Biomedical subjects

Albert J Pennings

Publications and source records attributed to Albert J Pennings.

4 recordsLinked to original sources

PubMed2005

Replacement of the knee meniscus by a porous polymer implant: a study in dogs.

BACKGROUND: Meniscectomy will lead to articular cartilage degeneration in the long term. Therefore, the authors developed an implant to replace the native meniscus. HYPOTHESIS: The porous polymer meniscus implant develops into a neomeniscus and protects the cartilage from degeneration. STUDY DESIGN: Controlled laboratory study. METHODS: In a dog model, a porous polymer scaffold with optimal properties for tissue infiltration and regeneration of a neomeniscus was implanted and compared with total meniscectomy. The tissue infiltration and redifferentiation in the scaffold, the stiffness of the scaffold, and the articular cartilage degeneration were evaluated. RESULTS: Three months after implantation, the implant was completely filled with fibrovascular tissue. After 6 months, the central areas of the implant contained cartilage-like tissue with abundant collagen type II and proteoglycans in their matrix. The foreign-body reaction remained limited to a few giant cells in the implant. The compression modulus of the implant-tissue construct still differed significantly from that of the native meniscus, even at 6 months. Cartilage degeneration was observed both in the meniscectomy group and in the implant group. CONCLUSION: The improved properties of these polymer implants resulted in a faster tissue infiltration and in phenotypical differentiation into tissue resembling that of the native meniscus. However, the material characteristics of the implant need to be improved to prevent degeneration of the articular cartilage. CLINICAL RELEVANCE: The porous polymer implant developed into a polymer-tissue construct that resembled the native meniscus, and with improved gliding characteristics, this prosthesis might be a promising implant for the replacement of the meniscus.

Animals↗

PubMed2005

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

Polyurethanes based on poly(epsilon-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 degrees 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.

Absorbable Implants↗

PubMed2002

Tissue ingrowth and degradation of two biodegradable porous polymers with different porosities and pore sizes.

Commonly, spontaneous repair of lesions in the avascular zone of the knee meniscus does not occur. By implanting a porous polymer scaffold in a knee meniscus defect, the lesion is connected with the abundantly vascularized knee capsule and healing can be realized. Ingrowth of fibrovascular tissue and thus healing capacity depended on porosity, pore sizes and compression modulus of the implant. To study the lesion healing potential, two series of porous polyurethanes based on 50/50 epsilon-caprolactone/L-lactide with different porosities and pore sizes were implanted subcutaneously in rats. Also, in vitro degradation of the polymer was evaluated. The porous polymers with the higher porosity, more interconnected macropores, and interconnecting micropores of at least 30 microm showed complete ingrowth of tissue before degradation had started. In implants with the lower macro-porosity and micropores of 10-15 microm degradation of the polymer occurred before ingrowth was completed. Directly after implantation and later during degradation of the polymer, PMN cells infiltrated the implant. In between these phases the foreign body reaction remained restricted to macrophages and giant cells. We can conclude that both foams seemed not suited for implantation in meniscal reconstruction while either full ingrowth of tissue was not realized before polymer degradation started or the compression modulus was too low. Therefore, foams must be developed with a higher compression modulus and more connections with sufficient diameter between the macropores.

Animals↗

PubMedDate not supplied

Hydrogels for an accommodating intraocular lens. An explorative study.

In this study it was investigated whether hydrogels could be used for an accommodating lens. The requirements of such a hydrogels are a low modulus, high refractive index, transparency, and strength. Since conventional hydrogels do not possess this combination of properties, a novel preparation method and new polymers are introduced. As starting materials poly(1-hydroxy-1,3-propanediyl), poly(ethylene-co-vinyl alcohol), poly(vinyl alcohol), and poly(allyl alcohol) were used. The first three were cross-linked with a number of diisocyanate compounds. Network formation was performed at low concentrations in a good solvent. Mixing of the polymer solution and cross-linker appeared to be crucial for transparency. Poly(1-hydroxy-1,3-propanediyl), cross-linked with a slow reacting diisocyanate block, shows the most promising properties with respect to refractive index, transparency, tensile strength, and modulus. Poly(allyl alcohol) hydrogel was made by compression molding. The hydrogel was transparent and had a high refractive index and low modulus. It was concluded that hydrogels could be used as accommodating lens material.

Accommodation, Ocular↗