Hwb Jansen

DEGRADATION OF AND TISSUE REACTION TO BIODEGRADABLE POLY(L-LACTIDE) FOR USE AS INTERNAL-FIXATION OF FRACTURES - A STUDY IN RATS

Samples of high-molecular-weight poly(L-lactide) (PLLA) (Mv = 9.0 x 10(5), a biomaterial developed for plates and screws used in internal fixation of jaw fractures, were implanted subcutaneously in the backs of rats to study tissue reaction to PLLA and to follow the degradation process. The PLLA seemed to follow the degradation pattern typical of biodegradable polyesters. After pure hydrolysis up to about 104 wk, phagocytic activity of macrophages was found at about 143 wk. Full resorption of PLLA was not demonstrated in this study. Except for the early and final parts of the implant period, no acute or chronic inflammatory reaction was observed. No implant was rejected. It is estimated that more than 3 yr will be required for total resorption of PLLA. For bone-healing this long period is of no practical importance. There is no need for removal of PLLA after fracture healing as is the case with metal fixation devices. Thus, PLLA has potential application in internal fixation of fractures and osteotomies in the maxillofacial region and other fractures that are not too heavily loaded in the human body.

Use of porous polyurethanes for meniscal reconstruction and meniscal prostheses

In the past, porous materials made of an aromatic polyurethane (PU) were successfully used to meniscal reconstruction in dogs. Since aromatic PUs yield very toxic fragments upon degradation, a linear PU was synthesized by curing a poly(epsilon-caprolactone) and 1,4-trans-cyclohexane diisocyanate based prepolymer with cyclohexanedimethanol. Porous materials of this polymer were also implanted for meniscal reconstruction. The results were comparable with the most successful implant series so far. Additionally, a porous meniscal prosthesis was developed to replace a total meniscus. Due to the very high shear stresses to which the prosthesis would be exposed, the stress hysteresis phenomenon linear PUs are known to exhibit could be of great consequence. Therefore an aliphatic PU network, synthesized by cross-linking poly(epsilon-caprolactone) and 1,4-trans-cyclohexane diisocyanate with glycerol, was used. Dislocation caused by tearing out of the sutures was found to be a problem because the tear resistance of the material was relatively low. In this study the tearing problem has been partly circumvented by using a complex suturing technique. Meniscal prostheses turned out to induce fibrocartilage upon implantation, and degeneration of articular cartilage was less severe than after meniscectomy.

Meniscal tissue regeneration in porous 50/50 copoly(l-lactide/ε-caprolactone) implants

Abstract Porous materials of a high-molecular-weight 50/50 copolymer of l -lactide and ɛ-caprolactone with different compression moduli were used for meniscal repair. In contrast to the previously used 4,4′-diphenylmethane and 1,4- trans -cyclohexane diisocyanates containing polyurethanes, degradation products of the copolymer are non-toxic. Two series of porous materials with compression moduli of 40 and 100 kPa respectively were implanted in the knees of dogs using a new, less traumatizing suturing technique. A porous aliphatic polyurethane series with compression modulus of 150 kPa was implanted for comparison. Adhesion of the implant to meniscal tissue was found to be essential for healing of the longitudinal lesion. Copolymer implants showed better adhesion, probably due to the higher degradation rate of the copolymer. Fibrocartilage formation was found to be affected by the compression modulus of the implant. Implants with a modulus of 40 kPa did not show ingrowth of fibrocartilage, whereas implants with compression moduli of 100 and 150 kPa yielded 50–70 and 80–100% fibrocartilage respectively. During degradation the copolymer phase separated into a crystalline phase containing mainly l -lactide and an amorphous phase containing mainly ɛ-caprolactone. The copolymer degraded through bulk degradation.

Effects of compressive forces on proliferation and matrix synthesis in mandibular condylar cartilage of the rat in vitro

The cartilage from 4-day-old rats were exposed to continuous and intermittent compressive forces. Proliferative activity and matrix synthesis in vitro were determined by measuring the incorporation of [3H]-thymidine, [35S]-sulphate and [3H]-proline by autoradiography and liquid-scintillation counting. The findings suggest that a continuously-applied force of approx. 0.5 g stimulated proliferation in the condylar cartilage but reduced the synthesis of the sulphated glycosaminoglycans and collagen. A stimulatory influence on the synthesis of these matrix components, on the other hand, was observed when the condylar cartilage was exposed to an intermittent force (0.7 Hz) of approx. 0.5-1.0 g; this intermittent force, however, reduced the proliferative activity. It appears that, at least in vitro, the basic growth processes in the condylar cartilage can be regulated by compressive forces.

Porous polymer implant for repair of meniscal lesions: a preliminary study in dogs

Artificial meniscal lesions extending into the avascular part of the meniscus, which do not heal by any other means, were repaired by suturing either a porous polymer implant or a synovial flap into the defect. The implant guided the ingrowth of vascular repair tissue into the defect. This fibrous tissue later on transformed into fibrocartilage. Reconstruction with a synovial flap was not successful. It appeared that healing can be achieved by implantation of a porous polymer implant in a large number of cases. Future research will be aiming at improvement of the results of meniscal repair and application of this type of polymer for repair of cartilage defects.

Meniscal replacement using a porous polymer prosthesis : A preliminary study in the dog

A porous polyurethane prosthesis was used to replace the lateral meniscus in the dog. After an initial ingrowth of fibrous tissue, the prostheses became filled with tissue strongly resembling normal meniscal fibrocartilage. Although less severe than seen after total meniscectomy, cartilage degeneration was frequent, possibly because tissue ingrowth in the prostheses occurred too slowly. Porous polymers can be useful for replacement of the meniscus, provided that chemical and physical properties are optimized.

BONE-PLATES AND SCREWS OF BIOABSORBABLE POLY (L-LACTIDE) - AN ANIMAL PILOT-STUDY

Poly (L-lactide), a polymer of lactic acid (PLLA), with an extremely high molecular weight (Mv up to 1 x 10(6] has been synthesised under strictly controlled conditions resulting in a new microporous material with excellent mechanical properties. Bone-plates and screws machined from PLLA were used for fixation of two artificial mandibular fractures in sheep effected by a specially designed bone clamp. Fracture healing was uneventful without visible callus formation. Plates and screws of PLLA gave good stability over a sufficiently long period to enable normal fracture healing. Application in humans seems to be justified.

Use of porous biodegradable polymer implants in meniscus reconstruction. 1) Preparation of porous biodegradable polyurethanes for the reconstruction of meniscus lesions

Porous biodegradable poly(urethanes) for reconstructing menisci have been prepared using two different combinations of techniques: freeze-drying/salt-leaching and in-situ polymerization/salt-leaching. Using these methods, homogenous porous materials with a controllable and reproducible morphology can be prepared. The materials were made of three different poly(urethanes): a methylenediphenyldiisocyanate-based polyurethane, a lysine diisocyanate-based poly(urethane), and a poly(ɛ-caprolactone)-based poly(urethane). The compressive stress-strain behavior of the Estane foams was determined. Foams made by the freeze-drying/salt-leaching technique implanted in dogs showed healing and good ingrowth of fibrocartilaginous tissue.

MUSCLE-FIBER TYPES AND MUSCLE-SPINDLES IN THE JAW MUSCULATURE OF THE RAT

The fibre composition and occurrence of muscle spindles was studied in the masticatory, the suprahyoid and the infrahyoid muscles of the rat. Muscle fibres were typed as fast-white, fast-intermediate, fast-red and slow-red according to their ATPase and SDH activity. Fibre type appeared to be closely related to fibre diameter. In most of the muscles, all four fibre types were found. Slow-red fibres were absent in the superficial masseter, the transverse mandibular and the omohyoid muscles; fast-white fibres were absent in the mylohyoid muscle. The masticatory muscles were mainly composed of the three fast-fibre types; the jaw-opener muscles (the anterior digastric, the posterior digastric, the posterior digastric, the stylohyoid and the lateral pterygoid muscle) showed more slow-red fibres. In the masticatory and most of the suprahyoid muscles, the slow-red fibres were restricted to an area with high SDH activity. In the infrahyoid muscles, the fibre types were evenly distributed. Many muscle spindles, often clustered, were found in the masticatory muscles, except in the lateral pterygoid. In most of the suprahyoid muscles, these sensory structures were absent. In the infrahyoid muscles, solitary muscle spindles were found.

EXPERIMENTAL MENISCAL LESIONS RECONSTRUCTED WITH A CARBON FIBER-POLYURETHANE-POLY(L-LACTIDE) GRAFT

Reconstructive procedures were investigated in meniscal lesions in 14 dogs. Large wedge-shaped lesions were repaired with a graft containing carbon fibers and an organic polymer, prepared from physical mixtures of poly(L-lactide) and a segmented polyurethane. Four and eight weeks postoperation, arthroscopy was performed and the implants were excised. In ten dogs, the reconstructed area appeared to be invaded almost completely by fibrous tissue and, occasionally, by repair-simulating hyaline cartilage. There were no signs of infection.