Journal of Tissue Viability 1992 Vol. 2 No 3 75

DERMIS IMPLANTS CONTAINING ANGIOGENIC FACTORS: AN ALTERNATIVE APPROACH TO SKIN

WOUND HEALING HUGO BURGOS

Clinical Scientist, Blond Mcindoe Centre for Medical Research, Queen Victoria Hospital, East Grinstead, Sussex

SUMMARY Use of dermal implants for the treatment of skin wounds carrying loss of tissue has regained considerable interest in the last few years. Allogenic and xenogeneic dennis and dermal collagen membranes have been implanted to replace lost tis­sues and give a substratum for cultured keratinocytes. These techniques rely on retarding the absorption of the dermal implant. Collagen synthesis and organisation of a new dermal matrix, however, are extremely slow. On the other hand, results of experimental studies with dennis implants containing pla­cental angiogenic and growth factors have shown accelerated collagen deposition and incorporation of dermal implants. Speeding the rate of collagen synthesis and dermal implant incorporation is put forward as an alternative approach for the treatment of skin wounds.

INTRODUCTION Healing and repair of wounds carrying loss of skin, especially burns, are slow in man, even under the most favourable condi­tions for treatment, and they often leave a sequela of scar formation. Autologous skin grafts are used as a treatment of choice but these all too often are not sufficient to cover extensive wounds. Research in the last decades has focused on the development of alternative ways of treatment. Cultured epidermis has been used for the treatment of skin wounds, in particular bums. The take of cultured epidermis autografts, however, currently runs at only 30 per cent even after transfer of successfully cultured epithelium1

, and contraction of the wound and scar inevitability appear even with split-thickness skin autografts 2

• Presence of a dermal bed appears to be an essential requirement for take and differentiation of cultured epidermis 3•

4• s, and presence of a dermal matrix for prevention

of wound contraction and scar formation 2• Studies on freeze injury (as opposed to burn injury) have shown that non­denaturated, residual dermal matrix prevents wound contrac­tion 6• Furthermore, if only epithelial and mesenchymal cells, but not matrix, are present in the wound bed, healing proceeds without evidence of actual skin regeneration s. An increasing amount of information provides evidence that dennis and dermal biomaterials may be useful in the treatment of skin wounds, particularly those involving loss of tissues. Two different approaches seem more promising along these lines: the development of biomaterials or extra-cellular matrices to temporarily replace lost tissues and cover the wound until the healing process can take over, and the development of biologic control methods to regulate the various phases of wound healing 7•

Mature collagen implants 8 and trypsin treated dermis implants have been used for replacement of lost or damaged skin 9,

10•11•12•

13•14

•2

• Mature, insoluble collagen and trypsin purified dermis are weaklyornon-antigenic,evenacrossspecies8•2• Trypsinremoves

all cellular elements of skin implicated in the immune rejection leavinganintact,cell-freederrnalmatrixofcollagenandelastin2• To be of practical use, however, dermal collagen implants should maintain their mass and, as far as possible, their original bundle architecture 2, yet degradation and absorption of dermal implants occurs much faster than collagen synthesis. Dermal implants loose 65 per cent of their original collagen after 20 weeks in incised skin wounds in the isogeneic rat while collagen synthesis reaches only 10 per cent mass replacement13• Crosslinking of dermal implants by aldehyde pretreatment has increased their stability and retarded collagen degradation and absorption. Collagen loss has been reduced to 55 per cent by formaldehyde cross linking and 15 per cent by glutaraldehyde cross linking but collagen synthesis remains at the same low leveJI2• This is in contrast with skin homo grafts which also show 60 to 85 percent collagen loss at 20 weeks in isogeneic rats but this loss is matched by new collagen so that virtually no net loss of tissue mass occurs 15

•16

• 2

• This is an ideal process of remodelling and incorporation of the graft, where the rate of degradation and absorption of graft collagen is exactly matched by the rate of synthesis and deposition of new collagen. Epithelialization over dermis implants also occurs slowly, taking 4 to 5 weeks in skin wounds measuring 1 x 1 em in the rat 9• 10

•

On the other hand, placental angiogenic and growth factors produced enhanced angiogenesis, increased granulation and epithelial tissue, and accelerated rate of healing during the treatment of chronic ulceration of the legs in man 17

• 18

• 19 and accelerated incorporation of dermal implants in the rat20•

Moreover, placental growth factors can easily be incorporated in carrier and deli very biomaterials for topical application 21

• A combination of both systems may improve or solve this prob­lem: dermis allografts containing angiogenic and growth fac­tors may accelerate synthesis and deposition of collagen to match the rate of degradation and absorption of the collagen imp~nt.

DISCUSSION The rationale behind the use of crosslinked collagen based biomaterials and skin substitutes, and indeed all skin grafts, stands on retarding degradation and absorption of the implant or graft until the healing process can take over. Crosslinked allodermis implants maintained to a large extent their original size in skin wounds in the rat10

, and showed no evidence of absorption after 3 year subcutaneous implantation in man 22•23•

This, on the other hand, shows lack of dermal implant incor­poration. The rationale behind our studies stands on acceler­ating the rate of healing to match the rate of degradation and absorption of the dermal implant. Results of our studies show a rich vascularization and granulation tissue invading the implant at 3 days post-implantation, and well established

76 Journal of Tissue Viability 1992 Vol. 2 No 3

epithelialization at 7 days post-implementation 18• This is in

contrast with the slow vascularization and fibroblast coloniza­tion found in crosslinked dermal implants taking 2 to 5 weeks in the rat. Human studies showed the presence of fibroblasts at 6 to 36 months10

•22

•23

•

Thickness of the graft is an important feature for the outcome of collagen turnover, maintenance of graft viability and good quality healing. Skin grafts lose collagen at the same rate regardless of their thickness, about 85 per cent collagen loss in 20 weeks in isogenic rats. Thin full-thickness skin grafts, however, do better than thick full-thickness and split-thickness skin grafts. The thick full-thickness skin graft being too thick for survival heals poorly, with slough of the upper layers, and contracting all the time15

• 16

• Meshing of the graft seems to make graft thickness less important in our studies as, under the effect of placental angiogenic and growth factors, vascularization and granulation invasion occur quickly through the unexpanded dermal mesh 20• Meshing of the implant and light trypsinization do not appear to compromise the native structure of the dermis. Preservation of dermal structure has been considered important for skin regeneration5

• 24• Dermis allografts containing ang­iogenic and growth factors may thus provide a suitable bed not only for cultured epidermis but for skin grafts as well. The remarkably enhanced vascularization produced by these fac­tors should quickly establish adequate blood supply. This is particularly important in the treatment of bums where angio­genesis is slow to start and slow to proceed 25 •

It is interesting to consider our studies in connection with the transplantation of intermingled, sandwich and composite skin grafts, including those using keratinocyte suspensions and cultured epithelium 26

• 27

• 28

• 29

• 30

• 31

• 32

• These techniques also stand on retarding degradation and absorption of the dermal matrix. Progressive cellular replacement takes place in the dermal allograft in the first 5 to 6 weeks33 but degeneration of the allodermal collagen and invasion by granulation tissue last for months after grafting26

• Apart from the state of immuno­suppression that undoubtedly plays a role in bum hosts, the prolonged acceptance of dermis allografts has, in these cases, been explained on bases of the low antigenicity exhibited by fibroblasts34

• 35 and collagen fibres36

• Lack of antigenicity of cell-free dermal matrix has been previously reported15

• 8

• Ef­fects oflocal immunosuppressive mediators has been suggested by other workers37

• Various mechanisms may, indeed, play a role in allodermal graft survival.

The short life and short range of tissue penetration of placental growth factors, and the margin of growth factor concentrations showing biological activities make them suitable for repeated and carefully controlledadministration21

• This techinque should allow the factors to exert their initiator as well as their modu­lator effects on the wound healing process without adversely affecting normal healing.

ACKNOWLEDGEMENT This work was supported by grants from the East Grinstead Medical Research Trust.

ADDRESS FOR CORRESPONDENCE Mr H Burgos (Retd) c/o Blond Mcindoe Centre for Medical Research, Queen Victoria Hospital, East Grinstead, Sussex RH193DZ

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11. Oliver R F, Grant R A, Cox R W, Cooke A. Effect of aldehyde cross-linking on human dermal collagen implants in the rat Br J Exp Path 1980; 61: 544-9.

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13. Oliver R F, Barker H, Cooke A, Stephen L. 3H-collagen turnover in non-crosslinked and aldehyde-crosslinked dermal collagen grafts. Br J exp Path 1982; 63: 13-7.

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18. Burgos H. Polymer medical dressings containing wound healing factors; Clinical studies with placental angiogenic and growth factors. In: High Performance Biomaterials; A comprehensive Guide to Medical and Pharmaceutical Applica~ons. M Szycher (ed.) .. Technomic Publishing Co. Inc .. Lancaster-Basel, 1991, 573-81.

19. Burgos H, Herd A, Bennet J P. Placental an~iogenic and growth factors in the treatment of chronic vancose ulcers: preliminary communication. J Roy Soc Med 1989; 82: 598-9. Burgos H, Lindenbaum E S, Beach D, Maroudas N G, Hirshowitz B. Effect of decidua angiogenic factors on experimental dermis allografts. Burns 1989; 15: 310-4. Burgos H. Incorporation and release of placental growth factors in synthetic medical dressings. Clinical Materials 1987; 2: 133-9.

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Shakespeare P G & Griffiths R W. Dermal implants in man. Lancet 1980; i: 795-6. Griffiths R W & Shakespeare P G. Human dermal collagen allografts: a three year histological study. Brit J Plast Surg 1982; 35: 519-3. Hafemann B, Zuhlke A, Erdmann C, HettichR. Xenogeneic collagenous membranes with native structure as dermal substitutes. Personal communication, ETCS Meeting, Krakow 1991.

25. Hunt T K. Can repair processes be stimulated by modulators (cell growth factors, angiogenic factors, etc.) without adversely affecting normal processes? J Traum 1984; 24: $39-46.

26. Yang C C, Shih T S, Chu T A, Hsu W S, Kuo S Y, Chao Y F. The intermingled transplantation of auto- and homografts in severe burns. Burns 1980; 6: 141-5.

27. Yang C C, Shih T S, Xu W S. A Chinese concept of treatment of extensive third-degree burns. Plast Reconstr Surg 1982; 70: 238-53.

28. HeckL. BergstresserP,BaxterCR. Compositeskingraft: frozen dermal allografts support the engraftment and expansion of autologous epidermis. J Trauma 1985; 25: 106-12.

29. Gao Z R, Hao Z Q, Nie L J. Coverage of full thickness burns with allograft inoculated with autogenous epithelial cells. Burns 1986; 12: 220-4.

30. Cuono C, Langdon R, McGuire J. Use of cultured auto grafts and dermal allografts as skin replacement after bum injury. Lancet 1986; i: 1123-4.

31. CuonoCB;LangdonR,BirchallN,BattelborthS,McGuire J. Composite autologous allogeneic skin replacement: development and clinical application. Plast Recount Surg 1987; 80: 626-35.

Journal of Tissue Viability 1992 Vol. 2 No 3 77

32. Hafemann B, Frese C, Kistler D, Hettich R. Intermingled skin grafts with in vitro culturedkeratinocytes-experiments with rats. Burns 1989; 15: 233-8.

33. Young D, Langdon R, Kahn R, McGuireJ, Cuono C. Analysis of the fate of allografted dermis using a DNA fingerprinting technique . Abstr Proc Amer Burns Ass 1989; 12:71.

34. Li Y Y & Yang C C. Mixed epidermal cells, fibroblasts and lymphocyte cultures: a study on intermingled transplantation of autografts and allografts. Burns 1982; 8: 75-9.

35. Gibson T. The 'second set' phenomenon as first shown in allografts. An historical case which shows also the behaviour of cell free collagen. Brl Plast Surg 1986; 39: 96-102.

36. Kistler D, Hafemann B, HettichR. Morphological changes of intermingled skin transplants in rats. Burns 1988; 14: 115-9.

37. Hufnagel B, Ninemann J L, Hettich R. Immunology of intermingled skin grafts in rats: preliminary results. Burns 1989; 15: 31-5.

FIRST COMBINED NEDERLANDS/UK STUDY DAYS AMSTERDAM 28/29 OCTOBER 1992

Aetiology of Pressure Sores, Costs, Assessment of Patients and Preventive Aids Mrs J Waterlow, Nurse Tutor Pressure Sores- What How Why* Professor G Ribber, Professor of Geriatrics, Amsterdam Free University Assessment of Mattresses and Cushions Dr I Swain, Director of Medical Physics Dept, Odstock Hospital Salisbury Pressure Sores- A Case of Mobility* Mr J Oechies, Head of Paramedical Dept, Odijckhof Driebergen Protocol in Home care Ms M Zijlstra, District Nurse Pressure Sores Costs of Pressure Sores in the Nederlands * Dr Haalboom, University of Utrecht Swedish Practice and Experience in Wound Care* Mrs I Arndt, Director, Swedish Wound Care Society Protocol in the Clinic Mrs S Zwarts, Head Nurse, Dermatplique University of Amsterdam Assessment of Wounds and Wound Dressings Mrs C Dealey, Tissue Viability Nurse, Birmingham Health Authority Developing a Pressure Sore Policy Mrs R Nicholls, Nurse Tutor, Dorset and Salisbury School of Nursing Questions and Discussions * Speakers confirmed. Titles awaiting agreement

Supporting Exhibitors will include: Arjo Hospital Equipment AB (Sweden), Centromed (UK), Coloplast

(Nederlands), Charnwood Surgical Ltd (UK), ConvaTec (Nederlands), Egerton Hospital Equipment Ltd (UK), Health care Nederlands,

Hendricks en van Steenbergeit/Stopler (Nederlands), Pegasus Airwaves (UK), · Spenco (UK)

Further details can be obtained from the Secretary of the Society