Traian V. Chirila

Poly(2-hydroxyethyl methacrylate) sponges as implant materials: in vivo and in vitro evaluation of cellular invasion

The pore size and the in vivo behaviour of four poly(2-hydroxyethyl methacrylate) sponges were investigated. The sponges were synthesized by polymerization of monomer in 70, 80 and 90 wt% water, respectively. In one of the formulations, a high amount of initiator was added. The average pore diameter was calculated with Ferrys equation and the results compared to those obtained by examination of samples using environmental scanning electron microscopy. The use of the equation greatly underestimated the size of pores. We also showed that the pores in polymers obtained in 70 wt% water were not interconnected, whilst the pores in polymers obtained in 80 and 90 wt% water, respectively, were larger and interconnected throughout the polymer. When implanted subcutaneously in rabbits, only the latter polymers allowed invasion and proliferation of cells. Penetration and proliferation of cells in these sponges were also assessed by an in vitro method using cultured human fibroblasts. The procedure included the overlaying of a glass plate covered by confluent cultured cells on to the surface of polymer impregnated with collagen. The depth of migration and number of sections needed to be cut to count a fixed number of invading cells were measured after incubation for 2 wk and used as indicators in comparing the ability of various sponges to allow cellular invasion. The assay showed that more cells invaded a hydrogel sponge produced in 80 wt% water than one produced in 90 wt% water. It also showed that the cut polymer surfaces allowed a greater cellular invasion than the moulded ones.

The use of synthetic polymers for delivery of therapeutic antisense oligodeoxynucleotides.

Abstract Developed over the past two decades, the antisense strategy has become a technology of recognised therapeutic potential, and many of the problems raised earlier in its application have been solved to varying extents. However, the adequate delivery of antisense oligodeoxynucleotides to individual cells remains an important and inordinately difficult challenge. Synthetic polymers appeared on this scene in the middle 1980s, and there is a surprisingly large variety used or proposed so far as agents for delivery of oligodeoxynucleotides. After discussing the principles of antisense strategy, certain aspects of the ingestion of macromolecules by cells, and the present situation of delivery procedures, this article analyses in detail the attempts to use synthetic polymers as carrier matrices and/or cell membrane permeabilisation agents for delivery of antisense oligodeoxynucleotides. Structural aspects of various polymers, as well as the results, promises and limitations of their use are critically evaluated.

An overview of the development of artificial corneas with porous skirts and the use of PHEMA for such an application

An overview of the efforts to develop functional polymeric artificial corneas (keratoprostheses) by incorporating a porous skirt is presented. The development of such a device by the authors group using poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels, as a combination of their homogeneous and heterogeneous states, and the rationale of this choice are also discussed. The latest results of the clinical trials with the PHEMA keratoprosthesis in human patients indicate a lower risk of the complications traditionally associated with the implantation of artificial corneas.

Keratoprostheses: Advancing toward a true artificial cornea

Keratoprosthesis surgery is carried out in very few centers. Elaborate surgical techniques and high complication rates limit the application of currently available keratoprostheses (KPros). However, the clinical need for an alternative to donor tissue has sparked considerable research interest in the development of new KPros. This paper charts the evolution of KPros from the earliest devices to those currently used, describes their drawbacks and discusses the specifications of an ideal device. Recent research focuses upon the use of porous polymers as the skirt component of core-and-skirt KPros in order to obtain improved biological integration of the prosthetic material. Developments in biomaterials technology make a KPro analogous to a donor corneal button an increasingly realistic goal. However, two particular problems still need to be addressed. First, it must be demonstrated that secure long-term fixation that is able to withstand trauma is achievable in a full-thickness artificial cornea. Second, an ideal artificial cornea for a wet eye requires an epithelialized surface, and this has yet to be achieved.

Corneal replacement using a synthetic hydrogel cornea, AlphaCor: device, preliminary outcomes and complications.

AbstractPurpose Clinical assessment of outcome of corneal replacement with a synthetic cornea, AlphaCor™, in patients considered at too high risk for conventional penetrating keratoplasty with donor tissue to be successful, but excluding indications such as end-stage dry eye that might be suited to traditional prosthokeratoplasty.Methods All patients in the multicentre clinical trial were managed according to an approved protocol, with Ethics Committee approval in each centre. Preoperative visual acuity ranged from perception of light (PL) to 6/60 (20/200). Implantation was by means of an intralamellar technique, with a conjunctival flap in most cases. Tissues anterior to the optic were removed as a secondary procedure.Results Up to 30 November 2001, 40 AlphaCor™ devices had been implanted in 38 patients, of mean age 60 years. Follow-up ranged from 0.5 months to 3 years. There had been one extrusion (2.5%) and four cases (10%) where a device had been removed due to melt-related complications. All five of these cases received a donor corneal graft after the device was removed, with these grafts remaining anatomically satisfactory and epithelialised to date. Corneal melts in AlphaCor™ recipients were found to be strongly associated with a history of ocular herpes simplex infection. Two further devices (5%) were removed owing to reduced optic clarity after presumed drug-related deposition, and have been successfully replaced with second devices. Mean preoperative best-corrected visual acuity was hand movements. Visual acuities after surgery ranged from PL to 6/6−2 (20/20−2).Conclusions Early results suggest that the AlphaCor™, previously known as the Chirila keratoprosthesis (Chirila KPro), has a low incidence of the complications traditionally associated with keratoprostheses and can be effective in restoring vision in patients considered untreatable by conventional corneal transplantation. Importantly, the device can be replaced with a donor graft in the event of development of a significant complication. A history of ocular herpes simplex is a contraindication to AlphaCor™ implantation. Ongoing monitoring of clinical outcomes in all patients will allow the indications for AlphaCor™, as opposed to donor grafts, to be determined.

Development and clinical assessment of an artificial cornea

Keratoprosthesis research has been a gradual, rather fragmentary process with advances being made by isolated groups of researchers. This has arisen partly because of poor funding in the area; research groups which have achieved commercial support have often had constraints upon the full disclosure of their findings. Despite these difficulties there has been real progress over the last decade by several independent groups. This article concentrates upon our own development of a hydrogel core-and-skirt keratoprosthesis, the Chirila KPro, in order to illustrate the scientific and clinical problems common to keratoprosthesis research. Pilot data from a clinical trial is presented and the priorities for future research are discussed.

The Chirila Keratoprosthesis: phase I human clinical trial

OBJECTIVE To undertake a preliminary safety and performance evaluation of an artificial cornea, the Chirila Keratoprosthesis, in human patients. DESIGN A prospective, interventional case series. PARTICIPANTS Fourteen consecutive patients with blindness of corneal origin not treatable by repeated standard penetrating keratoplasty. METHODS Keratoprostheses were manufactured and implanted. The patients, all with preoperative visual acuity of light perception to count fingers (CF), were followed clinically in adherence to a protocol. MAIN OUTCOME MEASURES Safety (keratoprosthesis retention, incidence of serious complications) and performance (visual acuity, comfort, appearance). RESULTS Ninety-three percent of keratoprostheses were retained to the date of reporting, up to 2.5 years. One keratoprosthesis (7%) was removed in a manner that restored the patients preoperative condition. All but one patient maintained their preoperative level of visual acuity or improved on it, with most achieving their estimated full potential visual acuity, (range, count fingers - 20/20). CONCLUSIONS This keratoprosthesis is acceptably safe and has demonstrated an ability to restore vision in cases in which alternative management would have had a poor prognosis. More extensive trials are warranted.

Silk fibroin in ocular tissue reconstruction

The silk structural protein fibroin displays potential for use in tissue engineering. We present here our opinion of its value as a biomaterial for reconstructing tissues of clinical significance within the human eye. We review the strengths and weaknesses of using fibroin in those parts of the eye that we believe are most amenable to cellular reconstruction, namely the corneoscleral limbus, corneal stroma, corneal endothelium and outer blood-retinal barrier (Ruyschs complex). In these areas we find that by employing the range of manufacturing products afforded by fibroin, relevant structural assemblies can be made for cells expanded ex vivo. Significant questions now need to be answered concerning the effect of this biomaterial on the phenotype of key cell types and the biocompatibility of fibroin within the eye. We conclude that fibroins strength, structural versatility and potential for modification, combined with the relative simplicity of associated manufacturing processes, make fibroin a worthy candidate for further exploration.

Biodegradation in vitro and retention in the rabbit eye of crosslinked poly(1-vinyl-2-pyrrolidinone) hydrogel as a vitreous substitute.

To elucidate the relatively short retention of crosslinked poly(1-vinyl-2-pyrrolidinone) hydrogels in the eye when used as potential vitreous substitutes, a 14C-labeled hydrogel was produced and subjected to both in vitro biodegradation assays and in vivo experiments. The polymer was synthesized by the free-radical copolymerization of 99% 1-vinyl-2-pyrrolidinone with 1% 14C-methyl methacrylate in the presence of ethylene glycol dimethacrylate (0.1%) as crosslinking agent. The in vitro protocol for assessing the biodegradation included the incubation of hydrogel with hydrolases (trypsin or collagenase), followed by examination of changes in its physical characteristics and by monitoring its residual radioactivity, as well as by detection of possible degradation products. Within the maximum duration of experiments (4 weeks), none of the procedures indicated biodegradation of polymer. The hydrogel was also injected into the vitreous humor of rabbits and followed up to 4 weeks. Residual radioactivity measurements of the vitreous contents indicated that 50% of the polymer was removed by the end of this period. Histopathologic examination revealed cell infiltrates of the mononuclear phagocyte system in both vitreous and retinal tissue. A possible phagocyte-mediated mechanism for the dissipation of hydrogel is discussed.

Poly(I-vinyl-2-pyrrolidinone) hydrogels as vitreous substitutes: Histopathological evaluation in the animal eye

A homopolymer of 1-vinyl-2 pyrrolidinone and its copolymer with 2-hydroxyethyl methacrylate, both cross-linked with divinyl glycol, were produced as possible substitutes for the vitreous body of the eye. The hydrated polymers behaved like viscoelastic gels, displaying excellent physical and optical properties. The sterile gels (0.7-1.5 ml) were injected into the vitreous cavity of rabbits, which previously underwent gas-mediated vitrectomy. Clinically, the eyes were quiet, with the exception of transient opacities in the vitreous. After 4 weeks, the operated eyes were enucleated and subjected to histopathological analysis using light and transmission electron microscopy. The common feature in all sections was the invasion of inflammatory cells. Vacuoles containing granular material, assumed to be polymer, were seen in the intercellular spaces of the neural retina, in the retinal pigment epithelium cells, and in macrophages. These findings indicated the fragmentation and phagocytosis of synthetic gels. It appeared that the biodegradation of the internalized polymers did not proceed further, however, the fate of polymers and their usefulness as vitreous substitutes should be investigated through long-term experiments.