Alloplastic materials

for plastic surgery residents

1. ALLOPLASTIC MATERIALS PRESENTER:DR YAWAR NISSAR SKIMS,SRINAGAR

2. INTRODUCTION Alloplastic material is synonymous with synthetic ,that is ,formed from non human ,non organic sources. Should not be confused with allografts,heterografts and xenografts. Provide off the shelf solutions to reconstructive tissue needs.

3. Their frequency of modern surgical use has been possible due to development of broad spectrum antibiotics and refinement of sterile operative fields. Implant materials have wide application in plastic surgery including reconstruction or augmentation of soft-tissue defects, bony deformities, or the fixation of fractures.

4. Selecting the implant material depends on the specific requirement for its application,eg, tissue ingrowth into a polypropylene mesh or the rigid incorporation of a bone substitute is often desirable,while the encapsulation (or lack of tissue ingrowth) of a silicone Hunter rod allows for free gliding of a subsequent tendon graft.

5. ` These synthetic implants are constructed from wide array of biomaterials,have diverse physical structure and properties,and can be placed in different human tissues ranging from bone to skin. Regulated by US FDA. Plastic surgeon second only to orthopaedic surgeon frequently uses large number of implanted biomedical devices.

6. Advantages No donor site morbidity from a second surgical site Reduced operative time compared with harvesting a graft Unlimited supply of alloplastic materials Prefabricated implants can be tailored to the individual patient Unlike autogenous materials (bone, cartilage, dermis, fat, fascia), there is no scar formation or reabsorption of the implant over time

7. BIOCOMPATIBILITY AND WOUND HEALING

8. Acute inflammatory response Chronic inflammation,granulation tissue development,foreign body reaction and fibrosis Endstage healing response to biomaterials is the formation of envelope/ fibroconnective tissue scar. Fibrous capsule is aimed to separate the body from the foreign material ,a biological barrier from self and non self

9. Classification

10. The ideal implant Biologically compatible Nontoxic Nonallergenic Produces no foreign body inflammatory response Mechanically reliable Resistant to resorption and deformation Nonsupportive of microorganism growth Easy to shape, remove, and sterilize Radiolucent (does not interfere with computed tomography [CT] or magnetic resonance [MR] scans

11. PREREQUISITES OF SELECTION AND SURGICAL PLACEMENT

12. POINTS TO REMEMBER Appropriate matching of tissue plane within which it is to be inserted should be seriously considered. Decreased vascularity ,eg, as a result of multiple surgeries or irradiation compromised formation of normal fibrovascular tissue capsule and limited inflamatory response if infected secondarily.

13. TECHNICAL POINTS Soft tissue coverage –as thick as possible. Thinner the overlying tissue –increased likelihood of implant extrusion or exposure More deeply placed alloplastic material (subperiosteal,subgaleal,submuscular,subfascial) rarely develop exposure Alloplastic tolerance is very low for less than clean tissue pocket or sterile placement technique.

14. TECHNICAL POINTS Implant mobility should be minimised by fixation to adjacent most stable structure whenever possible. 2. Placing the incision as far as possible from the implant, handling the implant gently Shaping the edges to avoid hard corners 4. Patients undergoing alloplastic biomaterial placement should receive iv antibiotic during placement followed by oral course. 5. Additional antibiotic coverage is achieved by washing and soaking the implant before insertion.

15. 6 . More hydrophillic the implant—more the antibiotic impregnation. 7. Extensive handling or exposure before insertion should be avoided 8. Implant contact with the surrounding skin should be minimised to prevent final source of bacterial transmission to implant surface.

16. Oppenheimer effect In 1948, Oppenheimer reported that metal implants placed in experimental animals could induce tumors Composition of the material was unimportant Maximal tumorigenesis occurred when the material had a smooth, continuous surface. Minimum size requirement (0.5 × 0.5 cm in rats) and a minimum time requirement for the implant to remain in situ (6 months in rats). Tumors appeared after a latent period of approximately 300 days.

17. ALLOPLASTIC IMPLANT TYPES DIMETHYLSILOXANE (SILICONE) Long clinical history dating back to 1950s Initially implanted as urethral replacements and vp shunts Silicone is a polymer formed from silicon and oxygen Only non carbon chain polymer used in all medical implantations

18. Monomers of dimethylsiloxane formed are extremely resistant to degradation in body due to strong and stable silicon oxygen bonds.

19. When monomers of dms are linked--- polydimethylsiloxane is formed Amount of cross linking leads to various physical forms. Minimal cross linking—gel Silicon gel+ silica particles ---solid rubber wide variety of clinical use from thin breast implant shells to solid facial implants.

20. SOLID SILICONE One of the earliest alloplastic implant used in plastic surgery Implants can be used for chin,parasymphysis,inferior border,ramus,paranasal,infraorbital,maxillary,malar,orbital floor ,globe,nasal dorsum, columella ,ear,hand,wrist for joint arthoplasty,and tendon reconstruction

21. Advantages of solid silicone: easy sterilization by steam autoclaving or irradiation without degradation of implant easy intraoperative modification by scissors retained flexibility through a wide range of temperature stabilization by suture or screw fixation fairly economical price

22. 6. High degree of chemical inertness,hydrophobic,resistant to degradation 7. No significant allergic reaction 8. Tissue ingrowth to the implant does not occur

23. Disadvantages of using silicone include (1) a propensity of silicone rubbers to tear easily or fail in heavy stress applications (e.g., Swanson finger joint implants) (2) difficulty removing silicone gel from soft tissues in the case of implant failure, (3) bone resorption beneath silicone implants placed subperiosteally for augmentation (e.g., chin), (4) their “smoothness” makes them prone to extrusion when placed superficially (e.g., Silastic placed in the nose or ear)

24. (5) Silicone rubbers are permeable, allowing proteins or lipids to become adsorbed onto the surface of an implant, which may alter its physical properties and lead to failure. Extensive investigations by several prestigious scientific bodies have failed to show that systemic illness is associated with silicones. Anaplastic large cell lymphoma in breast implant recipients ? is still under trail

25. SILICONE FLUID Silicone liquid or gel—not as inert. Increased fibroplastic response with tendency to migrate. Can be broken down to smaller particles---macrophage phagocytosis. chronic inflammatory response,granuloma formation.

26. Thus silicone liquids and gels should not be injected in human tissues When placed in containment sac---eg elastic silicone shell—this reaction does not occur. Due to silicon implant shell aging,patients should be monitored anually and implant replacement considered after 15 – 20 years to prevent implant shell disruption.

27. In order to modify the soft tissue encaptulation response,outer implant shell alteration has been studied for long time. Textured silicone surface has a lower tendency for capsular contraction compared to smooth surface.

28. Histologically,flat and smooth breast implant surface—fibrous capsule with colagen fibers oriented parallel to surface Textured breast implant—collagenous capsule with multidirectional fiber orientation and increased tendency for pseudoepithelial lining at inner surface with presence of synovial metaplasia and villous hyperplasia

29. Polytetraflouroethylene Carbon based,with use in almost every surgical and dentistry speciality Cabon ethylene backbone with attached flourine molecules Not biodegradable in body due to lack of any human enzyme to disrupt carbon flourine bonds.

30. Its surface is non adherent with antifrictional properties. Flexible with low tensile strength. PTFE first introduced in plastic surgery in 1980s for facial skeletal augmentation as proplast 1 (ptfe +graphite),proplast 2 (ptfe+alumina),proplast –HA (ptfe +hydroxyapatite).

31. Nowadays used as subcutaneous augmentation material Also used in sutures,vascular prosthesis,soft tissue patches Variety of blocks,preformed implants,strips and strands are available for facial augmentation from subperiosteal to subdermal placement.

32. Ptfe fibrils with Surface openings with pore size between 10 to 30 micrometer Some soft tissue ingrowth Less fibrous encapsulation Little migration

33. ADVANTAGES Easily shaped with scalpel and scissors Stable at temperatures upto 325 degree f Can be anchored to adjacent tissues by sutures or screws. Easily removable in cases of infection Long history with established clinical safety

34. Used as subdermal lip implants,nasolabial folds,glabella,nasal dorsum,slings for ptotic tissues of eyelid and face and bony augmentation of malar,midface and mandibular areas. Comparatively expensive

35. Polyethylene Simple carbon chain with lack of fluorination Three grades available Low density High density Ultr high density

36. Ultra high density used ---load bearing orthopaedic implants High density used in plastic surgery because of high tensile strength,firm consistency and flexible

37. ADVANTAGES Initially used as a mesh for abdominal and chest wall reconstruction because of superior tensile strength. Fibrous ingrowth leads to stabilization of implant Can be loaded with antibiotics by syringe vacuum impregnation Drilling and fixation possible Cost friendly

38. Disadvantages More difficulty with removal Intraoperative shaping more difficult

39. Medpor is available in sheets and blocks that can be sculpted at the time of surgery. Used for chin augmentation, malar augmentation, and microtia reconstruction (placed beneath a temporoparietal fascial flap). It is useful for orbital floor blowout fractures and as a columellar strut for cleft rhinoplasty. Medpor implants become adherent to the surrounding bone, whereas silicone implants on the facial skeleton undergo fibrous capsule formation without fixation to bone.

40. Polyesters Most widely used family of biomaterials Include diverse group of surgical devices (suture,mesh,vascular conduits,plates and screws) Composed of large polymers with ester linkages between carbon bonds. Most comonly recognised as synthetic meshes eg dacron,mersiline .

41. Multifilament mesh is non reactive,non resrbable and becomes encased in interwoven fibrous tissue matrix Primarily used in genioplasty procedures in plastic surgery(inserted as an onlay in symphyseal region)

42. Can be fixed without palpable edges Other use include: bone fixation device These plates and screws included polylactic acid (hydrophobic) and polyglycolic acid (hydrophillic) Maintain low strength for 6 to 8 weeks before resoption (about 1 year) Pure PGA was first marketed as Dexon suture; Vicryl suture is a mix of 8% PLA and 92% PGA.

43. Resoption occurs by hydrolysis with separation of ester linkage metabolic response by fibrovascular ingrowth and macrophage recruitment to clear debris

44. Polyamides Derivatives of nylon ,known clinically as mesh material. Hydroscopic and unstable in vivo Historically used for nasal contouring and augmentation genioplasty Very rarely used nowadays

45. Acrylic Derived from polymerised esters Historically used as bone cement for joint prosthesis Polymethylmethacrylate resin is fabricated intraoperatively by mixing liquid monomer with powdered polymer. Exothermic reaction creating rigid plastic

46. PMMA is impervious,non biodegradable, Tolerated in body with an avascular fibrous capsule Used in plastic surgery in cranioplasty for filling full thickness cranial defects,or in secondary forehead contouring

47. Advantages: Low cost Intraoperative fabrication and adaptation possible Can be autoclaved and antibiotic impregnated Disadvantages : Offensive odour that can cause allergic reactions High temeratures require cool irrigation to prevent thermal damage Very high bacterial adhesion property,so not tolerated well once infected

48. Distinct variety of PMMA known as hard tissue replacement ---pmma+polyhydroxyethylmethacrylate Resultant material---increased strength,interconnected porosity,calcium hydroxide coating imparting negative surface charge Used as preformed craniofacial implant custom made to patients defect

49. Metals Used for skull reconstruction,reconstruction of craniofacial and upper extremity skeletal injuries Their biocompatibility determined by surface properties and corrosion resistance After implantation ,an oxide layer quickly forms over metal surface which determines resistance to corrosion

50. Corrosion +metal ion release pain and localized tissue reaction neccesating removal Stainless steel,vitalium,titanium are the main metals used

51. Stainless steel Alloy of iron,nickel,molybdenum with chromium oxide Higher corrosion potential and metal ion release Inceased allergic reactions due to nickel No permanently implanted materials presently available

52. Vitalium Was introduced to overcome corrosion problem with stainless steel Cobalt chromium alloy with comparable strength to stainless steel Highly resistant to corrosion due to high concentration of chromium although it also forms surface chromium oxide Lost its popularity due to radiographic imaging and artifact scatter concerns

53. Titanium Pure metal and thus no allergy,toxicity,tumourigenesis Available as pure titanium or as an alloy with small amount of other metals (6%aluminium) which improves strength Forms titanium oxide surface layer—resistant to corrosion Even if oxide layer damaged,it reforms in milliseconds

54. Advantages Low density of metal allows minimal x ray attenuation and lack of artifact on CT and MRI Associated with concept of osseointegration

55. Osseointegrated percutaneous implants give the ability to attach a prosthesis to an implant that is anchored to bone but is penetrating the skin or mucosa first stage a titanium implant is placed into bone and buried underneath the periosteum or soft tissues for 3 months to provide osseointegration. second stage the implant is uncovered and a permanent prosthesis is made for fixation to the implant. The implant must be absolutely stable during the first 3 to 6 months of healing, or connective tissue rather than bone may form at the implant surface

56. Newest application:bone anchored suturing device

57. Gold Historically used to repair cleft palate Does not develop oxide layer after implantation Lack of strength and expensive although tolerated exceptionally well in body Presently only surgical use is upper eyelid implant for treatment of acquired ptosis.Produced from 99.99% gold and available in different shapes and sizes and weight between 0.6 to 1.6gm. Platinum is an inert metal and is the material of choice for patients with gold sensitivity in need of eyelid implants for lagophthalmos.

58. Calcium phosphate It is Bioactive(capable of osteoconduction) and develop actual tissue ingrowth and integration into recipient site Provide a substrate into which new bone from adjacent surface is deposited Almost all manufactured as hydroxyapatite Ca10(PO4)6(OH)2 (pricipal 70% component of bone)

59. BoneSource is a synthetic HA cement that was first used clinically in 1991. When mixed with water and a drying agent (sodium phosphate), BoneSource powder forms a paste that hardens to form a microporous implant within 15 minutes.( biocompatible, no inflammatory tissue response, ease of application, low infection rate).

60. Alloderm AlloDerm is acellular dermal matrix (“cadaver skin”) commonly used in cosmetic procedures such as lip grafting. It is rendered immunologically compatible by chemically removing all immunoreactive components (epidermis, antigenic cell components) while leaving the collagen/elastin structure of skin intact. It has been used in reconstructive surgery to induce granulation tissue over exposed bone and tendon in refractory wounds.

61. Fibrin Tissue Adhesives Fibrin sealants consist of two parts: fibrinogen and thrombin ( derived from screened donors) A small amount of factor XIII and calcium is included to catalyze the reaction and form polymerized fibrin. The strength of the fibrin glue is directly proportional to the concentration of fibrinogen in the mixture, while the rate of polymerization is regulated by the concentration of the thrombin. Plastic surgery applications for fibrin sealants include brow lift, facelift, abdominoplasty, the latissimus dorsi donor site, DIEP/TRAM flap donor sites, and chronic seromas

62. Cyanoacrylate Studied for diverse applications like tissue adhesion,wound closue,vascular embolization,hemostasis,and application of skin grafts Handling problems and histotoxicity limit the use Adverse tissue reactions due to biproducts cyanoacetate anf formaldehyde

63. Butyl -2 cyanacrylate and octyl 2 cyanoacrylate(dermabond) has been aproved for skin closure in US Dermal suture support is still needed and adhesive applied over skin to prevent it from entering the wound Cost is twice that of nylon suture to cover same length wound. Dermabond polymerizes within 1 minute and begins to peel off in 7 to 10 days.

64. Management of Alloplastic infection Complications include migration,extrusion,palpability and most commonly infection Occurs in two phases: Initial reversible physical phase(physiochemical interaction between bacteria and material surface) irreversible cellular phase(cellular interaction between bacteria and material surface)

65. Ist phase can be reversed by mechanical washing and irrigation 2 nd phase involves bacterial capsules,pilli and slime biofilm,colonization,reduction in antimicrobial agent effectiveness,protection against phagocytosis

66. Ist phase occurs intraoperatively and 2 nd phase in immediate postoperative period Infections occuring years after implantation are attributed to hematogenous spread or by violation of capsule(needle injection,secondary surgery) Once purulent infection occurs—drainage and removal of implant is advisable

67. Reimplantation avoided for 3 to 6 months to allow complete resolution of infection Sterization of implant—reinsertion—prolonged postoperative antibiotic course

68. Various determining factors are: Chemical composition of material(st.epidermidis –polymer implant infection,st aureus –metal implant infection) Surface roughness(irregular surface promote bacterial adhesion) Surface configuration(porous material surfaces) Surface hydrophobicity(more resistant)

69. Thank you