage. Results: Wear of the implant's articulating surfaces was minimal, which was confirmed by the absence of wear particles in the synovial fluid. Implant deformation was limited. However, one implant failed by complete tearing of the posterior horn extension. No differences in cartilage histopathological condition were observed for the implant, allograft, and meniscectomy groups. However, locally, the cartilage scores for these groups were significantly worse than those of the nonoperated controls. Conclusion: Whereas this study demonstrated that the novel implant is resistant to wear and that deformation after 12 months of physiological loading is acceptable, reinforcement of the implant horns is necessary to prevent horn failure. Although the implant could not protect the cartilage from developing degenerative changes, the progression of damage was similar in the allograft group. Clinical Relevance: This novel polycarbonate urethane implant may have the potential to become an alternative treatment for symptomatic patients with total meniscectomy

Grafting a lubricious coating onto photo-crosslinked poly(trimethylene carbonate)

For biomaterial applications that involve moving parts such as artificial joints, lubricity is an essential property. Poly (trimethylene carbonate) networks are relatively hydrophobic. To create a lubricious layer, methacrylated poly(ethylene glycol) and methoxy-poly(ethylene glycol) were grafted onto poly(trimethylene carbonate) networks by photo-crosslinking. After conditioning for 24h in water, no delamination was observed, showing that the grafted hydrophilic layers were covalently attached to the poly(trimethylene carbonate) network. The lubricating properties were assessed by means of friction experiments, and the friction coefficients with relevant biomaterials were determined. It was shown that the grafting results in a significant decrease of the friction coefficients. These results show the potential of this approach to obtain lubricious materials for application in biomedical engineering. Copyright (C) 2015 John Wiley & Sons, Ltd

Uncatalyzed synthesis, thermal and mechanical properties of polyurethanes based on poly(ε-caprolactone) and 1,4-butane diisocyanate with uniform hard segment

Polyurethanes based on poly(ε-caprolactone) (PCL) (750–2800 g/mol) and 1,4-butane diisocyanate (BDI) with different soft segment lengths and constant uniform hard segment length were synthesized in absence of catalysts for the production of a degradable meniscus scaffold. First the polyesterdiols were endcapped with BDI yielding a macrodiisocyanate with a minimal amount of side reactions and a functionality of 2.0. Subsequently, the macrodiisocyanates were extended with 1,4-butanediol in order to obtain the corresponding polyurethane. The polyurethanes had molecular weights between 78 and 160 kg/mol. Above molar masses of 1900 g/mol of the polyesterdiol crystalline PCL was found while the hard segment showed an increase in melting point from 78 to 122 °C with increasing hard segment content. It was estimated that the percentage crystallinity of the hard segment varied between 92 and 26%. The Young’s modulus varied between 30 and 264 MPa, the strain at break varied between 870 and 1200% and tear strengths varied between 97 and 237 kJ/m2.